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1995 Tectonic Subsidence of the Cretaceous Western Interior Basin, United States. Ming Pang Louisiana State University and Agricultural & Mechanical College

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TECTONIC SUBSIDENCE OF THE CRETACEOUS WESTERN INTERIOR BASIN, UNITED STATES

A Dissertation

Submitted to the Graduate Faculty of the Louisiana State University and Agricultural and Mechanical College in partial fulfillment of the requirements for the degree of Doctor of Philosophy

in

The Department of Geology and Geophysics

by Ming Pang B.S., Chengdu College of Geology, 1982 M.S., China University of Geosciences, 1985 May 1995

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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ACKNOWLEDGMENTS

I would like to express my sincere thanks to members of my dissertation committee,

Dr. Roy Dokka, Dr. Joseph Hazel, Dr. Richard Kesel, Dr. Juan Lorenzo, Dr. C. M.

Molenaar, Dr. Jeffrey Nunn, and Dr. Andrew Schedl, and especially my advisor, Dr.

Dag Nummedal for their interest, encouragement, and constructive criticism.

Dr. Dag Nummedal's guidance was most instrumental to the completion of this

dissertation. Many of the ideas presented in this dissertation came about as the result of

discussions and arguments with him. Because of his careful reviewing and editing, the

structure and clarity of the manuscript has been greatly improved.

Discussions with Dr. Andrew Schedl on many aspects of foreland basins were very

helpful in early stages of this dissertation. Dr. Joseph Hazel taught me the essence of

biostratigraphy and generously provided me his own research results. Dr. Jeffrey Nunn's

knowledge of sedimentary basin mechanisms led to many significant improvements in the

approach taken in this study. Discussions with Dr. Roy Dokka on many occasions were

very constructive to the analysis of the subsidence data. His insights on the tectonics of

foreland basins resulted in improvements in this dissertation. "K" Molenaar helped me in

many ways throughout my work. Much of the subsurface data used in this dissertation

was obtained with his help and guidance at the USGS at Denver. More important, his

expertise and knowledge of the Cretaceous stratigraphy proved most valuable to the

compilation of the stratigraphic data base of my work.

Discussions with fellow students at LSU have also been constructive to this

dissertation. In particular, I recognize with appreciation Drs. Greg Riley, Mark Pasley,

Mr. Xiaogong Xie, and Mr. Mingji Chu for their interest and support of my work.

I would like to thank all those extremely helpful people at the Office of the

Department of Geology and Geophysics, especially Liz Keller and Thea Burchell.

I wish to thank Drs. R. Johnson, K. Franczyk, T. Fouch, and T. Dyman of the

USGS at Denver, each of whom contributed to my dissertation by making available their

ii

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. own research results on the Cretaceous stratigraphy of the Western Interior basin. The

American Association of Petroleum Geologists is thanked for a grant-in-aid.

iii

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. TABLE OF CONTENTS

Acknowledgments ...... ii

List of tables ...... vi

List of figures ...... vii

A bstract...... xi

Chapter

1. Introduction ...... 1 A statement of work ...... 1 The Cretaceous Western Interior basin, a tectonic overview ...... 4 Objectives...... 7 Dissertation structure ...... 8

2. The tectonic framework of the Cretaceous Western Interior basin, U.S.A 10 Introduction ...... 10 Precambrian basins and provinces ...... 11 Archean Provinces ...... 11 Proterozoic basins ...... 14 Late Proterozoic rifting ...... 15 Basement faults ...... 19 Paleozoic orogenies ...... 21 The early Paleozoic passive margin ...... 21 The Antler orogeny ...... 21 The ancestral rocky Mountain deformation ...... 23 Transformation into an active margin ...... 25 The Sevier orogeny ...... 25 Style of deformation ...... 25 Times of movement ...... 27 Magnitude of thrust loads ...... 37 Basement controls on the Sevier thrusting ...... 38 The overlap province and buttressing ...... 38 Inferred buttresses and their consequences ...... 40

