Jurassic Paleobiogeography 

of the Conterminous United 

in Its Continental Setting

GEOLOGICAL SLFRV£Y PRQFESSIQNAL PAPER
Jurassic Paleobiogeography

of the Conterminous United States

in Its Continental Setting

By RALPH W. IMLAY

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1062

Paleogeographic changes in the United States during Jurassic 

time are revealed by the distribution, succession, and 

differentiation of molluscan faunas; by gross stratigraphic 

changes; by the position, extent, and duration of 

unconformities; and by comparisons with Jurassic data 

elsewhere in North America

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1980
UNITED STATES DEPARTMENT OF THE INTERIOR 

CECIL D. ANDRUS, Secretary

GEOLOGICAL SURVEY 

H. William Menard, Director

Library of Congress Catalog-card No. 80-600017

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C. 20402

Stock Number 024-001-03105-1
CONTENTS

Page

Paleobiogeographic setting —————————————————————

Skllpppcai/YKl rj-p aTYlTYiri'nii'PQ 3TlH rlllp'hJf.G \\\T C^QOTAC — — — — — — ______

63,10013.11TM - - ———————————

BathonisnTMTM— • _ • _ — — — — — _

o±±:::z::::::::::i:i:z:::i:z::ii

Tith ^ glEn

Lower Tithonian of the Gulf region ———————— 

Upper Tithonian of the Gulf region ———————————

A.Tmnonite seouences - - ————————— ——

V ' f\ o oiyyt /iflfl- Dlf Wl » /TF?" //? Q Q TY1TY1 rty.1 i" P 9 CCPTY1 V_l Q OTP _____

Substeueroceras-Proniceras ammonite assemrPi'fliriyii£iyi n"f f^fllifrviTiiQ ayiH f}v&crf\n — —

rPl'f Vl/\y»igy» rt-p /"^ayiaHn 3TlH Aloclrs ———____-.__——____ _____

Intercontinental faunal relationships ————————————

1 

3 

3 

4 

4 

4 

17 

18 

19 

19 

19 

19 

19 

21 

23 

25 

29 

30 

30 

31 

31 

32 

34 

34 

34

35 

36 

36 

37

Gulf region of the United States ————————————

i!. astern L^ninudJiua and west iexas-~TMTM-TMTMTM~~~~TMTM-~TM

JT ddiic v^oa&t region ——————————————————————— ——————— —————

Western California and southwestern Oregon ——— — 

Eastern Oregon and western Idaho ——————————

Montana and North Dakota ——————————————— 

Southeastern Idaho to western South Dakota —————

Midcontinent region ——————————————————————

Gulf of Mexico and nearby regions ——————————————

Index ————————

39 

39 

39 

46 

48 

49 

51 

51 

51 

51 

52 

61 

63 

66 

66 

67 

67 

82 

91 

93 

96 

99 

99 

102 

102 

103 

106 

108 

114 

127

ILLUSTRATIONS

FIGURE 1. 

2-12.

Jurassic basins of deposition in North America ————————————————

Maps showing distribution of Jurassic fossils and inferred seas in North America: 

2

J-j

9.

10.

11.

12.

^\ Rai oClciriTM—TM"— — — ~

Early to early middle Oxfordian————————— 

Late middle Oxfordian to early Kimmeridgian-- 

Late Kimmeridgian to early Tithonian —————

13. Succession and correlation of Hettangian to Toarcian ammonites in North America: 

A. Mexico to southern British Columbia —————————————————————— 

B. Northern British Columbia to East Greenland—————————————————

6

7

8

9

10

11

12

13

14

15

16

20

21

III
IV CONTENTS

Page

FIGURE 14. Succession and correlation of Bajocian to Callovian ammonites in North America:

A. Mexico to western interior region-——————————————————————————————————————————————— 22 

B. British Columbia to East Greenland—————————————————————————————————————————————— 23

15. Succession and correlation of Oxfordian to Tithonian ammonites in North America:

A. Gulf of Mexico, Pacific Coast, and western interior region————————————————————————————————— 24 

B. Southwestern Canada to Greenland ——————————————————————————————————————————— 25

16. Comparisons of the Tithonian and Volgian Stages and the suggested subdivisions of the Tithonian————————————— 26

17. Index map of Jurassic areas in the Gulf of Mexico and nearby regions—————————————————————————————— 40

18. Index map of Jurassic areas in the Pacific Coast region from California and Nevada to Washington————————————— 41

19. Index map of Jurassic areas in the Pacific Coast region from British Columbia to southern Alaska————————————— 42

20. Index map of Jurassic areas in the western interior region————————————————————————————————————— 43

21. Correlations and comparisons of Jurassic rocks in the Gulf of Mexico and nearby regions:

A. Western Cuba to Victoria, Mexico————————————————————————————————————————-—————— 44 

B. Huasteca area, Mexico, to Malone Mountains, Tex————————————————————————————————————— 45

22. Correlations and comparisons of Jurassic rocks in the Pacific Coast region in California, Nevada, and western to eastcentral Oregon:

A. Western Nevada and eastern California ——————————————————————————————————————————— 54 

B. Western California to east-central Oregon —————————————————————————————————————————— 55

23. Correlations and comparisons of Jurassic rocks in the Pacific Coast region from eastern Oregon and western Idaho to north-

\VCStcFIi WclSiiliigjT'OIi --—-—TMTM~---——-—.———.„—.—.——_______.________.___..__._-.-._________.______.„_._______-..__._______-_.______.»-_,.____________.._._ u\/

24. Correlations and comparisons of Jurassic rocks in the Pacific Coast region in British Columbia, Yukon Territory, and southern Alaska:

A. Southwestern to central British Columbia—————————————————————————————————————————— 58 

B. Northwestern British Columbia to southern Alaska———————————————————————————————————— 59

25. Correlations and comparisons of Jurassic rocks in the western interior region from southwestern Alberta through central 

Montana to southern Saskatchewan:

A.. OOUtllin' GStGiTi A.lDCFt<** tO CCni/IclI JYLOntEliiclTMTM'—"~~~——-—<—._-___—______—________—_______—_____—__..___——______________________________—

B. Central Montana to southern Saskatchewan————————————————————————————————————————— 69

26. Correlations and comparisons of Jurassic rocks in the western interior region from southeastern Idaho to southwestern

South Dakota:

A. Ammon area, Idaho, to Red Creek, Wyo——————————————————————————————————————————— 70 

B. Hyattville area in north-central Wyoming to Minnekahta area, South Dakota————————————————————— 71

27. Correlations and comparisons of Jurassic rocks in the western interior region from north-central Utah to north-central

Colorado:

A. Burr Fork to Whiterocks Canyon, Utah———-*••——————————————————————————————————————— 72 

B. Dinosaur Quarry, Utah, to Hahns Peak, Colo———————————————————————————————————————— 73

28. Correlations and comparisons of Jurassic rocks in the western interior region from north-central Utah to southwestern

Colorado:

A. Monks Hollow to Black Dragon Canyon, Utah——————————————————————————————————————— 74 

B. San Rafael River, Utah, to McElmo Canyon, Colo-———-—~—————~———~—————————————-—— 75

29. Correlations and comparisons of Jurassic rocks in the western interior region from southwestern Utah to northeastern

Arizona:

A. Gunlock to Brown Canyon, Utah——————————————————————————————————————————————— 76 

B. Little Bull Valley, Utah, to Cow Springs, Ariz———————_~~——-—————-——-———-——-—————— 77

30. Jurassic unconformities in Gulf of Mexico and Pacific Coast regions———————————————————————————————— 100

31. Jurassic unconformities in western interior region —————————————————————————————————————————— 101

32. Inferred extent of Jurassic seas of early Bajocian to earliest Callovian Age in western interior region———————————— 110

33. Inferred extent of Jurassic seas of late early Callovian to early Kimmeridgian Age in western interior region——————— H2

TABLE

TABLE 1. Thickness of the Piper and underlying Gypsum Spring Formations in parts of north-central Wyoming and south-
CONTENTS

CONVERSION FACTORS

Metric unit Inch-Pound equivalent

Length

millimeter (mm) 

meter (m) 

kilometer (km)

= 0.03937 inch (in) 

= 3.28 feet (ft) 

= .62 mile (mi)

Area

square meter (m2 ) 

square kilometer (km2 ) 

hectare (ha)

= 10.76 square feet (ft2 ) 

= .386 square mile (mi2 ) — 2.47 acres

Volume

cubic centimeter (cm*) 

liter (L) 

cubic meter (m3 ) 

cubic meter 

cubic hectometer (hm3 ) 

liter 

liter 

liter 

cubic meter

cubic meter

= 0.061 cubic inch (in«) 

= 611.03 cubic inches 

= 35.31 cubic feet (ftf) 

= .00081 acre-foot (acre-ft) 

= 810.7 acre-feet 

= 2.113 pints (pt) 

= 1.06 quarts (qt) 

= .26 gallon (gal) 

= .00026 million gallons (Mgal or 

10" gal) 

= 6.290 barrels (bbl) (1 bbl = 42 gal)

Weight

gram (g) 

gram 

metric tons (t) 

metric tons

= 0.035 ounce, avoirdupois (oz avdp) 

= .0022 pound, avoirdupois (Ib avdp) 

= 1.102 tons, short (2,000 Ib) 

= 0.9842 ton, long (2,240 Ib)

Specific combinations

kilogram per square 

centimeter (kg/cm2) 

kilogram per square 

centimeter 

cubic meter per second 

(m*/s)

= 0.96 atmosphere (atm)

— .98 bar (0.9.869 atm) 

= 35.3 cubic feet per second (ft*/s)

Metric unit Inch-Pound equivalent

Specific combinations — Continued

liter per second (L/s) 

cubic meter per second 

per square kilometer 

[(m*/s)/km8 ] 

meter per day (m/d)

meter per kilometer 

i<m/km) 

kilometer per hour 

(km/h) 

meter per second (m/s) 

meter squared per day 

(mVd) 

cubic meter per second 

(mf»/s) 

cubic meter per minute 

(m3/min) 

liter per second (L/s) 

liter per second per 

meter [CL/s)/m] 

kilometer per hour 

(km/h) 

meter per second (m/s) 

gram per cubic 

centimeter (g/cm3 ) 

gram per square 

centimeter (g/cm2 ) 

gram per square 

centimeter

= .0353 cubic foot per second 

= 91.47 cubic feet per second per 

square mile [(ft?/s)/mi2 ]

= 3.28 feet per day (hydraulic 

conductivity) (ft/d) 

= 5.28 feet per mile (ft/mi)

— .9113 foot per second <ft/s)

— 3.28 feet per second

= 10.764 feet squared per day (fta/d) 

( transmissivity )

= 22.826 million gallons per day 

(Mgal/d) 

= 264.2 gallons per minute (gal/min)

= 15.85 gallons per minute 

= 4.83 gallons per minute per foot 

[(gal/min)/£t]

— .62 mile per hour (mi/h)

— 2.237 miles per hour

= 612.43 pounds per cubic foot (A/ft") 

= 2>048 pounds per square foot (lb/ft2 ) 

= .0142 pound per square inch Ob/In2)

Temperature

degree Celsius (°C) 

degrees Celsius 

(temperature)

= 1.8 degrees Fahrenheit (°F) 

= [(1.8x"C)+32] degrees Fahrenheit

JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS 

UNITED STATES IN ITS CONTINENTAL SETTING

By RALPH W. IMLAY

ABSTRACT

During Jurassic time, marine sediments of considerable thickness including bedded salt were deposited on the outer part of the Atlantic 

Continental Shelf of the United States. The inner part of the shelf may 

have been inundated also during Oxfordian to Tithonian time, coincident with extensive flooding elsewhere in the Atlantic Ocean and in the 

Gulf of Mexico.

During the Early Jurassic, neither marine nor continental sediments 

seem to have been deposited within the area now covered by the Gulf 

of Mexico. Nonetheless, a marine embayment of Sinemurian to possibly 

early Pliensbachian Age did extend northward from the Pacific Ocean 

to east-central Mexico, where it terminated against a mass of metamorphic and granitic rocks in eastern Veracruz. The marine sediments 

deposited are carbonaceous, contain much plant material and some 

coal, and evidently were laid down in a warm humid climate. During 

the later Early Jurassic, they were strongly folded, faulted, intruded 

by igneous rocks, slightly metamorphosed, and then eroded. Presumably, erosion took place mostly in Toarcian time after tectonic movements in Pliensbachian time.

During the Middle Jurassic, marine sediments apparently were not 

deposited within the Gulf region until the late Bathonian. Continental 

sedimentation, however, took place in both Mexico and Cuba. In eastcentral Mexico, plant fossils show that continental deposition began in 

the early Bajocian. Such deposition took place over a larger area than 

that covered by the Lower Jurassic marine beds, continued until sometime in the Bathonian, but was followed by erosion before the early 

Callovian. In Cuba thousands of feet of carbonaceous plant-bearing 

beds were deposited during the Bajocian and Bathonian and possibly a 

little earlier. These plant-bearing beds show that the climate was warm 

and humid throughout the Gulf region during most of the Middle Jurassic.

During Callovian to early middle Oxfordian time, the Gulf region 

subsided and received some marine waters from the major oceans, 

which deposited thick masses of salt at various places. One marine embayment apparently extended westward into Cuba and was probably 

the major source of the salt. Another embayment extended from the 

Pacific Ocean into the Huasteca area of east-central Mexico, where it 

was separated from the Gulf at least in part by a land barrier located 

near the present Gulf coast. Salt was deposited mainly during late Callovian to early middle Oxfordian time, but deposition may have started 

in middle Callovian time. At about the same time in nearby areas in 

east-central and northeastern Mexico, varicolored continental beds and 

some red-weathering lava were deposited. The climate during deposition of the salt and nearby varicolored continental beds was probably 

hot and dry in the Gulf region. The red silt and sand were probably 

derived from upland areas to the west or north where the climate was 

hot and seasonally rainy.

Near the middle of the Oxfordian, major portals to the oceans were 

opened abruptly by major structural movements, and as a result seawater of normal salinity flowed quickly across the saline deposits and 

far beyond. Subsequently, during the later Jurassic, the Gulf of Mexico 

gradually deepened and widened; landmasses arose north of the Gulf

basin and shed considerable sediment southward; and deposition prevailed in open marine water from Cuba and Florida westward to central 

Mexico. Deposition continued into the Cretaceous in most parts of the 

Gulf region except in some northern nearshore areas. The climate in 

the Gulf region during Oxfordian to Tithonian time was probably hot 

and moderately humid. Rainfall apparently became greater after the 

early Kimmeridgian and was greater in eastern Mexico than in the 

southeastern United States, as shown by the presence of coal beds in 

Mexico. On the whole, the climate was probably similar to that in the 

western interior region during deposition of the Morrison Formation.

On the Pacific Coast during Jurassic time, marine deposition took 

place at depths ranging from very shallow to very deep, involved tremendous thickness of sediment, included much volcanic material, and 

gradually shifted westward.

During the Early Jurassic, a sea extended from the Pacific Coast as 

far east as the Snake River in easternmost Oregon and a similar distance east in Nevada. The deepest part of the sea probably trended 

northward through westernmost Nevada into eastern Oregon and beyond, as indicated by continuous deposition of fine-grained sediments 

from the Triassic into the Jurassic. By contrast, in eastern California, 

Jurassic sedimentation apparently did not begin before the Sinemurian.

During Bajocian time, a shallow sea covered nearly the same area as 

the Early Jurassic sea, except for an eastward extension into the western interior region. This sea received a great variety of sediments that 

included much volcanic material, except in Nevada. Deposition of beds 

of Bathonian Age in the Pacific Coast region of the conterminous 

United States has been demonstrated by fossils only in eastern Oregon. 

The absence of Bathonian fossils elsewhere could be explained by collecting failure; it could also reflect the beginning of intense volcanism 

which lasted into the early Oxfordian and which may at first have produced conditions on the sea bottom that were unfavorable for the preservation of fossils.

During the Callovian, marine waters covered most of the present 

area of California, Oregon, and Washington, and during earliest Callovian they also extended eastward into the western interior region. Enormous amounts of coarse to fine volcanic debris were ejected from volcanoes and fissures into the sea, where they became mixed with 

sediments derived from islands and larger landmasses. Apparently 

deposition continued throughout the epoch, except in eastern Oregon. 

The formation of oceanic crust during the Bathonian or Callovian epochs, or both, is suggested by the characteristics of the Rogue Formation in western Oregon.

Marine sedimentation persisted in the Pacific Coast region without 

any apparent interruption, from Callovian to early Kimmeridgian time, 

over a large area including California, western Oregon, and probably 

northwestern Washington. During the early Oxfordian, deposition of 

highly volcanic sediments continued just as during the Callovian. By 

contrast, from late Oxfordian to early Kimmeridgian, the most common 

sediments deposited were dark clay and silt, which in most places included only fine volcanic material.

At the end of the early Kimmeridgian, marine deposition ceased in 

areas underlain by the Mariposa Formation in eastern California, and 

by the Galice Formation in western Oregon and in nearby California.
JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

Those areas were then uplifted, and the rocks were folded, intruded 

locally by igneous rocks, and strongly eroded before the end of the 

Jurassic.

In some other places near the present Pacific Coast, marine sediments were deposited from the late Kimmeridgian to the Tfthonian, 

but in many other places such deposition apparently only took place 

during the Tithonian. Some of the sediments, now represented by the 

Knoxville and Riddle Formations, consist mostly of nonvolcanic terrigenous clastic materials which locally contain limestone lenses and 

which were deposited in shallow waters. Other sediments, represented 

by the Dothan and Otter Point Formations and by the Franciscan assemblage, consist of volcanic elastic materials, breccia, lava, and chert 

and were deposited in deep waters. All available evidence indicates 

that the volcanic sediments were deposited far west of the nonvolcanic 

sediments and in much deeper waters, but that deposition of both began at about the same time on oceanic crust of late Oxfordian to early 

Kimmeridgian Age. Evidently, the oceanic crust was formed at the 

same time at which the Galice and Mariposa Formations were being 

deposited in areas far to the east.

That the climate in California and Oregon during Jurassic time was 

probably warm is indicated by the presence of ammonites of Mediterranean (Tethyan) affinities in those States and by the lack of certain 

ammonites that are common in the Arctic region and along the Pacific 

Coast as far south as British Columbia. The change is similar to that 

found in Jurassic ammonite faunules between northwest Europe and 

the Mediterranean region.

During the Early Jurassic, the western interior region south of Montana received as much as 3,000 feet (915 m) of continental sediments 

deposited under ftuviatiie and eofan environments. During the late Oxfordian, Kimmeridgian, and probably early Tithonian, the region received hundreds of feet of continental sediments deposited under fluviatile, lacustrine, and swampy environments. Between these two 

episodes, the area was invaded five times by marine waters that entered from the west through Idaho, Washington, or Alberta. Three of 

the invasions were followed by complete withdrawals of the sea from 

the region and two by partial withdrawals.

The sea first invaded southeast Idaho early in the Bajocian, extended 

from there northeast into the Williston basin and southward into southwest Utah, and then withdrew completely at about the beginning of 

the middle Bajocian. That sea left deposits of gypsum, red silt, limy 

mud, some chert, and locally in the Williston basin, a little salt. The 

characteristics of these sediments show that the sea was very shallow, 

that its initial sediments were laid down in highly saline waters, that 

later sediments were deposited in slightly deeper waters which supported some marine organisms^ and1 that the sea deepened a little in 

southeastern Idaho.

The second and greatest marine invasion of the western interior region started in the late middle Bajoeian and lasted until the early Callovian. The sea underwent marked shallowing in the middle Bathonian 

and then withdrew nearly completely in late early to middle Callovian. 

It entered across northern Utah, eastern Idaho, and southern Alberta, 

surrounded a large island in central Montana, and was much more extensive than the sea of the earlier Bajocian except in eastern and southern Wyoming during late Bajocian to early Bathonian. From late Bathonian to early Callovian, however, it advanced across Wyoming into 

South Dakota beyond the erosional eastern limit of beds of early Bajoeian Age. In this sea were deposited clayey to dense to oolitic lime mud, 

limy clay and silt, gray to yellow limy sand, and some red silt and gypsum. The sediments deposited at any one time were similar over great 

distances, except for the initial deposits that filled irregularities on the 

underlying erosion surface. Most of the sediments were deposited as 

the sea transgressed. Regressive deposits include the Boundary Ridge 

and Giraffe Creek Members of the Twin Creek Limestone and their 

equivalents.

The second marine invasion was terminated near the middle of the 

Callovian by the rise and enlargement of a large island in Montana that 

cut off marine waters from the north. South of this island in very shallow, probably highly saline waters were deposited unfossiliferous, red, 

even-bedded, fine-grained sand that thickens westward from 100 to 

1,000 feet (30 to 300 m) or more, and that extends from the Black Hills 

area southwestward through southern Wyoming and northernmost 

Utah into southeastern Idaho. Near Idaho Falls, the lower part of the 

sand was deposited along with some marine lime mud and sand. This 

marine fades thins eastward to an area near the western boundary of 

Wyoming where bedded salt and gypsum were deposited at about the 

same stratigraphic position over a distance of several hundred miles 

(several hundred kilometers) from north to south. Evidently, marine 

and lagponal conditions persisted to the west in Idaho at the same time 

that ced; sand was being deposited farther east in highly, saline or possibly brackish waters and at the same time that light-colored, crossbedded sand was being reworked by winds in the Colorado Plateau.

The third marine invasion into the western interior region apparently happened during the late middle to early late Callovian, in some 

places immediately after deposition of red even-bedded sand and equivalent eolian sand and in other places after a brief interval of erosion. 

The sea extended eastward across northern Utah, southern Idaho, 

northern Coloradb, and southern Wyoming into South Dakota. It may 

have also extended northward from the Black Hills area into southern 

Saskatchewan, where it could be represented by all or part of the glauconitic deposits called the Roseray Formation (equals middle member 

of the Vanguard Formation).

In this sea, highly glauconitic limy sand, sandy silt, some gypsum, 

and some limy mud (Curtis Formation and Pine Butte Member of the 

Sundance Formation) were deposited in very shallow water, as shown 

by the presence of Ostrea, Lopha, Lingula, and Meleagrinella. Such 

sediments in the San RafaeL swell were overlain conformably by, and 

passed laterally southeastward into, unfossiliferous chocolate-brown, 

red, or gray even-bedded sand; silt, and clay, and, locally, some gypsum. Such sediments were probably deposited in highly saline water in 

marginal areas of the sea. Deposition of both the marine, brackish-, and 

saline-water sediments was followed rather quickly by withdrawal of 

the sea completely from the western interior region and by an interval 

of erosion that lasted until early Oxfordian time.

The fourth marine invasion into the western interior region entered 

central Montana east of the Sweetgrass arch during the latest Callovian 

and possibly entered the Williston basin even earlier. During the early 

Oxfordian, the sea spread widely, but did not advance as far south in 

Utah as the preceding sea, and apparently did not spread west of the 

Sweetgrass arch. At the end of the early middle Oxfordian, the sea 

withdrew northward into northern Wyoming and the Williston basin 

bub, spread westward in Montana at least as far as the Sawtooth Range 

south of Glacier Park. It persisted in Montana at least to the end of the 

Oxfordian. The sea was bounded on the west in central Idaho and possibly in westernmost Montana by a landmass that shed considerable 

clastic sediment eastward. This is shown by a change from mostly glauconitic, calcareous sand, sandy lime, and sandy silt in the west to 

mostly silt and clay farther east. The sea was shallow, as shown by the 

presence of Ostrea, Mytilus, and Meleagrinella, and by abundant ripple marks and crossbedding. The climate was probably warm and humid, as shown by the presence of many wood fragments in the Swif(; 

Formation in western Montana.

The northward withdrawal of the sea in Montana during the early 

middle Oxfordian was followed by a brief fifth marine invasion southward from Montana and northern Wyoming as far as northwestern Colorado and northeastern Utah. In this sea was deposited a thin unit 

(Windy Hill Sandstone Member of the Sundance Formation) of yellowish-gray, limy, locally oolitic, ripple-marked sand, and a little gray to 

green mud that contains a few mollusks, such as Ostrea. These marine
ACKNOWLEDGMENTS

sediments were deposited unconformably on the Redwater Shale Member of the Sundance Formation and conformably below the continental 

Morrison Formation. As they are not recognizable as a lithologic unit 

north of the Wind River Basin in central Wyoming, they presumably 

pass northward into the upper part of the Redwater Shale Member in 

northern Wyoming.

During later Jurassic time, continental sediments (Morrison Formation) were deposited on flood plains and in lakes throughout much of 

the western interior region and in coal-forming swamps in Montana. 

Continental deposition began during the early or late Oxfordian in the 

southern part of the region, definitely during the late Oxfordian in the 

central part, and probably as late as the Kimmeridgian in northern 

Montana. It persisted in all parts at least through the Kimmeridgian. 

Sediments in the southern and central parts of the western interior 

region were derived from the south and west. In the northern part, 

they were derived from the east and west. Evidently, continental sedimentation began at about the same time as deposition of the marine 

Norphlet and Smackover Formations of the Gulf region. Uplift of land 

areas from which the continental sediments were derived apparently 

occurred at the same time as uplift of the land areas that shed sediment 

southward into the Gulf of Mexico during late Oxfordian to Tithonian 

time.

The Jurassic ammonite succession in North America from Hettangian through early Bajocian time is essentially the same as elsewhere 

in the world. Ammonite assemblages of late Pliensbachian Age are differentiated from north to south, just as they are in Europe. Ammonite 

assemblages of middle Bajocian Age in the Pacific Coast region contain 

some genera that are known only from areas bordering the Pacific 

Ocean, but overall their generic resemblances to European ammonites 

are striking.

In contrast, from late Bajocian time until the end of the Jurassic, 

marked differentiation of ammonite faunas took place from north to 

south. The ammonite successions in the Gulf region and in the Pacific 

Coast region as far north as southern California remained closely similar to those in the Mediterranean region. The succession from northern 

California to northern Alaska became similar to that in northern Eurasia, although some mingling of genera of Boreal and Mediterranean 

affinities occurred in California and Oregon. Such mingling and the 

presence of genera known only from the Western Hemisphere or from 

areas bordering the Pacific Ocean have aided greatly in making fairly 

accurate correlations of rocks in widely separated areas.

The differentiation of ammonite faunas from north to south can be 

reasonably ascribed to partial isolation of an arctic sea from the Pacific 

Ocean, except for at least one connection through Yukon Territory during Middle and most of Late Jurassic time, and another connection from 

East Greenland to northwest Europe from the beginning of Callovian 

time.

INTRODUCTION

This report is a successor to that written by Imlay 

and Detterman (1973) on the Jurassic Paleobiogeography of Alaska. It is more detailed because much more 

information is available concerning the conterminous 

United States. It deals in a broad way with changes in 

Jurassic geography, stratigraphy, and ammonite assemblages. It presents paleogeographic maps depicting the 

main areas of Jurassic marine deposition and most of the 

marine Jurassic megafossil occurrences in North America (figs. 1-12). It presents charts depicting the succession of ammonite taxa and Buchia species in North

America (figs. 13-16), the locations of some of the best 

known Jurassic sequences (figs. 17-20), the gross stratigraphic and lithologic changes in space and time (figs. 

21-29), and the position, extent, and duration of unconformities during Jurassic time (figs. 30, 31). In addition, 

the report discusses most existing published stratigraphic, lithologic, and faunule knowledge in sufficient 

detail to substantiate the interpretations presented on 

the maps, on the charts, and in the section on Jurassic 

geologic history.

Most of the geographic features, areas, and towns 

mentioned in this report are shown on figures 17-20. 

Further locality data concerning such features in the 

Gulf of Mexico region are shown in papers by Imlay 

(1943a, p. 1408, 1409, 1412, 1496, 1503, 1509; 1952a, p. 

954; 1953c, figs. 2-4), Swain (1944, p. 583), K. A. Dickinson (1968, p. E2), and Lopez Ramos (1974, p. 382, 

385, 388, 391). Such data for the Pacific Coast region of 

the United States and Canada are shown in papers by 

Imlay (1952a, p. 956; 1961, p. D15; 1973, pi. 48; Imlay 

and Jones, 1970, p. B19); Frebold and Tipper (1970), and 

Imlay and Detterman (1973, p. 7). Such data for the 

western interior region are shown in papers by Baker, 

Dane, and Reeside (1936), Imlay (1952a, p. 956; 1953a, p. 

12; 1956a, p. 563; 1957, p. 472; 1962b, p. C8, C9; 1967b, 

p. 5, 63-65), Frebold (1957, figs. 1, 2; 1969, fig. 1), 

Brooke and Braun (1972, fig. 1), J. A. Peterson (1957, p. 

402, 403), and Pipiringos and O'Sullivan (1975).

ACKNOWLEDGMENTS

For the data published herein, the writer is indebted 

to many geologists from Canada, the United States, and 

Mexico. Canadians who contributed include Hans Frebold, J. A. Jeletzky, and H. W. Tipper of the Canadian 

Geological Survey; M. M. Brooke, W. K. Brown, J. E. 

Christopher, and D. F. Paterson of the Saskatchewan 

Geological Survey; and L. W. Vigrass of the University 

of Saskatchewan. In the United States, information was 

provided by George Gryc, K. A. Dickinson, Arthur 

Grantz, D. L. Jones, J. D. Love, W. J. Mapel, A. A. 

Baker, W. A. Cobban, E. M. MacKevett, Fred Peterson, 

G. N. Pipiringos, Donald Richter, E. H. Bailey, W. P. 

Irwin, L. D. Clark, R. L. Detterman, and Robert Sharp 

of the U.S. Geological Survey; George Herman and Jules 

Braunstein of Shell Oil Co.; W. E. Humphrey of American International Oil Co. (Amoco); R. T. Hazzard of Gulf 

Oil Co.; W. B. Weeks of Phillips Oil Co.; F. M. Swain of 

the University of Minnesota; W. R. Dickinson of Stanford University; J. A. Peterson of the University of Montana; and many others. In Mexico, those providing data 

included Gloria Alencaster de Cserna, Manuel Alvarez, 

Jr., Abelardo Cantii Chapa, Edmundo Cepeda, D. A.
JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

Cordoba, Zoltan de Cserna, Teodoro Diaz-Gonzalez, E. 

J. Guzman Jimenez, Ernesto Lopez Ramos, Roberto Flores Lopez, G. P. Salas, Hector Ochoterana F., Francisco 

Viniegra 0., and J. P. Alor, all of whom are affiliated 

with either Petroleos Mexicanos or the Institute Geologico de Mexico.

Special thanks are due George Pipiringos and Fred 

Peterson of the U.S. Geological Survey for sharing information and exchanging interpretations concerning the 

stratigraphic relationships of Jurassic formations in the 

western interior region.

The writer is much indebted to John H. Callomon of 

University College, London, England, and to Tove Birkelund of the University of Copenhagen, Denmark, for 

ammonite biostratigraphic data concerning the position 

of the Bathonian-Callbvian boundary in East Greenland 

and its probable position in Alaska and Montana.

PALEOBIOGEOGRAPHIC SETTING

ATLANTIC COAST

Jurassic marine beds have not been identified definitely along the Atlantic Coast of the United States, although 45 feet (13.7 m) of limy beds of possible Late Jurassic age have been penetrated in two wells at Cape 

Hatteras, N.C. Three species of ostracodes have been 

found, of which two, belonging to the genus Schuleridea, 

have been found elsewhere in the Schuler Formation 

(Upper Jurassic) of the southeastern United States; one 

belongs to the genus Octocythere, which is known only 

from the Jurassic (Swain, 1952, p. 59, 60; Swain and 

Brown, 1972, p. 8, 9; Brown and others, 1972, p. 38). 

These possible Jurassic beds are about 370 miles (600 

km) west of the marine Upper Jurassic sequence about 

560 feet (170 m) thick that was cored at JOIDES Site 105 

in the Hatteras Abyssal Plain (Hollister and others, 

1972). It is about 60 miles (100 km) west of the western 

margin of Jurassic beds suggested by Emery and Uchupi 

(1972, p. 95).

No drilling reports have yet been published that 

prove the presence of Jurassic beds along the Atlantic 

Continental Shelf of the United States. Nonetheless, 

seismic data suggest the presence of thousands of feet of 

both Jurassic and Lower Cretaceous beds along the entire shelf area from Maine to Florida (Ballard and Uchupi, 

1974, p. 1158; Schultz and Grover, 1974, p. 1164, 1165; 

Minard and others, 1974, p. 1172, 1176; Olson, 1974, p. 

1196, 1197). Furthermore, salt concentrations in pre-Upper Cretaceous rocks in coastal areas between Delaware 

and Florida suggest that evaporitic facies of possible Jurassic age may be present seaward from the present 

coastline (Mattic and others, 1974, p. 1182, 1183). Marine Jurassic sedimentation along the Atlantic Coast was

probably influenced in places by the Palisade disturbance, which is now definitely dated as Jurassic, rather 

than Triassic, by the presence of palynofloras of Early 

Jurassic age from the top of the Newark Group (Cornet 

and others, 1973; Cornet and Traverse, 1975, p. 25-27). 

This evidence is supported by some K-Ar dates for the 

Palisades sill that intrudes the Newark Group in New 

Jersey (Dallmeyer, 1975) and by K-Ar dates for lava 

flows in the middle of the Newark Group in the Hartford 

basin of Connecticut and the Deerfield basin of Massachusetts (Armstrong and Besancon, 1970).

Jurassic beds of considerable thickness have been 

identified by means of microfossils found in deep wells 

drilled along the Atlantic Coast of eastern Canada (Sherwin, 1973, p. 529, 534-537; Upshaw and others, 1974, p. 

1132). For the Nova Scotia shelf, the fossil evidence 

shows that the marine Lower and Middle Jurassic beds 

are about 6,600 feet (2,012 m) thick, and those for the 

Upper Jurassic are at least 8,200 feet (2,500 m) thick 

(Mclver, 1972, p. 56-62). The sequence includes a basal 

salt unit about 2,500 feet (760 m) thick that is dated as 

probably earliest Jurassic on the basis of its microflora 

and its stratigraphic continuity with overlying marine 

beds that are dated as Early Jurassic (Pliensbachian). 

The Jurassic sequence may also include several hundred 

feet of red beds that are gradational upward into the 

main salt mass and that rest on metamorphosed sedimentary rock.

In the Grand Banks of Newfoundland, microfossils of 

Early to Late Jurassic age have been reported throughout at least 20,000 feet (6,100 m) of beds penetrated by 

drilling (Upshaw and others, 1974, p. 1132). These beds 

consist of clastic oolitic to dense limestone, gray to red 

siltstone and mudstone, and limy fine-grained sandstone. 

In the Murre well, the Lower Jurassic is represented by 

1,120 feet (341 m) of limestone whose basal 600 feet (183 

m) contains bedded anhydrite and some salt. In addition, 

some salt, penetrated in two salt domes, has been interpreted as of Early Jurassic age or older (Bartlett and 

Smith, 1971, p. 67-69; Amoco, 1974, p. 1112-1115; Upshaw and others, 1974, p. 1127-1129).

Studies of Foraminifera, ostracodes, dinoflagellates, 

spores, and pollen, obtained from well cutting on the Scotian Shelf and the Grand Banks, show that the oldest 

dated beds are of Bathonian to Callovian Age (Ascoli, 

1974, p. 132, 133; Williams, 1974). The underlying saltbearing beds are referred to the Early Jurassic, however, although the evidence for such dating is not yet 

published (Jansa, 1974, p. 141).

GULF OF MEXICO AND NEARBY REGIONS

Thick Jurassic deposits are widespread in Mexico, 

the southern United States, and Cuba. Marine beds of
PALEOBIOGEOGRAPHIC SETTING 

150° 140° 130° 30° 20° 10°

140°

130°

70°

120° 110°

FIGURE 1.—Jurassic basins of deposition in North America. Note small basins of continental deposition in central Michigan, northern New

Jersey, and Connecticut to southern Massachusetts. Land areas are ruled.
JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES 

150° 140° 130° 30° 20° 10°

160°

170°

180°

170

130

120° 110° 100° 90° 80°

FIGURE 2.—Distribution of Hettangian fossils (X) and inferred seas in North America. Land areas are ruled.
PALEOBIOGEOGRAPHIC SETTING 

150° 140° 130° 30° 20° 10°

0 500 1000 KILOMETERS

140°

130

120° 110° 100° 90° 80° 

FIGURE 3.—Distribution of Sinemurian ammonites (X) and inferred seas in North America. Land areas are ruled.
JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES 

150° 140° 130° 30° 20° 10°

160

130°

120° 80°

FIGURE 4.—Distribution of Pliensbachian fossils (X) and inferred seas in North America. Land areas are ruled.
PALEOBIOGEOGRAPHIC SETTING 

150° 140° 130° 30° 20° 10°

I I 

0 500 1000 KILOMETERS

130°

120° 110° 100° 90°

FIGURE 5.—Distribution of Toarcian fossils (X) and inferred seas in North America. Land areas are ruled.
10 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES 

150° 140° 130° 30° 20° 10°

120° 110° 100° 80°

0°

CONTINENTAL PLANT-BEARIN 

BEDS IN CUBA AND IN 

EAST-CENTRAL MEXICO

FIGURE 6.—Distribution of Bajocian fossils (X) and inferred seas in North America. Land areas are ruled. Extent of early Bajocian sea in 

western interior region is indicated by dotted line. Extent of late middle to late Bajocian sea in western interior region is indicated bv 

solid line. J
PALEOBIOGEOGRAPHIC SETTING 

150° 140° 130° 30° 20° 10°

11

160°

170°

130°

70°

120° 110° 100 90°

FIGURE 7.—Distribution of Bathonian fossils (X) and inferred seas in North America. Land areas are ruled. Extent of early Bathonian sei 

in western interior region is indicated by dotted line. Extent of late Bathonian sea in western interior region is indicated by solid line. 

Extent of late Bathonian tidal flat and continental deposits is indicated by dashed line.
12 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES 

150° 140° 130° 30" 20° 10°

130

120° 110"

70°

FIGURE 8.—Distribution of Callovian fossils (X) and inferred seas in North America. Land areas are ruled. Extent of earliest CaUovian sea 

in western interior region is indicated by solid line. Extent of late middle Callovian sea (Curtis and Summerville time) is indicated by 

dotted line. Extent of Callovian continental beds is indicated by dashed line. Possible extent of latest Callovian sea is indicated by 

alternating dots and dashes.
150°

PALEOBIOGEOGRAPHIC SETTING 

140° 130° 30° 20° 10°

13

160°

130°

70°

FIGURE 9.—Distribution of early to early middle Oxfordian fossils (X) and inferred seas in North America. Land are areas ruled.
14

160°

JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES 

150° 140° 130° 30° 20° '10°

taer

70°

120° t10° 90° 80°

FIGURE 10.—Distribution of late middle Oxfordian to early Kimmeridgian fossils (ammonites and buchias) (X) and inferred seas in North

America. Land areas are ruled.
160°

170°

180°

170°

PALEOBIOGEOGRAPHIC SETTING 

140° 130° 30° 209 109

15

COISTINENTAL 

EPOSITS <ll

120° 110°

FIGURE 11.—Distribution of late Kimmeridgian to early Tithonian fossils (ammonites and buchias) (X) and inferred seas in North America.

Land areas are ruled.
16 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES 

150° 140° 130° 30° 20° 10°

160

170

0°

120° 110° 100° 90° 80°

FIGURE 12.-Distribution of late Tithonian fossils (ammonites and buchias) (X) and inferred seas in North America. Land areas are ruled.
PALEOBIOGEOGRAPHIC SETTING 17

Early Jurassic age occur in southern and east-central 

Mexico and perhaps as far north as Catorce (Burckhardt, 

1930, p. 8-44, 91-93; Erben, 1957a, 1957b). In lastcentral Mexico, these beds contain ammonites of Sinemurian and early Pliensbachian Age and were deposited 

in an embayment (Huayacocotla) that opened only to the 

Gulf of Mexico, according to Erben (1957b, p. 38), but 

only to the Pacific Ocean according to Viniegra 0. (1971, 

p. 484) and Lopez Ramos (1974, p. 381^386). In southern Mexico, one ammonite of Early Jurassic age (late 

Pliensbachian) from the state of Guerrero (Erben, 1954, 

p. 5-12, pi. 1, figs. 4, 5) is the sole evidence for beds of 

that age near the Pacific Coast. Beds of Early Jurassic 

age have not been identified in Cuba or in the subsurface 

of the southern United States.

Marine beds of Bajocian and Bathonian Age have 

been identified definitely in Mexico only in northwestern 

Oaxaca and northeastern Guerrero (Burckhardt, 1927; 

1930, p. 25, 26; Erben, 1957a, p. 49, 50). They were deposited in an embayment (Guerrero) that probably opened 

into the Pacific Ocean rather than into the Gulf of Mexico 

(Erben, 1956b, p. 122-124, pi. 17; 1957b, p. 39, fig. 2; 

Viniegra 0., 1971, p. 484, 492). Marine beds of late Bathonian Age may occur also in the subsurface of east-central Mexico near Tampico, as shown by the presence of 

some small ammonites similar to the late Bathonian Wagnericeras (Cantii Chapa, 1969, p. 5).

Elsewhere in the Gulf region, a Bajocian to Bathonian Age seems probable for part of the San Cayetano 

Formation of Cuba (Meyerhoff, 1964, p. 152-153; Krommelbein, 1956; Khudoley and Meyerhoff, 1971, p. 37, 38) 

but most unlikely for the Louann Salt of the southern 

United States or for similar bedded salt deposits of 

southeastern Mexico (Imlay, 1943a, p. 1438; 1953c, p. 7; 

Viniegra 0., 1971, p. 482).

Marine beds of Callovian Age have been found in 

Mexico only in its east-central and southern areas 

(Burckhardt, 1927; 1930, p. 26, 32-36, 43; Erben, 1956b, 

p. 12-16, 31, 38; 1957a, p. 46-50; Cantii Chapa, 1969, 

p. 5, 6; 1971, p. 21-24, 36-38). Those beds in the eastcentral area may have been deposited in an arm of the 

Gulf of Mexico (Erben, 1957b, fig. 2) but more probably 

represent a transgression from the Pacific Ocean (Viniegra 0., 1971, p. 484, 492). Those beds in the southern 

area were deposited in waters that definitely connected 

with the Pacific Ocean (Erben, 1957b, p. 39^0, fig. 2). 

Marine beds of Callovian Age probably are also present 

in Cuba (Meyerhoff, 1964, p. 151, 152; Khudoley and 

Meyerhoff, 1971, p. 60), but the fossil evidence has not 

yet been published.

Later Jurassic beds of Oxfordian to Tithonian Age 

are widely distributed throughout the lands bordering 

the Gulf of Mexico (Burckhardt, 1930; Imlay, 1940b,

1943a, p. 1411-1422; 1953a, p. 20^61, figs. 4, 5; Murray, 1961, p. 287-297; Khudoley and Meyerhoff, 1971, 

p. 59-67; Maher and Applin, 1968, p. 9-11; Rainwater, 

1967). The Gulf of Mexico of that time must have had 

marine connections with the Atlantic Ocean via Cuba and 

southern Florida. It must also have been connected with 

the Pacific Ocean either through southern Mexico or 

Central America, or both (Viniegra 0., 1971, p. 484, 

486, fig. 10), judging from the similarities between the 

marine faunas in Mexico and California. The Gulf of Mexico during Late Jurassic time was separated from the 

seas in the western interior region by highlands that extended across parts of central Arizona and New Mexico 

(Harshbarger and others, 1957, p. 43, 44).

PACIFIC COAST

Jurassic rocks near the Pacific Coast of Mexico have 

been found only in the states of Oaxaca and Guerrero, as 

discussed above, and in northwestern Sonora (Burckhardt, 1930, p. 23, 24, 41, 42; Erben, 1957b, p. 36; King, 

1939, p. 1645-1659; Imlay, 1952a, p. 972). Farther north 

in the Pacific Coast region, many Jurassic outcrops are 

found between southern California and westernmost 

Alaska.

Northward through Nevada and California into 

southwestern Oregon, the distribution of outcrops of the 

various stages indicates that the Jurassic seaways gradually shifted westward (Taliaferro, 1942, fig. 2 on p. 80; 

Imlay, 1959a, p. 103-106). Thus, in the Sierra Nevada, 

beds of Callovian Age extend westward beyond beds of 

Bajocian and Early Jurassic age. Beds of Oxfordian to 

early Kimmeridgian Age occur with beds of Callovian 

Age in the foothills of the Sierra Nevada but crop out 

also at two places west of the Callovian beds (Santa Monica Mountains and Klamath Mountains). Beds of Tithonian Age crop out only in western California and in southwestern Oregon. Only in southwestern Oregon have they 

been found in the same sequence with beds of Oxfordian 

to early Kimmeridgian Age.

In east-central Oregon is a thick Jurassic sequence 

(Dickinson and Vigrass, 1965), ranging in age from Hettangian to early Callovian (Imlay, 1964a, 1968, 1973), 

that correlates faunally with thick Jurassic sequences in 

the Sierra Nevada, California, and in the Cook Inlet region, Alaska. In extreme northeastern Oregon and in the 

adjoining part of Idaho, along the Snake River, are beds 

of early Oxfordian Age containing Cardioceras (Imlay, 

1964a, p. D6, D15). Of paleogeographical interest is the 

fact that rocks of that particular age have not been identified in California or in southwestern Oregon but have 

been identified faunally at various places in British Columbia, Alberta, Montana, and Alaska.
18 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

In Washington, Upper Jurassic beds have been found 

only in three areas in the northern part of the State. 

Northward from Washington into Alaska, beds of Early, 

Middle, and Late Jurassic age are widespread, although 

in some areas certain stages are not represented or have 

not been identified faunally.

WESTERN INTERIOR REGION

Marine beds of Early Jurassic age have been identified in the western interior region of Canada as far east 

as westernmost Alberta (Frebold, 1957, p. 5-12; 1964d, 

p. 24-26; 1969). They probably were never deposited 

much farther east or southeast, and they have not been 

found in the western interior of the United States. Faunally, they represent only parts of the Sinemurian, Pliensbachian,.and Toarcian Stages.

Marine beds of earliest Bajocian Age have not been 

identified definitely by fossils in the western interior of 

the United States or Canada. In fact, they have not even 

been found in the eastern half of British Columbia along 

a line drawn from Whitesail Lake southeastward to Taseko Lakes (Frebold, 1951b, p. 18, 19; 1964d, p. 26; Frebold and Tipper, 1970, p. 9, 10). The projection of this 

line farther southeast coincides approximately with the 

easternmost occurrence of lower Bajocian beds in eastern Oregon. Nonetheless, an early to early middle Bajocian Age for the Gypsum Spring Formation (or member) 

in the western interior region is indicated by its position 

unconformably below a limestone whose middle .and upper parts contain late Bajocian ammonites (Imlay, 1967b, 

,p. 19, 26, 27).

By contrast, marine Jurassic beds of middle Bajocian 

to .late Oxfordian or early Kimmeridgian Age are widespread in the western interior of the United States, and, 

with the exception of the late Bajocian, are equally widespread in Canada. These beds were deposited in an embayment that spread eastward from the Pacific Coast region across the northernmost part of the United States 

and adjoining parts of Canada. At one time it was thought 

.that the embayiment in the western interior of Canada 

was partially separated from the Pacific Ocean by a landmass (Schuchert, 1923, p. 226, fig. 14; Crickmay, 1931, 

p. 89, map 10) whose position coincided approximately 

with the present Rocky Mountain trench. Recently, however, Frebold (1954; 1957, p. 37-41; Frebold and others, 

1959, p. 12-16) has presented evidence showing that 

such a landmass did not exist. In contrast with conditions 

in Canada, however, ample evidence exists that at least 

the southern part of the embayment in the western interior of the United States was bounded on the west by 

low landmasses or islands, or both, which furnished some 

sand and pebbles from late Bajocian until Oxfordian time 

(Imlay, 1950, p. 37-42; 1952c, p. 79-82; 1953d, p. 54-

59). The position of these landmasses coincides fairly well 

with that of the Paleozoic Antlers uplift (Roberts and 

others, 1958, p. 2825, 2850, 2851). Similarly, other 

landmasses surrounding the Jurassic embayment on its 

southern, eastern, and northern sides furnished most of 

the clastic sediment that was deposited in the embayment.

Major marine transgressions took place during middle to late Bajocian, late Bathonian to early Callovian, 

and early Oxfordian time. Regressions occurred during 

early Bathonian, middle Callovian, and middle Oxfordian 

to early Kimmeridgian time. Sedimentation was interrupted marginally during the Bathonian (Imlay, 1956a, 

p. 564, 579-580) and regionally during the late Callovian (Imlay, 1952b, p. 1747-1752; 1956a, p. 591; 1957, p. 

475; 1967b, p. 53-57).

The latest Jurassic marine regression began near the 

middle of Oxfordian time, as shown by the presence of 

the early Oxfordian ammonite Cardioceras less than 20 

feet (6 m) below the base of the continental Morrison 

Formation of Late Jurassic age in the Wind River and 

Bighorn Basins.

Farther north in northwestern Montana and in Canada, marine deposition continued into late Oxfordian or 

early Kimmeridgian time, as shown by the presence of 

Buchia concentrica (Sowerby) (Imlay, 1954, p. 60; 1956a, 

p. 595; Frebold, 1953, p. 1238, 1239; 1957, p. 68, Frebold 

and others, 1959, p. 10, 11) considerably below the top of 

the marine sequence. Furthermore, near Fernie, British 

Columbia, a large ammonite, Titanites, of early late Tithonian Age has been found (Frebold, 1957, p. 36, 66, 67; 

Frebold and Tipper, 1970, p. 14-17; Westermann, 1966). 

It appears, therefore, that marine waters disappeared 

from most of the western interior region of the United 

States by the end of early Oxfordian time but persisted 

in northern Montana into late Oxfordian time, and in the 

western interior of Canada, until late Tithonian time.

The characteristics and distribution of the Jurassic 

sediments were greatly influenced by tectonic features 

in the Jurassic embayment (Imlay, Gardner, and others, 

1948; Nordquist, 1955; McKee and others, 1956, pi. 8; 

Imlay, 1957, p. 470-477; J. A. Peterson, 1957, p. 401- 

404; 1972, p. 177). These include broad gentle uplifts in 

north-central Montana (Belt Island) and west-central 

Colorado (Uncompahgre uplift); the large Williston basin 

in eastern Montana, western North Dakota, and adjoining parts of Canada; the Alberta trough extending northward from Belt Island across northwestern Montana far 

into Canada; the Twin Creek trough extending south 

from Belt Island along the Wyoming-Idaho border into 

north-central Utah; the Sheridan arch extending northeast from north-central Wyoming into southeastern 

Montana and separating the Williston basin from the 

Powder River basin (J. A. Peterson, 1954a, p. 474, 477,
SUCCESSION OF AMMONITES AND BUCHIAS BY STAGES 19

489); and the Hardin trough (J. A. Peterson, 1954a, p. 

474; 1957, p. 403), which connects the Williston basin 

with the Twin Creek trough across northwestern Wyoming. Of these tectonic features, Belt Island had the 

greatest influence on the marine currents, salinities, and 

temperatures because of its geographic position and its 

large size, but it supplied very little clastic sediment (Imlay, Gardner, and others, 1948; J. A. Peterson, 1957, p. 

403).

ARCTIC REGION

Beds of Early to Late Jurassic age in northern Alaska 

(Imlay, 1955) bear a succession of ammonites similar to 

that in northern Canada (Frebold, 1958; 1960; 1961, p. 

6-24; 1964a, c; Tozer, 1960, p. 9-12, 15, 19, 20). The 

ammonite successions of these regions do not include any 

ammonite faunules resembling those of middle to late Bajocian, Bathonian, or late Callovian Age in northwest 

Europe. The Bathonian is represented faunally, however, by the ammonite genera Arcticoceras, Arctocephalites, and Cranocephalites, as in East Greenland and 

arctic U.S.S.R. This age determination is based on their 

stratigraphic position below beds of early Callovian Age 

in Greenland (Callomon, 1959).

In southern Alaska, the basal Hettangian is represented by the ammonite Waehneroceras at Wide Bay and 

Puale Bay on the Alaska Peninsula, in the Seldovia area 

south of Cook Inlet, and in the southern part of the 

Wrangell Mountains. Psiloceras occurs in those same 

mountains and also north of Old Rampart near the Porcupine River in northeastern Alaska. The Hettangian is 

probably represented also on Hagermeister Island and in 

the Kuskokwim area by pelecypods identical with species 

found in the basal Jurassic near Seldovia (Imlay and Detterman, 1973, p. 22). The lack of Hettangian ammonites 

in most of northern Alaska is matched by a similar lack 

in arctic Canada and in East Greenland. To date, the 

presence of Hettangian deposits in northern Alaska is 

based on one specimen of Psiloceras (Franziceras) obtained from a core at the depth of 2,170.5 feet (661.6 m) 

in the South Barrow test well 12, about 10 miles (16 km) 

southeast of Point Barrow.

SUCCESSION OF AMMONITES AND BUCHIAS BY 

STAGES

HETTANGIAN

In Mexico, the Hettangian Stage has not been identified faunally. The presence of one ammonite similar to 

the Hettangian genus Psiloceras is not valid evidence of 

such an age because of its association with the early Sinemurian ammonite Coroniceras (Flores Ldpez, 1967, p. 

26, 29, 30, pi. 8, fig. 1).

In western Nevada and eastern Oregon, the basal 

Jurassic has furnished ammonite genera that specifically 

and stratigraphically correspond close to Hettangian ammonites in Europe (Muller and Ferguson, 1939, p. 1611, 

chart opposite p. 1590; Corvalan, 1962; Hallam, 1965, p. 

1485-1487, 1494). These include, in particular, the genera Waehneroceras and Psiloceras in the lower part of 

the Hettangian sequence and the genera Schlotheimia, 

Caloceras, and Alsatites in the upper part.

SINEMURIAN

In east-central Mexico, the highest and lowest parts 

of the Sinemurian are represented by ammonites closely 

similar to or identical with ammonites in Europe (Burckhardt, 1930, p. 8-23; Erben, 1956a, p. 124-149; 1957a, 

p. 44; Flores Ldpez 1967, p. 29, 30). No evidence exists, 

however, for the presence of the European zones of 

Caenisites turneri and Asteroceras obtusum (Hallam,

1965. p. 1491-1493).

In northwestern Mexico near El Antomonio, Sonora, 

the early Sinemurian is represented by Arnioceras (Imlay, 1952a, p. 973). Pelecypods of Hettangian or Sinemurian Age are present in west-central and southern 

Sonora (Burckhardt, 1930, p. 23, 24, 41, 42; King, 1939, 

p. 1655-1659, pi. 5). The late Sinemurian is probably 

represented by Crucilobiceras about 25 miles (40 km) 

south-southeast of Caborca, on the basis of collections 

made by L. T. Silver (California Inst. Technology).

In western Nevada, the Sinemurian succession is 

nearly the same as that in eastern Mexico; it has the 

same faunal gaps and includes similar species, some of 

which may be identical with species in Mexico and Europe (Muller and Ferguson, 1939, p. 1611, 1612, table 3). 

Similar faunal successions have been found also in eastern Oregon, western and northwestern Canada, and 

southern and northern Alaska. (See fig. 13.) Nearly all 

successions contain ammonites representing the highest 

and lowest parts of the Sinemurian (Frebold, 1957, 1959,

1966. 1975; Frebold and Tipper, 1970) but lack any evidence for much of the middle part of the stage. Thus, the 

European Caenisites turneri zone has been identified 

only in the Wrangell Mountains, Alaska (Imlay and Detterman, 1973, p. 22); the Asteroceras obtusum zone, only 

in southern British Columbia (Frebold, 1964d); and the 

Oxynoticeras oxynotum zone, only in the Richardson 

Mountains of northwestern Canada (Frebold, 1960, p. 

16, pi. 4, figs. 1^5).

PLIENSBACHIAN

Ammonites of Pliensbachian Age have been found in 

southeastern and south-central Mexico, western Nevada 

(Muller and Ferguson, 1939, p. 1621, 1622; Silberling,
20 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

Stages

Toarcian

Pliensbachian

Sinemuriart

0)

§:

D

_l

0,

aD

0)

_j

0)&D

_i

5

o>

c

i

Northwest European 

ammonite zones 

(after Dean and others, 1961)

Dumortieria lavesquei

Grammoceras thouersense

Haugia variabilis

Hildoceras bifrons

Harpoceras falcifer

Dactylioceras tenuicostetum

Pleuroceras spinatum

Ameltheus mergaritatus

Prodactylioceras devoei

Tregophylloceras ibex

Uptonie jamesoni

Echioceras raricostatum

Oxynoticeras oxynotum

Asteroceras obtusum

Caenisites turner!

Arnioceras semicostatum'

Arietites bucklandi

Schlotheimia anguleta

Alsatites liasicus

Psiloceras planorbis

Eastern and 

southern Mexico 

(Erben, 1956a, 

1957a; 

Hallam, 1965)

Lower part 

of coal and 

plant-bearing 

beds

Arieticeras 

(Guerrero embayment 

only)

Uptonia?

Crucilobiceres?

r- ,3nd Echioceres

Oxynoticeras

—————— ? ——————

Arnioceras

Coroniceras

Not exposed

Western Nevada 

(Mullerand 

Ferguson, 1939; 

Hal lam, 1965}

Grammoceras 

and 

Pseudotioceras

Catecoeloceras 

and 

Dactylioceras

Nodicoeloceres

Arieticeres

Uptonie?

——————— ? ———————

Eoderoceras and 

Crucilobiceres

Oxynoticeres 

f

Arnioceres, 

Arietites, 

Coroniceras, and 

Megerietites

Schlotheimia 

and Alsatites 

-\

Waehneroceras 

and Psiloceres

East-central 

Oregon 

(Imlay, 1968)

Catulloceras 

and Dumortierial

Heugia and 

Potyplectus

—————— ? ——————

Arieticeras,Reynesoceres, Peltarpites, 

Prodactylioceras, 

and Lepte/eoceras 

—————— ? ——————

Eoderoceras and 

Crucilobiceres

f

Arnioceres

——————— ? ———————

Schlotheimie 

and Alsatites 

?

Waahneroceres 

and Psiloceras

Canadian Rocky 

Mountains 

(Frebold, 1969; 

Frebold and Tipper, 

1970)

Phylseogrammoceras 

and 

Gremmoceras

Phymatoceras 

and 

Paronoceres

Harpoceras 

cf. H. exaretum and 

Dactylioceres

Pleuroceras and 

Dactylioceras

Ameltheus

7

Phricodoceras

Eoderoceres and 

Gleviceras'

Arietites 

and 

Arnioceres

Probably absent

British Columbia, 

southern part, 

including islands 

(Frebold, 1964a, d; 

Frebold and 

Tipper, 1970)

Phylseogrammoceres 

and 

Grammoceras

Harpoceres 

cf. H. exaratum and 

Dactylioceres

Fanninoceres

Acanth'opleuroceras , 

Uptonia, Trfpidoceras

Echioceres

Asteroceras

Coroniceras 

bisulcatum and 

Arnioceras

Psiloceras canadense, 

Paracalo ceres , a nd 

Charm asseiceras

Psiloceraf 

aff. P. planorbis

A. Mexico to southern British Columbia.

FIGURE 13.—SUCCESSION AND CORRELATION OF

1959, p. 26-29; Corvalan, 1962; Hallam, 1965, p. 1485- 

1488), east-central California (Clark and others, 1962, 

p. B19), east-central Oregon, both southern and northern Alaska (fig. 13) (Imlay, 1952a, p. 981; 1955, p. 87; 

Howarth, 1958, p. XXVI), and in western and northwestern Canada.

The faunal evidence for the Pliensbachian in Mexico 

is meager. It consists only of two fragments resembling 

Uptonia from Puebla (Erben, 1956a, p. 365, pi. 41, figs. 

14, 15) and of one specimen of Arieticeras from Guerrero 

(Erben, 1954, p. 5, pi. 1, figs. 4, 5).

Bed of early Pliensbachian Age have not been identified faunally in Oregon or California, and their presence 

in Nevada is questionable. Beds of late Pliensbachian 

Age in Nevada contain the ammonite Arieticeras. Such 

beds in Oregon and California contain the ammonites 

Reynesoceras, Arieticeras, Fontanelliceras, Canavaria, 

Protogrammoceras, Fuciniceras, Leptaleoceras, Prodactylioceras, Tragophylloceras, Fanninoceras, Liparoceras (Becheiceras), and Paltarpites, With these ammonites in the upper part of their range are some 

specimens of Dactylioceras. This assemblage is characterized by an abundance of genera of the families Dactylioceratidae and Hildoceratidae and by an absence of 

the Amaltheidae. In these respects this assemblage 

shows much more resemblance to the late Pliensbachian 

ammonites of the Mediterranean region than to those of 

northwest Europe. Its age until recently was considered 

to be early Toarcian (Hallam, 1965, p. 1485-1488; Dickinson and Vigrass, 1965, p. 37, 41), but the association 

of genera listed previously is excellent evidence for a late 

Pliensbachian Age.

In Alaska, by contrast, the beds of late Pliensbachian 

Age contain genera of the family Amaltheidae, such as 

Amaltheus and Pleuroceras, that are specifically identical wit^h or closely similar to species in northwestern Europe. Faunally, the late Pliensbachian ammonites of 

Alaska have much more in common with ammonites of 

that age in northwestern Europe than with ammonites in 

Oregon and California.
SUCCESSION OF AMMONITES AND BUCHIAS BY STAGES 21

Southern Yukon 

and northern 

British Columbia 

(Frebold and Tipper, 1970)

Catulloceras 

and 

Grammoceras

Phymatoceras 

and 

Peronoceras

Pleuroceras?, 

Amaltheus, Paltarpites, Arieticeras, 

Leptaleoceras

Prodactylioceras 

davoei, Becheiceras

 >

Platypleuroceras ?

Paracoroniceras 

and 

Arniotites

Psiloceras canadense

Psiloceras erugatas

Southern Alaska 

(Imlay, 1968; Imlay 

and Detterman, 1973}

Grammoceras

Haugia and 

Phymatoceras

Dactylioceras

cf. D. commune 

——————— ? ———————

Pleuroceras, Amaltheus, 

and Paltarpites

Uptonia, Apoderoceras, 

and Acanthopleuroceras

Crucilobiceras

Microderoceras 

7

Arnioceras 

f

Coroniceras

Waehneroceras 

and Psiloceras

Northern Alaska 

(Imlay, 1955; Imlay 

and Detterman, 1973)

Pseudolioceras

Dactylioceras. cf. 

D. commune

Dactylioceras cf. 

D. semicelatum

Pseudoamaltheus

Amaltheus margaritatus

Amaltheus stokesi

Crucilobiceras

Arnioceras

Coroniceras

Psiloceras

Richardson and 

British Mountains, 

northwestern Canada 

(Frebold, 1964a, b; Frebold 

and others, 1967)

Peronoceras and 

Pseudolioceras

Dactylioceras aff. 

D. commune

Harpoceras aff. 

H. exaratum

Amaltheus stokesi

Echioceras

Oxynoticeras oxynotum

——————— ? ———————

Arietitesl

Canadian 

Arctic Islands 

(Frebold, 1960, 

1964a, b, 1975)

Peronoceras and 

Pseudolioceras

Dactylioceras commune 

and Harpoceras

Hilda ites and 

Harpoceras

Amaltheus stokesi

Echioceras arcticum

Gleviceras plauchuti

f ,

Coroniceras and 

Charmasseiceras

Nonmarine beds

East Greenland 

(Rosenkrantz, 

1934; Donovan, 

1957)

——————— ? ———————

Pseudolioceras 

compactile

Dactyiloceras and 

Catacoeloceras

Androgynoceras ?

Uptonia jamesoni

Nonmarine beds

Stages

D

1

10.

_1

1Q.

_1

Toarcian

Pliensbachian

Sinemurian

Henangian

. B. Northern British Columbia to East Greenland. 

HETTANGIAN TO TOARCIAN AMMONITES IN NORTH AMERICA.

In western Canada, most parts of the Pliensbachian 

Stage are represented in at least one of the sequences 

exposed in the Rocky Mountains, British Columbia, and 

the northern Yukon. (See fig. 13.) The lower Pliensbachian is best known from the Queen Charlotte Islands 

(Frebold, 1967a, p. 1146, 1147; Frebold and Tipper, 1970, 

p. 4-6). The middle and upper Pliensbachian are best 

known from northern British Columbia and the southern 

Yukon (Frebold, 1964d, p. 25; Frebold and Tipper, 1970, 

p. 6).

In arctic Canada, the Pliensbachian is represented 

to date only by an occurrence of Amaltheus stokesi in 

the British Mountains, Yukon Territory (Frebold and 

others, 1967). This species furnishes an accurate correlation with the upper Pliensbachian ammonite sequence 

in northern Alaska and in Europe.

TOARCIAN

Ammonites of Toarcian Age have been found in the 

United States in the same general areas as ammonites of

Pliensbachian Age (fig. 13). They greatly resemble the 

ammonites in Toarcian beds in Europe in appearance and 

in stratigraphic succession.

In western Nevada, Toarcian ammonites have been 

found at several places, and a fairly complete sequence 

of Toarcian beds has been identified near Westgate 

(Muller and Ferguson, 1939, p. 1621; Corvalan, 1962; 

Hallam, 1965, p. 1486-1488). At this place, correlation 

with the lower, middle, and upper parts of the Toarcian 

Stage of Europe is furnished by the presence of an ammonite succession consisting ofNodicoeloceras, Catacoeloceras, and Grammoceras. Of these, Nodicoeloceras occurs a few feet above Arieticeras of probable late 

Pliensbachian Age, Catacoeloceras, about 165 feet (50 m) 

above Arieticeras, and Grammoceras, about 125 feet (38 

m) higher than Catacoeloceras.

In east-central Oregon southwest of John Day, the 

lower and middle parts of the Toareian have not been 

identified faunally. The upper Toarcian is represented, 

however, by a few ammonites obtained from the basal
22 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

Stages

ovian

"5 

o

Bathonian

Bajocian

1 

a

D

£ •a 

•a

i

_i

&a

D

a> •a 

•a

i

o

&QD

a> •a 

•a

i

1

Standard zones in northwest 

Europe (Callovian, after 

Callomon, 1964; Bathonian, 

after Torrens, 1965; 

Bajocian,after Arkell, 1956; 

and Gabilly and others, 1971}

Quenstedtoceres lamberti

Peltoceres ethlete

Erymnocaras coronetum

Kosmoceras Jason

Sigeloceras calloviense

Mecrocephalites macrocephalus

Clydoniceras discus

Oppelia aspidoides

Hecticoceras retrocostatum

Morrisiceras morrisi

Gracilisphinctes progracilis

Zigzag iceras zigzag

Parkinsonia parkinsoni

Garantiana garentiane

Strenoceres subfurcatum

Stephanoceras humphriesianum

Otoites sauzei

Sonninia sowerbyi

Graphoceres concavum

Ludwigia murchisonae

Leioceras opal in urn

Mexico (Burckhardt, 1927, 

1930; Arkell, 1956; Imlay, 

1952a; Erben, 1956b, 

1957a; Cantu Chapa, 1963, 

1967, 1971)

Peltoceres spp.

Erymnoceras mixtecorum

Neuquenicerasl neogeeum, 

Reineckeia, Reineckeites,

Eurycephalites boesei 

and XenocephalHes

Epistrenoceres 

paracontrarium

Zigzegiceras floresi

Parastrenoceres mixtaca

Leptosphinctes?

Normannites undulatum 

and Stephanoceras

Upper part of coal- and 

plant-bearing beds

Eastern Oregon and California 

(Imlay, 1961, 1964a, 1973)

Peltoceras (Metapeltocerasl) 

(eastern California only)

Lilloettia cf. L. stantoni and 

Pseudocadoceras grewingki

Lilloettie buckmani, 

Xenocephelites vicar ius, 

Kepplerites cf . K. torrensi, 

Iniskinites intermedius

Cobbenites and 

Parareineckaia

Megasphaeroceres rotundum, 

Leptosphinctes, Normannites, 

and Spiroceres bifurcetum

Chondmceras ellani and 

Normannites crickmayi and 

Teloceras itinsae

Dorset en sia oregonensis

Parabigotites crass/cost at us

Papilliceras stantoni

Euhoploceres modesta, 

Docidoceras, Eudmetoceras,

freest rig ites and 

Eudmetoceras Tmetoceres

scissum 

 f

Western interior region of 

United States (Imlay, 

1952a,b,c, 1962b, 1967b)

Quenstedtoceras collieri

Disconformity in Montana 

and northern Wyoming

Kepplerites maclearni

K. cf. K, tychonis

K. subitus

K. costidensus

Warrenoceres codyense

Parecephalites 

sewtoothensis 

and Cobbenites

Gryphaea 

nebrascensis

£

Gryphaea impressimar

 7 ——————— ——— |

Schlites spinosus, 

Parechondroceres andrewsi, 

and Gyphaea planoconvexa

Megasphaeroceres, Spiroceras, 

Stephanoceras, Stemmetoceras, 

and G. plenoconvexe fratema

Chondmceras cf. C. elleni 

and . • Stemmatoceres arcicostatum

Canadian Rocky Mountains 

(Frebold, 1957, 1963, 1964a, b; 

Frebold and Tipper, 1970)

Imlay o car as miettense

Kepplerites maclearni

K. cf. K. tychonis

Werrenoceres spp., 

Kepp/erites,and Cobbanites

ParacephaHtes glabrescens

<

Chondmceras allani, 

Stemmatoceras, Stephanoceras, 

Teloceras, and Zemisteohanus

^

Arkelloceres and 

Stemmetoceras

Sonninia (Euhoplocerasf) and 

Latiwitchellia gracilis

A. Mexico to western interior region.

FIGURE 14.—SUCCESSION AND CORRELATION OF

part of the Snowshoe Formation (Dickinson and Vigrass, 

1965, p. 49). Of these, Haugia, Polyplectus, and Grammoceras! were obtained about 75 feet (23 m) above the 

base of the formation, Polyplectus and Catulloceras, 

from 100 to 125 feet (30 to 38 m) above the base, and 

Dumortieria!, about 125 feet (38 m) above the base. At 

one place, Tmetoceras was found 125-200 feet (38-61 m) 

above the base of the Snowshoe Formation.

In the Talkeetna Mountains in south-central Alaska 

northeast of Anchorage, the early Toarcian is represented by both finely and coarsely ribbed species ofDactylioceras, the middle Toarcian, by Haugia and Phymatoceras, and the late Toarcian, by Grammoceras. 

Available collections do not include any specimens of 

Dumortierial or Catulloceras, such as characterized the 

uppermost Toarcian beds in east-central Oregon.

In northern Alaska, the early Toarcian is represented by the ammonites Nodicoeloceras and Dactylioceras obtained at depths of 1,772 to 2,063 feet (540 to 

629 m) in the South Barrow test well 3, near Point Barrow (Imlay, 1955, p. 82, 87-88, pi. 10, figs. 6, 9-16,

pi. 12, figs. 12-14). The early Toarcian is represented 

also by Harpoceras cf. H. exaratum (Young and Bird) 

obtained from outcrops near the Sadlerochit River. The 

late Toarcian is possibly represented by species ofPseudolioceras resembling P. compactile Simpson (Imlay, 

1955, p. 89, pi. 12, figs. 17, 18, 21). The genus Pseudolioceras, however, ranges from early Toarcian to early 

middle Bajocian and is not very useful as a guide fossil.

In western Canada, the early Toarcian is represented by Harpoceras cf. H. exaratum (Young and Bird) 

and several species of Dactylioceras; the middle Toarcian, by Phymatoceras and Peronoceras; and the late 

Toarcian, by Phylseogrammoceras, Grammoceras, and 

Catulloceras (Frebold and Tipper, 1970, p. 17). These 

ammonites correlate closely with the Toarcian ammonite 

succession in southern Alaska.

In arctic Canada, the ammonite succession is likewise similar to that in southern Alaska, except for the 

presence of Pseudolioceras in its upper part as in northern Alaska and East Greenland (Frebold, 1960, 1964b, 

1964c, 1975).
SUCCESSION OF AMMONITES AND BUCHIAS BY STAGES 23

British Columbia and 

southern Yukon (Frebold, 

1964a-d, 1967a,b; Frebold 

and others, 1969; Frebold 

and Tipper, 1970, 1975)

Quenstedtoceras henrici

?

Cadoceras (Stenocadoceras] 

striatum, C. (S.) spp., 

Pseudocadoceras spp.

Lilloettia buckmani, 

Cadoceras catostoma, 

Kepplerites , Cadoceras, 

Psaudocedoceras,and 

C. (Paracedoceras)

Cranocaphalites costidensus

Zemistephanus, Cobbanites, 

and Megasphaeroceras?

Normannites crickmayi, 

Teloceras itinsae, and 

Zamistephanus richardsoni

Wfcchellia (LaHw/tchelliat). 

Guhsania be/la, and Sonninia

Erycites and Tmetoceras

Southern Alaska (Imlay, 1953b, 

1962a,b, 1964b; Imlay and 

Detterman, 1973; Westermann, 

1964, 1969)

Absent

Cadoceras (Stenocadocera. 

stenoloboide and 

Lilloettia stantoni

Cadoceras catostoma, 

C. (Paracadoceras} __ 

tonniense, and 

Lilloettia buckmani

Disconfyrmjty^---^j(jnitas

f)

1

Arctocephalites cf. A. alegans

CranocaphalHas spp

C. costidensus

lit as

Angular unconformity on 

Iniskin Peninsula

Megasphaeroceras rotundum, 

Leptosphinctes.and Normannitas

Chondroceras allani, 

Normannites crickmayi, 

and Teloceras itinsae

Stephanoceras kirschneri

Parabigothas crassicostatus 

and Arkelloceras

?

Docidoceras widebayensa 

and Sonninia

Erycitoides howelli, 

Pseudolioceras whiteavesi. 

and Tmetoceras scissum

Northern Alaska 

(Imlay, 1955; Imlay 

and Detterman, 

1973)

Cadoceres sp.

'

Arcticoceras ishmae y

Arctocephalites cf. 

A. alegans

Cranocephalites 

ignekensis

Cranocephalites sp.

