CONIACIAN EPEIRIC SEA

Biostratigraphic Data from Upper Cretaceous Formations—

Eastern Wyoming, Central Colorado, and Northeastern

New Mexico 

By E.A. Merewether, W.A. Cobban, and J.D. Obradovich

Pamphlet to accompany

Scientific Investigations Map 3175

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2011

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Suggested citation: 

Merewether, E.A., Cobban, W.A., and Obradovich, J.D., 2011, Biostratigraphic data from Upper Cretaceous 

formations—eastern Wyoming, central Colorado, and northeastern New Mexico: U.S. Geological Survey Scientific 

Investigations Map 3175, 2 sheets, pamphlet, 10 p.

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Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Chronostratigraphy........................................................................................................................................2

Cenomanian and Turonian Strata.......................................................................................................4

Turonian Strata......................................................................................................................................4

Turonian and Coniacian Strata...........................................................................................................6

Coniacian, Santonian, and Campanian Strata .................................................................................6

Coniacian, Santonian, Campanian, and Maastrichtian Strata......................................................6

Interpretations................................................................................................................................................7

Acknowledgments.........................................................................................................................................8

Selected References.....................................................................................................................................8

Figures

1. Location of cross sections in counties of Eastern Wyoming, Central Colorado, and

 Northeastern New Mexico....................................................................................................................2

2. Molluscan fossil zones, informal zone numbers, fossil ranges, and radiometric ages 

 for marine strata of Cenomanian, Turonian, Coniacian, Santonian, Campanian,

 and Maastrichtian Stages (Upper Cretaceous) in the Western Interior of the

 United States ...........................................................................................................................................3

3. Lacunae (lined pattern) in Upper Cretaceous formations in Eastern Wyoming,

 Central Colorado, and Northeastern New Mexico with informal fossil numbers

 and radiometric ages .............................................................................................................................3

Table

1. Thicknesses and approximate rates of deposition for three information stratigraphic

 units of Late Cretaceous age at localities in Eastern Wyoming, Central Colorado,

 and Northeastern New Mexico............................................................................................................5

Sheets

1. Biostratigraphic outcrop sections of Upper Cretaceous formations along a south-

 trending transect from Northeastern Wyoming to North-Central Colorado.......................link

2. Biostratigraphic outcrop sections of Upper Cretaceous formations along a south-

 trending transect from North-Central Colorado to Northeastern Wyoming.......................link
Biostratigraphic Data from Upper Cretaceous Formations—

Eastern Wyoming, Central Colorado, and Northeastern

New Mexico 

By E.A. Merewether, W.A. Cobban, and J.D. Obradovich

Abstract

Lithological and paleontological studies of outcrops of 

Upper Cretaceous formations were conducted at 12 localities 

in eastern Wyoming, central Colorado, and northeastern New 

Mexico. The sequence extends upward from the top of the 

Mowry Shale, or age-equivalent rocks, through the Graneros 

Shale, Greenhorn Limestone, Carlile Shale, Niobrara Formation, Pierre Shale, and Fox Hills Sandstone, or age-equivalent 

formations, to the top of the Laramie Formation, or laterally 

equivalent formations. The strata are mainly siliciclastic and 

calcareous, with thicknesses ranging from about 3,300 ft in 

northeastern New Mexico to as much as 13,500 ft in eastern 

Wyoming. Deposition was mainly in marine environments 

and molluscan fossils of Cenomanian through Maastrichtian 

ages are common. Radiometric ages were determined from 

beds of bentonite that are associated with fossil zones. 

The Upper Cretaceous formations at the 12 study localities are herein divided into three informal timestratigraphic units based on fossil content and contact relations 

with adjacent strata. The basal unit in most places extends 

from the base of the Graneros to the top of the Niobrara, 

generally to the horizon of the fossil Scaphites hippocrepis, 

and spans a period of about 14 million years. The middle unit 

generally extends from the top of the Niobrara to the approximate middle of the Pierre, the horizon of the fossil Baculites 

gregoryensis, and represents a period of about 5 million years. 

The upper unit includes strata between the middle of the Pierre 

and the top of the Upper Cretaceous Series, which is the top of 

the Laramie Formation or of laterally equivalent formations; 

it represents a period of deposition of as much as 11 million 

years. 

Comparisons of the collections of fossils from each 

outcrop with the complete sequence of Upper Cretaceous 

index fossils can indicate disconformable contacts and 

lacunae. Widespread disconformities have been found 

within the Carlile Shale and between the Carlile Shale and 

the Niobrara Formation. Less extensive disconformities are 

within the Greenhorn Formation, the Niobrara Formation, and 

the Pierre Shale. 

Introduction

Biostratigraphic descriptions of outcropping Upper 

Cretaceous strata are presented herein for 12 localities in a 

south-trending transect from northeastern Wyoming to northeastern New Mexico (fig. 1), a distance of some 550 miles. 

The descriptions were obtained mainly from the publications 

listed at the end of this report. In regional cross sections 

(sheets 1 and 2), occurrences of the latest Campanian fossil 

Baculites eliasi are used as a reference plane. This study is 

related to the Western Interior Cretaceous (WIK) program, a 

cooperative investigation by geologists representing academia, 

commercial organizations, and State and Federal governments. 

It supplements east-trending stratigraphic cross sections in (1) 

Montana, South Dakota, and Minnesota by Dyman and others 

(1995); (2) Utah, Wyoming, and South Dakota by Merewether 

and others (1997); (3) Arizona, New Mexico, Colorado, and 

Oklahoma by Molenaar and others (2002); and (4) Utah, Colorado, and Kansas by Anna (in preparation). 