3. Stratigraphy of the Upper Cretaceous rocks, the U.S. Western Interior basin ...... 44 Introduction ...... 44 Depositional setting ...... 46 The molluscan biostratigraphic time scale ...... 51 Transgressive-regressive cycles ...... 54 Neocomian to Aptian ...... 57 The Kiowa-Skull Creek cycle...... 57 The Greenhorn cycle...... 60 The Niobrara cycle...... 66 The Claggett cycle ...... 69 The Bearpaw cycle...... 70 Stratigraphic correlations ...... 71 Data...... 71 Correlation method ...... 72 Study interval ...... 73

iv

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. A note on the cross sections...... 74 Regional stratigraphic cross sections ...... 75 Cross sections 1 and 2: western Montana to North and South Dakotas ...... 75 Cross sections 3 and 4: western Wyoming to South Dakota and Nebraska...... 84 Cross sections 5: central Utah to Denver Basin ...... 92 Cross sections 6: Kaiparowits region-San Juan Basin-Raton Basin-Pueblo ...... 99

4. Backstripping analysis ...... 108 Introduction ...... 108 Airy backstripping ...... 109 Flexural unloading sedimen ...... I l l Decompaction of sediment ...... 117 Sea level corrections and the meaning of subsidence ...... 123 Water depth corrections ...... 124 A note on error sources ...... 125 Results...... 126

5. Flexural subsidence and basement tectonics ...... 127 Introduction ...... 127 Previous work ...... 128 Subsidence patterns in space and time ...... 132 Subsidence profiles ...... 132 Subsidence curves ...... 134 Modeling flexural subsidence ...... 136 Model description...... 136 Method ...... 138 Model results ...... 138 A note on the lithosphere’s elastic thickness...... 141 Discussion ...... 144 Complexities of foreland basin subsidence ...... 144 Basement structures and their influences on lithospheric flexure 145

6. Residual subsidence and speculations on its causes ...... 152 Introduction ...... 152 Nature of the residual subsidence ...... 154 Epeirogenic subsidence mechanisms...... 158 Sublithospheric loading and cooling ...... 160 Continental tilting ...... 161 Mantle dynamic topography ...... 164

7. Conclusions ...... 167

References ...... 171

Appendix: Wireline logs used in the stratigraphic cross-sections 1 to 6 ...... 214

Vita...... 218

v

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF TABLES

1. Empirical constants in the exponential porosity-depth relationships

vi

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LIST OF FIGURES

I. The Cretaceous Western Interior Seaway during late Campanian time ...... 3

2 a: Generalized stratigraphic cross section of the Western Interior basin by King (1977). Also shown are tectonic" zones" proposed by Kauffman (1985). 2 b: foreland basin subsidence model ...... 5

3. Precambrian tectonic elements of the North American craton ...... 12

4. Protrozoic basins along the Cordillera. Dashed patterns in northwest part of craton indicate possible extension of craton ...... 13

5. Isopach maps of: a, Precambrian and Lower Cambrian rocks; b, Cambrian, Ordovician, and Silurian rocks ...... 16

6. Inferred crustal profile of the western North American continental margin prior to the initial terrane-accretion in the Late Devonian ...... 17

7. Tectonic subsidence curve showing the early Paleozoic passive margin subsidence history of western North America ...... 18

8. Normal faults and lineaments along the Sevier thrust front or the Cordilleran hingeline ...... 20

9. A generalized stratigraphic crosss section of the Antler foreland basin ...... 22

10. Principal tectonic elements of the Ancestral Rocky Mountain orogeny during Middle and Late Pennsylvanian time ...... 24

II. Sketch map of the Cordilleran region showing the Cretaceous Sevier orogenic belt relative to the Laramide trend and other tectonic elements at the time of the Mesozoic/Cenozoic boundary ...... 26

12. Chart showing the thrust chronology at three segments of the Sevier belt 28

13. Schematic map showing the major structural features of western Montana 30

14. Timing of major thrust faults in the Idaho-Wyoming salient and the contemporaneous uplift and fault in the adjacent foreland ...... 32

15. Generalized tectonic map of the Idaho-Wyoming salient showing the locations and extent of the major thrust faults ...... 33

16. A structural cross section of west-central Utah ...... 36

17. a: Location of the overlap province between the Cordilleran thrust belt and the Rocky Mountain foreland, b: A cross section of the overlap province.. . . 39

18. An interpretative structural block diagram showing the inferred relationship between the Proterozoic Willow Creek fault, the transverse zone, and frontal ramps of the Helena salient ...... 42

vii

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 19. Map showing the extent of the Cretaceous outcrops (shaded) in the U.S. Western Interior ...... 45

20. Map showing the distribution of Laramide structural basins in the U.S. Western Interior ...... 47

21. Generalized map of the Western Interior Seaway during the maximum transgression in the Late Cretaceous ...... 48

22. Restored Cretaceous isopach patterns in the Western Interior, a: Albian through Santonian strata and b: Campanian and Maastrichtian strata. Isopach contours in 1000 ft interval ...... 50

23. Molluscan time scale and reference sequences of the Western Interior Basin 52

24. Late Jurassic to Early Cretaceous correlation chart for parts of the Western Interior basin ...... 55

25. Transgressive-regressive depositional cycles of the North American Cretaceous Western Interior ...... 56

26. Early Cretaceous drainage pattern in the Western Interior ...... 58

27. Generalized stratigraphic section for the Rock Canyon anticline area, northwestern Pueblo quadrangle, Colorado, showing principlal lithologies and zonal fossils of the Dakota, Greenhorn, Carlile, Niobrara, and lower Pierre Shale...... 61

28. Map showing the extent of the Cretaceous Western Interior Sea Ways at three different times...... 62

29. Generalized time-stratigraphic correlation chart for Upper Cretaceous strata from northwestern Montana to North Dakota ...... 76

30. Regional stratigraphic cross section 1 of the lower Upper Cretaceous rocks from northwestern Montana to North Dakota ...... 77

31. Generalized time-stratigraphic correlation chart for Upper Cretaceous strata from southwestern Montana to South Dakota ...... 78

32. Regional stratigraphic cross section 2 of the lower Upper Cretaceous rocks from southwestern Montana to South Dakota ...... 79

33. Generalized time-stratigraphic correlation chart for Upper Cretaceous strata from northwestern Wyoming to South Dakota ...... 85

34. Regional stratigraphic cross section 3 of the lower Upper Cretaceous rocks from northwestern Wyoming to South Dakota ...... 86

35. Generalized time-stratigraphic correlation chart for Upper Cretaceous strata from southwestern Wyoming to Nebraska ...... 87

36. Regional stratigraphic cross section 4 of the lower Upper Cretaceous rocks from southwestern Wyoming to Nebraska ...... 88

viii

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 37. Generalized time-stratigraphic correlation chart for Upper Cretaceous strata from Uinta to Denver Basins ...... 94

38. Regional stratigraphic cross section 5 of the lower Upper Cretaceous rocks from central Utah to western Nebraska ...... 95

39. Generalized time-stratigraphic correlation chart for Upper Cretaceous strata from Kaiparowits region to Raton Basin ...... 100

40. Regional stratigraphic cross section 6 of the lower Upper Cretaceous rocks from southern Utah to western Kansas ...... 101

41. Illustration and comparison of Airy and flexural backstripping schemes 110

42. Subsidence profiles (b and c) in response to the loading of a sedimentary wedge (a). The wedge represents the real geometry of strata on the regional stratigraphic cross section 5 of this study ...... 115

43. Tectonic subsidence profiles resulting from different backstripping schemes: a. Airy backstripping; b. flexural backstripping ...... 116

44. Exponential porosity -depth relationships used in decompacting the Cretaceous rocks of the Western Interior basin ...... 120

45. Effects of the underlying rocks on results of flexural backstripping. Profile a was obtained by ignoring the compaction of the underlying strata; profile b by decompacting the underlying strata. A siltsone lithology was used in calculations ...... 121

46. Qualitative representation of the flexural responses to loading. Curve 1 depicts flexure resulting from initial emplacement of a load, or an elastic response. Curves 2 and 3 dipict flexure involving viscous relaxation under a constant load ...... 130

47. Flexurally backstripped subsidence profiles across basin ...... 133

48. Temporal subsidence trends at six locations 100-150 km east of the thrust belt... 135

49. Flexural half wave-length as a function of lithosphere's elastic thickness...... 137

50. Best-fitting flexural profiles for the backstripped subsidence profiles across the Wyoming foreland ...... 139

51. Bi-modal distribution of continental lithospheric elastic thickness ...... 142

52. Distribution of continental elastic thickness Te versus age of lithosphere at the time of loading ...... 143

53. Interpretative diagram showing differential crustal shortening as a result of buttressing near Uinta Mt. and in southwestern Montana ...... 147

54. Diagramatic sketch of the paleotectonic blocks during the middle Proterozoic time...... 148

ix

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 55. Spatial variations in the present day lithospheric elastic thickness across parts of Idaho, Wyoming, and Utah ...... 150

56. Diagram illustrating the two main subsidence components in the Western Interior basin: flexural subsidence to the west and residual subsidence over the entire basin ...... 153

57. Eustatic sea level curve (heavy line) of Haq et al. (1988) and predicted sea level curves by Engebreston et al. (1992) using global spreading rate data (dashed lines) ...... 157

58. Vertical continental movements during the past 180 Ma ...... 159

59. Continental tilt model by Mitrovica et al. (1989). A. Schematic illustration of the net effect of Late Cretaceous subsidence and Tertiary uplift across Wyoming. B. The proposed tilting mechanism resulting from subduction and mantle convection ...... 162

60. Diagram showing changes in continental topography relative to sea surface during continental breakup ...... 165

x

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ABSTRACT

The tectonic subsidence history recorded in middle Cenomanian to early Campanian

(96 to 80 Ma) strata in the U.S. Cretaceous Western Interior basin was studied by

applying two-dimensional flexural backstripping techniques to six regional stratigraphic

sections across different segments of the basin. Results indicate that tectonic subsidence

over the 16 m.y. study interval consists of two distinct components: a westward-

increasing flexural subsidence confined within a few hundred kilometers of the thrust

belt, and a spatially uniform "residual" subsidence that affected the entire basin. The

residual subsidence does not represent signals of eustatic sea level changes but instead

reflects epeirogenic movements specific to the North American Western Interior. The

flexural component exhibits significant spatial and temporal variations along the strike of

the Sevier thrust belt. The greatest cumulative subsidence occurred in southwestern

Wyoming and northern Utah, whereas concurrent subsidence in northwestern Montana

and southern Utah was insignificant. Temporal trends in subsidence also show a distinct

regional pattern. From middle Cenomanian to late Turanian (96 to 90 Ma), subsidence

rates were high in Utah and much lower in Wyoming and Montana. In contrast, during

the Coniacian and Santonian stages (90 to 85 Ma) subsidence accelerated rapidly in

Wyoming, increased slightly in Montana, and decreased in Utah. The observed variations

in flexural subsidence were probably manifestations of basement structures, particularly

those zones of crustal weakness inherited from the Precambrian rifting and early

Paleozoic passive margin development.

xi

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 1 INTRODUCTION

A STATEMENT OF WORK

The past three decades have witnessed significant progress in our understanding of

the evolution of sedimentary basins. Plate tectonic concepts, particularly knowledge of

the physics of lithospheric processes, provide an elegant conceptual framework within

which to synthesize formerly separate geological data and comprehend the causes of

sedimentary basins. This theoretical breakthrough together with improved seismic,

gravity, borehole, biostratigraphic, and other geologic data has led to the development of

quantitative geophysical models for a great number and variety of basins. In such

models, basin subsidence history can be predicted according to theories of lithospheric

flexure or thermal cooling. In conjunction with backstripping techniques for data

reduction, the models have served as a powerful analytic tool furnishing valuable insights

into the tectonic mechanisms of various basins.

Foreland basins are distinct asymmetrical depressions coupled with orogenic belts.

Our understanding of these basins has been greatly enhanced by the use of quantitative

models (e.g., Stockmal et al., 1986; Beaumont et al., 1987). These models consider the

evolution of foreland basins as a result of lithospheric flexure under the loading of

orogenic belts. Such models have been used to predict foreland basin subsidence history,

or inversely, to extract information on the kinematics of orogenic belts or the attributes of

the lithosphere from basin stratigraphic records. In recent years, the burgeoning interest

in foreland basins and unprecedented computing capabilities have lead to the development

of highly integrated stratigraphic models (Flemings and Jordan, 1990; Jordan and

Flemings, 1991; Sinclair et al., 1991; Jervey, 1992). In these models, the kinematics of

orogenic belts, the resultant lithospheric flexure, sea level changes, and sedimentation

and erosion are all coupled together as independent variables that interact to determine the

1

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2

stratal stacking pattern and facies distribution. To field geologists, these models promise

to provide a theoretical framework to guide observations of particular stratigraphic,

sedimentologic, and structural expressions that are otherwise hidden or difficult to

comprehend.

As attention focused on the development of quantitative foreland basin models,

however, inadequate efforts went into collecting geologic data to document basin

subsidence history and patterns. More often than not, quantitative models are developed,

but their viability and geologic relevance go unchecked. The models, though impressively

capable in predicting particular stratal architectures, appear to be outstripping the data

needed to calibrate and test them. Unless deliberate efforts are taken to address this

discrepancy, further progress in developing realistic basin models will be hindered.

This dissertation is an effort pointed toward bridging the gap between foreland basin

models and observations. It focuses on the regional tectonic subsidence history and

mechanisms of the U.S. Western Interior basin during the Cretaceous Period (Fig. 1).

Although arguably one of the best understood foreland basins in the world, the Western

Interior basin has not been systematically studied with respect to its subsidence history on

sufficiently large spatial and refined temporal scales. Hence, many attributes and

complexities of this 'classic' foreland basin remain poorly understood. The overall

objective of this dissertation is to document basin subsidence history as preserved in the

stratigraphic record across different parts of the basin so that relevant basin models can be

evaluated. To achieve this, a regional stratigraphic data base was first compiled by

integrating a large amount of surface and subsurface stratigraphic data from the U.S.

Western Interior. Then, flexural backstripping techniques were applied to extract the

tectonic subsidence history from this stratigraphic data base. On the basis of this

documentation, possible tectonic mechanisms of basin formation and evolution were

evaluated. Results of this study present significant new data and insights into the tectonic

control on the development of the Western Interior basin. Beyond the immediate concern

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ,___ ARCTIC OCEAN

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Figure 1. The Cretaceous Western Interior Seaway during late Campanian time From Gill and Cobban (1973).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4

on this basin, these results are also of value in the generation of more realistic models in

the future.

THE CRETACEOUS WESTERN INTERIOR BASIN, A TECTONIC OVERVIEW

The interior of western North America was occupied by a large epeiric seaway during

much of the Cretaceous (Fig. 1). At its peak, the seaway connected the Arctic ocean and

the Gulf of Mexico, a longitudinal distance of more than 5,000 km, and reached a width

of 1,000 km or more. