Physical Stratigraphy 

of the Phosphoria 

Formation in 

Northwestern Wyoming

GEOLOGICAL SURVEY BULLETIN 1042-E

CONTRIBUTIONS TO ECONOMIC GEOLOGY

PHYSICAL STRATIGRAPHY OF THE PHOSPHORIA 

FORMATION IN NORTHWESTERN WYOMING

By Richard P. Sheldon

ABSTRACT

The rocks of the Ph'osphoria formation in northwestern Wyoming fall into five 

stratigraphic units, which, from oldest to youngest, are provisionally called the 

A, B, C, D, and E units. Units A, C, and E are composed dominantly of chert, 

carbonate rock, and sandstone, whereas units B and D are composed dominantly 

of mudstone, phosphorite, and dark carbonate rock. Units C and D are continuous over all of northwestern Wyoming, whereas unit A grades into unit B 

and unit -E grades into unit D to the southwest. Both units A and B pinch out 

to the north. . With the possible exception of unit A, these units can be recognized

 in southwestern Montana. Units B, C, and D are. equivalent to the phosphatic 

phale, Rex, and upper shale .members of the Phosphoria formation in southeastern 

Idaho. The formation as a whole exhibits a facies change from dominantly 

chert, mudstone, and phosphorite in the southwestern part of northwestern 

Wyoming, to dominantly Carbonate rock and sandstone in the northeastern part. 

The facies change with thinning and pinching out of units and the intergradation 

of units, " .. . . -

. The rocks of the formation in the area of the report are cyclically deposited. 

The rock record of a single ideal cycle consists, from base to top, of carbonate 

rock, chert, phosphorite, chert, and carbonate rock. Sandstone and glauconite 

in general are found in the carbonate phase of the cycle, whereas mudstone, 

pyrite,.and organic matter are found in the chert and phosphorite phases of the

 cycle. An eastward facies transition from phosphorite to chert and chert to 

carbonate rock is analagous to the upper half of the cycle, which is: phosphorite, 

chert, and carbonate rock in ascending order. The phosphorite phase of the 

cycle is represented by units B and D, whereas the other phases are represented 

by units A, C, and E. Two complete cycles are found in southwestern Wyoming. 

These stratigraphic relations represent two transgressions and regressions of 

areally zoned environments. The phosphorite phase is the more transgressive; 

the carbonate rock phase is the more regressive. The physical-chemical environments in which the sediments accumulated probably varied between an environment with a pH of above 7.8 and an Eh of greater than zero for the carbonate 

rock phase of the cycle, and an environment with a pH of less than 7.8 and an 

Eh of less than about 0.25 for the phosphorite phase of the cycle. These

105
106 CONTRIBUTIONS TO ECONOMIC GEOLOGY

environments probably were effected by an upwelling of cold water on a shelf 

to the east. The transgressive and regressive migrations of the shelf probably 

were tectonically controlled.

INTRODUCTION

The sediments which formed the Phosphoria formation of Permian 

age and its equivalents were deposited in the Cordilleran miogeosyncline in Idaho and north-central Utah and on the adjoining platform 

to the east in Wyoming, Montana, and northeastern Utah. These 

rocks consist of a number of relatively uncommon types such as 

phosphorite, black shale, bedded chert, evaporites, and red beds as 

well as more common rocks such as limestone, dolomite, and sandstone. 

In general, chert, mudstone, and phosphorite were deposited in the 

miogeosyncline, and carbonate rock and sandstone were deposited on 

the platform. Farther east a red bed and evaporite facies is developed 

(McKelvey and others, 1953) (fig. 10).

The manner hi which these facies changes are effected has been 

difficult to determine because Cretaceous and Tertiary orogeny, 

volcanic activity, and erosion have combined to isolate most of the 

principal areas where the Phosphoria now crops out in southwestern 

Montana, central Wyoming, and southeastern Idaho. The northwestern Wyoming area, however, contains a number of closely spaced 

outcrops of the Phosphoria formation that help to bridge the gap 

between the other areas. This key area, therefore, was selected for 

studies designed to provide stratigraphic correlation between the 

components of the Phosphoria formation hi the other areas and to 

define the nature of the facies changes from one area to another.

The preliminary results of these studies are presented here. In 

substance, they show that the formation can be divided into five 

lithologic units, provisionally termed units A, B, C, D, and E, from 

base to top; that these units are continuous over most of northwestern 

Wyoming (pi. 9); and that for the most part they are correlative with 

the major lithologic units of the formation in adjacent areas. The 

chief aspects of the facies change both by an eastward thinning or 

pinching out of chert, mudstone, and phosphorite units, and by 

gradation of beds of one rock type into beds of another. The most 

significant gradations are the eastward gradation of phosphorite to 

chert and chert to carbonate rock. In the area transitional between 

the chert-mudstone-phosphorite facies and the sandstone-carbonate 

facies in northwestern Wyoming, the depositional sequence from bottom to top is: carbonate rock and chert; phosphorite and mudstone; 

chert; carbonate rock and sandstone; phosphorite and mudstone;

chert; and, finally, carbonate rock and sandstone. This sequence 

records two transgressions represented by the phosphorite and mud-
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 107

M 0 N TANA

PHOSPHORIA OR EMBAR FORMATION 

NOT DEPOSITED OR REMOVED 

IE-JURASSIC EROSION

C=0=L 0 R A D 0

EXPLANATION

Chert, phosphate rock, and mudstone

Carbonate rock and sandstone Area of report

FIGURE 10. Index map showing location of area of this report and dominant llthologic character of the 

Phosphoria formation and its correlatives.

stone, and three regressions represented by the carbonate rock, sandstone, and chert.

FIELD WORK AND METHODS OF STUDY

The investigations on which this report is based were carried out by 

the U. S. Geological Survey during the summers of 1950, 1951, and 

1952. About 20 complete sections of the Phosphoria formation 

(fig. 11) were measured and described in detail and the phosphatic 

portions of the formation were sampled and analyzed for P205 and
108 CONTRIBUTIONS TO ECONOMIC. GEOLOGY

r-'«*'Xr rv-v, H ---*r XJv*

^//,,,, 1 w< 2ZI\2fc ^ ^ ' >>_ jff^s.v /.»*/ i ^."^ '"«"/» . ' 

10 40 Miles

Plate 10

Orientation of the correlation charts 

~ "rTaleTl~~Plate lT~ Plate 13

FIGURE 11. Map showing mountain ranges in northwestern Wyoming and localities where the Phosphoria

formation has been sampled and described. 

Localities:

1. Fall Creek 11. Forellen Peak

2. Bear Creek 12. Red Creek

3. Trench E (a) 13. Togwotee Pass

4. Trench D (a) 14. Gros Venire Slide

6. Hungry Creek 15. Flat Creek

6. Teton Pass 16. Crystal Creek

7. Trench H (a) 17. Darwin Peak (b)

8. Hoback 18. Tosi Creek

9. Buck Creek 19. Kock Creek (c)

10. Steer Creek 20. Bartlett Creek

References;

(a) Gardner (1944)

(b) Blackwelder (1918)

21. South Fork of Gypsum Creek

22. Sbeep Mountain (d)

23. White Rock (d)

24. Burroughs Creek

25. Dinwoody Canyon

26. Bull Lake

27. Cottonwood Creek (e)

28. Poison Creek

29. Middle Plney Lake

30. Lakeridge 1 well

31. Baldwin Creek (f)

(c) Blackwelder, Eliot, (unpublished manuscript)

(d) Baker (1946)

(e) Love, J. D., and Smith, L E.,

(unpublished manuscript)

(f) King (1947)
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 109

acid insoluble (Smart and others, 1954; Sheldon and others, 1954; 

Cheney and others, 1954; Sheldon and others, 1953).

The rock descriptions are based on megascopic examination, supplemented by microscopic examination of most of the beds at Flat 

Creek and Fall Creek (pi. 9; tables 1, 2) and some beds in the upper 

half of the core from the General Petroleum Company's 1 well, and 

also on chemical analyses for phosphate and acid insoluble.

ACKNOWLEDGMENTS

Many members of the U. S. Geological Survey during the last 15 

years have contributed to the growing understanding of the Phosphoria formation. I have tried not to anticipate the conclusions of 

those currently working with the Phosphoria, but in placing the strata 

studied for this report in their regional setting I have relied heavily on 

the work of others. The current studies of V. E. McKelvey, E. R. 

Cressman, and T. M. Cheney in particular have been used. V. E. 

McKelvey, hi addition, pointed out the problem to me in 1950, and 

has since generously aided me in its study. K. B. Krauskopf kindly 

reviewed the manuscript. I would like to acknowledge R. A. Smart,, 

T. M. Cheney, M. A. Warner, R. G. Waring, and H. W. Peirce who, 

with the author, described and sampled most of the sections studied. 

Members of the National Park Service in Yellowstone and Grand 

Teton National Parks, the U. S. Forest Service rangers in the many 

national forests in the area, and the Shoshone tribe in the Wind River 

Indian Reservation have all been very cooperative. This work was 

done partly on behalf of the Division of Raw Materials of the U. S. 

Atomic Energy Commission.

STRATIGRAPHY

The Phosphoria formation in northwestern Wyoming consists of 

three to five lithologic units, provisionally called units A, B, C, D, 

and E in ascending order. Unit A is composed of chert and carbonate 

rock; unit B of phosphorite, mudstone, and carbonate rock; unit C of 

carbonate rock, chert, and sandstone; unit D of phosphorite, mudstone, and carbonate rock; and unit E of chert, carbonate rock, and 

sandstone (pi. 9). The nomenclature of this sequence of rocks has 

been changed frequently in the past, causing several inconsistencies 

in the present nomenclature. In order to help in a better understanding of the present system, it is appropriate to review the history of 

the nomenclature before further defining the units used in this report 

and describing their areal variations and vertical lithologic sequences.

REVIEW OF NOMENCLATURE

In Yellowstone Park, Hague, Iddings, and Weed (1899) named a 

sequence of sandstone, red and green shale, and chert the Teton
1.10 CONTRIBUTIONS TO ECONOMIC GEOLOGY

formation. They defined the formation as the beds overlying the 

Quadrant quartzite of Carboniferous age and overlain by the Ellis 

formation of Jurassic age. They thought that the Teton formation 

was "Juratrias" in age. The name has since been discarded, because 

it was subdivided later into other formations, which do not logically 

form a group.

In 1906 Darton gave the name Embar formation to limestone and 

shale beds lying above the Pennsylvanian Tensleep sandstone and 

below the Triassic( ?) Chugwater formation in the Owl Creek Mountains, Wyo. These beds were thought to be Pennsylvanian in age. 

Blackwelder (1911) tentatively extended the name Embar into the 

Wind River and Gros Ventre Ranges.

In 1907 Boutwell named a sequence of calcareous rocks, which 

had been included in the Upper Coal Measures by King (1878), the 

Park City formation,

in recognition of the fact that it is the formation which has yielded the bonanzas 

that. . . have made the (Park City) district famous ....

The formation was defined as overlying the Pennsylvanian Weber 

quartzite and underlying a sequence of red shales which he designated 

the "Permo-carboniferous" Woodside shale. The Park City formation 

was thought to be Pennsylvanian in age. Also in 1907 Veatch recognized similar rocks in southwestern Wyoming and extended the name 

Park City formation to them. Gale and Richards (1910) applied the 

name Park City to similar rocks in southeastern Idaho, northern 

Utah, and western Wyoming. They differentiated a lower cherty 

limestone member, a middle phosphatic shale, and an upper chert 

and limestone member, which they also recognized at the type section 

of the Park City in Utah. Blackwelder (1911) extended the name 

Park City to the north to the Snake River Range, Idaho.

Richards and Mansfield in 1912 reorganized the stratigraphic 

nomenclature in southeastern Idaho. Faunal evidence suggested that 

the lower member of the Park City formation was Pennsylvanian in 

age, whereas the middle and upper members were thought to be 

Permian (?). Thus they grouped the Weber quartzite and lower Park 

City member and called the unit the Wells formation of Pennsylvanian age; its type section is in Wells Canyon, Caribou County, 

Idaho. The rest of the Park City formation was renamed the Phosphoria formation and assigned a Permian (?) age; its type section is 

in Phosphoria Gulch, Caribou County, Idaho. The Phosphoria 

formation thus included the middle and upper members of the Park 

City formation. The middle member, consisting of dark phosphatic 

shale, was not given a formal name, but the upper member, consisting 

of chert, limestone, and cherty mudstone, was called the Rex chert 

member; its type section is at Rex Peak, Rich County, Utah. ..
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 111

From 1911 until 1924 the two names, Park City and Phosphoria, 

were in competition in Wyoming. Schultz in 1914 used the name 

Park City in the Salt River and Wyoming ranges, applying it to strata 

lying above the Weber quartzite and below a sequence of red beds. 

He thereby included beds at the top which are now placed in the 

Triassic Dinwoody formation, a tune correlative of the Woodside 

formation of Utah (Newell and Kummel, 1942). Mansfield in 1916 

reassigned the lower portion of the beds in the Salt River Range 

to the Phosphoria formation.

In 1918 Blackwelder split the Embar formation into an upper unit 

of Triassic age, which he named the Dinwoody formation, and a 

lower unit of Permian age, which he did not name but which he said 

was the correlative of the Park City formation. In 1919, Collier 

called these two units the Embar group, containing the Park City 

and Dinwoody formations in the Maverick Springs anticline east of 

the Wind River Mountains. In 1924, however, Condit placed the 

same beds in the Phosphoria formation, stating that

studies by several workers had proved that the part of the Embar formation 

beneath the Dinwoody formation corresponds to only the upper or Phosphoria 

part of the Park City formation of Utah. . . .

The name Phosphoria has been extended eastward to include 

Permian red beds in central Wyoming (Ketterer and Swirczynski, 

1952; Frielinghausen, 1952), but others (Thomas, 1934, 1948, 1949; 

Tourtelot, 1952) apply the name only to marine tongues in the red 

bed facies. However, some authors prefer the name Embar formation 

in central Wyoming and southern Montana where the Phosphoria 

and Dinwoody formations are dominantly made up of red beds and 

are separated only with difficulty (Gardner arid others, 1945; Pierce, 

1948).

Subdivision of the Phosphoria formation into members has hitherto followed local usage. The division into phosphatic shale and Rex 

members has been used in western Wyoming by Mansfield (1916), 

Gardner (1944), Rubey 1 and McKelvey. 2 Rubey and McKelvey, 

in addition, have distinguished an upper shale member overlying 

the Rex member. In southwestern Montana two to five lithologic 

units have been distinguished 3 and have been provisionally termed

1 Rubey, W. W.( 1942, Unpublished descriptions of the Phosphoria formation In the Salt Elver and 

Wyoming ranges.

2 McKelvey, V. E., 1946, Stratigraphy of the phosphatic shale member of the Phosphoria formation In 

western Wyoming, southeastern Idaho, and northern Utah: U. S. Geol. Survey open-file report.

a Klepper, M. R., Lowell, W. R., Myers, W. B., Swanson, R. W., and Kennedy, O. C., 1948, Distribution 

and stratigraphy of the Phosphoria formation in southwestern Montana: Paper read at Northwest Science 

meeting, Spokane, Wash, in December 1948.

Lowell, W. R., 1949, Geology of the Small Horn Canyon, Dalys Spur, Cedar Creek, and Dell areas, 

Montana: U. S. Geol. Survey open-file report.

Butler, A. P., and Chesterman, C. W., 1945, Investigation of trace elements in the Phosphoria formation 

In southwestern Montana, preliminary report: U. S. Geol. Survey Trace Elements Inv. Rept. 5.
112 CONTRIBUTIONS TO ECONOMIC GEOLOGY

by Klepper units A, B, C, D, and E from base to top respectively. 

Unit A consists of sandstone and cherty carbonate rock, unit B of 

phosphate rock and phosphatic mudstone, unit C mainly of carbonate 

.rock, unit D of phosphatic mudstone, and unit E of chert and sandstone (Cressman, 1955). In the Lander, Wyo. area/King (1947) divided the Phosphoria into lower, middle, and upper units on the 

basis of resistant limestone beds (pi. 13).

The terminology of the Phosphoria, as it now stands, is unsatisfactory. For one thing, the base of the beds that disconformably 

overlie the Tensleep sandstone defines the base of the Phosphoria 

formation in the Wind River Mountains, Wyo. (Condit, 1924), 

whereas in southeastern Idaho the base of the dark phosphatic 

shale of the phosphatic shale member defines the base of the formation (Richards and Mansfield, 1912). Thus the formation includes 

a chert and carbonate rock unit underlying the phosphatic shale in 

the Wind River Mountains, but excludes this unit in the Wyoming 

and Snake River ranges, although the unit is continuous over both 

,areas. For another, the Phosphoria formation now includes three 

.distinct facies (fig. 10): (1) a chert-phosphorite-mudstone facies in 

southeastern Idaho and immediately adjacent areas; (2) a carbonate 

rock-sandstone facies hi western Wyoming; and (3) a red bed-carbonate rock-evaporite facies in central Wyoming.

NOMENCLATURE USED IN THIS REPORT

No permanent solution to the problems of stratigraphic nomenclature is attempted in this paper, since a revision of the nomenclature 

based on a study of a relatively small area would not be warranted. 

Instead, the provisional nomenclature used by Klepper and others in 

Montana is extended to this area. Five units A, B, C, D, and E, 

.from base to top respectively are thus distinguished.

METHOD OF CORRELATION

The units of the formation in northwestern Wyoming are defined 

wholly on the basis of their lithologic character. Therefore, the correlation of unit boundaries in general is based on gross lithologic changes 

such as the break between beds of phosphatic mudstone of unit B and 

.the overlying beds of chert of unit C. Similarly, within units some 

correlations are based on the lowermost or uppermost occurrence of 

'a lithologic type. However, certain lithologic sequences are repeated 

in detail from one section to another. Moreover, certain beds of 

'Unique lithologic character, for the most part phosphorites, can be 

.recognized from section to section. Each of these key beds probably 

represents synchronous deposition, because it seems unlikely that such 

unique rock sequences or rock types would be repeated in time.
These key beds have been used to help delineate some of the fades 

relations. The correlation of such beds is indicated on plates 10 to 

13 by a special type of line.

REGIONAL STRATIGRAPHY

The Phosphoria formation varies significantly in thickness and 

lithologic character in the four states in which it crops out. For this 

reason stratigraphic correlation has been difficult and the stratigraphic units delimited in various areas have not always incorporated 

the same rocks nor been called by the same name. Therefore the 

regional variations of thickness and lithologic character of the Phosphoria formation are described, and the units delimited in this report 

are correlated with previously described units in adjacent areas.

THICKNESS

The thickness of the formation ranges between 200 and 300 feet 

over most of northwestern Wyoming, but thins to about 150 feet in 

the northern part of the area and thickens to about 400 feet in the 

southwestern part (fig. 12). To the southwest, in southeastern 

Idaho, the formation thickens to more than 500 feet. The thickness 

of the formation is about the same hi northwestern Wyoming as in 

immediately adjacent parts of Montana (Cressman, 1955), but over 

the whole of southwestern Montana the formation shows a greater 

variation in thickness. East of the area of this -report the formation 

thins to the north (Frielinghausen, 1952; Ketterer and Swirczynski, 

1952). To the northeast, in the Big Horn Basin, variations in the 

thickness of the Phosphoria are almost wholly accounted for by relief 

on the Tensleep surface (Agatson, 1952, 1954). That is, where the 

Tensleep is thin, the Phosphoria is thick and the combined thickness 

of the Tensleep and Phosphoria remains fairly constant.

UTHCXLOGIC DESCRIPTION

In general the lithologic character of the formation varies with 

the thickness. Where the formation is thick, in southeastern Idaho, 

it is composed dominantly of chert, mudstone, and phosphorite. 

Where the formation is thin, in the eastern portion of the area of the 

report and in Montana, it is composed dominantly of carbonate rock 

and sandstone. In central Wyoming and central Montana the Phosphoria formation is thin and consists chiefly of red beds (fig. 10).

CORRELATION WITH THE PHOSPHORIA OF OTHER AREAS

Unit A of this report has not been definitely recognized in other 

areas. To the southwest the unit grades into the lower beds of unit 

B. Unit A in northwestern Wyoming is possibly the stratigraphic 

equivalent of unit A in areas such as the Centennial Range and
114 CONTRIBUTIONS TO ECONOMIC GEOLOGY

111° 110° 109"

YE LLOWSTON E 

NATIONAL

PARK 10 20 Miles

44'

IDAHO

11

200

W \Y 0 M I N G

43'

EXPLANATION

Contour, showing thickness, in feet. 

Contour interval 50 feet

.16

183

Upper figure is sample locality (see 

fig. 11); lower figure shows thickness of Phosphoria formation, in 

feet

FIGURE 12. Isopach map of the Phosphoria formation in northwestern Wyoming.

Madison Range, Mont. Beds assigned to unit A in the western part 

of Beaverhead County, Mont, are possibly equivalent to beds included 

in the upper part of the Wells formation in western Wyoming.

Unit B has been designated the phosphatic shale member in the 

southwestern part of the area of the report (Gardner, 1944) and is 

correlative with the 200-foot phosphatic shale member in southeastern

Idaho (McKelvey, op. cit.). The unit probably is the correlative 

of unit B in. southwestern Montana (Klepper and others, op. cit.;

Oessman, 1955).

Unit C has been included in the Rex member in the southeastern

part of the area of the report (Gardner, 1944), At Brazer Canyon,

Utah near the type locality of the Rex, T. M. Cheney (oral communi-
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 115

cation 1953) of the U. S. Geological Survey has recognized chert and 

mudstone beds at the top of the Rex that probably are equivalent to the 

chert and mudstone of units D and E. Thus unit C is probably 

equivalent to only the lower massive chert of the Rex member at the 

type locality. Unit C is probably the equivalent of unit C in southwestern Montana (Klepper and others, op. cit.; Cressman, 1955).

Unit D is probably equivalent to the upper shale member in southeastern Idaho and southwestern Wyoming and was included in the 

Rex member by Gardner (1944). As stated above, the unit is possibly 

present at the type section of the Rex chert and is represented by 

cherty mudstone near the top of the member. Unit D is probably 

equivalent to the unit D in southwestern Montana (Klepper and 

others, op. cit.; Cressman, 1955).

Unit E, as has been stated above, is possibly present at the type 

section of the Rex chert in Utah and is equivalent to the uppermost 

chert beds of the Rex there. It also is probably the equivalent of 

unit E in southwestern Montana (Klepper and others, op. cit.; 

Cressman, 1955). Beds of this lithologic type have not been recognized in southeastern Idaho because the chert beds of northwestern 

Wyoming grade into mudstone in westernmost Wyoming.

In central Wyoming the units of this report cannot be recognized 

owing to the change to the red bed facies. Three carbonate rock 

tongues of the carbonate rock facies do extend into the red bed facies, 

however (Condit, 1917; Thomas, 1934). Thomas (1948) presented 

the detailed correlation of the units of the red bed facies of the Phosphoria with the carbonate rock facies of the Phosphoria to the west, 

at the Little Popo Agie River section in the southern Wind River 

Mountains. The Opeche shale is made up of red beds, which lie 

at the base of the formation at the same stratigraphic position as 

the lower part of King's (1947) lower member of the Phosphoria in 

the southern Wind River Range. The Minnekahta limestone, 

formerly called the Sybille tongue of the Phosphoria (Thomas, 1934), 

contains abundant calcite geodes. Thomas (1949) states:

because it carries abundant geodes and because of its stratigraphic position in 

respect to the unconformity at the base of the Phosphoria, the Minnekahta is 

tentatively correlated with the geodal limestone just above the lower phosphate 

zone in the southern Wind River Mountains.

This geodal limestone is the upper part of King's lower member 

of the Phosphoria. The next stratigraphically higher unit is the 

Glendo shale of Condra, Reed, and Scherer (1940), a red bed unit 

that is equivalent to the lower part of King's middle member. The 

Forelle limestone overlies the Glendo shale of Condra, Reed, and 

Scherer (1940) and is not lithologically distinctive from other car394091 56 2
116 CONTRIBUTIONS TO ECONOMIC GEOLOGY ,

bonate rocks in the Wind River Mountains; however, on the basis 

of its stratigraphic position it is probably correlative with a 14-foot 

cherty carbonate rock that is 60 feet above the base of King's middle 

unit. The unnamed red bed unit above the Forelle limestone is 

equivalent to the rest of King's middle member. The Ervay tongue 

marks the top of the Phosphoria and was correlated by Thomas 

(1934) with the upper limestone member of King at the Little Popo 

Agie River section, on the basis of both stratigraphic position and 

similar faunules. A number of species contained in these faunules 

are restricted to the uppermost beds of the formation. These faunules 

are also described by C. C. Branson (1930) and includes his Aulosteges 

and Hustedia faunules.

King (1947) presented the detailed correlation of the Phosphoria 

strata from Little Popo Agie River to Baldwin Creek. His Baldwin 

Creek section is reproduced in figure 12, which shows his member 

breakdown as well as the Minnekahta, Forelle, and Ervay correlatives. 

Thomas' and King's correlations, as well as the correlation of the 

units of this report from Bull Lake to Baldwin Creek, indicate that 

the Minnekahta limestone lies at the base of unit C; the Forelle 

limestone probably lies about 75 feet above the base of unit C; and 

the Ervay tongue lies at the top of unit E.

PETBOQBAPHIC DESCBIPTION

Before describing the individual units of the formation, it is appropriate to describe the rock types that occur in the formation. Rocks 

from two localities in the area of the report have been selected for 

petrographic study; they are the Fall Creek and the Flat Creek 

sections (fig. 11). The Fall Creek section was selected as a representative of the miogeosynclinal rocks, and the Flat Creek section as 

a representative of the platform rocks. In addition, some specimens 

from a few other localities were studied., The petrographic descriptions of the rocks from Flat Creek and Fall Creek are presented in 

tables 1 and 2 and a description and interpretation of the textures, 

minerals, and mineral associations of phosphorite, chert, carbonate 

rock, mudstone, and sandstone are presented below.

PHOSPHORITES

Phosphorites of the Phosphoria formation are those rocks composed 

dominantly of apatite. Altschuler and Cisney (1952) have identified 

several samples of apatite from the Phosphoria as carbonate fluorapatite. Both anisotropic and isotropic forms of apatite are found;

they have similar compositions and structures, but the isotropic form

has been called cellophane, and the anisotropic form francolite

(Frondel, 1943; Deitz, Emery, and Shepard, 1942; and Lowell, 1952).

Phosphorites, perhaps more than any of the other rocks studied,
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 117

show wide variations in texture and in the mineral habit and morphology of constituent grains. The types of grains include structureless pellets and nodules, oolites and pisolites, apatite fossil'fragments, 

compound pellets and nodules, phosphate sand, and euhedral apatite 

crystals. In addition, apatite commonly forms cement. Most 

phosphorites are composed dominantly of one type of grain, but 

contain minor, and in many cases prominent, amounts of others. 

The various types of phosphorite may be described by the use of

 adjectives depending on the prominent types of grains. Thus, pelletal 

phosphorite is one composed dominantly of pellets, and .pelletaloolitic phosphorite is one composed dominantly of pellets but with 

prominent oolites. A phosphorite composed dominantly of fossil 

remains is termed an organic phosphorite. The most common phosphorites pelletal and nodular phosphorite, oolitic and pisolitic 

phosphorite, and organic phosphorite are described below.

PELIETAI AND NODULAR PHOSPHORITES

Phosphorites that are composed dominantly of structureless grains 

of cellophane and francolite less than 2 mm in diameter are termed 

pelletal phosphorite; if the constituent grains are larger than 2 mm 

in diameter, the rock is termed a nodular phosphorite. These grains 

range in color from brownish black to almost white. Pellets arid 

nodules are generally spherical to oblate ellipsoidal in shape, but some 

have irregular shapes. Their shapes are made more irregular by 

compaction, solution, and accretion. The larger grains are, in general, 

better rounded than the smaller. ' Most pellets are composed of 

cellophane, but francolite pellets are not uncommon. The francolite 

is a microcrystalline aggregate of grains oriented at random. Many 

pellets and nodules contain nuclei and inclusions of nonphosphatic 

material, generally detrital grains of quartz and muscovite and crystals

 of fluorite, dolomite, and calcite. Judging from the study of the Flat 

Creek and Fall Creek thin sections, these grains generally have unimodal size distributions and are fairly well "sorted"; however, some 

phosphorites have a bimodal distribution because the diagenetic 

solution and redeposition of apatite increases the size of larger pellets 

at the expense of smaller ones. This bimodal distribution is emphasized if compound grains are counted rather than the smaller pellets 

within the compound grains.

Pelletal or nodular phosphorite is, in general, a light to dark-colored, 

soft to medium-hard, thin-bedded rock commonly interbedded with 

mudstone and carbonate rock, and commonly stratified by alternating 

laminae of phosphorite containing various - proportions of clastic 

material, carbonate, and carbonaceous matter. Most pelletal phosphorites contain minor amounts of silt and clay, but some of the richest
118 CONTRIBUTIONS TO ECONOMIC GEOLOGY

are associated with minor amounts of very fine to fine sand. In these 

slightly sandy phosphorites, the sand is generally well sorted and 

occurs in the matrix of the rock. Inclusions of detritus in the apatite 

grains are finer in size, ranging down to fine quartz and muscovite 

silt. Pelletal phosphorites commonly contain dolomite as a microcrystalline matrix. Fluorite occurs as void fillings.

Dark-colored pellets and organic fragments are not commonly 

associated. Dark pelletal phosphorites, in fact, are fairly free of 

admixtures of all other types of grains, except compound pellets and 

nodules.

OOIITIC AND PIS01ITIC PHOSPHORITES

Oolitic phosphorite is composed dominantly of francolite or collophane grains that exhibit concentric structure and are less than 2 mm 

in diameter. If the constituent grains are similar but are larger than 2 

mm in diameter, the rock is termed a pisolitic phosphorite. The size, 

shape, and roundness characteristics of these grains are similar to those 

of pellets and nodules. Nuclei of quartz and phosphatic fossile fragments are more common in oolites and pisolites than in pellets and 

nodules. The concentric structure of oolites and pisolites is shown 

both by alternating rings of francolite and cellophane and by alternating rings of differing color. In general francolite rings, if present in 

a grain, are of lighter color than cellophane and contain fewer inclusions of foreign material. Francolite rings are made up of fibers of 

francolite with the c crystallographic axis coincident with the long 

dimension of the fiber and oriented perpendicular to the circumference 

of the ring. The inner rings of oolites conform with irregularities of 

nuclei. The number of rings in oolites and pisolites ranges from 2 to 

about 10. The color contrast between rings varies widely so that 

there is a continuous series from dark pellets to oolites with mostly 

dark rings to oolites with mostly light rings to light pellets.

Oolitic phosphorites are commonly medium-dark, medium-hard to 

hard, thin- to thick-bedded rocks, commonly interbedded with pelletal 

phosphorites, mudstone, and carbonate rock. Most are generally only 

crudely laminated if at all. They generally contain minor amounts 

of very fine to fine sand in the matrix of the rock, and minor amounts 

of bioclastic apatite grains; only a few contain silt and clay. They 

are commonly cemented with coarse-grained calcite and have a 

poikiloblastic texture or are cemented with apatite. Some oolitic 

phosphorites contain fibrous glauconite in the matrix of the rock.

ORGANIC PHOSPHORITES

Organic phosphorite is composed dominantly of apatite fossil 

fragments. The fragments found in this study include brachiopod 

shells, fish scales, fish teeth, bone, bryozoans, echinoid spines, casts
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 119

of the axial canals of sponge spicules, internal casts of gastropod 

shells, and internal casts of the holes in bryozoans. These ma,y be 

divided into three groups depending on whether the fragment is a 

cast or original fossil and, if it is the original fossil, whether or not it 

was phosphatic originally. The phosphatic brachiopod shells and fish 

scales, teeth, and bone were probably originally phosphatic, whereas 

the bryozoans and echinoid spines were originally calcium carbonate. 

The brachiopod shells, fish teeth, and bone are now composed of 

francolite, whereas the other types are usually cellophane. Fossil 

fragments range in shape from angular to well-rounded grains and in 

size from much larger than the quartz detritus to slightly smaller.

Organic phosphorites are generally medium-dark to light-colored, 

medium hard to hard, thin-bedded rocks showing sharp and irregular 

contacts with the beds below. They are commonly interbedded 

with chert, oolitic phosphate, and sandstone, but they show little 

lamination in thin section. The bioclastic fragments, if elongate or 

tabular, are usually oriented with the long axis parallel to the bedding. 

They generally contain minor amounts of very fine to fine sand. 

Glauconite is not uncommon in the matrix as grains. Most organic 

phosphorites contain at least minor amounts of oolites.

MISCELLANEOUS APATITE GRAINS

Grains of apatite consisting of an aggregate of smaller oolites or 

pellets cemented by apatite are termed compound pellets if less than 

2 mm in diameter, and a compound nodule if larger. Such nodules 

and pellets are common in the phosphorites. The cement can be 

either francolite or collophane and generally is lighter in color than 

the cemented apatite grains. Compound grains range from spherical 

to irregular.

Many, if not most, of the sandstones in the Phosphoria contain 

grains of apatite which are slightly smaller than the quartz grains 

and are generally better rounded. It seems likely that they were 

transported and deposited with the quartz grains and thus are best 

classed as apatite sand grains, regardless of whether they are oolites, 

pellets, or fossil fragments.

Minute euhedral apatite tablets are found in some of the chert 

beds of the Phosphoria. They are generally disseminated throughout 

the rock but are somewhat concentrated in the phosphatic casts of 

axial canals of sponge spicules. These crystals are minor in occurrence 

and have not been found to make up more than 1 percent of the rock.

CHERT

Chert in the Phosphoria is composed of three different lithologic 

types: dark bedded chert, light-colored nodular and concretionary 

chert, and a chert made up of tubular concretions, 0.5-1.5 feet long
120 : > " CONTRIBUTIONS TO ECONOMIC GEOLOGY

and several inches in diameter. These tubular concretions are usually 

oriented parallel with one another and at an oblique angle to the 

bedding. They commonly are composed of conical, concentric layers. 

They occur in matrices of sandstone and carbonate rock, but in 

places make up all of individual beds. Petrographically, no distinct 

differences can be seen between bedded, nodular, and tubular chert. 

However, all gradations may be found between chert fairly rich in 

carbonaceous matter, which outlines relict sponge spicules, and white 

chert recrystallized to spherulites (a roughly spherical structure of 

radially arranged fibers) up to 0.25 mm in diameter, which contains 

no carbonaceous matter and no relict sponge spicules. In general, 

the more coarsely crystalline cherts are lighter colored, which is 

caused mostly by the smaller amount of carbonaceous matter and in 

part by the coarser grain size. Some of the relict sponge spicules are 

shown by slightly more coarsely crystalline chalcedony than the 

matrix chalcedony. The extent to which cherts are formed of sponge 

spicules is unknown. E. R. Cressman (oral communication, 1954) has 

found that much of the chert in the Phosphoria in Montana is composed of sponge spicules. In Wyoming, many of the cherts studied 

contain prominent spicules and many of those that do not contain 

spicules have been recrystallized, judging from the abundance of 

spherulites and coarse crystalloblastic texture.

Some of the cherts show a globular texture similar to that of the 

spherulitic opal reported by Bramlette (1946) from the Monterey 

formation.

Many of the spherulites and circular sections of sponge spicules in 

chert under crossed nicols resemble negative uniaxial crosses; whereas 

others, especially the larger spherulites, show positive crosses, as 

would be expected if the quartz grew with the c crystallographic axis 

of the quartz fibers oriented radially from a nucleus.

Quartz silt and sand and accessory detrital grains are found in 

most cherts. In general, the cherts that contain larger spicules contain coarser detrital quartz, which shows that the spicules were sorted 

before deposition. Many of the quartz grains show spongy overgrowths. Dolomite rhombs are generally scattered throughout chert 

and make up a prominent part of some of them. Both glauconite 

and euhedral pyrite cubes occur in cherts but were not found together. 

Apatite in chert generally consists of fossil fragments, well-rounded 

sand grains, phosphatic casts of axial canals of sponge spicules, or 

euhedral apatite tablets.

CARBONATE BOCK

The carbonate rock of the Phosphoria formation in the area of the 

report comprises a wide range of lithologic types. The two most com-
mon types are medium-hard, dark-colored, thin-bedded dolomite 

and hard, medium-gray to light-colored, massive limestone.

The dark dolomites are commonly interbedded with pelletal and 

oolitic phosphorite, siltstone, and claystone. They are generally 

homogeneous, but some are stratified by alternating laminae containing various amounts of sand and silt. They are composed of cryptocrystalline to finely crystalline dolomite crystals, which range from 

anhedral grains to euhedral rhombs. Commonly, porphyroblastic 

rhombs of dolomite, consisting of a core of dolomite with many 

inclusions of carbonaceous matter and runs of clear dolomite, occur 

in a matrix of microcrystalline dolomite. Euhedral pyrite cubes are 

common, and the dolomite generally contains important quantities 

of carbonaceous matter both as inclusions and as crusts around 

dolomite grains. Apatite pellets are common in dark dolomites.

The light-colored limestones generally are interbedded with sandstone and chert and have a heterogeneous texture due to scattered 

fossil fragments. They are generally composed of finely to medium 

crystalline anhedral calcite grains which give the rock a mosaic 

texture. They generally contain very fine to medium, etched quartz 

sand grains, apatite fossil fragments, and grains of glauconite.

MUDSTONE

Mudstone in the Phosphoria in the area of the report is generally 

soft to medium-hard, dark- to medium-gray, and fissile to thinbedded rock composed of quartz and clay detritus. The grains range 

from silt-sized to clay-sized particles. Quartz silt is universally associated with flakes of muscovite in about a 20-to-l ratio. Carbonaceous matter and pyrite are prominent in some mudstones and occur 

in minor amounts in most. Cellophane pellets are commonly in 

laminae in mudstone.

SANDSTONE

Sandstone in the Phosphoria is generally a medium-hard to hard, 

medium- to light-gray, thin- to thick-bedded and commonly crossbedded rock. The sandstones show a wide range of sorting. Wellsorted sandstones are composed of medium well rounded quartz 

grains and minor amounts of accessory detrital grains such as feldspar, 

tourmaline, glauconite, and chert, and varying amounts of apatite 

grains. They commonly are cemented by'calcite or dolomite. The 

poorly sorted sandstones from Fall Creek and Flat Creek contain 

large quantities of chert, phosphorite, and carbonate rock grains, 

admixed with quartz grains. The matrix of poorly sorted sandstones 

is commonly dolomite or silty clay. The larger grains are better 

rounded than smaller quartz grains.
122 CONTRIBUTIONS TO ECONOMIC GEOLOGY

CONCLUSIONS

Several generalizations, which shed some light on the sedimentation 

and diagenesis of the rocks of the formation, can be made as the 

result of this study.

SEDIMENTATION

Laminations that reflect compositional and textural differences are 

quite common in rocks containing various amounts of argillaceous 

material. They are several millimeters thick and are found in mudstone, argillaceous pelletal phosphorite, some argillaceous oolitic 

phosphorite, argillaceous dolomite rich in carbonaceous matter, and 

argillaceous chert. On the other hand, sandstone, some sandy oolitic 

phosphorite, sandy organic phosphorite, light-colored sandy carbonate 

rock, and sandy chert generally do not show such lamination.

The laminated rocks, most common in the geosynclinal assemblage, 

were deposited under a current action quiet enough not to mix up 

bottom sediment and destroy the lamination. Platform rocks, on 

the other hand, tend to be massive and cross bedded and were deposited 

under somewhat turbulent current action.

The field observations that sandstone is associated with lightcolored carbonate rock and some chert, and that mudstone is associated with some chert, phosphorite, and dark-colored carbonate 

rock, are substantiated by petrographic study. This association is 

manifested by both interbedding and admixture. An important 

exception to this is the occurrence of very fine to fine sand in the 

matrix of otherwise pure phosphorite. E. R. Cressman, who studied 

the Phosphoria in Montana, and the author separately came to the 

conclusion that this association was probably due to the winnowing 

out of mud from phosphatic sediments. The original presence of 

this mud is indicated by silt and clay inclusions in apatite grains. A 

very small percentage of the mud originally consisted of sand grains 

too large to be winnowed out by currents and, thereby, left intermixed 

with the apatite grains. The concentration of apatite to form phosphorites is therefore probably mainly due to three causes: (1) a small

supply of clastic material (Kazakov, 1937), (2) the winnowing out of 

what fine-grained clastic material might have been deposited with the 

apatite, and (3) a physical-chemical environment in which apatite is 

Stable and Other major chemical rock constituents are not (W. W.

Rubey, oral communication).

Cressman (oral communication) has concluded that the concentration of sponge spicules to form chert is also probably due in part to the 

winnowing out of fine-grained clastic material from a sediment 

containing larger sponge spicules.

The stratigraphic position of poorly sorted sandstones gives a clue 

to its possible sedimentation. They most commonly lie between
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 123

chert zones and light-colored carbonate rock and well-sorted sandstone 

zones. If, as is discussed later, the chert is deposited in deeper water 

than the carbonate rock, the poorly sorted sand is the first sandstone 

to be deposited in a shelving basin or the last to be deposited in a 

deepening basin. The sand probably was dumped into the deeper 

water by abnormal currents and not winnowed sufficiently to yield 

well-sorted sand.

DIAGENESIS

The sediments of the Phosphoria have been appreciably affected 

during diagenesis. Solution, deposition, and recrystallization have 

been particularly important.

The diagenetic solution of cellophane is shown by stylolites and 

by the interfering relations between pellets and oolites. It is evident 

that much of the silica has also moved during diagenesis. Solution 

has occurred as shown by stylolites in chert and the replacement of 

chert by carbonate.

The diagenetic deposition of phosphate is shown by several features. Phosphate is deposited around pellets, in some cases, which 

causes the development of a mosaic texture. Apatite is also deposited 

as a simple cement in many rocks, and in one limestone cellophane 

was deposited in a vug. Several generations of phosphatic cement 

can be recognized in some rocks, owing to color variation or collophanefrancolite differences. The cement is generally lighter in color than 

the cemented apatite grains. The diagenetic deposition of apatite 

is further shown by a siltstone from Fall Creek. The siltstone contains many muscovite flakes oriented parallel to the bedding. Spherical nodules of phosphatic siltstone up to 5 mm in diameter are 

scattered throughout the rock and differ from the surrounding rock 

only by the presence of cellophane cement. Flakes of mica within 

the nodules are also oriented parallel to the bedding. Thus the 

formation of nodules did not disturb the mica flakes and must have 

occurred after sedimentation and compaction.

Deposition of silica is shown by the overgrowths of quartz on 

quartz detritus and the silicification of fossils. Chert nodules are 

generally found in light-colored limestone and differ little from the 

rest of the rock except for the replacement of microcrystalline matrix 

calcite with chert and the presence of relict sponge spicules. Apparently sponge spicules were deposited throughout these rocks and 

the silica subsequently dissolved and was redeposited to form nodules 

or, less commonly, euhedral quartz crystals.

There is abundant evidence for the diagenetic recrystallization of 

light-colored chert, carbonate rock, and phosphorite. Porphyroblastic textures are common in dolomite and chert.

Diagenetic recrystallization of apatite to form euhedral or micro-
124 CONTRIBUTIONS TO ECONOMIC GEOLOGY

crystalline apatite is an important process in the formation of phosphorites. Lowell (1952) has suggested that the francolite rings in 

oolites are formed by recrystallizatiion of cellophane. The francolite 

rings are generally lighter in color than cellophane rings, suggesting 

that a ring containing little carbonaceous matter might recrystallize 

more easily than one containing much carbonaceous matter. Sander 

(1951, p. 115-119) described laminated dolomite, rich in carbonaceous 

matter, from the Hauptdolomite in the Marienberg Alps. The lamination is due primarily to the variation in carbonaceous matter, and 

the laminae richer in carbonaceous matter are finer grained. Sander 

ascribed this possibly to the cessation of grain growth due to the bituminous intergranular films. Work on metamorphic rocks has shown 

that the fine grain size of some phyllites and schist associated with 

coarser-grained schists is correlative with finely divided carbonaceous 

material or graphite (Eskola, 1927, 1935; Gevers, 1937). It seems 

likely that the enlargement of crystalloblasts in some of the sediments 

of the Phosphoria has been impeded by films of carbonaceous matter. 

Thus, original sediments that were similar, but contained different 

amounts of carbonaceous matter, have given rise to rocks which texturally are quite dissimilar.

.DESCRIPTION AND ABEAL VARIATION OF STRATIQRAPHIC UNITS 

 UNIT A

Unit A, the lowermost unit of the Phosphoria formation, in northwestern Wyoming, is composed of variable proportions of carbonate 

rock, chert, and sandstone. In the southwestern part of the area the 

unit grades into calcareous and slightly phosphatic mudstone. To the 

north the unit pinches out. Its thickness in the area ranges from a few 

inches to 60. feet; the maximum thickness occurs in the southeastern 

part of the area.

In the eastern part of the area beds of unit A lie disconformably on 

the Tensleep sandstone. The pre-Phosphoria erosion surface is widespread in central Wyoming 4 (pis. 9-11, 13). Five feet of local relief 

on this erosion surface was measured at Bull Lake (Branson, 1939). 

The erosion surface becomes less prominent toward the west. At the

Flat Creek and Gros Ventre localities a lenticular conglomerate of 

chert pebbles several inches thick (too thin to be shown on plate 10) 

lies on an erosion surface which has a few inches of relief. To the west 

and south of Flat Creek no erosion surface has been noted. The base 

of unit A there is placed at the lithologic break between beds of chert 

and carbonate rock and beds of sandstone and sandy carbonate rock.

< Thomas, H. D., talk given at the seventh annual field conference of the Wyoming Geological Association, 1952.
The top of unit A is best defined as the base of unit B, discussed 

below.

In the southwestern part of the area, at Fall Greek and Bear Creek 

(pi. 12), beds of calcareous mudstone at the base of the formation 

probably are equivalent to unit A. The sandy cherty carbonate rock 

below constitutes the upper member of the Wells formation and is 

underlain by the middle sandstone member of the Wells formation. 

At Middle Piney Lake (pi. 11) and at Steer Creek (pi. 12), unit A of the 

Phosphoria formation lies dir.ectly on the sandstone member of the 

Wells formation; thus the upper unit of the Wells probably pinches 

out eastward and does not grade into unit A. Stated another way, 

beds of unit A seem to grade westward into and be equivalent to 

mudstones at the base of unit B and to have no correlatives in the 

Wells formation.

Unit A seems to grade from chert to carbonate rock between Middle 

Piney Lake and the General Petroleum Company's Lakeridge 1 well 

and farther.to the east is composed dominantly of carbonate rocki 

Thus, unit A and equivalent strata at the base of unit B show a calcareous mudstone facies in the western part of, the area, a chert or 

cherty carbonate rock facies in the central part, and a sandy carbonate

rock facies in the eastern part. " ' ' !

 i ' i

UNIT B

Unit B overlies unit A in the central portion of the area, but in 

both the north and southwest it is the lowermost unit of the Phosphoria formation. The unit thins from about 60 feet in the southwest 

portion of the area to a few inches on the northeast flank of the 

Wind River Range, and pinches out entirely northeastward (fig. 13).

In the southwest part of the area dark mudstone beds, which grade 

eastward into unit A, mark the base of unit B. In the central portion 

the lower contact of unit B is placed below a widespread basal medium 

dark oolitic and nodular phosphorite. Northeastward this bed grades 

into phosphatic sandstone which rests directly on the Tensleep sandstone. This basal phosphatic bed is unique in lithologic character and 

it has been used as a key bed in the regional correlation.

In the western part of the area an organic phosphorite marks 

the top of unit B (pi. 12); it consists of white tablets of phosphatic 

fish scales and brachiopod shell fragments in a dark phosphatic matrix. 

Farther east at Flat Creek, for example the upper beds of unit B 

grade into chert; the top of unit B there is placed on the gross lithologic break between mudstone and chert. Still farther to the east 

the top of unit B is placed at the top of the phosphatic sandstone, 

which constitutes all of unit B in that area.
126 CONTRIBUTIONS TO ECONOMIC GEOLOGY

EXPLANATION

Contour, showing thickness, in feet. 

. Contour interval 20 feet

Contour, showing feet-percent P20s.

Contour interval 200 feet-percent

 10

Sample locality 

(see fig. 11)

FIGUBE 13. Isopacb map of unit B of the Phosphoria formation in northwestern Wyoming, showing areal

variation in feet-percent PaOs.

Unit B is composed mainly of clay and quartz silt. The relative 

sand content increases northward and eastward, and in the Wind 

River Mountains it makes up nearly all the clastic portion of the rocks.

The phosphate content of unit B changes over the area. The total

phosphate content decreases from 900 feet-percent of P205 in the

southwestern part of the area to zero feet-percent hi the northeastern 

part (fig. 13). A petrographic change in the phosphorite accompanies 

this decrease in phosphate content. In the southwestern part of the 

area, the phosphatic material is dominantly pelletal; in the central 

part, oolitic and nodular; and in the eastern part, organic. Organic

phosphorite shows greater variations in thickness over the area than 

the other types. For example, at Bear Creek (pi. 12), 12 feet of organic
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 127

phosphorite lies at the top of unit B. Fourteen miles to the northwest 

at Fall Creek and ten miles to the northeast at trench H this bed is 

only about two feet thick.

The vertical distribution of phosphorite hi unit B also changes 

over the area. In the eastern part, a bed of sandy phosphorite comprises the entire unit; in the central part, phosphorite occurs only at 

the base of the unit and is overlain by mudstone; in the southwestern 

part, beds of phosphorite are intercalated with mudstone beds thrpughout the unit, and, where this is the case, the petrographic types of 

phosphorite have a roughly symmetrical distribution. Pelletal phosphorite, which usually makes up the major part of the phosphorite 

of the unit, occurs in the central part of the unit. Above and below 

are beds of oolitic phosphorite, and at the top and bottom of the 

unit usually are organic and nodular phosphorite. Thus, the four 

types of phosphorite show the same vertical sequence that occurs 

laterally. V. E. McKelvey (oral communication, 1950) first noticed 

this type of symmetry in the phosphatic shale member, the correlative 

of unit B in southeastern Idaho.

In the southeastern part of the area carbonaceous material is a 

prominent constituent of unit 5. Although very few chemical analyses 

have been made, the value 5 or darkness of the rock may serve as a 

rough index of the abundance of carbonaceous matter in the absence 

of better data (Patnode, 1941). Eastward the unit is lighter in color 

and may therefore be assumed to be less carbonaceous.

Iron minerals in unit B consist of disseminated pyrite in the southwestern part of the area, nodular pyrite in the central part, and glauconite in the eastern part. If, as seems likely (Thomas, 1934; Tourtelot, 1952), the lower portion of the Phosphoria formation grades 

into red beds east of the area, hematite would represent the easternmost facies of the iron minerals.

In the southwestern part of the area, at Fall Creek and Bear Creek, 

beds of dark carbonate rock are intercalated with mudstone and 

phosphorite beds. At Hoback and Buck Creek, carbonate concretions several feet in diameter are found at the same horizon. Further 

to the east, in the Gros Ventre Range, little carbonate rock is present 

in unit B.

UNIT C

Unit. 0 overlies unit B and'is present over all 'of the area of the 

report. The unit thickens from less than 75 feet in the north to 

150 feet in the southwestern part of the area and to 125 feet in the 

southeastern part (fig. 14). The unit is composed of various amounts 

of interbedded chert, carbonate rock, and sandstone, as well as a

* Value, chroma, and bue components of color are those used in the Munsell color chart.
128 CONTRIBUTIONS TO ECONOMIC GEOLOGY

EXPLANATION

Contact

-75 -

Contour, showing thickness, in feet; 

dashed .where approximately located. 

Contour interval 25 feet

.10

Sample locality 

(see fig. 11)'

FIGURE 14. Isopach map of unit C of the Phosphoria formation in northwestern Wyoming, showing areal 

variation in dominant rock types. The dominant lithologic character of unit C at each locality was computed by totaling the feet-percent of each component; i. e. the thickness of each bed was multiplied by the 

estimated percentage of each component in the bed. Isopach maps were then constructed for each component and superimposed to give the dominant lithologic character throughout the field.

few thin intercalated beds of phosphorite and mudstone. In the 

north, where the unit is less than 75 feet thick, it is composed dominantly of sandstone. In the southwest, where it is thickest, it is 

composed dominantly of chert. In. the rest of the area it is composed 

dominanfcly of carbonate rock. (fig. 14). . . The lower contact of unit C, as was discussed above, is placed at 

the lithologic break between mudstone of unit B and chert of .unit 

C. In the-southwestern part of the area, the base is. marked-by a.
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 129

key bed of organic phosphorite at the top of unit B. The upper 

contact of unit C is best defined by the lowermost bed of unit D, 

which is discussed later.

The proportion of clastic material in unit C increases northward 

(fig. 15). Corresponding to this change, the proportion of sand in 

the clastic fraction also increases northward (fig. 15). The total 

amount of chert in the unit decreases from about 6,000 feet-percent 

in the southwest to about 1,000 feet-percent in the northeast (fig. 

16). The total amount of carbonate rock decreases northward from 

about 7,000 feet-percent to about 1,000 feet-percent and southwestward to about 3,800 feet-percent (fig. 17).

NATIONAL Vs.

EXPLANATION

Contour, showing clastic ratio; dashed 

where approximately located. Ratio 

of feet-percent sandstone and mudstone to feet-percent carbonate 

rock and chert

Contour, showing sandstone-mudstone 

ratio. Ratio or feet-percent sandstone to feet-percent mudstone

 3

Sample locality 

(see fig. 11)

FIOTJKE 15. Clastic ratios and sandstone-mudstone ratios of unit C of the Pbosphoria formation in northwestern Wyoming.
130 CONTRIBUTIONS'TO .ECONOMIC GEOLOGY

EXPLANATION

-IOOOContour, showing feet-percent chert. 

Contour interval 1000 feet-percent

.3

Sample locality 

(see fig. 11)

FIGURE 16. Areal variation in feet-percent chert in unit C of the Phosphoria formation in northwestern

Wyoming.

These variations are caused both by interfingering and intergradation of rock types and by thinning of individual beds. Chert 

beds at the base and at the top of unit C at Fall Creek, in the southeastern part of the area, interfinger with the beds of sandstone in 

the northeast (pi. 10). Similarly, chert at the base of the unit at 

Lakeridge 1 well interfingers with beds of sandstone at Tosi Creek in 

the northeast (pi. 11). Unit C at Red Creek in the northeastern 

part of the area is dominantly made up of sandstone and chert (pi. 

13). These beds of sandstone grade into carbonate rock in the 

southeast at Burroughs Creek (pi. 13).

The chert of unit C is composed of three different lithologic types, 

which may be found at most localities. However, the proportions 

among these types of chert vary over the area. In the southwest, 

the most common type is dark bedded chert. In the east and north,
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 131

EXPLANATION

-2000-

Contour, showing feet-percent carbonate 

rock. Contour interval 1000 feet-percent

.is

Sample locality 

(see fig. 11)

FIGURE 17. Areal variation in feet-percent carbonate rock In unit C of the Phosphoria formation In northwestern Wyoming.

light-colored, nodular, and concretionary chert is more common. 

At the easternmost arid northernmost trenches, the chert is dominantly made up of tubular concretions.

The carbonate rock of unit C is fairly constant lithologically over 

the area. It is generally light-colored fine- to medium-grained crystalline limestone. In the southwest, however, the carbonate rock in 

the unit is darker in color. Brachiopods and bryozoa are common in 

many of these beds.

The sandstone of unit C is also fairly constant lithologically over 

the area. At Flat Creek the lowermost sand of the unit is poorly 

sorted, whereas the stratigraphically higher sandstones in the unit 

are well sorted. The sandstones contain minor quantities of organic 

and light-colored pelletal apatite grains, and several thin beds of 

sandy organic phosphorite are intercalated in the unit.

394091 56 3
132 CONTRIBUTIONS TO ECONOMIC GEOLOGY

The core of General Petroleum's Lakeridge 1 well contains a bed 

of anhydritic dolomite about 6 feet thick near the center of unit C. 

The anhydritic dolomite overlies a sandy carbonate rock. About 25 

feet of core immediately above the bed is missing, and the next known 

bed above is a calcareous sandstone. At the surface exposure of the 

Phosphoria at Middle Piney Lake, nine miles to the west of Lakeridge 

1 well, a 2-foot covered zone below a porous carbonate rock unit 

possibly represents this anhydritic bed.

The sequence of rocks in unit C suggests a symmetry about the 

center of unit C. At Fall Creek (pi. 10), beds of chert occur at both 

the bottom and top of the unit, separated by beds of carbonate rock. 

Similarly at Cottonwood Creek, unit C is made up from base to top 

of a chert zone, a carbonate rock zone, and an interbedded chert 

and sandstone zone. In the eastern part of the area, the upper chert 

zone is not present at all localities although the lower two zones are 

recognized everywhere.

Vertical sequence of the petrologic types of chert also suggests a 

symmetry about the center of the unit. In general, dark-bedded 

chert occurs at the bottom of unit C and is overlain by light-colored 

nodular chert. Tubular chert bodies occur above this and usually are 

found in a carbonate rock matrix within the carbonate rock zone. In 

the southwestern part of the area, the upper chert zone, where it is 

developed, is composed of dark bedded chert. In the central and 

eastern part of the area, dark bedded chert is not found in unit C.

UNTT D

Unit D overlies unit C in the area of the report; it is composed 

of black mudstone and a few intercalated beds of phosphorite and 

dolomite. The unit thickens from a few feet in the southwestern 

part of the area to a maximum of 60 feet in the Wind River Range. 

Northwest of the Wind River Range the unit thins and pinches out

(fig- 18).

The base of unit D over the whole area is marked by a widespread 

dark nodular phosphorite that generally contains small amounts of 

phosphatic fossil remains, such as sharks' teeth and fish scales. At 

many localities this bed is underlain either by carbonate rock or by 

sandstone containing fragments of light-colored phosphatic fossils, 

and it is generally overlain by black fissile mudstone.

In the southwestern part of the area, the top of unit D marks the 

top of the formation. The boundary is placed at the sharp break 

between the uppermost dark beds of unit D and the lowermost beds of 

buff to tan thin-bedded calcareous siltstone of the Dinwoody formation. Eastward and northeastward the upper beds of mudstone of 

unit D grade into beds of chert (pis. 10, 11) which make up unit E;
PHYSICAL STRATIGRAPHY, PHOSPHOEIA FORMATION, WYOMING 133

EXPLANATION

Contour, showing thickness, in feet; 

dashed where approximately located. 

Contour interval 20 feet

Contour, showing feet-percen 

Contour interval 50 feet-percent

.3

Sample locality 

(see fig. 11)

FIOURB 18. Isopach map of unit D of the Phosphoria formation in northwestern Wyoming, showing areal

variation in feet-percent PiOi.

where this is the case, the upper contact of unit D is placed at the 

boundary between the dark mudstone of unit D and the chert of 

unit E. At most places this contact is gradational; thin beds of chert 

appear in the upper part of unit D, and the interbeds of mudstone 

disappear in the lower part of unit E. Farther to the northeast, 

the black fissile mudstone that overlies the basal phosphorite grades 

into chert. Where this is the case the phosphorite wholly composes 

unit D and the upper boundary is sharp.

Unit D is composed dominantly of fissile black mudstone made 

up of clay and quartz silt. Several thin beds of hard dark microcrystalline dolomite are intercalated in the unit and apparently are 

fairly widespread.
134 CONTRIBUTIONS TO ECONOMIC GEOLOGY

In the southwestern part of the area, thin beds of phosphorite are 

intercalated throughout the unit. In the northeast, however, phosphorite occurs only at the base, though several phosphatic mudstones 

occur higher in the unit. The phosphorite changes in character over 

the area. Pelletal phosphorite is dominant in most of the southwestern part, whereas in the extreme southwest, where the unit is thin, 

nodular phosphorite is dominant. Nodular phosphorite is also 

dominant in the eastern and northeastern part of the area.

A systematic vertical distribution of the phosphorite occurs within 

unit D and a part of unit C. The uppermost beds of unit C are 

composed of sandstone or carbonate rock containing organic phosphate grains. The lowermost bed in unit D is nodular phosphorite. 

Pelletal phosphatic mudstone beds occur within unit D.

Organic material and pyrite are abundant in the southwestern 

part of the area and decrease eastward. On the east flank of the 

Wind River Mountains, the mudstones of unit D are greenish, possibly 

owing to the presence of glauconite and the scarcity of organic matter.

UNIT E

Unit E forms the uppermost part of the Phosphoria formation in 

the Central and eastern part of the area but is absent in the southwestern part. It is composed dominantly of chert, carbonate rock, 

and sandstone. The unit has a maximum thickness of about 100 

feet in the Gros Ventre and Teton Ranges and thins northeastward to 

less than 50 feet (fig. 19). Toward the southwest, the unit thins; 

its lower chert beds grade into mudstone and are included in 

unit D.

The base of the unit, discussed above, is placed at the boundary 

between mudstone below and chert above. Where unit E is present, 

its upper contact is also the upper contact of the formation. The 

contact is placed at the break between the gray chert, light-colored 

carbonate rock, or sandstone of unit E (fig. 20) and the basal, buff to 

tan thin-bedded calcareous siltstone of the Dinwoody formation. In 

western Wyoming, Newell and Kummel (1942) have divided the Dinwoody into three units which, from base to top, are: the basal siltstone, 

the Lingula, zone, and the Claraia zone. They postulate overlap of the 

upper beds Over the lower to the east arid suggest, therefore, that the 

Dinwoody unconformably overlies the Phosphoria in the eastern part 

of the area. There is no stratigraphic evidence for an erosion surface 

at the top of the Phosphoria in the area of this report. The lithologic 

character of the uppermost beds of the Phosphoria formation varies 

over the area. In the north, the uppermost bed is sandstone, which 

grades southeastward into carbonate rock. The carbonate rock and 

the lower beds of sandstone grade westward into chert, and the chert
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 135

EXPLANATION

Contact

Contour, showing thickness, in feet; 

dashed where approximately located. 

Contour interval 25 feet

.10 

Sample locality 

(see fig. 11)

Sandstone

OUBK 19. Isopach map of unit E of the Phosphoria formation In northwestern Wyoming, shoving areal 

variation in dominant rock types.

grades westward into phosphatic mudstone of unit D (fig. 20). As 

discussed more fully later, the lithologic variation in the uppermost 

.bed of the formation is probably due to facies change rather than 

erosional truncation.

Unit E is composed dominantly of chert over most of the area. The 

total amount of chert hi unit E increases from none in the southwest 

to about 4,500 feet-percent in the northern part of the area, and to 

about 1,800 feet-percent of chert hi the southeastern part (fig. 21). 

The chert beds occur at the base of the unit; except in the Wyoming 

Range, they are overlain by beds composed dominantly of sandstone in 

the north and carbonate rock in the southeast (fig. 20). In the eastern
136 CONTRIBUTIONS TO ECONOMIC GEOLOGY

EXPLANATION

Phosphatic mudstone Carbonate rock

Small patterns represent lithologic character observed at measured sections; 

large patterns represent lithologic character inferred between measured sections

cr

Sample locality 

(see fig. 11)

Contact, approximately located

FIGURE 20 Dominant lithologic character of the uppermost bed of the Phosphoria formation in northwestern Wyoming.

part of the area, the unit is composed dominantly of carbonate rock.

The total amount of carbonate rock increases eastward from none in 

the west to 4,500 feet-percent carbonate rock in the east (fig. 22). 

The proportion of clastic material in the unit increases northwestward,
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 137

EXPLANATION

Contour, showing feet-percent chert. 

Contour interval 1000 feet-percent

 7

Sample locality 

(see fig. 11)

FIOURK 21. Areal variation in feet>percent chert in unit E of the Phosphoria formation in north-

.western Wyoming.

and the proportion of sand in the clastic fraction increases northwestward correspondingly (fig. 23). At the extreme west (fig. 19) unit E 

is composed of a thin bed of sandstone, which is correlative with the 

uppermost beds of sandstone at the top of the unit to the east. This 

sandstone offlaps the rest of unit E.

The chert of unit E is composed of three different lithologic types, 

which are identical to those contained in unit <7. The proportions 

between these types of chert vary over the area. The southwestern 

edge of unit E contains only bedded chert. Tubular chert overlies 

the bedded chert in the northeast and is dominant in the central part 

of the area. Concretionary and nodular chert is present in unit E but 

is dominant nowhere. The carbonate rock and sandstone of unit E 

are similar to those of unit C.
138 CONTRIBUTIONS TO ECONOMIC GEOLOGY .

EXPLANATION

Contour, showing feet-percent carbonate 

rock. Contour interval 1000 feet-percent

.3

Sample locality 

(see fig. 11)

FIOURB 22, Areal variation in feet-percent carbonate rock in unit E of the Phosphoria formation in northwestern Wyoming.

The sequence of rocks in unit E is also similar to that in unit C, except 

that no chert zone occurs at the top of the unit. The carbonate rock 

and sandstone, where present, overlie the chert, the lowermost bed of 

sandstone being more poorly sorted than the overlying sandstone beds 

at Flat Creek. The sequence of types of chert is also similar to that

in unit C.

SUMMARY OF STRATIGRAPHIC RELATIONS

The rocks of the Phosphoria formation may be grouped into rock 

suites whose members show persistent assocations. Kazakov (1937) 

observed that bedded pelletal phosphorite and dark carbonate rock 

are commonly associated; that nodular phosphorite, sandstone, and 

glauconite are associated; and that the bedded phosphorite suite 

commonly grades landward into the nodular phosphorite suite. Me-
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 139

EXPLANATION

 .25 

Contour, showing clastic ratio; dashed 

where approximately located. Ratio 

of feet-percent sandstone and mudstone to feet-percent carbonate 

rock and chert

Contour, showing sandstone-mudstone 

ratio. Ratio of feet-percent sandstone to feet-percent mudstone

Southwestern limit of unit E

.3

Sample locality 

(see fig. 11)

FIOURE 23. Clastic ratios aud sandstone-mudstone ratios of unit E of the Phosphoria formation in northwestern Wyoming.

Kelvey (McKelvey and others, 1953) noted that bedded chert and 

carbonaceous mudstone were other members of the bedded phosphorite 

suite, and that in the Phosphoria formation the nodular phosphorite 

suite graded landward into a red bed suite whose members include red 

beds, carbonate rock, and anhydrite.

In northwestern Wyoming these three rock suites are synchronous 

lateral equivalents, and where they interfinger an ordered depositional 

sequence is observed that is analogous to the detailed lateral sequence. 

These relations are discussed below.
140 CONTRIBUTIONS TO ECONOMIC GEOLOGY 

CYCLJCAJL, ROCK SEQUENCES

The rocks of the formation tend to be symmetrically arranged about 

the middle of each carbonate rock and chert member. Beginning in 

the middle of a carbonate rock and chert unit in an idealized section, 

the upward sequence of chemical and biolithic sediments is: carbonate 

rock, tubular chert, nodular and concretionary chert, bedded chert, 

organic phosphorite, oolitic and nodular phosphorite, pelletal phosphorite, oolitic and nodular phosphorite, organic phosphorite, bedded 

chert, nodular and concretionary chert, tubular chert, and, finally, 

carbonate rock. Anhydrite, where present, is found in the carbonate 

phase of the cycle. An idealized cycle is shown on fig. 24.

No such perfect cycles are found, however. The chert and carbonate phases of the cycle usually overlap and organic phosphorite 

is interbedded with bedded chert at many places. Generally, one 

or more of the phases are not present, especially the phases between 

the lower carbonate rock and the lower organic phosphorite. In 

addition, carbonate rock occurs in many places in the phosphorite 

phase of the cycle. However, most of this carbonate rock is dark, 

sparingly fossiliferous dolomite or dolomitic limestone and is not 

comparable to the light-colored fossiliferous carbonate rock of the 

carbonate phase of the cycle. Anhydrite has been found in the area 

of the report only in the core from Lakeridge 1 well, though it probably 

has been leached away by weathering from several other surface 

exposures near by.

The clastic rocks are systematically associated with this chemical 

and biolithic cycle. Sandstone is found in the bedded chert to carbonate rock to bedded chert portion of the cycle, whereas mudstone 

is found in the bedded chert to pelletal phosphorite to bedded chert 

portion of the cycle.

The iron minerals, which occur in the Phosphoria in only minor 

amounts, also appear to fit systematically into the cycle. Pyrite 

occurs in the bedded chert to pelletal phosphorite to bedded chert

portion of the cycle. Glauconite occurs in the concretionary and 

nodular chert to carbonate rock portion of the cycle, and iron oxide 

probably occurs in the anhydrite phase of the cycle. Organic matter, 

as would be expected, is associated with the pyrite in the bedded 

chert to pelletal phosphorite to bedded chert portion of the cycle. 

In the central part of the area, there are two full cycles: the lower,

beginning at the base of unit A and ending at the carbonate rock zone

of unit O, ancl tiie upper, beginning at the carbonate rock zone of

unit C and ending* at trie carbonate rock zone of unit E. In the southwest, the upper cycle reaches only the nodular phosphorite stage in

unit D. Eastward these cycles progressively lose their central 

portions; thus, in central Wyoming only carbonate rock and anhy-
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 141

Carbonate rock, light-colored, massive. Commonly contains 

brachiopods, bryozoa, and other fossils. Commonly 

glauconitic. Associated with sandstone.

Chert, tubular. Commonly sandy, glauconitic. Commonly occurs 

12 in carbonate rock matrix. Associated with sandstone.

Chert, nodular. Usually light in color. Commonly occurs in 

11 carbonate rock matrix. Associated with sandstone.

Chert, bedded, dark, massive. Bedding planes irregular. Laminated 

10 at some places. Associated with mudstone or sandstone.

Phosphorite, organic, light-colored. Composed of fish scales, phosphatic 

9 brachiopods, and fish teeth. Associated with mudstone or sandstone.

Phosphorite, oolitic and pelletal. Medium to dark gray, poorly sorted, 

evenly bedded. Associated with pyritic mudstone and rarely sandstone.

Phosphorite, pelletal, dark gray'to black, well-sorted, evenly 

bedded. Associated with pyritic mudstone.

Phosphorite, oolitic and pelletal. Medium to dark gray, poorly sorted, 

evenly bedded. Associated with pyritic mudstone and rarely sandstone.

Phosphorite, organic, light-colored. Composed of fish scales, phosphatic 

brachiopods, and fish teeth. Associated with mudstone or sandstone.

4 Chert, bedded, dark, massive. Bedding planes irregular. Laminated 

at some places. Associated with mudstone or sandstone.

Chert, nodular. Usually light in color. Commonly occurs in 

carbonate rock matrix. Associated with sandstone.

2 Chert, tubular. Commonly sandy, glauconitic. Commonly occurs 

in carbonate rock matrix. Associated with sandstone.

Carbonate rock, light-colored, massive. Commonly contains 

brachiopods, bryozoa, and other fossils. Commonly glauconitic. 

Associated with sandstone.

FIOURE 24. Idealized depositional cycle of chemical sediments of the Phosphorla formation In northwestern

Wyoming.

drite are present. Southwestward the outer portions of the cycles 

are progressively lost; thus, southwest of the area, in southeastern 

Idaho, only phosphorites and bedded chert are present.

LATERAL KELATION8

The variations in thickness and lithologic character of the rocks 

of each unit have been discussed. It was further shown that the 

units make up portions of a cyclic depositional sequence. The units 

which constitute the same portions of the cycles of deposition are 

areally compared here, and also the thickness relations between units 

making up one cycle. To aid in reconstructing the probable environments of deposition, it is important to establish whether or not 

adjacent phases of the vertical cycle grade into each other laterally. 

Thus the facies relations discussed previously in the treatment of 

individual units are summarized below and compared with the 

vertical cyclic rock sequence.

COMPARISON OF UNITS B AND D

Units B and D make up the portion of the depositional cycle from 

organic phosphorite to pelletal phosphorite to organic phosphorite.

The variation in thickness and feet-percent P2 05 of units B and 

D are shown in figures 13 and 18 respectively. Both units B and D
142 CONTRIBUTIONS TO ECONOMIC GEOLOGY

pinch out northeastward, but unit D extends the farther. Unit B 

thickens progressively southwestward, but unit D thickens and then 

thins southwestward. Southwest of the area, unit D probably 

thickens again.

In the southwestern part of the area, unit B and unit D have about 

equal amounts of phosphate rock in both the upper and lower parts 

of the respective units. In the east, however, the upper parts of 

units B and D consist of only weakly phosphatic to nonphosphatic 

mudstone; phosphate rock occurs at the base of the unit. In the 

extreme northeastern part of the area, both units consist wholly 

of phosphate rock or phosphatic sandstone. In the phosphate rock 

of both units, coarse-grained oolites and nodules increase in abundance 

from the southwest to the northeast. However, where unit D is 

thin in the extreme southwest, nodular phosphorite is dominant. 

To the east organic phosphate rock assumes prominence in both 

members and accompanying this lithologic change is an increase in 

variation of the thickness of individual beds of phosphate rock; 

that is, they become lenticular.

Finally, both shale units contain dark fine-grained dolomite beds 

that are megascopically indistinguishable from mudstone. They 

are quite different from the light-colored, massive, medium to coarsely 

crystalline fossiliferous carbonate rocks that are prominent in units 

C and E.

Thus, in general, the two units show similar areal lithologic variations. In addition, both units thin eastward. Unit D also thins 

southwestward, whereas unit B progressively thickens southwestward.

COMPARISON OF UNITS C AND E

The chert and carbonate rock portions of the cycles are composed 

of units C and E. Figures 14 and 19 show the variations in thickness 

and dominant lithologic character of the two units, and figures 15 

and 23 show the areal variation of their clastic ratios and mudstonesandstone ratios.

Unit C thins northeastward with a corresponding dominant lithoologic change from chert to carbonate rock to sandstone. Unit 

E, on the other hand, is absent in the southwest, lenses in, and then 

thins to the northeast. Lithologic changes in unit E are not as 

systematically associated with these thickness changes as they are in 

unit (7. Similarly to unit C, however, unit E changes eastward from 

dominantly chert to dominantly carbonate rock, though for unit E 

this change occurs farther east. A comparison of figures 15 and 23 

indicates that the ratio of sandstone to mudstone increases northward in both units. Therefore, the source of clastic sediment was 

probably at the north and northwest.
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 143

Thus, except in thickness, units C and E show somewhat similar 

depositional patterns; that is, an increase of elastics to the north 

and northwest and a dominant lithologic change from chert to carbonate rock to the east. A discrepancy in this generalization is that 

the uppermost sandstone of unit E offlaps the chert of unit E] that 

is, it extends farther west than the chert. In the western part of 

the area it composes the entire unit.

COMPARISON OF UNITS B AND C WITH UNITS D AND E

In order to analyze the areal thickness variations of single cycles 

of deposition it would be desirable to include the rocks from one 

carbonate rock phase to the next carbonate rock phase of the cycle. 

However, because the contacts can be placed more easily at unit 

boundaries, the units selected for thickness analysis have been the 

stratigraphic units B and C, to represent the lower cycle, and units 

D and E, the upper. Thus, the phases analyzed are actually those 

from one organic phosphorite to the next organic phosphorite. Since 

the lower chert phases are generally thin or absent, this approximately 

corresponds in thickness to the rocks encompassed by the carbonate 

phases of the cycle.

The areal variation of the combined thicknesses of units B and C 

are shown on figure 25. The thickness of the combined units increases 

southwestward hi the same manner as the individual units. The 

thickness variations of the combined units, however, are less irregular 

than of individual units.

The areal variation of the upper cycle is shown on figure 26. The 

cycle is an elongate lens trending northwest with a maximum thickness in the southeastern part of the area. It thins to the northeast 

and southwest. Units D and E individually show similar thickness 

variations (figs. 18 and 19). The variation of the combined thicknesses is somewhat less irregular than the individual thicknesses.

The thickness variations of the lower cycle (approximately the 

combined thicknesses of units B and C), however, are different from 

those of the upper cycle (approximately the combined thicknesses of 

units D and E). Therefore, the factors which governed the variations 

in thickness of units B and C were similar and the factors which 

governed the variations in thickness of units D and E were similar 

too, but these factors changed between cycles.

FACIES

The f acies changes within and between the units have been discussed 

above and are summarized here. The phosphatic beds of unit B 

cannot be correlated individually over the whole area of the report, 

but they are dominantly pelletal in the southwestern part of the 

area, dominantly oolitic and nodular in the central part, and domi-
144 CONTRIBUTIONS TO ECONOMIC GEOLOGY

EXPLANATION

-too 

Contour, showing thickness, in feet; 

dashed where approximately located. 

Contour interval 25 feet

 s

Sample locality 

(see fig. 11)

FIOUBE 25. Isopach map of units B and C Of the Phosphoria formation in northwestern Wyoming.

nantly organic in the eastern part. The same phosphorite facies are 

present in unit D although., in the extreme southwest of the area, 

unit D is only a few feet thick and only nodular phosphorite is present. 

There is little evidence to suggest wKetW this facies relation is the 

result of interfingering or of gradation. The basal nodular and oolitic 

bed of unit B in the central portion of the area, however, probably 

 does grade into organic phosphorite to the east. Also, petrographic 

investigations show that mixed phosphorite types occur.

At the base of the formation in the southwestern part of the area, 

the lower beds of unit B are composed of calcareous mudstone, which 

is slightly phosphatic, and several thin interbeds of phosphorite. 

Eastward these grade into chert and carbonate rock of unit A. The 

upper mudstone and phosphorite beds of unit B grade from the southwest to the northeast into chert of unit C. The organic phosphorite
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 145

EXPLANATION

Contour, showing thickness, in feet; 

dashed where approximately located. 

Contour interval 20 feet 

,10

Sample locality 

(see fig. 11)

FIOUKE 26. Isopach map of units D and E of the Phosphoria formation in northwestern Wyoming.

at the top of the formation in the southwestern part of the area 

grades into chert to the east. The upper beds of unit D similarly 

grade from the southwest to the northeast into chert of unit E. Thin 

organic phosphorite beds and chert beds are commonly interbedded 

at many localities and in many cherty parts of the section. Mixtures 

of phosphorite and chert are not rare. Thus some of the phosphorite 

grades eastward into chert. Organic phosphorite also probably 

grades into sandstone and limestone. Where the chert phases of the 

cycle are thin or absent, mixed rocks of organic phosphorite and 

either sandstone or carbonate rock are usually found at the top of 

the carbonate rock zones.

The lithologic types of chert probably grade into each other laterally. 

Although no individual chert bed can be demonstrated to change 

facies, chert zones change laterally in dominant lithologic type.
146 CONTRIBUTIONS TO ECONOMIC GEOLOGY

For example, the chert of unit C in the southwest is dominantly 

bedded chert; to the northeast it is dominantly nodular chert; still 

farther northeast it is dominantly tubular chert.

The facies change from chert to limestone may be postulated on 

the same grounds as were the facies changes of the chert; that is, 

some tubular chert zones are represented in the east by carbonate 

rock zones. Also, many tubular chert bodies are embedded in a 

carbonate rock matrix. Finally, the lateral relations between anhydrite and carbonate rock are not known, mainly because anhydrite 

has been found in the area of the report only in the core from Lakeridge 1 well.

Thus, the facies of the Phosphoria are analogous to the rock 

phases of the cycle of deposition. The eastward facies change of pelletal phosphorite to nodular and oo itic phosphorite is analogous to 

the passage from the pelletal phosphorite phase to the nodular and 

oolitic phosphorite phase; the eastward facies change from nodular and 

oolitic phosphorite to organic phosphorite is analogous to the passage 

from the nodular phosphorite phase to the organic phosphorite phase; 

and so forth to the tubular chert and carbonate rock facies and phases.

GENETIC SIGNIFICANCE OF STRATIQRAPHIC RELATIONS

The rocks of the Phosphoria are systematically arranged both 

vertically and laterally. Moreover, some of them are uncommon 

types. Thus, the combination of factors which controlled the 

deposition of the sediments was somewhat uncommon and changed 

in a systematic manner in both space and tune. It is not within the 

scope of this paper to discuss all the factors which appear to be 

significant to the genesis of the rocks of the formation, but this study 

has cast some light on several of these factors. These include the 

paleogeographic setting of the formation in the area of the report 

and adjacent regions, the depositional environments of the sediments, 

and the tectonic movements which were active during the deposition 

of the sediments and which caused transgressive and regressive 

relations.

The lithologic character and thickness of the rocks of the Phosphoria

formation in the area of the report supply several clues to the Permian 

paleogeography. McKelvey (McKelvey and others, 1953) suggested 

that the depth of water probably increased to the west, because

carbonaceous matter in the Phosphoria increases from Wyoming

to Idaho; clastic material in the Phosphoria decreases in grain size 

in the same direction; and, whereas crossbedding of the sandstone is 

not uncommon in Wyoming, the rocks in southeastern Idaho show 

no crossbedding but commonly show lamination. In the area of the
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 147

report the formation ranges in thickness from 150 to 400 feet. These 

variations are fairly uniform. Thus, according to McKelvey, the rate 

of deposition and, thereby, the rate of supply of sediment were 

probably fairly slow and uniform, especially because much of the 

sea floor in the area of the report probably was below wave base. 

This indicates that the relief on the sea floor and nearby land areas 

was probably gentle. In central Wyoming, beds of anhydrite indicate 

that restricted shallow basins were present on the eastern margin of 

the sea during some of the Phosphoria time.

The source of much of the sand in the formation was probably at 

the north; thus a low land mass probably was located in central 

Montana. East of the area, the transition into red beds marks an 

increase in the amount of clastic material in the formation (Ketterer 

and Swirczynski, 1952; Frielinghausen, 1952); it seems possible, 

therefore, that some of the clastic material in the formation was 

derived from the east. The red bed facies of the formation is fairly 

widespread at the east (Thomas, 1934) and the source of this clastic 

material probably was many miles east of the area of this report.

In summary, the Phosphoria sea was probably fairly deep in 

southeastern Idaho and shallowed gently eastward; in central Wyoming it terminated at times in shallow restricted basins. In central 

Montana a low land mass supplied some of the coarser clastic material 

deposited in the sea, and many miles east of the open ocean another 

low land mass supplied some finer grained clastic material. The total 

supply of clastic material was, however, small.

PHYSICAL CHEMISTRY OF ENVIRONMENTS OF DEPOSITION

Previous investigations of the geochemistry of phosphorite, carbonate rock, the iron-bearing rocks, and evaporites indicate that the 

temperature, acidity, redox potential, and salinity of the ocean water 

mainly control the type of sediment that is deposited (Halla, 1935; 

Cooper, 1937; Kazakov, 1937, 1938; Dietz, Emery, and Shepard, 1942; 

Blumer, 1950; Castano and Garrels, 1950; Kazakov, 1950; Kazakov 

and Sokolova, 1950; Krumbein and Garrels, 1952; Huber and Garrels, 

1953; Mann, 1953; Murray and Gravenor, 1953; James, 1954). The 

depositional environments of the rocks of the Phosphoria that may 

be deduced from these studies suggest progressive changes of acidity, 

redox potential, and salinity corresponding to the vertical and lateral 

rock changes. The physical chemistry of the deposition of phosphorite, calcium carbonate, the iron minerals, silica, anhydrite, and 

organic matter is briefly summarized below.

Kazakov (1937) synthesized physical-chemical, oceanographic, and 

geologic data in advancing an explanation of the origin of phosphorites.

394091 5ft 4
148 CONTRIBUTIONS TO ECONOMIC GEOLOGY

He concluded that phosphorites are precipitated chemically where 

cold phosphorus- and carbon dioxide-rich waters are warmed as 

they well up over a shelf, in a manner illustrated by the present 

oceanographic conditions off the coast of California. Phosphate cannot 

precipitate, he said, in the zone of photosynthesis, because it is 

vigorously consumed by phytoplankton. Neither can it precipitate 

in the deep regions of the sea, below about 200 meters, because of the 

high CC>2 content and resulting low pH. He further reasoned that 

calcium carbonate was precipitated under like conditions but at 

slightly lower pH and thereby earlier than phosphorite. McKelvey 

(McKelvey and others, 1953) adopted the Kazakov hypothesis to 

explain the rocks of the Phosphoria formation, but they concluded 

that phosphorites can form at depths exceeding 200 meters and 

probably down to the depth of 1,000 meters, as is evident from the 

distribution of phosphorites in the present sea floor, and that

The paragenetic relationships of the phosphorite facies of the Phosphoria indicate 

that the waters ascending the shelf of the Phosphoria sea became saturated first 

with carbonate-fluorapatite and then with calcium carbonate, rather than the 

reverse as Kazakov thought.

Krumbein and Garrels (1952) state that if calcite and phosphorite 

coprecipitate the ratio is very high in favor of calcite; but if the pH 

is below about 7.8, the activity product of calcite will not be reached, 

whereas that of phosphorite will, and a phosphorite-rich sediment 

will be formed. They also point out that the precipitation of phosphorite is independent of the redox potential of the environment.

In summarizing much of the previous work on the precipitation 

of calcium carbonate, Krumbein and Garrels conclude that both 

calcium and the carbonate ion are independent of the Eh of the 

solution and that the precipitation of calcium carbonate in sea water 

is primarily controlled by the pH of the system, the most favorable 

conditions being above a pH of about 7.8.

The mineralogy of the iron in sediments depends on both the 

acidity and redox potential of the system (Castano and Garrels, 

1950; Krumbein and Garrels, 1952). These studies show that at a 

pH of about 7.8 pyrite is stable if the redox potential of the environment is below about -0.25 Eh; siderite, if it is below about -0,05 

volts; and hematite, if it is above about -0.05 volts. A decrease of 

pH tends to raise these Eh stability ranges somewhat, the pyritesiderite boundary less than the siderite-hematite boundary. The

quantity of iron mineral in the sediment, on the other hand, does not

depend on the acidity or redox potential of the system, but primarily 

on the concentrations and continuing supply of the various ions. 

The physical-chemical environment in which glaucomte is formed is
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 149

not known, though it is placed by Krumbein and Garrels in both 

the siderite and hematite fields. On the basis of associated minerals, 

James (1954) deduced that greenalite (an iron silicate similar to 

glauconite) as well as other iron silicates of the pre-Cambrian ironbearing formation were deposited in mildly reducing to mildly oxidizing conditions.

The physical-chemical environment favorable for the deposition 

of silica is little known at the present tune, although speculations as 

to the controls of precipitation are many. An excellent review of 

these hypotheses is given by Bramlette (1946, p. 41). The relative 

effect of the acidity of sea water, if any, on the precipitation of silica 

is debatable.

The precipitation of anhydrite occurs when the activity product 

of calcium ion and sulfate ion is exceeded, owing to the evaporation 

of sea water. The state of oxidation or reduction of sulfur depends 

 on the redox potential of the system, but under normal saline conditions the sulfur is in the form of sulfate ion. Thus the main control 

of the precipitation of anhydrite is the salinity of the sea water.

Organic matter in general controls the lower limit of the redox 

potential and the poise or reducing capacity of the system. If the 

redox potential of the system is greater than zero, organic matter 

will be oxidized. Thus organic matter is stable at Eh less than zero 

(Krumbein and Garrels, 1952).

The preservation of sediments that are formed from the hard parts 

of organisms would also be controlled by the physical-chemical 

environment; that is, if the water in which the biogenic mineral is 

deposited is not saturated with that mineral, it will be unstable and 

will tend to dissolve (McKelvey, 1946; Krumbein and Garrels, 1952).

The minerals deposited under similar Eh and pH fields have been 

summarized by Krumbein and Garrels (1952) and presented in 

graphic form, which is reproduced in figure 27 by permission of the 

University of Chicago Press. Essentially seven fields are delineated 

by the boundaries: pH=7.0, the neutral fence; pH=7.8, the limestone fence; Eh=0, the organic matter fence; the boundary between 

the hematite and siderite stability fields, the oxide-carbonate fence; 

and the boundary between the siderite and pyrite stability fields, the 

sulfate-sulfide fence. These stability fields have been set up on 

theoretical grounds and in part verified by experiment (Huber and 

Garrels, 1953). Krumbein and Garrels point out that if a rock 

contains primary sedimentary minerals which fall into these fields, 

and if equilibrium conditions prevailed at the tune of deposition, 

approximate limits of original pH and Eh environments may be 

deduced.
150 CONTRIBUTIONS TO ECONOMIC GEOLOGY

P H 7.0

HEMATITE 

LIMONITE 

GLAUCONITE

Silica 

Calcite

Phosphorite

8.0

I

TAI CITE fSolinity >200%o 

Hematite \GYPSUM 

Limonite \AI\JhlYnRlTF Glauconite Lfc" vr7 ' urfl ' c. 

Phosphorite 

Silica

!F E N C.E h= OT

CALCITE Salinity>200%o"] 

ORGANIC 

MATTER tJ *TTCO 

GYPSUM I

SILICA 

PHOSPHQfjUE

Calcite .i .-^S«t|: Primary urqnlum 

concentrations

-0.3

PHOiHllRITE

PYR|

SILICJ|

Colcite 

Primary uranium 

concentrations 

Primary heavy metal

su If ides

Limonite 

Glauconite 

Phosphorite 

Silica

Hirnatite ANHYDRITE]

Limnnitd

CALCITE 

ORGANIC 

MATTER 

Phosphorite Glauconite

CALCITE 

ORGANIC 

MATTER

Pyrite 

Phosphorltt

After Krumbein and Garrels, 1952 Copyright 1952, University of Chicago

FIOTJRE 27. Sedimentary chemical end -member associations of rocks of the Phosphoria formation in north" 

western Wyoming in their relation to environmental limitations imposed by selected Eh and pH values. 

Shaded area indicates path of cyclic deposition environments.

TEMPORAX. r>rsTnrBtjrrroN8 OP ENVIRONMENTS

If the physical-chemical environments of the rocks of the Phosphoria 

formation are deduced in the order of the cyclic deposition, it is 

evident that the pH and Eh conditions cyclically progressed and
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 151

retrogressed. The light-colored carbonate rocks contain no organic 

matter and therefore probably were deposited at an Eh greater than 

zero and a pH greater than 7.8. Tubular chert is generally light in 

color and is commonly associated with light-colored carbonate rock 

and glauconite; it probably was deposited under similar conditions. 

The dark-bedded chert, on the other hand, is associated less commonly 

with light-colored carbonate rock and, therefore, probably was deposited at a pH lower than 7.8. Organic phosphorite commonly is 

associated with glauconite and generally is calcareous; therefore, it 

probably was deposited at a pH near 7.8. The pelletal and nodular 

phosphorites are generally fairly free from carbonate rock and are 

rich in organic matter and pyrite. They probably were deposited, 

therefore, at an Eh less than about 0.25 volts and a pH less than 

7.8. The half cycle of deposition from light-colored carbonate rock 

to carbonaceous pelletal phosphorite probably represents a progression 

of pH from about 8.4 to about 7.5 and of Eh from about 0.1 to about 

 0.3 volts.

Similarly, the facies of the formation indicate that the pH of the 

sea water progressively rose to the east, probably as the result of the 

loss of C02, and that the Eh progressively rose to the east, owing to 

greater aeration of the bottom and perhaps increased benthonic 

scavenger fauna. The presence of anhydrite as the easternmost 

facies indicates that shallow restricted basins, combined with rapid 

evaporation, allowed the salinity to become greater than 200 parts per 

thousand. The red beds contain the ferric iron oxides and thus 

probably were deposited at an Eh greater than about 0.05 volts. 

This reflects dissolved oxygen in the seawater.

Silica was apparently deposited in a physical-chemical environment intermediate to the environments of phosphorite and lightcolored carbonate rock. This would be in and near the center 

stability field. Thus, if the precipitation of silica is controlled by 

the acidity of the environment, this study shows that the optimum 

pH value is probably a little less than 7.8.

The detailed sequence of rocks of the formation does not fit so 

simple a picture as outlined above, but it seems likely that the change 

of environments, while fluctuating, showed this progressive trend 

(fig. 27). Furthermore, rocks which do not lie in adjacent environmental fields sometimes are vertically adjacent. This may seem 

anomalous, for if the main control were pH and Eh, intermediate 

type rocks representing intermediate values of pH and Eh should be 

found. However, the passage from one environment to another 

could be rapid enough so that little or no sediment had time to form.

As suggested by Kazakov and amplified by McKelvey, it seems 

likely that the areal zoning of environments probably was due to the
152; CONTRIBUTIONS TO ECONOMIC GEOLOGY

upwelling of cold bottom currents, rich in dissolved material, over a 

platform. The subsequent increase in temperature and decrease in 

pressure would cause a loss of C02 and, thereby, a rise in pH. Life 

would flourish in this nutrient-rich water and result in a large supply 

.of organic matter in the bottom sediment. In water below wave 

base, the organic matter would be plentiful and the oxygen content 

low, and thus the Eh would be low. In shallower waters above wave 

base, the oxygen content would be high enough to oxidize the organic 

matter and yield high Eh values. Benthonic scavengers could live 

in the oxygenated water and help in the destruction of organic matter.

TRANSGRESSION AND REGRESSION

The sediments of the Phosphoria formation in the area of the 

report are all marine, and inasmuch as no prominent erosion surfaces 

within the Phosphoria have been found, it is probable that the area 

was covered by the sea for all of Phosphoria tune. Thus no transgression or regression of the shore line of the sea occurred in the 

area while the sediments of the Phosphoria were being deposited. 

It appears likely, however, that the depositional environments, which 

were areally zoned as described above, transgressed eastward twice, 

followed in each case by regression, which thus completed the two 

cycles of deposition.

The horizons of maximum transgression and maximum regression 

in a very general way define tune horizons (Lowman, 1949). Four 

such horizons can be placed within the formation at about the centers 

of units B, C, and D, and at the top of the formation. The validity of 

these horizons as time lines ultimately rests on the interpretation that 

the key beds indicated on plates 11 to 13 are time horizons. The 

facies relations are based on this assumption and the transgressive 

and regressive relations are based 011 the facies relations.

During the first period of the deposition of Phosphoria sediments in 

the area of this report, phosphorite and mudstone were deposited in 

the southwestern part of the area, while chert and carbonate rock were 

deposited in the central and sandstone in the eastern parts. The 

northeastern part of the area was above sea level.

The first transgression emplaced the phosphorite environment 

farther eastward to the central part of the area; during this period 

thick beds of phosphorite were deposited in southeastern Idaho. 

These thinned to the northeastward and graded into sandstone in the 

eastern and northern part of the area. The whole area of the report 

was receiving, sediment during this period.

The first regression occurred in two pulsations, the first of which 

displaced the phosphorite environment to the southwestern part of 

the area and emplaced a chert environment over the central and east-
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 153

ern part, while sandstone was deposited in the north. A second regressive pulsation emplaced a carbonate environment over most of 

the area.

The second transgression apparently occurred in two pulsations 

also. The carbonate environment was displaced slightly northeastward, allowing a chert environment to be emplaced in the southwest. 

The second pulsation was rapid and emplaced a phosphorite environment over the whole area of the report.

The second regression was slow and even. The phosphorite environment was gradually displaced westward, allowing the progressive 

emplacement of a chert environment, followed by a carbonate environment. Near the close of this regression a phosphorite environment existed in the southwestern, a chert environment in the southcentral, and a carbonate environment in the southeastern parts of the 

area, and sand was being deposited in the north (fig. 20). At the very 

close of Phosphoria time sandstone was deposited over the northern 

part of the area, offlapping the phosphorite and chert deposits.

Superimposed on these two transgressions and regressions were a 

great number of minor changes of environment, which account for 

the intricate interbedding of the rocks of the formation. These changes 

included fluctuations of the physical-chemical environment and variations in the supply and deposition of clastic material.

GEOTECTONICS

TECTONIC CONTROL OF TRANSGRESSION AND REGRESSION

The transgressions and regressions of the Phosphoria sea could have 

been caused by eustatic changes of sea level or tectonic movements. 

For three reasons tectonic control is more plausible. First, the transgressions and regressions occurred in the transition zone between the 

two tectonic elements, the Cordilleran miogeosyncline and the bordering craton on the east. Second, the isopach maps of the lower and 

upper cycles (figs. 25, 26) indicate that the basin in which the lower 

cycle was deposited had a different configuration than the one in 

which the upper cycle was deposited. The major difference is that the 

basin of the lower cycle deepened progressively westward, whereas 

the basin of the upper cycle deepened westward, shallowed, and deepened again. This change of thickness variation of the two cycles is 

most easily explained by areal variation of tectonic movements. 

Finally, the Forelle limestone and Ervay tongue, which extend into 

the red bed facies of the formation, are probably correlative with the 

carbonate rock zones of the formation in the area under discussion 

(Thomas, 1934), and thus the middle and upper periods of maximum 

transgression east of the area probably correspond to the middle and 

upper periods of maximum regression in the area of the report. If
154 CONTRIBUTIONS TO ECONOMIC GEOLOGY

this is the case, eustatic changes of sea level alone cannot have caused 

the transgressive and regressive relations, and tectonic control was 

probably most important. These tectonic movements probably 

affected a large area of the Permian platform, because the intertonguing of rocks deposited in different depth environments occurs 

not only in Wyoming and Idaho, but also in Montana (Cressman, 

1954) and probably in Utah (Cheney, T. M., oral communication).

NATURE OF TECTONIC MOVEMENTS

If, as seems to be the case, the major cause of transgression and 

regression was tectonic movement, something of the nature of these 

movements can be deduced from the stratigraphic record. Because 

the transgressions were more rapid than the regressions, the downward 

movements were more rapid than the upward movements. Because 

the transgressions and regressions appear to have occurred in pulsations, the tectonic movements probably were pulsating also.

TECTONIC PROVINCES

McKelvey (McKelvey and others, 1953) has pointed out the 

coincidence of the phosphorite-mudstone-chert facies of the formation 

with the Cordilleran miogeosyncline and the sandstone-carbonate 

rock facies with the shelf and has discussed the genetic implications. 

The studies reported here further indicate that the shelf consists of 

two geotectonic provinces, the stable shelf and the unstable shelf.

The transition zone between the phosphorite-mudstone-chert 

facies essentially deep water facies and the sandstone-carbonate 

facies essentially shallow water facies is wide; moreover, tongues 

of the deep water facies extend nearly to the red bed facies, and one 

evaporite tongue extends into western Wyoming in unit C. Thus, 

the formation in western Wyoming is markedly heterogeneous and 

records unstable tectonic conditions. The red bed facies in central 

Wyoming, on the other hand, records fairly continuous shallow water 

deposition, although the sediment deposited ranged from carbonate 

rock to anhydrite to red beds. The area over which these sediments 

were deposited was, therefore, more stable than the area to the west 

and may be called the stable shelf.

CONCLUSIONS

The sediments of the Phosphoria formation were deposited in a 

basin hi northwestern Wyoming which shelved gently eastward and 

northward. Detritus was derived from a low land area in southwestern Montana and from another low land area many miles to the

east of northwestern Wyoming.

Cold sea water, rich in phosphorus and C02 welled up over the 

shelf areas with a consequent change in the physical-chemical char-
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 155

acter of the water, the most important changes being a landward 

increase in alkalinity and redox potential. The type of sediment 

reflected the change in physical-chemical environment: the pelletal, 

oolitic, and nodular phosphorite was deposited under conditions of 

low pH and Eh values; chert, of intermediate values; and carbonate 

rock, of high values. Of the minor constituents of the sediments, 

organic matter and pyrite are associated with the phosphorite and 

some of the chert; glauconite, with the rest of the chert and 

some of the carbonate rock; and hematite, with the carbonate rock in 

the red bed facies in northwestern Wyoming. Sand was deposited 

with the carbonate rock and some of the chert, and mud was deposited 

with the rest of the chert and the phosphorite.

Owing to tectonic movements, these environments transgressed 

and regressed twice across northwestern Wyoming, producing an 

interfingering of the different rock types. The vertical sequence of 

rocks is cyclic because of the alternation of environments.

The tectonic movements, as recorded by the rocks, were pulsatory: 

the downward movement rapid and the upward movement slow. 

Northwestern Wyoming, where the pulsatory movements were active, 

was the unstable shelf. At the east, in central Wyoming, lay the 

stable shelf, where tectonic movements were minor. At the west, in 

Idaho, lay the miogeosyncline, which in Permian tune was a negative 

area, relatively unaffected by the upward tectonic movements.

TABLE 1. Stratigraphic and petrographic description of the strata of the Phosphoria 

formation at Fall Creek, Idaho

[The Phosphoria formation measured and sampled in a bulldozer trench and at natural exposures on the 

north side of Fall Creek near Swan Valley, SWH sec. 18, T. 1 N., K. 43 E., Bonncville County, Idaho, on 

the southwest limb of an anticline trending northwest. The beds strike N. 40° W. and dip 45° SW. 

Section measured and sampled by R. P. Sheldon, F. D. Frieske, T. M. Cheney, and R. Q. Waring in 

September 1950. Petrographic descriptions made by R. P. Sheldon. Color terms and numerical designations are from the Munsell color chart. Size terms are from the Wentworth size system. In the bed numbers, the first number indicates the locality (flg. 11); the letter indicates the unit or member that contains 

the bed; and the second number indicates the bed, in ascending order from the base of the unit. Percentages 

of constituents are visual estimates, except where the beds are analyzed for PsOs and acid insoluble constituents. These data are published in Smart, R. A., and others, 1954]

No. of Thickness 

bed Description (feet)

Rex Member of the Phosphoria formation (top not exposed, but only a few feet 

not described):

1R15__ . Chert, sandy, hard, medium-gray (N 5/0), massive. Con- 26. 5 

sists of 75 percent chalcedony: 60 percent as indistinct 

structureless spheres, and 20 percent as sponge 

spicules; 20 percent detrital quartz: very fine to fine, 

subangular sand; 1 percent apatite: clear euhedral 

tablets up to %4 mm in diameter; 1 percent dolomite: 

euhedral rhombs up to J4 mm in diameter; less than 

1 percent cellophane: grains up to J4 mm in diameter, 

probably replacement of bioclasts; less than 1 percent 

pyrite: euhedral; and traces of detrital grains of
156 CONTRIBUTIONS TO ECONOMIC GEOLOGY

TABLE 1. StratiffrapMc and petrograpliic description of the strata of the Phosphoria formation at Fall Creek, Idaho Continued

No. of Thickness 

bed Description (feet) 

muscovite, tourmaline, and sphene. Stratification of 

rock is shown by laminae containing various amounts 

of sand. Stylolites occur in chert.- Apatite, collophane, dolomite, and pyrite are disseminated throughout rock.

1R14____ Limestone, siliceous, hard, medium-gray (N 5/0), mas- 22. 0 

sive. Rock closely resembles bed lR13h, except that 

euhedral quartz crystals up to % mm wide and % mm 

long make up about 20 percent of the rock. They are 

evenly scattered through the rock and are unoriented. 

A few beds of dolomitic chert occur in the unit and 

are described as follows: Chert, dolomitic, hard, light 

brownish-gray (10 YR 5/1). Consists of 80 percent 

chalcedony: 60 percent as microcrystalline matrix, 

15 percent as sponge spicules, and 5 percent as replaced bioclasts including echinoid spines (?); 20 percent dolomite: euhedral rhombs up to }i mm in diameter; and 1 percent detrital quartz: very fine, subangular, well-sorted sand. Many rhomb-shaped molds 

occur in rock; rock is veined with calcite.

1R13____ Chert, dolomitic, and cherty limestone, hard, dark-gray 41. 0 

(N 4/0), massive. Tubular chert concretions make 

up a large part of unit. Five rock specimens in unit 

were examined petrographically and are described as 

follows: . .

h. 41.0 feet above base. Top of unit. Limestone, contains chert concretions, hard, yellowish-gray (10 YR 

7/1), massive. Consists of 95 percent calcite: 50 percent as coarsely crystalline echinoid spines (?), 

bryozoan fragments, and shell fragments, and 45 

percent as microcrystalline matrix; 3 percent detrital 

quartz: fine, etched, well-sorted sand; and 1 percent 

cellophane: brown, as replacement of fossils, casts of 

holes in fossils, and fine, subrounded pellets. Chert 

concretions are identical to rest of rock except that 

microcrystalline calcite cement is replaced with 

microcrystalline chalcedony.

g. 36.0 feet above base. Carbonate rock, cherty, 

sandy, hard, dark-gray (N 4/0), massive. Consists of 

60 percent carbonate: anhedral irregular grains up to 

Ys mm in diameter; 20 percent chalcedony: cryptocrystalline matrix; and 20 percent detrital quartz: 

very fine, angular, well-sorted sand. Stratification of 

rock is shown by a coarse lamination due to color 

differences. Carbonate is more coarsely crystalline in 

light to colored laminae.

e. 25.0 feet above base. Chert, sandy, dolomitic, hard, 

dark-gray (N 4/0), laminated, massive. Consists of 

60 percent chalcedony: 55 percent as cryptocrystal-
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 157

'.TABLE 1. StratigrapMc and petrographic description of the strata of /Tie Phosphoria formation at Fall-Creek, Idaho Continued

JSFo. of' Thickness 

bed Description (feet)

line chert and 5 percent as microcrystalline sponge 

spicules; 20 percent detrital quartz: very fine, angular, 

well-sorted sand; and 20 percent dolomite: euhedral 

to subhedral rhombs up to % mm in diameter. Rock 

is stratified by laminae containing various proportions of the above components as well as various 

amounts of organic matter. Rock contains lensshaped single-crystal calcite bodies which may be 

fossil shell fragments. The tubular concretions are 

texturally much the same as the rest of the rock except 

there is more chert, sponge spicules are more obvious, 

and more organic matter is present, especially in axial 

canals of sponge spicules. Stratification of the concretions is shown by orientation of sponge spicules 

and is parallel to the bedding.

c. 15.1 feet above base. Chert, carbonatic, hard, darkgray (N 4/0), laminated, massive. Consists of 50 

percent chalcedony: 45 percent as microcrystalline 

to nearly cryptocrystalline matrix, and 5 percent as 

sponge spicules; 45'percent carbonate: 5 percent as 

euhedral rhombs up to Me mm in diameter, and 4.0 

percent as irregular-shaped aggregates of anhedral 

grains; and 5 percent detrital quart/: very fine, subangular, well-sorted sand. Stratification of rock is 

shown by chert and carbonate laminae. Carbonate 

euhedra occur in chert laminae. Sponge spicules occur 

in carbonate rock laminae. Boundary between 

laminae is gradational. Sand occurs as lenses parallel 

to lamination. Rock is veined with calcite. 

b. 10.0 feet above base. Chert, dolomitic, hard, darkgray (N 4/0), laminated, massive. Consists of 60 

percent chalcedony: 40 percent as microcrystalline to 

nearly cryptocrystalline matrix, and 20 percent as 

sponge spicules; 30 percent dolomite: euhedral grains 

up to Y& mm in diameter; 10 percent detrital quartz: 

very fine, angular, well-sorted sand; and traces of 

detrital grains of plagioclase, sphene, and muscovite. 

Stratification of rock is shown by thin laminae of sandstone; otherwise texture is very homogeneous.

1R12_...__ Phosphorite, argillaceous, medium to coarsely pelletal, 0. 2 

and nodular, medium-hard, dark-gray (N 2/0), thinbedded. Nodules consist of phosphatic fossils.

1R11._.___ Siltstone, carbonatic, sandy, hard, pale-brown (IQYR 1.4 

6/2), thin-bedded. Consists of 60 percent detrital 

quartz: 35 percent as coarse, angular silt and 25 percent as fine, medium well rounded sand; 20 percent 

carbonate: euhedral to subhedral rhombs up to % 

mm in diameter; 10 percent cellophane: nodules full 

of silt inclusions up to 8 mm in diameter, replaced
158 CONTRIBUTIONS TO ECONOMIC GEOLOGY

TABLE l. 8tratioraphic and petroffraphic description of-the strata of the Phosphoria formation at Fall Creek, Idaho Continued

No. of Thickness 

bed Description (feet)

bryozoa, fine, well-rounded pellets, francolite brachiopod(?) shells, and a tooth of francolite 4 mm 

long; less than 1 percent muscovite: flakes up to J4a 

mm in diameter; and traces of detrital grains of chert, 

sphene, and tourmaline. Rock is stratified as shown 

by orientation parallel to the bedding of sand lenses, 

elongate cellophane bioclasts, and muscovite flakes.

1R10_.__-. Limestone, phosphatic, sandy, hard, medium-gray (N 1.9 

5/0), massive. Consists of 60 percent calcite: 30 percent as bryozoa, echinoid spines (?), and shell fragments, and 30 percent as microcrystalline matrix; 20 

percent cellophane: 10 percent as structureless forms, 

possibly shell fragments up to Yz mm long, and 10 

percent as cement and casts of holes in bryozoa; 20 

percent detrital quartz: fine, medium well rounded 

sand; and traces of detrital grains of chert, sphene, 

and tourmaline. Quartz sand grains are scattered 

through the matrix of fine-grained calcite and 

cellophane.

1R9___. Dolomite, hard, medium-gray (N 5/0), massive. Con- 5.2 

sists of 80 percent dolomite: clear, euhedral to subhedral crystals up to He mm in diameter showing overgrowths; 10 percent detrital quartz: fine, angular, 

medium well sorted sand; less than 1 percent chalcedony: sponge spicules; and 10 percent cellophane: 

poorly sorted, fine, angular nodules. Larger collophane grains contain more quartz silt and sand. Rare 

francolite brachiopod shell fragments and cellophane 

echinoid spines (?) are scattered throughout rock. 

Stratification of rock is shown by orientation parallel 

to the bedding of fossil fragments, lenses of quartz 

sand, and lenses of darker carbonate.

1R8____- Sandstone, cherty, contains chert nodules, hard, medium- 6. 4 

gray (N 5/0), thick-bedded. Consists of 50 percent 

detrital quartz: fine, medium well rounded sand; 35 

percent chalcedony: 30 percent as microcrystalline 

matrix, and 5 percent as microcrystalline sponge spicules which are as long as % mm and l/& mm wide; 10

percent dolomite: 5 percent is in euhedral rhombs up 

to % mm in diameter, and 5 percent as coarsely crystalline cement; 5 percent cellophane: 2 percent as fine, 

well-rounded sand and 3 percent as replaced bryozoa 

and casts of sponge spicule axial canals, which are in 

part recrystallized to clear, euhedral apatite tablets; 

and traces of detrital grains of tourmaline. Stratification of rock is shown by laminae containing various 

amounts of sand and chert. Mixed quartz and carbonate veins cut rock. Carbonate cement gives 

poikiloblastic texture. Chert nodules consist of do-
TABLE 1. Stratigraphic and petrographic description of the strata of the Phosphoria formation at Fall Creek, Idaho Continued

No. of Thickness 

bed Description (feet)

lomitic chert that is petrographically similar to bed 

1R1.

1R7__ __ Chert, dolomitic, hard, dark-gray (N 4/0), thick-bedded. 4.2

1R6__.__ Phosphorite, hard, brownish-gray (10YR 3/1), massive. 0.4 

Consists of 65 percent collophane: 40 percent as 

echinoid spines (?), bone fragments, and brachiopod 

shell fragments, and 25 percent as fine, well-rounded 

pellets and compound nodules composed of pellets up 

to 6 mm in diameter cemented by francolite; 10 percent detrital quartz: fine, well-rounded, medium well 

 sorted sand; less than 1 percent muscovite: flakes up 

to YIQ mm in diameter; and 25 percent organic matter, 

opaque. Rock is crudely laminated with alternating 

laminae of organic apatite, pelletal apatite, and silt 

rich in organic matter. Quartz sand grains are concentrated in matrix. Stylolites are common throughout rock and have altered original shapes of many 

grains.

1R5___. Dolomite, sandy, phosphatic, finely to coarsely pelletal, 1. 8 

hard, light brownish gray (WYR 6/1), massive.

1R4__._ Dolomite, silty, hard, medium-gray (N 6/0). Contains 2.7 

glaucouite.

1R3__ -_ Chert, dolomitic, hard, dark-gray (N 4/0), thick-bedded. 7. 4 

j Rock is petrographically similar to bed 1R1.

1R2____ Chert, dolomitic, hard, medium-gray (AT 6/0), thick- 2.4

( bedded. Consists of 50 percent chalcedony: clear 

microcrystalline matrix that contains a few relict 

sponge spicules; 50 percent dolomite: euhedral rhombs 

up to YIQ mm in diameter; less than 1 percent detrital 

quartz: coarse, angular silt; and less than 1 percent

. collophane: pellets and casts of axial canals of sponge 

spicules. Rock is homogeneous with dolomite rhombs 

scattered evenly throughout rock. The rock is texturally similar to bed 1R1 but contains less organic 

matter and fewer and less distinct sponge spicules.

1R1____ Chert, dolomitic, hard, dark-gray (N 4/0), thick-bedded. 18. 0 

Consists of 50 percent chalcedony: sponge spicules up

j to Yz mm long and Y» mm wide; 10 percent detrital 

quartz: coarse, angular silt; 40 percent dolomite: euhe-

^ dral rhombs up to Me mm in diameter that have rims of 

clear dolomite and cores of dolomite containing many 

inclusions; and less than 1 percent muscovite. Organic 

matter occurs in chalcedony cement. Axial canals 

of sponge spicules are made up of darker silica than 

the spicules; circular spicule sections resemble neg-

' ative uniaxial crosses under crossed nicols; chalcedony cement is microcrystalline. Rock is homogeneous, but traversed by veins of calcite and silica. 

Stratification is shown by lens-shaped areas of organic
160 : CONTRIBUTIONS TO ECONOMIC GEOLOGY

TABLE 1. Stratigraphic and petrographic description of the strata of the Phosphoria formation at Fall Creek, Idaho Continued

No. of Thickness 

bed Description (feet)

matter, muscovite, and sponge spicules oriented parallel to the bedding.

Phosphatic shale member of the Phosphoria formation:

1P33__-_ Dolomite, hard, light brownish gray (10YR 5/1), thin- 1.0 

bedded. Slightly oolitic in lower 0.2 feet.

lP32b_._ Phosphorite, sandy, hard, dark-gray (N 3/0), thick- 0. 5 

bedded. Thin section composed of three contorted 

laminae. The lowest lamina is composed of 85 percent collophane: dark brown, medium, poorly formed 

pellets commonly with quartz and chert nuclei; 15 percent detrital quartz: very fine, angular sand; and less 

than 1 percent unoriented muscovite. Middle lamina 

is composed of 85 percent collophane: light-brown, 

medium, well-rounded, spherical oolites, which commonly have nuclei of quartz and chert; and 15 percent 

detrital quartz: very fine, angular sand. Oolites are 

cemented by francolite; phosphatized sponge spicules 

are common. Rock has a submosaic texture. The 

upper lamina is composed of 60 percent francolite: 

medium, well-rounded oolites and brachiopod fragments, cemented in part by francolite; less than 1 percent apatite: clear euhedral to subhedral crystals; 

less than 1 percent chalcedony: coarsely crystalline, 

replacements of fossils and cement; and 40 percent 

detrital quartz: medium sand. Quartz sand occurs 

mostly in the matrix. The contacts between these 

laminae are sharp and irregular. Fossil fragments in 

the upper lamina are oriented roughly parallel to the 

contact. The rock shows apparently contemporaneous slump structures. Stylolites occur in the lower 

two laminae parallel to the bedding.

lP32a.-___ Phosphorite, argillaceous, finely to medium coarsely 0. 5 

pelletal, medium-hard, dark-gray (N 3/0), thin-bedded.

1P31C _ Phosphorite, hard, dark-gray (N 4/0, thick-bedded. 

Consists of 90 percent collophane: fine to very coarse, 

ellipsoidal oolites which interfere with one another and 

many of which have a nucleus of quartz or francolite 

fossil fragments, compound pellets cemented by francolite, and francolite fossil fragments and structureless 

nodules up to 3 mm in diameter; 10 percent detrital 

quartz: coarse, angular, medium well sorted silt 

included in collophane and as matrix. The matrix 

quartz is better sorted and a little larger in grain size.

Rock has a heterogeneous texture due to scattered 

large grains of collophane and francolite. Matrix has 

a submosaic texture.
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 161

TABLE 1. Stratigraphic and petrograpMc description of the strata of tJie Phosphoria formation at Fall Creek, Idaho Continued

No. of Thickness 

bed Description (feet)

lP31b__- Phosphorite, calcareous, hard, dark-gray (N 4/0), thick- 0. 4

bedded. Consists of 70 percent cellophane and 

. francolite: a mixture of coarse francolite fossil fragments, oolites, and collophane pellets in about equal 

proportions, and collophane cement; 30 percent 

calcite: coarsely crystalline, replaces collophane and 

francolite; and 2 percent detrital quartz: coarse, angular silt. Contact between beds P31b and P31a is 

sharp, irregular, and in some places overhanging. 

Tabular fossil fragments in 3lb lie parallel to this 

surface. Angular pebbles of bed 3la occur in bed 31b. 

The rock shows apparently contemporaneous slump 

structure.

lP31a_..._ Phosphorite, sandy, hard, dark-gray (JV4/0), thick- 0.4 

bedded. Consists of 65 percent collophane: brown, 

subpelletal to structureless matrix with some fine, 

well-rounded pellets and some nodules up to 8 mm in 

diameter; 30 percent detrital quartz: very fine, angular 

sand; and 5 percent muscovite: flakes up to 3/32 mm 

in diameter. Muscovite flakes show no apparent orientation. Rock is homogeneous.

1P30_... Dolomite, silty, medium-hard, pale-brown (10Y.R 5/2), 0.6 

thin-bedded. Consists of 70 percent dolomite: subhedral grains up to He mm in diameter; 30 percent 

detrital quartz: very fine, angular, irregular-shaped 

silt; and traces of detrital flakes of muscovite. Rock 

has a homogeneous porphyroblastic texture. Chert 

and calcite veins cut the rock.

1P29____ Phosphorite, argillaceous, very finely to very coarsely 0.4 

pelletal, medium-hard, dark-gray (N 3/0), thinbedded.

1P28____ Mudstone, dolomitic, medium-hard, light brownish 0. 7 

gray (1QYR 5/1), spheroidally weathered.

lP27b___ Phosphorite, soft, crumbly, brownish-gray (WYR 3/1), 0.5 

thin-bedded. Consists of 95 percent cellophane: 

medium to coarse, well-rounded, spherical pellets 

whose boundaries are irregular; 2 percent calcite: 

coarsely crystalline cement having poikiloblastic texture; and less than 1 percent detrital quartz: coarse, 

angular silt. Rock is homogeneous except for patches 

of calcite cement. Quartz silt is wholly included in 

collophane pellets.

lP27a.-_._ Phosphorite, argillaceous, finely pelletal, soft, brownish- 0. 9 

gray (1QYR 3/1), thin-bedded.

1P26_-.. Mudstone, medium-hard, brownish-gray (WYR 4/1), 1.3 

thin-bedded, spheroidally weathered.
162 CONTRIBUTIONS TO ECONOMIC GEOLOGY

TABLE 1. Stratigraphic and petrographic description of the strata of the Phosphoria formation at Fall Creek, Idaho Continued

No. of Thickness 

bed Description (feet)

1P25______ Dolomite, silty, medium-hard, light brownish gray 1. 1

(10 YR 5/2), massive. Rock is similar petrographically 

to bed 1P22. Contains a silty dolomite concretion 1 

foot long.

1P24__ Mudstone, dolomitic, soft, brownish-black (1QYR 2/1), 0.6 

thin-bedded.

1P23___. Mudstone, soft, brownish-gray (10 YR 3/1), thin-bedded. 2. 1

1P22____ Dolomite, medium-hard, light brownish gray (1QYR 2.8 

5/1), thin-bedded. Consists of 70 percent dolomite: 

euhedral to subhedral grains up to % mm in diameter 

in a matrix of granular dolomite whose grains are up to 

YM mm in diameter; 30 percent detrital quartz: coarse, 

angular silt; and less than 1 percent muscovite. Organic matter occurs in matrix. Rock has homogeneous 

porphyroblastic texture. Quartz is scattered evenly 

throughout rock.

1P21._____ Dolomite, silty, medium-hard, brownish-gray (IOYR 2. 2 

4/2), thin-bedded. Consists of 70 percent dolomite: 

euhedral to subhedral grains up to ys mm in diameter; 

30 percent detrital quartz: very fine, angular, wellsorted sand; and less than 2 percent muscovite: flakes 

up to l-i mm in diameter. Rock has homogeneous 

texture.

1P20______ Mudstone, phosphatic, dolomitic, soft, brownish-black 1. 2

(10YR 2/1).

1P19____ Dolomite, medium-hard, brownish-gray (10 YR 3/1), 0.9 

thick-bedded. Consists of 90 percent dolomite: 

euhedral to subhedral grains up to }i mm in diameter; 

5 percent detrital quartz: coarse, angular, well-sorted 

silt; and 5 percent cellophane: dark-brown, medium, 

angular, elongate pellets. Rock is stratified by 

laminae of ellipsoidal cellophane pellets, lenticular 

areas of organic matter, and laminae containing various amounts of quartz and muscovite silt. Irregular 

boundaries of collophane pellets caused by protrusion 

of quartz or carbonate grains. Pellets are elongate 

parallel to bedding.

1P18 _-. Mudstone, phosphatic, dolomitic, soft, brownish-gray, 0.4 

(10 KB 4/1), fissile.

1P17___- Dolomite, medium-hard, brownish-gray (107/2 4/1). 0.9 

Rock is petrographically similar to bed 1P14C.

lP16b__. Dolomite, argillaceous, soft, brownish-gray (IQYR 4/1), 0. 4 

fissile.

lP16a_____ Phosphorite, argillaceous, coarsely pelletal, soft, black l-0

(N 2/0).

lP15b_ - Phosphorite, calcareous, finely to medium coarsely pelle- 0. 8 

tal, soft, dark-gray (N 3/0), fissile.

lP15a_-___ Phosphorite, finely to medium coarsely pelletal, soft, 0.8 

dusky-brown (10 YR 2/2), fissile.
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 163

TABLE l. Stratigraphic and petroffraphic description of-the strata of the Phosphoria formation at Fall Creek, Idaho Continued

No.1 of Thickness 

bed Description (feet)

lP14c___-_ Dolomite, medium-hard, light brownish gray (107/2 1.9 

5/1), thin-bedded. Consists of 80 percent dolomite: 

anhedral to euhedral crystals up to YI& mm in diameter; 

10 percent detrital quartz: coarse, angular, well-sorted 

silt; traces of detrital grains of plagioclase and orthoclase; 10 percent cellophane: very fine to medium, wellrounded pellets containing quartz and carbonate 

nuclei. Collophane also occurs as cement in nodules. 

Organic matter occurs in matrix. Rock shows a crude 

lamination due to variation in abundance of pellets. 

Pellets in individual laminae are well sorted.

lP14b_.- Mudstone, dolomitic, medium-hard, grayish-brown 0.2 

(10 YR 4/2), thin-bedded.

lP14a---__ Dolomite, medium-hard, light brownish gray (107/2 1.2 

6/1), thin-bedded.

lP13b_.- Mudstone, dolomitic, phosphatic, soft, brownish-gray 0. 3 

(107/2 3/1).

lP13a_.._-. Dolomite, silty, soft, brownish-gray (10772 3/1), thick- 0. 6 

bedded. Consists of 65 percent dolomite: subhedral 

to euhedral crystals up to YIQ mm in diameter that 

contain many minute inclusions of organic matter; 15 

percent detrital quartz: coarse, angular silt; 5 percent 

cellophane: brown, spherical pellets that contain many 

inclusions of organic matter; 15 percent pyrite: anhedral grains up to KG mm in diameter; less than 1 

percent muscovite: flakes up to YIG mm in diameter. 

Rock has homogeneous granular texture.

1P12_.___. Interbedded phosphorite, argillaceous, 20 percent, med- 2. 4 

ium coarsely pelletal, soft, brownish-black (107/2 2/1), 

thin-bedded; and argillaceous dolomite, 80 percent, 

soft, brownish-black (10712 2/1), thin-bedded.

IP 11__-_ Interbedded phosphorite, argillaceous, medium coarsely 2. 6

pelletal, soft, brownish-black (107/2 2/1), thin-bedded; 

. and. dolomitic mudstone, soft, brownish-black (107/2 

2/1), thinrbedded.

-IPlOb__ _ - Phosphorite, argillaceous, coarsely to very coarsely pelle- 1. 9 

" tal and finely nodular, soft, crumbly, brownish-black 

: (107/2 2/1); Unit contains a few mudstone partings 

. which make up less than 2 percent of the unit.

lP10a._.__ Mudstone, phosphatic, medium coarsely pelletal, soft, 0.2 

brownish-black (107/2 2/1), fissile.

lP9__-_-__ Dolomite, medium-hard, dark-gray (N 3/0), thin-bedded. 1. 7

Consists of 90 percent dolomite: colorless, anhedral 

. crystals from }'u to }i mm in diameter; minor pyrite: 

anhedral, opaque grains partly altered to hematite; 

and organic matter, occurring as cement. Rock has a 

homogeneous granular texture.

394091 56-^ 5 " - - -
164 CONTRIBUTIONS TO ECONOMIC GEOLOGY

TABLE 1. Stratigraphic and- petrographic description of the strata of the Phosphoria formation at Fall Creek, Idaho Continued

No. of Thickness 

bed Description (feet)

lP8b__ __ Dolomite, phosphatic, and dolomitic phosphorite, inter- 0.2 

laminated, soft, brownish-gray (10YR 3/1), thinbedded. Consists of 60 percent dolomite: subhedral 

to euhedral rhombs up to y^z mm in diameter; 30 percent cellophane: dark-brown, fine to medium, wellrounded, ellipsoidal pellets, showing rims of lightbrown cellophane about J-lzs mm thick; 10 percent 

illite: slight mass-extinction effect; and less than 1 

percent detrital quartz: coarse, medium well sorted, 

angular silt, some grains up to % mm in diameter. 

Unit contains a few compound nodules up to 3 mm 

in diameter. Rock is stratified by alternating laminae 

containing various amounts of collophane pellets. 

Contacts between laminae are indistinct.

lP8a_ _ _ _ Phosphorite, finely to very coarsely pelletal, soft, brown- 0. 5 

ish-black (WYR 2/1), thick-bedded.

1P7.______ Dolomite, silty, medium-hard, grayish-brown (2.5YR 1. 0

3/2), thin-bedded, contains fluorite near base of unit. 

Consists of 50 percent dolomite: subhedral to euhedral 

grains up to % mm in diameter but most less than J4e 

mm in diameter; 30 percent detrital quartz: coarse, 

angular, medium well sorted silt; 20 percent collophane: coarse, ellipsoidal, well-sorted, medium well 

rounded pellets, containing a few inclusions of carbonate and quartz silt; and less than 1 percent muscovite: flakes up to Ys mm in diameter. Rock is stratified by alternating laminae of silty dolomite and phosphatic silty dolomite. Ellipsoidal collophane pellets 

are oriented parallel to bedding. Quartz silt is somewhat concentrated in phosphatic laminae. Muscovite 

flakes are parallel to bedding. Nonphosphatic laminae are darker.

1P6____- Phosphorite, calcareous, medium to very coarsely pel- 0.9

letal, soft, brownish-black (10 FT? 2/1). 

lP5c_---__ Phosphorite, calcareous, coarsely pelletal to finely nod- 1. 2

ular, soft, crumbly, brownish-black (IQYR 2/1). 

lP5b-__.__ Mudstone, phosphatic, very finely pelletal, soft, brown- 0. 2

ish-black (10F.R 2/1), fissile. 

lP5a.-__.- Phosphorite, soft, crumbly, black (N 2/0), thin-bedded. 1. 0

Consists of 75 percent collophane and francolite: fine

 to very coarse, well-rounded, spherical oolites; 1 percent francolite: fossil fragments; less than 1 percent 

fluorite: purple and colorless euhedral and anhedral 

crystals; 20 percent calcite: poikiloblastic cement; 5 

percent detrital quartz: medium-fine, angular, medium 

well sorted sand; and traces of detrital grains of feldspar and sphene. About 5 percent of the apatite grains

show no concentric structure, and about 30 percent 

have nuclei of quartz grains, calcite, or fluorite; con-
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 165

TABLE 1. Stratigraphio and petrographic description of the strata of the Phosphoria formation at Fall Creek, Idaho Continued

No. of Thickness 

bed Description (feet)

centric structure is due to rings of dark- and lightcolored collophane as well as francolite; both collophane and francolite form cement; francolite forms 

compound nodules. Basal 0.2 foot of unit contains 

pisolites up to 4 mm in diameter. Some oolites are 

truncated or interfered with by other oolites, giving 

a submosaic texture. Rock shows a crude lamination 

due to variations of collophane and calcite cement 

and laminae of sandstone.

1P4_._ Mudstone, dolomitic, soft, brownish- gray (10 YR 4/1), 1.2 

thin-bedded. Spheroidally weathered. Contains a 

a few phosphatic nodules 0.05 foot above base of unit.

1P3__-._ Phosphorite, soft, crumbly, black (N 2/0), thick-bedded. 0. 9 

Consists of 80 percent collophane: very fine to coarse, 

poorly sorted and bimodally distributed, rounded, 

spherical pellets; 5 percent detrital quartz: very fine 

to fine, subrounded sand; and less than 1 percent fluorite: purple, anhedral, microcrystalline. About 5 

percent of the pellets, including mostly the larger 

grains, show crude concentric structure; pellets interfere with one another, which gives a submosaic texture; 

some of the larger pellets are compound. Quartz 

grains occur as inclusions in pellets and are finer 

grained than quartz grains in matrix. Fluorite occurs 

as cavity fillings between pellets.

1P2_-.._ Siltstone, soft, black (N 2/0), fissile. Consists of 80 0.7 

percent detrital quartz: medium to coarse, angular, 

well-sorted silt; 5 percent muscovite: flakes up to 

YIQ mm in diameter; and 10 percent collophane: dark 

brown, occurs as cement in spherical areas up to 4 mm 

in diameter and scattered, irregular-shaped patches. 

Rock is homogeneous except for phosphatic siltstone 

nodules. Muscovite is oriented parallel to bedding 

throughout rock as well as within nodules. Boundaries between nodules and rest of rock are gradational.

IPlb__-. Dolomite, medium-hard, brownish-black (10F.R 2/1), 7.6 

thick-bedded. Consists of 90 percent dolomite: 

euhedral rhombs to anhedral grains up to Yaz mm in 

diameter, some grains showing overgrowths; 5 percent 

detrital quartz: medium, angular silt; and'less than 

1 percent muscovite: flakes up to y\& mm in diameter. 

Rock is stratified by interbedded laminae composed of 

dark, fine-grained dolomite and light, coarse-grained 

dolomite. Muscovite flakes are oriented parallel to 

bedding.

IPla__-_ Dolomite, phosphatic, soft, grayish-brown (7.5YR 4/2), 2. 0 

indeterminate bedding. Consists of 60 percent dolomite: anhedral to subhedral rhombs up to Ys mm in 

diameter and microcrystalline dolomite less than 

%i mm in diameter; 5 percent detrital quartz: medium
166 CONTRIBUTIONS TO ECONOMIC GEOLOGY

TABLE 1. Stratigraphic and petrographic description of the strata of the Phosphoria formation at Fall Greek, Idaho Continued

No. of Thickness 

bed Description (feet)

to coarse, angular silt; 5 percent francolite: medium 

to coarse pellets; less than 1 percent muscovite: flakes 

up to Yii mm in diameter; less than 1 percent feldspar: 

medium to coarse silt; and organic matter, darkbrown. Overgrowths of dolomite occur on larger 

dolomite grains. Stratification of rock is shown by 

laminae containing various amounts of organic 

matter. Francolite grains are evenly distributed 

throughout rock.

Wells formation (upper part only):

1W25 and Chert, sandy; and sandy, cherty carbonate rock, hard, 2. 2

1W24 medium-gray (N 5/0), thin-bedded. Bed is composed 

of interbedded lenses of chert and carbonate rock. 

The carbonate rock has replaced chert. The chert 

consists of 65 percent chalcedony: 50 percent as 

brownish sponge spicules, in rods up to %* mm long 

with a 1:4 ratio of width to length, and 20 percent as 

spherulitic microcrystalline chert matrix in crystals 

up to XU mm in diameter; 30 percent detrital quartz: 

medium, subrounded, well-sorted sand, with quartz 

overgrowths and some rutilated grains; 5 percent 

collophane: fine, well-sorted sand, most grains elongate with 1:3 ratio of width to length, partially 

recrystallized to clear, colorless apatite euhedra up 

to %4 mm in diameter; and 2 percent carbonate, 

mostly dolomite, but in part calcite: rounded grains 

up to Y* mm in diameter. Apatite euhedra are scattered through chert sponge spicules. Rock is homogeneous. In general, quartz grains are slightly larger 

than collophane grains. Collophane grains are oriented 

parallel to bedding. The sandy, cherty carbonate 

rock is similar to the sandy chert, except that microcrystalline chalcedony has been replaced by carbonate 

whereas coarse-grained quartz of spherulites and sand 

grains has not.

1W23__.__ Dolomite, sandy, hard, light brownish gray (107/2 6/1), 5. 8 

massive. Consists of 75 percent dolomite: euhedral 

rhombs and rounded grains, both up to Y» mm in

diameter, and possible dolomitized fossils composed 

of euhedral to subhedral rhombs less than %± mm in 

diameter; 20 percent detrital quartz: fine, etched, 

well-sorted sand; less than 5 percent collophane and 

francolite: very fine, subrounded, tabular sand; 

traces of detrital grains of chert and sphene; and 

traces of hematite grains, possibly pseudomorphous 

after pyrite. Except for dolomitized fossils, rock is 

homogeneous. Some apatite grains are rimmed with 

dolomite and tabular grains are roughly oriented 

parallel to bedding.
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 167

TABLE 1. Stratigraphio and petrographic description of the strata of the Phosphoria formation at Fall Creek, Idaho Continued

No. of Thickness 

bed Description (feet)

1W22_____ Dolomite, medium-hard, brownish-gray (1QYR 4/1), 11.0 

thin-bedded. Contains black (N 1/0) chert lenses, 

which make up about 30 percent of the unit. Although 

a few lenses are isolated, most of the chert lenses occur 

at definite horizons and are closely spaced, which 

gives the appearance of bedded chert. Dolomite 

consists of 95 percent dolomite: euhedral to subhedral 

rhombs up to Xo rnm in diameter, but many euhedral 

rhombs less than }£4 mm in diameter; 5 percent detrital 

quartz: coarse, angular, well-sorted silt; less than 1 

percent muscovite; and less than 1 percent hematite: 

pseudomorphous after pyrite. Rock is homogeneous. 

Muscovite is oriented parallel to bedding. Hematite 

is scattered throughout rock.

1W21 _____ Dolomite, sandy, soft, porous, yellowish-gray (10 YR 8/l)> 9. 8 

massive. Contains thin zones of concretionary chert 

which coalesce to form thin beds of chert near top of 

unit. Chert makes up less than 5 percent of the unit. 

Sandy dolomite consists of 60 percent dolomite: 

euhedral rhombs up to }i mm in diameter in microcrystalline dolomite matrix; and 40 percent detrital 

quartz: very fine, angular, etched, well-sorted sand. 

Eock is very roughly stratified with laminae that 

contain slight variations in amount of quartz sand.

1 W20b_. _ _ Mudstoue, soft, yellowish-gray (2.5 YR 8/2), fissile. Con- 0. 9 

sists of 60 percent detrital quartz: coarse silt to 

very fine sand, subrounded to angular; 30 percent 

illite: shows mass extinction parallel to bedding; 10 

percent chalcedony: microcrystalline; less than 1 percent hematite: pseudomorphous after pyrite; and 

traces of detrital grains of tourmaline and microcline. 

Stratification of rock is shown by alternating laminae 

of cherty siltstone and claystone. Chert occurs as 

cement. Hematite pseudomorphs are " scattered 

throughout rock.

lW20a_.__ Dolomite, calcareous, soft, yellowish-white (2.5 YR 9/2), 0. 3 

thick-bedded.

lWl9-____ Dolomite, argillaceous, soft, yellowish-gray (2.5 YR 7/2), 5.5 

massive. Consists of 50 percent dolomite: 30 percent as rounded grains up to YIQ mm in diameter and 

20 percent as microcrystalline matrix; 20 percent 

detrital quartz: 15 percent as coarse, angular, etched 

silt and 5 percent as very fine, subrounded sand; 5 

percent cellophane: very fine, angular, light-brown 

sand; 15 percent illite: brown, gives mass extinction 

effect; 5 percent hematite: pseudomorphous after pyrite and disseminated throughout rock; and traces of 

detrital grains of muscovite and chert. Rock is crudely 

stratified with lenses of clayey dolomite and silty 

dolomite.
168 CONTRIBUTIONS TO ECONOMIC GEOLOGY

TABLE 1. StratigrapMc and petrographic description of the strata of the phosphoria formation at Fall Creek, Idaho Continued

No. of Thickness 

bed Description (feet)

1W18.____ Dolomite, silty, ';sandy, medium-hard, yellowish-gray 5. 0 

(2.5YR 8/2), thin-bedded, contains calcite geodes 3.5 

feet from base. Consists of 30 percent detrital quartz: 

15 percent as coarse, angular silt and 15 percent as 

very fine, subangular sand; 65 percent dolomite, 20 

percent as euhedral to subhedral rhombs up to Me mm 

in diameter and 45 percent as microcrystalline matrix; 

5 percent hematite: euhedral cubes pseudomorphous 

after pyrite disseminated throughout rock; and traces 

of detrital grains of orthoclase, plagioclase, muscovite, 

tourmaline, and sphene. Rock is stratified by alternating laminae composed of various proportions of 

dolomite, silt, and sand.

1W17_____ Siltstone, dolomitic, medium-hard, yellowish-gray 18.0 

(2.5YR 7/2), thick-bedded. Consists of 80 percent 

detrital quartz: 75 percent as coarse, angular silt and 

5 percent as very fine, medium well rounded sand; 

20 percent dolomite: euhedral to subhedral rhombs 

up to Yi6 mm in diameter in an anhedral, microcrystalline matrix; less than 1 percent muscovite; less than 1 

percent hematite: pseudomorphous after pyrite; and 

traces of detrital grains of microcline, chert, sphene, 

and tourmaline. Rock is crudely stratified with several irregular lenses of very fine sand in very coarse 

silt. Hematite occurs in lenses parallel to bedding 

but is also disseminated throughout rock. Muscovite flakes are oriented roughly parallel to bedding.

1W16----- Sandstone, medium-hard, pale-brown (2.5 YR 5/2), thick- 14. 0 

bedded, in fault contact with unit below. Consists of 

90 percent detrital quartz: medium to fine, wellrounded sand; less than 1 percent hematite: euhedral 

to subhedral crystals pseudomorphous after pyrite' 

1688 than 1 percent Chalcedony: clear, microcrystalline

cement; and traces Of detrital grains of plagioclase, 

orthoclase, tourmaline, and sphene. Calcite, dolomite, 

and illite were identified by X-ray but not found

netrographjcally; they probably occur as cryptocrystaiiine cement. Some quartz grains are strained; 

others include crystaintea which are in linear arrangement. Rock is stratified by laminae of medium and 

fine quarts sa.nd.
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 169

TABLE 2. Stratigraphic and pelrographic description of the strata of the Phosphoria 

formation at Flat Creek, Wyoming

Phosphoria formation measured and sampled at natural exposure near Flat Creek, 2.9 miles east of Teton 

National Forest boundary, sec. 6, T. 41 N., R. 114 W., Teton County, Wyo. Beds dip gently north. 

Beds measured and sampled by H. W. Peirce, R. O. Waring, R. A. Smart, and M. A. Warner In August 

1950. Petrographic descriptions made by R. P. Sheldon. Color terms and numerical designations are 

from the Munsell color chart. Size terms are from the Wentworth size system. In the bed numbers, the 

first number indicates the locality (fig. 3); the letter Indicates the unit or member that contains the bed, in 

ascending order from the base of the unit. The percentages of constituents are visual estimates, except 

where the beds are analyzed for T?iOi and acid-soluble constituents. Analyses for PaOu and acid Insoluble constituents are published in Sheldon and others, 1963]

No. of Description Thickness 

bed (feet)

Unit E of the Phosphoria formation (overlain by Dinwoody formation):

15E8.___ Sandstone, dolomitic, cross-bedded, hard, very pale 10.2 

brown (10 YR 7/2), thin-bedded. Consists of 80 percent detrital quartz: medium, subangular, etched, 

well-sorted sand; 20 percent dolomite: subhedral to 

anhedral grains up to %i mm in diameter; less than 

1 percent collophane: medium, well-rounded pellets; 

and traces of detrital grains of glauconite and chert. 

Many quartz sand grains show overgrowths. Dolomite occurs as cement.

15E7__-__- Sandstone, phosphatic, hard, dark-gray (N 4/0), thick- 0. 3 

bedded. Consists of 65 percent detrital quartz: very 

fine to medium, angular to well-rounded, poorly sorted 

sand; 20 percent collophane and francolite; very fine 

pellets and fragments up to 8 mm in diameter which 

are made up of fossil fragments, pelletal phosphorite 

fragments and collophane pellets; 5 percent illite; 

cryptocrystalline cement; 10 percent calcite: microcrystalline cement and rare rock fragments; less than 

1 percent glauconite: fine to medium, rounded sand; 

and traces of detrital grains of chert, muscovite 

and sphene. Stratification of rock shown by several 

lenses of fine sand.

15E6-___-_ Sandstone, very fine grained, hard, dark-gray (N 4/0), 0. 7 

thick-bedded.

15E5_---__ Chert, sandy, silty; silt coarse, sand very fine, hard, I. 2 

dark-gray (N 4/0), massive.

15E4._.__. Chert, made up of tubular concretions, hard, brecciated, 26. 3 

pale-brown (2.5 YR 5/2). Consists of 80 percent chalcedony : microcrystalline grains up to Yu mm in diameter and a few relict sponge spicules; 10 percent dolomite: euhedral rhombs up to }iz mm in diameter; 10 

percent detrital quartz: very fine, angular sand; and 

less than 1 percent collophane: very fine, angular sand. 

Rock is veined with calcite and chalcedony. Stylolites filled by a thin seam of organic matter occur in 

the chert. Quartz, glauconite, and collophane are 

evenly distributed throughout the rock.
170 CONTRIBUTIONS TO ECONOMIC GEOLOGY

TABLE 2. Stratigraphic and.petrographic description of the strata of the Phosphoria formation at Flat Greek, Wyoming Continued

No. of . Thickness 

bed Description (feet)

15E3______ Chert, hard, brecciated, medium-gray, (N 5/0), thick- 4. 3

bedded. Consists of 95 percent chalcedony: sponge 

spicules and microcrystalline grains up to %4 mm in 

diameter; 2 percent detrital quartz: very fine, angular 

sand; 3 percent dolomite: euhedral rhombs up to YI& 

mm in diameter; less than 1 percent glauconite: very 

fine, well-rounded sand. Sponge spicules are oriented 

parallel to bedding. Stratification of rock is shown 

by lenses of dark-colored chert. 

15E2_____- Dolomite, hard, pale-brown (10 YR 5/2), thick-bedded. 0. 7

15E1_.__ Chert, hard, medium-gray (N 5/0), thin-bedded, similar 0. 5 

megascopically to 15E3. Phosphatic in lower 0.2 

foot of unit.

Unit D of the Phosphoria formation:.

15D16- . . . Mudstone, hard, light brownish gray (WYR 6/1), fissile. 1. 6 

15D15-.-- Claystone, contains elongate chalcedony grains up to 2.3 

YB mm in length and similar grains of dolomite which 

probably have replaced chert; otherwise unit is petro- 

. graphically similar to 15D9.

15D14---. Claystone, contains elongate chalcedony sponge spic- 3.8 

ules(?) up to % mm in length; otherwise unit is petrographically similar to 15D9.

15Dl3_-__ Claystone, medium hard, black (N 1/0), fissile. 2. 4 

15D12. _ _ _ Dolomite, clayey, hard, light brownish gray (1QYR 5/1), 0. 7 

thick-bedded. Consists of 70 percent dolomite: euhedral to subhedral rhombs up to %\ mm in diameter; 

30 percent clay: dark- brown matrix between dolomite 

rhombs; and less than 1 percent detrital quartz: fine, 

angular silt. Rock is homogeneous.

15D11____ Claystone, petrographically similar to 15D9. 3. 1 

15D10_-__ Dolomite, clayey, hard, brownish-gray (1QYR 3/1), 2.3

massive. Consists of GO percent dolomite: euhedral to

subhedral rhombs up to %* mm in diameter; 40 percent illite; leSS than 1 percent detrital quartz: fine,

angular silt; and less than 1 percent muscovite: flakes 

up to fa mnrin diameter. Rock is homogeneous.

15D9____. Claystone, medium-hard, brownish-black (N 2/1), fis- 2.8 

sile. Consists of 80 percent illite; 10 percent detrital 

quartz: fine, angular silt; 5 percent muscovite; and 

5 percent organic matter. Rock is homogeneous.

15D8_. _ _ _ Claystone, silty, petrographically similar to 15D7. 3. 5 

i5:n>7__--- oi^stono, .Biity, medium-Hard, dark-gray (N 4/0), in- 4.2

determinate bedding. Similar petrographically to 

i5D6a except that .more organic matter is present in 

15D7.

15D6b...- Mudstone, soft, light-brown (10YR 5/4). 0. 6
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 171

TABLE 2. Stratigraphic and petrographic description of the strata of the Phosphoria formation at Flat Creek, Wyoming Continued

No. of Thickness 

bed Description (feet)

15D6a___. Claystone, silty, medium-hard, dark-gray (N 4/0), thin- 1. 4 

i bedded. Consists of 60 percent illite: microcrystalline, 

shows mass extinction; 30 percent detrital quartz:

* medium to coarse, angular silt; 5 percent muscovite: 

flakes up to #0 mm in diameter; and 3 percent collophane: shown by analysis but not recognized in thin 

section. Rock is homogeneous. Muscovite and 

illite are oriented parallel to bedding.

15D5__ Phosphorite, medium-hard, dark-gray (N 3/0), thick- 0.5 

bedded. Consists of 75 percent cellophane, 45 percent

K as fine, well-rounded, well-sorted pellets, and 30 percent as irregular nodules up to 20 mm in diameter;

5 percent francolite: fossil fragments and cement;

6 percent detrital quartz: medium to coarse, angular 

silt, and rare grains of fine sand; and 3 percent muscovite: flakes up to Me mm in diameter. Cellophane 

nodules are made up of relict pellets on their edges and

» grade into structureless cellophane in their centers. 

Organic matter is found throughout the rock but is 

practically lacking in nodules except for prominent 

concentrations in patches.. Francolite occurs as cement 

in pellets. Quartz and muscovite are less abundant in 

nodules than pelletal area. 

15D4___. Claystone, silty, medium-hard, brownish-black (1QYR 2. 2

j 2/1), thin-bedded. Similar petrographically to 15D2 

except that this rock is composed of 50 percent illite;

11 25 percent detrital quartz; 10 percent carbonate; 5 

percent collophane; and the remainder organic matter 

and muscovite. .

15D3___ Phosphorite, argillaceous, medium-pelletal to finely 0. 5 

nodular, medium-hard, dark-gray (N 4/0), thickbedded.

15D2___ Claystone, medium-hard, brownish-gray (1QYR 3/1), 1. i 

thin-bedded. Consists of 70 percent illite: cryptocrystalline, shows mass extinction parallel to bedding; 

10 percent collophane: dark-brown, very fine to fine,

^ elongate, well-rounded, medium well sorted pellets; 

10 percent carbonate: microcrystalline grains up to

> Y&I mm in diameter; 5 percent detrital quartz: medium 

to coarse, angular silt; and 2 percent muscovite: flakes

* up to }{& mm in diameter. Stratification of rock is 

shown by laminae containing varying proportions of 

illite, carbonate, and collophane.' The inore carbonatic laminae are lighter in color.

.'* 15D1____ Phosphorite, sandy, medium to .coarsely pelletal and 0.5 

finely to coarsely nodular, fine quartz sand, mediumhard, brownish-black (IOYR 2/1), fissile.

* 394091 56 6
172 CONTRIBUTIONS TO ECONOMIC GEOLOGY

TABLE 2. 8tratigraphic and petrographic description of the strata of the Phosphoria formation at Flat Creek, Wyoming Continued

No. of Thickness 

bed Description (feet)

Unit C of the Phosphoria formation:

15C22 __ Sandstone, calcareous, phosphatic, hard, medium-gray 11. 5 

(N 7/0), massive, contains chert inclusions. Consists 

of 60 percent detrital quartz: medium, subrounded, 

well-sorted sand; 20 percent calcite: coarsely crystalline cement; 20 percent cellophane and francolite: 

medium, well-rounded, well-sorted sand and fossil 

fragments; and traces of detrital grains of chert, 

chalcedony spherulites, glauconite, and sphene. 

Calcite cement gives rock poikiloblastic texture. Near 

top of unit phosphatic fragments become larger than 

quartz grains, reaching 1 mm in diameter. Rock is 

homogeneous.

15C21__. Chert, calcareous, hard, yellowish-gray (10 YR 7/1), 12. 4 

massive. Consists of 45 percent chalcedony: microcrystalline grains up to ^4 mm in diameter, spherulites 

up to YI& mm in diameter common, sponge spicules 

common; 40 percent calcite: 20 percent as euhedral 

rhombs up to Y& mm in diameter and 20 percent as 

anhedral, coarsely crystalline calcite; 10 percent 

detrital quartz: very fine, subangular, well-sorted 

sand; 5 percent cellophane: very fine, well-rounded, 

elongate, well-sorted sand; and less than 1 percent 

glauconite: very fine, well-rounded, well-sorted 

sand and rare fragments up to 1 mm in diameter. 

Anhedral calcite occurs as patches in rock and euhedral calcite as rhombs in chert. Quartz, cellophane, 

and glauconite are evenly scattered throughout rock.

15C20b__ Phosphorite, calcareous, very finely to very coarsely 0. 5 

oolitic and organic, and coarsely nodular, hard, light 

brownish gray (IQYR 6/1). Contains grains of 

glauconite. 

. 15C20a__ Carbonate rock, phosphatic, finely pelletal, medium- 1. 0

j^B hard, yellowish-gray (IQYR 7/1).'

15C19___ 'Limestone, phosphatic, hard, yellowish-gray (2.5 YR 13. 3 

8/2), massive. Consists of 70 percent calcite: 30 percent as coarsely crystalline fossil fragments and 40 

percent is medium crystalline matrix; 20 percent collophane: fine to medium, well-rounded, well-sorted 

pellets and angular fragments of cellophane, in part

replaced echinoid spines (?) up to 2 mm long; 5 percent

detrital quartz: fine to medium, subrounded, wellsorted sand; less than 1 percent glauconite: fine to 

medium sand; and less than 1 percent chert: fine to

medium sand. Sparry calcite and calcite spherulites

line voids. Cellophane fills holes in bryozoa. Rock is 

heterogeneous.

15C18___ Dolomite, medium-hard, yellowish-gray (IQYR 7/1), 4.8 

massive. Rock is similar petrographically to 15C17.
PHYSICAL STRATIGRAPHT, PHOSPHORIA FORMATION, WYOMING 173

TABLE 2; >Stratigraphic and petrographic description of the strata of the Phd8~ 

phoria formation at Flat Creek, Wyoming Continued

No. of Thickness 

bed Description (feet)

15C17___ Dolomite, medium-hard, light brownish gray (IQYR 2.0 

5/1), bedding indeterminate. Consists of 95 percent 

dolomite: microcrystalline grains up to }it mm in diameter; 5 percent detrital quartz: very fine, subrounded, well-sorted sand; and traces of hematite: 

euhedral grains up to fa mm in diameter pseudomorphous after pyrite. Rock is homogeneous.

15C16___ ' Dolomite, medium-hard, light brownish gray (IQYR 6/1), 1. 6 

thin-bedded.

15C15___ Dolomite, argillaceous, sandy, soft, light-brown (7.5YR 2.9 

6/4), indeterminate bedding. Rock is petrographically 

similar to 15C13, except for different proportions of 

quartz, dolomite, and illite. Also rock is heterogeneous, in that sand occurs in lenses.

15C14___ Dolomite, argillaceous, soft, weak yellowish-orange 1. 2 

(2.57728/2).

15C13___ Sandstone, calcareous, medium-hard, yellowish-gray 3.8 

(IQYR 7/1), indeterminate bedding. Consists of 60 

percent detrital quartz: very fine to medium, angular 

to well-rounded, poorly sorted sand; 30 percent calcite: 

' microcrystalline, anhedral grains up to YM mm. in diameter; 10 percent illite: mass extinction effect; traces 

of detrital grains of muscovite, calcite, chert, sphene, 

and tourmaline; and less than 1 percent hematite: 

euhedral grains up to )ie mm in diameter, pseudomorphous after pyrite. Illite is distributed through 

calcite cement. Rock has homogeneous texture.

15C12__ _ Sandstone, dolomitic, contains scattered white chert in- 2. 9 

elusions, hard, very pale brown (IQYR 7/2), indeterminate bedding. Dolomitic sandstone is petrographically similar to 15C11. Chert inclusions are 

composed of spherulitic, microcrystalline chalcedony. '

15C11__ _ Sandstone, dolomitic, hard, very pale brown (10 YR 7/2), 1.9 

massive. Consists of 70 percent sand and 30 percent 

dolomite, otherwise petrographically similar to 15C10. 

Also contains a few scattered grains of cellophane 

equivalent to the quartz grains in size.

15C10___ Dolomite, sandy, hard, yellowish-gray (IQYR 8/1), inde- 3.3 

terminate bedding. Consists of 80 percent dolomite: 

microcrystalline, anhedral grains up to %& mm in 

diameter; 20 percent detrital quartz: very fine, well~ 

sorted, angular sand; less than 1 percent muscovite: 

flakes up to }le mm in diameter; and less than 1 percent hematite: grains up to J-io mm in diameter, pseudomorphous after pyrite. Muscovite grains are 

oriented parallel to bedding. Quartz and muscovite 

are scattered almost evenly throughout the rock, but 

a slight vertical variation is apparent. Hematite is 

somewhat more abundant in the more sandy laminae.
174 CONTRIBUTIONS TO ECONOMIC GEOLOGY

TABLE 2. Stratigraphic and petrographic description of the strata of the Phosphoria formation at Flat Creek, Wyoming Continued

No. of Thickness 

bed Description (feet)

15C9____ Sandstone, cherty, calcareous, hard, yellowish-gray ^ 1. 1 

(10YR 7/1), massive. Consists of 60 percent detrital 

quartz: very fine to medium, subangular to rounded, 

poorly sorted sand; 20 percent calcite: microcrystalline grains up to y$± mm in diameter; 20 percent chalcedony : well-rounded fragments up to 2 mm in diameter; less than 1 percent cellophane: fine to medium, 

well-rounded sand; less than 1 percent hematite, 

grains up to %i mm in diameter, pseudomorphous 

after pyrite; and traces of detrital grains of tourmaline, 

sphene, feldspar and muscovite. Rock has a heterogeneous texture. Calcite occurs as cement. Chert 

fragments are scattered throughout the rock.

15C8___ Dolomite, cherty, hard, light brownish gray (WYR 5/1), 2. 2 

indeterminate bedding. Consists of 70 percent dolomite; euhedral to subhedral grains up to Me mm in 

diameter and anhedral grains down to %i mm in diameter; 30 percent chalcedony: cryptocrystalline matrix 

occurring in patches, sponge spicules common; and 

less than 1 percent detrital quartz: very fine, angular, 

well-sorted sand. The larger grains of dolomite are 

more common near voids in rock. Rock is 

homogeneous.

15C7.._.__ Chert, spherulitic, hard, very pale brown (1QYR 7/3) 10.8 

and white (N 9/0), massive. Consists of 100 percent 

chalcedony, of which 50 percent is spherulites up to 

% mm in diameter and 50 percent is microcrystalline 

grains up to %* mm in diameter. Contains 5.0 feet 

by 1.0 foot limestone concretion 2.8 feet above base 

of unit.

15C6____ Chert, nodular, hard, medium-gray (JV 5/0). . 1.2

15C5____ Chert, spherulitic, hard, white (N 9/0), thick-bedded. 0.4 

Similar petrographically to bed 15B14.

15C4b__ Mudstone, cherty, nodular, hard, pale-brown (lOyjR 5/3). 0. 4

15C4a._-. Chert, hard, light brownish gray (10YR 5/1), thin- 0.2 

bedded.

15C3____ Carbonate rock, hard, light brownish gray (10YR 5/1), 0. 7 

thick-bedded. Contains chert nodules near base.

15C2__. Chert, hard, medium-gray (N 5/0), thin-bedded, lam- 0.8 

inated. Consists of 95 percent chalcedony: most as 

microcrystalline grains up to }{Q mm in diameter, 

some spherulitic, and the rest cryptocrystalline; 5 percent detrital quartz: fine, subrounded, well-sorted

sand; less than 1 percent cellophane and francolite: 

fossil fragments and rounded grains up to % mm in 

diameter. Stratification of rock is shown by laminae 

of light-colored microcrystalline and dark-colored 

cryptocrystalline chert. 

15C1__._ Chert, hard, medium-gray (N 5/0), thin-bedded. 1. 3
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 175

TABLE 2. Stratiffraphic and petroffraphic description of the strata of the Phosphoria formation at Flat Creek, Wyoming Continued

No. Thickness 

bed Description (feet)

Unit B of the Phosphoria formation:

15B17___ Mudstone, soft, light brownish gray (7.SYR 5/6), fissile. 1. 7 

Contains ellipsoidal chert nodules. The centers of 

some of the chert nodules contain pyrite.

15B16___ Chert, hard, medium-gray (TV 5/0), thin-bedded. Con- 0. 7 

sists of 90 percent chalcedony: macrocrystalline grains 

up to %4 mm in diameter, much of which is possibly 

sponge spicules; 10 percent detrital quartz: very fine, 

angular, well-sorted sand; less than 1 percent muscovite: flakes up to Me mm in diameter; less than 1 

percent cellophane and francolite: fossil fragments 

and rounded grains up to % mm in diameter. Rock 

is homogeneous.

15B15...__ Mudstone, soft, pale greenish brown, fissile. 0. 5

15B14___ Chert, spherulitic, hard, white (N 9/0), massive. Con- 1. 3 

sists of 99 percent chalcedony and quartz: 50 percent 

as spherulites of quartz up to 2 mm in diameter and 

49 percent as microcrystalline chalcedony matrix with 

grains up to #6 mm in diameter; 1 percent calcite: 

coarsely crystalline patches; and less than 1 percent 

muscovite: flakes up to J4e mm in diameter. Spherulites resemble crude uniaxial positive crosses under 

crossed nicols.

15B13___ Dolomite, cherty, hard, brownish-gray (lOFjR 4/1), 1. 7 

thick-bedded. Consists of 70 percent dolomite: microcrystalline, euhedral to subhedral grains up to %t mm 

in diameter; 25 percent chalcedony: spicules up to }i 

mm long and J4e mm wide; 5 percent detrital quartz: 

very fine, angular, well-sorted sand; and less than 1 

percent muscovite: flakes up to Me mm in diameter. 

Stratification of rock is shown by orientation of sponge 

spicules parallel to bedding and laminae containing 

varying amounts of quartz sand.

15B12__ Chert, sandy, hard, pale-brown (2.5 YR 6/2), thin- 1. 0 

bedded. Consists of 75 percent chalcedony: 60 percent, as spicules up to % mm long and Yzz mm wide, 

and 15 percent as cryptocrystalline matrix; 20 percent 

detrital quartz: very fine, angular, well-sorted sand; 

5 percent calcite: anhedral to subhedral grains up to 

)le mm in diameter and irregular patches of calcite up 

to Y\ mm in diameter; and less than 1 percent muscovite: flakes up to }le mm in diameter. Stratification 

of rock is shown by sponge spicules oriented parallel ' 

to the bedding, and laminae that contain various 

amounts of quartz sand.

15B11___ Dolomite, cherty, silty, hard, medium-gray (N 5/0), 1. 0 

thin-bedded. Consists of 60 percent dolomite: microcrystalline, euhedral grains up to ^28 mm in diameter; 

20 percent chalcedony: microcrystalline, anhedral
176 CONTRIBUTIONS TO ECONOMIC GEOLOGY :

TABLE 2.~-8$ratigraphic and petrographic description of the strata of the Phosphoria formation at Flat Creek, Wyoming Continued

No. of Thickness 

. bed Description (feet)

grains up to Yizs mm in diameter; 20 percent detrital 

quartz: very coarse, angular, well-sorted silt; less than . , 

1 percent muscovite: flakes up to YI& mm in diameter; 

traces of cellophane: very coarse, subangular, wellsorted, silt; and traces of detrital grains of tourmaline 

. and sphene. Stratification of rock is shown by laminae 

composed of various proportions of dolomite, chert, 

and quartz. Dolomite gives rock a granular texture.

15B10___ Carbonate rock, cherty, hard, dark-gray (N 4/0), thick- 0. 9' 

'. bedded.

15B9____ Mudstone, medium-hard, pale-brown (2.5 YR 5/2), fis- 1. 7 

sile. Contains a few laminae of organic phosphorite.

15B8____ Dolomite, argillaceous, medium-hard,pale-brown (2.5 YR 1. 0- 

5/2), fissile. Consists of 70 percent dolomite: microcrystalline, less than #28 mm in diameter; 5 percent 

detrital quartz: coarse, angular silt; 20 percent illite: 

microcrystalline, gives mass extinction effect; and 5 

percent hematite: euhedral grains up to ^2 mm in diameter, pseudomorphous after pyrite. Rock is homogeneous. Quartz, illite, and hematite are disseminated 

throughout the rock.

15B7 _ Mudstone, medium-hard, pale-brown (2.5F.R 6/2), 1.6- 

fissile.

15B6 Dolomite, medium-hard, grayish-brown (2.5YR 4/2), . 0T & 

fissile. Consists of 99 percent dolomite: microcrystalline, anhedral grains up to Ysz mm in diameter; and 1 

. percent detrital quartz: very coarse, angular, wellsorted silt. Rock is homogeneous with a mosaic texture.

15B5____ Dolomite, argillaceous, medium-hard, grayish-brown 0. 6 

(2.5YR 4/2), fissile. Contains films of glauconite.

15B4__._ Siltstone, calcareous, hard, light yellowish brown (2.5 YR ' 2.2

6/4) at base to yellowish gray (2.5YR 7/1) at top, 

 massive. Consists of 50 percent detrital quartz: >

coarse to very coarse, angular silt; 40 percent calcite: 

. coarse-grained cement; 10 percent glauconite: cryptocrystalline, shows mass extinction that is length slow 

parallel to bedding; traces of hematite, anhedral grains 

. up to #6 mm in diameter, and a few grains pseudomorphous after pyrite; and less than 1 percent muscovite: flakes up to Me mm in diameter. Stratification 

of rock is shown by laminae of siltstone containing 

. glauconite and siltstone containing hematite. Glauconite and hematite do not occur together in rock. 

Calcite cement gives rock a poikiloblastic texture.

15B3___ Phosphorite, medium-hard, brownish-gray (IQYR 4/1), 0. 9- 

, thin-bedded. Consists of 65 percent francolite: 

medium to very coarse, well-grounded, ellipsoidal 

pellets;, 30 percent calcite: coarse-grained fracture
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 177

TABLE 2. Stratiffraphic and petrographic description of the strata of the Phosphoria formation at Flat Creek, Wyoming Continued

No. of Thickness 

bed Description (feet)

K fillings; 5 percent glauconite: cryptocrystalline, 

shows mass extinction, length slow parallel to bedding; 

and less than 1 percent detrital quartz: very fine,

^ subrounded, well-sorted sand. Francolite pellets 

show mass extinction, length fast parallel to bedding; 

pellets distorted by compaction. Glauconite occurs 

as thin seams in rock, mostly as matrix, and is draped 

around francolite grains. Quartz occurs almost exclusively in matrix. Rock in general is homogeneous.

15B2____ Limestone, siliceous, hard, light brownish gray, thick- 0.5 

bedded. Consists of 60 percent calcite: coarsely 

crystalline, twinned crystals up to 4 mm in diameter; 

and 40 percent quartz: 20 percent as euhedral crystals 

up to 1 mm in diameter and 20 percent as anhedral 

^ grains from M 28 to % mm in diameter. Calcite occurs in

in some quartz areas as a matte of unoriented rods up , 

to % mm long and #e mm wide, large areas of which 

are in crystallographic continuity. Quartz euhedra

* occur in coarsely crystalline calcite. Granular quartz

and calcite exhibit a mosaic texture.

15B1._____ Phosphorite, calcareous, medium-hard, brownish-gray 2. 7 

(10 YR 4/1), thick-bedded. Consists of 80 percent 

cellophane and francolite: light-brown to colorless,

./ fine to very coarse, well-rounded, ellipsoidal to 

spherical oolites and fine-grained pisolites; 20 percent

J, calcite: cement, poikiloblastic texture; less than 1 ; 

percent detrital quartz: fine to medium, subangular

^ sand; and less than 1 percent muscovite: flakes up to 

%4 mm in diameter. Concentric rings in oolites are 

formed by alternating layers of cellophane and 

francolite; most francolite is slightly lighter in color 

and contains few muscovite inclusions; francolite 

rings give negative uniaxial cross. Oolites interfere 

with one another, caused in part by solution and in

> part by compaction, as shown by truncation of oolite 

rings and contortion of rings. They are oriented with 

long diameter parallel to bedding. Muscovite is 

included in oolites. Sand grains occur almbst wholly ' 

in matrix.

4 Unit A of the Phosphoria formation:

15A4__._ Chert, veined with calcite, hard, brownish-gray (10YR 1.3 

4/1), thick-bedded. A bed of phosphorite occurs 0.3 

feet from base. Consists of 75 percent chalcedony: 

spherulites up to ^ie mm in diameter, and relict sponge

^ spicules which form slightly more coarsely crystalline 

chalcedony than the microcrystalline chert matrix; 

5 percent detrital quartz: fine, medium well rounded, 

well-sorted sand; less than 1 percent cellophane:

* irregularly shaped pellets up to 2 mm in diameter;
178 CONTRIBUTIONS TO ECONOMIC GEOLOGY

TABLE 2. Stratigraphic and petroffraphic description of the strata of the Phosphoria formation at Flat Creek, Wyoming Continued

.No. of Thickness 

-bed Description (feet)

less than 1 percent francolite: brachiopod shell fragments, which show rounding and some overgrowths 

of collophane, up to 1 mm in diameter; 20 percent 

 calcite: larger areas of clear, coarsely crystalline and 

brown, finely crystalline calcite. Chert at the boundaries of the calcite has a crystalline rim oriented with 

the c axis of the quartz at right angles to the boundary.

15A3____ Dolomite, cherty, hard, light brownish gray (1QYR 6/1), 1. 0 

massive. Consists of 80 percent dolomite: euhedral 

crystals up to He mm in diameter; 20 percent chalcedony: microcrystalline matrix and sponge spicules; 

1 percent detrital quartz: very fine to fine, subrounded, 

well-sorted sand; and less than 1 percent collophane: 

very fine, well-rounded, well-sorted sand and fossil 

fragments. Rock is homogeneous.

15A2____ Chert, sandy, hard, medium-gray (N 5/0), massive, 1.0 

brecciated. Consists of 80 percent chalcedony: 

spherulites up to % mm in diameter, microcrystalline 

matrix; 20 percent detrital quartz: fine, subangular, 

well-sorted sand with overgrowths of clear quartz; 

and traces of detrital grains of tourmaline and muscovite. Brecciated fragments Of clear spherulitic chert 

in a brown, sandy, spherulitic chert matrix. Some 

overgrowths of detrital quartz grains in clear breccia 

fragments are irregular and spongy in texture.

15A1_.._ Dolomite, sandy, hard, pale-brown (IQYR 6/2), massive. 1. 5 

Consists of 75 percent dolomite: microcrystalline, 

anhedral grains less than }£4 mm in diameter; 5 percent 

calcite: coarsely crystalline fossils; 20 percent detrital 

quartz: fine to medium, subrounded, well-sorted, 

etched sand; and traces of detrital grains of orthoclase, sphene, plagioclase, microcline, and chert. 

Dolomite has a mosa|c. texture. Many fossil molds 

lined with sparry dolomite crystals. Sand grains 

evenly distributed throughout rock.

Tensleep sandstone (upper part only):

15T1___ Sandstone, hard, very pale brown (10 YR 7/3), massive. 25.8 

Consists of 95 percent detrital quartz: fine to medium, 

subrounded, well-sorted sand; less than 3 percent 

calcite; euhedral crystals up to Me mm in diameter; 

and traces of detrital grains of tourmaline, plagioclase,

orthoclase, microcline and sphene. Quartz grains show 

crystallographic continuous overgrowths of quartz 

giving rock a mosaic texture.
PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 179

LITERATURE CITED

Agatson, R. S., 1952, Tensleep formation of the Big Horn Basin: Wyo. Geol. 

Assoc. Guidebook, 7th Ann. Field Conf., p. 44-48.

 1954, Pennsylvanian and Lower Permian of northern and eastern Wyoming: Am. Aasoc. Petroleum Geologists Bull., v. 38, no. 4, p. 508-583.

Altschuler, Z. A., and Cisney, E. A., 1953, X-ray evidence of the nature of carbonate-apatite: Internat. Geol. Cong., 19th sess., Algiers, Comptes rendus, 

sec. 11, fasc. 11, p. 9.

Baker, C. L., 1946, Geology of the northwestern Wind River Mountains, Wyo.: 

Geol. Soc. America Bull., v. 57, p. 565-596.

.Blackwelder, Eliot, 1911, A reconnaissance of the phosphate deposits in western 

Wyoming: U. S. Geol. Survey Bull. 470, p. 452-481.

: 1918, New geologic formations in western Wyoming: Washington Acad. 

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180 CONTRIBUTIONS TO ECONOMIC GEOLOGY - -

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PHYSICAL STRATIGRAPHY, PHOSPHORIA FORMATION, WYOMING 181

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Wyo.: U. S. Geol. Survey Bull. 620, p. 331-350.

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INDEX

Acidity of ocean water.. . . 147-148

relation to deposition___.. _____ 148-152

Acknowledgments.__.._....______ 109

Age- . .... 106

Anhydrite.. . - 139,151

association in chemical cycle _...... 140,147

deposition 149

Apatite, compound nodules and pellets 119

concentration .. ... 122

diagenetic recrystallization. _........ 123

euhedral . ......_......_. . 123-124

Apatite casts...._______ __.__ 118-119

Apatite grains, nuclei_____ _____ 117,118 

Apatite sand grains.. .. . 119 

Areal variation, lower and upper cycles....... 143

Areal zoning, relation to upwelling currents.. 148,

151-152,154

transgression... . . 152 

Aulosteges faunule__...__ ____... 116

B

Baldwin Creek, Wyo. .... 116

Basins of deposition. . 153-154 

Bear Creek, Idaho, organic phosphorite..... 126-127

Beaverhead County, Mont- ... 114

Bedded chert-. - . 119-120 

Biogenic minerals, preservation..... . .. 149

Brachiopod shells, phosphatic.. _..... 119

Brazer Canyon, Utah....... 114

Bryozoans, apatite casts....... ...... 119

Buck Creek, Wyo., carbonate concretions.... 127

Burroughs Creek, Wyo., unit C.............. 130

Oalcite geodes, Minnekahta formation ..... 115

Calcite-phosphorite ratio... . . 148 

Calcium'carbonate, precipitation............. 148

Carbonate environment.._ _ .._... 153

Carbonate fluorapatite.___ ..__-__ 116

Carbonate rock:.: .. 106,120,121,140

facies___.... .._ ............ 115

precipitation-__ __. ___-..-.- 151 

sandstone facies, western Wyoming._... 112 

tongues.. ------ .--_ -.- . 115

unitC .r 129,130

unit E.............................. 134,135-136

Centennial Range, Mont__ .____... 113 

Chert.- 106,119-120,121,140

bedded. - .- 137,140 

concretionary and nodular....._...... 137-140

facies. 145-146

chert-limestone_ ___ _........ 146

chert-phosphorite-mudstone.............. 112

solution....--__.___...__ 123

tubular... - -- - 119,137,140

unit C.......................... 129,130-131,132

unitS.......-----.-.-- 132,134,135-136,137

Page

Chert environment- _. ___. _____ 152 

Chugwater formation, Owl Creek Mountains,

Wyo- 110

Claraia zone, Dinwoody formation..___.. 134 

Clastic materials, source...___....... 147,154

unit C.................................... 129

unit E.................................. 136-137

Clastic rocks, association with chemical cycle. 140 

Cellophane 116,118,121,124

Conclusions_.__.___.________ 154-155

Concretionary chert . ____ -______ 119

tuiit C.................................... 122

Cordilleran miogeosyncline... .___ 106,153,154 

Cordilleran shelf.. 154

Correlation.____...__....___..___ 112

phosphorites. _________.. 112-113 

with Phosphoriaof other areas.-------- 113-116

Cottonwood Creek, Wyo., unit C............ 132

Cross-bedded rocks...______....._._ 122

D

Deposition, diagenetic ... ___... 123

Depositional cycles, distribution of rocks... 140-141 

areal variation.____._________ 143 

relation to facies change ----- _____ 146,152

relation to physical-chemical environment.-------.------.--...-. 150-152

Depositional environments, physical chemistry... - 147-150

Dlagenesls 123-12-1

Dinwoody formation........ 111,132,134

Dolomite, anhydritic, Lakeridge 1 well, Wyoming. ________________ 132 

dark.... 121,124,133

E

Embar formation_. -_- _ 110

Embar group, Maverick Springs anticline,

Wyoming.. .... ____ .. Ill 

Erosion surface, pre-Phpsphoria.. __ 124 

Ervay tongue of Phosphoria formation..-.- 116,.153 

Euhedral apatite._ . ._..... 119 

Eustatic changes of sea level. . 153-154 

Evaporite fades.. ............ ......... 151

F

Fall Creek, Idaho, carbonate rock and chert 132 

miogeosynclinal rocks.................... 116

organic phosphorite_...... ... 127

sandstones .. ...-. - 121 

stratigraphic and petrographic descriptions.....--.------.--.- 155-168

Facies changes. . 106,143-146,154 

relation to cycle of deposition............. 146

relation to tectonic movement.... 153-154

relation to time horizons_..-.-.......-.. 152

183
184 INDEX

Page 

.Facies relations, comparison with cyclic rock

sequence.......--- 141-146

Field work_ -- ... .. . ...-.-.-.- 107

Fish remains, phosphatic.-.. ..__ 119

Flat Creek, Wyo., platform rocks. ____ 116

pre-Phosphoria erosion surface_-.. 124

sandstone.... -..- ------- 121

stratigraphic and petrographlc descriptions.-.. . - 169-178

Forelle limestone.----------- ----- 115,116,153

Fossils, phosphatic.. . 118-119,132,140 

Francolite .......................... 117,118,124

O

General Petroleum Co., Lakeridge 1 well__ 109 

Glauconite.. . 118,121,134,138,140,148-149,151

 Olendo shale.... -- _ 115

 Globular chert.. --------------------------- 120

Greenalite, deposition......-.. _ 149

Gros Ventre, Wyo., pre-Phosphoria erosion

surface.--------- ___ . 124

Gros Ventre Range, Wyo_ _..... 110

Hustedia faunule_-...- 116

I

Iron minerals, relation to chemical cycle.. 140 

relation to physical-chemical environment 148-149

unit B - - 127

K

Key beds, correlation..___ 112-113 

King, R. H., correlations, Little Popo Agio 

River, Wyo. to Baldwin Creek, 

Wyo.-...- -- -- 116

Lakeridge 1 well, Wyoming. ..._.___ 132,140

Laminations_... 122

Lateral relations, Phosphoria formation_.. 141-146

comparison of un its P and C with D and E. 143

comparison of units FandZ>____.. 141-142

comparison of units C and E........... 142-143

Limestone, light- . . 121 

Llngula zone, Dlnwoody formation_____ 134 

Llthologlc character, Phosphoria formation.-- 113 

Little Popo Agle River, Wyo., section_ 115,116

M

Madison Range, Mont.___ __ -. 114

Marienberg Alps, laminated dolomite........ 124

Maverick Springs anticline, Wyoming..___ 111

Methods of study. ___-_ .... 107

Middle Piney Lake, Wyo., unit C .__... 122

 Mineral stability fields.. 149

Mlnnekahta limestone, calclte geodes. . 115

correlatives ----- 110

Migeosyncline, Cordilleran................. 106,116

Mudstone -- . 106,121,132,140

associations_ ... 122

transgressive and regressive relations..... 152

unlt-D.- 132,133,135

Page 

Mudstone-chert facies............ ___ 144-145,152

Muscovite, in quartz silt......_______ 121

N

Nodular chert, unit C. __.________.... 131 

Nodular phosphorite suite_ ____-..-.. 139

Nomenclature, re view. -___....__._ 109-112

O

Oolitic phosphorites_.----.-.._.--__.. 118

Organic matter, precipitation_________ 149 

Organic phosphorites..-------------- 118-119,134

Orogeny, Cretaceous and Tertiary.....__. 106

Owl Creek Mountains, Wyo...._______ 110

Paleogeographic setting____.____... 146-147 

Park City formation.....- -... ..... 110,111

Pelletal phosphorites...... ......... 117-119

Petrographic description.-.___.___.. 116-121 

Phosphate, diagenetic deposition.....__.. 123

Phosphoria formation., ...__ ____ 111 

correlation with Phosphoria of other

areas.-.-------------..-..---- 113,116

Fall Creek, Idaho, phosphatic shale member, description _______ 160-166 

Rex member, description. -___- 155-159 

Flat Creek, Wyo., unit A, description.. 177-178 

unit P, description._............. 175-177

unit C, description...---..----.... 172-174

unit D, description. ....... 170-171

unit E, description.....__ __ 169-170

llthologic character.... _ ___ 113

paleogeographlc setting.. ___.. ___ 146-147 

phosphatic shale member_ . .. Ill, 112 

stratigraphic and petrographlc description..... .... 155-178

thickness---------------------------- - 113

type section, Phosphoria Gulch, Idaho... 110

units A to E, basal contacts. 124,125,128,132,134

composition.. ..........'..... . 125,

126,129-132,133-134,135-137 

facies....... 112,125,127,132,134,134-135,137

phosphate content..._............. 126

transgress'ive and'regressive relations. 152 

unit-D -- 132,133,134

upper contacts.. . 125,129,132,134

vertical distribution_________.. 12r

units Pand D, lateral relations. .. 141-142

units Cand E.......................... 144-145

upper shale member.----._ 111

Phosphoria rocks, environments of deposition.._-------___.----...-. 150-152

Phosphorite --- - 106,121,126-127

transgress!ve and regressive relations... 147-148

Phosphorite environment-_ .. .. 152-153

Phosphorite, facies.._--_-_-___. 144,148

precipitation...__.______________ 147,148

Phosphorites, oolitic and plsolitlc ~ 118-140 

organic.. . 118-119,140,151

origin.......... .... 147

petrographic description._............ 116-117

Phosphoria sea, depth of water. ______ 146-147
INDEX 185

Page

Physical-chemical environments, cyclic

changes.._... ----- -- 150-151

distribution... . 150-152

relation to type of sediment ... -- 122,155 

Physical chemistry of environments of deposition. ---------------------- 147-150

Pisolitic phosphorites........ 118

Platform rocks, Flat Creek, Wyo. section . 116 

Precipitation from ocean water, physicalchemical conditions.-...--- 147,148,151 

Pulsations of transgression and regression... 152-153 

Pyrlt'61 - 120, .121,134,140,148,' 151

Quadrant quartzite... _ 110

Quartz overgrowths... ........ .. 120

R

Hod bed fades. ... 106,115.154

Red bed phosphorite suite.....-. - . 139

Red bed-carbonate rock-evaporite fades, central Wyoming...... _... .. 112

Redbeds. 111,139

deposition _ ... .... ... . 151

Red Creek, Wyo., unit C.. .... ... 130

Rodox potential, ocean water.- - -. 147,148 

gelation to deposition___.....-.-...- 148-U2

Regression..-,..-.......-...-.........---..... 152-153

tectonic control. ... . 153 

Rox member.....-.--._...-.- ...,-.-. 110,115

correlation with unit C.............. 11,114,155

description..... ........... ...... 155-159

Rex Peak, Utah..-...---..--...-...-.--. 110 

Rock sequence, cyclical..---..-.......-..-. 140-141

relation to physical-chemical environment. 151 

unit C.................................... 132

unit E.......... . 138

Rock suites, .Phosphoria formation.,.. .. 138-139

 Salinity of ocean water..................... 147,151

Sand grains, apatite....-- .-.... 119

.Sandstone. - ............ 106,121,122

association, in chemical cycle ......... 122,140

unit C..*........................... 129,130,131

unit E.............................. 134,135,137

Sediment, rate of deposition_............... 147

stable and unstable shelf... .... 154

Sldcrite deposition..............._... .. 148

Silica deposition . . . ...... 123,149

acidity control... ..... .......... 151

Siltstone, Dinwoody formation..-.. .._... 134 

Solution, dlagenetic... - -_ 123

Spherulites, chert..........-...... ......... 120

Sponge spicules, apatite casts..... ....... 118-119

concentration_ ...................... 122

Stable shelf....------..----..---. ....... 154

Stratigraphic nomenclature....-.-_....... 109-112

Stratigraphic relations.--.-.-------.-..- 138-146

Stratigraphic units, petrographic description 

and areal variation.......... ...-. 124-125

Stratigraphy, regional.................. 109,113-116

Tectonic movements, Phosphoria time....... 154

Tectonic provinces...--------. --... -.-,-- 154

Tensleep sandstone, Flat Creek, Wyo., 

descrip tion................................. 178

Teton formation.. . .. ._..... 110

Thickness of Phosphoria formation........... 113

unit E..................................... 134

Thickness relations. - .. . . 141-142,143 

Time horizons.. _. _........ __ 152

Tosi Creek, Wyo., unit C.................... 130

Transgression.'._'...... ._ ... .-152-164

Trench / /, Idaho, organic phosphorite. .. . 127 

Tubular concretions, chert........ ........ 119,137

Unstable shelf -........................... 154

Upper Coal Measures....... . _.._ __. 110

Upper shale member. .S'«e under Phosphoria

formation.

Upwelling currents, influence on areal zoning . 148,151-152,154

W 

Weber quartzite..........._................ 110

Wells Canyon, Idaho..__.................. 110

Wells formation, correlation._._....___ 114

Fajl Creek, Idaho, description ....... 166-168

Wind River Range, wVo: 110,115,132

Woodslde shale..........__................. 110

o