I 

————— > _____

Arkelloceras

Erycitoides howelli, 

Pseudolioceras 

whiteav'asi

Pseudolioceras 

maclintocki

Richardson and 

British Mountains, 

northwestern Canada 

(Frebold, 1964a-c; 

Frebold and others, 

1967)

Cadoceras septentrionale, 

C. (Stenocadoceras)

V

;anadanse,and > 

ylloceras bakeri /

'

Arcticocaras ishmae

Arctocephalites spp.

>

Cranocephalites borealis

————————— 7 —————————

Arkelloceras

Erycitoides cf. 

E. howelli

Canadian Arctic 

Islands (Frebold, 

1960, 1964a-d)

Cadoceras 

saptentrionale

'

Arcticoceras ishmae

Arctocephalites spp.

Cranocephalites

Arkelloceras

Pseudolioceras 

maclintocki and 

Leioceras opalinum

East Greenland (Donovan, 

1957; Callomon, 1959; 

Surly k and others, 1973)

Kosmoceras and Longaevicaras

Kosmoceras 

and 

Pseudocadoceras

Sigaloceras calloviensa

Cadoceras cf. C. septentrionale 

Cadocaras n. sp.

Cadoceras n. so.

Cadoceras calyx

Cadoceras variabila

Arcticoceras n. sp.

Arcticocaras ishmae

Arctocephalitas greenlandicus 

Arctocephalites arcticus

Cranocaphalites pompeckji

Cranocephalites indistinctus

Cranocephalites borealis

Stages

1 

a

£

i

. 

I

1

a

D

a> •o 3

I

I 

a

D

a>

i

.

c 

a

1

u

Bathonian

.§

'I 

m

B. British Columbia to East Greenland. 

BAJOCIAN TO CALLOVIAN AMMONITES IN NORTH AMERICA.

BAJOCIAN

The only Bajocian ammonites found in southern Mexico are from upper Bajocian strata in northeastern Guerrero and northwestern Oaxaca. Of these, Normannites 

(Burckhardt, 1927, p. 22, pi. 12, figs. 1-4), in association 

with Stephanoceras, could represent the Stephanoceras 

humphriesianum zone of Europe, or the next younger 

zone. Leptosphinctesl (Burckhardt, 1927, pi. 11, figs. 11, 

12) could represent the early late Bajocian. Parastrenoceras mixteca Ochoterena F. (Ochoterena F., 1963, p. 7, 

pi. 1; Burckhardt, 1927, pi. 16, figs. 10, 11, 16) probably 

represents some part of the late Bajocian younger than 

the beds containing Normannites.

Fairly complete and closely similar ammonite successions of Bajocian Age have been found in east-central Oregon (Imlay, 1973, p. 16-31, figs. 3-8) and in southern 

Alaska (Westermann, 1964, 1969; Imlay, 1962a, 1964b; 

Imlay and Detterman, 1973, p. 23-24). In neither area 

is there any faunal evidence for the earliest Bajocian 

(Lioceras opalinum zone). Otherwise, in both areas, the

succession of ammonite genera from Tmetoceras at the 

base up to Teloceras is remarkably similar to that in Europe and in other parts of the world. Exceptions include 

a few genera that have been found only in areas bordering the Pacific Ocean (Imlay, 1965, fig. 1 on p. 1024). 

Among such genera are Pseudotoites, Parabigotites, and 

Zemistephanus, which occur in stratigraphic succession 

associated respectively with the genera Docidoceras, 

Otoites, and Teloceras.

In both southern Alaska and Oregon, beds of late Bajocian Age are identified by the presence of Leptosphinctes and Sphaeroceras. In Oregon, associated ammonites include Spiroceras, Normannites, and Megasphaeroceras. In southern Alaska, associated ammonites 

include Megasphaeroceras, Oppelia (Lyroxyites), and 

Normannites (Imlay, 1962a). Of these, Megasphaeroceras and the subgenus Lyroxyites are known 

only from North America. The presence of Normannites 

suggests that the fauna is not younger than the earliest 

late Bajocian.
24 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

'Stages

Tithortian

Kimmeridgian

Oxfordian

Q>

a3

Q>

_1

1

Q.

1

3

a> •D 

T3

i

&

_i

Nqrthwest European ammonite 

zones (Arkell, 1956; CaHomon,1 964; 

Enay, 1964, 1971, 1972; Cope, 

1967; Enav anrf others, 1971; 

Saks and Shulgina, 1972)

Titanites giganteus

Glaucolithites gorei

Zaraiskites albani

Pavlovia pallasioid&s

Pavlovia rotunda

Pectinatites pectinatus

Arkellites hudlestoni

Virgatoaphinctoides wheatleyensis

Virgatosphinctoides scitulus

Virgatosphinctoides elegans

Aulacostephanoceras 

acutissiodorensis

Aulacostephanus eudoxus

Rasenia mutabilis

Rasenia cymodoce

Pictonia baylei

Ringsteadtia pseudocordata

Decipia decipiens

Perisphinctes cautisnigrae

Gregaryceras trensversarium

Perisphinctes plicatilis

Cardioceras cordatum

Quenstedtoceras mariae

Cuba (Imlay, 1942, 1943&, 

1952a; Burckhardt, 1930; 

Jaworski, 1940; Judoley 

and FurrazQla-Bermudez, 

1965)1968; Berrnudez;T961; 

Arkell, 1956)

Gulf region of United 

States (Imlay, 1943a, 1945)

Substeueroceras

Durangrtes vu/garis, \. 

Parodontoceras butt/, 

Corongoceras, Simocaras, 

Protaneyloceras, Lytohoplftes, 

Virgatosphinctes , 

Metahapioceras, Dickersonia, 

Micracanthocaras, andPseudO;. 

i lissoceras zfcteli i

Virgetosphinctes and 

Subp/anites

Discosphinctes carribeanus, 

Ochetoceras canal iculatum 

var, 

Dichotomosphinctes 

p/icatiloides, 

Orthosphinctas, Decipia, 

Arisphinctes, Perisphinctes, 

Euaspidocaras, and 

Aspidoceras

Glochiceras fialar

Idoceras cf. /. durangense 

Idoceras cf. /. balderum

Ataxioceras

Discosphinctes cf . D. 

carribeanus, 

Dichotomosphinctas, 

Orthosphinctes, 

Ochetoceras 

canaliculatum,and 

Euaspidoceras

Eastern1 and. northern Mexico 

(Irnlay, 1943», b,1952a,1953c, 

T961; Erben, 1957a; Cantii 

Chapa,1963, 1967, 1971; 

Bridges, 1965; Burckhardt, 

1906, 1&12, 1919,1927,1930)

BerriaseUe ^-o 

Substeueroceras, ts § 

Aulacosphinctes , ^~ 

Protacanthodiscus , jjgw 

Proniceras, and |§ « 5 

Protancyc/oceras fCoo

Kossmatia victoris, 8 i «? 

Durangitas vu/garis, § § S 

Parodontoceras butti, g h^ 

Dickersonia, Sinmcarast gj| 

Virgatosimoceras, ij"r 

LytohopJites, Sg 

Pseudolissoceras zfttali, £ g

Virgatosphinctes, 

Aulacosphinctoides, 

Torquatisphinctes , 

Subp/anites, 

Pseudolissoceras 

(rere),and 

Mazapilites

Hybonoticaras

Glochiceras fialar, Buchia 

mosquensisr,ar\d Buchia

Idoceras cf. 1.. balderum

 >

Ataxioceras, Rasenia, and 

Sutneria cf. S. platynota

Discosphinctas carribeanus , 

Ochatoceras canaliculatum , 

Dichotom osphinctes 

plicatiloides, and 

Euaspidoceras

Dichotomosphinctes 

durangensis

California, Oreqon.and 

western Idaho (Imlay, 

1961, 1964a; Imlay and 

Jones, 1070)

Substeueroceras: 

Pronicaras, 

Sprticeras, 

Parodontoceras^

Spit/ceres-, | 

Parodontoceras^

Kossmatia

Buchia 

aff. 

B.okensis

 Buchia 

fischariana

BucMa 

piochii

Angular 

unconformity

Idoceras and 

Amoeboceras 

(Amoebites) 

dubium

Discosphinctes 

virgulatiformis 

and 

Dichotomosphinctas 

muhlbachi

Buchia concentrica

——————— ? ———————

Cardioceras(Scarburgiceras) 

martini (only in Idaho)

Western interior United 

States (Imlay; 1947, 1948; 

1952a, b, c, 1966% b; 

Reaside,19ia)

Continental beds

Buchia concantrica in 

northwestern Montana

Cardioceras spp.

Cardioceras cordiforme

Scarburgicaras and 

Pavloviceras

A. Gulf of Mexico, Pacific Coast, and western interior region.

FIGURE 15.—SUCCESSION AND CORRELATION OF

The Bajocian is poorly represented in the western 

interior of the United States. A middle Bajocian Age, 

probably corresponding to the European zone of Stephanoceras humphriesianum, is shown by one specimen 

of Chondroceras and several fragments of Stemmatoceras from the basal part of the shale member of the 

Sawtooth Formation exposed at Swift Reservoir in 

northwestern Montana (Imlay, 1948, p. 19, pi. 5, figs. 

1-5; 1967b, p. 28). A late Bajocian Age is shown by an 

association of Spiroceras, Stemmatoceras, Stephanoceras, and Megasphaeroceras in the upper part of the 

lowermost limestone (Sliderock Member) of the Twin 

Creek Limestone near the border of Wyoming and Idaho 

(Imlay, 1967b, p. 28, 29). The association of the first 

three genera in the Twin Creek Limestone, by comparison with the European faunal succession, indicates a 

correlation with the basal part of the upper Bajocian.

The presence of Megasphaeroceras furnishes a correlation with lower upper Bajocian beds in southern Alaska. 

The overlying beds (Rich Member) of the Twin Creek, 

containing Parachondroceras saidSohlites (Imlay, 1967b, 

p. 31), are correlated with the uppermost Bajocian on the 

basis of stratigraphic position and the resemblances of 

the ammonites to genera of Bajocian Age.

In northern Alaska, only the lower Bajocian and part 

of the middle Bajocian have been identified. The European zone ofLioceras opalinum is probably represented 

by Pseudolioceras maclintochi (Haughton) (Westermann, 1964, p. 422-424; Imlay, 1955, p. 89, pi. 12, figs. 

15, 16), which in arctic Canada has been found with Lioceras opalinum (Reinecke) (Frebold, 1958, p. 23; 1960, 

p. 28). The European zone of Tmetoceras scissum is 

probably represented by one fragment of Tmetoceras obtained from a test well (Imlay, 1955, p. 89, 90) and by
SUCCESSION OF AMMONITES AND BUCHIAS BY STAGES 25

Canadian Rocky Mountains 

(Frebold, 1964a; FrebQld and 

others, 1959; Frebold and 

Tipper, T970)

Buchia tf. B. fischeriana 

f

Titan&es occidentaHs 

and Buchia piochii

f

Buchia 

 mosquensis

Amoeboceras and 

Buchia concentrica

Cardioceras and 

Go/iathiceras

British Columbia and • southern Yukon <frebo»d, 

t964a;Frebotd and Tipper, 

1970; Jeletzky, 1965)

Buchia fischeriana

?

Buchia piochii and 

Buchia blemfordiana

——————— ? ————————

Buchia 

mosquensis

Amoeboceras and 

Buchia concemrica

'?

Cardioceras 

(Sub vertebriceras } canadense

Cardioceras (Scarburgiceras) 

martini

Southern Masks dm lay, 

1963b, 1961; Im lay and 

Detterman, 1973)

Buchia fischeriana and 

Buchia piochii

 Buchia rugosa and 

'Buchia mosquensis

Amoeboceras 

(Peionodoceras) 

spiniferum and 

Dichotomosphina.es

Buchia concentrica

7

Cardioceras distans

Cardioceres (Scarburgiceras) 

martini

Northern Alaska (Imlay, 

1955; Imlay and 

Oetterman, 1973)

Buchia unscherrsis and 

Buchia ci B. fischeriana

•j»

Buchia rugosa and 

Buchia mosquensis

•8

1

Amoeboceras § 

(Prionodoceras) „

I

Cardioceras (Scarburgiceras)

Arctic Canada (Frebold, 

1964a; Jeletzky, 1965, 1966)

Craspeetftes 

canadensis and 

Buchia unschensis

Buchia fischeriana

Buchia richardsonensis

Buchia piochii

^

Buchia mosquensis

Amoeboceras and 

Buchia concentrica

Cardioceras (Scarburgiceras)

East Greenland (After Spath, 

1935,1936; Arkell, 1956; 

Oonovan, 1957)

aff . Chetatites chelae

Subcraspedites cf . S. 

p/tcompha/us

Laugeftes vogulicus

Claucolithites 1

f Pavlovia and Buchia § 

mosquensis o

Q

Pectinatites

SuhpJanitesl

; Hoplocsrdioceras

BnCj Euprionoceras

Buchia 

concentrica Rasenia

Amoeboceras 

(Prionodocaras) 

and 

Ringsteattm

Cardioceras

Stages

1 

a

D

1

a 

a 

a

Z)

<u

_i

S

a. 

n.

O

.2 

?

i

_i

Tithonien

Kimmeridgian

Oxford ian

B. Southwestern Canada to East Greenland. 

OXFORDIAN TO TITHONIAN AMMONITES IN NORTH AMERICA.

several specimens of Erycitoides obtained from outcrops 

(Imlay, 1955, p. 90, pi. 13, figs. 12, 13). The middle Bajocian is represented only by Arkelloceras, whose age is 

based on stratigraphic occurrences on the Alaska Peninsula (Imlay, 1964b, p. B18, B53) and in the Canadian 

Rocky Mountains (Westermann, 1964, p. 405-409; Frebold and others, 1967, p. 20).

Bajocian ammonites in the Canadian Rocky Mountains, British Columbia, and southern Yukon bear close 

resemblances specifically and stratigraphically to the Bajocian ammonites in eastern Oregon and in southern 

Alaska. The main difference is the rarity in western Canada of ammonites of early and late Bajocian Ages and of 

the Otoites sauzei zone of the middle Bajocian.

In arctic Canada, the Bajocian ammonite sequence is 

identical with that in northern Alaska, except for the 

presence of Leioceras opalinum near the base. As in

northern Alaska, the only middle Bajocian ammonite 

present is Arkelloceras.

BATHCPNIAN

Lowermost and uppermost Bathonian sediments have 

been identified in northeastern 'Guerrero and northwestern Oaxaca, Mexico, on the basis of ammonite evidence. 

These beds were deposited in .an embayment (Guerrero) 

from the south that apparently connected with the Pacific Ocean and did not extend to the Gulf of Mexico (Erben, 1957b, p. 35, 39, fig. 2). The -earliest Bathonian is 

represented by Zigzag'iceras floresi Burckhardt (Burekhardt, 1927, p. .25, pi. 12, figs. 14-16, 18-20; Arkell, 

1956, p. 564; Erben, 1956b, p. 110,122; 1957a, p. 50) and 

the latest Bathonian, by Epistrenoceras paracontrarium
26 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

Staga

Tithonian

D

_i

Northwest Europe 

(Enay, 1971, 1972)

Titan ites giganteus

Glaucolithites gorei

Zaraiskites albani

Pavlovia pallisioides

Pavlovia rotunda

Pectinatftes 

pectinatus

Arkellites 

hudlestoni

Virgatosphinctoides 

wheatleyensis

Virgatosphinctoides 

scitulus

Virgatosphinctoides 

elegans

Southern Europa 

{Enay, 1971, 1972)

Paraulacosphinctes 

transitorius

Pseudovirgatites 

scruposus

Pseudolissocaras 

bavaricum

Sublithacoceras 

penicillatum

Franconites vimineus

Dorsoplanitoides 

triplicatus

Hybonoticeras 

hybonotum 

and 

Glochiceras 

lithographicum

Argentina 

(Gerth, 1925; Weaver, 193 

Leanza, 1945; Arkell, 193

Substeueroceras 

koeneni

7

Corongoceras alternant

7

Windhauseniceras 

interspinosum

•»

Pseudolissoceras 

zitteli

 >

Virgatosphinctes 

mendozanus

———————— ? —————

(Burckhardt) (Burckhardt, 1927, p. 80, 94, 95, pi. 16, 

figs. 14, 15; Arkell, 1956, p. 564; Erben, 1956b, p. 119; 

1957a, p. 50).

The latest Bathonian is probably also represented in 

the subsurface of northern Veracruz by some small ammonites resembling Wagnericeras (Cantii Chapa, 1969, 

p. 5). This occurrence is in the Huayacocotla embayment, 

which may have been connected eastward with the AtFIGURE 16.—COMPARISONS OF THE TITHONIAN

lantic Ocean (Erben, 1957b, p. 35, 39, fig. 2), or westward with the Pacific Ocean, or both.

In the United States, the assignment of certain beds 

to the Bathonian is based mainly on stratigraphic position, as the ammonites present are mostly generically 

different from those in the typical Bathonian of Europe.

In eastern Oregon, southwest of John Day, the Bathonian is represented by beds containing Cobbanites, Par-
Mexico (Imlay, 1952a; 

Erben, 1957a; Cantti 

Chapa, 1967, 1971)

Substeueroceras

and

Proniceres

•»

Kossmatia, 

Durangftes, 

Lytohoplites, and

"^seudolissoceras zitteli

Subplanites,

Pseudolissoceras,

and

Virgatosphinctes

Mazapilites,

Virgatosphinctes,

and

Subdichotomoceras

Hybonoticeras

Subd&yo^^ftfioiQE AMMONITES ANE

Enay, 1964

Upper

Middla

'

Lower

Upper

Lower

Cantu 

Chapa, 

1967, 

1971

Upper

Middle

Lower

Zeissi 

1968

Uppar

Middle

Lower

Judoley and 

FurrazolaBermtidez, 

1968

Upper

Middle

Lower

Imlay 

and 

Jones, 

1970

Upper

Middle

7

Lower

Enay, 1971

Upper

Middle

Lower

Uppar

Lower

Enay, 

1972

Upper

Lower

BUCHIAS BY STAGES Russian platform 

(Gerasimov and 

Mikhailov, 1967; 

Saks and Shulgina, 1964; 

Saks and others, 1968)

Craspedites nodiger

Craspedrtes subditus

Kecbpurites fulgens

Epivirgatftes nikftini

Virgatites virgatus

Dorsoplanites 

panderi

Zaraiskftes 

zarajskensis

Pavlovia

pavlovi

Subplanites

( llowaisKya;

pseudosycthica

Subplanites

(=Howaiskya)

sykolovi

Subplanites klimovi

Stage

k

tt

£

1

o

c 

.5•5*

>

27

AND VOLGIAN STAGES AND THE SUGGESTED SUBDIVISIONS OF THE TITHONIAN.

areineckeia, and Choffatia beneath beds containing Lilloettia buckmani (Crickmay) and Reineckeia.

In the western interior of North America, the early 

to middle Bathonian is probably represented by the ammonites Paracephalites (Frebold, 1963, p. 5, 8-13, 27- 

29) and Cobbanites. In western Montana, Paracephalites 

includes the species formerly referred to as Arctocephalites (Cranocephalites) (Imlay, 1962b, p. C24, C25). Paracephalites differs from Arctocephalites and Cranocephalites, according to Frebold (1963, p. 8), by having a 

wider umbilicus that opens up at a later growth stage 

and by retaining ribbing later on the adult body chamber. Its Bathonian Age is based primarily on stratigraphic position beneath beds containing Cadoceras and 

Kepplerites, of early Callovian Age (Frebold, 1963, p. 

29-31; Imlay, 1962b, p. C19). The age of Paracephalites
28 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

must be about the same as that of Cranocephalites in 

Alaska, as both are associated with Gryphaea impressimarginata McLearn and with the lowest occurrences of 

Cobbanites (Imlay, 1962b, tables 5 and 6).

The late Bathonian in the western interior of North 

America is represented by species that were once assigned to Arcticoceras by Imlay (1953a, p. 19-22) because of their general resemblance to that genus in shape 

and rib pattern. They were subsequently assigned to a 

new genus, Warrenoceras (Frebold, 1963, p. 13, 14), that 

differs from Arcticoceras in its narrower umbilicus, less 

sharp ribs, absence of constrictions, and broader elements of the suture line, and by becoming smooth at a 

much earlier growth stage. These differences do not justify more than a subgeneric status for Warrenoceras under Arcticoceras, according to J. H. Callomon (written 

commun., 1972).

The exact age of Warrenoceras is not known. Its 

general resemblance to Arcticoceras suggests, however, 

that it is either a provincial time equivalent of Arcticoceras or is a descendant. If so, it could be of the same 

age or could be younger. Its association with Cadoceras 

suggests that it is younger than the typical Arcticoceras 

of the Arctic region. Against such a suggestion, however, is the fact that all species of Cadoceras in the western interior of North America have a rounded instead of 

a sharp umbilical edge (Imlay, 1953a, p. 3; 1953b, p. 45) 

and hence may not have the same age significance as Cadoceras proper. Furthermore, the exact time relationships of Warrenoceras to the older Paracephalites are 

uncertain because of the presence of a disconformity of 

unknown magnitude at the base of the Warrenoceras - 

bearing beds in Montana, northern Wyoming, and western South Dakota (Imlay, 1962b, p. C9). Nonetheless, 

the association of Cobbanites with Warrenoceras in Alberta (Frebold, 1963, p. 5) indicates a Bathonian Age, 

because Cobbanites in southern Alaska has not been 

found above beds of Bathonian Age and is closely related 

to the late Bajocian genus Vermisphinctes.

The late Bathonian in the northern part of the western interior region may be represented also by species of 

Kepplerites that were assigned previously to "Gowericeras" costidensus Imlay, "G." subitum Imlay, and 

Kepplerites cf. K. tychonis Ravn (Imlay 1953a, p. 7, 8). 

This age is indicated by the close resemblance of K. costidensus to an undescribed species (No. 3149 in Geological Museum, Univ. Copenhagen) from the Kepplerites tychonis zone on Fossil Mountain, East Greenland; by the 

resemblance of K. cf. K. tychonis Ravn (Imlay, 1948, p. 

16, 25, pi. 8, figs. 3, 4, 6) to K. tychonis (Ravn) (Ravn, 

1911, p. 490, pi. 37, fig. 1) from East Greenland; and by 

the occurrence of these ammonites in Montana below 

beds characterized by K. maclearni Imlay in association

with Lilloettia and Xenocepkalites (Imlay, 1953a, p. 8, 

18, 19, 25, pis. 1, 15, 16, and part of 17), Such an association by comparison with ammonites of southern Alaska 

(Imlay, 1975, p. 6, 14) is definitely of early Callovian 

Age. In feet, with one exception, Xenocephalites in 

Alaska is not known above the basal part of the range of 

Lilloettia or Kepplerites.

In southern Alaska between Cook Inlet and the 

Wrangell Mountains the early to early middle Bathonian 

is probably represented by Cranocephalites, Arctocephalites, Parareineckeia, and Cobbanites (Imlay, 1962b, 

p. C20). The sequence containing these ammonites rests 

unconformably on beds of early late Bajocian Age and is 

overlain disconformably by beds of early Callovian Age 

(Imlay, 1962b, p. C2, C3; Detterman and Hartsock, 1966, 

p. 35, 40, 42). Arcticoceras has not yet been found in the 

sequence, but the time during which it lived could be represented locally near the top of the sequence or by the 

disconformity at the top.

In northeastern Alaska, the Bathonian is represented, in ascending order, by Cranocephalites spp., 

Arctocephalites cf. A. elegans Spath, and Arcticoceras 

ishmae (Keyserling) (Imlay and Detterman, 1973, p. 18, 

24, fig. 14). These fossils should represent most of the 

stage, because the ammonite sequence is similar to that 

in East Greenland (Callomon, 1959, p. 507, 508).

Concerning the age ranges of these genera in the arctic region, Spath (1932, p. 145) placed Arcticoceras in the 

Callovian and Arctocephalites in the Bathonian. Arkell 

(1956, p. 527) placed both genera as well as the somewhat 

older Cranocephalites in the Callovian. Callomon (1959), 

on the basis of field studies in East Greenland, assigned 

all three genera to the Bathonian and suggested that the 

earliest occurring species of Cranocephalites might be as 

old as latest Bajocian. He based these age assignments 

on the position of the Arcticoceras -bearing beds in East 

Greenland directly beneath beds that, according to him, 

contain a varied ammonite fauna closely similar to and in 

part identical with the fauna in the Macrocephalites macrocephalus zone of earliest Callovian Age in northwestern Europe. He discounted the presence of Cadoceras 

and Kepplerites at the top of the range of Arcticoceras, 

although both Cadoceras and Kepplerites are normally 

considered good evidence for a Callovian Age. Subsequently, Callomon (written commun., August 1972) determined that in Greenland the ranges of Cadoceras and 

Arcticoceras do not overlap but that Kepplerites does 

occur as low as the upper part of the range of Arcticoceras above Arcticoceras ishmae (Keyserling) (Callomon 

and others, 1972, p. 18, 19; Donovan, 1957; Surlyk and 

others, 1973).

In arctic Canada, the Bathonian is represented by an 

ammonite sequence that is nearly identical with that in
SUCCESSION OF AMMONITES AND BUCHIAS BY STAGES 29

Bathonian beds in East Greenland but that contains different species of Cranocepkalites from those known in 

northern Alaska. These differences probably reflect inadequate collecting.

CALLOVIAN

In Mexico, Callovian ammonites have been found in 

the south-central part (Guerrero embayment) and in the 

east-central part (Huayacocotla embayment) (Erben, 

1957b, fig. 2). In the east-central part, the early Callovian is represented by Kepplerites (Cantii Chapa, 1969, p. 

3) from a well core in Veracruz; the late early Callovian, 

by Neuqueniceras neogaeum and Reineckeia (Imlay, 

1952a, p. 970; Erben, 1956b, p. 39; Cantii Chapa, 1971, 

p. 21) from the Necaxa area of Puebla; and the middle 

Callovian, by Erymnoceras cf. E. mixtecorum from 

slightly higher beds in the Necaxa area (Erben, 1957a, 

p. 47). In south-central Mexico (Oaxaca and Guerrero), 

the Callovian ammonite sequence is essentially the same, 

but also includes Peltoceras at the top, and Eurycephalites and Xenocephalites at the base.

The Callovian ammonite sequence in Mexico (see fig. 

14) is similar to that in the Callovian of Chile (Hillebrandt, 1970, p. 176, 190, 202) and likewise includes taxa, 

characteristic of the Pacific Realm, such as Xenocephalites, Eurycephalites, and Neuqueniceras. The presence 

of Xenocephalites and the close resemblance of Eurycephalites to Lilloettia (Hillebrandt, 1970, p. 202) show 

that the lower Callovian of Mexico contains some ammonites similar to those in the lower Callovian of Oregon, British Columbia, and southern Alaska.

Ammonites of Callovian Age have been found in the 

United States in southern and northeastern California, 

east-central Oregon, western Idaho, Alaska, and in the 

northern part of the western interior region.

A few ammonites found in Callovian beds in California are closely related to ammonites from Mexico and the 

Tethyan Realm. These California specimens include the 

early Callovian genera Macrocephalites and Hecticoceras from the Santa Ana Mountains in southern California (Imlay, 1963; 1964c, p. 508) and the late Callovian 

genus Peltoceras from the Sierra Nevada in east-central 

California (Imlay, 1961, p. 27, pi. 6). None of these have 

been found farther north in the Pacific Coast region.

Most of the Callovian ammonite faunas in the Pacific 

Coast region from British Columbia northward to Alaska 

are dominated by genera of the Boreal families Cardioceratidae and Kosmoceratidae, including Iniskinites, 

Cadoceras proper, Stenocadoceras, Paracadoceras, 

Pseudocadoceras, and Kepplerites (Imlay, 1953b, 1961, 

1964a; Crickmay, 1930, 1933a, b; McLearn, 1929, 1949; 

Frebold and Tipper, 1967). Of these, only Iniskinites,

Pseudocadoceras, and Kepplerites are definitely identified south of British Columbia. The family Phylloceratietee is fairly common throughout the region and is represented by several genera or subgenera that occur 

nearly worldwide. With these occur some genera of endemic or Pacific affinities, including Lilloettia, Xenocephalites, and Parareineckeia. In addition, a few ammonites present belong to the genera Oppelia, Grossouvria, 

Procerites, and Choffatia, all of which are nearly worldwide. The succession of genera and species is similar 

throughout the Pacific Coast region. Faunal evidence for 

beds of late Callovian Age is completely lacking north of 

east-central California, except for one occurrence in British Columbia (Frebold and Tipper, 1975, p. 149, 156).

In the western interior region, only the early and 

very latest Callovian is represented by ammonites (Frebold, 1957, p. 19-27; 1963; Imlay, 1953a). The early Callovian ammonites include Imlayoceras, Lilloettia, Xenocephalites, and Grossouvria and are dominated by the 

families Cardioceratidae, Macrocephalitidae, and Kosmoceratidae. Despite some generic resemblances with 

ammonites from the Pacific Coast region, there appear 

to be no species in common; the families Phylloceratidae 

and Lytoceratidae are unknown from the western interior, and the genus Imlayoceras Frebold (Frebold, 1963, 

p. 20) has been found only in that region.

The latest Callovian in the western interior region is 

represented by Quenstedtoceras (Lamberticeras) collieri 

Reeside from the Little Rocky Mountains and Bearpaw 

Mountains in north-central Montana. Recent collecting 

shows that it underlies and does not occur with Cardioceras as previously stated (Imlay, 1948, p. 16, 17).

In the arctic region of Alaska and Canada, the Callovian is represented by typical species of Cadoceras that 

are associated with C. (Stenocadoceras) and Phylloceras 

bakeri Imlay in the Richardson and British Mountains, 

Yukon Territory, Canada. This association, plus the absence of Kepplerites, favors correlation with the upper 

part of the Paveloff Siltstone Member of the Chinitna 

Formation in southern Alaska (Detterman and Hartsock, 

1966, p. 48). That upper part is dated as middle to early 

late Callovian on the basis of the European range of C. 

(Stenocadoceras), the presence of C. (Longaevicerasl) 

pomeroyense (Imlay) near the top of the member, and 

the absence of Kepplerites in its upper half. Similarly, 

the Cadoceras-bearing beds in arctic Alaska and Canada 

are probably of middle Callovian Age because Kepplerites is unknown above the lower Callovian (Callomon, 

1964, p. 274, 275), Cadoceras proper is unknown above 

the middle Callovian (Callomon, 1955, p. 255; 1964, p. 

273-278), and C. (Stenocadoceras) is unknown below 

the uppermost part of the lower Callovian (Arkell, 1956, 

p. 26).
30 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

OXFORDIAN

In the subsurface of the southern United States, a 

few fragmentary ammonites of late Oxfordian Age have 

been found in the Smackover Formation (fig. 15). They 

include species of Perisphinctes (Dichotomosphinctes), 

P. (Discosphinctes), Euaspidoceras, and Ochetoceras 

(Imlay, 1945, p. 274, pi. 41, figs. 7-14), which appear to 

be identical with species from beds of late Oxfordian Age 

in Mexico (Burckhardt, 1912, p. 1^0, 203-312, pis. 1- 

7; Cantii Chapa, 1969, p. 6; 1971, p. 22, 37) and Cuba 

(Sanchez Roig, 1920, 1951; O'Connell, 1920; Jaworski, 

1940; Judoley and Furrazola-Bermiidez, 1965, 1968, p. 5, 

18, 22). The late middle Oxfordian is probably represented at San Pedro del Gallo, Mexico, by the lower part 

of the Oxfordian sequence, which is below an upper part 

characterized by Ochetoceras canaliculatum (von Buch) 

and Discosphinctes carribbeanus (Jaworski). In the 

lower part, Dichotomosphinctes occurs in association 

with Taramelliceras (Proscaphites) (Burckhardt, 1912, 

p. 211, 212; Arkell, 1956, p. 563) and Creniceras cf. C. 

crenatum (Bruguiere) (Burckhardt, 1912, p. 15, 16, pi. 7, 

figs. 15-17). Amoeboceras cf. A. alternans (von Buch) 

is reported by Burckhardt (1930, p. 66) from probable 

equivalent beds at another locality near San Pedro del 

Gallo. Early Oxfordian ammonites have not been found 

in the Gulf of Mexico region, except for unconfirmed reports of Creniceras renggeri (Oppel) at Huayacocotla in 

Veracruz, Mexico (Erben, 1957a, p. 47), and Fehlmannites at Xochapulco in Puebla, Mexico (Cantii Chapa, 

1971, p. 23). Most of these ammonites in the Gulf region 

have Tethyan affinities.

In California and southwestern Oregon, as in the 

southern United States, the late Oxfordian is represented by species of Perisphinctes (Dichotomosphinctes} 

and P. (Discosphinctes) that are similar to species in 

Mexico and Cuba (Imlay, 1961, p. D7-D8, D10, D23- 

D25, pi. 3, figs. 1-10, pi. 4, figs. 4, 7, 8). In west-central 

Idaho, the early Oxfordian is represented by Cardioceras (Scarburgiceras) martini Reeside (Imlay, 1964a, 

p. D15, pi. 2, figs. 1-5), which has Boreal affinities.

In the western interior of the United States, cardioceratid ammonites of early to early middle Oxfordian 

Age are fairly widespread, but ammonites of late Oxfordian Age have not been found (Reeside, 1919; Imlay, 1947, 

p. 264; 1948, p. 16, 17, 25, pi. 7, figs. 12, 14, 15, 18; 

Arkell, 1956, p. 548). The presence of upper Oxfordian 

beds in northwestern Montana is shown, however, by 

the presence of Buchia concentrica (Sowerby) (Imlay, 

1956a, p. 595). The oldest Oxfordian ammonites have 

been collected only in the lower part of the Swift Formation in north-central Montana, and belong to Quenstedtoceras (Pavloviceras), Prososphinctes, Cardioceras 

(Maltoniceras), and C. (Scarburgiceras). This assemblage probably corresponds to the basal Oxfordian (zone 

of Quenstedtoceras mariae) of northwest Europe.

The next oldest ammonites of the marine lower Oxfordian have been found in north-central Montana directly above the beds containing an association of Cardioceras and Quenstedtoceras (Pavloviceras). They also 

occur at many other places in the western interior region. These ammonites apparently represent a single 

faunal zone (Cardioceras cordifomne), although by European standards they probably correspond to the zones 

of Cardioceras cordatum and Perisphinctes plicatilis. 

They are closely related specifically to ammonites in 

British Columbia, Alaska, and the arctic region, but have 

nothing in common generically with Oxfordian ammonites in the Gulf of Mexico region.

In Alaska, both the early and the late Oxfordian are 

represented mostly by genera of the Cardioceratidae. 

Cardioceras is the most common genus in the lower Oxfordian, as is Amoeboceras in the upper Oxfordian. In 

the basal part of the Cardioceras-bearing beds, the 

subgenus Scarburgiceras is locally common. Perisphinctes (Dichotomosphinctes) is associated with Buchia 

concentrica (Sowerby), of late Oxfordian to early Kimmeridgian Age on the Alaska Peninsula (Imlay, 1961, p. 

Dll,. pi. 4, fig. 6). The presence of Phylloceras and Lytoceras in fair abundance contrasts with their complete 

absence in Oxfordian beds in the western interior of the 

United States.

The Oxfordian ammonite sequences in western and 

arctic Canada are nearly the same as those in Alaska 

(Frebold, 1961, p. 22-24, 29, 30, table 1 opposite p. 26; 

1964a, p. 4; Frebold and Tipper, 1970, p. 13, 14, 17; Frebold and others, 1959). Likewise, few ammonite taxa are 

present, and an exact faunal boundary between Oxfordian and Kimmeridgian cannot be drawn.

KIMMERIDGIAN

The Kimmeridgian Stage as used herein follows the 

recommendation of Enay and others (1971, p. 97). It is 

equivalent to the lower Kimmeridgian of Arkell (1956, p. 

21, 22) and to the lower part of the Kimmeridge Clay of 

England below the ammonite zone of Pectinatites (Yirgatosphinctoides) elegans (Cope, 1967, p. 66).

In eastern Mexico, the Kimmeridgian ammonite sequence from the base up, according to Cantii Chapa 

(1971, p. 25, 26, 36), is characterized by (1) Ataxioceras 

associated with Rasenia, (2) Idoceras, and (3) the Glochiceras group of G. fialar. In northern Mexico, the sequence recognized by Burckhardt (1930, p. 64, 66, 91, 92) 

is nearly the same, except for the presence of Sutneria 

cf. S. platynota (Reinecke) at the base. Also, in the lower 

part of the bed containing Glochiceras cf. G. fialar are 

species of "Aucella" (Burckhardt, 1906, p. 144, 155;
SUCCESSION OF AMMONITES AND BUCHIAS BY STAGES 31

1912, p. 50, 67, 80) that are now referred to as Buchia 

concentrica (Sowerby) and B. mosquensis (von Buch) 

(Imlay, 1955, p. 85).

This faunal sequence was modified slightly by Imlay 

(1939, p. 21, tables 4, 5; 1943a, p. 1471) because of an 

apparent association of the Idoceras group of /. durangense Burckhardt with Glochiceras cf. G. fialar at some 

localities. Still later, studies by Cantii Chapa (1970, p. 

42; 1971, p. 26), dealing with both subsurface cores and 

outcrops, showed that Idoceras invariably occurs in a 

lower bed than does Glochiceras cf. G. fialar.

A few ammonites of Kimmeridgian Age have been 

found in the southern United States (figure 15) in the 

subsurface of northwestern Louisiana (Imlay, 1945, p. 

271-274, pi. 41, figs. 15-28) and east Texas and in outcrops in west Texas (Cragin, 1905; Albritton, 1937; 1938, 

p. 1761-1764). Well cores in Louisiana have yielded species of Idoceras, Ataxioceras, Metahaploceras, and Glochiceras that appear to be identical with species from 

beds of early and middle Kimmeridgian Age in Mexico 

(Imlay, 1943a, p. 1471-1472); Burckhardt, 1906, p. 2- 

106). From the Malone Mountains in west Texas, early 

Kimmeridgian ammonites have been obtained that belong to the genera Haploceras, Idoceras, Nebrodites, 

Physodoceras, and Aspidoceras. Some of these are identical specifically with ammonites from beds of Kimmeridgian Age in northern Mexico. The ammonite species 

and genera of Kimmeridgian Age that have been found 

in the southern United States are only a small part of the 

assemblages of Kimmeridgian Age that are known in 

Mexico (see Burckhardt, 1930, p. 66-68; Imlay, 1939, 

tables 4-6, 10).

In California, the lower to middle Kimmeridgian has 

been identified faunally. This identification in California 

is based on an abundance of the pelecypod Buchia concentrica (Sowerby) in association with the boreal ammonite Amoeboceras (Amoebites) and the nonboreal ammonites Subdichotomocerasl and Idoceras (Imlay, 1961, 

p. D8, D22, D25, D26; pi. 2, figs. 24-28; pi. 5, figs. 1-3, 

9, 12-16).

In northwest Sonora, on Rancho Cerro Pozo Serna, 

the Kimmeridgian is represented by an association of 

Idoceras, Amoeboceras, and Aulacomyella (T. E. Stump, 

Univ. Calif, at Davis, written commun., Apr. 1973). Of 

these ammonites, Idoceras ranges through about 565 

feet of beds; Amoeboceras occurs in the lower 510 feet of 

that range; and Aulacomyella is associated with the 

highest occurrence of Amoeboceras. Aulacomyella occurs elsewhere in Mexico in beds characterized by Idoceras and Glochiceras cf. G. fialar (Burckhardt, 1930, p. 

51, 67, 86, 90, 92, 96, 97; Imlay, 1940a, p. 399; 1943a, p. 

1472) but ranges higher into beds containing the lowest 

occurrences of Virgatosphinctes (Cantii Chapa, 1971, p. 

27, 28, 36). The occurrence of Amoeboceras with Idoceras in Sonora is considerably younger than its reported 

occurrence with Dichotomosphinctes durangensis 

Burckhardt near San Pedro del Gallo, Durango (Burckhardt, 1930, p. 66).

Marine Kimmeridgian beds have not been identified 

in the western interior of the United States or east of the 

Canadian Rocky Mountains. Throughout western and 

arctic Canada and Alaska, the identification of beds of 

Kimmeridgian Age is based mostly on the ranges of species of Buchia (Imlay, 1955, p. 83-86), because ammonites of definite Kimmeridgian Age have not been found. 

Some of the specimens of Amoeboceras from Alaska 

(Reeside, 1919, p. 30, pi. 18, fig. 4, pi. 19, figs. 1-3; 

Imlay, 1955, p. 90, pi. 12, figs. 2-£) could be of early 

Kimmeridgian Age, but their resemblance to the 

subgenus Prionodoceras favors a late Oxfordian Age, 

judging by the range of that subgenus in northwest Europe (Arkell and others, 1957, p. L307).

TITHONIAN

DEFINITION AND CORRELATIONS

The Tithonian Stage is now defined (Enay, 1964, 

1971) so that it correlates at its base with the Volgian 

Stage of the Boreal Realm (Saks and Shulgina, 1964; 

Saks and others, 1968 and 1972; Gerasimov and Mikhailov, 1967) (equals North Temperate Realm of Kauffman, 

1973, p. 367). This correlation is based primarily on the 

local association in Europe of the subboreal ammonite 

Gravesia with the Tethyan ammonite Hybonoticeras, 

which is widespread in southern Europe, Madagascar, 

India, and Mexico (Enay, 1972, p. 370; Zeiss, 1968, p. 

137, 143-146).

The Tithonian is commonly divided into three parts, 

on the basis of the stratigraphic ranges and associations 

of certain ammonites (fig. 16). As thus divided, the lower 

Tithonian is equivalent to the middle and part of the upper Kimmeridgian of England as defined by Arkell (1956, 

p. 21) and to most of the upper Kimmeridgian as redefined by Cope (1967, p. 4, 70, 74). The middle Tithonian 

as defined by Enay in 1964 (p. 365) is equivalent to the 

remainder of the Kimmeridgian of England plus an indefinite part of the Portlandian. The middle Tithonian as 

defined by Zeiss (1968, p. 137) includes only the zones of 

Pavlovia rotunda and P. pallasioides of northwest Europe. As redefined by Enay (1971, p. 99, 100), it includes 

those zones plus part of the underlying zone of Pectinatites pectinatus; it does not include any faunal zone as 

young as the Portlandian. The middle Tithonian as used 

by Judoley and Furrazola-Bermudez (1968, p. 5) and by 

Imlay and Jones (1970, p. B8-B9) is nearly the same as 

that used by Enay in 1964. The upper Tithonian of these
32 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

various authors includes all Jurassic beds above the middle Tithonian.

The Tithonian has also been divided into two parts 

by Enay (1964, p. 363, 364; 1971, p. 99, 100) who considers a threefold division impractical except in those areas 

where Pseudolissoceras and Semiformiceras are present 

(Enay, 1972, p. 371). Also, the association of Pseudolissoceras with the typical late Tithonian ammonite Proniceras in Kurdistan (Spath, 1950, p. 125) suggests that 

Pseudolissoceras may range higher than recorded in Europe. Therefore, a twofold division is favored by Enay 

(1971, p. 99; 1972, p. 382), who has correlated the lower 

Tithonian with the upper part of the Kimmeridge Clay of 

England above the zone of Aulacostephanoceras acutissiodorensis (Cope, 1967, p. 4, 70). He correlated the upper Tithonian with the remainder of the overlying Jurassic above the zone of Pavlovia pallasioides. As thus 

defined, the base of the upper Tithonian corresponds to 

the first appearance of the calpionellid microfossils and 

to the first appearance of such ammonites as Kossmatia, 

Durangites, Corongoceras, Micracanthoceras, Lytohoplites, and Hildoglochiceras.

A threefold faunal division of the Tithonian within 

the Gulf region is feasible and useful, as discussed by 

Cantii Chapa (1967, p. 18-22, table 1; 1971, p. 27-31), 

but there is no assurance that the middle part is even 

approximately the same as the middle Tithonian as used 

in Eurasia. For correlations between the continents, 

preference is given herein to a twofold division of the 

Tithonian because the faunal boundary between the two 

divisions is much sharper than are the boundaries within 

the threefold division.

LOWER TITHONIAN OF THE GULF REGION

In the Gulf of Mexico and bordering areas, early Tithonian fossil sequences are well known only in northern, 

north-central, and eastern Mexico (fig. 15). In north-central Mexico near Mazapil, Zacatecas, the early Tithonian 

ammonite sequence from the base upwards apparently 

consists of (1) Hybonoticeras ( = Waagenia); (2) Mazapilites in association with Virgatosphinctes aguilari 

(Burckhardt), V. spp., Subdichotomoceras cf. S. nikitini 

(Michalski), Aulacosphinctoides and Aspidoceras; and 

(3) Virgatosphinctes mexicanus Burckhardt, V. spp., 

Subplanites cf. S. danubiensis (Schlosser), Parastreblites mazapilensis (Burckhardt) and Pseudolissoceras 

subrasile Burckhardt (Burckhardt, 1906, p. 110, 147- 

149; 1930, p. 68-71, tables 6-9; Imlay, 1939, p. 27-30, 

38, 39, tables 7-10). Of these, only the relative positions of Mazapilites and Virgatosphinctes mexicanus are 

questionable, because those taxa have not yet been collected in the same stratigraphic sequence in central or

northern Mexico. At first, Burckhardt (1906, p. 168- 

170) considered them to be of the same age because they 

both occur in similar phosphatic limestone in areas near 

Mazapil. Later, he decided that Mazapilites must be 

older because near Symon, Durango, about 70 miles (112 

km) west of Mazapil, the lowest occurrence of Mazapilites is in the same bed with Hybonoticeras (Burckhardt, 

1919, p. 74; 1930, p. 56). This association was confirmed 

by Imlay (1939, p. 10, 11).

The early Tithonian ammonite sequence near Symon, Durango (Burckhardt, 1919, p. 61-66; 1930, p. 56, 

57, 68, 69; Imlay, 1939, p. 9-11), resembles that near 

Mazapil except that its upper part above Mazapilites 

contains only rare specimens of Subplanitesl (Blanchet, 

1923, p. 74; Burckhardt, 1919, p. 39; 1921, pi. 14, figs. 1- 

3) and Virgatosphinctes'i (Imlay, 1939, p. 10). Also, all 

the beds above Hybonoticeras and below Kossmatia contain an abundance of ammonites that generally have been 

assigned to Torquatisphinctes rather than to Aulacosphinctoides (Spath, 1931, p. 466, 484, 1933, 865; Imlay, 

1939, p. 22, table 7; Arkell, 1956, p. 562; Enay, 1972, p. 

382).

Mazapilites has been found elsewhere in north-central Mexico only in the Sierra de 'Catorce, northern San 

Luis Potosi, about 75 miles (120 km) southeast of Mazapil. In this mountain, the early Tithonian is represented 

only by one ammonite assemblage consisting of Phylloceras, Virgatosphinctes (rare), Aulacosphinctoides, Subdichotomoceras, Andiceras, Aspidoceras, Simoceras, 

Haploceras, Pseudolissoceras zitteli (Burckhardt), and 

Mazapilites (rare). Most of these occur in 10 feet (3 m) of 

limestone (Verma and Westermann, 1973, p. 148) and do 

not occur in the higher (early late Tithonian) assemblage 

characterized by Kossmatia and Durangites. Mazapilites itself was obtained from just 2 feet (0.6 m) of limestone at only one place, in association with Pseudolissoceras zitteli, Aulacosphinctoides, Subdichotomoceras, 

and (eVirgatosphinctes" sanchezi Verma and Westermann (Verma and Westermann, 1973, loc. 23B on p. 141, 

148, 186). The last named species was described as similar to Subplanites'! sp. in Imlay (1939, p. 36, pi. 9, figs. 

1-3). Burckhardt (1919, p. 39; 1921, p. 14, figs. 1-3) 

found it similar toVirgatites sp. ind., which was renamed 

Perisphinctes burckhardti by Blanchet (1923, p. 74) and 

referred questionably to as Subplanites by Arkell (1956, 

p. 562).

Another early Tithonian ammonite sequence occurs 

near Placer de Guadalupe and Plomosas in east-central 

Chihuahua, about 450 miles (700 km) north-northwest of 

the one at Mazapil (Bridges, 1965, p. 66-77, 105, 118- 

120, 132-134; Imlay, 1943b). The oldest Tithonian is represented by Hybonoticeras (= Waagenia) (Imlay, 

1943b, p. 527-529), which was found about 15 miles (24
SUCCESSION OF AMMONITES AND BUCHIAS BY STAGES 33

km) south-southeast of Placer de Guadalupe. The remainder of the early Tithonian ammonite sequence is 

well exposed in a fairly thick section (Bridges, 1965, fig. 

15 on p. 76, p. 133-134) that was measured northeastward, starting from a point about 1.2 miles (2 km) N. 42° 

E. of Placer de Guadalupe.

In that section, some conglomerates that are probably Paleozoic are overlain by shale 152 feet (46 m) thick 

that contains Idoceras from 66-100 feet (20-30 m) above 

its base, and Idoceras! throughout its lower 126 

feet (38 m). Above this shale is about 160 feet (49 m) of 

unfossiliferous sandstone. Next higher is 1,075 feet (328 

m) of dark shale and shaly limestone that contains species of Virgatosphinctes, Subplanites, and Pseudolissoceras, which are like those found with V. mexicanus in 

southern Zacatecas, in 3-6 feet (1-2 m) of limestone. 

Above the dark shale and limestone is 565 feet (172 m) of 

shale that contains Virgatosphinctes cf. V. densiplicatus 

(Waagen). At the top of the section is 465 feet (142 m) of 

shale and sandstone that contains Kossmatia. Mazapilites has not been found in the sequence, but the time 

during which it lived could be represented by any one of 

several 50- to 60-foot (15- to 18-m) units that have not 

furnished any ammonites.

The lowest of these faunules is definitely of early Tithonian Age, judging by an association of Subplanites, 

Virgatosphinctes and questionable Pseudolissoceras 

(Arkell and others, 1957, p. 329, 330; Bridges, 1965, pi. 

3 on p. 76). It may be correlated with a faunule near Mazapil that is characterized by Virgatosphinctes mexicanus Burckhardt, Pseudolissoceras subrasile (Burckhardt), and Subplanites (Burckhardt, 1906, p. 155, 156; 

1930, p. 69). Thus, Subplanites aff. S. reise (Schneid) 

(Imlay, 1943b, p. 533, pi. 91, fig. 1) from Chihuahua is 

probably identical with Perisphinctes cf P, danubiensis 

(Schlosser) in Burckhardt (1906, p. 112, pi. 32, fig. 1) and 

Virgatosphinctes chihuahuensis Imlay (Imlay, 1943b, p. 

534, pi. 91, figs. 2-5) is probably the same as Perisphinctes aff. P. transitorius Oppel in Burckhardt (1906, 

p. 113, pi. 30, fig. 8).

Above this lowest faunule is a finely ribbed species 

of Virgatosphinctes (Imlay, 1943b, p. 535, pi. 89, figs. 

1-4), whose resemblance to V. densiplicatus (Waagen) 

suggests correlation with the basal upper Tithonian 

(Enay, 1972, p. 377, 378). Still higher are species of 

Kossmatia that represent the lower part of the upper 

Tithonian of Enay.

A much different early Tithonian ammonite sequence 

is present in the Huasteca area of east-central Mexico, 

according to Cantu Chapa (1971, p. 24-30, 33, 36, 38), 

whose conclusions are based on both surface and subsurface studies. That sequence is distinguished from all 

those just discussed by the local absence or scarcity of

Hybonoticeras at the base of Tithonian and by the presence of Mazapilites above instead of below Virgatosphinctes mexicanus (Burckhardt).

Of these differences, the rarity of Hybonoticeras is 

probably related to sparse occurrences in very thin beds, 

as suggested by Cantu Chapa (1971, p. 28). Hybonoticeras is present, however, at two localities in eastern 

Mexico. One specimen was obtained at the base of the 

Corona-San Manuel well 82, about 30 miles (48 km) 

southwest of Tampico, Tamaulipas (USGS Mesozoic loc. 

20854). Another was found in chalky limestone in Arroyo 

La Mula at the west end of the Huizachal anticline, west 

of Victoria, Tamaulipas (USGS Mesozoic loc. 20836). 

The occurrence of Mazapilites above Virgatosphinctes 

mexicanus in eastern Mexico but below it elsewhere 

could be explained if one or both of those taxa had longer 

or different stratigraphic ranges than those shown by 

studies in north-central Mexico, or if the Mazapilitesbearing beds in eastern Mexico were separated from 

overlying Kossmatia-beanng beds by a disconformity, or 

by a nonsequence, reflecting lack of deposition.

In summation, the biostratigraphic record, as discussed above, shows that Virgatosphinctes in northern 

and north-central Mexico ranges through the lower Tithonian above the beds containing Hybonoticeras. Locally, in north-central Mexico near Mazapil, species of 

Virgatosphinctes occur in two faunules, of which only the 

lowest contains Mazapilites and only the highest contains Pseudolioceras. The higher faunule is represented 

elsewhere in northern Mexico near Symon, Durango, 

and in east-central Chihuahua by identical or closely similar species of Virgatosphinctes and Subplanites. Against 

such a faunal division is the association of Mazapilites 

with Pseudolissoceras in the Sierra de Catorce of San 

Luis Potosi. That association may not be of stratigraphic 

value, however, if the 2 feet (0.6 m) of limestone in which 

the ammonites occur represents a condensed deposit that 

formed so slowly that organisms of different ages occur 

together. Much better evidence against the faunal division recorded for north-central Mexico is the presence of 

Mazapilites above Virgatosphinctes mexicanus in eastcentral Mexico. Evidently, more stratigraphic collecting 

is needed in order to determine the total range of Mazapilites and the correct ammonite succession in the lower 

Tithonian beds of Mexico. Nonetheless, the range of Mazapilites into the middle part of the lower Tithonian is 

favored by its association with Pseudolissoceras and 

Protancyloceras in Cuba below beds containing Torquatisphinctes and Parapallasiceras (Housa and de La Nuez, 

1975).

Elsewhere in the Gulf region, lower Tithonian beds 

may be represented in Cuba by an association of Virgatosphinctes and Subplanites! beneath beds containing
34 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

typical upper Tithonian ammonites such as Dumngites, 

Corongoceras, and Micracanthoceras (Judoley and Furrazola-Bermiidez, 1968, p. 5, 19, 23, 109-111). The 

lower Tithonian assignment is based on two facts: Virgatosphinctes is unknown from beds older than the Tithonian (Arkell and others, 1957, p. L330), and Subplanites is characteristic of the entire lower Tithonian (Enay, 

1964, p. 365; 1971, p. 99, 100; 1972, p. 382). One trouble 

with this correlation is that the species of Subplanitesl 

and Virgatosphinctes in question are reported by Judoley and Furrazola-Bermiidez (1968, p. 19) to be associated with Tintinids as well as with the ammonite Parodontoceras butti Imlay, which are not known below the 

upper Tithonian.

UPPER TITHONIAN OF THE GULF REGION 

AMMONITE SEQUENCES

Upper Tithonian ammonite sequences are well known 

in lands bordering the Gulf of Mexico (Burckhardt, 1906, 

p. 125-141, 148, 149, 170, 171; 1912, p. 127-172, 220- 

226; 1930, p. 70, 71, tables 6, 8, 9; Imlay, 1939, p. 23, 24, 

tables 8-10; 1942; Cantii Chapa, 1963, p. 27-29, 33, 

37-41, 70; 1967; 1968; 1971, p. 28-31, 37-39). They 

are divisible into two assemblages, of which the lower is 

characterized by Kossmatia, Durangites, Lytohoplites, 

Simoceras, Metahaploceras, Dickersonia, and Pseudolissoceras. The upper assemblage is characterized by 

Berriasella, Substeueroceras, Aulacosphinctes, Protacanthodiscus, Proniceras, and rarely Himalayites. With 

both assemblages occur Parodontoceras, Hildoglochiceras, Micracanthoceras, and Corongoceras. Virgatosphinctes occurs rarely in the lower assemblage in Cuba 

and in the upper assemblage in Mexico.

The ages of these ammonite assemblages have been 

discussed sufficiently elsewhere (Cantii Chapa, 1967, p. 

17-22; 1971, p. 30, 31; Imlay and Jones, 1970, p. BllB12; Enay, 1972, p. 361, 371, 376, 382). Substeueroceras 

and Proniceras must represent the latest Tithonian. 

Kossmatia and Durangites must represent slightly older 

Tithonian, but their exact ranges relative to the standard 

zones of Europe are difficult to determine. Nonetheless, 

the presence of calpionellid microfossils in the Kossma- 

&a-bearing beds indicates an age not older than late Tithonian as defined by Enay (1971, p. 99). Also, the presence of Buchia mosquensis (von Buch) locally in those 

beds at San Pedro del Gallo, Durango (Burckhardt, 1912, 

p. 206, 221) shows that some of those beds are at least 

as old as the Zaraiskites albani zone of northwest Europe and the equivalent upper part of the Dorsoplanites 

panderi zone in Russia (Imlay, 1955, p. 74, 75, 85; 1959b,

p. 157; Imlay and Jones, 1970, p. Bll; Gerasimov and 

Mikhailov, 1967, p. 9, 19, 20; Saks and others, 1963, 

table 5).

Both of these assemblages are associated with calpionellid microfossils of late Tithonian Age. Such microfossils occur with the higher assemblage characterized by 

Substeueroceras in Puebla, Mexico (Cantii Chapa, 1967, 

table 1 opposite p. 22) and also throughout the lower 

assemblage in Cuba (Bronnimann, 1954; Bermiidez, 1961; 

Judoley and Furrazola-Bermudez, 1968, p. 14-19). In 

Mexico, they are reported from La Casita and Pimienta 

Formations (Bonet, 1956, p. 417^19, 462, 463, 468, table opposite p. 398), and they occur also in the Sierra 

Cruillas, Tamaulipas (Bonet, 1956, localities 44, 45, and 

48 on p. 468), just below a sequence containing Kossmatia and Durangites.

KOSSMATIA-DURANGITES AMMONITE ASSEMBLAGE

The lowermost upper Tithonian ammonite assemblage in Cuba is dated confidently as Late Jurassic, but 

not the very latest, for reasons that have been discussed 

in detail elsewhere (Imlay, 1942, p. 1433, 1434; Arkell, 

1956, p. 572; Judoley and Furrazola-Bermudez, 1968, p. 

24, 25). It is rather peculiar, however, that Protancyloceras, with is common in the assemblage in Cuba, is unknown in Mexico below the uppermost upper Tithonian. 

It is also peculiar that Protancyloceras has not been 

found in Cuba in association with Durangites (Imlay, 

1942, p. 1428), an ammonite characteristic of the lowermost upper Tithonian in Mexico. These peculiarities are 

probably unimportant stratigraphically because Protancyloceras hondense Imlay (written commun. to Paul 

Bronniman, March 1953) occurs on Loma Sabinilla, Las 

Villas Province (Gulf Oil Co. Iocs. 21141 and 21142), at 

about the same place where Durangites was collected 

(Atlantic Refinery Co. Iocs. 268, 269, and 7539), and below the lowermost occurrences of calpionellas (Paul 

Bronniman, written commun., 1953). Also, Protancyloceras has been recorded in central Europe and in Kurdistan in beds that are slightly older than latest Tithonian 

(Wiedmann, 1973, p. 309, 310, 313, 314).

Durangites vulgaris Burckhardt in Cuba, in addition 

to the occurrences in Camagiiey and Las Villas Provinces 

previously listed (Imlay, 1942, p. 1428, 1453), occurs at 

Finca Ancon, 3 miles (5 km) west of Balneario San Vicente ih Pinar del Rio Province (Gulf Oil Co. loc. 24976). 

It is associated there with D. cf. D. incertus Burckhardt, 

Hildoglochicerast ecarinatum Imlay, and an ammonite 

fragment whose venter bears chevron-shaped ribs, as 

would Kossmatia or Proniceras. That species ofHildoglochicerasl or Glochiceras (Cantii Chapa, 1968, p. 20) 

occurs elsewhere in association with Durangites (Imlay, 

1939, p. 5, 28).
SUCCESSION OF AMMONITES AND BUCHIAS BY STAGES 35

The earliest late Tithonian assemblage, present in 

the subsurface of eastern Mexico and in the mountains 

and plateau to the west, contains many species in common with Cuba (Imlay, 1942, p. 1428, 1432). This is well 

illustrated by the ammonites present in the upper 394 

feet (120 m) of a 722-foot-thick (220-m) Jurassic sequence 

exposed on the Sierra Cruillas, southwest of Cruillas, in 

north-central Tamaulipas. That fossiliferous part of the 

sequence from top to bottom is as follows:

Partial Jurassic sequence on Loma Rinconada in the northeastern part of Sierra Cruillas, Tamaulipas, Mexico

[Measured and collected in June 1954 by William E. Humphrey, Paul 

Perez F., and Teodoro Oiaz G. Fossils identified by Ralph W. Imlay]

Measured interval Feet Meters

12. Limestone, thin-bedded, tabular, laminated

dark-gray to black; lenses of black chert;

intercalated gray shale. Contains

Micracanthoceras acanthellum Imlay————— 43 13.0 

11. Limestone, thin-bedded, laminated;

intercalated gray shale. Contains

Corongoceras filicostatum, Metahaploceras?

ana inoceramus————————————————— 18 5.5 

10. Mostly covered. Some tuffaceous limestone.

Contains Kossmatia victoris Burckhardt.

Probable float also contains Corongoceras 28 8.5 

9. Limestone, black, laminated, thin-bedded;

lenses of black chert. Contains Kossmatia

victoris (Burckhardt). Float contains

Lytohoplites caribbeanus Iml ay ar\d

Corongoceras filicostatum Imlay——————— 39 12.0 

8. Tuff, sandy, thin-bedded, platy, laminated.

Contains perisphinctid ammonites—————— 18 5.5 

7. Tuff, sandy, medium-bedded, siliceous———— 33 10.0 

6. Limestone, dark-gray, thin-bedded, laminated,

siliceous; limestone concretions and chert

bands. Contains Physodoceras and

Metahaploceras?. Float, probably from

same unit, contains Durangites,

Parodontoceras?. and Simoceras?——————— 20 6.0 

5. Mostly covered—————————————————— 26 8.0 

4. Limestone, siliceous, thin-bedded, shaly,

flaggy; gray limestone concretion.

Contains Corongoceras?————————————— 23 7.0 

3. Tuffs and black siliceous limestone—————— 59 18.0 

2. Mostly covered—————————————————— 43 13.0 

1. Limestone, gray to black, siliceous, banded,

laminated, medium- to thin-bedded; some

tuffaceous shale. Contains

Micracanthoceras acanthe11urn Iml ay and

Simoceras (Virgatosimoceras.) Float

contains Corongoceras filicostatum

———————————— 44 13.5

Other Mexican ammonites of the earliest late Tithonian assemblage that are similar to species in Cuba, or 

that are of stratigraphic significance, include the following:

1. Parodontoceras cf. P. butti Imlay. Petroleos 

Mexicanos lot 20851 from the Pimienta Formation 

3 km south of Jonotla on trail to Zacapoaxtla, 

Puebla (written commun. to M. R. Aguilar, 1948).

2. Dickersonia cf. D. sabanillensis Imlay. Chocoy 

well 2 at depth of 3,195 feet (974 m), about 28 

miles (45 km) northwest of Tampico, Tamaulipas. 

Associated ammonites include Parodontoceras and

Corongoceras cf. C. alternans Gerth (written commun. to Federico Bonet, 1959).

3. Pseudolissoceras zitteli (fturckhardt) in association with Kossmatia victoris (Burckhardt) and 

Grayicerasl mexicanum (Burckhardt), Mazatepec 

area, Puebla (Cantii Chapa, 1967, p. 4, 5, 21; 1971, 

p. 30).

4. Proniceras sp. associated with Durangites, Parodontoceras and Micracanthoceras. Petroleos 

Mexicanos lot AC-1933 from Bolson de Judas in 

Candela district near boundary of Coahuila and 

Nuevo Leon (written commun. to Teodoro DiazGonzalez, 1953).

The mentioned association of Proniceras with Durangites, as well as a similar association reported by 

Cantii Chapa (1968, p. 23-25) from Galeana in southern 

Nuevo Leon, could mean either that Durangites ranges 

up into the uppermost Tithonian or that Proniceras occurs lower than previously recorded.

The earliest late Tithonian ammonite assemblage of 

north-central Mexico is dominated by species of Kossmatia and Durangites (Burckhardt, 1930, p. 70, 71) but 

also includes Micracanthoceras, Hildoglochiceras 

( = Salinites Cantu Chapa, 1968, p. 20), Grayicerasl, 

Aulacosphinctesl', and Micracanthoceras (Imlay, 1939, 

p. 22, table 8). This lower faunule near Placer de Guadalupe in east-central Chihuahua is represented mainly by 

species of Kossmatia near the top of the Jurassic sequence. Of the species present, K. kingi Imlay is probably identical with Perisphinctes sp. ind. in Burckhardt 

(1906, p. 130, pi. 37, figs. 9, 11, 12), and K. varicostata 

Imlay is closely similar to K. victoris Burckhardt (Burckhardt, 1906, p. 131, pi. 26, figs. 1-6, pi. 27, fig. 1).

An associated species, Kossmatia rancheriasensis 

Imlay, has been found elsewhere, in the Malone Mountains of Texas. R. T. Hazzard collected the species about 

25 feet (7.6 m) below a conglomerate at the base of the 

Lower Cretaceous(?) Torcer Formation, approximately 

three-quarters of a mile (1.2 km) northwest of a cafe at a 

bend on U.S. Highway 80, 10 miles (16 km) west of 

Sierra Blanca, Tex. (USGS Mesozoic loc. 26956). Another fragment of Kossmatia found in the conglomerate 

(Albritton, 1937, pi. 4, fig. 1) was probably derived from 

the underlying Malone Formation.

SUBSTEUEROCERAS-PRONICERAS AMMONITE ASSEMBLAGE

The latest late Tithonian ammonite assemblage in 

the Gulf region, characterized by Substeueroceras and 

Proniceras, is not known in Cuba. It is represented in 

the subsurface of the southeastern United States only by 

one occurrence of Substeueroceras at the depth of 17,403 

feet (5,304 m) in the Humble Benavides well 1 in Webb
36 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

County, Tex. It is widespread in eastern and north-central Mexico in both the surface and subsurface, and is not 

represented in Chihuahua or in west Texas.

In southeastern Mexico (Huasteca area), two faunal 

units, or zones in the uppermost upper Tithonian are recognized by Cantii Chapa (1967, p. 22, table 1). Of these, 

the higher faunal unit is characterized by Parodontoceras cf. P. callistoides (Behrendsen) in association with 

Proniceras and Protacanthodiscus. The lower faunal 

unit is characterized by Suarites bituberculatum Cantii 

Chapa in association with the genera Acevedites, Wichmanniceras, and Corongoceras (Cantii Chapa, 1967, p. 

12-14, 18-20) and occurs below the lowest known occurrences of calpionellid microfossils.

Probably the most complete latest Jurassic ammonite sequence found in the subsurface in Mexico occurs at 

depths of 10,505 to 10,761 feet (3,202 to 3,280 m) in the 

San Javier well 1, Nuevo Leon (see location in Perez Fernandez and Diaz-Gonzales, 1964, p. 232); it is described 

as follows:

Latest Jurassic ammonite sequence in the San Javier No. 1 

well, about 90 miles (145 km) south of Laredo and 70 

miles (110 km) west of Reynosa in Nuevo Leon, Mexico

[Core and depth data furnished by Teodoro Diaz G., of Petroleos 

Mexicanos. Fossils identified by R. W. Imlay (written commun. to 

DiazG., 1957)]

Depth 

Core No. Feet Meters Fossil

47———.

47———-

48———-

48———- 

48———- 

48———- 

48———- 

48———- 

48———- 

48———- 

48———-

48———-

49————.

50 to 52-

3,202 

3,206 

3,270

3,271 

3,272 

3,273 

3,274 

3,276 

3,277 

3,278 

3,279 

3,280 

3,272.5 

3,372.5- 

3,418.5

Himalayites?. 

Proniceras, Parodontoceras

Substeueroceras? and

Pseudolissoceras?.

Virgatosphinctes?.

Perisphinctid ammonite. 

Substeueroceras.

Substeueroceras.

Substeueroceras?.

Perisphinctid ammonite. 

Himalayites. 

Virgatosphinctes?.

Substeueroceras.

Perisphinctid ammonite. 

Exogyra cf . E. virgula 

(Def ranee).

10,505

10,518

10,728

10,732

10,735

10,738

10,741

10,748

10,751

10,755

10,758

10,761

11,065

11,065-

11,216

In this well, the contact with the Cretaceous is not 

indicated by megafossils, but cores from depths of 

10,028 to 10,064 feet (3,056.5 to 3,067.5 m) contain the 

ammonites Olcostephanus, Bochianites, Thurmanniceras, Sarasinella, and Kilianella of Valanginian to 

early Hauterivian Age.

Occurrences of most of the latest Jurassic ammonite 

genera in Mexico are well documented. Occurrences of 

the uncoiled ammonite, Protancyloceras, are listed below, however, because the presence of the genus in Mexico was not recognized until recent years, and because 

some species are similar to or identical with species in 

Cuba (Imlay, 1942, p. 1456, 1457, pi. 10, fig. 1 to 9, 11, 

12).

1. Protancyloceras cf. P. hondense Imlay. Tantima 

well 2 at depths of 8,036 to 8,045 feet (2,449 to 

2,452 m), near Tantima, Veracruz. Associated with 

Substeueroceras and Parodontoceras (written 

commun. to M. R. Aguilar, 1953).

2. Protancyloceras cf. P. catalinense Imlay. Piedra 

de Cal well No. 8 at depths of 5,837 to 5,850 feet 

(1,779 to 1,783 m), about 60 miles (100 km) southwest of Tampico, near Tantoyuca, Veracruz. Associated with Substeueroceras (written commun. 

to Federico Bonet, 1959).

3. Protancyloceras anahuacense Cantii Chapa 

(1963, p. 28, 73, pi. 1, figs. 2-4) from the Anahuac 

well 1 at depths of 8,200-8,213 feet (2,499.3- 

2,503.3 m), near Anahuac in northern Nuevo Leon 

(Perez Fernandez and Diaz Gonzales, 1964, p. 232). 

Associated with Proniceras, Substeueroceras^ and 

Protacanthodiscus.

4. Protancyloceras barrancense Cantii Chapa 

(Cantii Chapa, 1963, p. 27, 73, pi. 1, fig. 5) from 

the Barranca 1 well at depths of 8,755 to 8,768 

feet (2,668.5 to 2,672.5 m), Panuco-Ebano area, 

Veracruz.

5. Protancyloceras alamense Cantii Chapa (Cantii 

Chapa, 1963, p. 28) for Aegocrioceras sp., in Imlay 

(1939, p. 5, 57, pi. 11, figs. 1, 2) from Canon Alamo, Sierra Jimulco, Coahuila. Associated with 

Proniceras, Aulacosphinctes, Hildoglochiceras, 

Micracanthoceras, Parodontoceras, and Substeueroceras.

6. Protancyloceras ramirense Cantii Chapa (Cantii 

Chapa, 1963, p. 28) for Crioceras sp. incl. in 

Burckhardt (1919, p. 58, 69; 1921, pi. 21, fig. 3) 

from near the Jurassic-Cretaceous contact in the 

Sierra Ramirez, near Symon, Durango. Associated with Parodontoceras (Burckhardt, 1921, pi. 

20, figs. 1-3) and Substeueroceras.

TITHONIAN OF CALIFORNIA AND OREGON

In western California and southwestern Oregon, the 

upper Tithonian contains a sequence of ammonites similar to those present in the Gulf region (Imlay and Jones, 

1970, p. B6-B12). These are associated with species of 

Buchia that permit correlations with faunas to the north 

in Canada and Alaska. As Buchia mosquensis (von Buch) 

had not been found in California or Oregon, it is assumed 

that the base of the Kossmatia-bearing beds in those 

States is not as old as the base of the Kossmatia-bearmg 

beds in Mexico (Imlay and Jones, 1970, p. Bll).

TITHONIAN OF CANADA AND ALASKA

Tithonian beds are widespread in western and arctic 

Canada and in southern and northern Alaska, judging
INTERCONTINENTAL FAUNAL RELATIONSHIPS 37

from occurrences of certain species of Buchia that furnish correlations with those in Greenland and northern 

Eurasia (Jeletzky, 1965, p. 57; Imlay, 1965, p. 1034; Imlay and Jones, 1970, p. B8, 9, 19; Frebold and Tipper, 

1970, p. 17). Associated ammonites are rare and are generally poorly preserved (Frebold, 1957, p. 35, 66, pis. 

42^4; Frebold, 1961, p. 23, pi. 17, fig. 2; Jeletzky, 1966, 

p. 3-23, pis. 1-5, 8 in part; Frebold and Tipper, 1970, 

p. 14-16), in contrast with the situation in East Greenland.

INTERCONTINENTAL FAUNAL 

RELATIONSHIPS

The known Jurassic ammonite successions in North 

America from Hettangian through early Oxfordian time 

were in seas that were either extensions of the Pacific 

Ocean or of the Arctic Ocean. Nevertheless, the North 

American ammonite successions during Early Jurassic 

time were essentially the same as those in Europe and 

elsewhere in the world. The same statement applies to 

the early Bajocian, except for an apparent absence of any 

taxa typical of the Leioceras opalinum zone in the Pacific 

Coast region (Arkell, 1956, p. 607, 608; Imlay, 1965, p. 

1029-1031; Frebold, 1964a, p. 5; Frebold and Tipper, 

1970, p. 9,17). After early Oxfordian time, the ammonite 

successions in the Gulf of Mexico region were in waters 

connected with both the Atlantic and Pacific Oceans. 

After early Bajocian time, the ammonite successions 

along the Pacific Coast of North America became differentiated from north to south because of fairly complete 

separation of the Arctic Ocean from the Pacific Ocean 

and the Mediterranean. Similar differentiation took place 

in Europe and presumably elsewhere.

During the middle to late Bajocian, the ammonite 

successions in western and northern North America became different from those in Europe and the Tethyan region. For example, in the Arctic region, the sole known 

representative of middle Bajocian Age consists of Arkelloceras, and there are no ammonites of definite late Bajocian Age. In the Pacific Coast region, the ammonite 

successions of middle Bajocian Age contain some genera 

and species identical with taxa in Europe and the Tethyan region, but they differ in that they contain Alaskoceras, Pseudotoites, Parabigotites, Zemistephanus, and 

Arkelloceras (Westermann, 1964, 1969; Imlay, 1973, p. 

1, 35, 36; Frebold and Tipper, 1970, p. 17). Of these, 

Pseudotoites is known elsewhere in Argentina, Chile, 

and western Australia (Westermann, 1967, p. 67, 68; 

1969, p. 27, 28, 129, 130, 157; Arkell, 1954, p. 592; Hillebrandt, 1970, p. 176, 187, 199).

Ammonites of late Bajocian Age in the arctic region 

of North America have not been definitely identified but

could be represented by the lowermost occurrence of 

Cranocephalites. By contrast, in the Pacific Coast region, the ammonite successions of late Bajocian Age are 

definitely represented by such widespread genera as 

Spiroceras, Leptosphinctes, and Sphaeroceras. These 

successions differ from those in most parts of the world 

outside of the arctic region by the presence of Megasphaeroceras, Eocephalites, Parachondroceras, Sohlites, Lupherites, and Parastrenoceras and by lacking all 

genera of the Parkinsonidae. Of these ammonites, Megasphaeroceras and Eocephalites are reported elsewhere 

only in Chile and western Argentina, where they are associated with Spiroceras, Normannites, Teloceras, and 

Cadormtes but are not associated with the Parkinsonid 

genera (Hillebrandt, 1970, p. 176, 201).

It appears, therefore, that the middle and late Bajocian ammonite faunas along the Pacific Coast of North 

and South America evolved in a similar manner. Both 

can be correlated fairly closely with sequences in Europe 

and in the Mediterranean region, but both include genera 

that appear to be restricted to areas bordering the Pacific Ocean. Apparently, this development was entirely 

different from that in the arctic region of North America 

during the same time interval.

Bathonian ammonites belonging to genera characteristic of the Mediterranean (Tethyan) region and northwest Europe are present in the Pacific Coast region of 

southern Mexico and may occur in east-central Mexico. 

Elsewhere in North America, Bathonian ammonites have 

been found in the arctic region, southern Alaska, northern British Columbia, eastern Oregon, westernmost 

Idaho, and in the western interior region. The succession 

in southern Alaska and in the arctic region of Alaska and 

Canada consists, from bottom to top, mainly of the genera Cranocephalites, Arctocephalites, and Arcticoceras. 

The succession in the western interior consists of Paracephalites, which is similar to Arctocephalites, overlain 

by Warrenoceras, which is similar to Arcticoceras. Cobbanites, a genus similar to Vermisphinctes of late Bajocian Age, is associated with Cranocephalites in southern 

Alaska and with Paracephalites and Warrenoceras in the 

western interior of the United States and Canada. In 

eastern Oregon, Cobbanites is associated with a species 

of Parareineckeia that is similar to a species of Parareineckeia that occurs with Cranocephalites in southern 

Alaska. Both Warrenoceras in the western interior and 

Arcticoceras in southern Alaska are succeeded by species of Kepplerites similar to species in Greenland present below beds identified as earlier Callovian. These 

Bathonian ammonite successions, as far as is known, 

originated in the Arctic Ocean, had marine connections 

southward only through Yukon Territory and British Columbia into the western interior region, and were unlike 

any other Bathonian succession outside the arctic region.
38 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

The Callovian ammonite succession in southern Mexico resembles that in Europe by containing Peltoceras, 

Erymnoceras, and Reineckeia and its subgenera. It also 

resembles that in western South America by containing 

Xenocephalites, Eurycephalites, and probably Neuqueniceras. Similarly, the Callovian succession in southern 

and east-central California bears some resemblance to 

that in Europe, as shown by the presence of such genera 

as Macrocephalites, Hecticoceras, and Peltoceras. The 

successions in east-central and northeastern California 

and in eastern Oregon are characterized, however, by 

such genera as Kepplerites, Xenocephalites, Pseudocadoceras, and Lilloettia. They do contain species in common with successions in British Columbia and Alaska but 

differ from those successions by lacking Cadoceras proper 

and its subgenera. In the western interior region, the 

earliest Callovian is represented by Kepplerites, Xenocephalites, Lilloettia, and Grossouvria, and the latest 

Callovian by a species of Quenstedtoceras similar to Q. 

henrici R. Douville from the latest Callovian of Europe. 

In arctic Alaska and arctic Canada, the Callovian is 

rather poorly represented by species similar to those of 

middle Callovian Age in southern Alaska. Overall, the 

Callovian ammonite sequences from British Columbia 

northward are dominated by ammonites characteristic of 

the arctic region, such as Kepplerites, Cadoceras, and 

Pseudocadoceras, but include genera found only in the 

Pacific region, such as Xenocephalites, Lilloettia, and 

Parareineckeia.

The Oxfordian ammonite sequences in the Gulf of 

Mexico region, in California, and in western Oregon contain the same genera found in beds of late middle to late 

Oxfordian Age in the Mediterranean region and are characterized by Perisphinctes (Dichotomosphinctes) and P. 

(Discosphinctes). They do not contain any ammonites of 

boreal origin, but in California and western Oregon they 

do contain Buchia concentrica (Sowerby) of such origin. 

These sequences have not yielded any ammonites of 

early to early middle Oxfordian Age, apparently because 

of the deposition at that time of highly saline deposits or 

red beds in the Gulf region and thick submarine volcanic 

materials in California and western Oregon.

Elsewhere in North America, the Oxfordian ammonite sequences are very similar to those in areas bordering 

the Arctic Ocean. The early to early middle Oxfordian is 

characterized by Cardioceras in association with Quenstedtoceras (Pavloviceras) and Prososphinctes. The late 

middle to late Oxfordian is characterized by Amoeboceras in association with the pelecypod Buchia concentrica (Sowerby).

Like the Oxfordian sequences, the Kimmeridgian 

ammonite sequences in the Gulf of Mexico region comprise genera typical of the Mediterranean region and 

southern Europe. They also do not contain ammonites of

boreal origin, but in central Mexico they do contain the 

boreal pelecypods Buchia concentrica (Sowerby) and B. 

mosquensis (von Buch) in association with Idoceras and 

Glochiceras. In northwest Sonora, in California, and in 

western Oregon, the Kimmeridgian sequences contain 

ammonites of Mediterranean or nonboreal origin, such as 

Subdichotomoceras and Idoceras, associated with the 

Amoeboceras and A. (Amoebites) of boreal origin. Such 

ammonites in California and western Oregon are also associated with the boreal Buchia concentrica (Sowerby). 

From British Columbia northward to arctic Alaska and 

Canada, the faunal sequences do not contain ammonites 

that are definitely Kimmeridgian, although some of the 

occurrences of Amoeboceras could be of that age. Nonetheless, the top of the Kimmeridgian can be placed approximately at the top of beds containing an association 

of Buchia mosquensis (von Buch) with B. concentrica 

(Sowerby) and B. rugosa (Fischer).

The Tithonian ammonite sequences in the Gulf of 

Mexico region, in California, and in western Oregon include mostly genera that are similar to those in the Mediterranean (Tethyan) region and in South America, but 

they also include some ammonite genera that are found 

only, or mainly, in areas bordering the Pacific Ocean 

south of Oregon (Imlay, 1965, p. 1024, 1032). With these 

in California and Oregon are associated species of Buchia 

of boreal origin (Imlay and Jones, 1970, p. B5, B8). In 

contrast, from British Columbia northward to the arctic 

region of Canada, age determinations are based mainly 

on species of Buchia because ammonites are exceedingly rare (Frebold and Tipper, 1970, p. 14-16; Frebold, 

1964a, p. 4; Jeletzky, 1965, 1966; Imlay and Detterman, 

1973, p. 21). This rarity contrasts markedly with the 

presence of a fair abundance of Tithonian ammonites in 

East Greenland and in the arctic region of Eurasia. Evidently the environmental conditions permitting the existence or the preservation of ammonites in arctic Alaska 

and Canada became less and less favorable from Oxfordian time to the end of the Jurassic.

In summation, Jurassic ammonite successions in 

North America were essentially the same as elsewhere 

in the world from the Hettangian until the early Bajocian. Differentiation of ammonite faunas began in the 

middle Bajocian, continued through the remainder of the 

Jurassic, and was greatest during the Bathonian and Tithonian (Volgian). This differentiation was due to partial 

to fairly complete isolation of the Arctic Ocean. That 

ocean opened southward to the Pacific Ocean through the 

Yukon Territory after Early Jurassic time. It opened 

southward from the East Greenland area into western 

Europe and the Mediterranean region in early Callovian 

time and later. Also, from middle Bajocian time onward, 

some new ammonite genera evolved in the Pacific Ocean. 

Some of these are known only, or mainly, from the Pa-
COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 39

cific Coast region of North and South America, or from 

parts of that region; some extended to New Zealand and 

beyond; a few spread into the Mediterranean region; but 

none reached into the arctic region (Arkell, 1956, p. 

608-618; Imlay 1965, p. 1024; Enay, 1972).

COMPARISONS OF LITHOLOGIC AND 

STRATIGRAPHIC FEATURES

GULF OF MEXICO AND NEARBY REGIONS

CUBA

The Jurassic formations of Cuba have been discussed 

recently in detail by Khudoley and Meyerhoff (1971, p. 

34-44, 59-67, 104-108). Their conclusions concerning the 

formations have been modified by certain Polish geologists, as discussed briefly herein and depicted in figure 

21. At the base in western Cuba is the tremendously 

thick San Cayetano Formation, which is characterized 

by dark-gray to black carbonaceous shale, siltstone, and 

fine-grained sandstone. Locally it is slightly metamorphosed. It contains many carbonized plant stems and 

near the top contains marine pelecypods of probable Middle Jurassic age (Meyerhoff, 1964, p. 152, 153). It could 

be equivalent to all or part of the plant-bearing beds of1 

Toarcian to Bathonian Age in southern Mexico. Its upper 

part is now dated as early middle Oxfordian on the basis 

of its gradational contact with the overlying Francisco 

Formation, which is mostly of middle Oxfordian Age 

(Wierzbowski, 1976, p. 141). Such an age is supported 

by the presence of the Oxfordian ammonites Perisphinctes (Dichotomosphinctesl) and P. (Discosphinctes) 

in the upper 35 to 100(?) meters of the San Cayetano 

Formation in the Sierra del Rosario (Myczynski and 

Pszczolkowski, 1976).

Conformably above the San Cayetano Formation in 

the Sierra del Rosario is the Francisco Formation, which 

ranges in thickness from 43 to 82 feet (13 to 25 m), consists of rather soft shale, marl, limestone, and some 

sandstone, and contains ammonites of middle to probable 

early late Oxfordian Age (Kutek and others, 1976, p. 

300-305; Wierzbowski, 1976, table 2 opposite p. 141, p. 

152-159; Myczynski, 1976, p. 269, 292; Sanchez Roig, 

1920, 1951; O'Connell, 1920; Jaworski, 1940; Burckhardt, 1930, p. 61, 62; Spath, 1931, p. 400; Arkell, 1956, 

p. 572, 573).

Conformably above the San Cayetano in the Sierra 

de los Organos is the Jagua Formation (Wierzbowski, 

1976, p. 141-143; Hatten, 1967, p. 782), which consists 

of three members. The lower, or Azucar Member, ranges 

in thickness from 158 to 250 feet (48 to 76 m) and consists of gray to black thin-bedded limestone that varies

from dense to oolitic to sandy (Hatten, 1967, p. 782). The 

middle, or Jagua Vieja Member, ranges in thickness 

from 164 to 198 feet (50 to 60 m), consists of dark-gray 

silty to sandy shale, marl, and limestone, contains many 

limestone concretions in the marly and shaly beds, and 

grades into the adjoining members. The upper, or Pimienta Member, ranges in thickness from 131 to 198 feet 

(40 to 60 m) and consists of gray, dense, platy thin-bedded limestone. Ammonites present in all three members 

(Wierzbowski, 1976, table 2 opposite p. 141) show that 

the Jagua Formation is of the same age as the Francisco 

Formation in the Sierra del Rosario. In particular, the 

presence in the Azucar Member of the ammonites Vinalesphinctes, Perisphinctes, Discosphinctes, Cubaochetoceras, and Glochiceras shows that its age is not older 

than middle Oxfordian.

The uppermost Jurassic in the Sierra del Rosario is 

represented by the Artemsia Formation, which consists 

mostly of thin- to medium-bedded, dense cherty limestone and tuffaceous shale. Its basal beds are of middle 

or late Oxfordian Age, as shown by the presence of the 

ammonites Mirosphinctes and Cubaochetoceras (Wierzbowski, 1976, p. 145; Kutek and others, 1976, p. 302- 

306, fig. 6 on p. 307).

Most of the formation, however, contains ammonites 

of late early to early late Tithonian Age (Imlay, 1942; 

Judoley and Furrazola-Bermudez, 1968, p. 3, 17, 23-25) 

and perhaps also contains a later Tithonian assemblage 

characterized by Dalmasiceras and Spiticeras (Housa 

and de la Nuez, 1973). The earliest Tithonian fossils were 

found 165-230 feet (50-70 m) above the base of the formation near Cinco Pesos (Wierzbowski, 1976, p. 145; Kutek and others, 1976, p. 315; Judoley and Furrazola-Bermiidez, 1965, p. 15), which means that the latest 

Oxfordian, all of the Kimmeridgian, and the earliest Tithonian must be accounted for by the basal 50 m of the 

Artemsia Formation.

The uppermost Jurassic beds above the Jagua Formation in the Sierra de los Organos are now placed in the 

Guasasa Formation of Herrera (1961, p. 11-14) by Cuban and Polish geologists (Wierzbowski, 1976, p. 144; 

Kutek and others, 1976, p. 312). These geologists abandoned the term Vinales Limestone because it was poorly 

defined and had been used for different rock units in different areas. Thus, the term Vinales Limestone as used 

by Imlay (1942) includes both the Artemsia Formation in 

the Sierra del Rosario and the Guasasa Formation in the 

Sierra del Organos. The Vinales Limestone as used by 

Khudoley and Meyerhoff (1971, p. 10-11) and by Judoley and Furrazola-Bermudez (1968, p. 17) represents the 

lower member of the Guasasa Formation.

The Guasasa as used by these geologists ranges in 

thickness from about 4,265 to 4,600 feet (1,300 to 1,400 

m) and consists of two members. Its upper member is
40

104°

JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES 

98° 92° 86°

I A

Monterrey* NUEVO Reynosa r> 

£n • ^,\ LEON S rf O

18°

1. Western Cuba

2. Gulf region of United States

3. Monterrey area, northeastern Mexico

4. Mountains west of Ciudad Victoria, Tamaulipas, eastern Mexico

5. Huasteca area, northern Hidalgo to southern San Luis Potosi' eastern Mexico (5a=Huehuetla; 5b=Huauchinango;5c=Huayacocotla)

6. Sierra de Catorce, San Luis Potosi', central Mexico

7. Villa Juarez area, eastern Durango, central Mexico

8. Placer de Guadalupe and Plomosas areas, east-central Chihuahua

9. Malone Mountains, southeast of El Paso, west Texas

FIGURE 17.—Index map of Jurassic areas in the Gulf of Mexico and nearby regions. Numbers 1 to 9 refer to stratigraphic sequences shown in

figure 21.

990-1,320 feet (300-400 m) thick and consists of hard, 

compact, gray to black, highly fossiliferous thin- to thickbedded limestone. Its lower member, the San Vicente 

Member (Herrera, 1961, p. 11), is at least 3,280 feet 

(1,000 m) thick. It consists of gray to black, mostly thickbedded to massive limestone, some dolomite, and in 

places lentils and concretions of chert. It is marked basally by a breccia composed 'of rounded to angular black 

limestone fragments that have been interpreted as evidence for a disconformity (Herrera, 1961, p. 11; Judoley 

and Furrazola-Bermiidez, 1965, p. 20; Khudoley and 

Meyerhoff, 1971, p. 10-11).

The upper member of the Guasasa Formation has 

furnished ammonite assemblages at several levels, according to Housa and de la Nuez (1975). Of these, the 

lowermost, collected directly above the massive limestone of the lower member, contains Mazapilites, Protancyloceras, and Pseudolissoceras, of middle early Tithonian Age; the next higher contains Torquatisphinctes 

and Parapallasiceras of late early Tithonian Age; and 

the uppermost, obtained near the top of the Guasasa 

Formation, contains some early late Tithonian ammonites, which were described by Imlay (1942) as late Portlandian.
124°

COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 

120° 116° 112°

41

108°

LOCATION OF STRATIGRAPHIC SEQUENCES

1. Santa Ana and Santa Monica Mountains,southern California

2. Western Nevada

3. Taylorsville area, northeastern California

4. Gold-belt area, east-central California

5. Big Bend area, north-central California

6. Western California from San Diego northward

7. Parts of northwestern California and southwestern Oregon

8. Parts of southwestern Oregon

9. Suplee and Izee-Seneca areas, east-central Oregon

10. Ironside-Brogan-Huntington area, eastern Oregon, and Mineral 

area, Idaho

11. Wallowa Mountains, northeastern Oregon

12. Snake River Canyon, 32 miles south of northeast comer of Oregon

13. Snake River Canyon, northeast corner of Oregon

14. Cascade Mountains, northwestern Washington

till 

0 50 100 150 200 KILOMETERS

FIGURE 18.—Index map of Jurassic areas in the Pacific Coast region from California and Nevada to Washington. Numbers 1-9 refer to stratigraphic sequences illustrated in figure 22. Numbers 10-14 refer to stratigraphic sequences shown in figure 23.
42

148°

JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES 

144° 140° 136° 132° 128° 124° 120° 116°

50 100 150 KILOMETERS

QUEEN

CHARLOTTE^ 4 

ISLANDS

1. Harrison Lake area, British Columbia

2. Taseko Lake area, British Columbia

3. Vancouver Island, British Columbia

4. Queen Charlotte Islands, British Columbia

5. Sm it hers area-Tenas Creek-McDonell Lake, British Columbia

6. Tulsequah area, British Columbia

7. Whitehorse area, Yukon Territory

8. Eastern Alaska Range and Nutzotin Mountains, Alaska

9. Wrangell Mountains, Alaska 

10. Talkeetna Mountains (Nelchina area), Alaska

VANCOUVER ISLAND

50°

FIGURE 19.—Index map of Jurassic areas in the Pacific Coast region from British Columbia to southern Alaska. Numbers 1-10 refer to stratigraphic sequences shown in figure 24.

This lower member of the Guasasa Formation has 

not been dated by fossils. Its age, however, must be 

mostly Kimmeridgian on the basis of its disconformable 

relationship with the underlying Jagua Formation of 

middle to late Oxfordian Age and on the presence ofMazapilites in the basal beds of the upper member. The disconformity at the base of the lower member could be of 

latest Oxfordian or earliest Kimmeridgian Age, or both,

and could be contemporaneous with deposition of the 

Buckner Formation in the Gulf of Mexico region.

The Jurassic may also be represented in north-central Cuba by the Punta Alegre Formation, which consists 

of 2,000 feet (610 m) or more mostly of salt and anhydrite, but includes some red to gray shale and siltstone, 

and is known only from four salt domes. (Khudoley and 

Meyerhoff, 1971, p. 40, 41). Some red silty shale in the
COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 43

116° 112'° 108° 104° 100° 96° 92°

48°

44<

40°

36° t=:

SASKATCHEWAN

1 \ > I \ I

%——I \ __ CANADA _ 1

UNITED fSTATES BEAR PAW MTS

LITTLE ROCKS

MTS x 10 I NORTH

MONTANA 

'<£> * •Billings 

Columbus

"" ' "JZ. ___ __ "" ~ XT>

NEW MEXICO

• Santa Fe

ita

\ \

Rocky Mountains of southwestern Alberta

Swift Reservoir, Sun River area, northwestern

Montana

Southwest of Craig.Mont.

Smith River, south of Great Falls, Mont.

Bert Creek, southeast of Great Falls, Mont.

Near Utica on Judith River, Mont.

Big Snowy Mountains near Heath, Mont.

Button Butte, MontPorcupine Dome, Mont.

Northeastern Montana and northwestern

North Dakota

Southwestern Saskatchewan

Ammon Quad., southeastern Idaho

Red Mountain, southeastern Idaho

Lower Slide Lake, WyoGreen River Lakes, northwestern Wyoming

Red Creek, northwestern Wyoming

Near Hyattville, north-central Wyoming

Muddy Creek, north-central Wyomjng

Bush Canyon, northeastern Wyoming

East of Newcastle, northeastern Wyoming

Minnekahta area, southwestern South Da

Burr Fork, east of Salt Lake City, Utah

Peoa-Oakley area, north-central Utah

Duchesne River near Hanna, Utah

Lake Fork, northeastern Utah

Whiterocks River canyon, northeastern Utah

Dinosaur Quarry, northeastern Utah

Miller Creek, northwestern Colorado

Elk Creek erea, northern Colorado

Frarrtz Creek, northern Colorado

Hahns Peak, northern Colorado

Monks Hollow, north-central Utah

Nephi-Levan area, central Utah

Gunnison-Salina area, south-central Utah

Buckhorn Wash, east-central Utah

Black Dragon Canyon ..east-central Utah

San Rafael River, east-central Utah

Dewey Bridge, east-central Utah

John Brown Valley, southwestern Colorado

Slick Rock area, southwestern Colorado

McElmo Canyon, southwestern Colorado.

Gunlock, southwestern Utah

Danish Ranch, southwestern Utah

Kanarraville-Cedar City, southwestern Utah

Mount Carmel Junction, southwestern Utah

Brown Canyon, southwestern Utah

Little Bull valley, southwestern Utah

Pine Creek, south-central Utah

Sand Valley, north-central Arizona

Page, north-central Arizona

Big Hollow Wash, southeastern Utah

Cow Springs, northeastern Arizona

KANSAS

OKLAHOMA

TEXAS

FIGURE 20.—Index map of Jurassic areas in the western interior region. Numbers 1-11 refer to stratigraphic sequences shown in figure 25; 

numbers 12-21 refer to sequences shown in figure 26; numbers 22-31 refer to sequences shown in figure 27; numbers 32-41 refer to 

sequences shown in figure 28; and numbers 42-52 refer to sequences shown in figure 29. Western and southern limits of Jurassic deposition 

are indicated by a solid line.
44 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

Stage English 

Formations

Western Cuba 1

Sierra de 

tps , 

Organos

Sierra

del

Rosario

Gulf Region of United States

Monterrey area, western 

Nuevo Leon and eastern 

CoahuNa

Mountains west of 

Ciudad Victoria, 

Tamaulipas

Overlying beds Lower Cretaceous Lower Cretaceous

Tithonian

Kimmeridgian

Oxfordian

Callovian

Bathonian

Bajocian

Toarcian

Pliensbachian

Sinemrian

Hettangian

Purbeck 

Beds

Portland 

Beds

Kimmeridge 

Clay

Guasasa

Formation

3600-

4300ft

(1060-

1400m)

Corallian 

Beds

Jagua 

Formation 

460-655 ft 

(140-200 m)

Artemsia 

Formation 

750-2000 ft 

(240-700 m)

Cotton Valley Group, 

undivided

Lower Cretaceous Lower Cretaceous Lower Cretaceous

Schuler Formation 

0-2000 ft plus (0-640 m) 

Red to gray sandstone 

and shale.

Passes basinward into 

normal marine facies

ssier 

Formation 

0-2350 ft

La Cesita Formation 

860-2800 ft (275-895 m) 

Upper part mostly 

sandstone but includes 

some sandy limestone 

and some conglomerate. 

Lower part mostly shale 

and siltstone

-> l/OHinjurai 

Buekner Formation 0-890 ft (285 mK^alcareous

Francisco 

Formation 

43-82 ft

(13-25 m)

Smackoyer Formation 0-1650 ft (525 m) 

Mostly limestone, locally sandy_____

La Casita Formation 

110-330 ft (35-105 m) 

Dark shaly to thinbedded limestone and 

shale. Sandy beds at 

base and locally 

higher

Olvido Formation \ 

325-650 ft (100-200 m) > 

Limestone, gypsum, 

and red beta____

Norphlet Formation 15-150 ft (5-48 m) 

Red-gray shale and sandstone, pebbly at has

Zuloaga Limestone 

200-250 ft (64-80 m) 

Thin to thick-bedded

Louann Salt 5000 ft or less (1500 m)

Oxford 

Clay

Minas Vieias Formation 

0-4000 ft (1285m) 

Gypsum and salt

Kellaways 

Beds

Cornbrash 

Beds

Fullers 

Earth

San Cayetano 

Formation 

5000-10,000 ft 

(1500-3000 m) 

Carbonaceous to 

sandy shale, 

siltstone.and 

fine-grained 

sandstone. 

Many plant stems. 

Slight matamorphism 

of some beds

Ostrea and Vaugonia 

occur in upper 2000 ft

Werner Formation 

150-200 ft (48-64 m)

Inferior 

Oolite

Upper 

Lias

Middle 

Lias

Lower 

Lias

Underlying beds Paleozoic Paleozoic \

Anhydrite (50-110 ft)

Red shale and sandstone. 

Locally conglomeratic

Upper Triassicf?)

Zuloaga Limestone 

160-265 ft (50-85 m)

- -'JLa Joya Formation

0-200 ft (0-65 m) 

Varicolored 

siltstone and 

sandstone. 

Conglomerate in 

upper part and

Triassic Permian

A. Western Cuba to Victoria, Mexico.

FIGURE 21.—CORRELATIONS AND COMPARISONS OF JURASSIC ROCKS IN THE GULF OF MEXICO AND NEARBY 

REGIONS. Vertical lines indicate strata as missing; right-diagonal lines indicate strata are not exposed; left-diagonal lines indicate lack of 

fossil data; wavy lines indicate unconformity or disconformity; jagged lines indicate gradational or indefinite contact. Column numbers 

refer to locations shown on figure 17.
COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 45

Huasteca area,from Taman, 

San Luis Potosf,to 

Huauchinango, Hidalgo

Sierra de Catorce, 

San Luis Potosi"

7

Villa Juarez, 

eastern Durango

Placer de Guadalupe 

and Plomosas, 

eastern Chihuahua

Malone Mountains, 

west Texas

Characteristic Fossils

Gulf of Mexico region 

and nearby areas

Northeastern Guerrero 

and- western Oaxaca

Lower Cretaceous Lower Cretaceous Lower Cretaceous Lower Cretaceous ,ower Cretaceous

Pirn lent a Formation 

120-215 ft (40-70 m) 

Dark gray to black 

shale and thin-to 

medium-bedded limestone. 

Many thin lenses of black 

chert

Taman Formation 120-180ft 

(30-60 m) Locally absent. 

Black, medium-bedded to 

shaly limestone and shale 

Locally pebbly at base

La Caia Formation 

170 ft (53m)

Thin-bedded limestone 

and shale underlain 

by thick-bedded 

limestone

Conglomerate at base 

locally

Zuloaga Limestone 

810 ft (260m)

La Casita Formation 

1390 ft (445 m)

Sandstone, thickbedded; some 

shale, limestone 

and conglomerate.

Conglomerate at base

La Gloria Formation 

2395 ft (768 m) 

Mostly sandstone, 

conglomerate at base

Substeueroceras, Proniceras, 

and Autacosphinctes

La Casita Formation 

2425 ft (780 m). Dark 

shale and some 

shaly limestone. 

Sandstone 160 ft thick 

occurs 150 ft above 

base of shale. Limestone conglomerate 

locally at base

Malone Formation 

150-1060 ft (48- 

340 m) Black limestone mostly in 

upper 150-330 ft. 

Clastic rocks mostly 

in lower 170-685 ft. 

Conglomerate or 

locally gypsum 

st base

Kossmatia victor is and 

Durangites vulgar is

Virgatosphinctes and 

Subptanitesl

MazapithGs and 

Virgatosphinctes 

aguilari ,——? -

Hybonoticeras

Glochiceras fialar

Idoceras spp.

Santiago 

Formation 

0-500 ft (160m) 

Shale, dark gray, 

and some pebbly 

limestone La Joya Formation 375- 

500 ft (120-160 m) Red 

shale, sandstone.and 

siltstone- Conglomerate 

at base about 100ft 

thick

La Joya Formation 500- 

1000 ft (152-320 m) 

Red shale, sandstone, 

and lava. Age not 

confirmed

Cahuasas 

Formation 

130-3600 ft 

(40T1200 m) 

Varicolored shale, 

siltstone, sandstone.and 

conglomerate. 

Commonly 

cross bedded

Igneous intrusions, 

folding and faulting, 

some metamocphism, 

and then erosion of 

Lower Jurassic beds. 

Exact duration unknown

?J

Huayacocotla Formation 

170073600 ft (560-1200 m) 

Phyllitic carbonaceous 

shale and thin-bedded 

sandstone.

Conglomerate at base. 

Some coaly beds at top. 

Not deposited in easternmost Veracruz

Red phyllitic shale, 

may contain Arnioceras 

and Vermiceras(Erben, 

1996a, p. 46; Carrillo 

Bravo, 1961, p. 42). 

Not confirmed

iassic \ Permian Permian Permian

Ataxioceras and Rasenia

Discosphinctes carribeanus 

and Ochetoceras 

canaticulatum

Dichotomosphinctes 

durangensis and Creniceras

Erymnoceras cf. £. 

mixtecorum* (Erben, 

1956b. p. 40)_____

Neuqueniceras and 

Reineckeia

Kepplerites*

Wagnericerasi*

(Cantu 

Chapa, 

1969,p. 5)

Nonmsrine beds 

on surface in 

eastern Mexico

Nonmarine beds 

in subsurface in 

eastern Mexico

Uptonia7

Echioceras

Oxynoticeras

Arnioceras

Coroniceras

Substeueroceras* 

( Burckhardt/1930,

p. 99)_______

/_bcwas*(Burckhardt, 

1930, p. 99)

Peltoceras

Erymnoceras 

mixtecorum

Neuqueniceras and 

Reineckeia

Eurycepha/ites and 

Xenocepha/ites

Epistrenoceras

Planfand coalbearing beds

Zigzagiceras

Parastrenoceras

Leptosph metes!

Normannites and 

Steohanoceras

Plant-and coalbearing or nonmarine beds

Arieticeras

Permian

* Reported but not described

B. Huasteca area, Mexico, to Malone Mountains, Tex.
46 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

salt has furnished pollen dated as post-Permian and preCretaceous (Meyerhoff and Hatten, 1968, p. 327). An 

Early to Middle Jurassic age is favored by Meyerhoff, 

and an Early to Late Jurassic age, older than the Artemsia Formation, is favored by Khudoley (Khudoley and 

Meyerhoff, 1971, p. 38). Apparently both geologists favor correlation of the Punta Alegre Formation with the 

Louann Salt and probable equivalent salt masses in 

northeastern and southeastern Mexico.

GULF REGION OF THE UNITED STATES

The lithologic characteristics, stratigraphic relationships, and ages of the Jurassic formations of the southeastern United States have been discussed in many papers (Weeks, 1938; Hazzard, 1939, p. 155-158; Hazzard 

and others, 1947; Philpott and Hazzard, 1949; Imlay, 

1940b, 1943a, 1952a; Swain, 1944,1949; Vestal, 1950; Applin and Applin, 1944, 1953, 1965, p. 18-29; Forgotson, 

1954; McKee and others, 1956; Murray, 1961, p. 282- 

297; Jux, 1961; Thomas and Mann, 1963; Rainwater, 

1967; Bishop, 1967, 1973; K. A. Dickinson, 1968; Maher 

and Applin, 1968, p. 9-11, pis. 2-4; Dinkins, 1968; 

Kirkland and Gerhard, 1971) and are presented briefly 

here. The stratigraphic relationships shown in figure 21 

for formations younger than the Louann Salt are modified from a chart by K. A. Dickinson (1968, p. E7), which 

shows the changes in interpretations of those relationships during the past 30 years.

All these Jurassic formations in the southeastern 

States, although defined on the basis of subsurface sequences in southern Arkansas and northern Louisiana, 

are fairly consistent lithogkally over great distances. All 

of them extend eastward from northeast Texas to Mississippi, and all except possibly the Werner Formation are 

present in the southwest corner of Alabama (Oxley and 

others, 1967; Rainwater, 1967, p. 191; Hartman, 1968; 

Oxley and Minihan, 1968; Maher and Applin, 1968, p. 

&-11). In Alabama, however, some of the formational 

boundaries are less sharply defined than they are farther 

west.

The lithologic characteristics of the Werner Formation and the Louann Salt, as shown in figure 21, are particularly constant over hundreds of miles. The Werner 

Formation rests unconformably on upper Paleozoic rocks 

in northeastern Louisiana and in southern Arkansas (Imlay, 1943a, p. 1425; Hazzard and others, 1947, p. 486, 

487), and it probably rests on the Eagle Mills Formation 

of Late Triassic age in southern Arkansas (Bishop, 1967, 

p. 245; Scott and others, 1961).

The Norphlet Formation consists mainly of red to 

gray shale and sandstone but locally contains anhydrite 

or is conglomeratic. It is overlain sharply by the Smackover Formation. It rests disconformably on the Louann

Salt in places, as shown by the fact that updip, it successively overlaps the Werner Formation, the Eagle Mills 

Formation, and then the underlying Paleozoic rocks. By 

contrast, in Clarke County, Miss., the Norphlet Formation, as interpreted by Badon (1975), passes laterally into 

the Louann Salt. He considers that the basal black-shale 

unit was formed in a depression on the surface of salt 

beds during a retreat of the evaporitic basin; that the 

overlying red siltstone unit was deposited in an intertidal 

to supratidal environment during further retreat of the 

evaporitic basin; and that the highest unit, consisting of 

red to gray quartz sandstone, was deposited in both intertidal and eolian environments near the end of deposition of the evaporitic deposits. Badon interprets the 

sharp contact of the Norphlet Formation with the overlying Smackover Formation as evidence of a major 

transgression related to partial opening of connections 

with a major ocean. His interpretation of the nature of 

the contact between the Norphlet Formation and the 

Louann Salt is not based on cores that show the contact, 

because such cores areN not available in Clarke County. 

Evidently his interpretation needs confirmation by additional studies.

The Smackover Formation in the Arkansas-Louisiana-east Texas area is divisible into three units or members (K. A. Dickinson, 1968, p. E10-12). Of these, the 

upper unit is typically an oolitic limestone, but locally it 

is dolomitic or sandy. The middle unit is typically a dense 

limestone that contains anhydrite, but locally it is dolomitic, oolitic, or silty. The lower unit is a dense silty to 

shaly limestone, which is usually laminated.

The Smackover Formation in Mississippi and Alabama is divisible only into two units (Oxley, and others, 

1967, p. 30-34, figs. 3-5). Of these, the upper unit consists mostly of limestone, which varies from oolitic to 

dense to dolomitic and which at one place in Mississippi 

is replaced laterally by sandstone. The lower unit consists mostly of a dense limestone, which is locally dolomitic near its top and thinly laminated near its base, but 

which at two places in Mississippi is replaced laterally by 

sandstone. The Smackover Formation from east Texas 

to southwest Alabama is underlain concordantly by the 

Norphlet Formation, although the contact is sharp.

The Buckner Formation (Weeks, 1938), redefined as 

the lower member of the Haynesville Formation by Philpott and Hazzard (1949), is used in this paper as a formation for reasons discussed by K. A. Dickinson (1968, 

p. E8). It does not necessarily replace the local use of 

the term Haynesville Formation. As used by K. A. Dickinson (1968, p. E13-E17), the Buckner Formation consists mostly of red shale, anhydrite, and dolomite; locally 

contains salt, siltstone, sandstone, and limestone; is conformable with adjoining formations, except possibly 

where it thins; extends as a rather narrow lens-shaped
COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 47

body from east Texas to southwestern Alabama; pinches 

out northward; and interfingers southward with the Bossier and Smackover Formations (Bishop, 1973, p. 861).

The Bossier Formation as defined by K. A. Dickinson (1968, p. E17-19, figs. 3, 10, pi. 1) consists mostly 

of gray calcareous shale but includes a little shaly or oolitic limestone. It has been identified in northern Louisiana and adjoining parts of Arkansas and east Texas, 

where it passes laterally into the upper part of the 

Smackover Formation, the entire Buckner Formation, 

and the lower part of the Schuler Formation. All contacts 

are conformable.

The Schuler Formation consists of red, pink, to gray 

beds that pass basinward into thicker gray sandstone 

and shale and that extend from east Texas to southwestern Alabama (Imlay, 1943a, p. 1459; Swain, 1944, p. 

594-600; Forgotson, 1954, p. 2490-2494; Oxley and 

others, 1967, p. 37-40). East of Louisiana, the formation consists of varicolored to red clastic sediments, 

which in southwestern Alabama contain a great deal of 

coarse sandstone and conglomerate. The formation rests 

on the Smackover or Buckner Formations in nearshore 

(northern) areas and on the Bossier Formation in offshore areas. This contact has generally been considered 

disconformable (Swain, 1944, p. 592, 1949, p. 1228; Forgotson, 1954, p. 2478, 2492) but, according to K. A. 

Dickinson (1968, p. E23), is probably conformable except in areas where the Buckner is thin or absent. The 

Schuler Formation is reported to be overlain disconformably by Lower Cretaceous beds in nearshore (updip) 

areas (Swain 1944, p. 609; Forgotson, 1954, p. 2490; Imlay, 1943a, p. 1467-1471).

Elsewhere in the southern United States, the Jurassic is represented in south Texas by both the Cotton 

Valley Group and the Smackover Formation (Halbouty, 

1966, p. 10, 14, 15, 21) and presumably also by the 

Louann Salt, as shown by the presence of salt domes. In 

southern Florida, the Jurassic is possibly represented by 

part of the Fort Pierce Formation, which consists of 

380-^590 feet (116-180 m) of limestone, dolomite, and 

anhydrite, is overlain by beds containing the Aptian ammonite Dufrenoya, and has microfossils of both Late Jurassic and Early Cretaceous age (Applin and Applin, 

1965, p. 18-29; Maher and Applin, 1968, p. 11).

The age of the Louann Salt has been variously interpreted (1) as Permian (Hazzard and others, 1947, p. 

484), mainly on the basis of a disconformable relationship with the overlying Norphlet Formation; (2) as Late 

Triassic to Early Jurassic, on the basis of pollen and 

spores (Jux, 1961); (3) as Jurassic, because the conformably underlying Werner Formation rests unconformably 

on the Eagle Mills Formation, which contains Late Triassic plants (Scott and others, 1961); and (4) as early Late 

Jurassic, because the Louann Salt as well as similar

evaporitic sequences in Mexico directly underlie beds of 

late Oxfordian Age and must have been covered by those 

beds shortly after deposition in order to escape extensive 

erosion (Imlay, 1940b, p. 12; 1943a, p. 1437-1438; 1952a, 

p. 974, 1952b, p. 1750, 1751). All these interpretations 

and the data on which they are based have been analyzed 

by Murray (1961, p. 283-287) and Bishop (1967, p. 248, 

249), who conclude that the evidence favors deposition 

of the Louann Salt during Jurassic time prior to the late 

Oxfordian or prior to the deposition of the Norphlet Formation, which formed a seal over the salt. In addition, 

an age not older than Middle Jurassic for the Louann 

Salt is indicated by studies of palynomorphs obtained 

from cap rock overlying halite on the Challenger Knoll 

near the middle of the Gulf of Mexico (Kirkland and Gerhard, 1971, p. 681).

The Louann Salt and the underlying Werner Formation were assigned an early Oxfordian (Divesian) Age 

by Imlay (1943a, p. 1437, 1438), partly because similar 

evaporitic deposits in Mexico underlie upper Oxfordian 

beds (Imlay, 1943a, p. 1506-1508) and partly because 

conditions were unfavorable for salt deposition in southeastern Mexico before latest Callovian time (Imlay, 1943a, 

p. 1438, 1508-1510; 1953c, p. 31). These reasons have 

since been strongly upheld by Viniegra 0. (1971, p. 480, 

484). The term Divesian, as used by this writer in 1943, 

however, followed Spath (1933, p. 872) and included the 

zones of Quenstedtoceras lamberti and Peltoceras athleta. As these zones are now placed in the upper Callovian (Arkell, 1946, p. 12, 13; 1956, p. 10, Cariou and others, 1971, p. 93), the Louann Salt is herein correlated 

with the upper Callovian and also with the lower to lower 

middle Oxfordian as now defined (Callomon, 1964, p. 

288, 289; Cariou and others, 1971, p. 93, 94.

The Werner Formation, however, could be somewhat older than latest Callovian, provided its origin is 

related to major changes in the Gulf region that coincided 

with major marine invasions of the western interior of 

North America and of southern Mexico from the Pacific 

Ocean. Of these invasions in the western interior region, 

the most restricted took place during late middle to late 

Bajocian time (Imlay, 1967b, p. 54), a fairly extensive 

invasion occurred during latest Bathonian to early Callovian time (Imlay, 1967b, p. 56), and the greatest invasion came during latest Callovian to middle Oxfordian 

time (Imlay, 1957, p. 471). The sea partially withdrew 

during early Bathonian time and during middle to early 

late Callovian time. Comparisons with the ammonite sequence in Mexico (see fig. 21) show that the first two 

marine invasions from the Pacific Ocean took place there 

at the same time as in the western interior region, but 

that the third, if present, is represented by evaporitic 

deposits and red beds below marine beds of late Oxfordian Age, and, locally in east-central Mexico, by sparsely
48 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

fossiliferous marine beds between normal marine beds of 

middle Callovian and late Oxfordian Ages.

Dating the Werner Formation as Early Jurassic or 

as Middle Jurassic older than Callovian is unreasonable 

considering (1) the tectonic events that occurred in eastcentral Mexico during those times, (2) the fact that the 

Bajocian sea in Mexico was apparently restricted to a 

small area near the Pacific Ocean (fig. 6), and (3) that in 

east-central Mexico the Bajocian as well as part of the 

Bathonian are accounted for by continental beds (fig. 7). 

Overall, dating of the Werner Formation as early to middle Callovian is favored because the marine invasion 

across southern Mexico reached the Gulf region in eastcentral Mexico during that time, and this area presumably was one source for saline deposits later in the Callovian and Oxfordian.

The time represented by the disconformity between 

the Louann Salt and the overlying Norphlet Formation 

is probably very short because there appears to have 

been little, if any, erosion of the salt (Andrews, 1960, p. 

220, 225; Bishop, 1967, p. 248, 249). This condition could 

be explained by a sudden deepening of the Gulf region, 

or of the marine inlets from the Atlantic and Pacific 

Oceans, which allowed sea water to invade widely beyond the area of salt deposition. The presence of conglomerate and other clastic sediments at the base of the 

Norphlet Formation could then be explained partly by 

reworking of soil as the sea advanced beyond the salt 

basins and partly by uplift of landmasses bordering the 

Gulf region. Thus, the Coahuila Peninsula in northern 

Mexico at that time contributed a great deal of sandstone 

and gravel, called the La Gloria Formation, which passed 

seaward into the Zuloaga Limestone, which closely resembles the Smackover Formation. Similar uplifts in 

Mississippi and southwest Alabama apparently started 

at the same time (Oxley and others, 1967, p. 47^48).

The ages of the Jurassic formations above the Louann 

Salt are fairly well established. Thus, the middle and upper parts of the Smackover Formation have yielded late 

Oxfordian ammonites (Imlay, 1945, p. 274, pi. 41, figs. 

7-14) that are identical specifically with ammonites in 

the lower member of the Jagua Formation in Cuba, in 

the upper part of the Santiago Formation in eastern 

Mexico, and in the La Gloria Formation at San Pedro del 

Gallo in central Mexico. As the Norphlet Formation 

grades upward into the Smackover Formation, and as it 

is much thinner, it is probably also of late Oxfordian Age, 

or no older than middle Oxfordian.

The Buckner Formation has not yielded fossils of any 

value in determining its age. It was once dated as probably early Kimmeridgian on the basis of stratigraphic position in Arkansas between the Smackover Formation, 

which contains late Oxfordian ammonites, and the Cotton Valley Formation (now called Group), which contains

middle Kimmeridgian fossils. Such an age was supported 

by an apparent southward gradation of the Buckner Formation into the basal part of the Cotton Valley Group, 

which in northern Louisiana contains early Kimmeridgian ammonites (Imlay, 1943a, fig. 8 on p. 1429, p. 1471; 

1945, p. 258-259). Subsequent studies in northeastern 

Texas and southern Arkansas indicate that the lower 

part of the Buckner Formation interfingers basinward 

with the highest part of the Smackover Formation (Swain, 

1949, p. 1207, 1219-1223; K. A. Dickinson, 1968, p. 

Ell) and, therefore, could be partly of latest Oxfordian 

Age in some areas.

The age of the lower part of the Cotton Valley 

Group, as just discussed, is definitely Kimmeridgian, and 

its basal part south of the southern limit of the Buckner 

Formation is earliest Kimmeridgian. The upper part of 

the Cotton Valley Group between east Texas and southwest Alabama has furnished only a few pelecypods (Imlay, 1943a, p. 1472). It is dated as Jurassic mainly on the 

basis of stratigraphic position beneath the Hosston Formation (Lower Cretaceous) (Swain, 1944, p. 609; Oxley 

and others, 1967, p. 38), with which it is disconformable 

in updip areas.

CENTRAL AND NORTHEASTERN MEXICO

Most of the Jurassic formations of central and northeastern Mexico are lithologically and stratigraphically 

closely similar to the Jurassic formations in the southeastern United States. Thus, the Zuloaga and the La 

Gloria Formations in Mexico match the various facies of 

the Smackover Formation and contain the same ammonites (Imlay, 1943a, p. 1484). The Olvido Formation, 

which overlies the Zuloaga Limestone at various places 

in the mountains from Victoria, Tamaulipas, northward 

to eastern Coahuila, is lithologically identical with the 

Buckner Formation and occupies the same stratigraphic 

position (Imlay, 1943a, p. 1495; Carrillo-Bravo, 1963, p. 

16). The overlying La Casita Formation in Mexico occupies the same stratigraphic position as the Schuler Formation of the Cotton Valley Group of the southeastern 

United States. It differs by being gray to black, instead 

of reddish, and commonly is marked by a basal conglomerate in areas where the Olvido Formation is absent. The 

La Caja Formation is the thin offshore equivalent of the 

La Casita Formation and Olvido Formation and the 

stratigraphic equivalent of the Cotton Valley Group plus 

the Buckner Formation. The La Caja Formation in contrast to the dark offshore facies of the Cotton Valley 

Group is much thinner and contains phosphatic beds.

Below the Zuloaga Limestone in the Sabinas basin of 

northeastern Mexico is a thick mass of salt and anhydrite, called the Minas Viejas Formation, that extends 

from eastern Coahuila southeastward into Nuevo Leon
COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 49

and Tamaulipas and northeastward into southernmost 

Texas (Humphrey, 1956, p. 25; Weidie and Wolleben, 

1969; Wall and others, 1961; Murray, 1961, p. 284). This 

evaporitic sequence occupies the same stratigraphic position as the Louann Salt but differs by containing much 

more anhydrite.

Outside the Sabinas Basin at many places, the Zuloaga Limestone and the equivalent La Gloria Formation 

are underlain unconformably by red or varicolored shale, 

sandstone, and conglomerate and locally by some redweathering lava. These deposits, in turn, rest unconformably on rocks of Triassic, Permian, or older age (Imlay, 1943a, p. 1475-1477; 1953c, p. 20-28, fig. 4; Imlay, 

Cepeda, and others, 1948, p. 1753-1758; Perez Fernandez and Diaz Gonzalez, 1964; Mixon and others, 1959; 

Mixon, 1963; Carrillo-Bravo, 1961, p. 34^51). These red 

beds cannot yet be dated closely at any place and can be 

dated definitely as Jurassic at only a few places. One of 

these places is west of Charcas in north-central San Luis 

Potosi, where 160 feet (50 m) of red, pink, and gray conglomerate and sandstone, called the La Joy a Formation, 

lies unconformably between the Zuloaga Limestone and 

Upper Triassic marine beds (Martinez Perez, 1972, p. 

346-347).

Another place where a Jurassic age has been established is in the mountains west of Victoria, Tamaulipas, 

where the red beds are divisible into two formations that 

are separated by an angular unconformity. The lower red 

bed formation, referred to variously as the La Boca Formation (Mixon and others, 1959, p. 762; Mixon, 1963, p. 

28) or as the Huizachal Formation (Carrillo-Bravo, 1961, 

p. 34), attains a thickness of 6,500 feet (2,000 m) or more 

and contains plant fossils that have been identified as 

Late Triassic to Early Jurassic (Mixon, 1963, table 1, p. 

31). The upper red bed formation, called the La Joya 

Formation, attains a thickness of 165-260 feet (50^-80 m) 

and has not been dated by fossils. Carrillo-Bravo (1961, 

p. 34; 1963, p. 14, 15) considered it to be younger than 

Early Jurassic on the basis of its stratigraphic position and probably of Callovian to early Oxfordian age 

on the basis of comparisons with Jurassic sequences in 

east-central and northern Mexico (Carrillo-Bravo, 1961, 

p. 51; 1965, p. 78, 81-S8).

EAST-CENTRAL MEXICO

Studies of the Jurassic sequence exposed in the 

mountainous Huasteca area and penetrated by drilling in 

the Tampico embayment to the east have produced paleontologic, stratigraphic, and structural evidence that 

most of the salt masses in the Gulf region are closely related in age to the overlying Upper Jurassic limestones, 

are probably not older than Callovian, and are definitely 

not older than Middle Jurassic. All evidence indicates

that conditions during the Early Jurassic made the accumulation of thick masses of salt and anhydrite impossible in the western part of the Gulf region. Thus the 

marine Huayacocotla Formation of Sinemurian and questionable early Pliensbachian Age is carbonaceous, contains considerable plant material at both top and bottom, 

and contains some coal at its top. It lies unconformably 

between Upper Triassic and Middle Jurassic red beds; 

was strongly folded, faulted, and slightly metamorphosed before the overlying red beds were deposited; 

and, finally, was intruded by diabase before marine Callovian beds were deposited (Diaz-Lozano, 1916; Burckhardt, 1930, p. 12-20; Imlay, 1943a, p. 1497; Imlay, Cepeda, and others, 1948, p. 1750-1753; Carrillo-Bravo, 

1965, p. 85, 87, 92-95). The diabase may actually be 

older than the Middle Jurassic red beds (Cahuasas Formation), but in the place where the diabase is exposed 

those red beds are missing.

The overlying Cahuasas Formation (Carrillo-Bravo, 

1965, p. 87-38), formerly included in the Huizachal 

Formation (Imlay, Cepeda, and others, 1948, p. 1755- 

1757; Erben, 1956a, p. 31-34, 1956b, p. 9-12), rests 

with angular unconformity on the Huayacocotla Formation. The Cahuasas is overlain disconformably by the 

Santiago Formation or in places by the Taman Formation, is locally absent within its area of distribution, is 

more extensive in the subsurface than the Huayacocotla 

Formation (Lopez Ramos, 1972, compare sections CC to 

FF),and is dated as Bajocian to Bathonianon the basis of 

stratigraphic and structural relationships. The Cahuasas 

Formation must be older than Callovian because in outcrops it lies disconformably below beds of early to middle 

Callovian Age (Erben, 1956b, p. 12; Carrillo Bravo, 1965, 

p. 88; Cantii Chapa, 1971, p. 36), and in the subsurface 

it probably underlies beds of latest Bathonian Age (Cantii 

Chapa, 1969, p. 4, 5). The Cahuasas must be younger 

than Toarcian because in the Pemex-Comales test well 

102, about 75 km south-southeast of Tampico, it passes 

downward into beds containing plant species identical 

with species that in Oaxaca occur in the upper part of 

the Rosario Formation, which part is dated as early Middle Jurassic (Erben, 1957a, p. 45; 1956a, p. 137).

The Jurassic formations overlying the Cahuasas Formation are all marine. On the outcrop, they consist of the 

Santiago Formation (Cantii Chapa, 1969, p. 5, 6; 1971, p. 

21-24, 37) of early or middle Callovian to late Oxfordian 

Age, the Taman Formation of Kimmeridgian to earliest 

Tithonian Age, and the Pimienta Formation, which represents the remainder of the Jurassic. All these formations are present also in the subsurface of the Tampico 

embayment (see lists in Lopez Ramos, 1972, p. 304- 

317), but, in addition, about 45 miles (72 km) northwest 

of Poza Rica, Veracruz, the Santiago Formation is underlain by the marine Palo Blanco Formation (Cantii
50 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

Chapa, 1969, p. 5), which is above ced beds. The age of 

the Palo Blanco Formation is early Callovian, on the basis of the presence of Kepplerites in three test wells. It is 

possibly also late Bathonian, on the basis of small ammonites resembling Wagnericeras that were found about 

79 feet (24 m) below Kepplerites in the Palo Blanco test 

well 112 and about 750 feet (230 m) above the bottom of 

the well, which did not penetrate into red beds. In another nearby well (Pemex-Coyote 3), Kepplerites was obtained about 950 feet (290 m) above red beds. Evidently 

an appreciable thickness of marine beds that could be of 

Bathonian Age is present below the occurrences of Kepplerites.

The age limits of the Santiago Formation are well 

established (Cantii Chapa, 1969, p. 6; 1971, p. 22-24). A 

late Oxfordian Age for the upper part of the formation 

has been demonstrated at many places by the presence 

of ammonites identical with species in the Jagua Formation of Cuba, in the Smackover Formation of the southeastern United States, and in the Zuloaga and La Gloria 

Formations of central and northeastern Mexico. A late 

early Callovian Age for the basal part of the formation is 

shown by the presence of Neuqueniceras in a local facies 

called the Tepexic Limestone (Cantii Chapa, 1969, p. 4; 

1971, p. 18, 24, 36). Above this limestone in the lower 

part of the Santiago Formation, the middle Callovian is 

probably represented by Reineckeia at two localities 

(Cantii Chapa, 1971, p. 24) and by Erymnoceras at one 

locality (Erben, 1956b, p. 40; 1957a, p. 47).

The Tepexic Limestone is dated as late early Callovian because it contains both Neuqueniceras and Reineckeia. In Europe, Neuqueniceras ranges through at least 

the middle part of the lower Callovian and is associated 

at the top of its range with the lowest occurrences of Reineckeia and R. (Reineckeites) (Zeiss, 1956, p. 83; Bourquin, 1968, p. 23, 155-157), both of which range higher 

into the lower part of the upper Callovian. In Japan, 

Neuqueniceras occurs below Kepplerites (Sato, 1962, p. 

18, 19, ,50, 56, 75-79), which does not range above the 

lower Callovian. In Argentina, Neugueniceras occurs 

above Macrocephalites of earliest Callovian Age and below Reineckeia, and is correlated with the Sigaloceras 

calloviense zone of Europe (Hillebrandt, 1970, p. 171, 

191), In Oaxaea and Guerrero, Mexico, Neuqueniceras is 

associated with Reineckeia, but its stratigraphic and age 

relations have not yet been established with respect to 

such taxa as R. (Reineckeites), R. (Kellawaysites), Xenocephalites, Choffatia, Subgrossouvia, Eurycephalites, 

and possibly Macrocephalites or Lilloettia (CantiiChapa, 

1971, p. 19). The evidence to date shows that Neuqueniceras occurs definitely in beds of early Callovian Age and 

has not yet been found in younger beds.

In contrast to this age evidence for the upper and 

lower limits of the Santiago Formation, the middle part

of the formation has yielded no ammonites of late Callovian Age and none that are definitely of early Oxfordian 

Age. The early Oxfordian may be represented, however, 

by one deformed ammonite that Cantu Chapa (1971, p. 

23) assigned to the subgenus Ochetoceras (Fehlmannites) and by other ammonites that Erben (1957a, p. 47) 

assigned to Creniceras renggeri (Oppel) and to Peltoceras (Parapeltoceras) annulare (Reinecke).

Any age determination based on these ammonites 

must await adequate descriptions and illustrations and 

probably the discovery of other ammonite genera. At 

present, the total age range of Fehlmannites is unknown 

because the genus is recorded from only one locality in 

Switzerland (Jeannet, 1951, p. 2, 89). The generic status 

and exact stratigraphic position of Parapeltoceras is unknown, according to Arkell and others (1957, p. L336). 

The genus Creniceras in Europe is most common in the 

lower and middle Oxfordian but ranges from the uppermost Callovian into the Kimmeridgian (from the upper 

part of the Quensjkedtoceras lamberti zone into the Aulacostephanus eudoxus zone). Among the species present, Creniceras renggeri (Oppel) ranges from the top of 

the Quenstedtoceras lamberti zone to the Cardioceras 

cordatum zone (Arkell, 1939, p. 151; 1956, p. 43, 47, 59, 

74), Creniceras crenatum (Bruguiere) ranges from the 

Cardioceras cordatum zone to the Gregoryceras transversarium zone (Jeannet, 1951, p. 101; Ziegler, 1956, p. 

572), and Creniceras dentatum (Reinecke) occurs entirely in the Kimmeridgian (Ziegler, 1956, p. 567; Enay 

and others, 1971).

The scarcity or absence of fossils of late Callovian to 

middle Oxfordian Age in outcrops of the Santiago Formation was ascribed by Cantii Chapa (1971, p. 22, 37) to 

small exposures, incomplete sequences (except at Huehuetla in Hidalgo), poorly fossiliferous beds, and the local 

absence of beds of that age. He notes, however, that no 

fossils of that age have yet been found in the subsurface—a fact that he cannot explain biogeographically 

(Cantii Chapa, 1971, p. 37). Their absence or scarcity 

during late Callovian to early middle Oxfordian time 

could be explained readily, however, if the major evaporitic sequences in the Gulf region were deposited during 

that time. This seems reasonable, considering the position of both the Louann Salt and the Minas Viejas Formation directly below beds of late middle Oxfordian Age, 

the position of the Salina Formation in the Isthmus of 

Tehuantepec a little below beds of Kimmeridgian Age 

(Burckhardt, 1930, p. 97; Imlay, 1953a, p. 28-30; Contreras and Castilldn, 1968, p. 244), and the lack of evidence that these evaporitic sequences underwent any appreciable erosion at all before the overlying beds were 

deposited (Andrews, 1960, p. 220, 225; Bishop, 1967, p. 

248, 249). Dating the major salt masses in the Gulf region as late Callovian to early middle Oxfordian does not
COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 51

bar the deposition of some salt at other times during the 

Jurassic or Cretaceous, as has been demonstrated (Imlay, 1943a, p. 1529; K. A. Dickinson, 1968, p. E13-E15; 

Viniegra 0., 1971, p. 478, 482-485).

If this explanation is correct, then the poorly fossiliferous beds in the middle part of the Santiago Formation 

could have been deposited during late Callovian to middle Oxfordian time in waters that were more saline than 

normal sea water, that entered east-central Mexico from 

the Pacific Ocean, and that were a source for at least part 

of the thick masses of salt and anhydrite deposited in 

places around the Gulf of Mexico. That the marine waters 

came from the southwest or west is indicated by eastward thinning and wedging out of Middle and Upper Jurassic marine sedimentary rocks in the Tampico embayment, according to Viniegra 0. (1971, p. 482, 483). Similarly, Cantii Chapa (1973) stated, "In the northwestern 

Poza Rica area the Middle Jurassic transgression began 

during the Bathonian. Later it advanced to the central, 

east and west parts, and the covered area is characterized by distinct transgressive lithofacies."

The marine invasion from the Pacific Ocean during 

salt and anhydrite deposition, as discussed by Viniegra 

0. (1971, p. 482, 484, 486, fig. 10 on p. 492), could have 

been from the south across the present Isthmus of Tehuantepec, or from the west or southwest across the 

present States of Puebla, Oaxaca, and Guerrero, or by 

both routes. The distribution of Jurassic rocks in southern Mexico (Viniegra 0., 1971, p. 481, 483; Sanchez Mejorada and Lopez Ramos, 1968) shows that both marine 

connections probably existed during Kimmeridgian to 

Tithonian time but that a connection from the southwest 

across Guerrero was most likely during Callovian and 

Oxfordian time. The presence of either or both of these 

marine routes does not bar another marine connection 

from the Atlantic Ocean while the Louann Salt was accumulating.

In summation, all available faunal and stratigraphic 

evidence shows that the upper Bathonian to middle Callovian marine beds in east-central Mexico were deposited 

in a sea that transgressed northward or northeastward 

from the Pacific Ocean. This sea did not reach the Gulf of 

Mexico region until early or (more probably) middle Callovian time. Apparently, it then became a source of salt 

and anhydrite deposited during late Callovian to early 

middle Oxfordian time in southeastern and northeastern 

Mexico and in the southeastern United States. Deposition of these thick evaporitic deposits during that time is 

favored by their stratigraphic position, by the lack of appreciable, if any, erosion of their upper surfaces, and by 

the lack or scarcity of marine fossils of that time in eastcentral Mexico within a sequence that appears to be 

stratigraphically continuous from early Callovian to late 

Oxfordian.

SOUTHEASTERN MEXICO

In the Chiapas salt basin the Jurassic is represented 

by a thick mass of salt and associated red to black shale 

overlain by a thin unit of red beds, which is overlain in 

turn by several hundred feet of limestone, marl, and 

black shale of early Kimmeridgian to early Neocomian 

Age (Burckhardt, 1930, p. 97, 98; Imlay, 1943a, p. 1506- 

1508; Viniegra 0., 1971, p. 482, 484). Outside the salt 

basin, the late Jurassic is apparently represented mainly 

by red beds that underlie beds of Early Cretaceous age. 

On the Chiapas massif, south of the salt basin, some 

early Kimmeridgian ammonites are reported to be within 

red beds that underlie Lower Cretaceous beds (Viniegra 

0., 1971, p. 479,480,483).

EASTERN CHIHUAHUA AND WEST TEXAS

Upper Jurassic beds exposed in eastern Chihuahua 

near Placer de Guadalupe and Plomosas (Bridges, 1965, 

p. 66-76, 118-120, 132-134) contain ammonites of the 

same age as those in the Malone Formation in west 

Texas (Imlay, 1952a, p. 973; Albritton, 1938, p. 1758- 

1761; Cragin, 1905). The beds in Chihuahua differ by consisting mostly of dark calcareous shale and by being 

much thicker. Also, the sequence in eastern Chihuahua 

is overlain by 630 feet (192 m) of limestone and marl that 

could be uppermost Jurassic, whereas the Jurassic sequence in west Texas contains Kossmatia near its top 

and is overlain by a conglomerate at the base of the Cretaceous^) Torcer Formation. Upper Oxfordian beds have 

not been found in either area, in contrast to their presence throughout most of central, eastern, and southern 

Mexico.

PACIFIC COAST REGION

WESTERN MEXICO

Jurassic beds have been identified near the Pacific 

coast of Mexico in northwestern Oaxaca, Guerrero, Michoacan, western Sonora, and Baja California^ Most occurrences have not been described in detail and some 

shown on the Geologic Map of Mexico (Sanchez Mejorada 

and Lopez Ramos, 1968) have not been described at all. 

That map does not show the presence of Jurassic rocks in 

Baja California, although Buchia piochii (Gabb), of latest 

Tithonian Age, is reported to occur at La Punta de San 

Hipolito, northwest of Bahia Ballenas (Lopez Ramos, 

1974, p. 392; Minch, 1969, p. 42).

Furthermore, the Jurassic rather than the Triassic 

may be represented by specimens of the pelecypod Otapiria from Arroyo de San Jose, which is south of Punta 

Canoas in the central part of Baja California (Lopez Ramos, 1974, p. 375). Such an age is suggested by the close
52 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

resemblance of these specimens to 0. tailleuri Imlay 

(Imlay, 1967a, p. B3-B6), which is associated with the 

Early Jurassic (Sinemurian) ammonites in northern 

Alaska (Imlay and Detterman, 1973, p. 16, 17).

In northwestern Oaxaca and northeastern Guerrero, 

the Jurassic sequence consists mostly of Toarcian to Oxfordian beds that range from 2,300 to 2,950 feet (700 to 

900 m) in thickness (Burckhardt, 1927, 1930, p. 24-35, 

98-100; Guzman Jimenez, 1950; Salas, 1949; Erben, 

1956a, p. 107-124; 1956b, p. 18-34, 51-121; 1957a, p. 

48-51). Marine Lower Jurassic beds are not present except possibly at one place in Guerrero (Erben, 1954, p. 

4-12). Coal-bearing and nonmarine clastic beds are dated 

by plant taxa and stratigraphic positions as Toarcian to 

early middle Bajocian and middle Bathonian. Marine 

limestone, shale, and sandstone between the nonmarine 

units are dated by ammonite genera as late middle Bajocian to early Bathonian. Above the highest coal-bearing beds are marine limestone and marl dated by ammonite genera as late Bathonian to late Callovian. 

Gradationally above are other limestone and marl beds, 

which have not furnished ammonites but which are dated 

as Oxfordian because they contain species of pelecypods, 

gastropods, and echinoderms similar to and in part identical with species in the Zuloaga Limestone of northern 

Mexico. Younger Jurassic beds are represented definitely only by single occurrences of the ammonites Idoceras and Substeueroceras in western Oaxaca (Erben, 

1957a, p. 51). These Jurassic sequences could represent 

an embayment directly from the south (Guerrero embayment), as suggested by Erben (1957b, p. 36-41), or from 

the southwest (Balsas Portal), as suggested by Lopez 

Ramos (1974, p. 385-391, 395-397), or from both directions.

In western Sonora, only parts of the Lower and Upper Jurassic have been identified faunally. Pelecypods of 

Sinemurian and possibly Hettangian Age have been obtained at several places from shale, shaly sandstone, and 

shaly limestone at least 2,500 feet (762 m) thick in the 

upper part of the Barranca Formation (Burckhardt, 1930, 

p. 23, 24, 41, 42; Jaworski, 1929; King, 1939, p. 1655- 

1659, pi. 5; Wilson and Rocha, 1949, p. 23-29). An early 

Sinemurian Age is confirmed by the presence of the ammonite Amioceras near El Antimonio, about 30 miles 

(48 km) west of Caborca (Imlay, 1952a, p. 973), and Arietites in the Sierra de Santa Rosa, about 30 miles (48 

km) west of Puerto (Burckhardt, 1930, p. 23). A late Sinemurian Age is indicated by the presence of Crucilobiceras in association with probable Aegasteroceras about 

25 miles (40 km) south-southeast of Caborca (identified 

by Imlay, 1975, for L. T. Silver, California Inst. Technology). A late Oxfordian Age is shown by the presence 

of Dichotomosphinctes and Discophinctes in the Cucurpe

area about 30 miles (50 km) southeast of Magdalena 

(identified by Imlay, 1975, for Claude Rangin, University of Sonora). The Kimmeridgian ammonites Amoeboceras and Idoceras have been found a little south of Caborca throughout nearly 600 feet (183 m) of calcareous, 

gray to brown shale that is interbedded with some gray 

sandy shale and sandstone (T. E. Stump, Univ. California at Davis, written commun., April 1973). The ammonite-bearing beds are 2,000-2,565 feet (610-782 m) above 

the base of a sequence that is more than 5,000 feet (1,524 

m) thick and that has otherwise not been dated. Presumably much more than Kimmeridgian time is involved.

WESTERN NEVADA TO CENTRAL CALIFORNIA

Jurassic marine rocks older than Tithonian that are 

now exposed in California and western Nevada have the 

following characteristics: (1) they generally contain a 

great deal of volcanic material; (2) they generally change 

lithologically within fairly short distances; (3) they attain 

tremendous thicknesses; (4) their major sites of deposition gradually shifted westward; and (5) they have not 

yielded any fossils of Bathonian Age.

These Jurassic rocks, according to W. R. Dickinson 

(1962, p. 1243-1247, 1253), were deposited in a eugeosyncline whose eastern margin extended northeastward 

through central Nevada, then northward through western Idaho and eastern Washington, and then northwestward in Canada. Within this eugeosyncline were deposited enormous quantities of andesitic material derived 

from numerous volcanoes and now preserved as marine 

lava flows, tuffs, breccia agglomerates, and as an important constituent of marine clastic sediments. Within this 

eugeosyncline were also deposited some sediments derived from pre-Jurassic volcanic or sedimentary rocks 

exposed as islands (W. R. Dickinson, 1962, fig. 1 on p. 

1243; Dickinson and Vigrass, 1964, p. 1042-1043). As 

most of these sediments were derived locally from volcanic vents, rather than from landmasses east of the eugeosyncline, their lithic characteristics and thicknesses 

change markedly within short distances. Evidently, volcanoes were most common in easternmost California 

along or near the site of the Sierra Nevada but also occurred in adjoining northwestern Nevada and in northcentral California (Stanley, 1971, p. 474, 475; Stanley and 

others, 1971, fig. 2 on p. 12).

The Lower Jurassic beds in this area extend westward across western Nevada into eastern California 

slightly beyond the crest of the Sierra Nevada, extend 

northwestward into the Big Bend area of north-central 

California, and attain their greatest thickness in Nevada. 

Bajocian beds are similarly distributed but occur also in 

the Santa Ana Mountains southeast of Los Angeles and
COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 53

attain their greatest thickness in the Sierra Nevada. 

Bathonian rocks have not been identified faunally in Nevada or California but, if present, are most likely to be 

found at high altitudes in the Sierra Nevada. Callovian 

rocks are known mainly from the western and higher 

parts of the Sierra Nevada, where they attain apparent 

thicknesses of 6,000-8,000 feet (1,830-2,440 m). Lowermost Callovian rocks are also found in the Santa Ana 

Mountains as part of a very thick sequence. Oxfordian 

rocks are known from the western part of the Sierra Nevada, from the Santa Monica Mountains just north of Los 

Angeles, and from the western part of the Klamath 

Mountains in northwest California. Tithonian rocks, although possibly present in the Sierra Nevada (Crickmay, 

1933b, p. 903), have been identified faunally in California 

only in the western part of the State from San Diego 

northward.

Most of the Jurassic sedimentary rocks of western 

Nevada are assigned to the Sunrise and Dunlap Formations of Early Jurassic age (Muller and Ferguson, 1939, 

p. 1611-1613; Silberling, 1959, p. 29-31; Silberling and 

Roberts, 1962, p. 9, 21, 29, 32; Silberling and Wallace, 

1969, p. 47). Of these, the Sunrise Formation ranges in 

thickness from 1,200 to 2,400 feet (366 to 732 m); consists 

mostly of interbedded gray massive limestone, laminated 

dolomitic limestone, shale, and siltstone; includes tuff 

beds and some brown sandstone beds whose particles are 

of volcanic origin; and ranges in age at most places from 

earliest Hettangian to early or late Pliensbachian (Muller 

and Ferguson, 1939, p. 1610, 1611; Stanley, 1971, p. 

458). Near Westgate, Nev., the Sunrise Formation also 

includes beds of Toarcian Age (Hallam, 1965, p. 1487, 

1488).

The Dunlap Formation ranges in thickness from a 

featheredge to about 5,000 feet (1,520 m) and consists 

mainly of dark-red to reddish-brown crossbedded sandstone interbedded with some breccia, conglomerate, 

mudstone, and volcanic rock. The formation is overlain 

locally by volcanic rocks, generally intertongues basally 

with the Sunrise Formation, but in place rests unconformably on Triassic or older rocks. Its age is late Pliensbachian to Toarcian on the basis of the presence of the 

ammonite Harpoceras (Muller and Ferguson, 1939, p. 

1621), stratigraphic position above the Sunrise Formation, and the presence of the pelecypod Plicatostylus, 

which in eastern Oregon occurs directly below beds of 

late Pliensbachian Age (Imlay, 1968, p. C6).

The Jurassic is also represented at one place in western Nevada by the Westgate Formation of Corvalan 

(1962; Hallam, 1965, p. 1487, 1488). This formation is 

560 feet (171 m) thick, rests conformably on 1,200 feet 

(366 m) of the Sunrise Formation, consists of limestone 

and calcareous quartzose sandstone, and contains ammonite fragments suggestive of Sonninia dominans 

Buckman (Corvalari's loc. A-ll) of early middle Bajocian Age.

The Jurassic sedimentary rocks of western Nevada, 

as interpreted by Stanley (1971, p. 467-475; Stanley and 

others, 1971, p. 15-18), were not deposited in a eugeosyncline but in a miogeosyncline that extended to, or 

nearly to, the western boundary of the State, shown by 

the presence of (1) normal shallow-water marine carbonate rocks in both the Sunrise and Dunlap Formations; 

(2) quartz sandstone in the Dunlap and Westgate Formations that is nearly identical with that in the Navajo 

and Aztec Sandstones farther east; and (3) interbedded 

red mudstone and red laminated siltstone in the Dunlap 

Formation, which are suggestive of tidal-flat deposits. 

These rocks are interbedded, however, with some eruptive volcanic rocks and with locally derived clastic sediments, which are not typical of the miogeosyncline. 

Thick volcanic deposits characteristic of the eugeosyncline are found in Nevada, according to Stanley (1971, p. 

455, 474), only in Douglas County east of Lake Tahoe.

Most Jurassic sequences of California east of the 

Coast Ranges and of the western part of the Klamath 

Mountains are characterized by much volcanic material 

and generally by facies changes within short distances. 

Such sequences occur in the Big Bend area of the eastern 

Klamath Mountains in north-central California (Diller, 

1895, p. 4; 1906, p. 5; Sanborn, 1960, p. 11-15; Irwin, 

1966, p. 23), in the Santa Ana Mountains about 50 miles 

southeast of Los Angeles (Silberling and others, 1961; 

Imlay, 1963; 1964c), and at many places in the Sierra 

Nevada (Diller, 1892; Bateman and others, 1963; Bateman and Wahrhaftig, 1966, p. 113-115; Crickmay, 1933b; 

McMath, 1966, p. 181, 182; Clark and others, 1962, p. 

B19; Clark, 1964, p. 15-41, Lindgren, 1900; Lindgren 

and Turner, 1894; Turner, 1894; Turner and Ransome, 

1897; Taliaferro, 1942; Eric and others, 1955; Rinehart 

and others, 1959). An exception consists of the nonvolcanic Boyden Cave pendant near the junction of the 

South and Middle Forks of Kings River in the southcentral Sierra Nevada, a little west of roof pendants consisting of metavolcanic rocks (Jones and Moore, 1973).

Jurassic sequences in the Sierra Nevada occur in 

three parallel northward-trending belts that occupy a 

synclinorium (Bateman and Wahrhaftig, 1966, 113-115). 

One belt in the eastern part of the Sierra extends for 

more than 150 miles (240 km) as roof pendants. These 

consist of metamorphosed volcanic rocks and graywacke, 

many thousands of feet thick, which have furnished a few 

poorly preserved Early Jurassic ammonites. Another 

Jurassic belt, just west of the crest of the Sierra, extends 

northward for nearly 90 miles (145 km) from lat. 39° N. 

near Colfax to the Taylorsville area; it is dated by means
54 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

Western Nevada

Taylorsville area in 

northern Sierra Nevada, 

Calif.

Gold-belt area in 

western part of 

Sierra Nevada, 

eastern California

Big Bend area 

of Pit River in 

north-central 

California

Tertiary

Westgate Formation3 

(Rests only on 

Sunrise Formation) 

560 ft (170m)

Dunlap Formation 

0-5000 ft. (1524m) 

Red, crossbedded 

sandstone and 

conglomerate 

overlain locally 

by volcanic ^ 

breccia and ^^ 

tuff ^

Tertiary Upper Cretaceous

foariposaForrn st ion 

4000 ft (1220 m)

ray to black slate.

ome siltstone. 

graywacke.

Eocgne\Cretaceous

Trail Formation 2000-4000 ft (610- 

J220 m). Conglomerate, sandstone/

Luckey S Argillite1 600-1500 ft 

v(T82~457m) Black slate.gray acke>

Cooks Canyon Agglomerate1 1900 ft 

^ Breccia, tuff, sandstone (580 m)

Logtown Ridge 

Formation 

6200 ft (1890m) 

Tuffs, conglomerates, 

lavas and breccias in 

upper 4300 ft. 

Interbedded slaty 

rocks and tuffs in 

lower 1900 ft

. Foreman Formation 350 ft (107 m) 

^ Shale and sandstone_____. /

North Ridge Agglomerate1 200 ft 

\(63 m) Breccia and tuff

Hinchman Sandstone 160 ft (49 I 

Breccia and sandstone_____

Hull Meta-andesite 700 ft (213 m) 

Andesite breccia and tuff _____

Dacite tuff-breccia 600 ft (183 m)

Fault contact with 

a brecciated mass 

containing blocks of 

Permian and possibly 

of Mesozoic age 

older than latest 

Jurassic

'Moonshine Conglomerate 300 ft 

(91 m) Agglomerate and red shale

Mormon Sandstone 950 ft (290 m) 

Volcanic clastic rocks, black shale

Potem Formation 

1000-2000 ft 

(305-610 m) 

Argillite and 

tuffaceous sandstone. 

Some clastic 

limestone and 

conglomerate

Sunrise 

Formation 

(1200-2400 ft) 

(366-732 m) 

Interbedded 

shale and 

limestone 

and some 

sandstone

Thompson Limestone 400 ft(122 m 

Red tuff, lava, breccia, 

some limestone lenses

Fant Andesite 800 ft (244 m) 

Andesite flows and red tuff

Hardgrave Sandstone400 ft(122m) 

Red volcaniclastic sandstone

Bagley Andesite \ 

700 ft (213m) \ 

Lava, tuff, breccia,/ 

agglomerate / 7

Lilac Argillite1 725 ft (221 m) 

Gray sandstone and mudstone. 

Dacite flows and tuff ,

Fault contact with 

volcanic rocks of 

uncertain age

Arvison Formation 

of Sanborn (1960) 

6000 ft (1830 m) 

Agglomerate, tuff, 

volcanic breccia,and 

tuffaceous sandstone

Permian Triassic Triassic Permian!?) Upper Triassic

'Lucky S Argllfte, Cooks Canyon Agglomerste, North Ridge Agglomerate, Moonshine Conglomerate,

and Llac Argllite of Crickmay (1933b) herein adopted for U.S. Geological Survey usage, 

lonesome Formation and Trowbridge Shale of Lupher (1941) herein adopted for U.S. Geological - Survey usage. 

Westgate Formation of Corval^n(1962) herein adopted for U.S. Geological Survey usage.

A. Western Nevada and eastern California
COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 55

Western California Northwestern 

California

Southwestern 

Oregon

Southwestern Oregon

West Central East

East-central Oregon

Suplee area (west) Izee-Seneca area (east)

Characteristic fossils

Lower Cretaceous Lower Cretaceous Lower Cretaceous Cenomanian Cenomanian

Franciscan 

assemblage 

'in part)

noxville 

Formation 

2000-13,000

Thrust fault contact 

of Franciscan rocks 

with Knoxville 

Formation and 

underlying volcanic 

rocks or locally with 

possible Paleozoic 

rocks

Uplift, folding, 

faulting, granitic 

intrusions, 

metamorphism, 

and erosion

Gal ice Formation 10,000- 

15,000ft (3050-4570 m) 

Dark gray to black slaty 

to phyllitic shale. Some 

chert,sandstone, conglomerate. Many andesite flows and agglomerates. In California,Galice 

includes 

m eta volcanic 

rocks equivalent to those 

of Rogue 

Formation

Otter 

Point

Formation 

(in part) 

11,000ft 

(3353 m)

Dot nan 

Formation 

(in part) 

18,000ft 

(5040m)

Riddle 

Formation 

(in part)

Volcanic 

rocks, 

greenstone/ 

and 

gabbro

Thrust fault contacts. 

Dothan Formation is 

thrust under Riddle 

and Rogue Formations. 

Otter Point Formation is 

thrust under Colebrook 

Schist, the probable 

metamorphosed equivalent 

of the Galice and Rogue 

Formations

Rogue 

Formation 10,000- 

15,000ft 

(3056-4570 

m) Lava 

flows, agglomerates. 

Breccias, 

and tuff

Thrust fault contacts 

with Dothan Formation, Franciscan 

assemblage, or 

Triassic rocks

Substeuwocwas, \ Buchia aff. 

B. okensis

Kossmatia

Buchia piochii and 

Buchia fischeriana

Buchia rugosa

Amoeboceras (Amoebites) 

and Idoceras

Discosphinctes and 

Dichotomosphinctes

Buchia 

concentrica

Cardioceras (Scarburgiceras\ 

martini (western Idaho on|yf

/Lonesome Formation* \ 

10,000 ft (3050m) 

Volcanic sandstone 

and black mudstone

Peltoceras (Metapeltocerast) 

(eastern California only)

Lilloettia stantoni.Xanocepha/ites 

vicarius and Pseudocadoceras grewingki

Trowbridga Shale2 3000 ft (91

Basev Member 

500-2500ft (152 

Volcanidastic rocks

nber \. .KM'ddlaX : 52-762 m) \ member\ 

ic rocks 1000ft \

Warm Springs Member 

100-300 ft (30-90 ml

SllviesN 

Member 

1500ft

, ——— Lower member 

ii 500-750 - ft ( 1 52-- 50r250 ft(15-76mN 228 m) Dark limy 

SiHyto sandy lime-S^ siltstone, clay- 

^ jtone > stone.and

mudstone. Some 

limestone beds. 

differs from middle 

member by lacking 

volcanic sandstone

V— X. 

W^

Lilloettia buckmani, Keppleritas, 

Xcnocephalrtes,_________

Macrocephalites (southern California)

Cobbanrtes and 

Parareineckeia

Spiroceras, Leptosphinctes

Teloceras, Chondroceras. Normannites

Dorsetensia oregonensis

Papilliceras stantoni, Parabigotites

Euhoploceras, Docidoceras

Praestrigites, Eudmetoceras Tmetoceras 

scissum

Catulloceras, Grammoceras, 

and Pseudoliocaras

Haugia, Po/yp/ectus, Catacoeloceras

Hyde Formation 700-1500 ft 

(213-457 m)Massive andesitic 

marine tuff and volcanic 

graywacke

Dactylioceras cf. D. commune

Nodicoeloceras

r^y~^s~-' Nicely Formation 75-300 ft 

(23-91 m) Dark limy claystone and siltstorne

Suplee Formation 30r150 ft (9-45 m) 

Gray limestone and limy sandstone

S,

Arieticeras, Reynesoceras, 

Paltarpites, Prodactylioceras, 

and Lepta/eoceras

Robertson Formation 

0-335 ft (1

Keller

Creek

Shale

5000ft

(1524m)

Siltstone,

shale.and

tuffaceous

graywacke

______UptpniaT._______ 

Eoderocerasarid Crucilobiceras

Oxynoticeras

Arnioceras, Arietkes, 

Coroniceras.and Megarietites

Murderers 

Creek 

Graywacke 

3000ft

Schlotheimia and A/satites

Waehnerocaras and Psiloceras

Paleozoic ^Triassic Upper Triassic

B. Western California to east-central Oregon.

FIGURE 22.—CORRELATIONS AND COMPARISONS OF JURASSIC ROCKS IN THE PACIFIC COAST REGION IN CALIFORNIA, 

NEVADA, AND WESTERN TO EAST-CENTRAL OREGON. Vertical lines indicate that strata are missing; diagonal lines indicate 

lack of fossil data; wavy lines indicate unconformity or disconfirmity; jagged lines indicate gradational or indefinite contact. Column 

numbers refer to locations shown on figure 18.
56 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

Stage

Eastern Oregon in 10 

Huntington-BroganIronside area, and 

western Idaho 

near Mineral

11

Wallowa Mountains 

near Enterprise, 

northeastern 

Oregon

12 Snake River Canyon 13

Pfttsburg Landing, 

32 miles south 

of northeast corner 

of Oregon

Northeast corner 

of Oregon

Northwestern i A 

Washington in 

northern and 

western parts of 

Cascade Mountains

Characteristic foasils

Overlying beds Miocene Miocene

Tithonian

Kimmeridgian

Oxfordian

Callovian

Bathonian

Bajocian

Toarcian

Pliensbachian

Sinemurian

Hettangian

Black phyllrtic shale 

and slate

Probably 

absent

Unnamed beds 

3000-5000 ft 

(1220-1524 m) 

Mostly graywacke, 

tuffaceous sandstone, 

and siltstone. 

Some limestone, 

conglomerate.and 

lava flows

Miocene Miocene Lower Cretaceous

Fault contact 

at top with 

Triassic 

intrusives

I 7.LI

Nooksack 

Formation 2 

(Lower part) 

4000 ft (t220 m) 

Mostly dark 

siltstone

Buchia piochii

Buchia mosquensis 

and Buchia rugosa

Buchia concentrica

Form st ion' 

2000 ft (610m) 

Black mudstone. 

Some graywacke 

id conglj

Cardioceras (Scarburg/ceras) martini

Black shale and brown graywacke

Hurwal Formation 

(upper part) 

2000 ft (61 Om) 

Very hard, dark 

gray to black 

claystpne 

and siltstone

Underlying beds

Red, purple, and 

green conglomerate 

at base.

Upper Triassic Upper Triassic Upper Triassic

Wells Creek 

Volcanics 

of M isch 

(1966) 3500 ft. 

(1067 m) Some 

interbedded 

marine 

slate and 

graywacke.

Li/loettia buckmani, Kepplerites, 

and Xenocephalites vicar/us___

Spiroceras, Leptosphinctes, Normannkes

Witchelliat Parabigotkesl

Fontannesia, Eudmetoceras, D.ocidocerasl, 

and Asthenoceras delicatum________

Tmetoceras, Eudmetoceras, 

Erycitoides.and Grypheea culebra

Protogrammoceras, Fucinicsras, 

Arieticeras, and Prodactylioceres

Crucilobiceras and Wey/a

Arnioceras and Megarietites7

Upper Triassic

'Coon Hollow Formation of Morrison (1964) herein adopted for U.S. Geological Survey usage. 

Nooksack Formation of McKee and others (1956) herein adopted for U.S. Geological Survey usage.

FIGURE 23.—Correlations and comparisons of Jurassic rocks in the Pacific Coast region from eastern Oregon and western Idaho to 

northwestern Washington. Vertical lines indicate that strata are missing; diagonal lines indicate lack of fossil data; wavy lines indicate 

unconformity or disconformity. Column numbers refer to locations shown on figure 18.
COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 57

of ammonites as Sinemurian to Callovian. The third Jurassic belt extends along the western side of the Sierra 

Nevada for about 190 miles (306 km) from western Madera County northward to Butte County and contains ammonites of Callovian to early Kimmeridian Age.

Within these belts, the most complete Jurassic sequence is exposed in the middle belt in the upper parts of 

canyons on the west side and at the north end of the 

Sierra Nevada. The best section on the west side is exposed on the North Fork of the American River about 25 

to 30 miles (40-48 km) east-northeast of Coif ax, where 

it is called the Sailer Canyon Formation; it is at least 

11,000 feet (3,350 m) thick and is possibly 20,000 feet 

(6,100 m) thick. The lower 10,000 feet (3,000 m) of this 

sequence, according to Clark and others (1962, p. B18- 

B19), consists of graywacke, tuff, and dark-gray siltstone. Of this, the lower 500 to 700 feet (150-210 m) 

consists of tuff that rests unconformably on limestone of 

probable Late Triassic age. The Jurassic sequence, according to Taliaferro (1942, p. 100), consists of 12,800 

feet (3,900 m) of conglomerate, sandstone, slaty shale, 

and andesitic tuff that is overlain by 9,500 feet (2,900 m) 

of volcanic rocks, lava flows, agglomerates, and tuffs. He 

reports Early Jurassic fossils 2,500 feet (760 m) above 

the base and Middle Jurassic fossils 9,500 feet (2,900 m) 

above the base. Fossils collected by geologists of the 

U.S. Geological Survey include Crucilobiceras of late Sinemurian Age, about 800-1,000 feet (240-300 m) above 

the base of the Sailor Canyon Formation (Clark and others, 1962, p. B19); Arieticeras and Reynesoceras of late 

Pliensbachian Age, about 2,000 feet (610 m) above the 

base (Imlay, 1968, p. C16, C17); and Tmetoceras of early 

Bajocian Age, about 8,500-11,000 feet (2,590-^3,350 m) 

above the base (Imlay, 1973, p. 35).

The best known Jurassic sequence in the middle belt 

is exposed near Taylorsville at the northern end of the 

Sierra Nevada. The sequence was originally described 

by Diller (1892; 1908, p. 34-60) and dated by Hyatt 

(1892, p. 400-412). It was later revised by Crickmay 

(1933b, p. 896-903), who proposed a number of new formation names. Still later, it was studied by McMath 

(1966, p. 181-183), who confirmed most of the stratigraphic succession and most of the formational names advocated by Crickmay. McMath was not able, however, to 

find the "Combe Formation," which was reported by 

Crickmay (1933b, p. 903) to contain Aulacosphinctoides 

of early Tithonian Age. The sequence as modified by 

McMath is shown in figure 22.

The Jurassic sequence exposed on Mount Jura near 

Taylorsville (fig. 22) has furnished fossils of Sinemurian 

to Callovian Age exclusive of the Bathonian. At the base, 

the Lilac Argillite of Crickmay (1933b, p. 896-^897) contains the ammonite Echioceras of late Sinemurian Age in 

association with Weyla alata (von Buch) (Muller and 

Ferguson, 1939, p. 1613), which was described by Crickmay (1933b, p. 905, pi. 25, figs. 4-6) as Parapecten 

praecursor and ranges from upper Sinemurian to basal 

Toarcian, according to S. W. Muller (oral commun., 

1958). The overlying Hardgrave Sandstone is probably 

only slightly younger, as it also contains Weyla alata 

(von Buch) ( = Parapecten acutiplicatus Meek in Crickmay, 1933b, p. 906, pi. 25, figs. 1-3). The next higher 

formation, the Fant Andesite, is assigned to the early 

Pliensbachian solely on the basis of stratigraphic position 

beneath beds of probable middle to late Pliensbachian 

Age.

The overlying Thompson Limestone is provisionally 

assigned a Pliensbachian Age because some gray limestone lentils within the formation contain the pelecypod 

Plicatostylus. That genus has been found elsewhere in 

beds of that age in eastern Oregon (Lupher and Packard, 

1930; Lupher, 1941, p. 239; Dickinsonand Vigrass, 1965, 

p. 36, 37) and in western Nevada (Muller and Ferguson, 

1939, p. 1621, table 3; Silberling, 1959, p. 27). It has also 

been found in Chile in a sequence dated by means of ammonites as early Toarcian (Hillebrandt, 1973, p. 168, 

175, 193, 195). Presence of this genus in the Thompson 

Limestone was first recognized by Bruce Batton and 

David Taylor, geology students from the University of 

Oregon at Eugene and the University of California at 

Berkeley, respectively, while doing fieldwork with the 

writer in 1975. Previous assignments of that limestone to 

the early Bajocian were based on the presence of the gastropod Nerinea, which in Europe is not known in preBajocian beds (Alpheus Hyatt, cited in Diller, 1908, p. 

44). That age assignment, however, is not valid for the 

Pacific Coast region of North America, because Nerinea 

occurs in abundance in the Pliensbachian Robertson Formation of eastern Oregon (Dickinson and Vigrass, 1965, 

p. 36; Hallam, 1965, p. 1496).

The Bajocian is definitely represented by the Mormon Sandstone and by the Moonshine Conglomerate. 

The Mormon Sandstone contains species of the ammonites Sonninia, S. (Papilliceras), Normannites, and Stephanoceras (Crickmay, 1933b, p. 898, 899, 908-913) 

that furnish a correlation with the European Otoites 

sauzei zone and with the Oregon Warm Springs Member 

of the Snowshoe Formation, as discussed by Imlay (1973, 

p. 34, 35).

In addition, the report of Teloceras near the top of 

the Mormon Sandstone (Crickmay, 1933b, p. 898) suggests a correlation with the European zone ofStephanoceras humphriesianum. Furthermore, the lower 75 feet 

(23 m) of the Mormon Sandstone on the south side of 

Mount Jura contains specimens of Euhoploceras (D. G. 

Taylor, written commun., 1976), which in Europe are 

characteristic of the lower middle Bajocian (Sonninia 

sowerbyi zone) but also occur at the top of the lower Bajocian (Graphoceras concavum zone) (Parsons, 1974, p. 

170).
58 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

Staga

Harrison Lake area, 1 

southwestern British 

Columbia. (Crickmay, 

1930, 1962; Frebold 

and Tipper, 1967)

Taseko Laka area ) 

(Frebold 1951, 1967b; 

Frebold endTipper,1967; 

Frebold and others, 

1969; Jelatzky and 

Tipper, 1968)_____

Vancouver Island, on'

west side

(Jeletzky, 1950,1954,

1970; Frabold and

Tippar, 1967)

Queen Charlotte «

Islands

(McLearn, 1929, 1932,

1949; Frebold, 1967a;

Brown, 1968)

Sm it hers araa, Tenas 5 

Creek,and McDonall 

Lake,( Frebold and 

Tipper, 1973, 1975)

Characteristic fossils 6 

in British Columbia 

(Frabold, 1964a; Frebold and 

Tipper, 1970; Jelatzky, 

1965)

Overlying beds Lower Cretacaous

Tithonian

Kimmaridgian

Oxfordian

Callovian

Bajocian

Toarcian

Pliansbachian

Sinemurian

Hettangian

Lowar Cretaceous Lower Cretaceoua

Erosion 

and granitic 

intrusions

Gray shale and sandy 

glauconitic siltstone 

225-518 ft (69-158m) 

Passes laterally 

^into thin graywacke

Lowar Cretaceous Lower Cretaceous!

Division B, 450-550 ft (137- 

168m)Mostly gray ahale

Mostly graywacke, 

some siltstone. 

500-1500 ft (152-456 m)

Passes laterally 

into 150 ft (46m) 

of siltstone 

and shale

Gray siltstone and

silty shala. Soma

graywacke and pabble

conglomarate. Some

gran it a pebblas

present

454-800 ft (138-152 m)

Agassiz Prairie Form at ton 

5000 ft(1524 m) Argillfte

Kent Formation 3000 ft 

(914 m) Conglomerates

Black shala and 

soma siltstone 

1,100 ft (335m) 

Faulted basal ly

Billhook Formation 

1800 ft (549m) 

Badded tuffs

Shale, tuff, siltstone, 

and some graywacke 

150-300 ft (45-91 m)

Mysterious Craek 

Format ton 

2300-2900 ft (700-884m) 

Black argil

Conglomarate and 

grit. Boulders of 

hmestona at base.

Echo Island 

Formation

Shala, siltstone, 

ergillite.end soma 

graywacke 

1000 ft (305m) 

Base not exposed

Harrison Laka 

Formation

Upper

shale member 

230-250 ft 

(70-76 m)

Sendstone

member

200-250 ft (61-76 m)

.ower shale member 

250-300 ft (76-91 m)

£hala and limestone ^

Erosion and possible 

granitic intrusions

Buchia fischeriana and 

B. terabratuloides

Buchia oiochii iand B. cf. 

B. olanfordiana

Buchia mosquansis

Amoeboceras and 

Buchia concentrica

Cardioceras

Cardioceras canadense

Cardioceras martini

Ashman Formation 

2493 ft (760 m) 

Gray to black 

shala, sandstone, 

tuff, braccia, 

and conglomarate

Quenstedtocaras henrici

Cadoceras (Stenocedocerast 

striatum _

Lilloettia buckmani, 

Cadoceras catostoma, 

Keppla rites, Paracadoceras, 

and Pseudocedoceras

Mostly andesitic 

agglomerate, 

tuff,end volcanic 

sandstone. Some 

coal. 1750 ft (533m) 

(not datad)

Tuffaceous shele^ 

and sandstone 

100 ft (30 m)

Cranocaphalftes costtdansus 

and Cobbanites talkeetnanus

/ Megasphaeroceras and \ 

Cobbanites talkaetnanus

Lapilli tuff 600- 

800 ft (183-244 m)

Erosion and igneous 

intrusions

Smithers Formation 

985-2625 ft 

(300-800 m) 

Graywacke, tuff, 

sandstone, breccia, 

and conglomarate

Teloceras, Chondrocaras, 

\ and Normannhes /

Sonninia and Latiwitchellia

Erycites and Tmetoceras 

scissum__________

Grammoceras, Catulloceras, 

and Phlysaogrammoceras

Graywacke, dark gray. 

Basal part contains 

pebbla conglomerata 

1000-3000 ft (305-915m) 

Disconformity may 

occur at base

Lava and breccia 

300-400 ft (91-122 m)

Maude Formation 

600-700 ft 

(182-210 m) 

Mostly gray 

argil life, shale, 

and sandstone. 

Soma thin beds 

of limestone 

and sandstone. 

Gradas into 

underlying ; 

formation

Argillite 150 ft (45 m) 

Volcanic breccia 

600ftn82m)

Phymatoceras and 

Peronoceras

Harpoceras cf. H. exaratum, 

Prodactylioceras, and 

Dactvliocaras_______

Amaltheus, Paltarpites, 

Arieticeras, Pleuroceras, 

and Leptaleoceras___

Prodactylioceras

Shale, siltstone, 

and argil lite

Mostly gray argil lite. 

Some graywacke and 

limestone. Soma tuff 

in middle. 

720-1350 ft (219-411 m)

Kunga Formation 

upper mamber 

1630 ft (497m) 

Black argil lite, 

siltstona, and shale. 

Lower contact abrupt 

but conformable

Telkwa Formation 

3280-8200 ft (1000- 

2500 m) Volcanics, 

marine and 

nonmarine

Uptonia, Tropidoceras, 

and Acanthooleuroceras

Echioceras

Greywscke, gray-green.

Some green pebbly

beds

30-35 ft (9-11 m)

Volcanic breccia 

and lava. 

7000-9000 ft 

(2133-2742 m)

Asteroceras

Arnioceras, Coronicaras, 

Arietites.and 

Paracoroniceras_____

Psiloceras canadense

Psiloceras erugatus

Underlying beds Upper Paleozoic)?) Upper Triassic Upper Triassic Upper Triassic

A. Southwestern to central British Columbia.
COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 59

Tulsequah area, 

northwestern 

British Columbia 

(Souther, 1971; 

Frebold, 1964a)

Whitehorse area, 

Yukon Territory 

(Wheeler, 1961; 

Frebold and Tipper, 

1970)

Eastern Alaska Rangen 

Nutzotin Mountains ° 

(Richter and Jones, 

1973; Berg, Jones,and 

Richter, 1972)

Wrangell Mountains, g 

south-central part 

McCarthy C-4 to 6 

Quadrangles 

(Mackevett, 1969, 1971)

10

Talkeetna Mountains, 

Nelchina area 

(Grantz, 1960, 1961)

Characteristic fossils in 

southern Alaska

Up >er Cretaceous

Takwahoni 

Formation 

11,000ft 

(3352 m)

Lower Cretaceous

Inklin 

Formation 

10,000 ft 

(3048 m)

Not identified

Graywacke, 

siltstone, 

and shale. 

Interbedded 

in lower 

part with 

conglomerate 

containing 

chert pebbles 

or granitic 

boulders.

Volcanic rocks 

present only 

near base

Interbedded 

graywacke, 

siltstone, 

sandstone, 

and some 

conglomerate 

of volcanic, 

granitic, or 

limy pebbles.

Intertongues 

southwest 

with the 

Takwahoni 

Formation

Lower Cretaceous Lower Cretaceous Lower Cretaceous

3000 ft (914 m) 

(Basal part only) 

Mostly argillite. 

Mostly not graded

5000 ft (1524m) 

Conglomerate, 

graywacke, 

argillite, 

massive, graded

3000 ft (915m) 

Mostly dark gray 

argillite. 

Some siltstone, 

mudstone, graywacke, 

and limestone

Root Glacier 

Formation 

0-3800 ft (1158m) 

Mudstone, siltstone, 

graywacke, limestone 

and conglomerate

2500 ft (762 m) 

Conglomerate, 

quartzite, 

argil lite.and 

some graywacke. 

Age uncertain

3000 ft (914m) 

Argillite, 

siltstone.and 

graywacke

4000 ft (1219m) 

Conglomerate 

with granitic 

fragments. 

Grades laterally 

into graywacke

Pre-Carnian Upper Triassic

Present near 

Laberge.

- ^^~s-^

Upper Triassic

.5

IE 

52

u.co 

**

II

Buchia fischeriana and 

Buchia piochii

Buchia rugosa and 

Buchia mosquensis

Sandstone and 

siltstone

Siltstone and 

shale

Ampeboceras 

(Prionodoceras) 

and 

Dichotomosphinctes

Conglomerate

Cardioceras distans

Cardiocaras martini

Chinrtna FormaTion 

80.0-2500 ft (244-762 m 

Siltstone ana shale. 

Some sandstone or 

has

Cadoceras (Stanocadoceras) 

stano/oboida

Cadoceras catostoma and 

Lilloattia buckmani

Kepplaritas

Nizina Mountain

Formation

0-1500 ft (457m)

Graywacke,

fine-grained

J

44m) andstone, silt- , 

stone, conglomerate,^ 

• ilyabeds_

Arctocephalites

Cranocephalites

Cranocaphalites costidansus

Tuxedni Group 

790-1200 ft(213-366 m) 

Siltstone and 

sandstone. Locally 

some pebbly or 

shelly beds

Megasphaerocaras, Leptosphinctes

Chondroceras allani, Talocaras 

Stephanoceras kirschnari

Parabigotites crassicostatus

Sonninia and Docidoceras

Erycitoidas howel/i, Tmetoceras

Grammocaras

Haugia and Phymatoceras

Lubbe Creek Formation 

100-300 ft (30-91 m) 

Spiculite, coquina, 

and chert

McCarthy Formation 

(in part), upper 

member 2000 ft 

(609 m) Chert, 

spiculite, shale, 

and limestone

Talkeetna 

Formation 

6000-8000 ft 

(1828-2438 m) 

Upper part: 

sandstone 

and argillite.

Middle part: 

volcanic flows 

and pyroclastics.

Lower part: 

argillite and 

sandstone

Dactyliocaras cf. D. commune

Plauroceras, Amaltheus, Paltarpites

Uptonia and Apoderocaras

Crucilobicaras

Mk

Waahnaroceras and Psiloceras

Upper Triassic Upper Triassic

B. Northwestern British Columbia to southern Alaska.

FIGURE 24.—CORRELATIONS AND COMPARISONS OF JURASSIC ROCKS IN THE PACIFIC COAST REGION IN BRITISH 

COLUMBIA, YUKON TERRITORY, AND SOUTHERN ALASKA. Vertical lines indicate that strata are missing; right diagonal lines 

indicate strata not exposed; left-diagonal lines indicate lack of fossil data; wavy lines indicate unconformity or disconformity. Column 

numbers refer to locations shown on figure 19.
60 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

The overlying Moonshine Conglomerate is dated as 

early late Bajocian because it contains several fragments 

of loosely coiled ammonites (USGS Mesozoic loc. 27322) 

belonging to the family Spiroceratidae and closely resembling specimens of Spiroceras bifurcatum (Quenstedt) 

from eastern Oregon (Imlay, 1973, pi. 1, figs. 3-8).

Next higher in the Mount Jura Jurassic sequence is 

an unnamed dacite tuff of McMath (1966, p. 182), which 

is overlain by the Hull Meta-andesite. These units have 

not furnished fossils but could represent any time between latest Bajocian and earliest Callovian. They are 

herein provisionally assigned a Bathonian Age mainly on 

the basis of stratigraphic positions but partly because 

the early Callovian appears to be accounted for by the 

overlying formations.

The lower to middle Callovian is represented on 

Mount Jura by ammonites from the Hinchman Sandstone, the North Ridge Agglomerate, and the Foreman 

Formation (Imlay, 1961, p. D9). The next three overlying formations have not furnished any identifiable fossils 

and could be in part younger than Callovian. They are 

herein provisionally assigned to the Callovian because 

the thickness of the sequence from the Hinchman Sandstone to the Trail Formation is not much greater than 

that of the Logtown Ridge Formation in the western 

part of the Sierra Nevada and is much less than that of 

the Callovian beds in eastern Oregon.

Jurassic sequences exposed in the western part of 

the Sierra Nevada consist of partially metamorphosed 

sedimentary and volcanic rocks that differ from those exposed in the higher part of the Sierra in the following 

ways: (1) none is older than Callovian; (2) they are, in 

part, of early Oxfordian to early Kimmeridgian Age; (3) 

they are much more extensive; and (4) they contain more 

slaty beds. They have been divided into many formational units based generally on local lithologic and stratigraphic features (Turner, 1894, 1897; Lindgren, 1900; 

Lindgren and Turner, 1894; Becker, 1885, p. 18, 19; 

Taliaferro, 1942, p. 98, 99; 1943a, p. 282-284; Heyl and 

Eric, 1948, p. 51-53; Eric and others, 1955, p. 10-12; 

Imlay, 1961, p. D2-D9; Clark, 1964, p. 15-41; Sharp 

and Duffield, 1973, p. 3971-3974). Apparently most formational boundaries have been difficult to trace laterally 

because of complicated and extensive faulting, lithologic 

changes laterally within short distances, and scarcity of 

fossils.

Thus, the sequence exposed in a central fault block 

near the Cosumnes River (Clark, 1964, p. 17-21, 23- 

26, pi. 9) was dated by Imlay (1961, p. D3-D8) as Callovian to early Kimmeridgian. Within this age span, the 

Mariposa Formation was dated as late Oxfordian to early 

Kimmeridgian on the basis of the presence of the ammonites Discosphinctes, Dichotomosphinctes, and Amoeboceras (Amoebites), in association with the pelecypod 

Buchia concentrica (Sowerby). The underlying Logtown 

Ridge Formation was dated as late early Callovian to 

late Oxfordian on the basis of the presence of Pseudocadoceras in its lower 600 feet (180 m) and Idoceras cf. /. 

planula (Heyl) near its top. The underlying "Cosumnes 

Formation" (of former usage) was dated as early Callovian because of its gradational relationship with the 

Logtown Ridge Formation. Subsequent studies by Sharp 

and Duffield (1973, p. 3971-3974; Duffield and Sharp, 

1975, p. 1, 5, 8, 22, 29) showed, however, that the "Cosumnes Formation" is not a mappable unit, because it 

consists of scattered blocks of graywacke, clay slate, and 

conglomerate that are bounded by faults and are part of 

a melange. This melange is separated from the Logtown 

Ridge Formation by a major fault involving considerable 

displacement and brecciation of beds. The melange may 

involve beds of several ages but is not younger than Late 

Jurassic, because it bears foliation that predates intrusions of Upper Jurassic granitic rocks.

Marked lateral variation within the Jurassic beds of 

the central fault block has been demonstrated by Clark 

(1964, p. 22, 23, pi. 9), who showed that the Logtown 

Ridge Formation passes southward near the Merced 

River into at least 15,000 feet (4,570 m) of volcanic rocks 

called the Perion Blanco Volcanics. Also, the Mariposa 

Formation locally contains thick volcanic members that 

consist mostly of breccia.

The Jurassic rocks exposed in a western fault block 

have been described by Clark (1964, p. 27-33) under 

formational names different from those used for the central block. These rocks are called, from youngest to oldest, the Copper Hill Volcanics, the Salt Spring Slate, and 

the Gopher Ridge Volcanics, Of these, the Salt Spring 

Slate resembles the slaty part of the Mariposa Formation, has been mapped previously under that name (see 

list of names in Clark, 1964, p. 29), and contains Buchia 

concentrica (Sowerby), a fossil common in the Mariposa 

Formation (see Imlay, 1961, p. D14). Presumably the 

Gopher Ridge Volcanics is roughly equivalent to the 

Logtown Ridge Formation, and the Copper Hill Volcanics, to the upper part of the Mariposa Formation.

In comparison with the Jurassic sequence near Taylorsville, the lower part of the Logtown Ridge, which 

contains Pseudocadoceras grewingki (Pompeckji), is correlated with the Foreman Formation. The lowest part 

of the Logtown Ridge Formation, which was separated 

from the "Cosumnes Formation" by Sharp and Duffield 

(1973, p. 3971, 3972) should be equivalent to the Hinchman Sandstone and the North Ridge Agglomerate. The 

middle to upper parts of the Logtown Ridge Formation 

are possibly equivalent to some or all of the three uppermost Jurassic formations near Taylorsville (see fig. 22).
COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 61

The Mariposa Formation may be correlated by the 

presence of Buchia concentrica (Sowerby) with the Santa 

Monica Slate just north of Los Angeles (Imlay, 1963, p. 

103, pi. 14, figs. 14-19), with the Monte de Oro Formation exposed northeast of Oroville in Butte County, Calif., 

and with the Galice Formation in northwest California 

and adjoining parts of southwest Oregon. All these are 

characterized by dark-gray to black slaty to phyllitic 

beds that contain Buchia in places. Failure to find Buchia 

in slaty beds in the uppermost Jurassic formations near Taylorsville suggests that those formations are older than late 

Oxfordian.

Jurassic rocks older than Callovian occur at only two 

places in California outside the eastern and middle Jurassic belts in the Sierra Nevada. One of these is along 

the Pit River in the eastern Klamath Mountains about 

30-40 miles (48-64 km) northeast of Redding. It appears to be a northwestward extension of the Jurassic 

beds exposed near Taylorsville, although the two sequences are separated by about 75 miles (121 km) of volcanic rocks exposed at the south end of the Cascade 

Range. The other occurrence is in the Santa Ana Mountains southeast of Los Angeles. It could represent a 

southward extension of the metamorphosed Jurassic rocks 

of the central part of the Sierra Nevada, just as the 

Santa Monica Slate near Los Angeles could represent a 

southern extension of the Mariposa Formation of the 

western Sierra Nevada.

The Jurassic sequence exposed along the Pit River 

in north-central California is about 8,000 feet (2,440 m) 

thick. At its base is the Arvison Formation, which is 

about 6,000 feet (1,830 m) thick, consists mostly of volcanic flows, breccia, agglomerate, and tuff, and contains 

some conglomerate and tuffaceous sandstone. The Arvison rests unconformably on Triassic beds and at one 

place has yielded the Sinemurian ammonites Asteroceras 

and Arnioceras (Sanborn, 1960, p. 11-14). The overlying Potem Formation (Diller, 1906, p. 5), which is 1,000- 

2,000 feet (305-610 m) thick, passes laterally in its lower 

part into the Bagley Andesite. The Potem consists mostly 

of argillite and calcareous tuffaceous sandstone but includes some conglomerate and limestone lentils and apparently is conformable with the Arvison Formation of 

Sanborn (1960, p. 6, 14-16, pi. 1). The age of the lower 

part of the Potem Formation is definitely Early Jurassic, 

not younger than early Toarcian, as shown by the occurrence of Weyla aff. W. alata (von Buch) (S. W. Muller, 

oral commun., 1958). The age of the upper part is not 

older than late Toarcian, as shown by the occurrence of 

Bositra buchii (Romer) (Guillaume, 1928), and could be 

as young as Bajocian, according to Sanborn (1960, p. 16).

The Jurassic beds cropping out in the Santa Ana 

Mountains of southern California are all included in the

Bedford Canyon Formation, which consists mostly of 

dark-gray to black slates and argillite, includes some 

quartzite and fossiliferous limestone lentils, and is estimated to be 20,000 feet (6,100 m) thick (Larsen, 1948, p. 

18-24; Engel, 1959, p. 16-25). Fossils from the limestone lentils were once considered to be of Triassic age 

(Engel, 1959, p. 22-24) but are now dated as Jurassic on 

the basis of ammonites (Silberling and others, 1961, p. 

1746, 1747). Thus, the pelecypod originally described as 

Daonella sanctea-anea Smith (Smith, 1914, p. 145) is 

now assigned to the genus Silberlingia (Imlay, 1963, p. 100) 

and dated as early Callovian because it occurs with Macrocephalites and Hecticoceras (Imlay, 1963, p. 98, 99, pi. 14, 

figs. 1-9,26-36; 1964c, p. 506,508, pi. 78, figs. 22-26). Also, 

some brachiopods that were once considered to be of Triassic 

age (G. A. Cooper, cited in Larsen, 1948, p. 18), were 

apparently collected at the same stratigraphic level as some 

middle Bajocian ammonites identified as Dorsetensia and 

Telocerasl sp. juv. (Imlay, 1964c, p. 506-508, pi. 78, figs. 

3-18).

WESTERN CALIFORNIA AND SOUTHWESTERN OREGON

Jurassic marine sequences exposed in and near the 

Coast Ranges in California and in the western Klamath 

Mountains in northwest California and southwest Oregon have the following characteristics, geologic relationships, and historical developments:

1. They are entirely of Late Middle to Late Jurassic age (Callovian and younger).

2. They are generally many thousands of feet thick.

3. They include sequences of two or three different 

age ranges that are associated only in the western 

Klamath Mountains and are therein separated by 

thrust faults.

4. Some sequences are of Callovian to early Kimmeridgian Age; contain a great deal of volcanic material; were deposited in deep to fairly deep waters, 

on the basis of lithologic characteristics; were 

uplifted, folded, metamorphosed, intruded, and 

eroded during late Kimmeridgian to Tithonian time; 

and were then overlain unconformably in places by 

shallow-water marine Cretaceous beds. These sequences include the Logtown Ridge-Mariposa sequence in the Sierra Nevada and the Rogue-Galice 

sequence in the Klamath Mountains.

5. Other sequences are of late Kimmeridgian to late 

Tithonian Age; are mostly nonvolcanic; originated 

in shallow to fairly shallow water, on the basis of 

fossils and lithologic features; and pass conformably upward into shallow-water marine sediments
62 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

of earliest Cretaceous age. They include the Knoxville Formation of California and possibly the Riddle Formation of Oregon, although the last named 

has not furnished fossils older than the late Tithonian. They are underlain by unfossiliferous metavolcanic rocks that, on the basis of stratigraphic 

position, should be at least of early Kimmeridgian 

and Oxfordian Age.

6. Still other sequences are only of late Tithonian 

Age, are volcanic, pass conformably upward into 

beds of earliest Cretaceous age, and appear to be 

of fairly deep to deep-water origin, on the basis of 

lithologic features. They include the Dothan Formation and most of the Otter Point Formation of 

Oregon and the Franciscan assemblage of California.

7. The sequences of Callovian to early Kimmeridgian Age were deposited in different areas from 

those of later Jurassic age and are now juxtaposed 

in the Klamath Mountains by eastward underthrusting of the younger sequence.

In the Dayville-Riddle area of southwestern Oregon, 

the slaty Galice Formation overlies the metavolcanic 

Rogue Formation. These rocks crop out in an arcuate 

belt 10-30 miles (16-48 km) wide that extends about 

190 miles (306 km) south into southern Trinity County in 

northwest California, where they are all included in the 

Galice Formation. The Galice ranges from Oxfordian to 

early Kimmeridgian time. Along the west side of the 

belt, these rocks are in contact with the Josephine ultramafic mass, the South Fork Mountain Schist, and the Dothan Formation. Along the east side, they are in fault 

contact with upper Paleozoic rocks in California and 

Triassic(?) rocks in Oregon (Diller, 1907, p. 403; Wells 

and others, 1949, p. 47; Cater and Wells, 1953, p. 84; 

Wells and Walker, 1953; Irwin, 1960, p. 27, 28; Dott, 

1971, p. 9, 10; Beaulieu, 1971, p. 3, 15, 19, 20, 38). Thicknesses cannot be measured owing to intense crumpling, 

faulting, and intrusions, but estimates range from 10,000 

to 30,000 feet (3,050 to 9,140 m) (Irwin, 1960, p. 27).

At the top of the Galice Formation, a normal sedimentary contact, instead of a faulted contact, has only 

been found near the Oregon coast on Barklow Mountain 

in northwestern Curry County. On that mountain, the 

formation is overlain unconformably by a conglomerate 

that contains Buchia pacifica Jeletzky (USGS Mesozoic 

loc. M5006) of early to middle Valanginian Age (Dott, 

1966, p. 94; 1971, p. 11). This relationship, plus the fact 

that no Upper Jurassic beds have yet been found above 

the Galice Formation or the equivalent Mariposa Formation, suggests that both these formations were above 

sea level and that they provided sediment during deposition of the Knoxville Formation and the older part of 

the Franciscan rock assemblage (Bailey and others, 

1964, p. 126, 146, 147).

The Galice Formation is correlated with the Mariposa Formation of the western Sierra Nevada because it 

is strikingly similiar lithologically and likewise contains 

the pelecypod Buchia concentrica (Sowerby) and the ammonite Perisphinctes (Dichotomosphinctes) (Imlay, 1961, 

p. D10). The underlying Rogue Formation, which apparently is gradational with the Galice, consists of many 

kinds of volcanic rocks similar to those in the Logtown 

Ridge Formation of the western Sierra Nevada. It may 

be of the same age, but to date it has not yielded any 

fossils. These facts show that the Galice Formation is a 

northward extension of the Mariposa Formation and was 

deposited under the same environmental conditions. 

Similarly, the Rogue Formation may be the northern extension of the Logtown Ridge Formation, but the Rogue 

was deposited under somewhat different environmental 

conditions, as shown by its lack of some ammonites that 

are present throughout the Logtown Ridge Formation.

Upper Tithonian beds crop out in the Coast Ranges 

of western California as far south as San Diego, in the 

Klamath Mountains of northwestern California, and in 

southwestern Oregon (fig. 22). In California, they occur 

in the Franciscan rock assemblage and in the Knoxville 

Formation (Taliaferro, 1943b). In Oregon, they occur in 

the Otter Point, Dothan (Taliaferro, 1943b), and Riddle 

Formations.

Among these rock units, the Franciscan assemblage 

and the Dothan and Otter Point Formations closely resemble each other. The Franciscan consists mostly of 

graywacke but includes some dark shale, altered volcanic 

rock (greenstone), chert, limestone, and blue schist and 

is estimated to be at least 50,000 feet (15,240 m) thick 

(Bailey and others, 1964, p. 5, 20-122). The Dothan consists mostly of massive hard graywacke but includes 

black mudstone, chert, and conglomerate. It is estimated 

to be at least 18,000 feet (5,490 m) thick and passes 

southward into the Franciscan assemblage in California 

(Beaulieu, 1971, p. 15; Dott, 1971, p. 43^6; Wells and 

Walker, 1953). The Otter Point consists of graywacke, 

black mudstone, argillite, altered volcanic breccias and 

flows (greenstone), much conglomerate^ chert, and some 

limestone lentils and appears to be thousands of feet 

thick (Koch, 1966, p. 36-43; Beaulieu, 1971, p. 30; Dott, 

1971, p. 27-31). It greatly resembles the Dothan Formation but is distinguished lithologically by being darker 

and more sheared, by containing more volcanic fragments, pillow lavas, and fossils, and by its graywacke 

being less indurated (Dott, 1971, p. 46). All contacts of 

these formations are marked by thrust faults.

Resemblances between the Knoxville and Riddle 

Formations are not nearly as close as those among the 

three formations just described. The Knoxville Formation consists of gray shale, siltstone, thin-bedded sandstone, conglomerate lenses, and some limestone concretions in shale units and is 2,000-13,000 feet (610-3,960 

m) thick. The Riddle Formation consists of gray silt-
COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 63

stone, thin-bedded graywacke, lenses of conglomerate, 

and some limestone lentils and is at least 1,100 feet (335 

m) thick. Most of that thickness, however, involves beds 

of Berriasian Age, which are younger than any part of 

the Knoxville Formation as now defined. Comparisons 

between the two formations are difficult to make because 

the Riddle Formation is much broken by faults and has 

not been studied as thoroughly as the Knoxville Formation.

On the basis of fossils, the Franciscan assemblage is 

dated as late Tithonian to Turonian and possibly Campanian (Bailey and others, 1964, p. 115-122, table 16). 

A late Tithonian Age is based mainly on four occurrences 

of Buchia piochii (Gabb) in the northern Coast Ranges, 

including one at the south end of Lake Pillsbury. This 

age is supported by the occurrence of B. piochii with Aulacosphinctest sp. juv. near Stanley Mountain in the 

southern Coast Ranges.

The upper part of the Knoxville Formation is dated 

as late Tithonian on the basis of both ammonites and 

buchias at many levels, as recently documented in detail 

(Bailey and others, 1964, p. 124-130; Jones and others, 

1969, p. A9-A12; Imlay and Jones, 1970, p. B5-B12, 

B17-B19). The lower part is dated as late Kimmeridgian to early Tithonian by the presence of Buchia rugosa 

(Fischer) about 50-100 feet (15-30 m) above the base 

of the formation in the Paskenta area (Jones, 1975). Assignment to the late Kimmeridgian is also favored by the 

presence of a few specimens that bear very fine ribs, as 

on B. concentrica (Sowerby), and by the absence of B. 

mosquensis (von Buch) (D. L. Jones, oral commun., 

1975), an associate of B. rugosa, which becomes more 

common upward. This occurrence does not imply that the 

basal part of the Knoxville Formation is of late Kimmeridgian Age throughout its extent.

A late Tithonian Age for the Otter Point Formation 

in southwestern Oregon is proven by the presence of 

Buchia piochii (Gabb) at many localities (Koch, 1966, p. 

42, 43). However, a Berriasian Age for part of the formation is shown by the presence of many specimens of 

B. uncitoides (Pavlow) (USGS Mesozoic loc. 2074) in association with the ammonite Neocosmoceras, a genus 

that is much more common in Berriasian than in Tithonian beds. With these occur one immature specimen of 

Proniceras and a few specimens of B. piochii (Gabb), 

both of which are good evidence of a late Tithonian Age 

and both of which have a different colored matrix from 

the specimens of Neocosmoceras and B. uncitoides. 

Therefore:, the fossils were probably collected from different beds of different ages (Imlay and Jones, 1970, p. 

B5, B32, B51, B52).

A late Tithonian Age for part of the Dothan Formation is proven only by the occurrence of Buchia piochii 

(Gabb) at one place on the Chetco River in Curry County, 

Oreg. (Ramp, 1969, p. 245). The probability that the formation is partly of younger age is suggested by its great

thickness and by its close lithologic similarities to the Otter Point Formation and to the Franciscan assemblage, 

both of which have yielded fossils younger than Tithonian.

The Riddle Formation is definitely of Tithonian to 

Berriasian Age in its type section near Days Creek, 

Oreg. Buchia fischeriana (Keyserling) and Aulacosphinctes of late Tithonian Age occur just above the basal 

conglomerate. B. uncitoides (Pavlow) of Berriasian Age 

occurs from 20 to 1,004 feet (6 to 306 m) above the basal 

conglomerate (Imlay and others, 1959, p. 2775-2778; Imlay and Jones, 1970, p. B13, BIT). The late Tithonian 

Age for the lower part of the Riddle Formation is confirmed by the presence of B. fischeriana with Proniceras 

on Cow Creek near the mouth of Iron Mountain Creek 

in the NEV4 sec. 4, T. 31 S., R. 7 W., Dutchman Butte 

Quadrangle, Douglas County, Oreg. In addition, the 

ammonite Durangites, obtained from a limestone lentil 

in the Dillard area south of Roseburg, Oreg. (Imlay and 

others, 1959, p. 2778; Imlay, 1960, p. 169, pi. 31, figs. 

11, 12), could be from either the Riddle or the Dothan 

Formation.

EASTERN OREGON AND WESTERN IDAHO

The stratigraphic and lithologic features and correlations of the Jurassic formations exposed in an inlier in 

Tertiary volcanic rocks south and southwest of John 

Day, Oreg. have been described in considerable detail. 

(Lupher, 1941; Dickinson and Vigrass, 1965, p. 30-64; 

Buddenhagen, 1967; Brown and Thayer, 1966a, b; Imlay, 

1964a, p. D2-D9; 1968, p. C4-C21; 1973, p. 8-25) and 

are summarized on figure 22. As a whole, the Jurassic 

sequences in that inlier are characterized by enormous 

thicknesses, by rapid facies changes, and by consisting 

mostly of volcanic ejecta, flows, and breccias. They also 

include some sedimentary material that was derived 

mostly from a landmass to the west where Triassic and 

Paleozoic rocks were exposed but that was derived in 

part from a landmass to the north where only Triassic 

rocks were exposed.

Overall thicknesses of the Jurassic sequences range 

from about 1,800 feet (550 m) on the west to about 24,000 

feet (7,300 m) on the east. Lower Jurassic beds thicken 

eastward from about 400 to 1,600 feet (120 to 490 m), to 

which may be added about 8,000 feet (2,400 m) of Hettangian and Sinemurian beds exposed in the northeastern part of the Izee Quadrangle, the northern parts of 

the Logdell and Seneca Quadrangles, and the southern 

part of the Mount Vernon Quadrangle. Bajocian and 

Bathonian beds vary in thickness from about 1,800 to 

2,750 feet (550 to 838 m) and are thinnest in the central 

part of the inlier. Callovian beds vary in thickness from 

about 1,000 feet (300 m) on the west to about 14,000 feet 

(4,300 m) on the east.
64 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

These variations in thickness are related to nearness 

to volcanic sources, to positions relative to land areas, 

upwarps, and basins, and to the presence and extent of 

unconformities (Dickinson and Vigrass, 1965, pi. 3). 

Widespread angular unconformities, involving intense 

folding, some faulting, erosion, and changes in direction 

of folding, developed in early Pliensbachian time (Brown 

and Thayer, 1966a, b) and after middle Callovian time. 

A local unconformity involving folding, uplift, and erosion developed in the Suplee area in Toarcian to early 

Bajocian (Aalenian) time. Another unconformity, involving some warping and erosion, formed in the Suplee-Izee 

area between deposition of the Snowshoe Formation and 

the Trowbridge Shale but within beds of early Callovian 

Age, according to Dickinson and Vigrass (1965, p. 83, pi. 

3). Nonetheless, the presence of the early Callovian ammonites Iniskinites and Lilloettia 300-500 feet (90-150 

m) below the top of the upper member of the Snowshoe 

Formation suggests that the exact stratigraphic position 

and age of the unconformity needs confirmation.

The fact that the Suplee Formation of late Pliensbachian Age rests on the Graylock Formation of Hettangian Age at one place and on the much thicker Keller 

Creek Shale of early to late Sinemurian Age only 6 miles 

(9.6 km) away suggests considerable erosion locally during early Pliensbachian time. It is not proof, however, 

because the two occurrences are separated by a major 

fault of unknown displacement. Before faulting they could 

have been much farther apart, could have been parts of 

different structural plates, and could have had a different 

sedimentary history. Perhaps the best evidence for erosion is the presence of an angular unconformity between 

the Keller Creek and Suplee Formations (Brown and 

Thayer, 1966a). This unconformity is well exposed on a 

road near fossil locality D66 (Dickinson and Vigrass, 

1965. pi. 1) in the NEV4 NEV4 sec. 2, T. 17 S., R. 28 E., 

in the Izee Quadrangle.

Beds of early Sinemurian to early late Bajocian Age 

and of possible Callovian Age are present in southern 

Baker County and northern Malheur County in east-central Oregon (fig. 23) from the Snake River westward at 

least 50 miles (80 km). Beds of early Callovian Age and 

of probable older Jurassic age are present nearby, east 

of the Snake River near the abandoned mining town of 

Mineral, Idaho.

From Juniper Mountain, about 10 miles (16 km) 

west-southwest of Brogan, Oreg., the eastern (lowermost) boundary of the Jurassic extends northeastward 

about 25 miles (40 km), crosses the Snake River about 64 

miles (104 km) north-northeast of Huntington, and continues another 10 miles (16 km) in Idaho to Dennett 

Creek, where it curves eastward just south of the old 

mining town of Mineral (abandoned).

The lower boundary of the Jurassic in the Huntington area, Oregon, is marked by 30-800 feet (9-240 m) 

of red, purple, and green conglomerate that rests unconformably on Upper Triassic beds (Brooks, 1967, p. 114- 

118) and consists of clasts derived from those beds. 

These clasts are typically compressed and sheared except for certain discontinuous rock bodies of late Pliensbachian Age that occur in the lower part of the conglomerate. Within these bodies, such fossils as ammonites, 

pelecypods, and corals occur in thin calcareous graywacke that is associated with mostly round, nonsheared 

clasts that are a peculiar dark green (H. C. Brooks, written commun., April 1974). In the Mineral area, Idaho, 

similar coarse conglomerate beds grade downward into 

tuffs that overlie a quartz diorite sill (Livingston, 1932, 

p. 33). In the Juniper Mountain area of Oregon, the lower 

boundary is marked by a thin unit of reddish sandstone 

and shale that rests on massive limestone of possible 

Early Jurassic, Triassic, or late Paleozoic age.

The late Pliensbachian ammonites in the basal conglomerate are not proof that the conglomerate is of that 

age, because the conglomerate is overlain by graywacke 

that basally contains ammonites of early to late Sinemurian Age. It appears, therefore, that rock bodies of late 

Pliensbachian Age in the lower part of the conglomerate 

must have attained that position as a result of southeastward thrusting after Pliensbachian time or by deposition in channels or pockets that were cut into the conglomerate or into the Triassic beds during early 

Pliensbachian time. The possibility of erosion during that 

time is suggested by the lack of fossils of that age anywhere in eastern Oregon and by the fact that considerable erosion took place during early Pliensbachian time 

in the Suplee-Izee area farther west.

Above the basal conglomeratic unit in the Huntington area are some thousands of feet of beds that contain 

fossils of Sinemurian to early late Bajocian Age (fig. 23). 

This sequence consists mostly of sheared and slightly 

metamorphosed gray to yellowish-gray, green, brown or 

black massive to thin-bedded graywacke, tuffaceous 

sandstone and siltstone, but it also includes some beds 

of water-laid tuff, conglomerate, quartz sandstone, limestone, and lava flows.

Above the thin basal unit of reddish sandstone and 

shale in the Juniper Mountain area is at least 5,000 feet 

(1,500 m) of gray shale, siltstone, graywacke, and conglomerate (Wagner and others, 1963, p. 688). Within 

this sequence, the upper 2,000 feet (600 m) has been 

dated as early to early late Bajocian on the basis of ammonites (Imlay, 1973, p. 30), and the lower 3,000 feet 

(900 m) has been dated as Early Jurassic on the basis of 

stratigraphic position and the presence of Crucilobicerast 75-100 feet (2&-30 m) above the base.
COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 65

In the Mineral area, Idaho, a coarse conglomerate 

unit is overlain by some 100 feet (30 m) or more of darkgray, sandy, thin- to medium-bedded tuff, which contains a species of Gryphaea (Imlay, 1964a, p. D13). This 

species has been found elsewhere about 64 miles (104 km) 

north-northwest of Brogan, Oreg., in association with 

the early Bajocian ammonites Tmetoceras and Erycitoides (USGS Mesozoic loc. 30142).

Still younger beds of early Callovian Age are exposed along Dennett Creek and its tributaries near Mineral, Idaho. These beds are probably several hundred 

feet thick and consist of dark-gray calcai ^s shale that 

contains many black concretions (Livingstuu, ^932, p. 33, 

34; Imlay, 1964a, p. D3). From a few concretions have 

been obtained such ammonites as Lilloettia buckmani 

(Crickmay), Xenocephalites vicarius Imlay, and evolute 

Kepplerites apparently identical with K. snugharborense 

(Imlay) (1964a, p. D6, D7). This shale contains the same 

ammonites as the lithologically similar Trowbridge Shale 

in the Suplee-Izee area southwest of John Day, Oreg. 

(Lupher, 1941, p. 263; Dickinson and Vigrass, 1965, p. 

60-64). Faunally, it correlates with the lower part of the 

Tonnie Siltstone Member of the Chinitna Formation in 

southern Alaska (Imlay, 1975, p. 3, 6, 14).

Similar dark-gray to black shale, slightly to strongly 

metamorphosed locally, occurs at several places in Baker 

and Malheur Counties, Oreg., above beds of late Bajocian Age. It is represented (1) in the northern part of the 

Huntington Quadrangle near Dixie Creek and farther 

northeast near Morgan, Hibbard, and Connor Creeks by 

thick, tightly folded, gray to black phyllite and slaty beds 

(Brooks, 1967, p. 118, location map on p. 114); (2) on the 

northern side of Juniper Mountain (T. 15 S., R. 41 E., 

sees. 30-32), southwest of Brogan, by 1,000 feet (300 m) 

or more of black phyllitic shale that contains limestone 

lentils and concretions (Wagner and others, 1963, location map on p. 689); and (3) by dark-gray to black slate 

and phyllitic shale exposed southwest of Ring Butte in 

the northeast part of T. 16 S., R. 37 E., in the Ironside 

Mountain Quadrangle (W. D. Lowry, unpub. data, 1968). 

No fossils have been found in any of these dark shales, 

phyllites, or slates in easternmost Oregon, but a Callovian Age for them is indicated by their lithologic resemblance to the Trowbridge Shale in the Suplee-Izee area 

and to the unnamed black shale near Mineral, Idaho, and 

by their superpositions on Bajocian beds.

Lower Jurassic beds are represented in the upper 

2,000 feet (600 m) of the Hurwal Formation (Smith and 

Alien, 1941, p. 6, 13, 14) exposed in the Wallowa Mountains south of Enterprise in northeast Oregon. They consist of partially metamorphosed dark-gray to black claystone and siltstone that weathers brownish red and 

contains Sinemurian and Pliensbachian fossils (Imlay,

1968, p. C7, C15, C16). The most complete sequence is 

exposed in the northeast part of the mountains (NWV4 

NWy4 sec. 19 (unsurveyed), T. 2 S., R. 44 E.), is 980 

feet (299 m) thick, is covered by debris basally, and contains ammonites of late Sinemurian to late Pliensbachian 

Age. Elsewhere in the mountains, early Sinemurian ammonites are known at five places. At one of these places, 

near Twin Peaks (center of SWV4 sec. 17, T. 3 S., R 44 

E.), the beds of that age grade downward into unfossiliferous beds that, in turn, grade downward into Upper 

Triassic beds. On the basis of these occurrences, the 

thickness of the Pliensbachian beds is about 680 feet (207 

m), of the upper Sinemurian beds, at least 300 feet (90 

m), of the lower Sinemurian beds, 700-800 feet (210-240 

m), and of the beds of possible Hettangian Age, 200-300 

feet (60-90 m).

Within the Lower Jurassic sequence exposed in the 

Wallowa Mountains, the early Sinemurian is represented 

by crushed and deformed ammonites of the family Arietitidae that probably include Coroniceras, Metophioceras, and Megarietites. The late Sinemurian is represented by Gleviceras, Crucilobiceras, Eoderoceras, 

Oxynoticerasl, Echiocerasl, Coelocerast, and Arctoasteroceras. The early Pliensbachian is either absent or is 

represented by 60 feet (18 m) of unfossiliferous beds. 

The late Pliensbachian is identified throughout about 620 

feet (189 m) of beds by such genera as Canavaria, Harpoceras (Harpoceratoides), Arieticeras, Prodactylioceras, Protogrammoceras, and Fuciniceras. Fanninoceras was collected from the lower 350 feet (107 m) of 

these beds (USGS Mesozoic Iocs. 28809, 28810) in association with the ammonites listed.

This association of Fanninoceras with ammonite 

genera of late Pliensbachian Age is confirmed by a similar association in the Izee-Suplee area southwest of John 

Day, Oreg. In that area, Fanninoceras has been collected with Fuciniceras in concretions and beds in the 

upper third of the Suplee Formation (USGS Mesozoic 

loc. 29223) and with Leptaleoceras and Arieticeras, from 

a 6-inch (15-cm) layer about 15-20 feet (4.5-6 m) above 

the base of the Nicely Formation (Lupher's loc. 125 in 

Imlay, 1968, p. C13, C15). Arieticeras, Paltarpites, and 

Lioceratoides are about 54 feet (16.5 m) above the base 

of the Nicely (USGS Mesozoic loc. 29218), and Leptaleoceras, Fuciniceras, Reynesoceras, and Arieticeras are 

about 20 feet (6 m) below the top of the Nicely (USGS 

Mesozoic loc. 27360). In that area, as well as in the Wallowa Mountains, Fanninoceras is associated with Prodactylioceras but not with Dactylioceras. The presence 

of Fanninoceras in beds of late Pliensbachian Age has 

recently been confirmed by Hans Frebold (written commun., 1975), who has found Fanninoceras associated 

with ammonites of early Pliensbachian to early Toarcian
66 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

Age on Maude Island in the Queen Charlotte Islands of 

British Columbia.

The Jurassic is represented in the Snake River Canyon at Pittsburg Landing, about 32 miles (52 km) south 

of the northeast corner of Oregon, by at least several 

hundred feet of tightly folded soft black shale, darkbrown graywacke, and some limestone, which rests unconformably on Upper Triassic clastic rocks (Vallier, 

1968, p. 247). An early to middle Callovian Age is shown 

by the presence of Lilloettia, Xenocephalites vicarius 

Imlay, and probable Grossouvria. Correlation with the 

Trowbridge Shale instead of the Lonesome Formation of 

the Suplee-Izee area of eastern Oregon is suggested by 

the absence of Pseudocadoceras.

Upper Jurassic beds that are lithologically and faunally distinct from any known elsewhere in Idaho and Oregon are exposed along both sides of the canyon of the 

Snake River for about 4 miles (6.4 km) just south of the 

northeast corner of Oregon (Morrison, 1961). These beds, 

named the Coon Hollow Formation by Morrison (1964), 

are about 2,000 feet (610 m) thick and consist mostly of 

hard, splintery, thin-bedded, black noncalcareous mudstone. They include also some beds of graywacke and 

chert-pebble conglomerate that are most common in the 

upper 400 feet (120 m). Their base is marked by a 

crossbedded sandstone that contains some pebbles derived from plutonic rocks and some large rounded limestone boulders. Their age is early Oxfordian, at least 

partly, as shown by the presence of Cardioceras (Scarburgiceras) martini Reeside about 400 feet (120 m) above 

their base (Imlay, 1964a, p. D6, D15, D16).

NORTHERN WASHINGTON

In the Cascade Mountains of northwestern Washington, the Upper Jurassic is represented in the lower part 

of the Nooksack Formation by Buchia piochii (Gabb) 

(USGS Mesozoic Iocs. 26253, 26267), by B. rugosa 

(Fischer) associated with B. mosquensis (von Buch) 

(USGS Mesozoic Iocs. 26249, 26265) (Popenoe and others, 1960, p. 1533), and by Buchia fischeriana 

(d'Orbigny) and B. cf. B. blanfordiana (Stoliczka) (Univ. 

California, Berkeley, Nos. 34709^11; Jeletzky, 1965, pi. 

3, figs. 2-4). In addition, B. concentrica (Sowerby) may 

be represented by specimens identified as Aucella erringtoni Gabb by T. W. Stanton (in Smith and Calkins, 

1904, p. 27). The presence of B. rugosa and B. mosguensis is significant because they are widely distributed 

from Washington northward to Alaska and the arctic region (Frebold and Tipper, 1970, p. 14-21; Frebold, 

1964a, p. 4; Imlay and Detterman, 1973, p. 11, 13, 19, 

26, 27). They are unknown, however, in the United 

States south of northern Washington, except for one occurrence of B, rugosa at the base of the Knoxville Formation near Paskenta, Calif.

Disconformably beneath the Nooksack Formation in 

the Mount Baker area of Washington, about 3,500 feet of 

volcanic beds and some interbedded marine slate and 

graywacke is exposed that Misch (1966, p. 103, 118) 

named the Wells Creek Volcanics. In the lower part of 

these volcanic rocks, a few fossils were obtained that 

were identified as Middle Jurassic or younger by J. A. 

Jeletzky (cited in Misch, 1966, p. 118). Lower Jurassic 

beds have not yet been identified faunally in northwestern Washington, but they may be represented near the 

Canadian border by nonvolcanic shaly to silty sandstone 

that Misch (1966, p. 103, 117) named the Bald Mountain 

Formation.

The Lower Jurassic is possibly represented in northcentral Washington by a fairly large ammonite that has 

evolute coiling and straight simple ribs, as does the Arietitidae of Sinemurian and Pliensbachian Age. This ammonite (USGS Mesozoic loc. 17460) was collected in the 

SEy4NEy4NEy4 sec. 21, T. 35 N., R. 26 E., about 2 miles 

northwest of Riverside in Okanogan County. This locality is nearly due south of Amy Lake, a little above the 

2,000-foot contour on a northward-draining slope. The 

specimen is preserved in a black, thin-bedded phyllitic 

noncalcareous rock that was obtained from a limestone 

unit 300 feet (90 m) thick. That unit underlies 200 feet 

(60 m) of gray limestone and dolomite and overlies the 

same thickness of amphibole-pyroxene.

The Jurassic is possibly represented about 30 miles 

(48 km) west-southwest of Riverside near Twist and 

Winthrop by the Twist Formation of Barksdale (1975, p. 

22-24, 65, 66, figs. 4, 8, 14, 15). That formation consists 

mostly of argillitic black shale that is interbedded with 

some dark volcanic siltstone and volcanic sandstone. It is 

at least 4,000 feet (1,220 m) thick, but its total thickness 

cannot be determined because of tight folding. It rests 

unconformably on gneiss, schist, and coarse-grained igneous rocks and is overlain unconformably by the Buck 

Mountain Formation of Early Cretaceous (Hauterivian 

to Barremian) age. Its exact age is uncertain because it 

has yielded only molds of belemnites and of fragments of 

cycads. Barksdale (1975, p. 22-24) suggested, however, 

that the Twist Formation is possibly of Early to Middle 

Jurassic age. Such an age is supported by the presence 

of an Early Jurassic ammonite in similar black rock near 

Riverside.

BRITISH COLUMBIA TO SOUTHERN ALASKA

Reasonably accurate interpretations of Jurassic history in California, Nevada, Washington, and Oregon require that the Jurassic sequences exposed there be compared and correlated with some of the best known 

sequences in westernmost Canada (Brown, 1968; Crickmay, 1930, 1962; Frebold, 1951a, b; 1964a, 1964d, 1966, 

1967a, 1967b; Frebold and Tipper, 1967, 1970, 1973; Fre-
COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 67

bold, Tipper and Coates, 1969; Jeletzky, 1950, 1953, 

1965; Jeletzky and Tipper, 1968; McLearn, 1929, 1932, 

1949; Tipper and Richards, 1976) and southern Alaska 

(Berg, Jones, and Richter, 1972; Grantz, 1960, 1961; Imlay and Detterman, 1973, p. 10, 11; MacKevett, 1969, 

1971; Richter and Jones, 1973). Such comparisons (fig. 

24) aid greatly in determining the time, duration, and 

geographic extent of major events in the Pacific Coast 

region during Jurassic time.

These sequences show that the Jurassic beds of British Columbia resemble those of southern Alaska in many 

respects. First, they contain essentially the same succession of ammonites and buchias. Second, they contain 

enormous amounts of volcanic sedimentary rocks of Sinemurian to middle Callovian Age but generally only minor amounts of volcanic sedimentary rocks of older and 

younger Jurassic age. Third, they include unconformities 

of early Bajocian, late Bathonian, and late Callovian 

Age. Fourth, the early Bajocian unconformity coincides 

in time with igneous intrusions, as in parts of southern 

Alaska (Detterman and Hartsock, 1966, p. 63, 64, 69, 71; 

Grantz and others, 1963, p. B58). Fifth, an unconformity 

of possible late Oxfordian to latest Tithonian Age in British Columbia coincides partly in time with an unconformity at the top of the Jurassic in the Cook Inlet region in 

southern Alaska (Imlay and Detterman, 1973, p. 10, 11, 

15, 16). Sixth, granitic intrusions that cut lower Oxfordian rocks in the Harrison Lake area of British Columbia 

could be of the same age as a granodiorite intrusion in 

Alaska's Wrangell Mountains (Imlay and Detterman, 

1973, p. 11).

The Jurassic sequences in British Columbia are likewise similar to those to the south in certain respects. Sequences in these two areas have the same general succession of ammonites and of species of Buchia, enormous 

amounts of volcanic material, granitic intrusions younger 

than early Oxfordian and possibly of Tithonian Age, and 

unconformities, or disconformities, of earliest Bajocian, 

Bathonian, late Callovian, and locally of late Kimmeridgian to Tithonian Age.

The Jurassic sequences in the westernmost conterminous United States differ from those in British Columbia in several respects. Faunally, they lack the pelecypod 

Buchia mosquensis (von Buch) except in northwestern 

Washington; lack ammonites of Bathonian Age except in 

eastern Oregon; lack the Callovian ammonite Cadoceras; 

contain the ammonites Macrocephalites and Peltoceras 

of earliest and latest Callovian Age, respectively; and 

contain ammonites of Tethyan affinities in beds younger 

than early Oxfordian. Lithologically, they contain much 

greater thicknesses of volcanic beds of Callovian Age and 

much more volcanic material in beds younger than Callovian. Orogenically, they include a widespread unconformity of early Pliensbachian Age that is not recognized 

in British Columbia except possibly in the western part

of Vancouver Island (Jeletzky, 1970, p. 22, 23). The most 

striking difference is that Tithonian beds in California 

and Oregon occur only in the westernmost parts of those 

States and represent mainly the upper part of that stage. 

In contrast, on the mainland of British Columbia, 

beds of Tithonian Age locally pass conformably downward into beds of Kimmeridgian and Oxfordian Age (Jeletzky and Tip, 1968) and occur at many places throughout the central and southern part of the province as far 

east as westernmost Alberta (Frebold and Tipper, 1970, 

p. 15). Evidently, in latest Jurassic time, marine waters 

spread much farther east in British Columbia and apparently also in Washington than in areas to the south. 

This eastward spread is related to the presence of certain 

major structural features (Jeletzky, 1970; Jeletzky and 

Tipper, 1968, p. 3-5, 71^83, fig. 7 on p. 76). These features include several southeast trending sedimentary 

troughs separated by land areas (TippeV and Richards, 

1976, p. 8, 41). Presumably, the sea that occupied these 

troughs once extended eastward to the sea that occupied 

the western interior region from early Bajocian to late 

Oxfordian or early Kimmeridgian time.

WESTERN INTERIOR REGION OF THE UNITED STATES

MONTANA AND NORTH DAKOTA

Marine Jurassic beds in Montana and North Dakota 

(fig. 25) are of early or middle Bajocian to late Oxfordian 

Age (Reeside, 1919; Crickmay, 1936; Imlay, 1948, 1953a, 

1954, 1962b, 1967b; J. A. Peterson, 1954a, 1954b; Swain 

and Peterson, 1951, 1952; Loeblich and Tappan, 1950a, 

1950b; Carlson, 1968, p. 1973-1979; Schmitt, 1953). 

They rest unconformably on beds of Mississippian to 

Triassic age (Imlay, Gardner, and others, 1948; McKee 

and others, 1956; J. A. Peterson, 1972, p. 186); and are 

overlain gradationally by the continental Morrison Formation of Kimmeridgian to possible early Tithonian 

(Portlandian) Age (Yen, 1952; Peck, 1956; Mitchell, 1956). 

The Morrison Formation thins northward, disappears 

near the Canadian border, and is overlain unconformably by the Kootenai Formation of Aptian and possibly 

also Neocomian Age (Cobban and Reeside, 1952, p. 1016; 

McGookey and others, 1972, p. 192, 193, 195).

The Nesson Formation is the oldest known Jurassic 

formation in Montana and North Dakota. It occurs only 

in the subsurface of the Williston basin between central 

Montana and central North Dakota and consists of three 

lithologically distinct members (Nordquist, 1955, p. 104- 

106; Rayl, 1956, p. 36-38). The oldest, the Poe Evaporite Member, averages about 120 feet (36 m) in thickness 

and consists of massive salt or gypsum overlain by interbedded gypsum, dark-red shale and some beds of
68 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

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'Piper Formation divided into (ascending): Tampico Shale Member (Bajocian), Firemoon Limestone 

Member (Bajocian), and Bowes Member (Bathonian) of Nordquist (1955), all herein adopted for 

U.S. Geological Survey usage.

Wesson Formation of Ncxdquist (1955) with Nordquefs three members (ascending), Poe Evaporite 

Member, Picard Shale Member, and Kline Member, herein adopted for U.S. Geological Survey 

usage.

A. Southwestern Alberta to central Montana.
COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 69

Big Snowy Mountains ' 

near Heath and Piper, 

7 miles southeast of 

Lewistown, Mont .

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32 miles east of 

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in subsurface

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passes westward into 

sandy limestone

F remoon Limestone 

Memberl 70ft (21 m) 

vLimestone, oolite /

fampicoShele Member1 

85 ft (26 m) Red shale 

and gypsum

Possibly absent

/ Kline Member 2 \ 

145 ft (44m) 

Dolomite. Limestone

Picard Shale Member^ 

Red shale 40 ft ( 12m)

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subsurface

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Characteristic fossils 

in western interior of 

United States

Buchia concentrica

Cardioceras spp.

«

Cardioceras cordiforme

Scarburgiceras and 

Pavloviceras

Quenstedtoceras collieri

Kepplerfces maclearni

K. aff. AC. tychonis

K. subitus

K. costidensus

Warrenocerascodyense

Paracephalites 

sawtoothensis

Gryphaea 

nebrascensis

Gryphaea 

impressfmarginata

Sohlfces, Parachondroceras, 

and Gryphaea planoconvexa

Megasphaeroceras, Spiroceras, 

and Stemmatoceras

Chondroceras cf. C. allani 

and Stemmatoceras

B. Central Montana to southern Saskatchewan.

FIGURE 25.—CORRELATIONS AND COMPARISONS OF JURASSIC ROCKS IN THE WESTERN INTERIOR REGION FROM 

SOUTHWESTERN ALBERTA THROUGH CENTRAL MONTANA TO SOUTHERN SASKATCHEWAN. Vertical lines indicate that 

strata are missing; diagonal lines indicate lack of fossil data; wavy lines indicate unconformity or disconformity. Column numbers refer to 

locations shown on figure 20.
70 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

Stage

Ammon Quad., Idaho/12 

Wolverine Canyon, in sees. 

27 and 28, T. 1 N., R. 39 E.; 

Willow Creek at Big Bend,in 

sees. 17-20, T. 1 N., R. 40 E.

Red Mountain,ldaho.'3

southwest side,

SWVi sec. 33, T. 4 N., R.44 E.,

Teton County

Lower Slide Lake, ** 

north side, about 16 miles

northeast of 

Jackson, Wyo.

Green River Lakes, 15

sec. 29, T. 39 N., R. 108 W.,

northwest end of Wind River

Mountains, Sublette County,

Wyo.

Red Creek, 16 

NEVi sec. 7, T. 6 N., R. 3 W., 

Fremont County, Wyo.

Overlying beds Lower Cretaceous Lower Cretaceous Lower Creteceous Lower Cretaceous Lower Cretaceous

Tithonien

Kimmeridgian

Oxford! en

Cello vian

Bethonian

Bajocian

Toarcian

Pliensbachian

Sinemurien

Probably absent 

Contact shown 

as a fault 

by Mansfield 

1952, pi. 1)

/Stump Sandstone \

/ Shele 65 ft (20 m). M

Sendstone 145 ft (44 m)

Preuss Sendstone 1043 ft(318rnT| 

Sendstone, red 600 ft (183 miLimestone, sendy 193 ft (59 m). I 

Sandstone, red 250 ft (76 m)

Morrisen Formation 

370 ft (112m) 

Varicolored shale. 

Some beds of sandstone 

and dense limestone

Morrison Formation 

Varicolored to gray 

silty shale and 

sandstone. Changes 

laterally into white 

sandstone

Gleuconitic sandstone, 

red 50 ft (15m) 

Siltstone glauconitic, 

greenish-gray 23 ft (7 m)

Limestone above 

quartzite 53 ft (16 m)

Giraffe Creek Member 

295 ft (90 m)_____

Leeds Creek Member 

1145 ft (349m)

'VVatton Canyon Member 

151 ft (46 m)____

Boundary Ridge Member 

187 ft (57 m) 

Red siltstone above 

silty limestone

Rich Member 380 ft 

(116 m) Limestone, shely

Sliderock Member 140 ft 

(33 m) Limestone, 

massive at base

ypsum Spring Member 

430ft?(131 m) 

Limestone, leminated, 

silty, sandy, dense, 

or vuggy 260 ft. 

Siltstone, red 160

Nugget Sandstone1 

1000-1500 ft (305-457 m)

Underlying beds

Preuss Sandstone 

68 ft (21 m) Siltstone, 

red, limy, above gray 

siltstone

Giraffe Creek Member 

26 ft (5 m)_______

Leeds Creek Member 

471 ft (144m)

Watt on Canyon Member^ Jj 8 

75 ft (23 m)_____

BoundaryRidge Member 

36 ft (11 m) Siltstone, 

red to green

Rich Member 208 ft 

(62 m) shely limestone

Sliderock Member

69 ft (21 m\ Limestone,

medium-bedded

Gypsum Spring Member 

12 ft (3.5m) 

Limestone breccia

Sandstone,green, grey, 

glauconitic 200 ft (61 m), 

Some siltstone. Bentonite 

bed at base

Sandstone, silty, 

y green 13.5 ft (4m) /

Siltstone, sandy, green 

to pink 26.5 ft (8m)

Shale, gray, limy 

163 ft (50 m)

Limestone, oolitic 

57 ft (17m)

Mostly red siltstone. 

Gray, shely limestone 

at top. 38 ft (12 m)

Shely limestone 

gray. 85 ft (26 m)

Limestone, oolitic, 

medium-bedded to 

shaly 21 ft (7 m)

Shale,silty.greento gray 

100 ft (30 m). Sandstone 

green, pebbly at bese. 

248 ft (63 m)

8|*

Shele, limy, grey, 

Gryphaea common. 

230 ft (70 m)

Limestone dense to 

oolitic 20 ft (6m)

Redwater Shele Member 

148 ft (45 m) Sandstone, 

gleuconite, some 

limestone, overlying 

silty to sandy shale

iulett Sandstone 

Member 20 ft (6 m)

Stockede Beaver Shele 

Member 93 ft (27m)

Limestone oolitic and 

sandy shale. 67 ft (21 m)

Shale, red 

40 ft (12m)

Piper Formation 

54 ft (17m) 

Shale, red. Pebbly 

limestone lens et bese

Shele and limestone 

33 ft (10.5m)

Limestone, massive, 

dense, gray, glauconitic 

14 ft (4 m)

Gypsum Spring Formation 

46 ft (14m) 

Siltstone, red 15ft. 

Limestone, brecciated 28 ft. 

Siltstone, red.soft 3 ft

Gypsum Spring Formation 

75 ft (23 m)

Red siltstone and shale. 

Gypsum messes and some 

dense limestone

_,,___... ....

254 ft (80m) 

Gypsum, dolomitic limestone, 

and red shele 107 ft. 

Gypsum, massive 114ftRed sand' Siltstone 33 ftNugget Sandstone1 

255-300 ft (78-92 m)

Nugget Sandstone1 

150 ft (46m)

Triessic

'In this author's opinion.

A. Ammon area, Idaho, to Red Creek, Wyo.
COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 71

Southeast of Hyattville

3Va miles,in sec. 16,

T. 49 N., R. 89 W.,

Big Horn County,Wyo.

Lower Cretaceous

Morrison Formation 

180 ft (55m)

Upper part:

Gray pebbly sandstone, 

brown conglomerate.and 

carbonaceous shale

Lower part: 

Varicolored shale 

and brown to gray 

sandstone

18

Muddy Craek area,

sees. 2 and 11.T. 49 N.,

R. 83 W., Johnson County,

Wyo.

Lower Cretaceous

Morrison Formation. 

185 ft (56m)

Thin beds of sandstone 

and siltstone 

interbedded with 

varicolored claystone

Gypsum Spring Formation 

170 ft (51 m) 

Red shale, dolomitic 

limestone.and chert 

above massive gypsum 

xTriassic

Gypsum Spring Formation 

106 ft (32m) 

Limestone and red shale 

above limestone, 

breccia,and gypsum

Triassic

19

Bush Canyon, 2'/2 miles

north of Hulett, 

Crook County, Wyo,

Lower Cretaceous

Morrison Formation 

100 ft (30m)

Mostly claystone, 

greenish-gray

Gypsum Spring Formation 

6? ft (22 m) 

Limestone, chert,and red 

shale overlying massive 

gypsum

Triassic

East of Newcastle, 20 

SE'/i sec. 7,T. 45 N., 

R. 60 W., SWVi sec. 23,

T. 43 N., R. 61 W., 

Weston County.Wyo.

Lower Cretaceous

Morrison Formation

110 ft (34m)

Mostly claystone,

greenish-gray to

grayish-red.

Some beds of limestone

and sandstone

/ Windy Hill \ 

/WindyHill Sandstone /Sandstone Menrjber\

Member 30 ft (9 m)

Windy Hill Sandstone\'

Redwater Shale Member 184 ft (56m) 

Fissile claystone. 

Some sandstone in 

upper 41 ft (13m)

Redwater SheleMember 175 ft (53 m) 

Mostly silty shale. 

Some sandstone in 

upper 13 ft (4m)

fRedwater Shale Member

160 ft (49 m)

Mostly grey shale. Some 

[sandstone and limestone

tedwater Shale 

Member 158 ft (48 m)

Redwater Shale Member 174 ft (53 m) 

Mostly siltstone and 

shale.Some limestone

Mostly gray shale. Cardioceras cord/forme

Some limestone Scarburgiceras and Pavlovicaras

Pine Butte Member 

5ft (1.5m)

Lak Member 42 ft 

(13m) Red siltstone 

and sandstone

Lak Member 75 ft 

(23 m) Red siltstone 

and sandstone

HulettSandstone 

Member 62 ft (19m)

HulettSandstone 

Member 27 ft (9 m)

Hulett Sandstone 

Member 82 ft (25m)

Hulett Sandstone 

Member 71 ft (22 m) 

Stockade Beaver Shale 

Member 63 ft"(20 m)

Stockade Beaver 

Shale Member 21 ft

Stockade Beaver Shale 

Member 90 ft (27m)

Stockade Beaver Shale 

Member 23 ft (7 m)

'Chert pebbles in 

basal sandstone

Limestone, oolitic 

2 ft (0.6 m)

canyon springs ban en 

>ne Member 25 ft

Sohlites, Parachondrocaras, 

and Gryphaea planoconvexa

Megasphaerocaras.Spiroceras 

and Stemmatoceras____

Chondroceras cf. C. alteni 

and Stemmatoceras____

Aaypsum Spring " \ 

/ Formation 8-12 ft (3.7 m)\ 

Gypsum, " " nrr massive

Triassic

21 Minnekahta area,

sees. 11, 33, and 34,

T. 7S., R. 3 E., Fall River

County, S.Dak.

Lower Cretaceous

Morrison Formation

65-100 ft (20-30m)

Claystone, greenish-gray,

limy.

Many limestone beds.

A few sandstone beds

Triassic

Characteristic fossils

in western 

interior region

B. Hyattville area in north-central Wyoming to Minnekahta area, South Dakota.

FIGURE 26.—CORRELATIONS AND COMPARISONS OF JURASSIC ROCKS IN THE WESTERN INTERIOR REGION FROM 

SOUTHEASTERN IDAHO TO SOUTHWESTERN SOUTH DAKOTA. Vertical lines indicate that strata are missing; diagonal lines 

indicate lack of fossil data; wavy lines indicate unconformity or disconformity. Column numbers refer to locations shown on figure 20.
72 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

Stage

Overlying beds

Tithonian

Kimmeridgian

Oxfordian

Callovian

Bathonian

Bajocian

Toarcian

Pliensbachian

Sinemurian

Underlying beds

22

Burr Fork,

sees. 21,22,and27,T. 1 N.; R. 2 E., Salt Lake County

Utah

Lower Cretaceous

Morrison(?JFormation 

102 ft (31 m) 

Red beds. Some algal 

limeatone. Conglomerate 

at base

?„

""PrS JssSSl nJstoni

1020 ft (311 m). Red, silty. 

Limestone unit near base

Giraffe Creek Member

200 ft (61 m)_____

Leeds Creek Member 

1520 ft (464m)

'Watton Canyon * 

Member 348 ft (107m) 

Boundary Ridge 

Member 102 ft (31 m) 

Yellow, silty 

or oolitic limestone

Rich Member 391 ft 

(119 m).Shaly limestone 

Sliderock Member 

150ft(46 m) Limestone, 

medium-bedded,

OTtaJ

Gypsum Spring 

Member 140 ft (33m) 

Siltstone, soft, 

reddish-brown

Nugget Sandstone1 

830 ft (253 m)

23

Near Peoa and Oakley, 

cs.11and14,T. 1 S., R. 5 E. 

sec. 1,T. 1 S., R.6E., 

Summit County .Utah

Lower Cretaceous

Morrison Formation 

440 ft (134m) Variegated 

shale and white 

sandstone. Some 

fresh-water limestone

Redwater Member 

182 ft (65m) 

Mostly gray shale. 

Some green sandstone

. _ _ - _ endstone 

1196 ft (365m). Red, soft silty, even-bedded

Giraffe Creek 

Member 82 ft (25 m)

Leeds Creek Member 

776 ft (237 m) ___

Wattpn Canyon Member 220 ft (69m)

Boundary Ridge Membei 

107 ft (33 m) Limestone, 

shaly to sandy. 

Some redbeds

Rich Member 125 ft 

(38 m) Shaly limestone

Sliderock Member

47 ft (14 m) Limestone,

medium-bedded,

saQdybsjsally

Gypsum Spring Member 

22 ft (7 m)

Glen Canyon Sandstone 1 

1290 ft (394m)

24

Duchesne River near Hanna,

sees. 3, 4, 9, and 10, T. 1 S.,

R. 8 W., Duchesne County,

Utah

Lower Cretaceous

Morrison Formation 

700 ft (213m) 

Sandstone, siltstone, 

and shale. Mostly

§

rayish-white. 

ome beds variegated. 

Some pebbly lenses

Redwater Member 

137 ft (45m) 

Mostly gray shale. Some 

limestone and sandstone

PreUss Sanastone 

669 ft (204m). Red, silty, 

aft. even-bedded

Giraffe Creek Member 

165 ft (50m)_________

Leeds Creek Member 

280 ft (85 m)

Watton Canyon \ 

Member 104 ft (32 m)

Boundary Ridge Member 

68 ft (21 m) Red 

siltstone and yellow, 

sandy limestone___

Rich Member 91 ft 

28 m) Shaly Limestone 

Sliderock Member 42 ft

Glen Canyon Sandstone1 

1200 ft (366m)

25

Lake Fork,

sees. 1 and 2, T. 1 N., R.5W., 

Duchesne County, Utah

Lower Cretaceous

Morrison Formation 

700 ft (213 m)

Redwater Member 

98 ft (30 m) Gray shale. 

Some glauconitic 

sandstone

reuss Sandstone 

858 ft (262 m). Red, soft, 

iltv. even-bedded

Watton Canyon Member

1Q9ft<33 ml_______

Giraffe Creek Member 

49 ft (15m)________

Leeds Creek Member 

114 ft (35m)_____

Boundary Ridge Member 

30 ft (9 m) Red siltstone 

and sandy limestone,

Rich Member 109 ft 

(33 m) Shaly limestone

Sliderock Member 

32 ft (10 m) Limestone 

medium-bedded, sandy 

some crgsjbeddi

Glen Canyon Sandstone1 

1190ft (363m)

26

Whiterocks Canyon,

secs.18and19,T.2N., R. 1 E.

Uintah County, Utah

Morrison Formation 

Gray siltstone, sandstone, 

and pebbly beds. 

Poorly exposed

Redwater Member 

113 ft (34m) Limestone, 

>andy,oolitic, glauconitic 

Lower third mostly 

shale. Pebbles at base

Curtis Member 55 ft

Entrada Sandstone 

240 ft (73 m). Sandstone 

crossbedded, fine-grained, 

red to gray________

Siltstone, greenish-gray

76 ft (23 m)_______

Gypsum. Red to. green 

siltstone. 191 ft (58 m)

' Limestone, shaly at 

base, 17 ft (5 m)

Red siltstone. Some 

sandy limestone 

21 ft (6m)

Shaly limestone 

40 ftJ12 m)

Glen Canyon Sandstone1 

970 ft (326m)

'In this author's opinion.

A. Burr Fork to Whiterocks Canyon, Utah.
COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 73

Dinosaur Quarry, 27

center WV2 sec.26, T. 4 S.,

R. 23 E., Uintah County,

Utah (Pipiringos.

unpublished data)

28

Miller Creek,

SWVi sec. 27, f. 4 N.,

R. 101 W.,Moffat County,

Colo.

29 Elk Creek area, SWVi sec 

33, T. 1S.,R.84W.;NWVi 

sec. 4, T. 2 S., R. 84 W., 

Routt County, Colo.

Frantz nCreeek,

SEVi sec. 32, T. 4'N.,

R 82 W.,Grand County,

Colo.

31

Hahns Peek.NEVi sec. 9, 

T. 10 N., R. 85 W., 

Routt County, Colo.

Characteristic fossils

in western 

interior region

Cretaceous Cretaceous Cretaceous Cretaceous Cretaceous

Morrison Formation 

750 -800 ft (244 m) 

Gray sandstone, 

variegated mudstone, 

shale and sandstone, 

and some pebbly lenses

Morrison Formation

Morrison Formation 

400 ft±( 124m) 

Variegated beds

Morrison Formation 

380ft±(119m) 

Variegated mudstone. 

Some sandstone and 

limestone beds.

Morrison Formation 

267 ft±(81 m) 

Variegated claystone 

and freshwater 

limestone 192 ft (58 m) 

Sandstone, gray 

75 ft (23 m)

Windy Hill Sandstone Mem; 

berSundance Formation

Redwater Member 

125 ft (38m)

Curtis Member 72

Windy Hill SandstoneN, / 

Member 8 ft (2.4 I

Redwater Shale 

Member 179 ft (54m)

12 ft (3.6m)

Entrada Sandstone 

137 ft (45m) 

Crossbedded, white

Entrada Sandstone 

120 ft (36m)

Cairoe! Formation 

103 ft (31 m) 

Red beds, soft. 

Chert pebblea basalhy

Carmel Formation 

SOJtOmj,

Windy Hill Sandstone\/ 

Member 9 ft (2.7 m)

Windy Hill Sandstone \/ Windy Hill Sandstone \

Pine Butte Member > 

62 ft (19 m)

/ Pine Birttel?) \ 

Member 28 ft (9 m)

Canyon Springs 

Sandstone Member. 

188 ft (60m) Massive, 

pink to gray. Chert 

pebbles basal ry.

Glen Canyon Sandstone1 

670 ft (204 m)

Glen Canyon Sandstone1 

840 ft (256 m)

Buchia concentrica

Member 1 ft Member

Cardioceras spp.

Lak{?) Member 

47 ft (14m) 

Gray sandstone and 

shale.________

Canyon Springs 

Sandstone Member. 

166 ft (57 m) 

Massive, buff to 

pink. Chert pebbles 

basal ly

Redwater Shale Mem be 

m)

Cardioceras cord/forme

Scerburgiceras and Pavtoviceras

Quenstedtoceras collier/

Pine Butte Member 

30 ft (9 m)

Canyon Springa 

Sandstone Member 

60 ft (218 m) 

Maasive, gray to 

pink, fine-grained, 

crossbedded. Chert 

pebbles basal ry.

Kepplerites maclearni

K. aff. KTtvchonis

K. subitus

K. costidensus

Warrenoceras codyens >

Paracephalites 

sawtoothensis

Gryphaea

nebrascensis

Gryphaea 

impressimarginata

Sohlites, Parachondroceras, 

and Gryphaea p/anoconvexa

Megesphaeroceras, Spiroceras, 

and Stemmatoceras_____

Chondroceras cf. C. allani 

and Stemmatoceras___

Triassic Triassic Triassic Triassic-Permian Triassic

B. Dinosaur Quarry, Utah, to Hahns Peak, Colo.

FIGURE 27.—CORRELATIONS AND COMPARISONS OF JURASSIC ROCKS IN THE WESTERN INTERIOR REGION FROM 

NORTH-CENTRAL UTAH TO NORTH-CENTRAL COLORADO. Vertical lines indicate that strata are missing; right-diagonal lines 

indicate strata not exposed; left-diagonal lines indicate lack of fossil data; wavy lines indicate unconformity or disconformity. Column 

numbers refer to locations shown on figure 20.
74 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

Stage

Tfthonian

Kimmeridgian

Oxfordian

Callovian

Bathonian

Bajocian

Toarcian

Underlying beds

32

Monks Hollow,

sec. 32, T. 4S., R. 5E., and

sec. 5, T. 5 S., R. 5 E.,

Utah County, Utah

Morrison Formation 

1240 ft (378 m) 

Variegated shale 

interbedded with red 

mudstone and sandy 

shale and red to gray 

sandstone

Some conglomeratic 

sandstone at top

Light brownsiltetone^X 

ome gray sandstone and \ 

shale 250 ft(76m)

Preuss Sandstone 

1270 ft (387m). Brown 

even-bedded sandstone

Giraffe Creek Member 

288 ft (88 ml______

Leeds Creek Member 

275 ft (84 m)

r Watton Canyon " 

Member 305 ft (93 m)

Boundary Ridge 

Member 57 ft (17 m) 

Red siltstone above 

silty-sandy limestone

Rich Member 123 ft 

(37 m) Limestone, shalv

' 5 Sliderock Member 91 ft 

1 e (28 m). Limestone, 

og thin to medium-bedded,!

Gypsum Spring 

Member 49 ft (15m) 

Red to green siltstone 

and brecciated or 

laminated limestone

Nugget sandstone1 

1450 ft (442m)

Triassic

33

Nepni-Levan area, 

west side of Gunnison 

Plateau, Juab County,

north-central Utah

1874ft n«« ml

Sandstone, shale, and 

limestone 1500 ft (457m) 

Red shale and limestone 

800 ft (228 m) 

Limestone, gray 800 ft

"gKLimestone, medium? 

bedded. 100 ft (30 m)

Limestone, sandy to 

oolitic, yellow 

Some red siltstone. 

100 ft (30m)

Limestone, shaly

10&-?flDft<fi1 ml

Limestone, mediumthick-bedded, sandy, 

oolitic, 50-80 ft '15-24.

Siltstone, redVJ 

soft 1-10 ft {3 mi

Nugget Sandstone1 

100 ft (30m) 

incomplete

Triassic

34

Gunnison-SalinaRichfield area,

Sevier and Sanpete

Counties, Utah

Morrison ? Formation 

848 ft (259 m) 

Interbedded, gray to 

white conglomerate 

and sandstone and 

red to gray shale

Twelvemile Canyon 

Member 1600-2700 ft 

(823 m). Red to gray 

shale. Sa[t at top

35

Buckhorn Wash area,

south of Cedar Mountain

InT. 19 S., R. 11 E.,

Emery County, Utah

Morrison Formation 

750 ft (229 m) 

Variegated mudstone, 

siltstone,and sandstone

Locally some thin 

beds of limestone

_..-_oa Sandstone 

425 ft (129 m). Red, earthy 

sandstone and siltstone

Variegated shale and 

sandstone. Some 

gypsum.182 ft (56 m)

Sandstone and 

limestone. 29 ft (9m)

Sandy shale and 

sandstone, gray, 

ripple-marked 

47 ft (14)

Limestone, sandy and 

sandstone. 66 ft (20 m)

Page Sandstone 

100 ft (31 m) Massive, 

crossbedded, gray. Chert 

' lies at base

Navajo Sendstone1 

380 ft (116m)

Keyenta Formation'' 

190 ft (88 m)

Wingate Sandstone 1 

320 ft (98 m)

36

Black Dragon Canyon, 

sec.5and6,T. 22 S., R. 14E., 

Emery County, Utah

Morrison Formation 

600 ft (183m) 

Variegated mudstone 

siltstone and sandstoneBecomes less sandy upward 

Massive gypsum at base

Entrada Sandstone

405 ft (123m). Red.earthy

to arav.and crossbedded

.S

«

II

F h

Sandstone, siltstone, 

and shale, red 

125 ft (38 m)

Sandstone, shaly to 

thin-bedded.and 

mudstone, gray to 

red. Some limestone. 

105 ft (32 m)

Page Sandstone 

30-35 ft (11 m). Massive, 

crossbedded, gray. Chert 

pebbles at^base

Navajo Sandstone bands 1

520 ft (159m)

Kayenta Formation 1 

240 ft (103 m)

Wingate Sandstone 1 

323 ft (99 m)

'In this author's opinion.

A. Monks Hollow to Black Dragon Canyon, Utah.
COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 75

37

San Rafael River,

sees. 4,9, and 18,

T. 24 S., R 16 E.,

Emery County, Utah

38 Dewey Bridge,

sec. 8, T. 23 S., R. 24 E.,

Grand County,Utah

Valley of John Brown Cree

sees. 31 and 32, T. 51 N.,

R. 19 W., and sec. 5,

T. SON., R. 19 W., 

Mesa County, Colo.

Slick Rock area, 40

sees. 13, 25, 32 and, 36,

T. 44 N., R. 19 W., and

sec. 30, T. 44 N., R.18W.,

San Miquel County, Colo.

41 McElmo Canyon area7

sec. 26, T. 36 N., R. 18 W.,

Montezuma County,

Colo.

Characteristic fossils

in western 

interior region

Lower Cretaceous

Morrison Formation 

600 ft±(183 m) 

Variegated shale, 

siltstone, and sandstone. 

Some conglomerate. 

Locally gypsum and (or) 

limestone at base

Lower Cretaceous

Morrison Formation 

650ft±(201 m)

Upper part: 

Variegated silty to 

limy shale. Some 

thin dense limestone 

and chert pebble 

conglomerates.

Lower part: 

White to gray crossbedded sandstone and 

red to gray claystone.

Lower Cretaceous

Brushy Basin Shale 

Member 333ftfl04m) 

Mostly siltstone 

and claystone, 

soft, bentonrtic, 

and variegated

Salt Wash Sandstone 

Member 337ft(l03m) 

Sandstone- tedgy 

brown.to pink, 

interbedded with 

soft siltstone 

and claystone

.2 

«

I

Lower Cretaceous

Brushy Basin Shale

Member

350ft(110m)

Variegated

bentonrtic

mudstone

Lower Cretaceous

Brushy Basin Shale 

Member 

150-300 ft (91 m)

Salt Wash Sandstone 

Member 300 ft(91 m) 

Interbedded 

sandstone 

and mudstone, 

gray to brown

§5 

o£L

c*

.88

b£

Westwater Canyon 

Sandstone Member 

72-200 ft (61 m)

Recapture Shale 

Member 

0-200 ft (61 m)

Salt Wash Sandstone

Member

0-200 ft (61 m) Buchia concentrica

Contact locally 

disconformable and 

locally gradatkmal

Contact gradat tonal 

at most places

Summervilte Formation^ 

82 ft (25 m) N

Curtis Formation 75 ft

^fraSaSarlSstone^^""^ 

435 ft (133 m). Tan, crossbedded. Some earthy

.S

E

Red silty sandstone, 

sand,shale,and 

mudstone. Some 

gypsum 71 ft (22 m)

Sandstone, red to 

gray, thin-bedded. 

Some limestone. 

Chert pebbles locally 

at base. 58 ft (18m)

Page Sandstone 5-10 ft 

Chert pebbles at base

Slick Rock Member 

273 ft (83 m)

Dewey BridgeMember

54 ft (16m)

Chert pebbles basal ly

Slick Rock Member 

225 ft (69m) 

Massive sandstone, 

white to orange

Dewey Bridge 

Member 56ft U 7m) 

;hert pebbles basally

s

is

Sandstone 31 ft

Slick Rock Member 

103 ft (31 m) 

Massive sandstone

Dewey Bridge 

Member 32 ft (10 m)

Slick Rock Member 

70-80 ft (24 m) 

Sandstone, pink 

brown, white 

crossbedded

DeweyBridgeMembet 

30 ft (9 m) Kepplerites maclearni 

K. aff. AC. tychonis

K. subitus

K. costidensus

Narreno csras codyense

Paracephalkes 

sawtoothensis

Gryphaea

nebrascansis

Gryphaea 

impressimarginata

Sohlites, Parachondrocaras, 

and Gryphaea planoconvexa

Megasphaeroceras, Spirocaras, 

and Stemmatoceras______

Chondroceras cf. C. allani 

and Stemmatoceras

Navajo Sandstone1 

100 ft (30 m) 

incomplete

Navajo Sandstone1 

215 ft (66m)

Navajo Sandstone'1 

0-500 ft (153m)

Navajo Sandstone1 

0-420 ft (128m)

Navajo Sandstone 1 

300 ft (91 m)

Kayenta Formation 1 

320 ft (98 m)

Kayenta Formation 1 

180-220 ft (55-70m)

Kayenta Formation 1 

160-300 ft (49-92 m)

Kayenta Formation 1 

subsurface only 

30 ft (9m)

Not exposed Wing ate Sandst one 1 

300 ft (91 m)

Wingate Sandstone1 

280-300 ft (86-91 m)

Wingate Sandstone1 

275 ft (84 m)

Wingate Sandstone1 

775-790 ft (236-241 m)

B. San Rafael River, Utah, to McElmo Canyon, Colo.

FIGURE 28.—CORRELATIONS AND COMPARISONS OF JURASSIC ROCKS IN THE WESTERN INTERIOR REGION FROM 

NORTH-CENTRAL UTAH TO SOUTHWESTERN COLORADO. Vertical lines indicate that strata are missing; right-diagonal lines 

indicate strata not exposed; left-diagonal lines indicate lack of fossil data; wavy lines indicate unconformity or disconformity. Column 

numbers refer to locations shown on figure 20.
76 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

to 

<o 'i

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Stage

Overlying beds

«

1—>D

1

a

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Middle Jurassic

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Callovian

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Pliensbachian

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Hettangian

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Underlying beds

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Cedar City, sees. 7 

and 18, T. 38 S., R. 11 W; 

sees. 11 and 14, T. 37 S., 

R. 11 W., Iron County, Utah

\ \ Formation mel. 

(m) (323-375 /ft230

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sees. 12, 13, 24,and25, 

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Brown Canyon , 

sees. 7,1 9, and 21, T.. 41 S., 

R. 5 W., Kane County ,Utah

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270 ft (82 m)

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'In this author's opinion.

A. Gunlock to Brown Canyon, Utah.
COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 77

Little Bull Valley, 47 

sees. 27 and 38,T. 38 S.,

R. 3 W., 8 miles

southwest of Cannonville,

Kane County, Utah

Pine Creek/ 43

SWVi sec. 29 and SE%

sec. 30, T. 34 S., R. 3 E.,

3 mi. north of Escalante,

Garfield County, Utah

Sand Valley, 49

sees. 30 and 34, T. 42 N.

R. 7 E., 13 miles

northwest of Page.

Coconino County, Ariz.

Page, 50 

SWVi sec. 19,1.41 N.,

R. 9 E., 

Coconino County, Ariz.

Big Hoi low Wash, 51 

sees. 7, 11,and12,T. 39 S., 

R. 6 E., and sec. 9,

T. 39 S., R. 7 E., 

Kane County, Utah

Cow Springs, 52

4 miles east of

trading post 

Coconino County Ariz Stage

Cretaceous Lower Cretaceous Cretaceous Lower ? Cretaceous Lower ? Cretaceous Cretaceous

Inti

to

§_

"eg 

o£ 

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5

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Salt Wash 

Sandstone Member 

149ft. Sandstone, 

crossbedded, 

pebbly______

Lower

member 140 ft 

Sandstone.flatbedded

/Entrada Sandstone \ 

493ft(150m)Flat-bedded

(314 m). Crossbedded, 

white 228ft.Flat-bedded, 

shaly 434 ft.Flat, 

thick beds 369 ft

Morrison Formation 

182 ft (56 m)

Sandstone, gray to green. 

Pebble lenses

' Entrada Sandstone \ 

445ft (135m). Gray, 

mostly crossbedded

Sandstone at Romana 

Mesa 115 ft (35m)

Entrada Sandstone 

640 ft (195m). White to 

red, mostly crossbedded

Upper member 

116 ft (35m)

Salt Wash

Sandstone

Member 363 ft

(111 m)

Lower member 

10 ft (3m)

J andstone at Romana 

Mesa 44 ft (13m)

Entrada Sandstone 

830 ft (253 m). Upper 

537 ft flat-bedded

Tithonian

Ommeridgian

Oxfordian

/ Entrada Sandstone \ 

773 ft (235 m) 

Mostly crossbedded

Callovian

. Tongue of Page /

\ Sandstone /

\25ft (8m) /

Winsor Member 

673 ft (205 m). Mostly 

sandstone-siltstone. 

16 ft of limestone 

155 ft above base

jypsum and , 

imestone 45 ft(14 mj

Carmel Formation 

upper member, 372 ft 

(134m). Gypsum and 

red to gray, silty 

sandstone 278ft. 

Limestone, gray 94 ft

Carmel Formation 

jpper member 433 ft 

137 m). Flat-bedded red 

shale and sandstone 166 ft 

>ossbedded sandstone 

53ft.Same as top unit 214ft

Carmel Formation 

upper member 255 ft 

(77 m). Sandstone and 

siltstone.flat-bedded 

to crossbedded, pink 

to gray

Carmel Formation 

205 ft (61 m)

Carmel Formation 

upper member 

188 ft (59m) 

Sandstone and mudstone, 

reddish-brown to gray. 

Chert pebbles at base

.25 ft (8m) 

Banded member 

V46ft(14m) , 

Limestone member 

138 ft (42m) Basal 

: 8 ft is red shale

Thousand Pockets Tongue 

of Page Sandstone 

72 ft (22 m). Red to gray, 

flat-to cross-bedded

Thousand Pockets Tongue 

of Page Sandstone 

104 ft (31 m). Light 

gray, crossbedded

Judd Hollow Tongue of

Carmel Formation 

iv 74 ft (23 m). Sandstone,/ 

\shale. sh some limestone/

Hai

Judd Hollow Tongue 

of Carmel Formation . 

V 40 ft (12m) _____/

Page Sandstone 

183 ft (56 m) 

Crossbedded, orange to 

brownish-red. Pebbly 

at base

Page Sandstone 

84 ft (25m) 

Crossbedded

Harris Wash Tongue of 

Page Sandstone 15 ft

\ Cross-bedded. Chert

\pebblejatl ase

Harris Wash Tongue of 

|e Sandstone 62 ft / 

H9m).Crossbedded

Bathonian

Bajocian

Toarcian

Navajo Sandstone1 

1400 ft (427 m)

Navajo Sandstone1 

1250 ft (384m)

Navajo Sandstone1 

1650 ft (500m)

Navajo Sandstone1 

1600 ft (486 m)

Navajo Sandstone 

1165 ft (355m)

Navajo Sandstone1 

1150 ft (350m)

Kayenta Formation 1 

370 ft (113m)

Kayenta Formation 1 

370 ft (113m)

Kayenta Formation 1 

165 ft (50m)

Kayenta Formation 1 

170 ft (51 m)

Kayenta Formation 1 

350 ft (107 m)

Kayenta Formation 1 

300 ft (92 m)

Pliensbachian

Moenave Formation 1 

480 ft (146m)

Wingate Sandstone1 

160 ft (49m)

Moenave Formation 1 

400 ft (122m)

Moenave Formation 1 

350 ft (107 m)

Wingate Sandstone1 

290 ft (89 m)

Moenave^

Formation 1/ Windgate 

250 ft / Sandstone1 

(76m) \ 50 ft (15m)

Sinemurian

B. Little Bull Valley, Utah, to Cow Springs, Ariz.

FIGURE 29.—CORRELATIONS AND COMPARISONS OF JURASSIC ROCKS IN THE WESTERN INTERIOR REGION FROM 

SOUTHWESTERN UTAH TO NORTHEASTERN ARIZONA. Vertical lines indicate that strata are missing; wavy lines indicate 

unconformity or disconformity; jagged lines indicate gradational or indefinite contact. Column numbers refer to locations shown on figure 

20.
78 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

dense dolomite. It is overlain gradationally by the Picard 

Shale Member, which is about 40 feet (12 m) thick and 

consists mostly of dark-red shale but contains some gypsum at its base. The Picard is overlain rather sharply by 

the Kline Member, which ranges from 80 to 190 feet (24 

to 58 m) in thickness, consists generally of an upper 

dense dolomitic unit and a thicker lower limestone unit 

that locally is oolitic, and also contains some beds of finegrained sandstone and green to purple shale. The upper 

contact of the Kline with the Piper Formation is sharp 

but concordant. The possibility of a disconformity at the 

top of Kline Member is suggested by the presence of 

chert pebbles at the top of the equivalent lower member 

of the Gravelbourg Formation in Saskatchewan (Milner 

and Blakslee, 1958, p. 71; Springer and others, 1966, p. 

144; Milner and Thomas, 1954, p. 257).

The exact age of the Nesson Formation is not known. 

An early Bajocian or older age was suggested by Nordquist (1955, p. 105) on the basis of stratigraphic position. 

An Early Jurassic age was suggested by Pocock (1970, 

p. 15) on the basis of pollen studies of the partially equivalent lower member of the Gravelbourg Formation in 

southern Saskatchewan. For the same lower member, an 

early to middle Bajocian Age was suggested by Brooke 

and Braun (1972, p. 4). Apparently no evaluation has 

been made of the many fossils reported from the Kline 

Member by Nordquist (1955, p. 105). The possibility exists that the subsurface Kline Member of the Nesson 

Formation and the overlying Firemoon Limestone and 

Tampico Shale Members of the Piper Formation are the 

expanded basinward subsurface equivalents of the outcropping middle member of Piper Formation in the Big 

Snowy Mountains, as proposed by J. A. Peterson (1957, 

p. 435). It is more probable, however, that the Nesson 

Formation is the time equivalent of the Gypsum Spring 

Formation of northern Wyoming (fig. 26), as originally 

defined by Love (1939, p. 42, 45; Love and others, 1945) 

and as proposed by Francis (1956, p. 22-26, 46, fig. 4).

Correlation of the subsurface Nesson Formation with 

the Gypsum Spring Formation rather than with parts of 

the surface Piper Formation is favored by the greater 

stratigraphic and lithologic resemblances of members of 

the Nesson to the successive units of the Gypsum Spring 

Formation and by the fact that the upper limestone 

member of the Nesson Formation is more dolomitic and 

much less fossiliferous than the middle limestone member of the Piper Formation. Also, the Gypsum Spring 

Formation extends northward into Montana unconformably beneath the Piper Formation along the flanks and 

northern ends of the Pryor and Bighorn Mountains.

Recognition of the presence of the Gypsum Spring 

Formation beneath the Piper Formation was made possible by joint field studies in 1964 and 1971 by G. N. Pipiringos and the writer, who traced typical exposures of

the Gypsum Spring Formation northward from the Wind 

River Basin. These studies showed that the limy units in 

the Gypsum Spring Formation are commonly dolomitic, 

dense, white to light gray, are locally pinkish or greenish, are nonoolitic, poorly fossiliferous, and contain blocky 

or banded chert in some beds. By contrast, the limy units 

in the Piper Formation are shaly to thin-bedded, commonly oolitic, highly fossiliferous, do not contain chert, 

and are not dolomitic. Also, the base of the Piper Formation at some localities contains small chert pebbles 

that are lithologically identical with the bedded chert in 

the Gypsum Spring Formation. Such pebbles were noted 

along the Pryor Mountains at the head of Gypsum Creek, 

at Red Dome, and at Grapevine Creek. Their stratigraphic occurrence should not be confused with that of 

much larger pebbles consisting of both chert and quartzite near the top of the limestone member of the Piper 

Formation in the Pryor Mountains (Imlay, 1956a, p. 572- 

574).

On the basis of the criteria cited, the thicknesses of 

the Piper and the underlying Gypsum Spring Formation 

have been determined for the area of the Pryor and Bighorn Mountains (table 1). Evidently, the Gypsum Spring 

is thinnest along the west side of the Pryor Mountains 

and thickens eastward from 17 feet (5 m) at Red Dome 

to about 150 feet (46 m) at the Montana-Wyoming State 

line on both sides of the Bighorn Mountains. Also, the 

Piper Formation is thickest on the west side of the Pryor 

Mountains and thins eastward from 163 feet (50 m) at 

Red Dome to about 55 feet (17 m) at the State line north 

of Cowley, Wyo., and to about 40 feet (12 m) at Lodge 

Grass Creek, near the State line on the east side of the 

Bighorn Mountains.

Lithologically, the thickest sequences of the Gypsum 

Spring Formation in the Pryor Mountains greatly resemble sequences typical of that formation in the Wind River 

Basin. At the base is a unit of massive gypsum and some 

red siltstone, or a unit of red siltstone that contains brecciated beds. Above this unit is one of soft red claystone. 

At the top is a unit consisting of interbedded gray limestone, white to light-gray dolomitic limestone, and some 

varicolored claystone. As the formation thins toward the 

west in the Pryor Mountains, the upper units disappear 

from the top downwards so that only the basal gypsiferous unit is present along the west side of the mountains. 

Evidently, the Gypsum Spring Formation was truncated 

by erosion before the Piper Formation was deposited.

Similarly, the thickest sequences of the Piper Formation in the Pryor Mountains contain all the units typical of the Piper elsewhere in Montana. For example, at 

Red Dome in Carbon County, Mont., the formation consists of a basal red claystone about 24 feet (7 m) thick, 

overlain by interbedded, fossiliferous gray shale and 

limestone about 60 feet (18 m) thick, which is overlain by
COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 79

TABLE 1.—Thickness of the Piper and underlying Gypsum 

Spring Formations in parts of north-central Wyoming and 

south-central Montana

[B, indicates the presence of breccia instead of massive gypsum]

Piper Gypsum 

Location Formation Spring Formation

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15

16 

17

18 

19 

20 

21 

22

Thickness 

Feet Meters

Lodge Grass Creek, sec. 8, T. 9 

S., R. 33 E., Big Horn County, 

Mont ——————————————————— 43

Grapevine Creek, center sec. 6, 

T. 6 S., R. 31 E., Big Horn

Shively Dome, west-central part 

sec. 23, T. 5 S. , R. 27 E., Big

Fivemile Creek, sec. 36 T. 5 

S., R. 24 E., Carbon County,

Red Dome, west flank, sec. 19, 

T. 7 S., R. 24 E., Carbon

South of Bowler 1-1/2 mi, 

sec. 1, T. 8 S., R. 24 E.,

South side of Pryor Mountains, 

S-l/2 sec. 14, T. 9 S., R. 26

East side of Gypsum Creek, 

SE-1/4 sec. 33, T. 9 S., R. 27

East side of Red Gulch, sec. 

22, T. 58 N., R. 89 W., Sheridan

Wolf Creek, NW-1/4 sec. 9, T. 

55 N., R. 86 W., Sheridan

Big Goose Creek, NE-1/4 sec. 2, 

T. 54 N., R. 86 W., Sheridan

Little Goose Creek, N-l/2 sec. 

36, T. 54 N., R. 85 W.,

North side of Sykes Mtn., 

NE-1/4 sec. 12, T. 57 N., R. 

95 W., Big Horn County, Wyo ——— 86

Northwest end of Little Sheep 

Mtn. NW-1/4 sec. 28, T. 56 N., 

R. 95 W., Big Horn County, Wyo — 44 

Northwest end of Spence Dome, 

north-central part sec. 6, T. 

54 N., R. 94 W., Big Horn 

County, Wyo —————————————— 36

Southeast end of Sheep Mtn., 

east-central part sec. 16, T. 

53 N., R. 93 W., Big Horn

About 7 mi north-northwest 

of Shell, south-central sec. 

21 and north-central sec. 28, 

T. 54 N., R. 91 W., Big Horn

About 8 mi south of Shell, 

east-central part sec. 3, T. 51 

N., R. 91 W., Big Horn County, 

Wyo —— - ———————————————— 22

About 9 mi north-northwest 

of Hyattville, SW-1/4 sec. 21, 

T. 51 N., R. 90 W., Big Horn 

County, Wyo —————————————— 30

2 mi northeast of 

Hyattville, central sec. 29, T. 

50 N., R. 89 W., Big Horn

County, Wyo —————————————— 11 

1 mi north of mouth of 

Clarks Fork Canyon, sec. 5, T 

56 N., R. 103 W., Park County, 

\Jvn--------- __ -- -__ _ _ ??1

Trail Creek, about 8 mi 

northwest of Cody, center sec. 

12, T. 53 N., R. 103 W., Park

r.nnntv Ui/n — --- — -----------_---?(¥>

13.1 (B) 

6.1 

20.1 (B) 

27.4 (B) 

49.7 

29.0 (B) 

27.7 

19.5 

14.0 

1.5 (B) 

1.5 (B) 

18.0 (B) 

26.2 

13.4

11.0 

13.4

10.4 

6.7 

9.1 

3.4 

68.0

fi? R

Thickness 

Feet Meters

120 

130 

53 

46 

17 

64 

43 

107 

150 

143 

142 

146 

164 

152

210 

110

162 

216 

192 

174 

D 

n

(B) 36.6

39.6 

(B) 16.2

(B) 14.0 

5.2 

(B) 19.5 

13.1 

32.6 

(B)45.7 

(B)43.6 

(B)43.3 

(B)44.5 

50.0 

46.3

64.0 

33.5

49.4 

65.8 

58.5 

53.0 

0 

n

TABLE 1.—Thickness of the Piper and underlying Gypsum 

Spring Formations in parts of north-central Wyoming and 

south-central Montana—Continued

Location

Piper 

Formation

Gypsum 

Spring Formation

Thickness Thickness 

Feet Meters Feet Meters

23 Shoshone Canyon 2 mi west

of Cody, NE-1/4 sec. 4, T. 52

N., R. 102 W., Park County,

Wyo————————————————-———196(B) 59.7 0 0

24 Six miles south of Cody along 

line between sees. 5 and 6, T. 

51 N., R. 101 W., Park County, 

Wyo————————————————————277 84.4 0 0

25 Red Creek, SE-1/4 sec. 6, T. 6 

N., R. 3 W., Fremont County, 

Wyo———————————————————— 40 12.2 220 67.1

26 Mavericks Spring anticline,

sees., 23 and 26, T. 6 N., R. 2

W., Fremont County, Wyo—————— 20 6.1 173? 52.7?

27 Tributary to East Fork of Sheep 

Creek, SW-1/4 sec. 2 to NW-1/4 

sec. 11, T. 6 N., R. 2 E., 

Fremont County, Wyo————————— 10 3.0 165 50.3

28 Bull Lake, SE-1/4 sec. 36, T. 3

N., R. 4 W., Fremont County, Wyo- 9 2.7 196 59.7

29 Sage Creek anticline, SE-1/4 sec. 

16, T. IN., R. 1 W., Fremont 

County, Wyo—————————————— 13 4.0 121 36.9

30 Mill Creek, NW-1/4 sec. 5, T. 2 

S., R. 1 W., Fremont County, 

Wyo———————————————————— 12 3.7 212? 64.6?

77 feet (23 m) of brownish-red claystone and siltstone 

that contains some thin layers of gypsum. As the formation thins toward the east, the units disappear from the 

base upwards, and at the State line east of the Bighorn 

Mountains, only the highest redbed unit is present. 

Thus, the Piper Formation overlaps eastward and southeastward over the Gypsum Spring Formation.

The Piper Formation consists of three members, is 

more widely distributed in the subsurface than is the 

Nesson Formation, and crops out at many places in 

north-central, central, and southern Montana. The oldest, or Tampico Shale Member (Nordquist, 1955, p. 101), 

is about 85 feet (26 m) thick in the subsurface and as 

much as 100 feet (30.5 m) thick on the surface. It consists 

mostly of red shale but includes some green to gray shale 

and siltstone, some thin beds of red to white sandstone, 

and some gray to brown dolomite and dolomitic limestone, and in places its lower part bears thick masses of 

gypsum (Imlay, Gardner, and others, 1948).

It is overlain by the middle, or Firemoon Limestone 

Member (Nordquist, 1955, p. 101), whose thickness averages about 75 feet (23 m) in the subsurface and ranges 

from 15 to more than 100 feet (4.5 to 30.5 m) on the surface. It consists mostly of gray shale and limestone, 

which may be shaly, oolitic, dense, or dolomitic. Its 

boundaries with adjoining members are transitional 

within narrow intervals (Imlay, Gardner, and others, 

1948b; Sandberg, 1959).
80 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

The youngest, or Bowes Member, of the Piper Formation (Nordquist, 1955, p. 102) averages about 50 feet 

(15 m) in thickness in the Williston basin and from 20 to 

130 feet (6 to 40 m) in thickness in outcrops. It consists 

mostly of red to varicolored shale and siltstone in the 

subsurface east of the Big Snowy and Bearpaw Mountains, as well as on the surface in southern Montana as 

far west as the Gallatin Range north of Yellowstone National Park. It passes westward and northward in Montana into yellowish silty to sandy limestone and calcareous sandstone that characterize the upper member of 

the Sawtooth Formation in western and north-central 

JVtontana.

Northward from the Williston basin, the Piper Formation continues into southern Saskatchewan, where its 

Tampico Shale Member passes into gray calcareous shale 

at the top of the Gravelbourg Formation, its Firemoon 

Limestone Member passes into the nearly identical lower 

member of the Shaunavon Formation, and its Bowes 

Member passes into shale, limestone, and sandstone in 

the upper member of the Shaunavon Formation (Christopher, 1964, p. 16; Brooke and Braun, 1972, p. 4; Milner 

and Thomas, 1954, p. 258-262).

The middle limestone member of the Piper Formation is dated as late Bajocian because in both the surface 

and subsurface in Montana it contains certain mollusks 

(Hearn and others, 1964, p. B8; Imlay, 1967b, p. 33-35) 

that also characterize the upper Bajocian Rich Member 

of the Twin Creek Limestone (Imlay, 1967b, p. 31, 32). 

These include particularly the ammonites Sohlites and 

Parachondroceras and the pelecypods Gryphaea planoconvexa Whitfleld and Gervillial montanaensis Meek., 

Dating the Rich Member as latest Bajocian is based on 

its gradational relationship with the underlying Sliderock Member, whose upper half contains the ammonites 

Megasphaeroceras, Spiroceras, Stemmatoceras, Stephanoceras, and questionable Normannites. These in association can only be of early late Bajocian Age (Imlay, 

1967b, p. 26, 27; 1973, p. 29, 34).

Elsewhere, the mollusks that characterize the middle limestone member of the Piper Formation are widely 

distributed. They occur in the middle of the Sawtooth 

Formation south of Belt Island in Gallatin and Madison 

Counties, southwestern Montana (Imlay, 1967b, p. 33, 

34, 65). They occur throughout 27 feet (8 m) of black 

limestone and shale in the middle of the Sawtooth Formation exposed on East Butte in the Sweet Grass Hills, 

Liberty County, Mont. They occur in the lower member of the Shaunavon Formation in southern Saskatchewan (Paterson, 1968, p. 15, 16) along with the coral Actinastrea cf. A. hyatti (Wells) (Wells, 1942, p. 2, pi. 2, 

figs, la-c, 2a, b). That coral is widespread in the middle 

limestone member of the Piper Formation in southern 

Montana, in the middle limestone member of the Sawtooth Formation in southwestern Montana, in the middle 

limestone member of the Sawtooth Formation in the 

Bearpaw Mountains, and in equivalent limestone beds in 

the northern part of the Bighorn Basin (Imlay, 1956a, 

p. 567, 568, 577).

Dating the middle limestone member of the Piper 

Formation as latest Bajocian means that the upper member must be of Bathonian Age and that the lower member must be at least in part of early late Bajocian Age, 

equivalent to the ammonite-bearing upper part of the 

Sliderock Member of the Twin Creek Limestone. This 

dating for these three members holds also for the three 

members of the Sawtooth Formation in southwestern 

Montana. However, the basal part of the lower member 

of the Piper Formation may be as old as the late middle 

Bajocian (Stephanoceras humphriesianum zone) because ammonites of that age occur near the base of the 

Sawtooth Formation (Imlay, 1967b, p. 50, 91-94) in 

northwestern Montana, because the lower part of the 

Sliderock Member could be of that age, and because marine invasion from the west probably took place at about 

the same time in eastern Idaho as in western Montana. 

Nonetheless, it is doubtful whether marine waters older 

than latest Bajocian ever crossed the Sweetgrass arch or 

Belt Island, because the members of the Sawtooth Formation thin considerably where they cross the arch (Cobban, 1945, p. 1271; Weir, 1949, p. 551, 552) and because 

the middle member of the Sawtooth Formation on East 

Butte in the Sweet Grass Hills correlates faunally with 

the upper Bajocian Rich Member of the Twin Creek 

Limestone (Imlay, 1967b, p. 35).

The Sawtooth Formation, in western and north-central Montana, is 230 feet (70 m) or less in thickness, consists of normal marine shale, sandstone, and limestone, 

and passes eastward gradually into the Piper Formation. 

Most of the gradation is near a line drawn northward 

from the northwest corner of Yellowstone National Park, 

although in north-central Montana the upper member of 

the Sawtooth Formation is represented by sandstone 

and silty limestone as far east as the Bearpaw Mountains 

in south-central Blaine County.

In northwestern Montana, north of Belt Island, the 

westernmost exposures of the Sawtooth Formation consist typically of a thin lower sandstone member, a middle 

shale member, and an upper calcareous siltstone-sandstone member. The lower sandstone member ranges 

from 8 to 30 feet (2.4 to 9 m) in thickness, is ripple 

marked, and locally bears a basal conglomerate. The 

middle shale member thickens northward from about 18 

feet (5 m) at the Sun River to about 170 feet (52 m) near 

Glacier National Park and consists mostly of poorly fossiliferous gray to black shale that contains lenses and 

nodules of phosphate throughout and some glauconitic 

sandstone at its base. The upper member thickens north-
COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 81

ward from 25 to 65 feet (7.6 to 20 m) and consists of gray 

to yellowish-gray siltstone, sandstone, and silty to sandy 

limestone. All these members thin eastward and locally 

pinch out on the Sweetgrass arch. East of the arch, the 

middle member passes into highly fossiliferous black 

thin- to thick-bedded limestone typical of the middle 

member of the Piper Formation. The upper boundary of 

the Sawtooth Formation with the Rierdon Formation is 

sharp but apparently not disconformable except possibly 

on the Sweetgrass arch, where the top of the Sawtooth 

Formation bears chert pebbles and broken and worn belemnite guards (Cobban 1945, p. 1273; Weir, 1949, p. 

551).

The Sawtooth Formation in southwestern Montana 

west of the Gallatin Range is also represented by three 

members which are well exemplified by the sequence on 

Indian Creek in the Madison Range (Imlay, Gardner, 

and others, 1948). At that place, the lower member rests 

on Triassic sandstone, is 79 feet (24 m) thick, and consists 

of interbedded green to brown siltstone and mudstone. 

The middle member is 67 feet (20.4 m) thick, consists of 

light-gray thin- to thick-bedded limestone and contains 

Gryphaea planoconvexa Whitfield. The upper member is 

84 feet (25.6 m) thick and consists of interbedded papery 

siltstone, sandy siltstone, thin- to medium-bedded sandstone and thin- to thick-bedded sandy limestone. The 

siltstones are greenish gray to greenish brown, and the 

other rock types are gray to brown. This sequence contrasts with those in the Gallatin Range to the east, because it has no red beds in its upper and lower members 

(Imlay, Gardner, and others, 1948; Ruppel, 1972, p. 

A25; Moritz, 1951; Scholten and others, 1955, p. 367, 395, 

396).

The westernmost sequence of the Sawtooth Formation in Montana, exposed in Little Water Canyon in the 

NEy4SWV4 sec. 10, T. 13 S., R. 10 W., Beaverhead 

County, is also divisible into three members. The lower 

member consists of 58 feet (17.7 m) of gray sandstone 

and sandy limestone that bears oysters and Camptonectes. The middle member consists of 120 feet (36.5 m) 

of fossiliferous gray calcareous shale and shaly limestone. The upper member consists of 14 feet (4.2 m) of 

interbedded oolitic limestone, fissile shale, and sandstone. Throughout southern Montana, exposures of the 

highest parts of the Sawtooth and the Piper Formations 

are overlain abruptly by an oolitic limestone bed at the 

base of the Rierdon Formation.

The base of the Sawtooth Formation in northwestern 

Montana is dated as late middle Bajocian (Imlay, Gardner, and others, 1948; Imlay, 1948, p. 19, pi. 5, figs. 1- 

5; 1967b, p. 35, 90, 93, pi. 6, figs. 1-3, 7, 8) because of 

the presence of Chondroceras in close association with 

Stemmatoceras. The upper member is dated as early to 

middle Bathonian on the basis of the resemblance of the

ammonite Paracephalites (Frebold, 1963, p. 5, 8-13, 

27-29) to Arctocephalites and Cranocephalites of the 

arctic region. The middle shale member in the Sweet 

Grass Hills is dated as late Bajocian because it contains 

a pelecypod fauna identical with that in the Rich Member 

of the Twin Creek Limestone and the Firemoon Limestone Member of the Piper Formation (Imlay, 1967b, p. 

35).

The Sawtooth Formation in southwestern Montana 

is dated only by the presence of the ammonites Sohlites 

and Parachondroceras in its middle member. Those ammonites in the Twin Creek Limestone are dated as latest 

Bajocian because they occur just above beds containing 

an association of Stemmatoceras, Spiroceras, and Megasphaeroceras (Imlay, 1967b, p. 26, 27, 31).

The Rierdon Formation occurs widely throughout 

Montana and North Dakota except in the area of Belt 

Island, ranges in thickness from a featheredge to 180 

feet (55 m) on the surface and to about 350 feet (107 m) 

in the subsurface, and consists mostly of calcareous gray 

shale and shaly to thin-bedded limestone. Shale predominates over limestone except in the Little Rocky Mountains and in the subsurface of south-central Montana. 

Some silty to sandy beds occur locally near the base of 

the formation near Belt Island. The basal unit in southernmost Montana from the Pryor Mountains westward 

consists of oolitic limestone that ranges from a few inches 

to about 30 feet (9 m) in thickness and represents the 

northern edge of the Canyon Springs Sandstone Member 

of the Sundance Formation. At the top of the Rierdon 

Formation in south-central Montana is an oolitic to sandy 

limestone that represents the northern extension of the 

Hulett Sandstone member of the Sundance Formation 

(Cobban, 1945, p. 1279, 1280; Imlay, 1945, p. 255; 1956a, 

p. 585-587; Imlay, Gardner, and others, 1948; J. A. 

Peterson, 1957, p. 408, 409; Richards, 1955, p. 40, 41). 

This limestone passes northward into chalky limestone 

at the top of the Rierdon Formation.

The Rierdon Formation extends from the Williston 

basin into southern Saskatchewan, where its upper part 

gradually becomes sandy to the north and northwest. In 

the subsurface of southern Saskatchewan, beds equivalent to this sandy upper part are called the Roseray Formation, which is much less extensive than the overlying 

and underlying subsurface formations. The Roseray consists mostly of even-bedded fine-grained sandstone but 

has some shaly beds near its tip and bottom (Christopher, 1974, p. 4, 8, 9, 13, 14, 49, 101). In those shaly 

beds are Foraminifera and ostracodes suggestive of ages 

intermediate between those of the Rierdon and Swift 

Formations of Montana (Brooke and Braun, 1972, p. 8, 

13, 20, pis. 23, 24).

The age of the Rierdon Formation in Montana has 

previously been considered as early Callovian (Imlay,
82 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

Gardner, and others, 1948; Imlay, 1948, p. 14-16; 

1953a, p. 5-8; 1967b, p. 60). However, the lowermost 

part of the formation, which is characterized by Warrenoceras (formerly called Arcticoceras), should be of late 

middle to early late Bathonian Age on the basis of the 

close resemblance of Warrenoceras to Arcticoceras; the 

latter genus in East Greenland occurs below ammonites 

characteristic of the earliest Callovian Macrocephalites 

macrocephalus zone of Europe, according to Callomon 

(1959) and Birkelund and others (1971, p. 254). Also, 

most of the overlying beds, characterized by Kepplerites 

costidensus (Imlay), K. subitus Imlay, and K. aff. K. 

tychonis (Ravn), should be of latest Bathonian Age on 

the basis of comparisons with East Greenland. Only the 

uppermost part of the Rierdon Formation, characterized 

by Kepplerites maclearni Imlay in association with Lilloettia and Xenocephalites, is definitely early Callovian.

The age of the Rierdon Formation in southern Saskatchewan is apparently the same near its top as that of 

the Rierdon Formation of Montana, as shown by the 

presence of certain species of Kepplerites (Frebold, 1963, 

p. 23-26, pi. 10, fig. 3, pi. 12, fig. 1; Paterson, 1968, p. 

35, 36, pi. 8, pi. 9, figs. 1-3).

The Swift Formation is more widespread than the 

underlying Jurassic formations. It ranges in thickness 

from a few feet to about 165 feet (50 m) in outcrops, and 

to more than 400 feet (122 m) in the subsurface. It consists of glauconitic sandstone, siltstone, and shale, and in 

surface sequences generally has a basal conglomerate. In 

the Sawtooth Range of northwestern Montana, the Swift 

is divisible into two transitional members. The upper 

member consists of thin-bedded, ripple-marked sandstone that contains partings of dark micaceous shale. The 

lower member consists of dark fissile micaceous noncalcareous shale. To the east, one or both members locally 

pinch out on the Sweetgrass arch but reappear farther 

east and gradually become much shalier eastward (Cobban, 1945, p. 1281-1286).

By contrast, the Swift Formation in southwestern, 

southern, and central Montana consists mainly of medium- to thick-bedded, glauconitic ripple-marked sandstone that persists as far east as the Big Snowy Mountains and the western part of the Pryor Mountains. Shale 

appears in these mountains at or near the base of the 

formation and gradually thickens eastward as the overlying sandstone thins (Imlay, Gardner, and others, 1948; 

Imlay, 1956a, p. 598, fig. 2 on p. 566; Moritz, 1951, p. 

1804-1810).

The age of the basal beds of the Swift Formation varies considerably from place to place. In the Bearpaw and 

Little Rocky Mountains, the basal beds contain Quenstedtoceras (Lamberticeras) collieri Reeside, which by 

comparison with Europe should represent the latest Callovian. Directly above in the lower part of the formation

is shale containing Cardioceras and Q. (Pavloviceras) of 

early Oxfordian Age. By contrast, in the Sawtooth Range 

of northwestern Montana, one specimen of Buchia concentrica (Sowerby) (USGS Mesozoic loc. 27058) of late 

Oxfordian Age was obtained from the base of the Swift 

Formation at the south end of Diversion Ridge south of 

the Sun River (NWy4SWy4 sec. 12, T. 21 N., R. 9 W., 

Sawtooth Ridge Quad.). The same species was also obtained from sandy shale above a thick sandstone ledge in 

the upper part of the lower member of the Swift Formation on the north side of the Great Northern Railway 

about 3 miles (4.8 km) southwest of Marias Pass (Imlay, 

1956a, p. 595).

The age of the upper part of the Swift Formation is 

uncertain because that part has not furnished any diagnostic fossils. It should be late Oxfordian to possibly 

early Kimmeridgian on the basis of its stratigraphic position.

The Morrison Formation in Montana rests conformably on the Swift Formation; ranges in thickness from 

250 to 400 feet (76 to 122 m); thins northward and disappears near the U.S.-Canadian border; consists mostly of 

clay shale, mudstone, dense limestone, and fine-grained 

sandstone; and at its top contains coal beds or carbonaceous beds (Cobban, 1945, p. 1268; Reeside, 1952, p. 25; 

Gardner and others, 1945; Hadley and others, 1945). The 

lowermost part of the Morrison Formation in western 

Montana should be of Kimmeridgian Age, as shown by 

the presence of the late Oxfordian to early Kimmeridgian 

Buchia concentrica (Sowerby) in the lower member of 

the underlying Swift Formation.

SOUTHEASTERN IDAHO TO WESTERN SOUTH DAKOTA

Marine Jurassic sequences in Wyoming and adjoining parts of Idaho and South Dakota (fig. 26) closely resemble the equivalent marine sequences in Montana and 

North Dakota at their top and bottom. At the top of the 

Jurassic, the Stump Sandstone, as exposed along the 

Idaho-Wyoming border, resembles the Swift Formation 

of western Montana and likewise passes eastward into 

shale (Redwater Shale Member of the Sundance Formation) that becomes shalier from the base upward and is 

predominantly shale east of the center of the Bighorn 

Basin. At the bottom of the Jurassic, the Gypsum Spring 

Formation (or Member of the Twin Creek Limestone), 

resembles the Nesson Formation of the Williston Basin. 

The lithologic units between the Stump and the Gypsum 

Spring show some resemblances to the units between the 

Swift and Nesson Formations but also show many differences.

The Gypsum Spring Formation, as originally defined 

by Love (1939, p. 42-46; Love and others, 1945), crops 

out in the northwestern part of the Wind River Basin
COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 83

west of long 108° W., in the Teton and Gros Ventre areas 

of northwestern Wyoming, along the east and west sides 

of the Bighorn Mountains, in the northwestern part of 

the Black Hills in eastern Wyoming and western South 

Dakota, and around the northern parts of the Bighorn 

and Pryor Mountains in south-central Montana. Also, the 

equivalent Gypsum Spring Member of the Twin Creek 

Limestone occurs near the Wyoming-Idaho border and 

in north-central Utah.

In the Wind River Basin, the Gypsum Spring Formation ranges in thickness from 250 feet (76 m) to a 

featheredge and consists of three lithologic units. At the 

base is 20 to 40 feet (6-12 m) of red, slightly sandy siltstone that is overlain by 13-95 feet (4-30 m) of massive 

white gypsum. At the top is 65-135 feet (20-41 m) feet 

of interbedded red siltstone, red claystone, slabby limestone, ribboned chert-bearing dolomite or dolomitic limestone, and some gypsum (Love and others, 1945; Love 

and others, 1947; Pipiringos, 1968, p. D18). The Gypsum Spring Formation rests unconformably on the Nugget Sandstone and is overlain unconformably by the 

Piper Formation or by sandy oolitic beds at the base of 

the Sundance Formation.

In northwestern Wyoming east of the belt of thrust 

faulting, the Gypsum Spring Formation is essentially the 

same as in the Wind River Basin except that the massive 

gypsum is locally replaced on the surface by a brecciated 

unit consisting of red siltstone and limestone. Here, as in 

the Wind River Basin, the formation is underlain unconformably by the Nugget Sandstone and overlain unconformably by normal marine limestone equivalent to the 

Piper Formation of Montana and north-central Wyoming 

(Imlay, 1956b, p. 70; 1967b, p. 6, 7, 19; Foster, 1947, p. 

1566; Wanless and others, 1955; Love and others, 1973).

Along the Idaho-Wyoming line and in north-central 

Utah, the Gypsum Spring member of the Twin Creek 

Limestone thickens westward from 12 to 400 feet (3.6 to 

122 m) and consists mostly of soft red to yellow claystone and siltstone that is interbedded with brecciated or 

vuggy limestone, or with chert-bearing limestone. The 

chert-bearing limestone thickens westward from a few 

feet to 70 feet (21 m). The brecciated limestone marks 

the position of thick masses of gypsum that are exposed 

about 32 miles (51 km) south-southeast of Jackson, Wyo. 

(Imlay, 1967b, p. 3, 17-19). Both lower and upper contacts of the member are sharp and presumably unconformable.

The Gypsum Spring Formation exposed along the 

flanks of the Bighorn Mountains and at the south end of 

the Bighorn Basin is similar lithologically to the formation in the Wind River Basin. Along the western flank of 

the mountains, the lower part of the formation consists 

of 25-100 feet (7.6-30.5 m) of massive white gypsum 

interbedded with some dark-red claystone, red siltstone,

and gray limestone and overlain by 20-40 feet (6-12 m) 

of dark-red claystone containing nodules and lenses of 

gypsum (Imlay, 1956a, p. 578). Along the eastern flank 

of the mountains, the lower 40-70 feet (12-21 m) or 

more of the formation at more places consists of dark-red 

claystone and siltstone whose basal 10-50 feet (3-15 m) 

contains some thin beds of gypsum, and some units of 

limestone breccia. At a few places, however, the basal 

beds consist of gypsum masses as much as 50 feet (15 m) 

thick (Hose, 1955, p. 52-54, 106, 107; Mapel, 1959, p. 

28-32, pi. 5).

Along both flanks of the Bighorn Mountains, the upper part of the Gypsum Spring Formation consists mostly 

of 70-110 feet (21-33.5 m) of alternating units of limestone and dark-red claystone. The lower limestone unit 

consists mostly of gray, dense, shaly to thin-bedded limestone, is locally dolomitic, locally contains blocky chert, 

and in some beds contains external molds of tiny gastropods. The middle limestone unit is similar, but some beds 

are mottled pink to light green, and some bear many 

poorly preserved molds of pelecypods. The upper limestone unit is white, dense, and partly dolomitic, contains 

many beds and lenses of blocky chert, and forms a prominent ledge.

Above these limestone units on both flanks of the 

Bighorn Mountains is 10-50 feet (3-15 m) or more of 

dark-red to pale-green siltstone and claystone (Imlay, 

1956a, p. 578, Mapel, 1959, p. 29). These beds could represent the uppermost part of the Gypsum Spring Formation, but they are herein considered to represent the 

southern pinch-out of the upper red-bed member of the 

Piper Formation.

The Gypsum Spring Formation pinches out southward along the flanks of the Bighorn Mountains. It 

rests sharply and unconformably on the Triassic part of 

the Chugwater Formation (Hose, 1955, p. 53; Mapel, 

1959, p. 29; Imlay, 1956a, p. 579). The Gypsum Spring is 

overlain with angular unconformity by the lower part of 

the Sundance Formation south of a line extending northeast from Hyattville to Banner, Wyo. North of that line, 

it is overlain sharply by red claystone, herein assigned to 

the Piper Formation, which in turn is overlain sharply 

by gray sandstone or calcareous shale at the base of the 

Sundance Formation.

In the Black Hills area, the Gypsum Spring Formation is exposed only in the northwestern and northern 

parts, where it ranges in thickness from a featheredge to 

125 feet; it attains its greatest thickness 10 miles northeast of Hulett, Wyo. At that place, its lowermost 75 feet 

(23 m) consists of massive gypsum and red claystone that 

rests sharply on the Triassic part of the Spearfish Formation. Its uppermost 50 feet (15 m) consists of interbedded limestone and red to gray claystone. Its upper contact is truncated and channeled in places by chert pebbles
84 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

in the basal bed of the overlying Sundance Formation 

(Mapel and Bergendahl, 1956).

The upper part of the Gypsum Spring Formation is 

definitely of Jurassic age, on the basis of an association 

of the pelecypods Grammatodon, Myophorella, Opis 

(Trigonopis), and Quenstedtia with the gastropods Neritina, Tylostomal, Nododelphinulal, Procerithium, and 

Lyosoma powelli White. These fossils were collected 

near Mill Creek, about 30 miles (48 km) northwest of 

Lander, Wyo., in a limestone bed about 20 feet (6 m) 

below the top of the formation, which is 224 feet (68 m) 

thick at that place (Love and others, 1945; Sohl, 1965, p. 

D10).

The Gypsum Spring Formation must be older than 

late Bajocian, because it underlies limestone of that age 

at Lower Slide Lake northeast of Jackson, Wyo. (Imlay, 

1967b, p. 567, 577, 583; 1967b, p. 19, 33, 34, 59), and 

because the equivalent Gypsum Spring Member of the 

Twin Creek Limestone underlies limestone of late Bajocian Age and probably late middle Bajocian Age along 

the Idaho-Wyoming border (Imlay, 1967b, p. 28). The 

Gypsum Spring cannot be much older than late Bajocian, 

however, because it contains the gastropod Lyosoma 

powelli White, which occurs elsewhere mostly in upper 

Bajocian beds such as the Sliderock and Rich Members 

of the Twin Creek Limestone, the middle limestone 

member of the Piper Formation near Cody, Wyo., and 

the basal limestones of the Carmel Formation in central 

Utah. That species also occurs in somewhat younger 

Canyon Springs Sandstone Member of the Sundance 

Formation in the Bighorn Basin (Sohl, 1965, p. D5, D10, 

Dll, D18). This evidence definitely favors an early to 

middle Bajocian Age for the Gypsum Spring Formation. 

The Piper Formation is exposed in Wyoming along 

the northwest side of the Bighorn Basin from about 30 

miles (48 km) southwest of Cody northward to the Montana border, in the northwestern part of the Wind River 

Basin nearly as far east as Lander, and along the flanks 

of the Bighorn Mountains north of Hyattville and 

Banner.

The Piper Formation exposed along the northwest 

side of the Bighorn Basin is of special interest because it 

consists of three members that are essentially identical 

with the three members of the Piper Formation in Montana (Imlay, Gardner, and others, 1948; Imlay, 1954, 

1956a) and that rest directly on the Triassic part of the 

Chugwater Formation. The sequence exposed at Clarks 

Fork Canyon near the Montana border (Imlay, 1956a, p. 

567) is essentially identical with that exposed 30 miles 

(48 km) southwest of Columbus, Mont. (Imlay, Gardner, 

and others, 1948). The sections exposed near Cody are 

essentially identical with the section exposed at Red 

Dome about 10 miles (16 km) southeast of Bridger, Mont., 

as well as closely similar to the Piper Formation in the 

subsurface in southern Montana and in the Williston

basin (Nordquist, 1955, p. 99^103; Rayl, 1956, p. 38- 

43; Imlay, Gardner, and others, 1948). The absence of 

the Gypsum Spring Formation along the northwest side 

of the Bighorn Basin is shown by the lack of any dolomitic beds, by the presence of much highly fossiliferous 

shaly limestone, and by the basal beds of the Piper Formation containing chert pebbles that are identical lithologically with chert beds or lenses in the Gypsum Spring 

Formation.

The Piper Formation elsewhere in north-central Wyoming is represented mainly by its upper red-bed member. In the Wind River Basin that member ranges from 

about 50 feet (15 m) to a featheredge, consists of red siltstone and claystone that becomes sandy near its eastern 

margin, and rests sharply on dolomitic beds or limestone 

at the top of the Gypsum Spring Formation (Love and 

others, 1945; Pipiringos, 1968, p. D10). The thickest section, exposed at Red Creek on the north side of the Wind 

River Basin, is of special interest because its base is 

marked by a chert conglomerate and at one place by a 

lens of pebbly limestone resembling that which occurs 

near the top of the middle limestone member of the Piper 

Formation along the western and southern sides of the 

Pryor Mountains, Mont. (Imlay, 1956a, p. 572-574).

Near the northern border of Wyoming, the upper 

red-bed member of the Piper Formation is represented 

by 10-86 feet (3-26 m) of red claystone and some gypsum, which is beneath the Sundance Formation and 

above dolomitic beds typical of the Gypsum Spring Formation (Imlay, 1956a, p. 578). This claystone and gypsum unit crops out nearly continuously along the east 

side of the Bighorn Mountains north of Banner, and 

along the west side of the Bighorns north of Hyattville. 

It correlates with, and is continuous with, the upper redbed member of the Piper found in south-central Montana. This correlation is supported by comparisons between sequences at Sykes Mountain, Wyo., and Gypsum 

Creek, Mont. (Imlay, 1956a, p. 568, 569), and between 

sequences at Red Gulch, Wyo., and Lodge Grass Creek, 

Mont, (see table 1 for exact locations)(Imlay and others, 

1948, columnar sections along line D-D'; Mapel, 1959, 

pi. 5).

A basal unconformity is indicated by the presence of 

chert pebbles found as float near the base of 43 feet (13 

m) of red claystone exposed at Lodge Grass Creek. This 

unconformity is further substantiated by the presence of 

dark-gray wind-polished chert pebbles at the base of 86 

feet (26 m) of dark-red claystone that underlies the Sundance Formation near the east end of Sykes Mountain. 

These pebbles, collected by G. N. Pipiringos and the 

writer, consist of chert identical with that in the underlying Gypsum Spring Formation.

The middle limestone member of the Piper Formation in the Cody area contains the same characteristic 

mollusks that occur (1) in that member in Montana, (2) in
COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 85

the Rich Member of the Twin Creek Limestone near the 

Wyoming-Idaho border, and (3) on the north side of 

Lower Slide Lake, Teton County, Wyo., in 85 feet (26 

m) of shaly limestone that represents a thin eastern extension of the Rich Member (Imlay, 1956b, p. 70; 1967b, 

p. 31). Accordingly, on the basis of stratigraphic position, the upper red-bed member of the Piper Formation 

in the Bighorn Basin is correlated with the similar-appearing Boundary Ridge Member of the Twin Creek 

Limestone and with the eastward extension of that member at Lower Slide Lake and at Green River Lakes (Imlay, 1967b, p. 39). Similarly, the lower red-bed and gypsum member of the Piper Formation from the Cody area 

northward to Montana is correlated with the Sliderock 

Member of the Twin Creek Limestone and with eastern 

extensions of that member, which underlies the Rich 

Member (Imlay, 1967b, p. 27, 29, 30).

The Sundance Formation comprises seven members 

in the Black Hills region of Wyoming and South Dakota 

and in southeastern and central Wyoming as far north 

as the southern side of the Wind River Basin (Imlay, 

1947; Pipiringos, 1953, 1957, 1968, p. D18-D24). These 

members, from the base upward, are Canyon Springs 

Sandstone, Stockade Beaver Shale, Hulett Sandstone, 

Lak, Pine Butte, Redwater Shale, and Windy Hill Sandstone. Regional unconformities occur at the base of the 

Canyon Springs, the Redwater, and the Windy Hill.

The Canyon Springs Sandstone Member represents 

the initial deposits of a transgressing sea. It rests on an 

irregular surface of erosion, varies considerably in thickness within short distances, becomes thicker to the south, 

and in many places is marked basally by pebbles, most of 

which consist of chert. As a lithologic unit it extends 

westward from the Black Hills to the Bighorn Mountains 

and northward from north-central Colorado to Sheep 

Mountain, about 18 miles (29 km) southeast of Lander, 

Wyo. Westward or northward from those mountains, it 

passes into sandy oolitic limestone that becomes less 

sandy away from the source.

In the Black Hills, the member is present only along 

the southern and western margins, ranges in thickness 

from a featheredge to 92 feet (28 m), and consists mostly 

of light-gray thin- to thick-bedded sandstone. Locally, 

the sandstone may be ripple marked, oolitic or massive, 

and red to white. Locally, the member includes beds of 

maroon to gray shale or siltstone (Imlay, 1947, p. 247- 

251; Gott and Schnabel, 1963, p. 139-140; Mapel and 

Bergendahl, 1956, p. 87).

In southern Wyoming, the Canyon Springs Sandstone Member consists of a lower unit of yellowish-white 

massive or crossbedded sandstone overlain by a unit of 

ripple-marked, oolitic fossiliferous sandstone (Pipiringos, 1968, p. D18-D21). It thickens southward from a 

featheredge to 65 feet (20 m) in Wyoming and to about

165 feet (50 m) in north-central Colorado (Pipiringos and 

others, 1969, p. N10).

The Canyon Springs Sandstone Member is probably 

of Bathonian Age because it contains Warrenoceras 

(USGS Mesozoic Iocs. 20496, 20497, 20503) in the Hartville uplift of southeastern Wyoming and in the type section of the member (USGS Mesozoic loc. 20337) about 4 

miles west of Horton, Wyo. (Imlay, 1947, p. 250; 1953a, 

p. 17, 22). Warrenoceras, formerly classified with Arcticoceras (Imlay, 1953a, p. 5, 19-23), is either a subgenus 

of Arcticoceras or a provincial time equivalent. Its resemblance to Arcticoceras suggests that it is of about the 

same age and probably early late or late middle Bathonian on the basis of the ammonite sequence in East Greenland (Callomon, 1959). Similarly, a late Bathonian Age is 

indicated by the presence of Warrenoceras in an oolitic 

limestone unit at the base of the Sundance Formation at 

Red Creek (USGS Mesozoic loc. 21635) in the Wind 

River Basin and in the Cody area of the Bighorn Basin 

(USGS Mesozoic loc. 17106). This oolitic limestone unit 

correlates, therefore, both stratigraphically and faunally 

with the Canyon Springs Sandstone Member.

The Stockade Beaver Shale Member of the Sundance 

Formation grades into the adjoining members and passes 

laterally southward entirely into the underlying Canyon 

Springs Sandstone Member in south-central Wyoming. 

In the Black Hills, the shale member consists of 5-90 

feet (1.5-2.7 m) of greenish-gray, fissile, calcareous 

shale that includes some limestone beds and nodules near 

its base and some siltstone and sandstone near its top 

(Imlay, 1947, p. 251, 252). In south-central Wyoming, 

the member consists of 12-110 feet (3.6-34 m) of 

greenish-gray shale and siltstone (Pipiringos, 1968, p. 

D21). In the Bighorn Basin, the shale member consists 

mostly of soft, gray fissile calcareous shale that is locally 

sandy toward its top, ranges in thickness from a featheredge to about 80 feet (24 m), is thickest in the northern 

part of the basin, and contains an abundance of Gryphaea, which genus is uncommon in the shale member in 

the Black Hills (Imlay, 1956a, p. 588^595).

The Hulett Sandstone Member of the Sundance Formation grades into the adjoining members. It consists 

mostly of light-gray, fine-grained, calcareous, fossiliferous, thin- to thick-bedded, ripple-marked, slightly glauconitic sandstone that is interbedded with some greenish-gray shale and siltstone. In the Black Hills, the 

thickness of the Hulett Sandstone Member ranges from 

20 to 120 feet (6 to 36.5 m) (Imlay, 1947, p. 255; Robinson 

and others, 1964, p. 15); in southern Wyoming, from 4 tox 

40 feet C1.2 to 12 m) (Pipiringos, 1968, p. D22); along the 

east side of the Bighorn Mountains, from 27 to 70 feet (8 

to 21 m) (Mapel, 1959, p. 33; Hose, 1955, p. 106; J. A. 

Peterson, 1954a, p. 477); along the west side of the Bighorn Mountains, from 16 to 104 feet (5 to 32 m); and 

around the Pryor Mountains and the northern end of the
86 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

Bighorn Mountains, from 0 to 48 feet (0 to 14.6 m) (Imlay, 1956a, p. 589). Farther west, the Hulett Sandstone 

Member is possibly represented by about 8 feet of sandstone and oolitic limestone at the top of the "Lower 

Sundance" Formation at Red Creek in the Wind River 

Basin (T. 6 N., R. 3 W.) (Love and others, 1945). It is 

also possibly represented at the same stratigraphic position in the gorge of the Shoshone River west of Cody 

by 24 feet (0.8 m) of gray sandstone and by the overlying 

14 feet (4.2 m) of sandy claystone and sandy oolitic lime- 

^tone (Imlay, 1956a, p. 592).

The Lak Member of the Sundance Formation grades 

into the adjoining members. In the Black Hills, it consists of 25-100 feet (7.6-30.5 m) of dark-brownish-red 

to pink to yellowish-gray, very fine grained, generally 

massive sandstone and sandy siltstone (Imlay, 1947, p. 

257; Robinson and others, 1964, p. 15; Gott and Schnabel, 

1963, p. E141, E142). In southeastern Wyoming near 

Glendo, the member consists of 50 feet (15 m) of finegrained nonglauconitic sandstone that is commonly red 

(Love and others, 1949). In south-central Wyoming, the 

member consists of 7-70 feet (2-21 m) of reddish-brown 

siltstone, sandy siltstone, and silty sandstone that changes 

southward to pale gray or pale yellow near Medicine Bow 

and Rawlins (Love and others, 1945; Love and others, 

1947; Love and others, 1949; Pipiringos, 1968, p. D22, 

D23). The Lak Member pinches out to the west in the 

Powder River Basin and to the north about 20 miles (32 

km) west of Lander. It is absent around the Bighorn 

Mountains and the Bighorn Basin, along the north side 

of the Wind River Basin, and apparently also at Green 

River Lakes at the northwest end of the Wind River 

Mountains.

The Pine Butte Member of the Sundance Formation 

in southern Wyoming (Pipiringos, 1968, p. D22-D23) 

consists of 60 feet or less of greenish-gray to white, thinbedded, glauconitic, limy, ripple-marked sandstone that 

is interbedded with gray to green limy siltstone and claystone and that near its middle generally contains 1-18 

feet of red sandstone and siltstone. Surfaces of sandstone 

beds are characterized by the presence of raised furrowed trails (GyrochorteT). Marine fossils are not common in the Pine Butte Member, but Pentacrinus columnals, echinoid spines, and pelecypods have been found. 

The member passes southward into north-central Colorado, where it intertongues with the underlying Canyon 

Springs Sandstone Member (Pipiringos, 1972, p. 27). It 

thins northward in Wyoming and pinches out about 17 

miles (27 km) southeast of Lander. It is overlain sharply 

by the Redwater Shale Member and is locally truncated 

by that member. The contact is marked by the presence 

of many belemnites in the basal beds of the Redwater 

Shale Member and by their absence in the Pine Butte 

Member. Sandstone beds at or near the base of the Redwater Shale Member can be distinguished from sandstone beds in the Pine Butte Member by the presence of 

belemnites and the absence of furrowed trails.

The Pine Butte Member in the Black Hills area was 

identified by G. N. Pipiringos in 1964 while on a field trip 

with the writer. At that time he noted that a sandstone 

unit 5-32 feet (1.5-10 m) thick at the base of the Redwater Shale Member (Imlay, 1947, p. 245, 260, 267-273; 

Robinson and others, 1964, p. 16-18) had all the characteristics of the Pine Butte Member of southern Wyoming. It graded downward into or was conformable with 

the Lak Member, contained raised furrowed trails, did 

not contain belemnites, and was overlain sharply by siltstone containing many belemnites. He found that the 

thickest section of the Pine Butte Member was exposed 

northeast of Spearfish, S. Dak., in the standard reference section of the Sundance Formation (Imlay, 1947, p. 

245). The characteristics of the member at that locality, 

as shown in a diagram by Pipiringos (1968, p. D12), are 

described as follows:

Stratigraphic section of the Pine Butte Member of the 

Sundance Formation

[Located in the Jolly Quadrangle, about three-quarters of a mile 

(1.2 km) northeast of Spearfish, S. Dak., in the SEV4NWV4SEV4SEV4 

sec. 3, T. 7 N., R. 2 E. Measured by G. N. Pipiringos, September 

1964]

Thickness 

Feet Meters 

Sundance Formation: 

Redwater Shale Member (in part): 

8. Siltstone, medium-gray, clayey, sandy, 

calcareous,, glauconitic, fossiliferous; 

basal few inches contains abundant 

belemnites; makes slope; basal contact 

is sharp; no belemnites were found below 

this contact——————————————————— 25 7.6 

Partial thickness of Redwater 

Shale Member——————————————— 25 7.6

J-4 unconformity 

Pine Butte Member: 

7. Siltstone, greenish-gray, clayey, sandy,

and some thin beds of light-olive-gray

silty clay shale; unit makes slope——— 8 2.4 

6. Sandstone, greenish-gray, weathers dusky

yellow at the top; very fine grained,

calcareous, clayey; contains worm borings

filled with gray clay; iron oxide nodules

about one-half inch (1.3 cm) in diameter

near middle of unit, and some olive gray

mudstone partings; unit makes rounded

ledge—————————————————————— 2.5 0.8 

5. Sandstone, siltstone, and clay shale; the

sandstone is light gray, very fine

grained, silty, clayey, structureless,

calcareous, finely glauconitic,

fossiliferous, and makes weak ledge in

middle; upper and lower parts of unit

consist of about equal parts of

light-greenish-gray clay shale and

light-gray clay siltstone————————— 8 2.4 

4. Sandstone, light-gray, very fine grained,

calcareous; middle part makes rounded

weak ledge overlain by a 1-foot bed of

light-greenish-gray, noncalcareous clay

shale; upper and lower parts of unit are

soft, structureless, clayey, and make

slopes—————————————————————— 7.5 2.3 

3. Clay shale, pale-olive to light-olive-gray;

contains a zone of pale-red clayey

siltstone about 2-3 feet above base;

unit makes slope——————————————— 5 1.5
COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 87

Stratigraphic section of the Pine Butte Member of the 

Sundance Formation—Continued

Sundance Formation—Con. Thickness 

Pine Butte Member—Con. Feet Meters 

2. Sandstone, yellowish-gray, very fine 

grained, calcareous; obscure low-angle 

crossbedding gives faintly varved 

appearance; fine grains of glauconite 

are alined along bedding; also some 

biotite muscovite flakes present; unit 

makes weak ledge in sharp contact with 

the underlying red beds. At an 

isolated exposure of this contact about 

30 feet (9 m) east of this section, the 

basal few inches of the Pine Butte 

consists of yellow-orange to rusty-brown 

siltstone and green clay shale that 

contains thin stringers of vitrain 

coal—————-——————....——————— 1 0.3 

Thickness of Pine Butte Member———— 32 9.8

Lak Member

1. Sandstone, pale-reddish-brown, silty; 

makes soft slope; not measured.

The Pine Butte Member is considered to represent 

the upper part of the "Lower Sundance" Formation on 

the basis of its conformable relationship with the underlying member, its unconformable relationship with the 

overlying Redwater Shale Member, and the presence of 

the pelecypods Vaugonia conradi (Meek and Hayden) 

and Quenstedtia cf. Q. sublaevis (Meek and Hayden). 

These species were originally described from the various 

members of the "Lower Sundance" Formation in the 

Black Hills and are widely distributed in the western 

interior region, but they are not known from the Redwater Shale Member or its equivalents. In addition, in 

the section of the Pine Butte Member described above, 

the fossiliferous ledge in the middle of unit 5 contains 

Myophorella montanaensis Meek (USGS Mesozoic Iocs. 

29128 and 29518). In Montana this species ranges from 

the middle limestone member of the Piper Formation 

into the lower part of the Rierdon Formation; along the 

Idaho-Wyoming border it ranges from the Sliderock 

Member of the Twin Creek into the Watton Canyon 

Member of the Twin Creek; and in Utah it occurs in the 

lower part of the Carmel Formation (Imlay, 1964d, p. 

C4, C31-C33; 1967b, p. 82).

The Redwater Shale Member of the Sundance Formation in south-central Wyoming, as defined by Pipiringos (1968, p. D23), consists of four units, which from the 

base to top are alternately siltstone and shale. Of these, 

the siltstone units contain beds of shelly coquinoid sandstone or limestone, and the shale beds contain limestone 

concretions. To the northwest, the upper two units pass 

into cliff-forming sandstone, and the lower two units pass 

into somewhat softer silty or clayey sandstone. This twofold division exists in the Bighorn Mountains and Bighorn Basin and in west-central Wyoming west of Sheep 

Mountain, which is about 20 miles (32 km) southeast of 

Lander (Pipiringos, 1968, fig. 2 on p. D3). The Redwater 

Shale Member ranges in thickness from about 75 to 165 

feet (23 to 50 m) in the Black Hills, from 50 to 120 feet 

(15 to 37 m) in southern Wyoming, from 130 to 160 feet

(40 to 49 m) in the Wind River Basin, and from 120 to 

175 feet (37 to 53 m) in the Bighorn Basin and Bighorn 

Mountains.

The age of the Redwater Shale Member is probably 

entirely early to early middle Oxfordian, on the basis of 

the presence of the cardioceratid ammonites Cardioceras 

and Goliathiceras throughout most of the member. Lowermost occurrences range throughout the basal 15 feet 

(4.5 m) (Mesozoic Iocs. 19359, 2434, 24736). The uppermost occurrence is 20 feet (6 m) below the top of the 

member where it is 230 feet (70 m) thick on Little Sheep 

Mountain southeast of Lovell, Wyo. (Mesozoic loc. 26717). 

At Horse Creek near the northwest end of the Wind 

River Basin (Love and others, 1945), Cardioceras occurs 

25 feet (7.6 m) below the top of the member where the 

member is 130 feet (40 m) thick (Mesozoic loc. 19398). 

On the Johnson Ranch about 17 miles (27 km) southeast 

of Lander, Wyo., Cardioceras occurs 29 feet (9 m) below 

the top of the member, which is 127 feet (39 m) thick 

(Mesozoic loc. 28400).

The Windy Hill Sandstone Member of the Sundance 

Formation in southern Wyoming (Pipiringos, 1968, p. 

D23-D25) consists of 5^57 feet (1.5-17 m) ledge-forming sandstone that is yellowish-gray, limy, ripple marked, 

weathers .bright yellow to orange to brown, and contains 

a few specimens of Ostrea and Camptonectes. Its upper 

part grades into and locally intertongues with the Morrison Formation. Its basal part rests sharply on and locally truncates the Redwater Shale Member. It pinches 

out northwestward a little west of Hanna, Utah, and a 

little west of Lander, Wyo. (G. N. Pipiringos, oral commun., 1974). It is not present along the north side of the 

Wind River Basin, or around the Bighorn Mountains, or 

anywhere in northwestern Wyoming or in Montana.

The Windy Hill Sandstone Member is represented 

in the Black Hills area, according to Pipiringos (1968, p. 

D24), by a bright yellow sandstone that is lithologically 

similar to the typical exposures of the member elsewhere 

and that occupies the same stratigraphic position. These 

similarities were recognized previously by Mapel and 

Pillmore (1963, p. N16) before the member was named. 

For mapping purposes, they placed the yellow sandstone 

in the top of the Redwater Shale Member because it was 

too thin to map separately but formed an easily recognizable formation boundary. They did not see any evidence that the yellow sandstone might rest unconformably on the underlying shale. They did note, however, 

that the yellow sandstone contained some thin seams 

of chert and some thin beds of gypsum and that locally 

beds of gypsum occurred both above and below the sandstone.

The exact age of the Windy Hill Sandstone Member 

is not known. Nonetheless, its unconformable relationship with the underlying dated Redwater Shale Member
88 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

in southern Wyoming suggests that it is younger than 

early Oxfordian and probably represents a small part of 

middle Oxfordian time. Its absence north of central Wyoming may be due to distance away from a source of 

sand, to its merging northward into deeper water marine 

deposits, or to both.

The Twin Creek Limestone, exposed along the Wyoming-Idaho border in an area of thrust faulting and in 

north-central Utah, has recently been described in detail 

and correlated member by member with marine beds 

elsewhere in the western interior region (Imlay, 1967b, 

p. 2^52). As this information is readily available, only 

the most essential is discussed here and is shown on figures 26 r 27, and 28.

East of the area of extensive thrust faulting, beds 

equivalent to the Twin Creek Limestone crop out in the 

south-central part of Yellowstone National Park, near 

the Gros Ventre River northeast and east of Jackson 

(Foster, 1947, p. 1565, 1566; Imlay, 1956b; 1967b, p. 6), 

and at the west end of the Wind River Mountains near 

Green River Lakes (Richmond, 1945). In those areas, 

however, the marine Jurassic beds above the Gypsum 

Spring Formation are referred to the Sundance Formation because they are much thinner, much less calcareous, and more fossiliferous than the typical Twin Creek 

Limestone. Nonetheless, the lower part of the Sundance 

Formation in those areas consists of units that are lithologically, stratigraphically, and faunally equivalent to 

the Sliderock, Rich, Boundary Ridge, Watton Canyon, 

and Leeds Creek Members of the Twin Creek Limestone. Also, the first three members are not represented 

in the typical Sundance Formation farther east but are 

represented in the Piper Formation.

Thus, at Bacon Ridge, in sees. 13 and 14, T. 40 N., 

R. Ill W., Teton County, Wyo., 125 feet (38 m) of soft 

limy shale resembles both the Stockade Beaver Shale 

Member of the Sundance Formation and the Leeds Creek 

Member of the Twin Creek Limestone. Above this shale 

is 8 feet (2.4 m) of gray, fine-grained, hard, ripplemarked sandstone (Love and others, 1948, p. 48) that 

could be interpreted either as an extension of the Hulett 

Sandstone Member of the Sundance or of the Giraffe 

Creek Member of the Twin Creek Limestone. Next 

higher is 4 feet of soft, gray, nonglauconitic siltstone that 

most probably is the bleached lateral extension of the 

Preuss Sandstone or of the Lak Member of the Sundance 

Formation. Sharply overlying is highly glauconitic sandstone and shale typical of the Stump Sandstone or of the 

"Upper Sundance" Formation in nearby parts of Wyoming.

Also, a section measured by G. N. Pipiringos and the 

writer north of Lower Slide Lake (see below) contains 

five well-exposed units that greatly resemble the named 

members of the Twin Creek Limestone from the Sliderock Member to the Leeds Creek Member. The uppermost of these, the Leeds Creek equivalent, also resembles the Stockade Beaver Shale Member of the Sundance 

Formation lithologically and faunally. This unit is overlain by 41 feet (12.5 m) of partially covered beds (units 23 

to 30 in the section below), which were exposed in a 

trench made when the section was measured. These beds 

extend up to an unconformity at the base of the "Upper 

Sundance" formation (equivalent to the Stump Sandstone, or the Redwater Shale Member of the Sundance):

Stratigraphic section of the Sundance Formation and its members with its Twin Creek Limestone member equivalents and 

Gypsum Spring Formation

[Exposed on the north side of Lower Slide Lake in sec. 4, T. 42 N., 

R. 114 W., Teton County, Wyo.]

Thickness 

Feet Meters

Sundance Formation: 

Redwater Shale Member:

35. Sandstone, gray, fine- to medium-grained, 

limy, glauconitic; basal 20 feet pebbly; 

overlain by Morrison(?) and Cloverly

Formations; estimated thickness—————— 100+ 30.4+ 

34. Sandstone, green, fine-grained, glauconitic;

forms vertical reentrant under cliff——— 17 5.2 

33. Sandstone, dark-gray to black, clayey to

silty, highly glauconitic; forms slope— 7 2.1 

32. Siltstone, dark-gray, clayey, glauconitic; 

contains 4-inch (10-cm) bed of siliceous 

nodules; contains many belemnites and 

ostracodes near base————————————— 7 2.1 

31. Bentonite, yellowish-white to gray,

fissile———————————— 1 0.3

Total Redwater Shale Member——————— 132+ 40.2+ 

Pine Butte(?) Member

30. Sandstone, greenish-gray, very fine 

grained, limy, ripple-marked; forms

prominent ledge--——————————————— 2 0.6 

29. Sandstone, greenish-yellow, soft, silty; 

includes some thin sandstone beds that 

form weak ledges———————————————— 9.5 2.9 

28. Sandstone, greenish-gray, very fine grained,

platy, nonglauconitic; forms ledge-——— 1 0.3 

27. Siltstone, pink, soft—————————————— 1 0.3 

26. Sandstone, greenish-gray, very fine grained,

platy, nonglauconitic; forms ledge———— 1 0.3 

Total Pine Butte(?) Member———————— 14.5 4.4 

Lak Member:

25. Siltstone, greenish- to yellowish-gray,

sandy, soft——————————————————— 5 1.5 

24. Siltstone, reddish-pink, sandy, soft———— 19.5 5.9 

23. Siltstone, greenish- to yellowish-gray,

sandy, soft——————————————————— 12 3.7 

Total Lak Member—————————————— 36.5 11.1 

Stockade Beaver Shale Member:

22. Shale, limy; several thin beds of limestone 

30-40 feet (9-12 m) above base. 

Contains Cadoceras and Gryphaea

nebrascensis————————————————— 163 49.7 

Total Stockade Beaver Shale Member—— 163 4g.7

Canyon Springs Sandstone Member:

21. Limestone, yellowish-gray, oolitic, thinto thick-bedded——————————————— 7 2.1

20. Shale, medium-gray, limy; contains

Gryphaea nebrascensis———————————— 20 6.1

19. Shale, medium-gray, limy, and thin beds

of soft brownish-gray limestone; contains

Warrenoceras————————————————— 10 3.0

18. Limestone, medium-gray, oolitic, massive— 3.5 1.1

17. Limestone, yellowish-gray, crumbly, mediumto thin-bedded———————————————— 4.5 1.4

16. Limestone, yellowish-gray, oolitic, mediumto thin-bedded———————————————— 12 3.7 

Total Canyon Springs Sandstone

Member————————-—————————— 57 17.4 

Boundary Ridge Member of Twin Creek Limestone

equivalent:

15. Limestone, yellowish-gray, soft, shaly—— 3.5 1.1

14. Limestone, olive-green to gray, soft,

shaly—————————————————————— 1.5 0.5
COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 89

Stratigraphic section of the Sundance Formation and its members with its Twin Creek Limestone member equivalents and 

Gypsum Spring Formation—Continued

Thickness 

Feet Meters 

Sundance Formation—Con.

Boundary Ridge Member of Twin Creek Limestone 

equivalent—Con.

13. Siltstone, brownish-red, soft; lower

contact sharp—————————————— 33-43 10.1-13.1 

Total Boundary Ridge Member of Twin

Creek Limestone equivalent———— 38-48 11.6-15.6 

Rich Member of Twin Creek Limestone equivalent: 

12. Limestone, medium-gray, shaly, partly

coquinoid——————————————————— 23 7.0 

11. Limestone, medium-gray, soft, shaly———— 27 8.2 

10. Limestone, dark-gray to nearly black, 

mostly soft and shaly; some beds 4 

-10 inches thick; contains 

Parachondroceras and Gryphaea

planoconvexa—~——————————————— 35 10.7 

Total Rich Member of Twin Creek

Limestone equivalent—————————— 85 25.9 

Sliderock Member of Twin Creek Limestone 

equivalent: 

9. Limestone, gray, partly oolitic, mediumto thin-bedded———————————————— 16 4.9 

8. Limestone, medium-gray, soft, shaly———— 4 1.2 

7. Shale, yellowish-gray, soft————————— 1 0.3 

Total Sliderock Member of Twin Creek

Limestone equivalent—————————— 21 6.4 

Gypsum Spring Formation:

6. Siltstone, brownish-red, soft———————— 15 4.6 

5. Limestone, pinkish-yellow; forms top of

cliff—————————————————————— 8 2.4 

4. Limestone, gray to yellow, brecciated;

forms cliff—————————————————— 16 4.9 

3. Limestone, purple, yellow, gray, brecciated,

silty—————————————————————— 2 0.6 

2. Limestone, yellow to pink, soft, silty—— 1-2 0.3-0.6 

1. Siltstone, brownish-red; rests sharply on

Nugget Sandstone———-——————————— 3 0.9 

Total Gypsum Spring Formation————— 46 14.0

The Preuss Sandstone crops out in the same area as 

the Twin Creek Limestone, thickens westward from 70 

feet (21 m) or less to about 1,300 feet (400 m), and consists mostly of pale- to dull-red, even-grained, finegrained, plane-bedded, locally ripple-marked sandstone. 

In addition, its lower part contains considerable bedded 

salt along the Idaho-Wyoming border, and a marine limestone member attains nearly 200 feet (61 m) in the area 

east of Blackfoot and Idaho Falls, Idaho. The formation 

grades downward into the Twin Creek Limestone and is 

overlain sharply and unconformably by the Stump Sandstone or by the Curtis Formation in Utah (Mansfield, 

1927, p. 98, 99, 338-^340; Baker, 1947; Thomas and Krueger, 1946, p. 1277, 1278; Imlay, 1952b).

A marine origin for the Preuss Sandstone is shown 

by the presence of salt, marine limestone, even grain 

size, even bedding and oscillation ripple marks. Marine 

fossils, including pelecypods, gastropods, and corals, are 

common only in exposures east of Blackfoot and Idaho 

Falls, Idaho, but oysters and crinoid columnals are found 

as far east as sec. 17, T. 31 N., R. 119 W., about 7 miles 

(11 km) southwest of Afton, Wyo.

The age of the Preuss Sandstone must be mostly 

middle Callovian, because it conformably overlies beds 

of early Callovian Age and unconformably underlies beds

of early Oxfordian Age. The Wolverine Canyon Limestone Member of the Preuss (Imlay, 1952b, p. 1742) cannot be much younger than early Callovian, as it contains 

the coral Actinastrea hyatti (Wells) (Imlay, 1967b, p. 35) 

and the gastropod Lyosoma cf. L. powelli White (Sohl, 

1965, p. Dll, D17, D18, pi. 2, fig. 4). Of these fossils, A. 

hyatti (Wells) has been recorded elsewhere only in beds 

of late Bajocian Age. Lyosoma cf. L. powelli White has 

been recorded from the Hulett Sandstone Member of the 

Sundance Formation in the Badwater area, Fremont 

County, Wyo., and from the Rierdon Formation in 

northern Yellowstone National Park, Mont.

The term Stump Sandstone has been applied to the 

uppermost Jurassic marine sandstone and sandy shale 

overlying the Preuss Sandstone in westernmost Wyoming, southeastern Idaho, and parts of north-central and 

northeastern Utah. Within that area, the Stump Sandstone ranges in thickness from 130 to 500 feet (40 to 152 

m). It is thickest in southeastern Idaho and thins irregularly northward and eastward (Mansfield and Roundy, 

1916, p. 76, 81; Mansfield, 1927, p. 99-101; 1952, p. 38; 

Gardner, 1944; Rubey, 1958; Cressman, 1964, p. 52, 53; 

Staatz and Albee, 1963, 1966; Pampeyan and others, 

1967; Albee, 1968; Schroeder, 1969; Thomas and Kreuger, 1946, p. 1269, 1276, 1278, 1285).

The Stump Sandstone exposed along the Idaho-Wyoming border consists mostly of sandstone and sandy 

shale units and has not hitherto been considered divisible into members. As described by Mansfield (1927, p. 

99-101), the sandstone is fine to medium grained, thin 

bedded to massive, ripple marked, calcareous, glauconitic, greenish-gray to gray, and locally crossbedded. Interbedded with the sandstone are some beds of calcareous, greenish-gray shale and sandy siltstone and some 

beds of glauconitic, greenish-gray, shaly, thin-bedded to 

massive limestone that may be sandy, oolitic, and ripple 

marked. Apparently all gradations between sandy limestone and calcareous sandstone are represented. The 

base is generally marked by a bed of fossiliferous coarsegrained sandstone or grit, according to Mansfield (1927, 

p. 99-101).

Recent field studies by George Pipiringos and the 

writer have shown that the Stump Sandstone exposed 

along the Idaho-Wyoming border includes members that 

are lithologically, stratigraphically, and faunally equivalent to the Curtis Formation of Utah and to the younger 

sandy facies of the Redwater Shale Member of the Sundance Formation of northern Utah and western Wyoming. As the Stump Sandstone at present is the most 

practical unit for mapping purposes, it is herein retained 

as a formation and is divided into the Curtis Member below and the Redwater Member above. This terminology 

applies to an area extending eastward from the Blackfoot Mountains east of Blackfoot and Idaho Falls in Idaho
90 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

to the Wyoming and Hoback Ranges in western Wyoming; extending southward from the Teton Range in the 

western part of the Jackson Hole area at least as far as 

Woodruff and Peoa in north-central Utah, Evanston in 

southwestern Wyoming; and eastward from Peoa along 

the length of the Uinta Mountains.

The Curtis Member near the Wyoming-Idaho border 

ranges in thickness from 30 to at least 395 feet (9 to 120 

m), thins eastward and northward, and extends considerably farther south and southwest than the Redwater 

Member. Its lower contact with the underlying Preuss 

Sandstone is sharp on McCoy Creek, Idaho (sec. 6, T. 37 

N., R. 46 E.), is gradational elsewhere within a few 

inches or a few feet, and is not marked by pebbles or by 

irregularities suggestive of a disconformity. The Curtis 

Member is distinguished from the Preuss Sandstone by 

a fairly abrupt color change upward from red to gray and 

by the presence of tracks and trails in abundance. These 

differences probably indicate a slight deepening of the 

sea that caused a change from hypersalinity to almost 

normal marine salinity. The change must have been very 

slight because the Curtis Member on Tincup Creek in 

Idaho (sec. 9, T. 5 S., R. 46 E., and sec. 10, T. 5 S., R. 

45 E.) and on Fish Creek in Wyoming (SEV4 sec. 32, T. 

30 N., R. 118 W.) contains a unit of red sandstone and 

siltstone that is nearly identical lithologically with red 

units in the Preuss Sandstone.

The Redwater Member of the Stump near the IdahoWyoming border is well developed along both sides of 

the Snake River and farther east, ranges in thicknesses 

from a featheredge to 175 feet (0-^53 m), and thins eastward and southward. It differs from the underlying Curtis Member by being much more fossiliferous, by containing belemnites and ammonites, by its shale being chunky 

instead of fissile, by being more glauconitic, and by its 

bedding surfaces being marked only rarely by tracks and 

trails. Unlike the Curtis Member, it does not bear claypebble impressions or cube-shaped imprints indicative of 

salt crystals. Its upper and lower contacts are marked by 

sharp lithologic changes that reflect unconformities. It 

has not yet been identified lithologically or faunally in 

southeastern Idaho or along the Idaho-Wyoming border south of the Caribou Range, which is just south of 

the Snake River. The Redwater Member is definitely 

not present in the type area of the Stump Sandstone cut 

or near Stump Peak.

The Redwater Member of the Stump Sandstone in 

southeastern Idaho and western Wyoming is correlated 

with the Redwater Shale Member of the Sundance Formation elsewhere because it contains belemnites in fair 

abundance from bottom to top (USGS Mesozoic Iocs. 

12125, 112126, 16024, 16028, 17897, 18183, 18185, 

30393, 18187, 30395) and contains Cardioceras near its 

base at Telephone Creek, Wyo. (USGS Mesozoic loc.

16024), and at McCoy Creek, Idaho (Mesozoic loc. 17897), 

as well as in the lower part of its upper third at McCoy 

Creek (USGS Mesozoic loc. 30395). In addition, the formation at its base at Telephone Creek contains the pelecypods Vaugonia quadrangularis (Hall and Whitfield) 

and Oxytoma wyomingensis (Stanton) along with Cardioceras and belemnites (USGS Mesozoic loc. 16024) and 

at its top on McCoy Creek contains 0. uryomingensis 

(Stanton) (USGS Mesozoic loc. 12125). The presence of 

these bivalves is important for correlation purposes because they occur elsewhere in the Redwater Shale Member of the Sundance Formation and in the Swift Formation, but they do not occur in older formations or 

members. The presence of Cardioceras shows that the 

Redwater Member is of early to early middle Oxfordian 

Age.

These facts show that the Curtis and Redwater 

Members of the Stump Sandstone were deposited in different seas that covered somewhat different areas, that 

erosion took place at the end of Curtis deposition and 

again after Redwater deposition, and that the present 

changes in thicknesses of the members is in part depositional as well as erosional.

The continental Morrison Formation in Wyoming, 

western South Dakota, and northernmost Utah and Colorado was deposited conformably on the Windy Hill 

Sandstone Member or on the Redwater Shale Member 

of the Sundance Formation. The Morrison attains thicknesses of 125-370 feet (38-113 m) in Wyoming and 

South Dakota and more than 800 feet (244 m) in northeastern Utah (Reeside, 1952, p. 24, 25; Craig and others, 

1955, p. 159; Hansen, 1965, p. 85). Westward increases 

in thickness and certain changes in lithologic characteristics (Mirsky, 1962, p. 1675-1678) indicate that its 

source was to the west in Utah and Idaho. On the basis 

of fresh-water mollusks, it should be older than the Purbeck Beds of England (Yen, 1952, p. 31-34), which are 

now correlated with the upper part of the upper Tithonian (Yen, 1952, p. 31-34). On the basis of vertebrates 

and stratigraphic position, its age should be mostly Kimmeridgian (Imlay, 1952a, p. 953, 958; Reeside, 1952, p. 

25). The basal beds of the Morrison, however, where 

they overlie the Redwater Shale Member, should be of 

late Oxfordian Age, as shown by the presence of Cardioceras and Quenstedtoceras throughout most of that 

member.

The continental Nugget Sandstone, as exposed in 

southeastern Idaho, western and central Wyoming, and 

north-central Utah, lies unconformably below the Gypsum Spring Formation, or the Gypsum Spring Member 

of the Twin Creek Limestone, of early to early middle 

Bajocian Age. Regionally, the Nugget rests unconformably on beds of Late Triassic age (Reeside, 1957, p. 

1480, 1482; Pipiringos, 1968, p. D16; Pipiringos and
COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 91

O'Sullivan, 1978). It consists characteristically of red to 

brown, or yellowish-gray to white, massive highly 

crossbedded sandstone, but in some places it includes 

considerable even-bedded, thin-bedded, ripple-marked, 

red to gray sandy shale, silty sandstone, and siltstone, 

which are most common in its lower 200 feet (Mansfield, 

1927, p. 96; Love and others, 1945; Pipiringos, 1968, p. 

D17; Poole and Stewart, 1964, p. D38; Cressman, 1964, 

p. 45; Rubey, Oriel, and Tracey, 1975, p. 4). The Glen 

Canyon Sandstone, as exposed in the Uinta Mountains 

of northeastern Utah and northwestern Colorado, occupies the same stratigraphic position as the Nugget Sandstone, is bounded by the same unconformities, and is 

reddish in the western part of the Uinta Mountains and 

white in the eastern part. Both of these formations on 

the basis of stratigraphic position could be of Late Triassic and (or) Early Jurassic age.

NORTHERN UTAH TO NORTHERN COLORADO

The Twin Creek Limestone and Preuss Sandstone in 

the Wasatch and Uinta Mountains of north-central Utah 

are nearly identical lithologically with the same formations exposed farther north, along the Wyoming-Idaho 

border. Eastward in the Uinta Mountains, however, the 

lower five members of the Twin Creek Limestone gradually wedge out from the base upwards (see fig. 27). 

Thus, the Gypsum Spring Member wedges out between 

Oakley and the Duchesne River; the Sliderock Member, 

between Lake Fork and Whiterocks River canyon; the 

Rich Member, between Whiterocks River canyon and 

Vernal; and the Boundary Ridge and Watton Canyon 

Members, eastward near Vernal. The two uppermost 

members of the Twin Creek Limestone change markedly 

east of Lake Fork into a sequence of gypsum, red sandstone and siltstone, and green claystone. This sequence 

closely resembles the Carmel Formation of the San Rafael Swell and persists eastward into Colorado.

The eastward lithologic changes from the Twin Creek 

Limestone to the Carmel Formation are well shown by 

the sequence at Whiterocks River canyon as described 

below:

Stratigraphic section of the Carmel Formation

[Exposed in the canyon of Whiterocks River in NW'A sec. 19 and 

SEVtSEVt sec. 18, T. 2 N., R. 1 E.t Uintah County, Utah]

Thickness 

Fei

Entrada Sandstone. 

Carmel Formation: 

Giraffe Creek equivalent:

25. Siltstone, greenish-gray, soft,

mostly covered-------------------------

24. Shale, greenish-gray, soft---------------

Leeds Creek equivalent:

23. Siltstone, red, interbedded with red

fine-grained sandstone containing thin 

streaks of gypsum——————-—---———

64

12

19.5 

3.7

2.7

Stratigraphic section of the Carmel Formation—Continued

Thickness 

Feet Meters 

Carmel Formation—Con.

22. Gypsum, white—————————————————— 2 .6 

21. Sandstone, red; some gypsum streaks———— 3 .9 

20. Gypsum, white—————————————————— 2 .6 

19. Shale, light-greenish-gray, finely sandy

to papery———————————————————— 6 1.8 

18. Gypsum, white—————————————————— 1 .3 

17. Siltstone, red; some green lenses————— 12 3.7 

16. Shale, light-green, sandy—————————— 23 7.0 

15. Shale, light-green, soft; some streaks of

red siltstone; poorly exposed——————— 86 26.2

14. Siltstone, red, interbedded with gypsum— 20 6.1

13. Gypsum, massive————————————————— 12 3.7

12. Shale, greenish, soft————————————— 15 4.6

Watton Canyon equivalent:

11. Limestone, grayish-white, lithographic—— 11 3.4 

10. Limestone, light-gray, shaly———————— 6 1.8 

Boundary Ridge equivalent:

9. Limestone, light-yellowish-gray, oolitic, 

thin-bedded, slightly sandy, ripple 

marked—————————————————————— 4 1.2 

8. Siltstone, red, soft—————————————— 17 5.2 

Rich equivalent:

7. Claystone, greenish-gray, soft, bentonitic 2 .6 

6. Sandstone, white, fine-grained, soft——— 2 .6 

5. Claystone", greenish-gray, very soft——— 6 1.8 

4. Limestone, yellowish gray; thin-bedded in 

middle, oolitic at top and bottom; 

contains Pleuromya and Camptonectes——— 4 1.2 

3. Claystone, yellowish-gray, soft; contains 

thin beds of nodular yellow limestone 

containing oysters—————————————— 12 3.7 

2. Claystone and sandy shale, light-gray, soft; 

contains a 6-inch (15 cm) bed of brown, 

sandy, oolitic limestone at base

containing Camptonectes—————————— 9 2.7 

1. Claystone, yellowish-green, soft; 

contains many very thin beds 

(0.2-0.5 in.; 0.6-1.3 cm) 1/4-1/2 inch 

of light-yellowish-gray shaly

sandstone.——————————————————— 5 1.5 

Total thickness—————————————— 345 105.2 

Sharp unconformity. 

Glen Canyon Sandstone (not measured).

The Sliderock Member of the Twin Creek Limestone, as exposed in the Uinta Mountains, is of particular 

interest stratigraphically because its lower beds are 

sandy, some are slightly crossbedded, and much of the 

member locally passes laterally into gray massive 

crossbedded sandstone that rests sharply on the brownish-red Glen Canyon Sandstone. Thus, in an exposure on 

the south side of the Duchesne River near Hanna (Imlay, 

1967b, p. 23), the member consists from bottom to top of 

5 feet (1.5 m) of fine-grained yellow sandstone, 25 feet 

(7.6 m) of fine-grained, sandy, medium- to thin-bedded 

limestone, and 12 feet (3.6 m) of gray massive oolitic 

limestone. Two miles to the west on Sand Creek, in the 

NWV4 sec. 7, T. 1 S., R. 8 W., the same member from its 

base upward consists of 4 feet (1.2 m) of deep-red, finegrained sandstone, 25 feet (7.6 m) of yellowish-gray, 

massive crossbedded sandstone that contains Gryphaea 

and Camptonectes, and then 12 feet (3.6 m) of gray, massive oolitic limestone. Except for this uppermost limestone, the member at Sand Creek is similar lithologically 

to the Page Sandstone of central and southern Utah 

(Fred Peterson and G. N. Pipiringos, unpub. data, 1977;
92 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

Pipiringos and O'Sullivan, 1975) and occupies the same 

stratigraphic position just below limestone that contains 

mollusks characteristic of the Rich Member of the Twin 

Creek Limestone (Imlay, 1967b, p. 31, 33). These sandstone beds were first recognized by G. N. Pipiringos 

(oral commun., 1974) as a northern extension of the Page 

Sandstone.

The Preuss Sandstone in the Wasatch Mountains resembles the same formation as exposed along the Wyoming-Idaho border by consisting mostly of red finegrained sandstone, by containing saline deposits in its 

lower part, and by containing locally near its base a 

sandy limestone member (Granger, 1953, p. 11) that 

could be equivalent to the Wolverine Canyon Limestone 

Member of the Preuss of southeastern Idaho (Imlay, 

1952b, p. 1740-1743). The exposures in the Wasatch differ from the others, however, by being softer, siltier, 

and darker red. This dark-red facies persists eastward 

into the Uinta Mountains as far as Lake Fork, but between Lake Fork and Whiterocks River canyon, it passes 

into light-colored, clean, crossbedded sandstone that is 

called the Entrada Sandstone and that extends eastward 

into Colorado.

Marine beds overlying the Preuss Sandstone, or the 

equivalent Entrada Sandstone, in the Uinta Mountains 

are commonly referred to the Curtis Formation (Huddle 

and McCann, 1947; Kinney and Rominger, 1947; Baker, 

1947; Kinney, 1955, p. 85-S9) or to the Stump Sandstone from Lake Fork westward and to the Curtis Formation from the Whiterocks River canyon eastward 

(Thomas and Krueger, 1946, p. 1278-1290). All authors 

cited here agree that the formation is readily divided into 

two distinct members. Recent studies by G. N. Pipiringos (oral commun., 1974) show that the lower member is 

identical lithologically and stratigraphically with the type 

Curtis Formation of central Utah (Gilluly and Reeside, 

1928, p. 78, 79) and with the Pine Butte Member of the 

Sundance Formation in southern Wyoming (Pipiringos, 

1968, p. D23). Assignment to the Curtis Formation (or 

Member) rather than to the Pine Butte Member is favored by the presence of basal unconformity. The Pipiringos studies also show that the upper member is identical with the Redwater Shale Member of the Sundance 

Formation of Wyoming and South Dakota (Imlay, 1947, 

p. 259-264; Pipiringos, 1968, p. D23) and is likewise 

characterized by an abundance of belemnites.

Recent studies by Pipiringos and Imlay (unpub. data) 

show also that the Redwater Member is widespread in 

the upper part of the Stump Sandstone, as exposed along 

the Wyoming-Idaho border, and that it overlies a lower 

member that is nearly identical with the Curtis Formation, or Curtis Member of Utah. These relationships 

show that the term Stump Sandstone was correctly applied by Thomas and Krueger (1946, p. 1278-1290) for 

the western part of the Uinta Mountains at least as far 

east as Lake Fork north of Duchesne, Utah. Usage of 

the term Stump Sandstone farther east in the Uinta 

Mountains is justified because the Curtis and Redwater 

Members are fairly continuous, because of their stratigraphic relationships with each other, because the Morrison Formation is the same throughout the mountains, 

and because geologists to date have not found it practical 

to map the two members separately.

As thus defined, the Curtis Member of the Stump 

Sandstone in the Uinta Mountains ranges from 30 to 110 

feet (9 to 33.5 m) in thickness; consists mostly of glauconitic, fine-grained to very fine grained, thin- to thickbedded sandstone that may be even-bedded and ripple 

marked, or crossbedded; contains glauconite grains of 

the same size as the surrounding sand grains; locally contains minor amounts of green fissile or sandy shale; is 

characterized by furrowed trails, by round, flat shale 

pebble impressions, and by salt casts on bedding plane 

surfaces; generally rests sharply on the underlying Entrada or Preuss Sandstone; is locally marked basally by 

a chert pebble conglomerate; and in places contains the 

pelecypods Meleagrinella and Camptonectes (Thomas 

and Krueger, 1946, p. 1279; Kinney, 1955, p. 87-88; 

Untermann and Untermann, 1954, p. 51; Pipiringos, oral 

commun., 1975).

The overlying Redwater Member of the Stump 

Sandstone ranges from 115 to 140 feet (35 to 43 m) in 

thickness; contains much soft greenish-gray shale and 

thin beds of glauconitic limy sandstone and sandy to oolitic limestone, which are especially common near its top 

and in the northern and eastern parts of the Uinta Mountains; is characterized by an abundance of belemnites and 

braciopods; rests sharply on the Curtis Member; and is 

locally marked basally by a pebble conglomerate (Thomas 

and Krueger, 1946, p. 1287). From Duchesne eastward, 

the Redwater Shale Member of the Sundance is overlain 

by the Windy Hill Sandstone Member of the Sundance 

(G. N. Pipiringos, oral commun., 1974). Elsewhere in the 

Uinta Mountains, the contact with the overlying Morrison Formation is generally drawn at the top of a unit of 

hard sandstone or oolitic limestone and is reported to be 

conformable but not gradational.

The Redwater Member of the Stump Sandstone in 

the Uinta Mountains is distinguished from the underlying Curtis Member by being generally much shalier and 

less glauconitic, by containing belemnites and brachiopods, by locally containing the ammonite Cardioceras, 

and by lacking furro^ ^ed trails. Evidently the sequence 

near Manila, Utah, that Hansen (1965, p. 82) assigned to 

the Curtis Formation actually belongs entirely to the 

Redwater Member, although the presence near Manila
COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 93

of a few feet of the Curtis Member is reported by G. N. 

Pipiringos (oral commun., 1967).

All these formations and members extend eastward 

along the margins of the Uinta Mountains into the western part of Moffat County, in the northwestern corner of 

Colorado (G. N. Pipiringos, oral commun., 1974). The 

Carmel Formation, however, wedges out east of Miller 

Creek (sees. 27 and 34, T. 4 N., R. 101 W.). The Redwater Shale Member of the Sundance Formation is absent east of Uranium Peak (sec. 28, T. 2 N., R. 92 W.) 

in the northeastern part of Rio Blanco County, Colo. The 

Curtis Formation and the equivalent Pine Butte Member 

of the Sundance Formation are locally absent at several 

places within their area of outcrop, even though the underlying Entrada Sandstone and the overlying Redwater 

Shale Member are present.

In north-central Colorado along the margin of the 

Park and Gore Ranges in Eagle, Routt, and Grand 

Counties, the marine Jurassic is represented near 

Kremmling, State Bridge, and Burns by the Canyon 

Springs Sandstone, Lak(?), Pine Butte(?), and Windy 

Hill Sandstone Members of the Sundance Formation (Pipiringos and others, 1969, p. N9-N35). The lower three 

of these members are transitional into each other, as at 

Frantz Creek (fig. 27), but locally the Canyon Springs 

grades upward into the Pine Butte, as at Elk Creek (fig. 

27). This relationship shows that the upper part of the 

Canyon Springs must locally be as young as the Entrada 

Sandstone of other areas. Its lower part, which is unfossiliferous, may or may not be as old as the typical member in Wyoming. The identification of both the Lak and 

the Pine Butte Members is tentative (Pipiringos and others, 1969, p. N12, N15).

Farther north along the Park Range in the Hahns 

Peak area of northern Routt County, the marine Sundance Formation is represented by the Canyon Springs 

Sandstone Member, the Pine Butte Member, the Redwater Shale Member, and the Windy Hill Sandstone 

Member (Pipiringos, 1972, p. 25-29). Of these, the Canyon Springs consists of about 60 feet (18 m) of gray to 

pink crossbedded sandstone and rests unconformably on 

Triassic rocks. The Pine Butte Member consists of about 

30 feet (9 m) of greenish-gray shale and some thin beds 

of ripple-marked sandstone that intertongues downward 

with the Canyon Springs. The Redwater Shale Member 

consists of 35 feet (10.6 m) of glauconitic siltstone and 

sandstone that correlates with only the lowermost of four 

units of that member exposed in south-central Wyoming 

(Pipiringos, 1968, p. D23). The Redwater Shale Member 

rests unconformably on the Pine Butte Member, is truncated by the Windy Hill Sandstone Member, and is unknown south of Corral Creek (sec. 18, T. 8 N., R. 84 

W.). This unconformable relationship and the widespread occurrence of the Windy Hill beyond the boundaries of the Redwater Shale Member demonstrates that 

these two members represent separate marine invasions.

The Jurassic exposed along the east side of the Front 

Range in northern Colorado is represented, from bottom 

to top, by 20 to 50 feet (6 to 15 m) of the Entrada Sandstone, by thinner marine units belonging to the Pine 

Butte Member and the Windy Hill Sandstone Member of 

the Sundance Formation, and by the Morrison Formation (G. N. Pipiringos, oral commun., 1974). All contacts 

between these units are conformable except that between the Windy Hill and the Pine Butte. The conformable relationship of the Entrada Sandstone with the Pine 

Butte Member shows that it is equivalent at least at its 

top to the Lak Member of the Sundance Formation in 

eastern Wyoming. It is probably equivalent also to the 

Canyon Springs Sandstone Member in the Park Range 

in north-central Colorado but may be younger than the 

typical Canyon Springs Sandstone Member in southern 

Wyoming and the Black Hills.

NORTH-CENTRAL UTAH TO SOUTHWESTERN COLORADO

The Jurassic sequence exposed in Monks Hollow 

(Baker, 1947; Imlay, 1967b, p. 11), about 18 miles (29 

km) southeast of Provo, Utah, is essentially the same as 

that exposed in the western part of the Uinta Mountains. 

A possible difference is in the 510 feet (155 m) of beds 

between the Preuss Sandstone and the Morrison Formation. The lower 260 feet (79 m) of these beds consists 

mostly of greenish-gray sandy shale interbedded with 

some gray to greenish-gray glauconitic sandstone and 

greatly resembles the unit in the Uinta Mountains that is 

identified with the typical Curtis Formation of central 

and northeastern Utah. The upper 250 feet (76 m) consists mostly of light-brown siltstone that contains a few 

beds of gray sandstone and greenish-gray shale and that 

was compared by Baker (1947) with the Summerville 

Formation. These identifications have now been confirmed by G. N. Pipiringos and the writer.

The lower 260 feet (79 m) of beds overlying the 

Preuss Sandstone at Monks Hollow occupies the same 

stratigraphic position as the Curtis Formation, resembles it lithologically, and likewise contains an abundance 

of Meleagrinella. These beds differ from the type Curtis 

Formation on the San Rafael Swell mainly by containing 

more soft clay shale and fewer hard sandstone beds and 

by the presence of a few cephalopods. Meleagrinella was 

collected throughout about 40 feet (12 m) of beds ranging 

from about 180 to 220 feet (55 to 67 m) above the top of 

the Preuss Sandstone. With these were found external 

and internal molds of the ammonite Lytoceras (USGS
94 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

Mesozoic loc. 30718). Also, four belemnites were obtained from the upper 10 to 15 feet (3 to 4.5 m) of the 

Meleagrinella-bearing beds.

The next higher 250 feet (76 m) of beds is definitely 

similar lithologically to the Summerville Formation of 

the San Rafael Swell. Like that formation, these beds are 

unfossiliferous and are gradational downward into the underlying Curtis Formation. These upper beds cannot reasonably be correlated with the Redwater Shale Member 

of the Stump Formation, as exposed nearby in the Uinta 

Mountains, because that member consists mostly of 

greenish-gray shale, rests unconformably on the Curtis 

Member, and contains a fair abundance of fossils.

The presence of belemnites in the Curtis Formation 

at Monks Hollow is not evidence that the Redwater 

Shale Member is present there, because in Montana, belemnites are in beds of middle Bajocian to late Callovian 

Age (Imlay, 1948, p. 17; 1962b, p. Cll, C21) and in the 

Pacific Coast region, they range throughout the Jurassic. 

Their presence along with Lytoceras, however, is evidence that the marine waters that deposited the Curtis 

Formation at Monks Hollow were deeper than those farther east in Utah and that the sea of Curtis time must 

have entered the western interior region from the west.

Marine Jurassic beds exposed on the west side of the 

Gunnison Plateau near Nephi and Levan, Utah, are defined as the Arapien Shale and are divided into two members (Spieker, 1946, p. 123-125; Hardy and Zeller, 1953, 

p. 1264-1266; Hardy, 1962, p. 52-54). The lower of 

these, the Twelvemile Canyon Member, greatly resembles the Twin Creek Limestone. It differs by being intensely folded, crinkled, and fractured and by containing 

more shale, more red units, and some gypsum in its upper 

part. Nonetheless, the lower part of the Twelvemile Canyon Member, as exposed on the south side of Red Canyon, 

about 2 miles (3 km) north of Nephi, contains units that 

resemble the members of the Twin Creek Limestone from 

the Gypsum Spring Member up to the basal part of the 

Leeds Creek Member (Imlay, 1964d, p. C6; 1967b, p. 30, 

40,44). The Twelvemile Canyon Member is overlain along 

the Gunnison Plateau by the Twist Gulch Member, which 

consists of red siltstone and sandstone more than 1,800 

feet (550 m) thick. This member is similar lithologically to 

the Preuss Sandstone in northern Utah, except for the 

presence of some gritty or pebbly beds.

Marine Jurassic beds exposed along the west side of 

the Wasatch Plateau near Gunnison and Salina are also 

referred mostly to the Arapien Shale (Hardy, 1952, p. 

14-24, 67-95). The Twelvemile Canyon Member, however, is represented only by its upper part, which consists mostly of much crinkled, gypsiferous red to gray 

shale, siltstone, and sandstone. At its very top, it also 

includes 165-200 feet (50-61 m) or more of red silty

shale and interbedded salt (Hardy, 1952, p. 21, 22, 91). 

It is conformably overlain by the Twist Gulch Member, 

which consists of 1,670-1,730 feet (509-527 m) of interbedded red calcareous siltstone and clay stone, reddish-gray to red sandstone, and some conglomerate. 

Above the Arapien Shale in the Salina Creek canyon east 

of Salina is 177 feet (54 m) of gray to green shale interbedded with and overlain by thin beds of gray sandstone. This shale contains 17 feet (5 m) of gray grit and 

some brown to red shale at its base (Hardy, 1952, p. 78). 

Fossils in the thin sandstone beds include Meleagrinella 

curia (Hall) and Ostrea.

Of these units, the upper 177 feet (54 m) of fossiliferous shale and sandstone is identical with the typical Curtis Formation of central Utah and is herein referred to 

that formation. The underlying Twist Gulch Member is 

similar to the Preuss Sandstone of northern Utah but 

differs in that it contains some pebbly beds and in that 

some of the sandstone beds are coarse grained or gritty, 

or crossbedded. The salt-bearing red silty shale, which is 

defined as being at the top of the Twelvemile Canyon 

Member, corresponds lithologically and stratigraphically 

with the salt-bearing red beds in the lower part of the 

Preuss Sandstone along the Idaho-Wyoming border 

(Mansfield, 1927, p. 99, 338-340; Imlay, 1952b, p. 1746). 

The underlying upper part of the Twelvemile Canyon 

Member probably correlates with the Leeds Creek and 

Giraffe Creek Members of the Twin Creek Limestone 

but differs by containing more red units, more sandstone, and more gypsum.

The described Jurassic sequences present on the 

west side and north end of the San Rafael Swell are 

typified by the sequence near Buckhorn Wash (Gilluly, 

1929, p. 99^-114; Gilluly and Reeside, 1928, p. 97-106, 

chart opposite p. 74). On the east side of the swell, they 

are typified by the sequences at the Black Dragon Canyon and at the San Rafael River (Baker, 1946, p. 6^-90). 

Lithologic units within those sequences are described, 

correlated, and dated in various papers (Baker and others, 1936, p. 11, 25, 26, 31, 58-63; Imlay, 1952a, p. 961- 

964; Wright and others, 1962; and Cater and Craig, 1970) 

and are summarized in figure 28, except for the Curtis, 

Summerville, and Morrison Formations discussed below.

Of these three, the Curtis Formation consists mostly 

of greenish shale, glauconitic sandstone, and shale. Sandstone is most common and is generally thin bedded, ripple marked, and crossbedded. Shale beds are generally 

sandy and some are red or lavender. Conglomeratic beds 

occur in the lower part of the formation in the northern 

and northwestern parts of the swell. The contact of the 

Curtis Formation with the underlying Entrada Sandstone is sharp, locally angular, and is locally marked by 

conglomerate (Gilluly, 1929, p. 105-108; Gilluly and
COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 95

Reeside, 1928, p. 78-106; Baker, 1946, p. 80-84). 

The Curtis Formation contains echinoid fragments, crinoid columnals, Ostrea strigilecula White, Meleagrinella 

curia (Hall), Tancredia, and Camptonectes.

The Summerville Formation on the San Rafael Swell 

consists mainly of thin-bedded, even-bedded shale and 

sandstone and locally contains considerable gypsum. 

Generally the shales are chocolate brown to maroon, and 

the sandstones are reddish brown. Ripple- marks are 

common in the sandstones. The formation grades downward into the Curtis Formation, replaces the Curtis gradationally near the Green River, and is overlain with 

angular unconformity by the Morrison Formation (Gilluly, 1929, p. 108-110; Gilluly and Reeside, 1928, p. 79- 

106; Baker, 1946, p. 84-86).

The Morrison Formation in the southern part of the 

western interior region attains maximum thicknesses of 

800-900 feet (240-270 m) (Craig and others, 1955, p. 

159) and was derived mainly from source areas in the 

west-central parts of New Mexico, in Arizona, in western and northwestern Utah, and in southeastern California (Craig and others, 1955, p. 126, 150, 151, 159). Its 

base cannot be dated as precisely here as in areas to the 

north where the formation rests conformably on the Redwater Shale Member of the Sundance Formation. Presumably the Morrison Formation south of northern Utah 

and northern Colorado is also of late Oxfordian to early 

Tithonian Age.

However, the basal part of the Morrison may be of 

early Oxfordian Age, equivalent to the Redwater Shale 

Member. Such is suggested by the presence of massive 

gypsum at the base of the Morrison Formation in the San 

Rafael Swell (Gilluly, 1929, p. 114, 117; Baker, 1946, p. 

87, 89, 90). As that gypsum rests unconformably on the 

Summerville Formation, it cannot be as old as that formation. Instead, its presence suggests deposition in lagoons at the margin of a shallow sea, such as existed in 

early Oxfordian time north of the San Rafael Swell.

Recent refinements in dating the Jurassic formations 

in the San Rafael Swell are based on three discoveries. 

First, G. N. Pipiringos (oral commun., 1974) recognized 

that the Curtis Formation in the San Rafael Swell is 

identical with the Pine Butte Member of the Sundance 

Formation in Wyoming (Pipiringos, 1968, p. D23) and 

with the lower member of the so-called Curtis Formation 

and Stump Sandstone of northern Utah, as used by 

Thomas and Krueger (1946, p. 1278, 1279). All these 

units occupy the same stratigraphic position above the 

Entrada Sandstone, or equivalent units. This identification means that the Curtis Formation of the San Rafael 

Swell must be older than early Oxfordian, because the 

equivalent beds in Wyoming and in northern Utah disconformably underlie the lower Oxfordian Redwater 

Shale Member of the Sundance Formation and of the

Stump Sandstone. Faunally, the Curtis Formation of the 

San Rafael Swell is distinguished from the Redwater 

Shale Member by its lack of belemnites and brachiopods. 

These taxa are also absent in the Pine Butte Member of 

the Sundance Formation and in the Curtis Member of 

the Stump Sandstone.

Second, the lowest limestone unit in the Carmel Formation on the west side of the San Rafael Swell was 

dated by Imlay (1967b, p. 32, 33) as latest Bajocian, because it contains certain pelecypods and ammonites that 

elsewhere are characteristic of the Rich Member of the 

Twin Creek Limestone and that do not range higher. In 

particular, the ammonite Sohlites spinosus Imlay was 

obtained 6-12 feet above the base of the Carmel Formation on The Wedge near Buckhorn Wash (Imlay, 

1967b, p. 92, pi. 11, fig. 24).

Third, 100 feet (30 m) or less below the base of the 

Carmel Formation on the San Rafael Swell, Pipiringos 

and O'Sullivan (1975) recognized an unconformity that 

is marked by chert pebbles and that probably correlates 

with the unconformity at the top of the Gypsum Spring 

Formation in Wyoming. These pebbles are overlain by 

massive, crossbedded gray sandstone, which was previously assigned to the Navajo Sandstone (Gilluly, 1929, 

p. 98; Gilluly and Reeside, 1928, p. 72; Baker and others, 1936, pis. 13, 14; Baker, 1946, p. 68, 69) but which 

has now been renamed Page Sandstone (Peterson and 

Pipiringos, unpub. data, 1977). This sandstone has been 

recognized above chert pebble beds at many places in 

southern Utah, where it is as much as 250 feet (76 m) 

thick and where it conformably underlies and laterally 

intertongues with the lower part of the Carmel Formation (Pipiringos and O'Sullivan, 1975, 1978). Therefore, 

inasmuch as the lower part of the Carmel has been correlated with the Rich Member of the Twin Creek Limestone (Imlay, 1967b, p. 33), the underlying Page Sandstone on the swell should be equivalent to the Sliderock 

Member of the Twin Creek.

On the basis of these discoveries, the Curtis Formation on the San Rafael Swell is considered to be of 

late middle Callovian Age. The overlying Summerville 

Formation is considered to be only slightly younger, as 

shown by its gradation downward and laterally into the 

Curtis Formation (Baker, 1946, p. 86) and by the angular unconformity at its top. This unconformity presumably correlates in part with the regional unconformity at 

the base of the Redwater Shale Member of the Sundance 

Formation. The basal limestone of the Carmel Formation 

on the San Rafael Swell is dated as latest Bajocian on 

the basis of fossils. Consequently, the beds overlying this 

unit, but below the Curtis Formation, are dated as Bathonian to early or early middle Callovian on the basis of 

stratigraphic position. Furthermore, the lower part of 

the Carmel Formation, between its basal limestone beds
96 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

and its varicolored gypsiferous beds, bears lithologic resemblances to the Boundary Ridge and Watton Canyon 

Members of the Twin Creek Limestone (Imlay, 1967b, 

p. 40, 44, 49), which members are now dated as early to 

middle Bathonian.

The Jurassic formations exposed east of the San Rafael Swell, in easternmost Utah and westernmost Colorado, have been studied in considerable detail (McKnight, 1940; Dane, 1935; Baker, 1946; Wright and 

others, 1962; Craig and others, 1955; Cater and Craig, 

1970; Shawe and others, 1968, Ekren and Houser, 1965) 

but are difficult to correlate and date precisely because 

fossils are scarce in all of them except the continental 

Morrison Formation. Lateral tracing of beds shows, 

however, that the lower, limestone-bearing part of the 

Carmel Formation thins eastward and pinches out a little 

east of the mouth of the San Rafael River (Baker, 1946, 

p. 71; McKnight, 1940, p. 87; Wright and others, 1962, 

p. 2058). The upper varicolored gypsiferous part of the 

Carmel Formation also thins gradually eastward, and 

east of the Green River in east-central Utah, it passes 

into reddish-brown siltstone and silty sandstone that 

most geologists have mapped as the eastern part of the 

Carmel Formation but that are now called the Dewey 

Bridge Member of the Entrada Sandstone (Wright and 

others, 1962, p. 2059). This member pinches out near the 

State line west of Grand Junction, Colo., but persists 

southeastward as a thin unit into southwestern Colorado.

East of the San Rafael Swell, the Entrada Sandstone 

consists of three members (fig. 28). The basal Dewey 

Bridge Member is conformably overlain by the Slick 

Rock Member, and the Moab Member is locally present 

at the top of the formation. The Entrada Sandstone of 

the San Rafael Swell extends eastward as the Slick Rock 

Member, a massive, crossbedded sandstone that thins to 

the east and southeast (Wright and others, 1962, p. 

2062). The overlying Moab Member consists of massive, 

white, crossbedded sandstone that is at least 100 feet 

thick near Moab but that thins laterally away from there 

into ledge-forming sandstone (Baker and others, 1927, 

p. 804; Dane, 1935, p. 94). It is reported to intertongue 

laterally in places with the Summerville Formation, in 

places to grade downward or laterally into the Slick Rock 

Member, and in other places to rest on an erosion surface 

at the top of the Slick Rock Member (McKnight, 1940, 

p. 89^97; Wright and others, 1962, p. 2063-2067; Cater 

and Craig, 1970, p. 30). In places where the Moab Member is absent, the Slick Rock apparently is overlain conformably by the Summerville Formation.

The Summerville Formation east of the Green Kiver 

in eastern Utah and in westernmost Colorado includes 

beds that are probably equivalent to the Curtis Formation, but otherwise it maintains its lithologic characteristics, except for the presence of a few sandstone lenses. 

Such lenses occur (1) at its base where the Moab Member 

intertongues, (2) in a fairly persistent marker bed a little 

above its middle (Wright and others, 1962, fig. 2, 3; 

Shawe and others, 1968, p. A45), (3) at its top in southwestern Colorado where the Junction Creek Sandstone 

intertongues (Shawe and others, 1968, p. A49, A50; Ekren and Houser, 1965, p. 12, 13; Stokes, 1944), and (4) 

where a similar sandstone called the Bluff Sandstone intertongues in southeastern Utah. (See summary in Craig 

and others, 1955, p. 132-134.)

Considerably different statements have been made 

concerning the nature of the boundary between the Morrison Formation and the underlying Summerville Formation, or equivalent units, as exposed along the UtahColorado border (fig. 28). Northeast of Moab, Utah, in 

the Salt Valley anticline area, as at Dewey Bridge, the 

contact is sharp, slightly irregular, and persistent (Dane, 

1935, p. 112). In the adjoining area in western Colorado, 

as at John Brown Valley, the contact as mapped is reported to be gradational within 15 feet or less (Cater and 

Craig, 1970, p. 40). Nonetheless, the absence of the Summerville Formation locally along crests of some salt anticlines could be due to erosion during early Morrison 

time (Cater and Craig, 1970, p. 34) or to nondeposition 

during Summerville time. To the southeast in the Slick 

Rock area, the same contact is disconformable at most 

places (Shawe and others, 1968, p. A58). Still farther 

south in the Ute Mountains area, as at McElmo Canyon, 

the contact of the Morrison Formation with the Junction 

Creek Sandstone is locally disconformable and locally 

gradational (Ekren and Houser, 1965, p. 13). If these 

statements are correct, then deposition of the Summerville Formation was succeeded in places directly by deposition of the Morrison Formation while erosion took 

place in other places nearby.

SOUTHWESTERN UTAH AND NORTHERN ARIZONA

Along the Utah-Arizona border the lowermost Jurassic may be represented by units of continental origin 

that from the base up include the Moenave Formation, 

the Kayenta Formation, and the Navajo Sandstone (fig. 

29). The Moenave Formation rests unconformably on the 

Chinle Formation, is mostly of fluvial origin, comprises 

three members, and drained southwestward. Of these 

members, the lowermost, or Dinosaur Canyon Sandstone Member, consists of reddish-orange to brown sandstone and siltstone (Harshbarger and others, 1957, p. 13; 

Wilson, 1965, p. 39); the middle, or Whitmore Point 

Member, consists mostly of gray to red siltstone and 

clay stone but includes some limestone (Wilson, 1967);
COMPARISONS OF LITHOLOGIC AND STRATIGRAPHIC FEATURES 97

and the upper, or Springdale Sandstone Member, consists mostly of pale-red to brownish-red sandstone but 

includes some siltstone and conglomerate. The Kayenta 

Formation consists of light-gray to reddish-orange sandstone and siltstone that becomes finer grained and thicker 

south westward, intertongues southwestward with the 

adjoining members, is mostly of fluvial origin (Wilson, 

1965, p. 40, 42), and drained southwestward. The Navajo 

Sandstone consists mostly of highly crossbedded sandstone, includes some beds of cherty limestone, and is 

mostly of eolian origin (Harshbarger and others, 1957, p. 

19-25; Wright and Dickey, 1958, p. 173; Stokes, 1963, 

p. 61; Wilson, 1965, p. 41, 42; Averitt, 1962, p. 17, 18).

The Moenave Formation occupies the same stratigraphic position as the Lukachukai Member of the Wingate Sandstone, which lies to the east and northeast and 

which consists mostly of eolian, large-scale crossbedded 

sandstone (McKee and MacLachlan, 1959, p. 22, pi. 8, 

figs. 5, 6, table 1; Wright and Dickey, 1958, p. 172, 173). 

The change from the eolian Wingate Sandstone to the 

fluvial Moenave Formation in southern Utah takes place 

within a few miles along a northwest-trending zone, 

which is an extension of that mapped by Harshbarger 

and others (1957, p. 3, 10) in the Navajo Indian Reservation in northern Arizona.

These formations are possibly of Early Jurassic age, 

as suggested (1) by the presence of an unconformity between the Moenave and the underlying Chinle Formation of Triassic age; (2) by an unconformity between the 

Navajo Sandstone and the overlying Temple Cap Sandstone of early to early middle Bajocian Age; and particularly (3) by palynomorphs dated as of late Sinemurian 

to early Pleinsbachian Age in the basal 15 feet (5 m) of 

the Whitmore Point Member of the Moenave Formation 

(Peterson and others, 1977, p. 755). Acceptance of this 

dating must await adequate description and illustration 

of the fossils and confirmation by other paleontologists. 

At present, the formations in question are dated by the 

U.S. Geological Survey as Triassic (or Triassic?) and (or) 

Jurassic (or Jurassic?).

This evidence suggests that the unconformity at the 

base of the Moenave Formation is possibly of Hettangian 

Age, that the unconformity at the top of the Navajo 

Sandstone is at least partly of late Toarcian Age, and 

that the Kayenta Formation and Navajo Sandstone may 

have been deposited during Piiensbachian and Toarcian 

time. Furthermore, the Navajo Sandstone may be correlated with the Dunlap Formation of western Nevada 

on the basis of the presence in common of nearly identical 

crossbedded quartz sandstone (Stanley, 1971, p. 467- 

475), on a vsimilar stratigraphic position, and on the main 

source area of both formations being an uplifted northward-trending area in central Nevada. However, the

sand in the Dunlap Formation may have been derived 

from the Navajo Sandstone by erosion. If this premise is 

correct, the Navajo should be at least as old as Sinemurian.

The Temple Cap Sandstone was originally described 

by Gregory (1950) as a member of the Navajo Sandstone. 

It was subsequently made a separate formation (Fred 

Peterson and G. N. Pipiringos, unpub. data, 1977). It 

consists of two facies, or members, which extend about 

75 miles (120 km) to the east from Gunlock, Utah, and 

which pinch out between the Carmel Formation and the 

Navajo Sandstone (fig. 29) a few miles east of Johnson 

Canyon. One facies, called the White Throne Member, 

consists of 170 feet (52 m) or less of pale-red to gray 

crossbedded sandstone that is identical with the sandstone of the underlying Navajo Sandstone but that is 

separated from it by 5 to 25 feet (1.5 to 7.6 m) of softer 

red or gray siltstone and silty sandstone. The other facies, called the Sinawava Member, consists of 372 feet 

(113 m) or less of red to gray, flat-bedded sandstone, 

silty sandstone, mudstone, and some bedded gypsum. 

This facies changes eastward from red to gray at Mount 

Carmel Junction. To the west, the White Throne Member intertongues with the Sinawava Member near the 

Hurricane Cliffs on the west side of Zion National Park, 

and to the east it overlies a thin extension of the Sinawava Member as far east as their pinchout near Johnson 

Canyon, about 10 miles (16 km) east of Mount Carmel. 

The formation contains small, rounded chert granules at 

its base, and rests sharply on the Navajo Sandstone.

Criteria that suggest an unconformity at the base of 

the Temple Cap, according to Peterson and Pipiringos 

(unpub. data, 1977), are (1) lack of interfingering between the Temple Cap and Navajo Sandstones; (2) clear 

separation of these formations by a continuous surface; 

(3) broad irregularities at the base of the Temple Cap 

that are interpreted as an expression of erosional relief 

developed on the Navajo prior to Temple Cap deposition; 

and (4) a thick bleached zone at the top of the Navajo at 

most places, which is interpreted as alteration product of 

ground-water seepage into the upper part of the Navajo 

during a long erosion interval. These criteria and relationships show that the Temple Cap Sandstone is not a 

tongue of the Navajo Sandstone and should not have 

been considered a member of that formation by Gregory 

(1950, p. 89) and later workers (Wright and Dickey, 

1963a, b; Thompson and Stokes, 1971; Lewis and others, 

1961).

The Carmel Formation of southwestern Utah between Gunlock and Johnson Canyon consists of four 

members (fig. 29) that from base to top were called the 

limestone member, the banded member, the gypsiferous 

member, and the Winsor Member by Cashion (1967). The
98 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

same members were also described by Gregory (1950, p. 

92-98) under the names Carmel Formation, Entrada 

Sandstone, Curtis Formation, and Winsor Formation, 

respectively. We now know, however, that rocks called 

the Entrada Sandstone and the Curtis Formation by 

Gregory are much older than those formations at their 

type localities in central Utah (Imlay, 1967b, p. 20, 33, 

40, 44). Of the four members, the limestone member is of 

most importance for age determinations because it is the 

only Jurassic member in southern Utah that contains 

datable marine fossils. Also, its lower 20-120 feet (6- 

36.5 m) of pink to red siltstone and claystone basally contains angular chert pebbles from Zion National Park 

eastward, but west of the park, the same unit contains 

granules of rounded chert and quartz. Its lower contact, 

according to Fred Peterson and Pipiringos (unpub. data, 

1977) is sharply defined and bevels out the Temple Cap 

Sandstone to the east near Johnson Canyon.

The fourfold division of the Carmel Formation persists eastward across southwestern Utah for about 90 

miles (144 km) with little change except for thinning of 

the lower three members. East of the Little Bull Valley 

area, however, the Winsor Member grades into the middle and upper parts of the upper member of the Carmel 

Formation, as described by Fred Peterson and Pipiringos (unpub. data, 1977). Near the Paria River, the gypsiferous member grades into the lower part of the upper 

member.

Also near Little Bull Valley, 8 miles (13 km) southwest of Cannonville, the banded member grades into 

crossbedded to flat-bedded sandstone of the Thousand 

Pockets Tongue of the Page Sandstone (Wright and 

Dickey, 1963a, p. E65, E66; Phoenix, 1963, p. 32, 33; 

Fred Peterson and Pipiringos, unpub. data, 1977). East 

of the Paria River near Cannonville, the lower limestone 

member is termed the Judd Hollow Tongue of the Carmel Formation (Phoenix, 1963). Farther east, this tongue grades into flat-bedded sandstone and siltstone that 

disappears eastward between two tongues of the Page 

Sandstone. Evidently, the Page Sandstone, where fully 

developed, as at its type locality near Page, Ariz., is 

equivalent to both the limestone member and to the 

banded member of the Carmel Formation farther west.

The Page sandstone, as defined by Fred Peterson 

and Pipiringos (unpub. data, 1977), is as much as 291 feet 

(89 m) thick about 10 miles (16 km) south-southwest of 

Page, Ariz. It consists mostly of gray, cliff-forming, 

crossbedded sandstone, contains angular, red to gray 

chert pebbles at its base and, locally, higher, and rests 

sharply and unconformably on the Navajo Sandstone 

along a surface that locally has a relief of as much as 37 

feet (11 m). According to Fred Peterson and Pipiringos 

(unpub. data, 1977) the evidence for an unconformity is 

strengthened by two facts: (1) the angular pebbles consist of the same kinds of chert that are formed in authigenic chert nodules in the Navajo Sandstone; and (2) the 

upper few feet of the Navajo Sandstone at many places 

contains crevices that they interpret as fossil joints 

weathered out prior to deposition of the Page Sandstone.

The Entrada Sandstone of south-central Utah, where 

fully developed, as at Pine Creek near Escalante, consists of three members, according to Fred Peterson and 

Pipiringos (unpub. data, 1977). At Pine Creek, the upper 

member consists of white crossbedded sandstone, the 

middle, of red to white to light-green flat-bedded silty 

sandstone and mudstone, and the lower, of red, thickbedded, flat-bedded silty sandstone. The upper member 

becomes truncated southward in Utah, but the middle 

and lower members persist considerably beyond the limits of the upper member and become sandier and more 

crossbedded both westward in Utah and southward in 

Arizona. At some places, as at Big Hollow Wash, Utah, 

and Page, Ariz., the middle member of the Entrada is 

overlain unconformably by a light-gray sandstone unit 

0-44 feet (0-13.4 m) thick, which has a thin red mudstone bed at its base, and which apparently occupies the 

same stratigraphic position as the Summerville Formation of central Utah (Fred Peterson, 1974, 1973; Fred 

Peterson and Barnum, 1973).

The Morrison Formation unconformably overlies the 

light-gray sandstone at Page and Big Hollow Wash (fig. 

29). In areas where the light-gray sandstone is missing, 

the Morrison rests unconformably on the upper or middle 

member of the Entrada Sandstone. The Morrison Formation is highly variable in thickness, comprises three 

members of which the lower and upper may be locally 

absent, and is overlain unconformably by Cretaceous 

beds (Fred Peterson and Barnum, 1973; Fred Peterson, 

1973, 1974; Zeller and Stephens, 1973).

The Jurassic formations of southern Utah are correlated with formations farther north by some lithologic resemblances, by their relative stratigraphic positions, and 

by the presence of certain species of mollusks in the middle to upper parts of the limestone member of the Carmel 

Formation. These mollusks have been found in exposures between Gunlock and the Mount Carmel-Glendale 

area and also in a thin limestone unit 12-20 feet (3.6- 

6 m) above the base of the Carmel Formation at Deep 

Creek north of Escalante and at Hells Backbone northwest of Boulder, Utah.

At least the upper three-fourths of the limestone 

member of the Carmel Formation between Gunlock and 

Mount Carmel is dated as late Bajocian. That age is 

shown by the presence or association of certain species 

of pelecypods that in Idaho and Wyoming are characteristic of the Rich Member of the Twin Creek Limestone 

and are not known from higher or lower members (Imlay, 1964d, p. C3; 1967b, p. 14,15, 31, 33). Near Gunlock,
JURASSIC UNCONFORMITIES 99

for example, correlation with the Rich Member is shown 

by the presence of Gervillia! montanaensis Meek, which 

occurs about 150 feet (46 m) above the base of the lowest 

limestone beds and also about 323 feet (98 m) higher, or 

50 feet (15 m) below the eroded top of the member. Vaugonia conradi Meek, not known below the Rich Member, 

was found 74 miles (12 km) east of Gunlock in the Diamond Valley sequence 60-^80 feet (18-24 m) above the 

lowest limestone bed, and 9 miles (14.5 km) northwest of 

Hurricane near the Danish Ranch about 60 feet (18 m) 

above the lowest limestone bed.

These fossil occurrences and others, as listed previously (Imlay, 1964d, p. C8, C9, C13; Sohl, 1965, p. D5, 

localities 8-12, 33-38 on p. D6, D7), show that only 

the lower one-fourth to one-fifth of the limestone member could be older than the Rich Member. Beds equivalent to the Sliderock Member of the Twin Creek Limestone could only be represented by the lowest 50-150 

feet (15-46 m) of unfossiliferous limestone of the limestone member and by the underlying gypsiferous red 

sandy siltstone beds at the base of the Carmel Formation. Such a correlation seems most likely for the thickest 

sequences of the member as exposed from Gunlock eastward to Pintura and thence northeastward to Shurtz 

Creek about 6 miles (10 km) south of Cedar City. If this 

correlation is correct, then the unconformably underlying Temple Cap Sandstone should be of about the same 

age as the Gypsum Spring Formation of Wyoming and 

adjoining States, which is of early to early middle Bajocian Age, only a little older than the Sliderock Member.

Similarly, on the basis of stratigraphic position, the 

banded member of the Carmel Formation, and its equivalent Thousand Pockets Tongue of the Page Sandstone, 

should correlate with the Boundary Ridge Member of the 

Twin Creek Limestone and should be of early Bathonian 

Age. The overlying upper part of the Carmel Formation 

in southwestern Utah should correlate with the higher 

members of the Twin Creek Limestone and should be of 

middle Bathonian to early Callovian Age.

Southeastward from Page, Ariz., according to Fred 

Peterson (1974, p. 467; oral commun., 1974), the Page 

Sandstone pinches out in about 15 miles (24 km), the 

Morrison Formation, in about 30 miles (48 km), and the 

underlying gray sandstone of Romana Mesa, in about 45 

miles (72 km). As a result, at Cow Springs, about 50 

miles (80 km) southeast of Page, the Jurassic is represented only by the Carmel Formation and the Entrada 

Sandstone. Peterson noted that the Carmel Formation 

at Cow Springs is 188 feet (57 m) thick, consists of flatbedded sandstone, silty sandstone and mudstone, is 

mostly reddish brown, includes some angular chert pebbles at its base, and rests unconformably on the Navajo 

Sandstone. At the same place, the Entrada Sandstone is 

773 feet (236 m) thick. Its lower 197 feet (60 m) consists

mostly of light-gray crossbedded sandstone but includes 

some thin beds of dark-brownish-red mudstone or sandstone. Its middle 274 feet (84 m) consists mostly of orange-brown to reddish-brown or white flat-bedded sandstone but includes some crossbedded sandstone. Its upper 

302 feet (92 m) consists mostly of light-gray to greenishgray crossbedded sandstone but includes some fairly thin 

beds of flat-bedded sandstone and is overlain unconformably by the Dakota Sandstone. This upper unit represents the Cow Springs Sandstone of Harshbarger and 

others (1957, p. 49-51), but it is considered by Fred Peterson (1974, p. 467) to be a bleached-out upper part of 

the Entrada Sandstone, such as occurs in many sections 

in northern Arizona and southern Utah.

MIDCONTINENT REGION

The only Jurassic deposit identified to date in the 

middle part of the continent is in the center of the Michigan basin. It consists of 100-400 feet (30-120 m) of red 

clay, shale, sandstone, and some gypsum. The deposit 

has lenticular bedding, rests on Pennsylvanian and Mississippian rocks, contains spores identified as Kimmeridgian in age, and presumably is entirely continental 

(Cohee, 1965). Its age apparently coincides with that of 

the Morrison Formation in Montana and the Dakotas.

JURASSIC UNCONFORMITIES

A major unconformity representing more than the 

lower half of Jurassic time occurs throughout the northern and western parts of the Gulf region as far south as 

Victoria, Tamaulipas, Mexico (figs. 21, 30). This unconformity probably continued into early Callovian time, on 

the basis of the probability that the overlying saline beds 

(Louann Salt, Werner Formation, and Minas Viejas Formation) were deposited at the same time as similar saline 

beds in southeastern Mexico, where conditions were unfavorable for salt deposition before late Callovian time 

(Imlay, 1943a, p. 1438, 1508-1510; 1953c, p. 31; Viniegra 0., 1971, p. 480, 484).

Farther south, in the Huasteca area of eastern Mexico, an unconformity of such magnitude is not recognizable except locally on certain uplifts. Instead, the same 

time interval is represented by (1) an unconformity of 

Hettangian Age, (2) marine and plant-bearing deposits 

of Sinemurian and questionably of early Pliensbachian 

Age, (3) an unconformity of Pliensbachian to Toarcian 

Age caused by orogenic activity, (4) continental beds of 

Bajocian to Bathonian Age, (5) an unconformity of latest 

Bathonian and earliest Callovian Age, and (6) marine 

beds of late early Callovian and younger ages. Bajocian
100 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

Southwest Oregon and 

northwest California

FIGURE 30.—Jurassic unconformities in Gulf of Mexico and Pacific Coast regions. Blank spaces indicate that marine strata are present; vertical 

lines indicate that strata are missing; left-diagonal lines indicate that strata are not exposed; right-diagonal lines indicate lack of fossil 

data.
JURASSIC UNCONFORMITIES 101

8 

1

Juressic Upper 

Middle Jurassic

Jurassic Lower 

Stage

Tithonian

Kimmeridgian

Oxfordian

Gallovian

Bathonian

Bajocian

Toarcian

Pliensbachian

Sinernurian

Hettangian

Western interior

Swift 

Reservoir 

and 

Sun River, 

northwest 

Montana

1

Nonmarine

^

-" 

•s

^

^

/

Williston 

basin, 

northeast 

Montane

\

\

Nor

\

\

ma

\

\

Ammo 

Quadrang 

southeas 

Idaho

, e Red Creek, 

central 

Wyoming

?

Nonmarine

?

Nonmarine

?

Bush 

Canyon, 

eastern 

Wyom ing

?

Nonmarine

region

Peoa-Oakley 

area, 

north-central 

Utah

No

?

rimarine

-

?

Nonmarine

?

Dinosaur 

Quarry, 

northeast 

Utah

?

Nonmarine

Nonmarine

I

Nonmarine

1

Buckhorn 

Wash, 

central 

Utah

?

Nonmarine

I 1 1 1

Nonmarine

Nonmarine

_ —

?

Mount Carmel 

Junction, 

southern 

Utah

Mostly 

nonmarine

Nonmarine

?

Pine Creek, 

south-central 

Utah

Nonmarine

Partly 

nonmarine

Partly 

nonmarine

Nonmarine

Nonmarine

?

Page area, 

north-central 

Arizona

Nonmarine

Partly, nonmarine

Nonmarine

7

Nonmarine

— i — —

FIGURE 31.—Jurassic unconformities in western interior region. Blank spaces indicate that marine strata are present; vertical lines indicate

that strata are missing.
102 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

and Bathonian continental beds in the Huasteca area correlate fairly well in time with similar plant-bearing beds 

in the States of Guerrero and Oaxaca in southern Mexico 

and with the plant-bearing San Cayetano Formation in 

Cuba. The fact that beds of Kimmeridgian Age locally 

rest on beds of Sinemurian to possible earliest 

Pliensbachian Age suggests that certain areas were islands from Middle Pliensbachian to late Oxfordian time, 

or that erosion occurred in late Oxfordian time, or that 

both things may have happened.

The erogenic activity associated with the unconformity of Pliensbachian to Toarcian Age (Imlay, Cepeda and 

others, 1948, p. 1750-1753; Carrillo Bravo, 1965, p. 85, 

87, 92-95) suggests that the unconformity developed 

mainly during Pliensbachian time and may be areally 

more extensive in the Gulf region than is now realized. 

Also, it may correlate roughly with an unconformity of 

early Pliensbachian Age in eastern Oregon, southwestern Alberta, arctic Canada, and Alaska (see fig. 13); with 

uplift of an area in eastern Nevada from which the sands 

of the Dunlap Formation were derived (Muller and Ferguson, 1939, p. 1616-1622); and with intrusion of diabase sills (Palisade disturbance) into continental beds of 

Sinemurian Age in New Jersey (Dallmeyer, 1975).

In addition, several minor unconformities of Late 

Jurassic age have been recognized in the northern and 

western parts of the Gulf region. These include (1) a 

probable minor disconformity of middle Oxfordian Age 

formed after deposition of the main saline beds (Louann 

Salt) by a swiftly transgressing sea (Norphlet Formation) which reworked the surface of the saline beds and 

transgressed beyond; (2) a minor disconformity of early 

Kimmeridgian Age formed locally in Mexico and possibly 

also in the southeastern United States, at the same stratigraphic position as a nearby gypsiferous red-bed unit 

(Olvido Formation and Buckner Formation); and (3) a 

disconformity formed locally at the top of the Jurassic in 

the Gulf region of the United States.

In the Pacific Coast region, the entire Jurassic is represented by unconformities at one place or another (fig. 

30). Of those unconformities found in two or more places, 

some represent Hettangian, early Pliensbachian, Bathonian, early Callovian, and late Callovian time. Others 

begin in middle Bajocian, middle Callovian, and late 

Kimmeridgian time and continue through the remainder 

of the Jurassic. These unconformities lack continuity 

over large distances, owing to westward shifting of depositional troughs during Jurassic time, to deposition in 

waters ranging from very shallow to very deep, to distances from sources of sediment, and to the presence of 

islands rising from waters of different depths. Thus, the 

unconformable relationships noted in the Suplee-Izee 

area of eastern Oregon (fig. 30) were produced by westward onlap of a sea across an island composed of Paleozoic and Triassic rocks and by periodic uplift of that island in early Pliensbachian time and later, perhaps 

accompanied by variations in sea level.

Six unconformities have been definitely identified in 

the Jurassic sequences of the western interior region 

(fig. 31) (Pipiringos, 1968, p. DIG, Dll). These, from oldest to youngest, represent (1) the later part of the Early 

Jurassic, (2) the middle part of the middle Bajocian, (3) a 

small part of the middle Callovian locally in Utah, (4) 

most of the late Callovian and locally some of the Oxfordian, (5) a small part of late early or early middle Oxfordian locally in the middle part of the region, and (6) at 

least part of the later Tithonian. Complete withdrawal of 

marine waters took place during the development of the 

first, second, fourth, and sixth unconformities listed. The 

lowest unconformity formed during the late Early Jurassic, as shown by its position below marine beds of early 

Bajocian Age and above the continental Navajo Sandstone, which is now dated as probably Early Jurassic 

(Fred Peterson, written commun., 1976) on the basis of 

the palynoflora present in the older Moenave Formation. 

The highest unconformity formed during the latest Jurassic, and it could represent all or only part of the Tithonian. Because it formed on continental beds, it probably represents more time than the unconformity at the 

top of some marine Jurassic sequences in the southeastern United States and in west Texas. It represents considerably less time than the unconformity (Nevadan orogeny) formed after deposition of the Mariposa and Galice 

Formations in parts of California and Oregon.

All these Jurassic unconformities in the western interior region could result from lowering of sea level by a 

few hundred feet or less, or from a slight elevation of the 

region, or from a rise of landmasses in eastern Nevada, 

western Utah, and central Idaho that blocked the entrance of marine waters from the west. Of these unconformities, only that of late Callovian Age can be matched 

definitely in the Pacific Coast region. In addition, the unconformity of middle Bajocian Age, corresponding 

roughly to the European zone Otoites sauzei, may be 

present locally in British Columbia and southwestern Alberta, as suggested by the rarity of ammonites characteristic of that zone (Imlay, 1973, p. 34).

JURASSIC GEOLOGIC HISTORY

ATLANTIC COAST REGION

Deposition of marine Jurassic sediments along the 

Atlantic Continental Shelf of the United States has not 

been demonstrated by fossils. Nonetheless, seismic evidence suggests that fairly thick Jurassic sequences were
JURASSIC GEOLOGIC HISTORY 103

deposited at least on the outer part of the shelf. This 

elusion is supported by the presence of (1) about 6,500 

feet (1,980 m) of Lower to Upper Jurassic beds in the 

Scotia Shelf area and at least 20,000 feet (6,100 m) of 

such beds in the Grand Banks of Newfoundland, (2) 

8,000-16,000 feet (2,440 to 4,880 m) of Middle to Upper Jurassic beds in Cuba, and (3) a thin Upper Jurassic 

sequence in the Hatteras Abyssal Plain. As the last mentioned sequence contains organisms characteristic of fairly 

deep waters (Luterbacher, 1972, p. 575; Bernoulli, 1972, 

p. 813; Bernoulli and Jenkyns, 1974, p. 145, 146), the 

Jurassic sea probably extended considerably farther west. 

Also, the marked lithologic and stratigraphic differences 

among these sequences suggest that the history of Jurassic sedimentation probably differed considerably from 

place to place. All available evidence indicates that the 

North Atlantic formed near the end of the Triassic, was 

much smaller during the Jurassic than today, was the 

site of salt deposition at one or more times, and was 

flooded extensively by marine water of normal salinity 

from Oxfordian to Tithonian time, coincident with extensive flooding in the Gulf of Mexico region (Gordon, 1974, 

p. 138; Berggren and Hollister, 1974, p. 130, 131, 176).

GULF OF MEXICO AND NEARBY REGIONS

Jurassic marine sedimentation in or near the Gulf region began at different times in different places. Marine 

sedimentation in Cuba probably began during the Bathonian, but possibly as early as Bajocian. In the southern 

United States and northeastern Mexico, deposition probably began during the Callovian, but possibly a little earlier. Sedimentation started in north-central Mexico during the middle Oxfordian, in northern Chihuahua and 

western Texas during the Kimmeridgian, and in the 

Huasteca area of east-central Mexico during the Sinemurian. In eastern Veracruz in east-central Mexico, marine deposition probably began as early as late Bathonian and definitely as early as Callovian. In south-central 

Mexico in the State of Guerrero, deposition definitely began as early as Pliensbachian and probably much earlier.

During Early Jurassic time, marine sedimentation 

probably did not take place within the drainage basin of 

the Gulf of Mexico. Field studies in southern Mexico and 

drilling in the region of Veracruz both show that an 

Early Jurassic sea entered southern Mexico from the Pacific Ocean and extended north jor northeast but did not 

quite reach the area of the present Gulf of Mexico. Consequently, marine Sinemurian and questionable lower 

Pliensbachian beds exposed in the Huasteca area pinch 

out eastward in the subsurface against ancient schist, 

gneiss, and granite in eastern Veracruz (Viniegra 0., 

1971, p. 484; Lopez Ramos, 1972, sections A-A' and 

B-B'; 1974, p. 381-386). Earlier studies favoring a

marine connection eastward with the Atlantic Ocean during Early Jurassic time were based on the close similarities between the Sinemurian ammonite faunules in 

southern Mexico and those in Europe (Burckhardt, 1930, 

p. 20; Erben, 1957b, p. 37, 38). It is now known, however, that the Early Jurassic ammonite succession is remarkably similar throughout the world from Hettangian 

to early Pliensbachian time (Imlay, 1971, p. 712-713; Imlay and Detterman, 1973, p. 21) and is fairly similar until 

Bajocian time.

Likewise, continental sedimentation may not have 

taken place within the Gulf of Mexico drainage area during Early Jurassic time. The best evidence for its occurrence consists of plant-bearing black shale within and directly overlying Sinemurian marine beds in the Huasteca 

area of east-central Mexico (Burckhardt, 1930, p. 20; Erben, 1956a, p. 129-132; 1957a, p. 45). That area, however, may have drained southward or southwestward 

rather than eastward, because the associated marine 

beds were deposited in an arm of the Pacific Ocean. If 

that is true, then at least the western part of the Gulf of 

Mexico may not have existed during Sinemurian and 

early Pliensbachian time. Such a possibility is supported 

by the fact that the Jurassic beds in the Huasteca area 

were folded, faulted, intruded by igneous rocks, metamorphosed, and then partially eroded away before deposition of the overlying continental Cahuasas Formation 

of Bajocian to Bathonian Age (Carrillo Bravo, 1965, p. 

85-87, 92-95).

During Bajocian time, and most or all of Bathonian 

time, marine sediments were not deposited within the 

drainage basin of the Gulf of Mexico, as far as is known. 

Well outside that basin, however, those stages are represented in part in western Oaxaca and northeastern 

Guerrero by marine beds deposited in an embayment of 

the Pacific Ocean (see fig. 6, 7, 14, and 21). Within the 

Gulf drainage basin, the latest Bathonian is possibly represented by some small undescribed ammonites resembling Wagnericeras, which were obtained from the subsurface near Tampico in east-central Mexico (Cantii 

Chapa, 1969, p. 5). Also, in western Cuba, the upper 

2,000 feet (610 m) of the enormously thick San Cayetano 

Formation has furnished a few marine pelecypods that 

could be of Bathonian Age, providing the overlying Azucar Member contains Callovian microfossils as reported 

(Meyerhoff, 1964, p. 151).

During Bajocian and Bathonian time, continental sediments were deposited widely in the Gulf region and in 

nearby areas. In the Tampico and Huasteca areas of eastcentral Mexico, some thick red to gray clastic non-marine 

beds, called the Cahuasas Formation, were laid down 

from middle Bajocian to at least middle Bathonian time 

on top of plant-bearing beds of early Bajocian Age (Carrillo Bravo, 1965, p. 87-88; Erben, 1956a, p. 137;
104 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

1956b, p. 43). In Cuba, those stages are probably represented by thousands of feet of plant-bearing beds in the 

San Cayetano Formation.

Outside the Gulf region, in northeastern Guerrero 

and western Oaxaca, some dark-gray to black carbonaceous plant-bearing shale and coaly beds were deposited 

during Toarcian to early middle Bajocian time and again 

during middle Bathonian time (Erben, 1957a, p. 49-50), 

as dated by marine fossils in adjoining beds. Studies of 

the plant fossils have made it possible to assign an early 

Bajocian date to the basal part of the Cahuasas Formation of east-central Mexico, as mentioned above. The 

presence of plant fossils and carbonaceous material in 

both east-central and southern Mexico suggests that the 

climate was generally warm and humid throughout the 

Gulf region during most of the Early and Middle Jurassic.

During Callovian time, marine sediments probably 

were deposited in Cuba (Meyerhoff, 1964, p. 151; Meyerhoff and Hatten, 1974, p. 1211), but the evidence has 

not yet been published. Marine sediments of early to 

middle Callovian Age were definitely deposited in eastcentral Mexico near the present Gulf of Mexico and may 

represent an embayment of the Gulf (Erben, 1957b, fig. 

2). Recent studies, however, strongly favor the theory 

that deposition took place in an embayment that extended northeastward from the Pacific Ocean and that 

was separated from the Gulf at least in part by a land 

barrier (Viniegra 0., 1971, p. 484, 492; Lopez Ramos, 

1974, p. 388).

Thick masses of salt and associated anhydrite probably were deposited during middle or late Callovian to 

early Oxfordian time in various parts of the Gulf region. 

Such an age is suggested by (1) the stratigraphic position 

of the salt and anhydrite below normal marine beds of 

middle Oxfordian to early Kimmeridgian Age, (2) lack of 

evidence of any appreciable erosion before the overlying 

normal marine beds were laid down, and (3) lack of any 

fossils that are definitely of late Callovian to early 

Oxfordian Age either above or below the saline deposits. 

In particular, the Santiago Formation of east-central 

Mexico contains early to middle Callovian ammonites in 

its lower part, late Oxfordian ammonites in its upper 

part, but apparently no fossils of any kind in its middle 

part.

Considering the distribution and stratigraphic positions of the main saline masses in the Gulf region, some 

marine waters from both the Atlantic and Pacific Oceans 

probably entered the Gulf at about the same time. The 

entrance of seawater into the Gulf during salt deposition 

probably resulted from some structural movement that 

either caused a rise in sea level, or a downwarping of 

landmasses in southern Mexico and between Cuba and

Florida. The fact that the Callovian sea in east-central 

Mexico was bounded on the east by a barrier or uplift 

suggests that most of the marine water that furnished 

the salt came from the east.

Some red to varicolored continental beds, called La 

Joya Formation, were probably deposited during Callovian time in northeastern and north-central Mexico. These 

beds differ from the Cahuasas Formation by containing 

some red-weathering lava, by being much thinner and 

redder, and by not passing downward into plant-bearing 

beds. They could be the same age as that formation, but 

their close geographic proximity in northeastern Mexico 

to thick salt and gypsum masses, called the Minas Viejas 

Formation, suggests that they were formed at the same 

time as the saline beds. Presumably, the red sand and 

silt in the red beds were derived from areas to the west 

or north, where red lateritic soil accumulated under a hot 

and seasonably rainy climate. The salt and the red beds 

probably were deposited under a hot and very dry climate.

The sequence of marine sediments deposited during 

Late Jurassic time were remarkably similar from Alabama westward to north-central Mexico. During the late 

middle to late Oxfordian in offshore areas, the deposits 

were mostly limy mud; in nearshore areas, they were 

limy mud or sand or both, and locally in nearshore areas 

they were limy sand and gravel. The upper part of the 

limy mud sequence was deposited in shallow agitated 

water, and the lower part, apparently in deeper and 

rather quiet water.

Seas having unrestricted circulation and normal salinity suddenly became widespread in the Gulf region 

near the middle of the Oxfordian and gradually expanded 

until near the end of the Jurassic. At the beginning of 

that time interval, the portals from the Atlantic Ocean, 

or the Pacific Ocean, or both, suddenly widened and 

deepened, allowing huge quantities of sea water to flood 

abruptly inland over older Jurassic saline and continental 

beds onto Triassic red beds and Paleozoic rocks. The extent of the late Oxfordian sea (fig. 10), far beyond the 

present Gulf of Mexico, suggests that either the older 

evaporite basins within the Gulf were dead seas considerably lower than ocean levels, or that the entire Gulf 

basin sank fairly rapidly during the (Jxfordian, or that 

both conditions existed. The first possibility is favored 

because the sea spread quickly over an area extending at 

least 1,500 miles (2,400 km) from east to west, because it 

reworked the saline beds only slightly as it advanced 

and because it then quickly covered those beds with a 

protective blanket of red to gray mud and sand (Norphlet 

Formation) that prevented further erosion. Nonetheless, 

the fact that considerable sand and pebbles were shed 

into the sea from the north during most of Late Jurassic
JURASSIC GEOLOGIC HISTORY 105

time shows that land areas to the north were rising as 

the Gulf basin itself was sinking. The fact that the saline 

deposits of the Gulf region extended at least as far east 

as Cuba and probably considerably farther east suggests 

that major tectonic movements allowed normal marine 

waters from the major oceans to flood smaller basins 

such as the Jurassic Atlantic basin and the Gulf of 

Mexico.

In the Gulf region of the southeastern United States, 

the initial deposits of the rapidly advancing middle Oxfordian sea were derived mostly from pre-Jurassic rocks 

and from Jurassic saline beds across which the sea transgressed. These deposits (Norphlet Formation) were succeeded rather abruptly in offshore areas by dense, finely 

laminated, silty to shaly, calcareous muds (lower part of 

the Smackover Formation) that contain well-preserved 

specimens of the fragile-shelled pelecypod Bositra (not 

Posidonia). Such muds must have been deposited in 

quiet, toxic waters, as indicated by the fine laminations 

and by the good preservation of the fragile pelecypod 

shells. However, these waters were not necessarily 

deeper than the lower part of the neritic zone. Also, 

rapid deepening of the sea at the beginning of Smackover 

time is indicated by the abrupt change from deposition of 

red mud, sand, and some pebbly beds to the deposition 

of laminated beds.

In offshore areas in the southern United States, 

these laminated limy beds in the lower part of the 

Smackover Formation were overlain by gray to black 

mud of the Bossier Formation in late Oxfordian to late 

Kimmeridgian time. In some nearshore areas, though, 

the laminated beds were succeeded by limy dense to oolitic mud and sand representing the middle and upper 

parts of the Smackover, which was in turn overlain by 

the Buckner Formation in early Kimmeridgian time. The 

Buckner consists of red to greenish-gray mudstone, anhydrite, dolomite, oolitic carbonate, and, locally, salt, 

which were deposited as a rather narrow lens-shaped 

body now extending from east Texas through Arkansas 

to Alabama.

Deposition of the Buckner and Smackover Formations was succeeded conformably in most nearshore (updip) areas by deposition of red to gray fine-grained sand 

and mud (Schuler Formation), which may have been deposited in brackish or nonmarine waters. However, the 

local thinning or absence of the Buckner Formation over 

the crests of some salt anticlines may indicate a local disconformity at the base of the Schuler Formation (Weeks 

and Alexander, 1942, p. 1475; K. A. Dickinson, 1968, p. 

E13, E23). The Bossier Formation is overlain by marine 

shale and gray sandstone (marine facies of the Schuler 

Formation) that become more shaly basinward, suggesting deeper waters offshore. Deposition apparently continued to the end of Jurassic time offshore but not in 

nearshore areas.

In summation, the Smackover Formation was deposited in a transgressive sea that was very shallow and agitated nearshore and apparently deeper than wave base 

offshore. The Buckner Formation was deposited in evaporitic basins partially blocked off from the sea by salt 

anticlines or by local uplifts. The Bossier Formation was 

deposited in moderately shallow waters in offshore areas. 

The Schuler Formation was deposited in shallow water 

that was brackish in part, or perhaps nonmarine in nearshore areas. It has been interpreted as a mostly regressive deposit. Nonetheless, the fact that it extends north 

of the Smackover and Buckner Formations in Arkansas 

(K. A. Dickinson, 1968, p. E10, E14, E23) shows that its 

lower part, at least, is transgressive with respect to 

those formations.

In north-central and northeastern Mexico, deposits 

of limy mud or sand of late middle to late Oxfordian Age 

were overlain by dark limy mud or clay (La Caja Formation), or by gray to black sand, limy mud, gravel, and 

some coaly beds (La Casita Formation), or by gypsiferous red beds and gypsum (Olvido Formation). These 

gypsiferous beds crop out only in the high mountains of 

eastern Mexico from Victoria, Tamaulipas, northward to 

eastern Coahuila. They are of particular interest because 

they were deposited at the same time as the Buckner 

Formation of the southern United States, they are nearly 

identical lithologically, and they also were deposited as a 

narrow lens-shaped body. They must represent a time of 

uplift and slight folding, because in areas where they are 

absent, the Oxfordian beds are generally overlain disconformably by La Casita Formation or by La Caja Formation, which were laid down during the remainder of the 

Jurassic.

Of these lithologic units, the Olvido and La Caja Formations were probably deposited under conditions similar, respectively, to those of the Buckner and Bossier 

Formations in the southern United States. La Casita 

Formation was deposited in shallow water or under nonmarine conditions, as was the Schuler Formation. Nonetheless, the dark-gray to black color of the La Casita and 

the presence of coal beds and considerable carbonaceous 

material within it contrast with the red to gray colors of 

the Schuler Formation and show that the climate on 

nearby landmasses must have been much more humid 

during deposition of La Casita Formation. Also, the fact 

that La Casita Formation in Chihuahua and equivalent 

beds in west Texas lap considerably beyond older Jurassic beds onto Permian rocks shows that the formation is 

distinctly transgressive.

Farther south, in the Tampico and Huasteca areas of 

east-central Mexico (fig. 21), the lithologic units of
106 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

Oxfordian to Tithonian Age differ considerably from 

those of the same age in northern Mexico. They consist 

almost entirely of dark-gray to black normal marine 

shale and shaly to thin-bedded limestone. Sandy beds 

and pebbles are uncommon, and the highest unit (Pimienta Formation) contains thin lenses of chert. Evidently these beds were deposited as soft limy mud in an 

open, shallow or fairly shallow sea that received very little sandy material. Locally within this sea, on platform 

areas or near shore, were deposited bioclastic, oolitic, 

and coralline reef carbonates (San Andres Member of Taman Formation) (Cantu Chapa, 1969, p. 8; 1971, p. 34- 

36).

Still farther south, drill cores from near Chinameca 

and Cerro Pelon, Veracruz, in the Chiapas salt basin, 

show that deposition of considerable salt and some associated red to black mud was followed by deposition of a 

thin unit of red mud and some salt. That in turn was followed by deposition of normal marine beds of early Kimmeridgian to early Neocomian Age. Elsewhere in southeast Mexico, the Upper Jurassic deposits outside the salt 

basin apparently were mostly red mud. On the Chiapas 

massif, however, the deposition of red mud was interrupted briefly by a marine incursion during early Kimmeridgian time. The deposition of red beds and salt 

masses implies arid conditions during Late Jurassic time, 

which was a marked climatic change from Early and Middle Jurassic time when considerable coal and carbonaceous material was deposited in nearby parts of southern 

Mexico. Furthermore, the characteristics of the marine 

beds of Kimmeridgian and Tithonian Age in the Chiapas 

basin indicate that water depth was generally shallow 

and that bordering land areas were very low (Viniegra 

0., 1971, p. 485-487).

PACIFIC COAST REGION

The Jurassic marine sequences deposited in the Pacific Coast region of the United States differ markedly 

lithologically within fairly short distances, attain enormous thicknesses, and contain a great deal of volcanic 

material. In addition, some represent different ages from 

others that are nearby. These differences are attributable to deposition under changing environmental conditions; to the relative positions of the sequences within 

rapidly sinking basins; to differing distances from volcanic vents, from islands, or from landmasses composed 

of pre-Jurassic rocks; to westward shifting of depositional sites during Jurassic time; and to major post-Jurassic thrust faulting that has brought together sequences that were originally deposited far apart under 

very different environmental conditions. Evidently, the 

changing environmental conditions reflect the gradual

westward shift in depositional sites, which in turn reflects major orogenic movements along the western margin of the continent.

During the Early Jurassic, a shallow to very shallow 

sea existed as far east as the Snake River in eastern Oregon and nearly as far east in Nevada. Fossil mollusks 

from this sea have been found as far west as the SupleeIzee area in east-central Oregon, the Big Bend area in 

north-central California, and the Sailor Canyon area a little west of the crest of the Sierra Nevada on the North 

Fork of the American River in eastern California. The sea 

in Nevada and eastern Oregon continued from latest 

Triassic time and during Hettangian to Sinemurian times 

received sediment similar to that deposited during the 

Triassic. In contrast, the lowermost Jurassic sediments 

deposited in the Sailor Canyon and Big Bend areas are of 

Sinemurian Age and were deposited unconformably on 

Triassic rocks or locally in Sailor Canyon on older rocks. 

These relationships suggest that the center of the Early 

Jurassic seaway was in western Nevada rather than in 

eastern California and probably trended northward 

through eastern Oregon. The fact that no Lower Jurassic 

beds are known in western California and western Oregon does not mean necessarily that an Early Jurassic sea 

did not also exist there. The absence of these beds, as 

well as the absence of Bajocian and Bathonian beds in 

those areas, could be a consequence of major tectonic 

events during Bathonian to early Kimmeridgian time 

that resulted in the formation of oceanic crust and that 

either altered or destroyed preexisting sediments.

During Bajocian time, the sea covered nearly the 

same area as it did during earlier Jurassic time, and as 

before, it had marine connections both northward into 

Canada and southward into Mexico. In addition, during 

the later Bajocian, this sea had marine connections eastward through Idaho into the western interior region. 

The marine sediments deposited near Westgate, Nev., 

consisted of limy mud and quartz sand; those deposited in the Santa Ana Mountains of southern California consisted of mud, sand, gravel and some limestone 

lenses; those deposited in the northern Sierra Nevada 

near Taylorsville consisted of volcaniclastic materials 

and some limy lenses; those deposited in the big Bend 

area of north-central California consisted of volcaniclastic materials, lava flows, and some clastic lime muds; and 

those deposited in eastern Oregon consisted of volcaniclastic materials, some silty to sandy lime mud, and much 

dark clay and silt associated with much fine volcanic material. Most of these sediments, as shown by their fossil 

content and lithologic features, were deposited in normal 

shallow marine waters that were much agitated in some 

places and were quiet in others. The shallowness of the 

sea in the Taylorsville area during Bajocian time is at-
JURASSIC GEOLOGIC HISTORY 107

tested to by the faunal content of the Mormon Sandstone 

(Crickmay, 1933b, p. 898, 899) and by the presence of a 

disconformity below the Mormon.

Marine beds of Bathonian Age have not been found 

in the Pacific Coast region south of eastern Oregon, but 

neither has any physical evidence been found for an unconformity of that age. In the Taylorsville area in eastern California, the Bathonian could be represented by 

about 1,300 feet (396 m) of volcanic breccia and tuff between the Moonshine Conglomerate of early late Bajocian Age and the Hinchman Sandstone of early Callovian 

Age. In the Izee area of eastern Oregon, the Bathonian 

is represented within a mudstone-siltstone unit 1,250- 

2,000 feet (381-610 m) thick that is called the upper 

member of the Snowshoe Formation. In that member, 

early Callovian ammonites have been collected from its 

highest 300-500 feet (91-152 m), Bathonian ammonites, 

from its next lower 300-400 feet (91-122 m), and one late 

Bajocian ammonite (Leptosphinctes), from near its base. 

That leaves hundreds of feet of beds that could also repregent the Bathonian and uppermost Bajocian. As marine Bathonian beds containing ammonites of boreal affinities occur in central British 'Columbia, southern 

Alberta, and western Montana, a Bathonian seaway 

probably extended from British Columbia southward and 

southeastward across parts of Washington and Idaho.

During Callovian time, a sea apparently covered 

most of California, all of Oregon, part of western Idaho, 

and probably most of Washington. During early Callovian time, it also extended eastward through southern 

Alberta and probably also through northern Idaho into 

the western interior region of the United ^States ,and 

Canada. That sea, so far as is known, did'not extend into 

Nevada as did the Bajocian sea but did extend into northeastern Oregon where Bajocian beds are unknown.

Sediments deposited in this Callovian sea in the Pacific Coast region are very thick and contain a great deal 

of volcanic ejecta such as agglomerate, breccia, lava 

flows, and ash (see figs. 22,23). Even the finer sediments 

deposited as sand, silt, and clay contain much fine volcanic material. Deposition swas nearly continuous from 

early to middle Callovian *time in eastern Oregon and 

apparently continued through the entire Callovian into 

early Oxfordian time in parts of California and southwest 

Oregon. One exception* occurs, however, in the Izee area 

of eastern Oregon, where an unconformity has been 

found near the middle of beds of early Callovian Age (W. 

R. Dickinson and Vigrass, 1965, p. 84). The presence.of 

an unconformity at that position is supported by .the 

much wider distribution of the beds above than below 

that position. Thus, the Trowbridge Shale overlaps westward onto beds of middle Bajocian Age (Imlay, 19<7JB, p. 

9, 14).

Early Callovian sediments in the Izee-Suplee area of 

eastern Oregon were deposited on beds of late Bajocian 

to Bathonian Age. In the Taylorsville area of northeastern California, they were deposited on beds of probable 

Bathonian Age. Elsewhere in California and in western 

Oregon, the age of the beds underlying Callovian sediments is not known, either because of lack of fossils or 

because of thrust faulting. As the age of the Rogue Formation in southwestern Oregon is based on its stratigraphic position gradationally beneath beds of late Oxfordian Age, its lower part could be as old as Bathonian. 

Similarly, the lower part of the Logtown Ridge Formation, or the equivalent Gopher Ridge Volcanics, as exposed along the foothills of the Sierra Nevada, could locally be of Bathonian Age.

The Callovian sediments in California and Oregon 

were deposited in rapidly sinking basins, which were receiving quantities of lava and coarse volcanic material 

from vents and volcanoes. Some of the Rogue Formation 

may represent newly formed oceanic crust, as indicated 

by the presence of lava flows, agglomerates, breccias, 

tuff, serpentine, and gabbro intrusive rocks. The Logtown Ritjge Formation or the Gopher Ridge Volcanics 

could also locally represent oceanic crust, although a 

somewhat different environment of deposition is indicated by the presence of ammonites at various levels.

During the Oxfordian to early Kimmeridgian, a sea 

covered much of California west of the crest of the Sierra 

Nevada, extended northwestward into Oregon, covered 

at least the northwestern part of Washington, and received much volcanic sediment. Another sea of early Oxfordian Age extended sowthwandl from easternmost 

Washington a short distance into Idaho .and Oregon near 

the present site of the Snake Hiver and received nonvolcanic mudstone, graywacke, and pebbles. Except for 

the area near the Snake River, highly volcanic marine 

sedimentation continued from the Callovian into the 

early Oxfordian. By contrast, the marine sediments deposited from late Oxfordian to early Kimmeridgian time 

were mostly dark clay but included some silt, sand, and 

gravel and only in places included appreciable volcanic 

material. Apparently near the middle of Oxfordian time, 

volcanism either decreased markedly or shifted far to 

the west of its position during Callovian or earlier Oxfordian time. Such a shift is indicated by the presence 

near Paskenta, Calif., of thousands of feet of mafic volcanic rocks (mostly breccias and flows) (Bailey and others, 1970, p. C72-C74) conformably below the Knoxville 

Formation, the base of which is .dated as late Kimmeridgian at that place (Jones, 1975).

At the end of the early Kini<raeridgiaaa, marine sedimentation ceased for the remainder of the Jurassic in 

areas underlain by the Galice and Mariposa Formations,
108 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

as well as in areas a little farther east. Such areas during 

the remainder of the Jurassic were subjected to uplift, 

folding, igneous intrusion, and much erosion associated 

with the Nevadan orogeny. Orogenic activity ceased, 

however, by the end of the Jurassic in western Oregon, 

where the Galice Formation locally was overlain by marine sediments of earliest Cretaceous age.

During the late Kimmeridgian, marine sediments 

were deposited in areas of northwestern Washington and 

northwestern California. During the Tithonian, deposition took place along a narrow belt whose position is now 

shown by fossiliferous beds near the present coast from 

Baja California to northwest Washington. All this deposition took place at least 100 miles (160 km) west of areas 

in which the Mariposa and Galice Formations were deposited during the late Oxfordian to the early Kimmeridgian. Evidently, the deposition of sediments of early 

Kimmeridgian Age coincided with the beginning of the 

Nevadan orogeny in areas underlain by the Mariposa and 

Galice Formations and in the Sierra Nevada.

Marine sedimentation during late Kimmeridgian to 

late Tithonian time varied considerably from place to 

place, apparently depending on the depth of the sea, the 

distance from shore, and the presence or absence of volcanoes or volcanic vents. Some sediments, now represented by the Knoxville and Riddle Formations, were 

deposited in shallow to fairly shallow waters as mostly 

nonvolcanic, highly fossiliferous mud, silt, sand, and 

gravel and locally as limestone lenses. Other sediments, 

now represented by the Dothan and Otter Point Formations and by the lower part of the Franciscan assemblage, were deposited in moderately deep to deep waters 

as highly volcanic, rather poorly fossiliferous mud, silt, 

sand, gravel, chert, volcanic breccias, and lava flows. 

Deposition of all these sediments continued into Cretaceous time. All available evidence suggests that the volcanic sequences were deposited at least several hundred 

miles west of the nonvolcanic sequences and in much 

deeper water but that all marine deposition began at 

about the same time, after the formation of oceanic crust 

in late Oxfordian to early Kimmeridgian time.

In summation, Jurassic marine sediments in the Pacific Coast region were deposited in waters ranging from 

very shallow to very deep; involved tremendous thicknesses; included a great deal of volcanic material, except 

in the Knoxville Formation of California and the Riddle 

Formation of Oregon; and were deposited in troughs 

whose positions gradually shifted westward. Furthermore, the scarcity of red sediments suggests that deposition took place mainly under reducing conditions. The 

absence of gypsum and salt deposits implies that lagoonal 

conditions did not last long and that shorelines shifted 

frequently. The fact that no sediments were derived 

from the east, except for the Dunlap Formation of Nevada, implies that the landmass in central Nevada was 

generally low or shed most of its sediment eastward.

These conclusions are of little help in evaluating the 

kind of climate that existed in the Pacific Coast region 

during Jurassic time. However, the presence of ammonites that have Mediterranean affinities indicates that 

the waters were fairly warm. Thus, the Pliensbachian 

ammonite fauna in eastern Oregon is characterized by 

the families Hildoceratidae and Dactylioceratidae but 

lacks the Amaltheidae, which is common in northwest 

Europe and from British Columbia northward (Imlay, 

1968, p. Cl, C21, C22). The Bajocian ammonites in Oregon and California include certain genera that are common in Europe but that are as yet unknown in Alaska 

(Imlay, 1973, p. 31, 36). The Callovian beds in those 

States lack Cadoceras, which is very common from British Columbia northward. Finally, the Tithonian beds of 

those States contain many ammonites of Mediterranean 

and South American affinities that are unknown from 

British Columbia northward (Imlay and Jones, 1970, p. 

B17-B19).

WESTERN INTERIOR REGION

During the Jurassic, most of the sediments deposited 

in the western interior region were derived from bordering areas on the southeast and north and from a persistently rising area in south-central Colorado. Some sediments were also derived from the west at certain times. 

Thus, during late middle to late Bajocian time, and again 

during earliest Callovian time, sand and pebbles derived 

from a landmass in south-central Idaho were deposited 

respectively as part of the Sliderock and Giraffe Creek 

Members of the Twin Creek Limestone (Imlay, 1967b, p. 

22, 23, 26, 30, 50-^53). Later, in the early Oxfordian, a 

northern extension of this landmass was the main source 

of sand deposited as parts of the Swift Formation and the 

Stump Sandstone (Imlay, 1957, p. 481^82; Imlay, 

Gardner, and others, 1948). Similarly, the sediments 

composing the Morrison Formation were derived from 

the west as well as from the south and northeast.

During Early Jurassic time, marine sediments were 

not deposited in the western interior of the United States 

or east of the foothills of the Canadian Rocky Mountains, 

so far as is known. A southeastward extension of marine 

waters into northwestern Montana is suggested by the 

presence of marine beds of Sinemurian and Toarcian Age 

near the International Boundary in southeastern British 

Columbia and in southwestern Alberta, but the facies 

present indicate deposition in very shallow waters near 

a southeastern shoreline (Frebold, 1969, p. 76, 78, 82, 

84).

In contrast, continental sediments may have been 

deposited, in my opinion, during earliest Jurassic time 

over fairly wide areas in the southern and central parts
JURASSIC GEOLOGIC HISTORY 109

of the western interior region. Near the border of Arizona and Utah, the earliest deposits (Moenave Formation) of possible Early Jurassic age were mostly fluviatile 

sand and silt. These sediments were succeeded from that 

border area northward to east-central Utah and to southwestern Colorado by fluviatile sand and silt (Kayenta 

Formation), which were interbedded with some eolian 

sand. Next followed deposition of buff to white, conspicuously crossbedded sand (Navajo Sandstone) of eolian 

origin over the same area as well as in eastern Nevada 

and northern Utah. Similar crossbedded sand (Nugget 

Sandstone and Glen Canyon Sandstone) was deposited at 

least in part at the same time in northernmost Utah, 

northwestern Colorado, southeastern Idaho, and western and central Wyoming. Its lower part, however, which 

contains some thin beds of ripple-marked, flat-bedded 

sand and silt, was probably deposited earlier than the 

Navajo Sandstone (Reeside, 1957, p. 1480, 1482; Pipiringos, 1968, p. D16, D17; Poole and Stewart, 1964, p. 

D38).

Early in Bajocian time, a very shallow sea entered 

the western interior region from the west across southeastern Idaho, western Wyoming, and northern Utah 

(fig. 32). It then enlarged itself northeastward through 

north-central and northeastern Wyoming into the Williston basin of eastern Montana, western North Dakota, 

and adjoining parts of Saskatchewan and Manitoba. The 

sediments it deposited now comprise the Nesson Formation of the Williston basin, the Gypsum Spring Formation farther south, and the Temple Cap Sandstone of 

southwestern Utah. Those sediments consist mostly of 

gypsum, even-bedded red to green silt and mud, laminated or dolomitic lime mud, and some chert nodules and 

layers. During the advance of the sea across Wyoming 

and Montana, the initial deposits were mainly gypsum 

interbedded with red silt and a little limy mud, but in the 

Williston basin they included some salt. These deposits 

are overlain by limy beds, some dark-gray chert, and 

some red silt. In southeastern Idaho, the sediments deposited in the same sea contained much less gypsum and 

much more limy mud and siliceous material (Imlay, 1967b, 

p. 21). A southward extension of the same sea into southwestern Utah deposited red, even-bedded silt and gypsum that to the east passed rather abruptly into 

crossbedded sand. Evidently the sea deepened toward 

the west both in Idaho and in Utah.

The initial sediments of the early Bajocian sea were 

deposited in very shallow, highly saline waters, as shown 

by an association of gypsum, red mud, silt, and locally 

some salt, and by an absence of any marine fossils. More 

limy sediments were deposited later in slightly deeper 

waters, as shown by the presence of some pelecypods, 

gastropods, echinoid spines, crinoid columnals, and worm 

tubes. An absence of ammonites in the limy rocks, however, suggests that the sea waters were either very shallow or were more saline than normal. The characteristics 

of the sediments indicate that the landmasses bordering 

the sea were low and that the climate was warm to hot 

and seasonally humid.

Near the middle of the middle Bajocian, the sea withdrew westward completely from the western interior region. It returned to some areas, however, by the late 

middle Bajocian (Stephanoceras humphriesianum zone), 

and by late Bajocian time, it spread over a larger area 

than in the early part of the epoch. This rapid retreat and 

readvance of marine waters over such a large area during part of middle Bajocian time suggests that the western interior region had little relief, was near sea level, 

and consequently was flooded or drained in response to 

minor vertical movements of landmasses or of ocean basins. The unconformity that developed between floodings, although representing only a small part of middle 

Bajocian time, could have represented 1 million or 2 million years. It was sufficiently long for erosion and local 

removal of the Gypsum Spring Formation and equivalent 

beds and for the accumulation of a lag deposit of weathered, dark-gray chert nodules on the surface of that formation. Such nodules were then reworked by the incoming sea and scattered widely.

The shallow sea that entered the western interior 

region in late middle to late Bajocian time lasted into 

earliest Callovian time and even then did not completely 

withdraw from the region. During the late Bajocian and 

early Bathonian, it extended eastward across about twothirds of Utah, across the western third and north-central part of Wyoming, and across most of Montana into 

the Williston basin, except for some islands in central 

Montana. During late Bathonian time, the sea deepened 

and extended even farther east across northern Utah 

and Colorado and across Wyoming into western South 

Dakota. It shallowed somewhat during the earliest Callovian. It was also shallower in Utah than farther north, 

as shown by a southward increase in red beds and gypsum, a southward decrease in molluscan species, an absence of ammonites south of the northwestern part of the 

San Rafael Swell in central Utah, and an absence ofGryphaea south of Thistle in north-central Utah.

The first sediments deposited in the advancing sea 

during late middle to early late Bajocian time filled in 

the irregularities of the underlying erosion surface and 

consequently/varied lithologically within moderate distances. The initial deposits include normal shallow-water 

marine shale and limestone containing Gryphaea and ammonites (Sliderock Member of the Twin Creek Limestone), gypsiferous shale (lower member of the Piper 

Formation), and massive crossbedded sand (Page Sandstone near Hanna, Utah). Succeeding sediments of latest 

Bajocian Age were deposited in slightly deeper water in
110 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

MOSTLY 

HYPERSALINE

MOSTLY 

-pJiYPERSALINE

EARLY BAJOCIAN X / LATE MIDDLE TO LATE BAJOCIAN

MARINE TO HYPERSALINE

AND INTERTIDAL I"

MOSTLY; TIDAL

FLA

LATE BATHONIAN TO EARLIEST CALLOVIAN

EARLY BATHONIAN

0 100 200 300 400 500 MILES |___i ii i___|

0 200 400 600 KILOMETERS

FIGURE 32.—Inferred extent of Jta-assic seas of early Bajocian to earliest Callovian Age in western interior region. Land areas are ruled. 

Modified from McKee and others (1956), Frebold (1957), Imlay (0.957),J..A. Peterson (1957), and Springer and others (1966).
JURASSIC GEOLOGIC HISTORY 111

broad, fairly uniform basins. Consequently, they maintain their lithologic and stratigraphic characteristics over 

considerable distances. Thus, during latest Bajocian time, 

oolitic to dense highly fossiliferous gray lime mud was 

deposited over nearly the entire seaway from Idaho to 

South Dakota and from Saskatchewan to southwestern 

Utah.

During early Bathonian time, the sea became shallower and a little more restricted than in latest Bajocian 

time. It was definitely hypersaline in southernmost Utah, 

as shown by an association of red silt and considerable 

gypsum (banded member of the Carmel Formation). It 

was definitely of normal salinity in western and northcentral Montana, as shown by an association of fossiliferous sandstone, siltstone, and limestone. It probably varied elsewhere from shallow marine to littoral or lagoonal, 

as shown by an association of variegated siltstone with 

silty to sandy limestone and locally a little gypsum.

During late Bathonian time, limy mud was deposited 

in shallow to moderately shallow marine waters over 

most of the western interior seaway as far south as the 

western part of the Uinta Mountains in northern Utah. 

Farther south in Utah, the limy mud (Watton Canyon 

and Leeds Creek Members of the Twin Creek Limestone) passes laterally into variegated sand, silt, limestone, and gypsum (Winsor Member and gypsiferous 

member of the Carmel Formation), which in places were 

deposited under hypersaline conditions. Southeastward 

from the Wind River Basin across south-central and 

southeastern Wyoming, the limy mud (Stockade Beaver 

Shale Member of the Sundance Formation) was gradually replaced entirely from the base upward by oolitic 

sand (Canyon Springs Sandstone Member of the Sundance Formation), which was deposited by the southeastward advancing sea partly in very shallow water and 

partly in intertidal and supratidal environments. Deepening of the sea northwestward across Wyoming is attested by the pelecypod Gryphaea being rare throughout 

central and eastern Wyoming but abundant from the 

Bighorn Basin northward. This change in abundance coincides roughly with the position of the northeastwardtrending Sheridan arch, as discussed by Wright (1973, p. 

13).

During earliest Callovian time, the sea became shallower than during late Bathonian time, as shown by deposition of fossiliferous ripple-marked sand throughout 

most of the central part of the western interior region 

and of nonfossiliferous variegated clay, silt, sand, and 

some gypsum in central and northern Utah. The deposition of fossiliferous chalky limestone in north-central 

Montana at that time shows that marine circulation in 

the Williston basin was unrestricted.

Near the middle of the early Callovian, a large island 

arose in Montana and northwestern Wyoming that eventually cut off the southern part of the sea from marine 

waters to the north teat not from those to the west (fig. 

33) (Imlay, 1952b, p. 1745, 1751-1753; 1957, p. 487, 

490). Southeast, south, and southwest of this island, red, 

even-bedded, fine-grained sandstone, silty sandstone, 

and shale were deposited in very shallow waters along a 

strip 100-150 miles :(liO-240 km) wide. Beds generally 

less than 100 feet (30 mDtfchick were deposited (Lak Member of Sundance Formation) in the eastern and southern 

parts of the strip; beds 400-1,800 feet (122-549 m) thick 

(Preuss Sandstone), in the Twin Creek trough in the 

western part of the strip; and beds more than 400 feet 

(122 m) thick (Entrada Sandstone), along the west side 

of the San Rafael Swell in central Utah.

Red beds deposited along the Idaho-Wyoming border and as far south as the Nephi area in Utah differ from 

those to the east and west by having bedded salt and a 

little gypsum in their lower third (Mansfield, 1927, p. 99, 

338-340; Spieker, 1946, p. 124; Eardley, 1933, p. 330- 

334; Hardy, 1952, p. 21, 22, 91). To the west, red beds 

near Blackfoot and Idaho Falls, Idaho, differ from those 

farther east by having nearly 200 feet (61 m) of fossiliferous marine limestone and red sandstone at about the 

same stratigraphic position as the salt. These fossiliferous limestone and unfossiliferous red sandstone beds extend eastward as a thin unit to within a few miles of Afton, Wyo. (Irnlay, 1952b, p. 1739-1746; 1957, p. 497).

These red beds were deposited at the same time as 

some light-colored, crossbedded sands (Entrada Sandstone) in the Colorado Plateau area, as is shown by intertonguing and interbedding of the two facies over large 

areas (Imlay, 1957, p. 480-490). These relationships 

show that deposition took place alternately on land and 

in shallow waters and imply that the bordering land 

areas were low.

These relations and the lithologic character of the 

rocks deposited show that a shallow sea of normal salinity existed in eastern Idaho during late early Callovian 

time and perhaps during part of middle Callovian time. 

The salt and gypsum were deposited a little farther east 

in lagoons or in stagnant water near the shore; the unfossiliferous, red, silty to fine-grained sandstones were deposited still farther east in Utah, Wyoming, and western 

South Dakota in highly saline rather than in brackish 

waters. The red sediments were probably derived mostly 

from an island in Montana on which lateritic soils had 

developed under a warm and seasonally rainy climate. 

The light-colored crossbedded sands that were deposited 

at the same time in the Colorado Plateau area presumably were derived from an uplift in west-central or southern Colorado, are at least partly eolian in origin, and 

formed under a hot and arid climate.

This red, even-bedded fine-grained sand and silt of 

late early to possible middle Callovian Age was overlain
112 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

HYPERSALIN

AND

TIDAL FLATS 

I

MARINE

TO 

FHYPERSALINS

—I

I o NORMAL MARINE

LH Tr—:

MOSTLY 

TIDAL 

FLATS

HYPERSALINE 

AND 

FLATSJK

l MOSTLY 

CONTINENTAL 

LLOVIAN DEPOSITS

l

A

LATE EARLY CALLOVIAN TO EARLY MIDDLE CALLOVIAN >LATE MIDDLE CALLOVIAN

EARLY TO EARLY MIDDLE OXFORDIAN i / 

(SOLID LINE) ' / 

LATE OXFORDIAN TO EARLY KIMMERIDGIAN/

^(DASHED LINE) y LATE CALLOVIAN,

0 100 200 300 400 500 MILES

I I II I I

I \ I I

0 200 400 600 KILOMETERS

FIGURE 33.—Inferred extent of Jurassic seas of late early Callovian to early Kimmeridgian Age in western interior region. Land areas are ruled. 

Modified from McKee and others (1956), Frebold (1957), Imlay (1957), J. A. Peterson (1957), and Springer and others (1966).
JURASSIC GEOLOGIC HISTORY 113

by shallow-water marine, green to gray glauconitic sand, 

silt, and clay. In western South Dakota, southern Wyoming, and northern Colorado, these glauconitic sediments (Pine Butte Member of the Sundance Formation) 

were deposited gradationally on the red Lak Member of 

the Sundance Formation. In north-central and northeastern Utah, these glauconitic sediments (Curtis Formation) were deposited unconformably in most places on 

the Preuss Sandstone or on the red earthy facies of the 

Entrada Sandstone. Similar glauconitic sediments in 

southeastern Idaho and in bordering parts of Wyoming 

and Utah (Curtis Member of the Stump Sandstone) were 

deposited conformably and gradationally on the Preuss 

Sandstone.

The sea of Curtis-Pine Butte time must have been 

very shallow except in its westernmost part. This conclusion is based on the presence ofOstrea, Lopha, Lingula, 

and Meleagrinella in the Pine Butte Member of the 

Sundance, the presence of Ostrea and Meleagrinella in 

the type section of the Curtis Formation on the San Rafael Swell, and the general scarcity of other pelecypods. 

It is based also on the fact that the glauconitic sediments 

of the Curtis Formation on the swell pass laterally southeastward and grade vertically into unfossiliferous, brown 

or gray, locally gypsiferous, even-bedded sandstone, siltstone, and clay (Summerville Formation) that probably 

originated under lagoonal to highly saline conditions. The 

westernmost occurrences of the Curtis Formation were 

deposited in slightly deeper waters, as shown by (1) the 

presence of Gryphaea with Ostrea and Meleagrinella in 

Salina Creek Canyon east of Salina, Utah (USGS Mesozoic loc. 21646) and (2) the presence of belemnites and 

the ammonite Lytoceras in Monks Hollow, about 18 

miles (29 km) southeast of Provo, Utah. The distribution 

of these cephalopods indicates that the sea entered from 

the west.

The age of the Curtis-Pine Butte beds is not precisely known. It is considered to be middle Callovian because those beds are overlain unconformably by beds of 

early Oxfordian Age, grade downward into the Preuss 

Sandstone of early to possibly early middle Callovian 

Age, and contain the pelecypods Vaugonia conradi (Meek 

and Hayden) and Myophorella montanaensis (Meek), 

which occur elsewhere only in older Middle Jurassic beds 

(Imlay, 1967b, p. 14).

During Curtis-Pine Butte time, the climate was warm 

and presumably more rainy than during deposition of the 

underlying red beds.

Marine waters withdrew from the western interior 

region at about the end of the middle Callovian. This 

withdrawal was followed by erosion during the late Callovian at least as far south as the San Rafael Swell in 

northeastern Utah (Pipiringos and O'Sullivan, 1978) 

and probably as far south as northern Arizona (Fred Peterson, 1974, p. 466). Erosion apparently was slight in

the central and southern parts of the region and was 

greatest in central and northwestern Montana in the Belt 

Island area.

Near the end of the Callovian, a sea entered central 

Montana and the Williston basin area from the northwest 

across southern Alberta. During the early Oxfordian, 

this sea spread eastward into South Dakota, southward 

into northwestern Colorado and northern Utah, westward across Wyoming into southeastern Idaho, and 

westward in Montana at least as far as the eastern side 

of the Sweetgrass arch. At the end of the early middle 

Oxfordian (Perisphinctes plicatilis zone), the sea withdrew northward at least as far as the Williston basin 

area, but it expanded westward in Montana as far as the 

Sawtooth Range south of Glacier Park, as shown by the 

presence ofBuchia concentrica (Sowerby) near the base 

of the Swift Formation in that range. The fossil evidence 

suggests that the sea in northern Montana persisted until at least the end of the Oxfordian and possibly into the 

early Kimmeridgian.

The initial retreat of the sea near the middle of the 

Oxfordian was followed in western South Dakota, eastern and southern Wyoming, northwestern Colorado, and 

northeastern Utah by a brief readvance, during which a 

very thin marine unit (Windy Hill Sandstone Member of 

the Sundance Formation) was deposited disconformably 

on middle Callovian to lower Oxfordian marine beds (Pipiringos, 1968, p. D23, D25). As this thin marine unit 

has not been recognized in north-central Wyoming or in 

Montana, it is assumed to have been deposited at the 

same time as the upper part of the Oxfordian marine 

beds lying conformably below the Morrison Formation in 

that area.

The sea of latest Callovian to Oxfordian Age did not 

extend south of northern Colorado or northern Utah, so 

far as is known. It probably did not enter the western 

interior region through either southern Idaho or western 

Montana, because the sediments deposited become 

coarser westward and in western Montana they contain 

many wood fragments. Also, the age of the basal sediments in Montana changes westward from latest Callovian in the Little Rocky Mountains of central Montana to 

late Oxfordian in the Sawtooth Range of northwestern 

Montana. This evidence indicates the presence of a landmass to the west that shed considerable clastic sediment 

into the sea. In western Montana at least, this landmass 

was gradually submerged during the late Oxfordian.

The marine sediments deposited in the western interior during latest Callovian and Oxfordian time changed 

from mostly silt and clay on the east to mostly glauconitic, calcareous sand, sandy coquinoid lime mud, and 

sandy silt on the west (Cobban, 1945, p. 1281-1286; 

Imlay, Gardner, and others, 1948; Imlay, 1956a, p. 595- 

597; Pipiringos, 1968, p. D23; Brenner and Davies, 

1974). The basal contact of sediments deposited in the
114 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

eastern part of the sea is sharp and is characterized by 

an abundance of belemnites (some of which are water 

worn), or by a few pebbles, or by a grit bed. The basal 

contact of sediments deposited in the western part of the 

sea is similar but is generally marked by pebbles of limestone, chert, or quartzite or by highly glauconitic sand 

in addition to many belemnites. Deposition of the sediments in shallow water is shown by the presence of a 

varied peleeypod fauna including Ostrea and Mytilus. 

The climate was probably warm and rainy.

The Morrison Formation was deposited during Late 

Jurassic time in fluviatile and lacustrine environments 

throughout much of the western interior region (Reeside, 1952; Craig and others, 1955, fig. 30, p. 159). In 

Montana, as far north as the Great Falls area, its upper 

part was deposited in coal-forming swamps. Deposition 

began during the late Oxfordian in Wyoming and bordering parts of Utah and Colorado, probably began at the 

same time or slightly earlier in areas farther south, but 

probably began in the Kimmeridgian in northern Montana. This northward change in age of the basal Morrison 

coincides with northward thinning of the formation across 

Montana to a pinch-out near the Canadian boundary. 

These relations, especially including the persistence of 

coaly beds at the top of the Morrison in Montana, suggest that continental deposition in the south coincided 

with marine deposition in the north during late Oxfordian time and that the northward pinch-out of the continental Morrison is not primarily due to post-Morrison 

erosion. In all parts of the western interior region, deposition of continental beds persisted during the Kimmeridgian and may have continued into the early Tithonian, 

as is shown by the freshwater mollusks and vertebrate 

fossils present (Yen, 1952, p. 31-34; Reeside, 1952, p. 

25; Imlay, 1952a, p. 953, 958). The climate during Morrison time apparently varied from warm and semiarid to 

warm and humid (Craig and others, 1955, p. 152, 157).

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INDEX

Page

Aalenian time ......_............... 64

Abstract -------_-..........-_......_.. 1

Acanthopleuroceras .._.......__. 20,21,58

Acevedites ............................ 36

Acknowledgments .---__-...------_.._. S

Actinastrea hyatti ..__..__........_.___ 80, 89

Aegasteroceras ....................._._ 52

Afton, Wyo _______________ 111

Agassiz Prairie Formation (Canada) ._ 58 

Alabama __________.. 46, 47, 48, 104, 105 

Alaska .____ 19, 20, 21, 22, 23, 24, 25, 28, 29, 

30, 31, 37, 38, 59, 66, 67 

Alaska Range, Alaska ...___..-......_. 59

Alaskoceras ............_...-.___._.. 37

Alberta ____._________ 18,107,108,113 

Alberta trough, Montana, Canada .__ 18 

Alsatites . ........_ _ ____ __ 19, 20, 55

liasicus zone ______________________ 20

Amaltheus ..............____ 20, 21, 58, 59

margaritatus ..................... 21

zone .. — ...___---__-__ 20

stokesi ........................... 21

American River, Calif _______.. 57, 106 

Ammon, Idaho ---------_------------ 70

Ammonite sequences, Gulf of Mexico

region ____________________ S4

Ammonite zones, northwest Europe. See

name of particular zone. 

Ammonites, succession of ........ 19, SI, 103

Amoebites ............................ 25

(Amoebites), Amoeboceras .... 31,38,55,60

dubium, Amoeboceras ............ 24

Amoeboceras ............ 25,30,31,38,52,58

alternans ......................... 30

(Amoebites) .............. 31,38,55,60

dubium ....................... 24

(Prionodoceras) .................. 25,59

spiniferum .................... 25

Amy Lake, Wash _____________ 66

Anahuac, Nuevo Leon ________________ 36

Andiceras ............................ 32

Androgynoceras ....................... 21

Anhydrite .......... 44, 46, 47, 49, 51, 104, 105

Antlers uplift .._____-...__ 18

Apoderoceras ......................... 21, 59

Aptian Age -__--____________--_.-_____ 67

Arapien Shale ..-_.__.__._--.-____.. 74, 94

Arctic region, paleobiogeographic setting of _.__--_---.-----.-. 19

Arcticoceras .............. 19, 23, 28, 37, 82, 85

ishmae ........................... 23, 28

Arctoasteroceras ...................... 65

Arctocephalites ........... 19,23,28,37,59,81

arcticus .......................... 23

elegans ........................... 23,28

greenlandicus --------------------- 23

(Cranocephalites) ................. 27

Argentina ______________._ 26,50

Arieticeras ........ 20, 21, 45, 55, 56, 57, 58, 65

Arietites .................... 20,21,52,55,58

bucklandi zone .................... 20

[Italic page numbers indicate major references]

Page 

Arisphinctes .......................... 24

Arizona ___________ ._ 17, 96, 109, 113 

Arkansas _______________ 46,47,48,105 

Arkellites hudlestoni zone ------__._ 24,26

Arkelloceras ................... 22,23,25,37

Arnioceras .. 19, 20, 21, 45, 52, 55, 56, 58, 59, 61

semicostatum zone ---------------- 20

Arniotites ............................ 21

Arroyo de San Jose, Baja California ... 51 

Arroyo La Mula, Tamaulipas --------- 33

Artemsia Formation (Cuba) __ 39,44,46 

Arvison Formation ___________________ 54,6.

Ashman Formation (Canada) -------- 58

Aspidoceras ........................ 24, 31, 32

Asterocsras ........................ 20, 58, 61

obtusum zone _____________________ 19,20

Asthenoceras delicatum ............... 56

Ataxioceras .................... 24, 30, 31, 45

Atlantic Coast region .___——------ 4, 102

Aucella eringtoni ..................... 66

Aulacomyella ......................... 31

Aulacosphinctes .......... 24,34,35,36,45,63

Aulacosphinctoides ................ 24,32,57

Aulacostephanoceras acutiasiodorensis

zone -__.._________ 24,32 

Aulacostephanua eudoxua zone --------- 24, 50

Aztec Sandstone ---------------------- 53

Azucar Member, Jagua Formation

(Cuba) ____...__._ 39,103

B

Bacon Ridge, Wyo ..____--.____- 88

Bagley Andesite _..____..__- 54,61

Baja California, Mexico ________- 51, 108

Bajocian Stage, Alaska ___-19,23,24,67

ammonite and buchias succession in . 23, 37

arctic region -------------------- 37

Arizona ____________--.. 97,99

California __17, 52, 57, 60, 61, 106, 107, 108 

Canada .-.____ 18, 25, 67, 102, 106, 109 

Cuba ...____________--. 17, 103, 104 

Gulf of Mexico region ------------ 47,48

Idaho ___________ 24, 65, 106, 108, 109 

Mexico -. 17, 23, 39, 49, 52, 99, 103, 104, 106 

Montana _______ 24, 67, 68, 80, 81, 109 

Nevada --------_________ 53

North Dakota ._________ 67, 78, 109 

Oregon ___ 17, 18, 23, 64, 65, 106, 107, 108 

Pacific Coast region ______ 37, 102, 106 

Utah --.__---___- 95, 97, 98, 99, 109 

western interior region --------18, 24, 67,

102, 106, 108, 111 

Wyoming _________________ 24, 84, 99, 109

Baker County, Oreg _-.._____---- 64,65

Bald Mountain Formation ------------ 66

Balsas Portal (Mexico) ________- 52 

Banner, Wyo _______-------__ 83,84

Barklow Mountain, Oreg ------------- 62

Barranca Formation (Mexico) -------- 52

Basey Member, Snowshoe Formation ._ 55

Page

Bathonian Stage, Alaska ——————19,28,37 

ammonites and buchias succession

in .......------------ 25,37

ammonites of __________________— 28

arctic region _____---————19,28,37 

Atlantic Coast ------------- — -___ 4

California ___________ 57, 60, 106, 107 

Canada __________________ 28, 37, 67, 107

Colorado _________________ 8&, 109 

Cuba ________________ 17, 103, 104 

Gulf of Mexico region ——— — ——— 47 

Idaho _____...__-_______ 37, 107 

Mexico _________-.-_---_-— 17, 25, 37,

39, 49, 50, 51, 52, 99, 103, 104 

Montana ____ 27, 67, 81, 82, 107, 109, 111 

North Dakota _______ — __— 67 

Oregon __.--.____ 17, 26, 37, 67, 106, 107 

Pacific Coast region ... —— ———102,107 

South Dakota ______——————85,109 

Utah _.______._ 95, 96, 99, 109, 111 

western interior region ..-- 18, 27, 37, 67 

Wyoming ______________ 85, 109, 111 

Bearpaw Mountains, Mont ————--29,80,82 

Beaverhead County, Mont ----------— 81

Becheiceras --------------------- ——— - 21

( Becheiccras) , Liparoceras ........... _ 20

Bedford Canyon Formation --------— 54,61

Belt Creek, Mont ______________ 68 

Belt Island uplift ______18, 19, 8>0, 81, 113 

Berriasetta ..................-......... 24,34

Berriasian Age _______________________ 63

Bibliography -_-__--_--. — ___ ———— __ 114 

Big Bend, Idaho -____._ ———— ——— 70 

Big Bend area, California —— 52, 53, 54, 106 

Big Hollow Wash, Utah _________ 77,98 

Big Horn County, Wyo ____—————— 71 

Big Snowy Mountains, Mont ... 69, 78, 80, 82 

Bighorn Basin, Wyo ___---————18,80,82, 

83, 84, 85, 86, 87, 111 

Bighorn Mountains, Wyo., Mont ------ 78, SS,

84, 85, 86, 87 

Billhook Formation (Canada) -------- 58

Black Dragon Canyon, Utah -_-- — --- 74, 94 

Black Hills, Wyo., S. Dak ____ 83,85,86,87 

Blackfoot, Idaho _______________ 89, 111 

Blackfoot Mountains, Idaho ------------ 89

Blaine County, Mont ____ ———— ——— 80 

Bluff Sandstone ._______—————_- 96 

Bochianites ........................... 36

Bolson de Judas, Candela district,

Mexico _____--------_ — _ 35

Boaitra ............................... 105

buchii ............................ 61

Bossier Formation ___-..-————44,47,105 

Boulder, Utah _________—————— 98 

Boundary Ridge Member, Twin Creek

Limestone .——————— 70,72,74, 

85, 88, 91, 96, 99

Bowes Member, Piper Formation ___ 68, 69, 80 

Boyden Cave pendant ------ — ------- 53

Bridger, Mont ____-.__ —————— - 84

British Columbia ____..———— 20,21,23,25,

29, 58, 59, 66, 67, 68, 107, 108

127
128 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

Page

British Mountains, Yukon Territory. 21, 23, 29 

Brogan, Oreg _________.___.56,64,65 

Brown Canyon, Utah ._...____.._ 76 

Brushy Basin Shale Member, Morrison

Formation ...___________ 75

Buchia, ______ ________ 3, 36, 37, 38. 61, 67

blanfordiana ________________ 25, 58, 66

concentrica ______ 18, 24, 26, 30, 31, 38, 55,

56, 58, 59, 60, 62, 63, 66, 69, 71,

73, 75, 82, 113

fischeriana ........ 24, 25, 55, 58, 59, 63, 66

mosquensis ...... 24, 25, 31, 34, 36, 38, 56,

58, 59, 63, 66, 67 

okensis .....____________._.... 24, 56

pacifica ........................... 62

piochii ........ 24, 25, 51, 66, 58, 59, 63, 66

richardsonensis ..._............... 25

rugosa ........... 25, 38, 55, 56, 59, 63, 66

terebratuloidea -------------------- 58

uncitoides ........................ 63

unschensis ________________________ 25

Buchias, succession by stages ____._ 19

Buck Mountain Formation ..______ 66

Buckhorn Wash, Utah __________ 74,94,95 

Buckner Formation . 42, 44, 46, 47, 48, 102, 105 

Burr Fork, Utah .____________ 72

Bush Canyon, Wyo _ ___________ _ 71 

Butte County, Calif ___________ 57 

Button Butte, Mont ___________ 69

Caborca, Sonora __________________ 19, 52

Cadoceras ........ 23, 27, 28, 29, 38, 67, 88, 108

calyx . _-.______-_-_-._____ 23

catostoma .. ___________________ 23, 58, 59

septentrionale . __________________ 23

variabtte _______-______--_.___ 23

{Longaevieeras) pomeroyenss ..... 29

(Paraeadoceras) ______.--__-_.__ 28

tonnienae ___________________ 23

(Stenocadoceras) ................. 23,29

canadense .................... 23

stenoloboide ________________ 23, 59

striatum ..........._________ 23, 58

Cadomites ............................ 37

Caenisites turneri zone ______________ 19, 20

Cahuasas Formation (Mexico) _ 45, 49, 103, 104

California __.. 20, 22, 24, 29, 30, 31, 36, 38, 52,

54, 65, 61, 106, 107, 108

Callovian Stage, Alaska _______19,29,38 

ammonite and buchia succession in __ 29, 38 

ammonites of ____________________ 28

arctic region __________28,29,38 

Arizona __________________ 113

Atlantic Coast region .----__.___ 4

California ____ 17, 29, 38, 53, 67, 60, 61,

62, 106, 107

Canada ________ 29, 38, 67, 107, 108, 113

Colorado ______________ 111, 113 

Cuba _________________ 103, 104 

Gulf of Mexico region __ 47, 48, 103, 104 

Idaho _____ 65, 66, 89, 107, 108, 111, 113 

Mexico 17, 29, 38, 49, 50, 51, 52, 99, 103, 104 

Montana _______ 29, 67, 81, 111, 113 

North Dakota ____________ 67

Oregon ____ 17, 38, 60, 64, 65, 66, 106, 107 

Pacific Coast region ____________ 102, 107

South Dakota ____________ 111, 113 

Utah ___________ 95, 99, 102, 111, 113 

western interior region ________ 18, 29, 67,

102, 107, 108, 109, 111

Wyoming _____________ 89, 111, 113 

Caloceras _____________________________ 19

Camagiiey Province, Cuba _____________ 34

Campian Age ..---_____-----._______ 63

Camptonectes _______ __ 81, 87, 91, 92, 95

Page

Canada, arctic ____________-.21, 22, 23,

25, 28, 29, 30, 31, 36, 37, 38

eastern _____________——— 4, 103

western ___________ 19, 22, 31, 36, 106

Canavaria ..._____________--_-_----_ 20, 65

Cannonville, Utah _________- —-_ 77,98 

Canon Alamo, Sierra Jimulco _________ 36

Cantii Chapa, Abelardo, quoted _-._— 51 

Canyon Springs Sandstone Member,

Sundance Formation ______ 71, 73,

81, 84, 85, 86, 88, 93, 111

Cape Hatteras, N.C. ____________ 4 

Carbon County, Mont __ ——— —.--_--. 78 

Cardioceras _.______-_ 17, 18, 24, 26, 29, 38, 58,

69, 71, 73, 75, 82, 87, 90, 92 

canadense ........................ 58

cordatum zone _.----.___ —— .24,30,50

cordiforme .......... 24, 30, 69, 71, 73, 75

distans .......................... _ 25,59

martini .... ______________----- 58, 59

(Maltoniceraa) ................... 30

(Scarburgiceros) ................. 25,30

martini .......... 24, 25, 30, 55, 56, 66

(Subvertebriceras) canadense ..... 25

Caribou Range, Idaho ___----------- 90

Carmel Formation ___.__ 72,73,74,75,76,

77, 84, 87, 91, 93, 95, 96, 97, 99, 111

Cascade Mountains, Wash ________-- 56,66

Catacoeloceras ..................... 20, 21, 55

Catulloceras __._________ 20,21, 22, 55, 58 

Cedar City, Utah _____.__---__... 76,99 

Cedar Mountain, Utah _________ 74 

Cerro Pelon, Veracruz __----__._---— 106

Challenger Knoll _______________ 47 

Charcas, San Luis Potosi ____--__ 49 

Charmasaeiceras --------------------— 20, 21

Chetatites chetae ...................... 25

Cheteo River, Oreg __________- 63

Chiapas massif, Mexico ____.-. —— -___ 51, 106

Chiapas salt basin (Mexico) —— — _ 51, W)6 

Chihuahua, Mexico - 32, 33, 35, 45, 51, 103, 105 

Chinameca, Veraeruz __.-_-------_- — - 106

Chinitna Formation ______------29, 59, 65

Chinle Formation _____________ 96,97

Choffatia ......... _________________ 27, 29, 50

Chondroceras _____________ 24, 55, 58, 81

allani ___________ 22, 23, 59, 69, 71, 73, 75

Chugwater Formation _____————— 83, 84 

Cinco Pesos, Cuba ____________ 39 

Clarke County, Miss ___----___--__-__ 46

Clarks Fork Canyon, Wyo _______ 84 

Climate, Jurassic .. 104, 108, 109, 111, 113, 114 

Cloverly Formation ______--_---.__--- 88

Clydoniceras discus zone ______..____._ 22

Coahuila, Mexico ._________ 36,44,48,105 

Coahuila Peninsula, Mexico __——___ 48 

Coast Ranges, Calif ___________ 53,61,63 

Cobbanites .........— 22, 23, 26, 27, 28, 37, 55

talkeetnanus ---------------------- 58

Coconino County, Ariz _._ — _.__------ 77

Cody, Wyo ________________ 84,85,86 

Coeloceras ____________________________ 65

Colebrook Schist .___-----._ —.__--- 55

Colfax, Calif __________________ 53, 57 

Colorado ____ 73,85,90,95,96,109,113,114 

Colorado Plateau ____________.- Ill 

Columbus, Mont .-_---.-___ — —— __ 84 

Combe Formation ___________________ 57

Connor Creek, Oreg ___---------------_ 65

Cook Inlet region, Alaska ___.. 17, 19, 28 

Cooks Canyon Agglomerate ____________ 54

Coon Hollow Formation ._-_---------- 56, 66

Copper Hill Voleanics _________— 60

Corongoceras ...___..._ 24,32,34,35,36

alternana --...................._ 26,36

filicoatatum ---..-...-.......--.... 35

Coroniceras ... ____ 19, 20, 21, 45, 55, 58, 59, 65

bisul.ca.tum ....... ________________ 20

Page

Corral Creek, Colo ———————————— 93 

Cosumnes Formation _______ — — ____ 60

Cosumnes River, Calif —————————— 60 

Cotton Valley Group _____-__ 44, 47, 48

Cow Creek, Oreg —————————————— 63 

Cow Springs, Ariz ———————————— 77,99 

Cow Springs Sandstone — ———— ___— 99 

Cowley, Wyo ____ ———————— ___- 78 

Craig, Mont ____________-____ 68 

Cranocephalites ...... 19, 23, 28, 29, 37, 59, 81

borealis .......................... 23

costidensws -------------------- 23, 58, 59

indistinctus ......................

pompeckji -..............---.....-

vulgaris --------------------------

(Cranocephalites), Arctocephalitea _____ 

Crospedites canodensis ................

23 

23 

23 

27 

25 

27 

subditus --------.— —........... 27

Creniceras ........................... 45, 50

crenatum ... __________---_-_--.-- 30, 50

dentatum _____--_---_------_-.__- 50

renggeri __ ——— .---____-- ——— __. 30,50

Crioceras --------------.....---------- 36

Crook County, Wyo ————————————— 71 

Crucilobiceras ........... 19, 20, 21, 52, 55, 56,

57, 59, 64, 65

Cuba ____ 17, 24, SS, 34, 59, 44, 103, 104, 105 

Cubaochetoceras ...................... 39

Cucurpe, Sonora ___ ——— — —— ------ 52

Gurry County, Oreg ——._-——_—— 62,63

Curtis Formation ._——————————— 74, 75, 89,

92, 93, 94, 95 96, 113

Curtis Member, Stump Sandstone __ 72, 73, 89, 

90, 92, 95, 113

D

Dactylioceras ............... 20, 21, 22, 58, 65

commune ...................... 21,55,59

semicelatum ---------------------- 21

tenuicoBtatum zone — — -_-__-_--- 20 

Dalmasiceras . ___-___--_-_---__----__ 39

Danish Ranch, Utah - ————— ————— - 76 

Daonella sanctea-anea ----............ 61

Days Creek, Oreg ————————————— 63 

Dayville, Oreg _____-- ——— --. —— __ 62 

Decipia .._.--__-.-__ — __-_-_____-__- 24

decipiens zone ___ ——— — - —— —— 24 

Deep Creek, Utah _____———._-__ 98 

Deerfield basin (Massachusetts) ———_. 4 

Dennett Creek, Idaho ——————————— 64, 65 

Dewey Bridge, Utah .____.„__-_--. 75,96

Dewey Bridge Member, Entrada

Sandstone _—————————— 75, 96 

Diamond Valley, Utah .- ——— .._„_.. 99 

Dichotomosphinctes .... 24, 25, 30, 52, 55, 59, 60

durangensis ................... 24, 31, 45

muhlbachi ......________ — _______ 24

plicatiloides _____-_-__-.__-_.. — _ 24

(Dichotomosphinctes), Psrisphinctes — 30,38,

39, 62 

Dickersonia .......................... 24,34

aabanUlensis .... ——— — --__-__.-_ 35

Dillard, Oreg ________————_ — — 63 

Dinosaur Canyon Sandstone Member,

Moenave Formation ______ 96

Dinosaur Quarry, Utah _____ — ___—— 73

Discosphinctes ----------------_ 39, 52, 55, 60

carribeanus -------------------- 24, 30, 45

virgulatiformis ------------------- 24

(Discosphinctes), Perisphinctes ....... 30,38

Divesian (term) __.-_---„_ ——. ———. 47 

Dixie Creek, Oreg ___--_----- —————.- 65

Docidoceras .................. 22, 23, 55, 56, 59

widebayense ...................... 23

Dorsetenaia ____-__-___--__--_--------. 61

oregonensis ........... -__--____— 22,55
INDEX 129

Pare 

Doraoplanites .........____..__.__. 25

panderi .......................... 27, 34

Doraoplanitoides triplicates ............ 26

Dothan Formation _______ 55,62,63,108 

Douglas County, Nev ___________.... 53

Douglas County, Oreg _--.-.__......._. 63

Duchesne County, Utah _______________ 72, 92

Duchesne River, Utah .______.. 72,91 

Dufrenoya ............................ 47

Dumortieria .......................... 20,22

levesguei zone ___________________ 20

Dunlap Formation ____.53,54,97,102,108 

Durangitea ................. 27,32,34,35,63

incertua .............___..___.___ 34

vulgaria ....................... 24,34,45

Durango, Mexico .-----_.... 32,33,34,36,45

E

Eagle County, Colo .__________.... 93

Eagle Mills Formation .____..__.... 46,47

East Butte, Mont ._____________ 80

Echioceraa .............. 20, 21, 45, 57, 58, 65

arcticum, .......................... 21

raricoatatum zone .._....__.______ 20

Echo Island Formation (Canada) ...... 58

El Antomonio, Sonora __._._....__.__. 19, 52

Elk Creek, Colo ..._..._......._ 73,93

Embayment, Gulf of Mexico __________ 104

western interior region ____________ 18

Emery County, Utah ____...____ 74,75 

England, Jurassic formations _______ 44,54,90

Enterprise, Oreg ___________________ 56, 65

Entrada Sandstone ___.--. 72, 73, 74, 75, 77,

92, 93, 94, 95, 96, 98, 99, 111, 113

Eocephalitea ......................... 37

Eoderoceras ....................... 20,55,65

Epistrenoceras ........................ 45

paracontrarium ................._ 22,25

Epivirgatitea nikitini .................. 27

Erycitea ............................. 23,59

Erycitoidea ........................ 25,56,65

howetti ........................... 23, 59

Erymnoceraa ......................... 38

coronatum zone ___________________ 22

mixtecorum ................... 22,29,45

Escalante, Utah .________._____ 77, 98

Euaapidoceros ........................ 24, 30

Eudmetoceras ..................... 22, 55, 56

Eugeosynclines -----------_--____._____ 52

Euhoploceraa ......................... 55, 57

modeata ...............__________ 22

(Euhoploceraa), Sonninia ............. 22

Euprionoceraa ..._.__......._._____.. 25

Europe, northwest, ammonite zones. 

See name of particular 

zone. 

Europe, southern, subdivisions of the

Tithonian in -.___....._... 26

Eurycephalitea .................. 29,38,45,50

boeaei ............................ 22

Evanston, Wyo _______________________ 90

Evaporitic sequences -__---__---.----_ 4, 50

Exogyra virgula ...................... 36

Fall River County, S. Dak ..______ 71 

Fanninoceras ......................... 20, 65

Fant Andesite ________________ 54,57 

Faunal relationships, intercontinental _. 37 

Fehlmannitea ------------------------- 30, 50

Ochetoceras ----------------------- 50

Fernie, British Columbia ________ 18

Fernie Group (Canada) .._.________-. 68

Finca Ancon, Pinar del Rio Province,

Cuba ___...._____ 34

Page

Firemoon Limestone Member, Piper Formation _.-.__ 68,69,78,79,80,81 

Fish Creek, Wyo ____..______ 90 

Florida _______________________ 47 

Fontanelliceras ........................ 20

Fontannesia .......................... 22,56

Foreman Formation ---------------_ 54, 60

Fort Pierce Formation ____________--- 47

Fossil Mountain, East Greenland .____. 28

Fossils, characteristic -----------_____ 45, 55,

56, 58, 59, 69, 71, 73 

Franciscan assemblage -------- 55, 62, 63, 108

Francisco Formation (Cuba) --_____-_ 39,44

Franconitea vimineua ................. 2'6

Frantz Creek, Colo -_________.. 73,93 

(Franziceraa), Pailoceras -------------- 19

Fremont County, Wyo _..___ —.__ 70, 89 

Front Range, Colo ____________ 93

Fuciniceras ........................ 20,56,65

G

Galeana, Nuevo Leon ____-_._____._-__ 35

Galice Formation .__ 55, 61, 62, 102, 107, 108 

Gallatin County, Mont _____._-._ 80

Gallatin Range, Mont _.___..__._ 80, 81 

Garantiana garantiana zone ___________ 22

Garfleld County, Utah ..____.__. 77 

Geologic history, Jurassic ----._------- 102

Gervillia montanaenais ................ 80, 99

Giraffe Creek Member, Twin Creek

Limestone __ 7'0, 72, 74, 88, 94, 108 

Glacier National Park, Mont __.__ 80, 113 

Glaucolithitea ......................... 25

gorei zone -----------.-_--_------- 24, 26

Glen Canyon Sandstone ..___ 72,73,91,109 

Glendale, Utah ________________ 98 

Gleviceraa ............................ 20, 65

plauchuti ......................... 21

Glochiceraa .................... 31,34,38,39

fialar ...................... 24,30,31,45

lithographicum ................... 26

Gold-belt area, Sierra Nevada, Calif ... 54 

Goliathiceraa .......................... 25, 87

Gopher Ridge Volcanics __...______ 60, 107 

Gore Range, Colo ___..________ 93 

Gowericeras costidenaua ............... 28

subitum .......................... 28

Graciliaphinctcs progracUis zone ______ 22

Grammatodon ......................... 84

Grammoceras ............ 20, 21, 22, 55, 58, 59

thouarsense zone _________----__--. 20

Grand Banks, Newfoundland .._._.__ 4, 103 

Grand County, Colo __.._____...__ 73,93 

Grand County, Utah ..________- 75 

Grand Junction, Colo __---_---------. 96

Grapevine Creek, Mont .___._--_----.. 78

Graphoceraa concuvum zone .._.__.-__ 22,57 

Gravelbourg Formation (Canada) __ 69, 78, 80 

Graveaia .............................. 31

Grayiceraa ...................... _____ 35

mexicanum ....................... 35

Graylock Formation -_-_----_--------- 55,64

Great Falls, Mont __.._______ 68, 114 

Green River, Utah ____________ 95,96 

Green River Lakes, Wyo ..___.70,85,86,88 

Greenland, East _. 19, 21, 22, 23, 25, 28, 82, 85 

Gregoryceraa transveraarium zone _._. 24,50 

Gros Ventre River, Wyo ..-._____.. 83,88 

Grosaouvria ........................ 29,38,66

Gryphaea ............. 65,85,91,109,111,113

culebra ........................... 56

impresaimarginata ... 22, 28, 69, 71, 73, 75 

nebrascensis .......... 22, 69, 71, 73, 75, 88

planoconvexa ...... 69, 71, 73, 75, 8*0, 81, 89

Guasasa Formation (Cuba) ..__._----- 39,44

Guerrero, Mexico ___ 17, 23, 25, 45, 51, 52, 102,

103, 104

Page

Guerrero embayment (Mexico) ._. —._ 17, 20,

25, 29, 52, 103 

Guhsania bella ........................ 23

Gulf of Mexico, Jurassic connections 

with Pacific and Atlantic 

Oceans .___.._.. — ___ 17,51 

Gulf of Mexico region, ammonite succession and correlation in __ 24, 38 

characteristic fossils of ———.--_--. 45 

geologic history of ———— — ------ 103

Jurassic formations in ——--------- 44

lithologic and stratigraphic features

of ___________ —— ____ 39 

locality bibliographic references _._ 3 

paleobiogeographic setting ________ 4

Tithonian Stage in __________ 32, 34 

United States, stratigraphic and

lithologic comparisons in — 46 

unconformities in --------- ——.— 99

Gunlock, Utah ____________ 76,97,98,99 

Gunnison, Utah _____ ————————— -74,94 

Gunnison Plateau, Utah _. ———— —— 74,94 

Gyphaea planoconvexa ---------------- 22

planoconvexa fraterna ............ 22

Gypsum _____ 67, 79, 83, 87, 95, 104, 109, 111 

Gypsum Creek, Mont ...._-.-.__----- 78, 84

Gypsum Spring Formation ------------ 18, 70,

71, 78, 82, 84, 88, 89, 90, 95, 99, 109 

Gypsum Spring Member, Twin Creek

Limestone ..___ ——— .. 18, 70,

72, 74, 82, 83, 9'0, 91, 94

Gyrochorte ........................... 86

H

Hagermeister Island, Alaska __.---_--_ 19 

Hahns Peak, Colo _____ ——— — — __ 73,93 

Hanna, Utah ...____.._———72,87,91,109 

Haploceraa ........................... 31,32

Hardgrave Sandstone ____---_--------- 54,57

Hardin trough, Wyoming ____----__---- 19

Harpoceraa ........................... 21. 53

exaratum ................... 20, 21, 22, 58

falcifer zone .__-__----_-----__---- 20

(Harpoceratoidea) ................ 65

(Harpoceratoidea), Harpoceraa ........ 65

Harris Wash Tongue, Page Sandstone . 77 

Harrison Lake, British Columbia —._ 58,67 

Harrison Lake Formation (Canada) .._ 58 

Hartford basin (Connecticut) ___-_-_ 4 

Hartville uplift ______———————————— 85

Hatteras Abyssal Plain .. ———————— _. 4, 103 

Haugia ...................... 20, 21, 22, 55, 59

variabilis zone ___-_-__________--_- 20

Haynesville Formation __-_-----_--—— 46

Heath, Mont ______------ ———— — 69

Hecticoceraa ....................... 29, 38, 61

retrocostatum zone _______________

Hells Backbone, Utah _______———_

Hettangian Stage, Alaska ___-__-----._

ammonites and buchias succession

22

98

19

in ___________-- 19

Arizona ..-------_---------------- 97

Mexico _________________ 19,52,99 

Nevada _________________ 19, 53, 106 

Oregon _________ 17, 19, 63, 64, 65, 106 

Pacific Coast region — ————— — 102 

Utah _________ — „_„„__----— 97

Hibbard Creek, Oreg .-._________ 65 

Hidalgo, Mexico --________----------_-_ 45, 50

HUdaites ............................. 21

Hildoceraa bifrona zone --------------- 20

HUdoglochiceraa ________ 24, 32, 34, 35, 36 

ecarinatum ...................... 34

Himalayitea .......................... 34, 36

Hinchman Sandstone _____——54,60,107 

Hoback Range, Wyo __.. ———— ————— 90 

Hoplocardioceroa ...................... 25
130 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

Page

Horse Creek, Wyo ____________. 87 

Horton, Wyo ________________. 85 

Hosston Formation _______..._-- 48 

Huasteca, Mexico ______ 33,45,99,103,105 

Huauchinango, Hidalgo ________________ 45

Huayacocotla, Veracruz _______________ 30

Huayacocotla embayment (Mexico) . 17, 26, 29 

Huayacocotla Formation (Mexico) ____ 45,49

Huehuetla, Hidalgo ___________ 50 

Huizachal anticline (Mexico) ._____ 33 

Huizachal Formation (Mexico) _______ '49

Hulett, Wyo _______________ 71, 83, 85 

Hulett Sandstone Member, Sundance

Formation -___70,71,81,88,89 

Hull Meta-andesite ____________ 54,60 

Huntington, Oreg __________________ 64

Hurricane, Utah ._-..-_........_.. 99

Hurwal Formation __________________ 56, 65

Hyattville, Wyo _____________ 71,83,84

Hybbnpticeras _ ______ 24, 27, 31, 32, S3, 45

hfybbnotum ....------_--..._.-.- 26

Hyde Formation ____________________ 55

I

Idaho ____ 17, 24, 30, 52, 6S, 70, 80, 82, 83, 89,

90, 92, 106, 107, 108, 109, 111, 113

Idaho Falls, Idaho _____________ 89,111

Idoceras ........... 24, 30, 31, 32, 38, 45, 52, 55

balderum ......................... 24

durangense ....................... 24, 31

planula ...............________ 60

(Ilowaiskya) pseudosycthica, Subplanitee 27 

(Ilowaiskya) sokolovi, Subplanitee ..... 27

Imlayoceras .......................... 29

miettense ......................... 22

Indian Creek, Mont .._.----__._----- 81

Iniskinites ......................... 23, 29, 64

intermedius ....................... 22

Inkin Formation (Canada) __.......... 59

Jnoceramus ........................... 35

Interior region. See Western interior

region. 

Introduction -.._-------_---------- S

Iron County, Utah _----________-----. 76

Iron Mountain Creek, Oreg ___-____-_._ 63

Ironside, Oreg ________________________ 56

Islands, Jurassic ...- 18, 52, 102, 106, 109, 111 

Isthmus of Tehuantepec ..._.._------. 50

Izee, Oreg _____ 55, 64, 65, 66, 102, 106, 107

Jackson, Wyo ___________.70,83,84,88 

Jackson Hole, Wyo _______..___ 90 

Jagua Formation (Cuba) _.59,42,44,48,50 

Jagua Vieja Member, Jagua Formation

(Cuba) _________—. 39 

Japan ——------__-_--_.--..---_---- 50

John Brown Creek valley, Colorado ..- 75, 96 

John Day, Oreg ___________ 21, 26, 63, 65 

Johnson Canyon, Utah ____________._ 97, 98

Johnson County, Wyo _______________ 71

Jonotla, Puebla -.._________________ 35

Josephine ultramafic mass ._----.----. 62

Juab County, Utah _____________ 74 

Juarez, Durango --.--_--___-__------_ 45

Judd Hollow Tongue, Carmel Formation 77, 98 

Judith River, Mont _____________ 68 

Junction Creek Sandstone ___________ 75,96

Juniper Mountain, Oreg -------———— 64, 65

K

Kachpurites fulgens .................. 27

Kanarraville, Utah _________... 76

Kane County, Utah ____________ 76,77

Page

Kayenta Formation -- 74, 75, 76, 77, 96, 97, 109 

Kettawaysites ......................... 22

(KeUawaysites), Reineckia ............ 50

Keller Creek Shale .____ —— __—_- 55,64 

Kent Formation (Canada) —------— 58

Kepplerites ........... 22,23,27,28,29,37,38,

45, 50, 55, 56, 58, 59, 82 

costidensus ........ 22, 28, 69, 71, 73, 75, 82

maclearni ........ 22, 28, 69, 71, 73, 75, 82

snugharborense ................... 65

subitua .............. 22, 69, 71, 73, 75, 82

torrensi .......................... 22

tychvnis .......... 22, 28, 69, 71, 73, 75, 82

Kilianetta ............................. 3'6

Kimmeridge Clay (England) ___— —— 32 

Kimmeriidgian Stage, Alaska -. — _-— 31, 38 

ammonite and buchia succession in . SO, 38 

Atlantic Coast region _—————— 103 

California 17, 31, 38, 60, 61, 63, 106, 107, 108 

Canada _____-_„_- — __ — _ 18, 31, 38, 67

Colorado ______-._ — ——— -- 90 

Cuba ._..__._.-__--------- 39,42

definition of ------------------ — - 30

England ___————————————— 31

Gulf of Mexico region .—————— 17, 38,

48, 102, 104, 105

Louisiana _—_ ——— — - — -— ———. 31

Mexico ___ 30, 38, 49, 51, 52, 102, 103, 106 

Michigan „..____..__.__„_._. 99

Montana _______ 18, 67, 82, 99, 113, 114 

North Dakota ________————— 67,99 

Oregon __________ 17, 38, 62, 106, 107 

Pacific Coast region ______— 102, 108 

South Dakota ._——-----—————— 90,99

Texas .-___—— --- —— —— 31. 103, 105 

Utah ____________________ 90 

Washington ______._____-____-— 107, 108

western interior region ----------- 18, 114

Wyoming _.- — ——— ——————— 90 

Kings River, Calif —_—— — —————— 53 

Klamath Mountains, Calif., Oreg . 17, 53, 61, 62 

Kline Member, Nesson Formation —— 69,78 

Knoxville Formation _ 55, 62, 63, 66, 107, 108 

Kootenai Formation _________——— 67, 68 

Kosmoceras ........................... 23

jason zone ------------------------ 22

Kossmatia ..... 24, 27, 32, 33, 34, 35, 36, 51, 55

kingi ............................. 35

rancheriasensis .................... 35

varicostata ----------------------- 35

Victoria ........................ 24, 35, 45

Kossmatia-Durangites ammonite assemblage ------__.--——-- 84

Kremmliing, Colo ---------------------- 93

Kunga Formation (Canada) ------ —. 58

Kuskokwim, Alaska ___--_—- — — ---—- 19

La Boca Formation (Mexico) ———— 49 

La Caja Formation (Mexico) _-.45,48,105 

La Casita Formation (Mexico) ------34,44,

45, 48, 105

La Gloria Formation (Mexico) —45,48,49,50 

La Joya Formation (Mexico) -.44,45,49,104 

La Punta de San Hipolito, Baja California _ — __——— — — -- — — - 51

Laberge Group (Canada) .... —..—— 59

Lak Member, Sundance Formation — — 71, 73, 

85,86,88,93,111,113

Lake Fork, Utah ___- —— —— ——— 72, 91, 92 

Lake Pillsbury, Calif _—_.__ — _ — — 63 

(Lamberticeras) collieri, Quenstedtoceras ._-___———.29,82 

Lander, Wyo ______________-84,85,87 

Las Villas Province, Cuba _ ——— ———— 34 

Latiwitchettia ......................... 58

gracilis ........................... 22

Page 

(LatiwitcheUia), Witchellia ........... 23

Laugeites vogulicws .................... 25

Leeds Creek Member, Twin Creek Limestone .——--70-, 72, 74, 88, 94, 111 

Leioceras opalinum .............-.23,24,25

opalinum zone ______.. 22, 23, 24, 37 

Leptaleoceras .............. 20,21,55,58,65

Leptosphinctes .... 22, 23, 37, 45, 55, 56, 59, 107

Levan, Utah ....__.______———. 74,94

Lewistown, Mont _... ———..—————— 69 

Liberty County, Mont . — —._.———— 80 

Lilac Argillite ——_________———— 54,57 

LUloettia ............. 28, 29, 38, 50, 64, 66, 82

buckmani ...... 22,23,27,55,56,58,59,65

stantoni ....................... 22,23,55

Lingula .............................. 113

Lioceratoides ......................... 65

Liparoceras (Becheiceras) ............. 20

LithologLc and stratigraphic features,

comparisons of —.————— 39 

Little Bull Valley, Utah ____________ 77,98

Little Rocky Mountains, Mont __ 29, 81, 82, 113 

Little Sheep Mountain, Wyo .—————— 87 

Little Water Canyon, Mont ——————— 81 

Locality data, bibliographic references to 3 

Lodge Grass Creek, Mont ————————— 78, 84 

Logtown Ridge Formation — 54, 60, 61, 62, 107 

Loma Rinconada, Sierra Cruillas ._—— 35 

Loma Sabinilla, Las Villas, Cuba ______ 34

Lonesome Formation —_____ ———— — 55,66

Longaeviceras ........................ 23

(Longaeviceras) pomeroyense, Cadoceraa 29 

Lopha ................................ 113

Louann Salt. 17, 44, 46, 47. 48, 49, 50, 51, 99, 102 

Louisiana ..______——————— 81, 46, 47, 48 

Lovell, Wyo _______—-————————- 87 

Lower Slide Lake, Wyo ._.___ 70,84,85,88 

Lubbe Creek Formation ———— — — — 59

Lucky S Argillite ____-____————, 54 

Ludwigia murchisonae zone ____________ 22

Lukachukai Member, Wingate Sandstone 97 

Lupherites ............................ 37

Lyosoma powelli ...................... 84, 89

(Lyroxyites), Oppelia ................. 23

Lytoceras ..................... 30, 93, 94, 113

Lytohoplites ................... 24, 27, 32, 34

caribbeanus ....................... 35

M

McCarthy Formation ------- ———— — — 59

McCoy Creek, Idaho _-____————— 90 

McDonell Lake, British Columbia ———. 58 

McElmo Canyon, Colo ——————————— 75,96 

Macrocephaiites .......... 29, 38, 50, 55, 61, 67

macrocephalus zone -__. — -.—— 22, 28, 82 

Madera County, Calif ——— ——— ——— 57 

Madison County, Mont - — ——— ———— 80 

Madison Range, Mont —————————— 81 

Malheur County, Oreg ——————————— 64, 65 

Malone Formation _—_---——-—— 45,51 

Malone Mountains, Tex ______.31,35,45 

(Maltoniceras) Cardioceras ............ 30

Manila, Utah ______-______——. 92 

Manitoba _____________________ 109

Marias Pass, Mont _—- ——— — ——— ___ 82 

Marine transgressions .—_ 17, 18, 46, 47, 48, 51, 

80, 85, 102, 103, 104, 105, 109, 113 

Mariposa Formation 54, 60, 61, 62, 102, 107, 108 

Masefield Shale (Canada) __-...———_ 69 

Maude Formation (Canada) ——— —— __ 58 

Maude Island, British Columbia ——.._ 66 

Mazapil, Zacatecas _________———_ 32, 33 

Mazapilites ........... 24, 27, 32, 88, 40, 42, 45

Mazatepec, Puebla —------ — — — — . 35

Megarietites .................... 20, 55, 56, 65
INDEX 131

Page

Megasphaeroceras .....___... 22, 23, 24, 37, 

58, 59, 69, 71, 73, 75, 80, 81

rotundum _.......____._.___..___ 22,23

Meleagrinella ................_._ 92, 93, 113

curia .........___r ________ 94,95

Merced River, Calif _________ 60

Mesa County, Colo .------............. 75

Metahaploce-Aas ................ 24, 31, 34, 35

(Metapeltoceras), Peltoceras .......... 22,55

Metophioceras ........................ 65

Mexico _ .. 17, 19, 20, 22, 23, 24, 25, 27, 29, 30,

31, 32, 34, 35, 36, 38, 44, 45, 48,

49, 51, 103, 105, 106

Mexico, Gulf of. See Gulf of Mexico.

Michigan basin _.-----_..-.......___ 99

Michoacan, Mexico -----.__.._.._______ 51

Micracanthoceras ............ 24, 32, 34, 35, 36

acanthellum ...................... 35

Microderoceras --------------------_.. 59

Midcontinent region (United States) .. 99 

Miles City, Mont _______.._____ 69 

Mill Creek, Wyo ______________.. 84 

Miller Creek, Colo .__.._______ 73,93 

Minas Viejas Formation (Mexico) ._ 44,48,

50, 99, 104 

Mineral, Idaho .------.._......._.. 56, 64, 65

Minnekahta, S. Dak ____________ 71 

Miogeosyncline _------------------..-_. 53

Mirosphinctes ......................__ 39

Mississippi .------........._______.. 46, 48

Moab, Utah __________________ 96 

Moab Member, Entrada Sandstone .... 75,96

Moenave Formation _.75,76,77,96,102,109

Moffat County, Colo __________ 73,93

Monks Hollow, Utah ______ 74, 93, 94, 113

Montana .______ 27, 28, 29, 30, 67, 68, 69, 78,

80, 81, 82, 84, 85, 87, 107, 108, 109,

111, 113, 114

Monte de Oro Formation ......_..... 61

Monterrey, Mexico ...-...._..._...._._ 44

Montezuma County, Colo __---------- 75

Moonshine Conglomerate ------- 54, 57, 60, 107

Morgan Creek, Oreg .-..__-._-----_. 65

Mormon Sandstone ..---.----_.... 54, 57, 107

Morrisiceras morrisi zone .--------.--._ 22

Morrison Formation ...... 18, 67, 68, 69, 70-75,

77, 82, 87, 88, 90, 92, 93, 95, 96,

98, 99, 108, 113, 114

Mount Baker, Wash .................. 66

Mount Carmel, Mount Carmel Junction,

Utah ____________ 76,97,98 

Mount Jura, Calif .._.._........_ 57, 60

Muddy Creek, Wyo ______________ 71 

Murderers Creek Graywacke -------__ 55

Myophorella .......................... 84

montanaensia .................... 87, 113

Mysterious Creek Formation (Canada) . 58 

Mytilus ............................... 114

N

Naknek Formation .-----------.--.._ 59

Navajo Indian Reservation, Ariz ...... 97

Navajo Sandstone -..._.----.--.. 53, 74-77,

95, 96, 97, 98, 99, 102, 109 

Nebrodites ............................ 31

Necaxa, Puebla ___________... 29 

Nelchina, Alaska ...._.-.---........_ 59

Neocomian Age --------..__-.-_._ 51, 67, 106

Neocosmoceras ........................ 63

Nephi, Utah ______________74,94,111 

Nerinea .............__._._...._...__. 57

Neritina _. —— -----._..-.-....--.---.-- 84

Nesson Formation ________ 67, 69, 82, 109 

Neuqueniceras .................. 29, 38, 45, 50

neogaeum ................._..... 22,29

Nevada _ 19, 20, 21, 52, 53, 54, 97, 106, 108, 109

Page

Nevadan orogeny ___.._____102,108 

New Mexico ----------..-------.-___ 17

Newark Group ______._-_-__--_-_-__._ 4

Newcastle, Wyo .___________ 71

Nicely Formation -------_.-------.--_ 55, 65

Nizina Mountain Formation ___________ 59

Nodicoeloceras .................. 20, 21, 22, 55

Nododelphinula ....................... 84

Nooksack Formation -..._----------- 56, 66

Normannites ... 22, 23, 37, 45, 55, 56, 57, 58, 80 

crickmayi ........................ 22, 23

undulatum ........................ 22

Norphlet Formation . 44, 46, 47, 48, 102, 104, 105 

North Dakota ___________67,69,81,109 

North Ridge Agglomerate ....--------. 54, 6>0

North Temperate Realm of Kauffman .. 31 

Nova Scotia shelf __________.. 4, 103

Nuevo Leon, Mexico _______ 35,36,44,48 

Nugget Sandstone ____ 70, 72, 74, 83, 90, 109 

Nutzotin Mountains, Alaska ...._.---. 59

o

Oakley, Utah ________________72,91

Oaxaca, Mexico ________ 23,25,45,49,51,

52, 102, 103, 104

Ochetoceras ....................... 30

canaliculatum .................. 24, 30, 45

(Fehlmannites) ------------------- 50

Octocythere --------------------------- 4

Okanogan County, Wash _____... 66 

Olcostephanus ------------------------ 36

Old Rampart, Alaska ._________ 19

Olvido Formation (Mexico) _ 44, 48, 102, 105 

Opis (Trigonopia) __..______--_.______ 84

Oppelia -_-.____._._.._...___-__._.- 29

aspidoides zone _...-._.-..._.-_..- 22 

(Lyroxyites) ---------------------- 23

Oregon .____ 17, 19, 20, 21, 22, 23, 24, 25, 26,

3'0, 36, 37, 38, 53, 55, 56, 61, 63.

106, 107

Orogenic activity _________ 102, 106, 108 

Orthosphinctes ______----_--------__--_ 24

Ostrea ...............___ 44, 87, 94, 113, 114

strigilecula ___._______---____--._- 95

Otapiria ._..__-_______--.-----_._____- 51

tailleuri ........__.____.__.._... 52

Otoites .... — -----. ____________. 23

sauzei zone --..___-... 22, 25, 57, 102

Otter Point Formation ____.55,62,63,108

Oxfordian Stage, Alaska _____ 17, 30, 31, 67

ammonite and buchia succession in . 30, 38

Atlantic Coast region .-...--.___.. 103

California ._____________ 17,30,

38, 53, 60, 61, 62, 106, 107

Canada ______________ 17, 18, 30, 67

Colorado ______________ 95, 113, 114

Cuba __________________ 30, 39, 42

Gulf of Mexico region _.--------.- 17,30,

38, 47, 48, 102, 104, 105

Idaho _________ 17, 30, 66, 90, 107, 113

Mexico _____ 30, 49, 50, 51, 52, 1*02, 103,

104, 105, 106

Montana ________ 17, 18, 30, 67, 82, 113 

North Dakota ____________-- 67 

Oregon ______ 17, 30, 38, 62, 66, 106, 107 

South Dakota ___________.- 87, 113 

Utah ........................ 95, 113, 114

Washington __________ 107

western interior region .-.-_------ 18, 30,

67, 102, 108, 113

Wyoming ______ 18, 87, 88, 9>0, 113, 114 

Oxynoticeras ------------- ___. 20, 45, 55, 65

oxynotum ........................ 21

zone .________________ 19,20 

Oxytoma wyomingensis ............._ 90

Page

Pacific Coast region, ammonite succession in __ ———————— —— 29,37 

characteristic fossils of ——— 55, 56, 58, 59 

geologic history of ---- — --------- 106

lithologic and stratigraphic features

compared in ___...__._____ 51

locality bibliographic references for . 3 

paleobiogeographic setting of ------ 17

unconformities in .-. ———— -----— 102

Pacific Ocean ------——————————— 17,23

Page, Ariz ....._....._....__...77,98,99

Page Sandstone . 72, 74, 75, 77, 91, 95, 98, 99, 109 

Paleobiogeography, setting of -....— 4

Palisade disturbance ——————————— 4, 102 

Palo Blanco Formation (Mexico) ..-- 49, 50 

Paltarpites — — — — — — 20, 21, 55, 58, 59, 65

Panuco-Elbano area, Veracruz .._..---. 36 

Papitticeras stantoni ----------------.. 22, 55

(Papitticeras) Sonninia ............... 57

Parabigotites ..........._____ 23, 37, 55, 56

craaiicostatus ................„ 22, 23, 59

Paracadocems ........................ 29, 58

(Paracadoceraa), Cadoceras ........... 23

tonniense, Cadoceras .............. 23

Paracaloceras ......................... 20

Paracephalites .................. 27, 28, 37, 81

glabrescens .............--..-.--.- 22

sawtoothensis ------------ 22, 69, 71, 73, 75

Parachondroceras .. 37,69,71,73,75,80,81,89 

andrewsi ...____.__.___.._._--_.__ 22

Paracoroniceras .... —— --------------- 21,58

Parapallasiceras -.._-. — ----- — --... 33, 40

Parapecten acutiplicatua .-...... ...... 57

praecuraor ----------------------- 57

Parapeltoceras ------------------- ..... 50

(Parapeltoceras) annulare, Peltoceras . 50 

Parareineckeia . ....... 22, 26, 28, 29, 37, 38, 55

Parastreblitea mazapilensia ..-.---..— 32 

Parastrenoceras ...................... 37,45

mixteca ...__________..__- 22,23 

Paraulacosphinctes transitoriua .. —... 26 

Paria River, Utah .___----- — ———— 98

Park Range, Colo ___—————————— 93

Parkinsonia parkinsoni zone .._._-.___. 22

Parodontoceras ___.______ 24, 34, 35, 55

butti — — — — . — ———— ——— 24, 34, 35

callistoides ........................ 36

Paskenta, Calif _____...————— 63, 66, 107 

Paveloff Siltstone Member, Chinitna Formation ..__----.-_—.-._-- 29

Pavlovia .............................. 25

pallaaioides zone ._.. — —24,26,31,32 

pavlovi ------------------------... 27

rotunda zone ______..———— 24,26,31 

Pavlovicerae ......____... 24, 69, 71, 73, 75

(Pavlovicerae), Quenstedtoceras ....30,38,82

Pectinatitea ........................... 25

pectinatus zone ...---.-_- — ...24,26,31

(Virgatosphinctoides) elegans zone . 30

Peltoceras ...................... 29, 38, 45, 67

athleta zone ____ —————— — — 22,47 

(Metapeltoceras) ................. 22,55

(Parapeltoceras) annulare ........ 50

Penon Blanco Volcanics .-.--..------. 60

Pentacrinua ------------------- .....-. 86

Peoa, Utah __________________- 72,90

Perisphinctca ..______________ 24, 35, 39

burckhardti ---------- — ----------- 32

cautisnigrae zone -- — -.. ——— —— 24 

danubiensis ---------------------- 33

plicatilis zone __.——————24,30,113 

transitoriua ------ ...------ — . — _ 33

(Dichotomosphinctes) .----- 30,38,39,62

(Discoaphinctes) ____________ 30, 38 

Peronoceraa ................... 20, 21, 22, 58

Phricodoceras ......................... 20
132 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

Page 

Phylloceras ----------__-._____________ 30,32

bakeri ____________________________ 23, 29

Phylseogrammoceras --------------- 2/0, 22, 58

Phymatoceras ...____.... 20, 21, 22, 58, 59

Physodoceras _-------_-_______________ 31,35

Picard Shale Member, Nesson Formation ------- _____________ 69, 78

Pictonia baylei zone __________________ 24

Pirofenta Formation (Mexico) 34, 35, 45, 49, 106 

Pimienta Member, Jagua Formation

(Cuba) -.__._____ 39

Pinar del Rio Province, Cuba _________ 34

Pine Butte Member, Sundance Formation 71, 73, 85, 86, 88, 92, 93, 95, 113 

Pine Creek, Utah __..________ 77,98

Pintura, Utah ______________ 99

Piper, Mont ..__________________ 69

Piper Formation ______________________ 68, 69,

70, 78, 79, 81, 83, 84, 87, 88, 109 

Pit River, Calif ___________________ 54, 61

Pittsburg Landing, Oreg _____________ 56,66

Placer de Guadalupe.Chihuahua __ 32, 35, 45, 51 

Platypleuroceras ---------------------- 21

Plettroceras _____________________ 20, 21, 58, 59

spinatum zone ____________________ 20

Pleuromya ---_-------_---_____________ 91

Plicatostylus -------------------------- 53, 57

Pliensbachian Stage, Alaska __----____- 20

ammonite and buchias succession in IS 

Arizona _--_----_---______________ 97

Atlantic Coast --___-_________-__ 4

California ----__-_________ 20, 57

Canada -----_______ 18, 21, 65, 67, 108

Gulf of Mexico region _________ 102, 103

Mexico _---_____-.__ 17, 20, 49, 99, 103 

Nevada ________________ 20, 53, 57 

Oregon ______ 17, 20, 57, 64, 65, 102, 108 

Pacific Coast region ______________ 102

Utah ___________________ 97

Plomosas, Chihuahua .-----______.__ 32, 45, 51

Poe Evaporite Member, Nesson Formation ------------------- 67, 69

Point Barrow, Alaska _________ 19, 22

Poker Chip Shale, Fernie Group

(Canada) ______ 68

Polyplectus __..______________ 20, 22, 55

Porcupine Dome, Mont _.____________ 69

Porcupine River, Alaska -_________-_-- 19

Posidonia ___________________________ 105

Potem Formation _____________________ 54, 61

Powder River Basin _-_---___________ 86

Poza Rica, Veracruz ._--.___________ 49, 51

Praeatrigites ------------ ____________ 22,55

Preuss Sandstone ___________70,72,74,

88, 89, 90, 91, 92, 93, 94, 111, 113 

Prionodoceras ------------------------- 31

(Prionodoceraa), Amoeboceras --------- 25, 59

spiniferum, Amoeboceras ---------- 25

Proceritea ---------------------------- 29

Proeerithium _________________________ 84

Prodactylioceras ..______ 20, 55, 56, 58, 65 

davoei ---------------------------- 2il

davoei zone ______________ — _____ 20

Proniceras .._.-. 24, 27, 32, 34, S3, 45, 55, 63 

(Proscaphites), Taramelliceras ________ 30

Prososphinctes ------------------------ 3ft, 38

Protacanthodiecus _______________ 24, 34, 36

Protaneyloceras __________._ 24, 33, 34, S6, 40

alamense _______________________ 36

anahuacense ____.__-.____.__--__ 36

barrancense ---------------------- 36

catalinense _______________________ 36

hondense ------------------- — ____ 34,36

ramirense ________________________ 36

Protogratnmoceras _________________ 23, 56, 65

Provo, Utah ______________ 93, 113

Pryor Mountains, Mont __ 78, 81, 82, 83, 84, 85 

Pseudoamaltheus ________________ 21

Page 

Pseudocadoceras _______ 23,29,38,58,60,66

grewingki . _____________ 22, 55, 60

Pseudolioceras __________ 20,21,22,33,55

compactile ------------------------ 21, 22

maclintocki ----------------------- 23, 24

whiteavesi ------------------------ 23

Pseudolissoceras ______ 24, 27, 32, 33, 34, 36, 40

bavarieum _________________-_-_-- 26

subrasile _____..-___________ 32,33

zitteli ...----.....- — _.__ 24, 26, 27, 32, 35

Pseudotoites ______-------_____-.-_ 23,37

Pseudovirgatites scruposus ------------ 26

Psiloceraa .__ —— —— _____ 10, 19, 20, 21, 55, 59 

canadense ..._______----- 20,21,58

eruffatas --------------__-.-.— 21, 58

planorbia ----------- _------------ 20

zone ..._-._________ 20

(Franziceras) -------------------- 19

Puale Bay, Alaska ____._--___ 19 

Puebla, Mexico ___________- 34, 35, 51

Punta Alegre Formation (Cuba) ______ 42

Purbeck Beds (England) ___.____ 90

Q

Queen Charlotte Islands, Canada -.-21,58,66 

Quenstedtia --------------------------- 84

sublaevis ------------------------- 87

Quenstedtoceras ----------------------- 90

collieri ------------ ___ 22, 69, 71, 73, 75

henriei ________..--_________ 23, 38, 58

lamberti zone .___________ 22, 47, 50

marine zone __---------_-------_-- 24, 30

(Lamberticeras) collieri _________ 29, 82

(Pavloviceras) ____------- 30, 38, 82

R

Ramona Mesa, Utah, Ariz ____________ 77

Rancho Cerro Pozo Sema, Sonora _____ 31

Rasenia . ________________._ 24, 25, 30, 45

cymodoee zone ___-_--___---------_ 24

mutabilis zone ______-__-_-_-----__ 24

Recapture Shale Member, Morrison Formation __---___-___ — .- — _ 75 

Red Canyon, Utah ____._-----__ — __ 94

Red Creek, Wyo ____________ 70,84,85,86 

Red Deer Member, Fernie Group

(Canada) —.-_.„—————— 68 

Red Dome, Mont ______________ 78, 84

Red Gulch, Wyo ___-_-_.-___.__._ 84 

Red Mountain, Idaho -_-----------_--- 70

Redding, Calif ___._______._———— 61

Redwater Member, Stump Sandstone __ 72, 73,

89, 90, 92

Redwater Shale Member, Sundance Formation _____.-- 70, 71, 73, 82, 85, 

86, 87, 88, 89, 90, 92, 93, 94, 95 

Reineckeia ___________ 22, 27, 29, 38, 45, 50

(Kellawaysites) ------------------- 50

(Reineckeites) -------------------- 50

Reineckeites -------------------------- 22

(Reineckeites), Reineckeia ------------- 50

Rsynesoceras -------------------- 20, 55, 57,65

Rich Member, Twin Creek Limestone . 70, 72,

74, 80, 81, 84, 85, 88, 89, 91, 92,

95, 98

Richardson Mountains, Canada _. 19, 21, 23, 29 

Richfield, Utah __.____________— 74 

Riddle, Oreg __________________ 62

Riddle Formation __.-_-_--___ 55, 62, 63, 1'08 

Rierdon Formation _____ 68, 69, 81, 87, 89 

Rierdon Gulch, Mont ____.___-. — — 68 

Ring Butte, Oreg __------- ___-_—— 65

Ringsteadia, --------------------------- 25

pseudocordata zone ________-------_ 24

Rio Blanco County, Colo --_---.-————— 93 

Riverside, Wash ____--_--_---__--_-_-- 66

Page 

Robertson Formation __-_---_----_---_ 55, 57

Rock Creek Member, Fernie Group

(Canada) __________ 68 

Rocky Mountains, British Columbia,

Alberta ----- 20, 21, 22, 25, 68, 108

Rogue Formation _._ — _ —— .55,61,62,107 

Romana Mesa, Ariz ________------__-- 99

Root Glacier Formation _______ —.---._ 59

Rosario Formation (Mexico) .-__-----_ 49

Roseburg, Oreg. ___———___—————— 63 

Roseray Formation, (Canada) ____---- 81

Routt County, Colo ———— — __ — — 73,93 

Russian platform __--_--___---_------_ 27

Sabinas basin, Mexico ________———— 48,49

Sadlerochit River, Alaska __.---__--. 22 

Sailor Canyon, Calif _____ — ——— — 106

Sailer Canyon Formation ____ — ——._ 57

Salina, Utah _______________ 74,94,113 

Salina Creek Canyon, Utah ______ 94, 113 

Salina Formation (Mexico) .__ — __— 50 

Salinites -------------------- _____ — __ 35

Salt ______________ 4, 17, 46, 47, 49, 50, 67,

99, 103, 104, 105, I0«, 109, 111

Salt domes __.___________-———— 42,47

Salt Lake County, Utah ______— 72 

Salt Spring Slate ______-_------_ 60

Salt Valley anticline __------——-— 96

Salt Wash Sandstone Member, Morrison

Formation --____--_--_--_- 75,77

San Andres Member, Taman Formation

(Mexico) ___________ 106 

San Cayetano Formation (Cuba) _____ 17, 39,

44, 1'02, 103, 104

San Luis Potosi, Mexico ___ — -.32,33,45,49 

San Miguel County, Colo —__. —— — 75 

San Pedro del Gallo, Durango _.. 30, 31, 34, 48 

San Rafael River, Utah ____._._ 75, 94, 96 

San Rafael Swell, Utah ___——————91,93, 

94, 95, 96, 109, 111, 113 

San Vicente Member, Guasasa Formation (Cuba) _ ——— — -. 40 

Sand Creek, Utah ____________ 91

Sand Valley, Ariz _________————- 77

Sanpete County, Utah ——__———————— 74

Santa Ana Mountains, Calif _————— 29, 52,

53, 54, 61, 106

Santa Monica Mountains, Calif .— 17, 53, 54 

Santa Monica Slate _________.. 54, 60, 61 

Santiago Formation (Mexico) —————45,48,

49, 50, 51, 104 

Sarasinella ------------------------- —— 36

Saskatchewan ____ 69, 78, 80, 81, 82, 109, 111 

Sawtooth Formation _————————24, 68, 80 

Sawtooth Range, Mont .-_.——————— 82, 113 

Scarburgiceras __________ 24, 69, 71, 73, 75

(Scarburgiceras), Cardioceras __.--_--- 25,30

martini, Cardioceras -------------- 24, 25,

30, 55, 56, 66 

Schlites spinosus -------------- — - __--- 22

Schlotheimia ___________ — — 19, 20, 55

angulata zone _ — ________-_-_-_— 20

Schuler Formation „ —— ._— 4, 44, 47, 48, 105 

Sehuleridea -------------------------— 4

Seaways, Jurassic .. ——— __ 17, 106, 107, 111 

Seldovia, Alaska _-----------__-----— 19

Semiformiceras ------------ _____ — __- 32

Seneca, Oreg ____-____---------_-—__- 55

Sevier County, Utah ———————————— 74 

Shaunavon Formation (Canada) ———— 69, 80 

Sheep Mountain, Wyo ____-_.--- —— __ 85, 87

Sheridan arch, Wyoming, Montana _._ 18, 111 

Shoshone River, Wyo ._--_--_--_-——— 86 

Shurtz Creek, Utah ______.. — _. 99

Sierra Blanca, Tex _..__ —— ———— 35 

Sierra Cruillas, Tamaulipas ———————34,35
INDEX 133

Page

Sierra de Catorce, San Luis Potosi .. 32, 33, 45 

Sierra de Santa Rosa, Sonora ______ 52 

Sierra del Rosario, Cuba _______ 39,44 

Sierra do los 6rganos, Cuba ..____ 39,44 

Sierra Jimulco, Coahuila ________ 36 

Sierra Nevada, Calif ___.-_17,29,52,53, 

54, 57, 60, 61, 62, 106, 107

Sierra Ramirez, Durango -...______ 36 

Sigaloceras cattoviense _.__.._______.... 23

calloviense zone _---__--___________ 22,50

Silberlingia ...__.__...___.._._.._.__._ 61 

Silvies Member, Snowshoe Formation _. 55 

Simoceras .....__________ 24, 32, 34, 35

(Virgatosimoceras) _____.....___.. 35

Sinawaya Member, Temple Cap Sandstone -.--____-_._.._.___._ 97

Sinemurian Stage, Alaska ------_.__ 19

ammonites and buchias sucession in 19 

Arizona -._-__.-__--_.___.__...__. 97 

California ._____________ 57, 61, 106

Canada ———_____.____ 18, 19, 67, 108 

Mexico ——___ 17, 19, 49, 52, 99, 102, 103 

Nevada .________..____ 19, 53, 106 

New Jersey .._____..-_.__.__.___. 102

Oregon ..._______. 17, 19, 63, 64, 65, 106 

Pacific Coast region ._____._ 52 

Utah ..-..-._................... 97

Slick Rock, Colo ______..______ 75,96 

Slick Rock Member, Entrada Sandstone 75, 96 

Sliderock Member, Twin Creek Limestone __ 24, 70, 72, 74, 80, 84, 85, 

87, 88, 89, 91, 95, 99, 108, 109 

Smackover Formation ................ 30, 44,

46, 47, 48, 50, 105 

Smith River, Mont ..-_......._..._.... 68

Smithers, British Columbia ......_... 58

Smithers Formation (Canada) -------- 58

Snake River, Oreg., Idaho __..__17,56, 

64, 66, 90, 106, 107

Snowshoe Formation _--__ 22, 55, 57, 64, 107 

Sohlites -----_..__ 37,69,71,73,75,80,81

spinosus -____.__....._.___.__...__ 95

Sonninia ...-_..........._.___. 23, 57, 58, 59

dominans ____._-_-_.__..___......_ 53

sowerbyi zone ..__-----_...... 22,57

(Euhoploceras) ..--__-_._._.._____ 22

(Papillicerat) _.__._______._......_ 57

Sonora, Mexico --------------17, 31, 38, 51, 52

South Dakota ____ 71, 82, 86, 90, 109, 111, 113 

South Fork Mountain Schist _______ 62 

Spearfish, S. Dak ._____________ 86 

Spearfish Formation ------------------ 83

Sphaeroceras ._...._________________ 23,37

Spiroceras ........____ 22, 23, 24, 37, 55, 56,

69, 71, 73, 75, 80, 81 

bifurcatum ........_.._...._....__ 22, 60

Spiticeras ..__--_______-_____.____.__ 24,39

Springdale Sandstone Member, Moenave

Formation ..------.-___.. 97

Stanley Mountain, Calif -....__--.-.. 63

State Bridge, Colo _____..______ 93 

Stemmatoceras .... 22, 24, 69, 71, 73, 75, 80, 81

arcicostatum .._..__.__.._____... 22 

Stenocadoceras _---.----_.___-.___..... 29

{Stenocadoceras), Cadoceras _.__--.._. 23,29 

canadense, Cadoceras .___-----_____ 23

stenoloboide, Cadoceras ________..._ 23, 59

striatum, Cadoceras --.-..--..._.. 23, 58 

Stephanoceras .......___. 22, 23, 24, 45, 57, 80

humphrierianum zone _..__..... 22, 23,

24, 57, 80, 109 

kirschneri __......._......._..._._ 23, 59

Stockade Beaver Shale Member, Sundance Formation .70, 71, 85, 88, 111 

Strenoceras subfurcatum zone _________ 22

Strigoceratidae ._.--___.---_-_... 22

Stump Sandstone _________ 70,72,73,82,

88, 89, 92, 95, 108, 113

Page 

Suaritea bituberculatum ...._-------- 36

Subcraspedites plicomphalus -------___ 25

Subdichotomoceras .._______ 27, 31, 32, 38 

nikitini ________._._._.____...__.. 32

Subgrossouvia __...________-_____.-_-__ 50

Sublette County, Wyo __________-- 70 

Sublithacoceras penicUlatum __.______- 26

Subplanitea ............ 24, 25, 27, 32, 33, 34,45

danubienais ....................... 32

klimovi ....__-------._----.-.--_- 27

reise .............................. 33

(Ilowaiskya) pseudosycthica ...... 27

sokolovi ...................... 27

Substeucroceras ....... 24, 27, 34, 35, 45, 52, 55

koeneni ........................... 26

Substeueroceras-Proniceras ammonite assemblage _.----------.----. 35

(Subvertebriceras) canadense, Cardioceras --------------------- 25

Summerville Formation ...----------.-74, 75,

93, 94, 95, 96, 98, 113 

Summit County, Utah __-------_--_---- 72

Sun River, Mont _--_____________ 68,80

Sundance Formation _.._-.------- 70, 71, 73,

81, 82, 83, 84, 85, 88, 93, 111, 113 

Sunrise Formation ------__---------- 53, 54

Suplee, Oreg ..__55,64,65,66,102,106,107 

Suplee Formation ---------------- 55, 64, 65

Sutneria platynota ------------------- 24,39

Sweet Grass Hills, Mont _______ 80,81 

Sweetgrass arch (Montana) .... 80, 81, 82, 113

Swift Formation ..____________ 30,68, 

69, 81, 82, 90, 108, 113

Swift Reservoir, Mont __-__-__.-.. 24,68 

Sykes Mountain, Wyo __-_---_--------- 84

Symon, Durango __--....---------32, 33, 36

Takwahoni Formation (Canada) __.__ 59 

Talkeetna Formation -_.------.-- ———. 59

Talkeetna Mountains, Alaska ....___ 22,59

Taman Formation (Mexico) ___45,49,106 

Tamaulipas, Mexico ..- 17, 33, 34, 35, 44, 48, 49 

Tamn, San Luis Potosi ------------_ 45

Tampico, Tamaulipas _- 17, 33, 35, 49, 103, 105 

Tampico embayment (Mexico) ..---_-- 49, 51 

Tampico Shale Member, Piper Formation __.-____ 68, 69, 78, 79, 80 

Tancrcdia __-_______________--__-__--__ 95

Tantima, Veracruz --.------_-------.-- 36

Tantoyuca, Veracruz ------_----.--_.. 36

Taramelliceras ( Prose aphites) ......... 30

Taseko Lake, British Columbia ..-._--. 58 

Taylorsville, Calif ...53,54,57,60,61,106,107 

Telephone Creek, Wyo _______._ 90 

Telkwa Formation (Canada) ---------- 58

Teloceras ......... 22, 23, 37, 55, 57, 58, 59, 61

itinsae ............................ 22,23

Temple Cap Sandstone ___ 76, 97, 98, 99, 109 

Tenas Creek, British Columbia ...-__ 58 

Tepexic Limestone (Mexico) -----—— 45,50

Tethyan Realm ________29,30,37,38,67 

Teton County, Idaho __..________ 70 

Teton County, Wyo ___________ 83,85,88 

Teton Range, Wyo __------- —— —— .—— 90

Texas _____ 31, 45, 46, 47, 48, 49, 51, 103, 105 

Thistle, Utah ____.___________ 109 

Thompson Limestone ---------------_. 54, 57

Thousands Pockets Tongue, Page Sandstone ___________.77,98,99 

Thnrmanniceras ..............._.___- 36

Tincup Creek, Idaho --__________ 90 

Titanites .............................. 18

giganteus zone ....._.__._.._..__ 24,26

occidentalis ....................... 25

Page

Tithonian Stage, Alaska .. ————— ——— 36,38 

ammonite and buchia succession in . 31 

arctic region ____-_----.-.--------- 38

Atlantic Coast region ______------. 103

California ___ 17, 36, 38, 53, 57, 61, 62, 63,

67, 108

Canada ..___________ 18, 36, 38, 67 

Colorado ______. ———— —— —— 95 

Cuba _.-________-- 33, Sit, 35, 39, 40 

definition and correlations of ———— 31 

Gulf of Mexico region ----———17,32,38

Mexico -_______- 32, 34, 35, 36, 106, 108 

Montana _----------------------- 67

North Dakota ______--- — ———— 67 

Oregon ______ 17, 36, 38, 62, 63, 67, 108 

Pacific Coast region --------------- 108

Russia -______--------------------- 34

subdivisions of -__-- —— --————— 26,32 

Texas _____--___----- —— ——— 35,36

Utah .-.....------- — --.------ 95

Washington _______————————— 108

western interior region ._..——— 102, 114 

Tmetoceras .............. 22,23,56,57,59,65

scissum ................ 22, 23, 24, 55, 58

Toarcian Stage, Alaska -------------- 22

ammonite and buchias succession in 21 

Arizona ___-___---_-- — ----------- 97

California -------- ———— ——— — 57,61

Canada ..._________ 18, 22, 65, 67, 108 

Gulf of Mexico region ------ — -.. 102

Mexico __ — ..-________ 39, 52, 99, 104 

Nevada ___________._______—— 21,53

Oregon __--_.--._____-------- 17, 21, 64

Utah __„_________.____ —---— 97

Tonnie Siltstone Member, Chinitna Formation ------------------- 65

Torcer Formation ------------------— 35,51

Torquatisphinctes _____----- 24, 32, 33, 40

Tragophylloceras ._.----------.-------- 20

ibex zone _________________________ 20

Trail Formation ...-——— — ——— —— 54,60

Transgressions, marine. See Marine

transgressions.

Trinity County, Calif - —.-——————— 62 

Tropidoceras .......... ———— —————— 20,58

Trowbridge Shale __-__.- 55,64,65,66,107 

Tulites subcontracts zone -------—___ 22

Tulsequah, British Columbia ----------- 59

Tuxedni Group _..--——————————— 59 

Twelvemile Canyon Member, Arapien

Shale ______________ 74, 94

Twin Creek Limestone -. 24, 70, 72, 74, 80, 81,

82, S3, 84, 85, 87, 88, 89, 91, 94,

95, 96, 99, 108, 109, 111

Twin Creek trough (Wyoming, Idaho,

Utah) ..-.----------18, 111

Twin Peaks, Oreg ____- —— ————— - 65 

Twist, Wash .._________..- ——— -- 66 

Twist Formation ---------------------- 66

Twist Gulch Member, Arapien Shale -- 74, 94 

Tylostoma ______________— ----------- 84

u

Uinta Mountains, Utah .. 90, 91, 92, 93, 94, 111 

Uintah County, Utah _____ ——— —— 72,73 

Uncompahgre uplift (Colorado) __-_— 18 

Unconformities, Jurassic ____---.---- 99, 107

United States, southern __ 17, 30, 31, 103, 105 

Uptonia .................. 20, 21, 45, 55, 58, 59

jamesoni ......................... 21

zone ____.-____---———— 20

Uranium Peak, Colo ______——- — -- 93

Utah ___-- 72, 73, 74, 75, 76,57, 89, 90, 91, 93,

96, 109, 111, 113, 114

Utah County, Utah ___..-—————— 74 

Ute Mountains, Colo — —— — -------- 96

Utiea, Mont ________________— 68
134 JURASSIC PALEOBIOGEOGRAPHY OF THE CONTERMINOUS UNITED STATES

Page

Vancouver Island, British Columbia -.- 58, 67 

Vanguard Group (Canada) --------— 69

Vaugonia .............. .....— ------- 44

conradi .. ______________ 87, 99, 113

quadrangularis .................... 90

Veracruz, Mexico . 26, 29, »0, 36, 49, 51, 103, 106 

Vermiceras ........................... 45

Vermisphinctes .................------ 28,37

Vernal, Utah ________________ 91 

Victoria, Tamaulipas _ 33, 44, 48, 49, 99, 105 

Vinales Limestone (Cuba) _______ 39 

Vinalesphinctes ....................... 39

Virgatites ............................ 32

virgatus .....--------------------- 27

Virffatosimoceras _____________________ 24

(Virgatosimoceras), Simoceras ........ 35

Virgatosphinctes ... 24, 27, 31, 32, 33, 34, 36, 45 

aguilari .......................... 32,45

chihuahuensis ..................... 33

densiplicatus ...............------- 33

mendozanus ....................... 26

mexicanus ........................ 32,33

sanchezi .......................... 32

Virgatosphinctoides elegans zone ----- 24,26

scitulus zone ______________________ 24, 26

•wheatleyensis zone --------------- 24,26

(Virgatosphinctoides) elegans, Pectinatites, zone ____--_--__-_--- 30

Volcanism, Jurassic .. 52, 53, 64, 106, 107, 108 

Volgian Stage ________________ 27,31

w

Waagenia ------------------........... 32

Waehneroceras .............. 19, 20, 21, 55, 59

Wagnericeras .............. 17, 26, 45, 50, 103

Wallowa Mountains, Oreg __.---------- 56,65

Warm Springs Member, Snowshoe Formation __..--_----_------_ 55, 57

Warrenoceras ............. 22, 28, 37, 82, 85, 88

codyense ............__ 22, 69, 71, 73, 75

Wasatch Mountains, Utah ______ 91,92,94 

Washington ____ ___ 18, 52, 56, 66, 107, 108

Page 

Washington County, Utah ------------- 76

Watrous Formation (Canada) _._--.--- 69

Watton Canyon Member, Twin Creek Limestone . 70, 72, 74, 87, 88, 91, 96, 111 

Webb County, Tex ______________ 35 

Weberg Member, Snowshoe Formation - 55 

Wedge, The, Utah ______________ 95 

Wells Creek Volcanics ___________ 56,66 

Werner Formation ________44,46,47,99 

Western interior region (United States), 

ammonite succession and 

correlation in .-.22,24,27,37,38 

Bajocian Stage in .-.. —... ——.. 24 

Callovian Stage in __..--____-. 29,38 

characteristic fossils of .... 69, 71, 73, 75

geologic history of -----__- 106, 107, 108

lithologic and stratigraphic features

compared in ------ ——— -.. 67

locality bibliographic references for 3 

Oxfordian Stage in ---_.----_----. 30

paleobiogeographic setting of _____ 18

unconformities in ----- — ------— 102

Westgate, Nev ________________ 21,106 

Westgate Formation ______ ____— 53, 54 

Weston County, Wyo -_______—- 71 

Westwater Canyon Sandstone Member,

Morrison Formation ------ 75

Weyla .................__________ 56

alata .............------------__ 57, 61

White Throne Member, Temple Cap

Sandstone __.-._ ——— —— 97 

Whitehorse, Yukon Territory - ——.-__- 59 

Whiterocks River canyon, Utah ...-72,91,92 

Whitmore Point Sandstone Member,

Moenave Formation ..._-- 96, 97 

Wichmanniecras ...................... 36

Wide Bay, Alaska ______________ 19 

Williston basin (Montana, North

Dakota) ___ 18, 67, 80, 81, 82, 84,

109, 111, 113

Willow Creek, Idaho ______—_.___-— 70

Wind River Basin, Wyo .. 18, 78, 82, 83, 84, 85,

86, 87, 93, 111

Wind River Mountains, Wyo ___—70,86,88

Page 

Windhauseniceras interspinosum ....... 26

Windy Hill Sandstone Member, Sundance

Formation 71, 73, 85, 87, 90, 92, 113 

Wingate Sandstone _________ 74,75,77,97 

Winsor Member, Carmel

Formation ______ 76, 77, 97, 111 

Winthrop, Wash _-.-._______________ 66

Witchellia ............................. 56

(LatiwitcheUia) ................... 23

Wolverine Canyon, Idaho .--. —— ------ 70

Wolverine Canyon Limestone Member,

Preuss Sandstone -..____ 59,92 

Woodruff, Utah _______________________ 90

Wrangell Mountains, Alaska __ 19, 28, 59, 67 

Wyoming __ 70, 71, 78, 82, 83, 90, 92, 109, 111,

113, 114 

Wyoming Range, Wyo ------__--_.--.-- 90

Xenocephalites .... 22, 28, 29, 38, 45, 50, 55, 82

vicarius ................. 22, 55, 56. 65, 66

Xochapulco, Puebla ___________ 30

Yakoun Formation (Canada) _________ 58

Yellowstone National Park, Wyo __ 80, 88, 89 

Yukon Territory _________ 21,23,25,29,59

Zacatecas, Mexico ______________ 32,33 

Zaraiskites albani zone ____________ 24, 26, 34

zarajskensis ...................... 27

Zemiatephanus .................... 22, 23, 37

richardsoni ....................... 23

Zigzagiceras .......................... 45

floresi ............................ 22,25

zigzag zone __________-__-_---___ 22

Zion National Park, Utah .________ 97,98 

Zuloaga Limestone (Mexico) .. 44,45,48,49,

50, 52

* U.S. GOVERNMENT PRINTING OFFICE: 1980 O— 311-344/22