The sedimentary rocks considered in this investigation 

consist of siliciclastic, calcareous, carbonaceous, and bentonitic strata of Cenomanian through Maastrichtian ages. They 

include rocks between the top of the Mowry Shale or ageequivalent beds and the top of the youngest Cretaceous formations. In eastern Wyoming, these strata have been assigned, 

in ascending order, to the Belle Fourche Shale, Greenhorn 

Formation, Carlile Shale, Niobrara Formation, Pierre Shale, 

Fox Hills Sandstone, and Lance Formation (see NW Black 

Hills section, sheet 1); or alternatively, to the Frontier Formation, Sage Breaks Shale, Niobrara Formation, Steele Shale, 

Rock River Formation, Pine Ridge Sandstone, Lewis Shale, 

Fox Hills Sandstone, and Medicine Bow Formation (see Rock 

River section, sheet 1). Laterally equivalent formations in central Colorado and northeastern New Mexico are, from oldest to 

youngest, the Graneros Shale, Greenhorn Limestone, Carlile 

Shale, Niobrara Formation, Pierre Shale, Fox Hills Sandstone 

(or Trinidad Sandstone), and Laramie Formation (or Vermejo 

Formation and Raton Formation) (see Pueblo and TrinidadAguilar sections, sheet 2). 
2 Biostratigraphic Data from Upper Cretaceous Formations

In the 12 outcrop sections, the thicknesses of the Upper 

Cretaceous strata range from about 13,500 ft in Albany 

County, southeastern Wyoming, to about 3,300 ft in Colfax 

County, northeastern New Mexico. Most of the strata were 

deposited in marine environments although some members, 

as well as the uppermost Cretaceous beds, accumulated in 

continental environments. Molluscan fossils from the marine 

beds and the associated informal zone numbers (fig. 2) are 

listed with lithologic symbols on the cross sections. The 

numbered zones generally include several fossil species in 

addition to those listed in figure 2. Sequences of fossils from 

the outcrops, when compared to the complete sequence of 

index fossils [fig. 2; Ireneusz Walaszczyk (written commun., 

2011), Cobban and others, 2006], are evidence for correlations of lithofacies, as well as for periods of nondeposition and 

erosion. Lacunae in the outcrop sections (fig. 3) are indicated 

by local discontinuities in the fossil sequence. The duration 

of several lacunae was estimated from the radiometric ages of 

fossil zones (fig. 2; Cobban and others, 2006). 

Chronostratigraphy

The sequences of Upper Cretaceous formations shown 

in this north-trending transect (fig. 1; sheet 1, 2) include strata 

that were deposited in continental, nearshore marine, and 

offshore-marine environments. Outcrop sections near Glenrock and Rock River in eastern Wyoming (fig. 1, sheet 1) 

contain continental and nearshore-marine beds, and are about 

10,000 ft and 13,400 ft thick, respectively. The sequences 

in eastern Wyoming that originated mainly in offshoremarine environments are about 7,300 ft thick at Red Bird, 

5,900 ft thick at Thornton Dome, and 4,500 ft thick near NW 

Black Hills. In central Colorado (fig. 1, sheet 2), outcrops 

of nearshore-marine and offshore-marine strata range from 

9,500 ft thick at Buckeye to about 6,800 ft thick near Pueblo. 

Near Trinidad/Aguilar in south-central Colorado and near the 

Continental Oil Co. borehole and Springer in northeastern 

New Mexico, the outcrop sections consist mainly of offshoremarine strata and are 3,300 ft to 3,400 ft thick. Shorelines of 

the north-trending epicontinental seaway in which the offshore-marine beds were deposited were located far to the west 

(Cobban and others, 1994). 

Strata in most of the outcrop sections of the transect are, 

herein, separated into the following three informal timestratigraphic units: a basal unit that extends generally from the 

base of the Graneros to the top of the Niobrara (fossil zones 

6 to 53); a middle unit that extends mostly from the top of 

the Niobrara to near the middle of the Pierre (fossil zones 53 

to 61); and an upper unit that extends from the approximate 

middle of the Pierre (fossil zone 61) to the top of Upper 

Cretaceous strata (fossil zones younger than 75). 

The basal unit is Cenomanian to early Campanian in 

age, represents a period of about 14 million years (m.y.), and 

contains more calcareous beds and disconformities than the 

Figure 1. Location of cross section in counties of eastern 

Wyoming, central Colorado, and northeastern New Mexico 

(click here for large version of figure).

x

A

x

x

x

x

x

x

x

x

x

x

x

B

C

COLORADO

NEW MEXICO

COLORADO

WYOMING

WYOMING

NW BLACK 

HILLS

THORNTON 

DOME

RED BIRD

GLENROCK

ROCK 

RIVER

BUCKEYE

LYKINS 

GULCH

KASSLER/LITTLETON AREA

PUEBLO 

AREA

TRINIDAD/AGUILAR AREA

AREA OF CONTINENTAL 

OIL CO. NO. 3

SPRINGER 

AREA

CAMPBELL

CROOK

WESTON

CONVERSE

NIOBRARA

PLATTE

ALBANY

GOSHEN

LARIMER

WELD

ADAMS

BOULDER

ARAPAHOE

JEFFERSON

DOUGLAS

EL PASO

PUEBLO

HUERFANO

LAS ANIMAS

UNION

COLFAX

Cheyenne

Broomfield

Denver

LARAMIE

50 MILES
Chronostratigraphy 3

Figure 3. Lacunae (lined pattern) in Upper Cretaceous formations in eastern Wyoming, central Colorado, and northeastern 

New Mexico with informal fossil zone numbers and radiometric ages. m.y., millions of years (click here for large 

version of figure).

Figure 2. Molluscan fossil zones, informal zone numbers, fossil 

ranges, and radiometric ages for marine strata of Cenomanian, 

Turonian, Coniacian, Santonian, Campanian, and Maastrichtian 

Stages (Upper Cretaceous) in the Western Interior of the United 

States [modified after Ireneusz Walaszczyk (written commun., 

2011); Cobban and others, 2006; Kennedy and others, 1996; 

Cobban, 1977]. m.y., millions of years (click here for large 

version of figure). UPPER CRETACEOUS Turonian SERIES Stages Informal substages

Western Interior ammonite age

spans and radiometric ages (m.y.)

Santonian Coniacian

Lower Upper Middle Lower Upper Middle

Informal zone nos.

Scaphites ferronensis 33

Prionocyclus macombi 31

Collignoniceras praecox 29

Collignoniceras woollgari 28

Clioscaphites saxitonianus Cladoceramus undulatoplicatus

 87.14 44 Magadiceramus crenelatus

Scaphites ventricosus 43 Volviceramus involutus

Western Interior inoceramid 

age spans

Cremnoceramus crassus inconstans

39 Cremnoceramus deformis erectus

Scaphites mariasensis 38 Cremnoceramus walt. waltersdorfensis

42 Volviceramus koeneni

 88.55

41

Prionocyclus germari 37 Mytiloides scupini

Scaphites nigricollensis 36 Mytiloides incertus

35 Inoceramus dakotensis Scaphites whitfieldi 34 Inoceramus perplexus

Scaphites warreni 32 Inoceramus dimidius

Prionocyclus hyatti 92.46 30 Inoceramus howelli

Mytiloides hercynicus

Mammites nodosoides 27

Lower

Vascoceras birchbyi 93.48 26

25 Pseudaspidoceras 

 flexuosum

Mytiloides subhercynicus

Mytiloides mytiloides

Mytiloides kossmati

Watinoceras devonense 24 Mytiloides puebloensis

Nigericeras scotti 23 Mytiloides hattini

Upper

Cenomanian 

Neocardioceras juddii 22

21

20

19

18

17

16

15

14

13

12

11 

10 

 9

Burroceras clydense

Euomphaloceras 

 septemseriatum

Inoceramus pictus

Vascoceras diartianum 

Dunveganoceras conditum

Dunveganoceras albertense

Dunveganoceras problematicum

Dunveganoceras pondi 94.71

Inoceramus ginterensis

Plesiacanthoceras wyomingense

Acanthoceras amphibolum 94.96

Acanthoceras bellense

Plesiacanthoceras muldoonense

Acanthoceras granerosense 

Conlinoceras tarrantense 95.73

Inoceramus prefragilis

Inoceramus rutherfordi

Inoceramus macconnelii

Middle

 

90.60

0.39

0.59

0.46

0.58

0.58

93.19 0.42

93.99 0.57

0.49

0.50

0.51

Magadiceramus subquadratus

Cremnoceramus crassus crassus

40

Inoceramus arvanus

Lower

(Gap in biostratigraphic record)

Neogastroplites maclearni 

 8

 7

 6

Neogastroplites americanus 

Neogastroplites muelleri 

Scaphites preventricosus 

93.82 0.30

93.32 0.38

Neogastroplites cornutus 

Neogastroplites haasi

99.6 0.9 

Inoceramus maclearni

98.88 

 0.35 

1

2

3

4

5

45

Middle

Clioscaphites vermiformis Cordiceramus cordiformis

Cordiceramus bueltenensis

Upper

46

Clioscaphites choteauensis

Desmoscaphites erdmanni

Desmoscaphites bassleri 84.30 

Cordiceramus muelleri

Sphenoceramus lundbreckensis

47

48

49

Scaphites leei III 50

Campanian

Lower

Scaphites hippocrepis I 51

Scaphites hippocrepis II 81.86 0.36 52

Scaphites hippocrepis III 

Baculites sp. (smooth) 

Baculites sp. (weak flank ribs) 

Middle

53

54

55

Cataceramus subcompressus

Cataceramus balticus

Baculites obtusus 80.58 0.55

Baculites maclearni 

56 “Inoceramus”azerbaydjanensis

Baculites asperiformis 

57

58

Baculites sp. (smooth) 

Baculites perplexus 

59

60

Baculites gregoryensis 61

Baculites reduncus 62

Baculites scotti 75.77 0.34 63

Scaphites depressus 

Didymoceras nebrascense 75.95 0.41 64

“Inoceramus” tenuilineatus

Didymoceras stevensoni 

Exiteloceras jenneyi 75.05 0.32 Sphaeroceramus pertenuiformis 65

66

Didymoceras cheyennense 74.74 0.23 67

Baculites compressus 73.52 0.39 

Baculites cuneatus 

“Inoceramus” altus

Baculites reesidei 

Baculites jenseni “Inoceramus” oblongus

Baculites eliasi 71.98 0.31 “Inoceramus” redbirdensis

68

69

70

71

72

Endocostea typica

“Inoceramus” incurvus Baculites baculus 73

Baculites grandis 70.00 0.45 74 Trochoceramus” radiosus

Upper

Baculites clinolobatus 

Maastrichtian

Lower Upper

 69.59 0.36 75 “Inoceramus” balchii

Hoploscaphites birkelundae

Hoploscaphites nicolletii

Jeletzkytes nebrascensis 

K-T boundary = 65.50 0.10 

76

77

78

Inoceramus aff. dimidius

Inoceramids present

0.34

Cremnoceramus walt. hannovrensis

“Inoceramus” gibbosus

±

±

±

±

±

±

±

±

±

±

±

±

±

±

±

±

±

±

±

±

±

±

±

±

±

±

UPPER CRETACEOUS

Turonian

SERIES

Stages

Informal substages

Radiometric 

ages (m.y.)

Santonian Coniacian

Lower Upper Middle Lower Upper Middle

Informal zone nos.

33

31

29

28

44

43

39

38

42

41

37

36

35

34

32

30

27

Lower

26

25

24

23

Upper

Cenomanian 

22

21

20

19

18

17

16

15

14

13

12

11 

10 

 9

Middle

90.60

0.39

0.59

0.46

93.19 0.42

93.99 0.57

40

Lower

 (Gap in 

biostratigraphic 

 record)

 8

 7

 6

93.82 0.30

99.6 0.9 

98.88 

 0.35 

1

2

3

4

5

45

Middle Upper

46

47

48

0.34 49

50

Campanian

Lower

51

0.36 52

Middle

53

54

55

 80.58 0.55 56

57

58

59

60

61

62

 75.77 0.34 63

64

65

66

67

 73.52 0.39 

 71.98 0.31 

68

69

70

71

72

73

 70.00 0.45 74

Upper

Maastrichtian

Lower Upper

 69.59 0.36 75

76

77

78

65.50 0.10

 74.74 0.23

 75.05 0.32

 75.95 0.41

 81.86 

 NW 

Black 

 Hills

 Fox Hills 

Sandstone

?

 Lance 

Formation

Pierre Shale

 (part)

Pierre Shale

 (part)

Pierre Shale

 (part)

 Niobrara 

Formation

?

?

Carlile 

Shale 

(part)

Carlile 

Shale 

(part)

Greenhorn 

Formation

 Belle 

Fourche 

 Shale

Mowry 

 Shale 

?

Red Bird

?

 Lance 

Formation

 Fox Hills 

Sandstone

?

Pierre Shale

 (part)

Pierre Shale

 (part)

Pierre Shale

 (part)

 Niobrara 

Formation

Greenhorn 

Formation

 (part)

Carlile 

Shale 

(part)

Carlile Shale (part)

Greenhorn 

Formation 

 (part)

?

Mowry 

 Shale 

 Belle 

Fourche 

 Shale

Rock River

?

 Fox Hills 

Sandstone

 Medicine 

 Bow 

Formation

Lewis Shale

Pine Ridge 

Sandstone

Rock River 

Formation

Steele 

Shale

?

 Niobrara 

Formation

Sage Breaks 

 Shale 

 Frontier 

Formation 

 (part)

?

 Frontier 

Formation 

 (part)

Mowry 

 Shale 

Buckeye

?

 Fox Hills 

Sandstone

Pierre 

Shale

(part)

?

 Niobrara 

Formation

Pierre Shale

 (part)

Greenhorn 

Limestone

 (part)

Greenhorn 

Limestone

 (part)

?

Mowry 

 Shale 

Graneros 

 Shale 

 Kassler/

Littleton 

 area

?

Dakota 

 Group 

?

?

 Fox Hills 

Sandstone

 Laramie 

Formation

Pierre 

Shale

 Niobrara 

Formation

Carlile Shale 

 (part)

Carlile Shale 

 (part)

Greenhorn 

Limestone

Graneros 

 Shale 

Pueblo 

 area

?

?

 Fox Hills 

Sandstone

 Laramie 

Formation

Pierre 

Shale

 Niobrara 

Formation 

 (part)

Carlile Shale 

 (part)

Carlile Shale 

 (part)

Greenhorn 

Limestone

?

 Dakota 

Sandstone 

Springer 

 area

?

? Trinidad 

Sandstone

 Raton

Formation

(part) and

 Vermejo 

Formation,

undivided 

Pierre 

Shale

 Greenhorn 

 Limestone

 (part)

Carlile Shale 

 (part)

Carlile Shale 

 (part)

Greenhorn 

Limestone

 (part)

?

Graneros 

 Shale 

Graneros 

 Shale 

 Dakota 

Sandstone 

Informal zone nos.

33

31

29

28

44

43

39

38

42

41

37

36

35

34

32

30

27

26

25

24

23

22

21

20

19

18

17

16

15

14

13

12

11 

10 

 9

40

 8

 7

 6

1

2

3

4

5

45

46

47

48

49

50

51

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

69

70

71

72

73

74

75

76

77

78

?

Carlile Shale 

?

95.73 0.51

94.96 0.50

94.71 0.49

92.46 0.58

93.48 0.58

?

Trinidad/

 Aguilar 

 area 

 Dakota 

Sandstone 

?

Graneros 

 Shale 

Greenhorn 

Limestone

 (part)

Greenhorn 

Limestone

 (part)

Carlile Shale 

 (part)

Carlile Shale 

 (part)

?

 Niobrara 

Formation

Pierre Shale

 (part)

Pierre Shale

 (part)

?

? Trinidad 

Sandstone

 Raton Fm.

 (part) and

Vermejo Fm.,

 undivided 

 Niobrara 

Formation 

 (part)

 Nb. Fm. (part)

 Niobrara 

Formation 

 (part)

 Niobrara 

Formation 

 (part)

K-T boundary =

93.32 0.38

?

?

?

?

? ? ? ?

? ?

? ?

?
4 Biostratigraphic Data from Upper Cretaceous Formations

younger units. It is as much as 2,200 ft thick near NW Black 

Hills (23 percent of that outcrop section) and as little as 770 

ft thick at Lykins Gulch (10 percent of that outcrop section). 

However, the ages of the tops of the underlying Mowry Shale 

or Dakota Sandstone in the 12 outcrop sections are probably 

not always the same. The apparent rates of deposition for the 

basal unit, which were affected by periods of erosion and nondeposition, as well as by differential crustal subsidence, range 

from 157 ft/m.y. near NW Black Hills to 54 ft/m.y. at Lykins 

Gulch (table 1). 

 The middle unit is of early to middle Campanian age, 

records deposition during about 5 m.y., consists generally of 

siliciclastic beds, and encloses a few apparently local disconformities. It is as much as 2,740 ft thick near Glenrock (28 

percent of that outcrop section) and as little as 460 ft thick 

near NW Black Hills (11 percent of that outcrop section). 

Apparent rates of deposition for the middle unit are as much 

as 548 ft/m.y. near Glenrock to as little as 92 ft /m.y. near NW 

Black Hills (table 1). 

The youngest unit, between fossil zone 61 and the top 

of the Cretaceous sequence, is of middle Campanian through 

Maastrichtian ages, and records about 11 m.y. of deposition. 

It is comprised generally of marine siliciclastic beds overlain 

by continental siliciclastic and carbonaceous beds, and it 

encloses several unconformities. This unit is 1,200 ft thick 

at Springer (36 percent of the outcrop section), 1,100 ft thick 

at the Continental Oil Co. borehole (33 percent of the total 

section), and thickens to 9,680 ft to the north near Rock River 

(72 percent of the total section). Northward from Rock River, 

thicknesses are 4,700 ft at Red Bird (65 percent of the total 

section), 3,000 ft at Thornton Dome (51 percent of the total 

section), and 1,700 ft near NW Black Hills (30 percent of the 

total section). Rates of deposition for the upper unit range 

from 880 ft/m.y. near Rock River, to 155 ft/m.y. near NW 

Black Hills, and to 100 ft/m.y. at the Continental borehole 

(table 1). 

 Cenomanian and Turonian Strata

Strata of Cenomanian age in eastern Wyoming (fig. 3, 

sheet 1) are assigned to the Belle Fourche Shale and to the 

overlying Greenhorn Formation (as young as fossil zone 20) 

or to the Belle Fourche Member of the Frontier Formation (as 

young as fossil zone 17). The Frontier can include, in ascending order, the Belle Fourche Member and the Wall Creek 

Member (Merewether, 1996). At Thornton Dome and Red 

Bird (fig. 1, sheet 1, and fig. 3), Cenomanian beds in the lower 

part of the Greenhorn (fossil zone 17) are disconformably 

overlain by beds of early Turonian age (fossil zone 27) in the 

upper part of the Greenhorn. 

At NW Black Hills, Cenomanian beds (containing fossils 

as young as zone 22) in the Greenhorn are disconformably 

overlain by middle Turonian beds (fossil zone 29) of the 

Pool Creek Member of the Carlile Shale (fig. 3). The Carlile 

in eastern Wyoming consists, from oldest to youngest, of 

the Pool Creek, Turner Sandy, and Sage Breaks Members 

(see NW Black Hills section, sheet 1). Near Rock River, 

Cenomanian strata (fossil zone 17) in the Belle Fourche 

Member of the Frontier Formation are overlain, possibly 

disconformably, by upper Turonian beds (fossil zones 34 or 

35) in the Wall Creek Member of the Frontier Formation. The 

Marker (gray-red) bentonite bed of middle Cenomanian age 

(fossil zone 13) is recognized at NW Black Hills, Thornton 

Dome, and Red Bird (sheet 1). 

In central Colorado and northeastern New Mexico, strata 

of Cenomanian age (fossil zone 9 to as young as zone 23) are 

within the Graneros Shale and in the overlying Greenhorn 

Limestone, which consists, from oldest to youngest, of the 

Lincoln, Hartland Shale, and Bridge Creek Members (see 

Pueblo section, sheet 2, fig. 3). The age of the Bridge Creek 

Member near Pueblo is late Cenomanian and lower and 

middle Turonian (fossil zones 19 to 28; Kennedy and others, 

2005). In that area, the Hartland Member is conformably 

overlain by the Bridge Creek Member. Incomplete sequences 

of Cenomanian and Turonian fossils probably indicate a 

disconformity and a hiatus within the Greenhorn and within 

strata of equivalent ages at other outcrop sections in central 

Colorado (sheet 2), as well as in outcrops near Thornton Dome 

and Red Bird in Wyoming (sheet 1). 

Turonian Strata

In eastern Wyoming (sheet 1), lower and middle Turonian 

beds of fossil zones 27–30 are near the top of the Greenhorn 

and in the overlying Pool Creek Member of the Carlile Shale. 

They are disconformably overlain by middle and upper 

Turonian strata within fossil zones ranging from 32 to 37 in 

the Turner Sandy Member of the Carlile and in the Wall Creek 

Member of the Frontier. An unconformity at the contact of 

the Pool Creek and Turner Sandy Members of the Carlile in a 

borehole near Thornton Dome in eastern Wyoming was shown 

by Weimer and Flexer (1985). The Turner is conformably 

overlain by the Sage Breaks Member of the Carlile, which 

is late Turonian in age (fossil zones 36 and 37). The Wall 

Creek is conformably overlain by the Sage Breaks Member of 

the Cody Shale, which is an age-equivalent unit of the Sage 

Breaks Member of the Carlile. 

In central Colorado and northeastern New Mexico, 

strata of early and middle Turonian ages in the Bridge Creek 

Member of the Greenhorn and in the overlying Fairport 

Member of the Carlile Shale contain fossils of zones 27 

and 28. The Carlile in this region can include the following 

members, from oldest to youngest: Fairport, Blue Hill, 

Codell Sandstone, Juana Lopez, and Montezuma Valley 

(sheet 2). In the vicinity of Continental Oil Co. borehole No. 

3, in northeastern New Mexico (fig. 1, sheet 2), the Fairport 

reportedly is overlain disconformably by the Blue Hill 

Member, which contains fossils of zone 30 (Molenaar and 

others, 2002). The Blue Hill and overlying Codell in central 

Colorado (sheet 2) are of middle Turonian age (fossil zone 
NW Black  Hills 

Thornton Red 

Bird 

Glenrock Rock 

River 

Kassler/ Pueblo 

Dome Littleton

Thickness 1,700 3,050 4,660 5,700 9,680 

Rate of

deposition 

155 

460

92

Rate of 

deposition 330 

Thickness 

Thickness 

1,130 1,200 

Rate of

deposition 81? 107? 94? 86 

Table 1. Thicknesses (ft) and approximate rates of deposition (ft/m.y.) for three informal stratigraphic units of Late Cretaceous age at localities in eastern Wyoming, centraNew Mexico.

LykinsGulch

 ? ?

 ? 1,500 2,740? 2,440 2,160 1,650 1,320 700

Location Buckeye Trinidad/ Aguilar

2,200

157 104?

 ?

278?

277 424 518 880 585 509 470 436 ?

300 548? 488

6,400 5,600 5,170 4,800 ? 

432?

1,500 1,310 890

64

770

54

264 140

1,170

84

1,260

90

UPPER UNIT

MIDDLE UNIT

LOWER UNIT
6 Biostratigraphic Data from Upper Cretaceous Formations

30) and the age-equivalent strata of the Pool Creek Member in 

Wyoming. 

The Codell Sandstone Member or the Blue Hill Member 

of the Carlile Shale are disconformably overlain by the Juana 

Lopez Member, which contains middle and upper Turonian 

fossils (zones 32–35) and is correlative with strata in the 

Turner Sandy Member of the Carlile Shale and in the Wall 

Creek Member of the Frontier Formation in Wyoming. At 

several outcrops in south-central Colorado and northeastern 

New Mexico, the Juana Lopez is conformably overlain by the 

Montezuma Valley (Leckie and others, 1997; Merewether and 

others, 2007), which is probably of late Turonian age. 

Turonian and Coniacian Strata 

At localities near Red Bird and Rock River in eastern 

Wyoming (fig. 3), the Sage Breaks Member of the Carlile and 

the Sage Breaks Shale, respectively, are of late Turonian age 

(fossil zone 36) and apparently are disconformably overlain 

by the Niobrara Formation of middle Coniacian age. Weimer 

and Flexer (1985) depicted an unconformity between the Sage 

Breaks and Niobrara in a borehole near Thornton Dome. The 

lower beds of the Niobrara at Red Bird contain fossils that 

represent zone 43. At other localities in this area, however, 

evidence is lacking for disconformities separating the Carlile 

and the Niobrara. 

In northeastern New Mexico near Springer (fig. 3, sheet 

2), the Montezuma Valley Member of the Carlile Shale is 

probably of late Turonian age and could be disconformably 

overlain by the Fort Hays Limestone Member of the Niobrara 

Formation of late Turonian age (fossil zone 36). The Niobrara 

in this region includes the Fort Hays Limestone Member and 

the overlying Smoky Hill Member. In central Colorado, near 

Trinidad/Aguilar, Pueblo, and Kassler/Littleton, the Juana 

Lopez is of middle and late Turonian ages (fossil zones 33 

and 34) and is disconformably overlain by the Fort Hays 

Member of late Turonian age (fossil zones 37 and 38). Near 

the Continental Oil Co. No. 3 borehole and at Buckeye (fig. 

3), the middle Turonian Codell Member (fossil zone 30) is 

disconformably overlain by the Fort Hays Member of late 

Turonian and early Coniacian ages (fossil zones 36 to 40). 

Coniacian, Santonian, and Campanian Strata 

The Niobrara Formation in eastern Wyoming and northcentral Colorado is of Coniacian and probable Santonian 

ages. It is conformably overlain by the Pierre Shale or the 

Steele Shale, the lower beds of which are either Santonian or 

Campanian (fig. 3). Near Glenrock, Wyoming, the Niobrara 

is a member of the Cody Shale and is conformably overlain 

by the Steele Member of the Cody. At outcrops in central 

Colorado near Kassler/Littleton, the Niobrara is latest 

Turonian, Coniacian, and Santonian, and is conformably 

overlain by lower Campanian strata of the Pierre Shale. In 

south-central Colorado and northeastern New Mexico, the 

Niobrara is late Turonian, Coniacian, Santonian, and early 

Campanian, and is conformably overlain by lower Campanian 

beds of the Pierre. Gaps in the sequence of lower and middle 

Coniacian Inoceramids (fig. 2) at outcrops near Pueblo and 

Springer indicate hiatuses within the Smoky Hill Member of 

the Niobrara (Walaszczyk and Cobban, 2006) which could 

extend to other outcrops in central Colorado (sheet 2). 

Coniacian, Santonian, Campanian, and 

Maastrichtian Strata

In eastern Wyoming, the Pierre Shale consists of the 

following units, in ascending order: Gammon Member, 

Ardmore Bentonite Bed, Sharon Springs Member, Mitten 

Member, Red Bird Silty Member, lower unnamed shale, Kara 

Bentonitic Member, and upper unnamed shale (see Red Bird 

section, sheet 1). Age-equivalent strata near Glenrock are 

assigned to the following formations, from oldest to youngest: 

Cody Shale, Mesaverde Formation, and Lewis Shale. The 

Gammon at NW Black Hills (sheet 1) is probably of late 

Santonian and early Campanian ages (fossil zones 49–55) and 

is overlain, possibly disconformably, by the Mitten Member 

of middle Campanian age (fossil zones 58–60). Lowermost 

strata of the Mitten in that area have been assigned to the 

Sharon Springs Member (Robinson and others, 1964). To 

the south near Red Bird and near Buckeye in north-central 

Colorado, the Gammon is much thinner and is disconformably 

overlain by the Sharon Springs of middle Campanian age 

(fossil zone 56). The sedimentology and southward thinning 

of the Gammon Member of the Pierre, at outcrops from the 

NW Black Hills to Red Bird, were interpreted and recorded 

by Asquith (1970). The Ardmore Bentonite Bed in the lower 

part of the Pierre was deposited during the middle Campanian 

(fossil zone 56) and is widespread in eastern Wyoming and 

central Colorado. 

The lower unnamed shale member of the Pierre in eastern 

Wyoming encloses a disconformity within upper Campanian 

strata that separates beds containing fossils of zones 66 or 67 

from beds containing fossils of zone 70. This disconformity 

has also been identified near Glenrock at the base of the Teapot Sandstone Member of the Mesaverde Formation and near 

Rock River at the base of the Pine Ridge Sandstone. Fossils 

of latest Coniacian and Santonian ages have not been found in 

outcrop sections in eastern Wyoming. 

The Pierre and Lewis Shales of eastern Wyoming 

are conformably overlain by the Fox Hills Sandstone; the 

lowest beds of which have an apparent age range from early 

Maastrichtian at NW Black Hills (fossil zone 72), Thornton 

Dome (fossil zone 74), Glenrock (fossil zone75), and Rock 

River (fossil zone 75) to late Maastrichtian at Red Bird (fossil 

zone 75). 

The Pierre Shale in north-central Colorado contains 

the following units, from oldest to youngest: (1) Gammon, 

Sharon Springs, Mitten, and Hygiene Sandstone Members; (2) 

a sequence of shales and sandstones that includes the Terry 
Interpretations 7

Sandstone, Rocky Ridge Sandstone, Larimer Sandstone, and 

Richard Sandstone Members; (3) unnamed sequence of shales 

and sandstones; and (4) an upper sandy transition member 

(see Buckeye section, sheets 1, 2). In the vicinity of Pueblo, 

the Pierre includes the following, in ascending order: transition member, Apache Creek Sandstone, Ardmore Bentonite 

Bed, Sharon Springs, Rusty zone of Gilbert, Tepee zone of 

Gilbert, Cone-in-cone zone of Lavington (1933), and a transition member (see Pueblo section, sheet 2). The lowest beds 

of the Pierre could be late Santonian (fossil zone 49, fig. 3) at 

Buckeye and Lykins Gulch and early Campanian near Pueblo 

(fossil zone 54) and in the area of Springer (fossil zone 53) 

(sheet 2). The age of the uppermost Pierre in central Colorado and northeastern New Mexico ranges probably from late 

Campanian near Springer to early Maastrichtian near Pueblo 

and Kassler/Littleton to late Maastrichtian at Buckeye (fig. 

3). Disconformities within the Pierre in this region probably 

are between the Gammon and Sharon Springs Members at 

Buckeye, and possibly within the lowermost Pierre at Lykins 

Gulch and Kassler/Littleton. A disconformity and lacuna 

near the top of the Pierre in the area of Trinidad/Aguilar are 

between beds of late Campanian age (fossil zone 68 or slightly 

younger) and early Maastrichtian age (fossil zone 74 or 

slightly older). 

In central Colorado and northeastern New Mexico, the 

Pierre is conformably overlain by the Fox Hills Sandstone at 

Buckeye, Lykins Gulch, Kassler/Littleton, and Pueblo, and by 

the Trinidad Sandstone at Trinidad/Aguilar, Continental Oil 

Co. No. 3 borehole, and Springer (sheet 2). In this region, the 

age of the basal Fox Hills probably is late Maastrichtian and 

the age of the basal Trinidad probably is late Maastrichtian at 

Trinidad/Aguilar, early Maastrichtian at the Continental Oil 

Co. No. 3 borehole, and late Campanian at Springer. 

Interpretations

Outcrop sections of Upper Cretaceous strata near Glenrock and Rock River In eastern Wyoming (sheet 1), include 

continental and nearshore-marine beds with thicknesses of 

about 10,000 ft and 13,400 ft, respectively. To the northeast 

and south (fig. 1), continental, nearshore-marine, and offshoremarine sequences are about 7,300 ft thick at Red Bird, 9,500 

ft thick at Buckeye, 6,800 ft thick near Pueblo, and 3,300 ft 

thick near Springer. For all outcrop sections in the transect, 

it was assumed that the tops of the underlying Mowry Shale 

or Dakota Sandstone are nearly the same age. The regional 

thinning and lateral changes in dominant depositional environments of the Upper Cretaceous Series probably reflect 

different distances from shorelines and sources of sediments, 

as well as the number and duration of lacunae and regional 

variations in rates of crustal subsidence. Shorelines of the 

north-trending Late Cretaceous seaway that correspond to 

many of the offshore-marine beds in the transect were located 

far to the west (Cobban and others, 1994).

Within the outcrop sections in the transect, the three 

informal time-stratigraphic units vary in thickness, percentage 

of each total section, dominant depositional environment, 

apparent rate of deposition, and distances from correlative 

shorelines. The calcareous basal unit is overlain by the 

siliciclastic middle unit, which suggests deposition while 

laterally equivalent shorelines were prograding generally 

eastward. 

Thicknesses of the lower and middle units vary laterally 

and have an inverse relation at several localities (table 1). 

At Buckeye, for example, the basal unit is comparatively 

thin (890 ft) and the middle unit is relatively thick (2,160 

ft), whereas at Springer, Pueblo, and NW Black Hills, the 

basal unit is comparatively thick (1,250–2,200 ft) and the 

middle unit is relatively thin (460–900 ft). Apparent rates of 

deposition for the basal unit are largest at NW Black Hills, 

Thornton Dome, and Glenrock (104–157 ft/m.y.), and least at 

Buckeye and Lykins Gulch (54–64 ft/m.y.). For the overlying 

middle unit, the rates of deposition are greatest at Glenrock 

and Rock River (488–548? ft/m.y.) and least at NW Black 

Hills (92 ft/m.y.) and Pueblo and Springer (140–180 ft/m.y.). 

These thicknesses and rates of deposition suggest that either 

the tops of the basal unit in the region of the transect formed 

an irregular wavy surface or that the rates of subsidence of 

the sea floor varied locally during deposition of the basal and 

middle units. 

The upper informal unit thickens northward almost 

uniformly from 1,100 ft at the Continental Oil Co. borehole, 

to 9,680 ft near Rock River, and thereafter thins northward 

to 1,700 ft near the NW Black Hills. Corresponding rates of 

deposition for the upper unit at those localities are 100 ft/m.y. 

at the borehole, 880 ft/m.y. near Rock River, and 155 ft/m.y. 

near NW Black Hills. These thicknesses and depositional 

rates probably reflect different distances from the main source 

of sediments, but could also indicate that the highest rates of 

crustal subsidence along the transect during late middle Campanian through Maastrichtian time were in the area between 

Pueblo and Red Bird. 

The proposed lacunae in the outcrop sections (sheets 1, 2; 

fig. 3), which are indicated by interruptions in the established 

sequence of fossil zones (figs. 2, 3), apparently have local and 

regional distributions. A disconformity and the associated 

lacuna within the Greenhorn extend southward from Thornton 

Dome and Red Bird in Wyoming and probably to localities 

in central Colorado and northeastern New Mexico. They are 

between beds containing fossils of zones 18–20 and overlying beds containing fossils of zone 27. The age of the eroded 

surface of the lower parts of the Greenhorn is irregular. The 

age of upper parts of the Greenhorn is more consistent. This 

lacuna reflects a marine regression, widespread erosion, and a 

transgression, all of which happened during about 0.5 million 

years in the late Cenomanian and early Turonian. 

The Carlile Shale in eastern Wyoming, central Colorado, 

and northeastern New Mexico encloses disconformities and 

variable lacunae that reflect events in the middle Turonian (fig. 

3). At outcrop sections in the region (sheets 1, 2; fig. 3), ages 
8 Biostratigraphic Data from Upper Cretaceous Formations

of lower and upper parts of the Carlile are not uniform. The 

apparent duration of the lacunae is least near Springer, most 

near Kassler/Littleton and Trinidad/Aguilar, and intermediate 

elsewhere (sheet 2). Variations in the ages of the Carlile 

and in the durations of the enclosed lacunae might represent 

contrasting rates of local crustal subsidence or lateral changes 

in depositional and erosional events. 

The lacuna at the contact of the Carlile or Sage Breaks 

and the overlying Niobrara also varies in duration, which is 

longest, as much as 2 m.y., in the outcrops near Buckeye (fig. 

3). Strata in the upper part of the Carlile (or Sage Breaks) 

range in age from middle to late Turonian (fossil zones 32 

to 38); they become progressively younger from Springer to 

Pueblo, Kassler/Littleton, and Rock River, possibly reflecting 

a northward decrease in the amount of erosion. Overlying 

beds in the lowermost part of the Niobrara transgress consistently northward from late Turonian (fossil zone 36) near 

Springer to middle Coniacian (fossil zone 42) near Red Bird. 

The ages of these strata suggest that the top of the Carlile/Sage 

Breaks was an irregular erosional surface that was buried by 

onlapping beds of the northward transgressing basal Niobrara 

(Merewether and Cobban, 1985). 

Lacunae of lower and middle Coniacian ages are within 

the Niobrara near Pueblo and Springer and probably at nearby 

localities. The erosion of strata in this offshore marine 

environment might indicate local uplifts of the sea floor and 

powerful submarine currents. 

Lower parts of the Pierre Shale at NW Black Hills, 

Thornton Dome, and Red Bird in eastern Wyoming, and 

probably at Buckeye, Lykins Gulch, and Kassler/Littleton in 

north-central Colorado, include a lacuna of variable durations. 

The temporal extent of this lacuna is represented by the length 

of time that elapsed between fossil zones 56 to 59 (middle 

Campanian) at NW Black Hills, between fossil zones 50 to 

55 at Red Bird and Buckeye (early Campanian), and possibly 

between fossil zones 50 to 51 (early Campanian) at Kassler/

Littleton. 

Another lacuna was recognized in upper Campanian 

strata in eastern Wyoming but it has not been recognized in 

central Colorado or in northeastern New Mexico. It is located 

in the upper part of the Pierre Shale at NW Black Hills and 

Red Bird, at the base of the Teapot Sandstone Member of the 

Mesaverde Formation near Glenrock, and probably is at the 

base of the Pine Ridge Sandstone near Rock River. The temporal extent of this lacuna at NW Black Hills is represented 

by the length of time that elapsed between fossil zones 68 and 

69, near Red Bird it is between fossil zones 67 to 69 (about 2 

m.y.), and near Glenrock it might be between fossil zones 66 

to 70. It is indeterminate at the outcrops near Rock River. 

The uppermost lacuna in the Pierre is located in southcentral Colorado, in the area of Trinidad/Aguilar, and 

apparently is a local feature. It is bounded by beds of late 

Campanian age (fossil zone 68 or slightly younger) and beds 

of early Maastrichtian age (fossil zone 74 or slightly older) 

and represents as much as 3.5 m.y. 

Acknowledgments

This report was reviewed by D.K. Higley-Feldman, 

T.W. Judkins, W.R. Keefer, and R.B. O’Sullivan, and edited 

by Gayle Dumonceaux of the U.S. Geological Survey. 

Information concerning several fossil localities was supplied 

by K.C. McKinney of the U.S. Geological Survey. Ireneusz 

Walaszczyk of the University of Warsaw, Poland, refined the 

enclosed record of fossil Inoceramids (fig. 2) and reported 

two additional stratigraphic lacunae. Their suggestions and 

corrections were important contributions to the completeness 

and quality of the report and are greatly appreciated. 

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Scott, G.R., 1963, Bedrock geology of the Kassler quadrangle 

Colorado: U.S. Geological Survey Professional Paper 421-

B, 125 p.

Scott, G.R., 1969, General and engineering geology of the 

northern part of Pueblo, Colorado: U.S. Geological Survey 

Bulletin 1262, 131 p.

Scott, G.R., 1986, Geologic and structure contour map of the 

Springer 30ʹ × 60ʹ quadrangle, Colfax, Harding, Mora, and 

Union Counties, New Mexico: U.S. Geological Survey 

Miscellaneous Investigations Series Map I-1705.

Scott, G.R., and Cobban, W.A., 1965, Geologic and biostratigraphic map of the Pierre Shale between Jarre Creek and 

Loveland, Colorado: U.S. Geological Survey Miscellaneous Investigations Series Map I-439, 1:48,000 scale. 

Scott, G.R., and Cobban, W.A., 1986, Geologic and biostratigraphic map of the Pierre Shale in the Colorado SpringsPueblo area, Colorado: U.S. Geological Survey Miscellaneous Investigations Series Map I-1627, 1:100,000 scale. 

Scott, G.R., and Cobban, W.A., 1986, Geologic, biostratigraphic, and structure map of the Pierre Shale between 

Loveland and Round Butte, Colorado: U.S. Geological 

Survey Miscellaneous Investigations Series Map I-1700, 

1:50,000 scale. 

Scott, G.R., Cobban, W.A., and Merewether, E.A., 1986, Stratigraphy of the Upper Cretaceous Niobrara Formation in the 

Raton Basin, New Mexico: New Mexico Bureau of Mines 

and Mineral Resources Bulletin 115, 34 p.

Scott, G.R., and Pillmore, C.L., 1993, Geologic and structurecontour map of the Raton 30ʹ × 60ʹ quadrangle, Colfax and 

Union Counties, New Mexico, and Las Animas County, 

Colorado: U.S. Geological Survey Miscellaneous Investigations Series Map I-2266. 

Scott, G.R., Taylor, R.B., Epis, R.C., and Wobus, R.A., 1978, 

Geologic map of the Pueblo 1o x 2o quadrangle, southcentral Colorado: U.S. Geological Survey Miscellaneous 

Investigations Series Map I-1022. 

Trimble, D.E., 1975, Geologic map of the Niwot quadrangle, 

Boulder County, Colorado: U.S. Geological Survey Geologic Quadrangle Map GQ-1229, 1:24,000 scale. 

Walaszczyk, Ireneusz, and Cobban, W.A., 2006, Palaeontology and biostratigraphy of the Middle-Upper Coniacian and 

Santonian inoceramids of the U.S. Western Interior: Acta 

Geologica Polonica, v. 56, no. 3, p. 241–348. 

Weimer, R.J., 1996, Guide to the petroleum geology and 

Laramide orogeny, Denver Basin and Front Range, Colorado: Colorado Geological Survey, Department of Natural 

Resources, Denver, Colo., Bulletin 51, 127 p.

Weimer, R.J., and Flexer, Akiva, 1985, Depositional patterns 

and unconformities, Upper Cretaceous, eastern Powder 

River Basin, Wyoming: Wyoming Geological Association 

Guidebook, Thirty-sixth Annual Field Conference-1985, p. 

131–147.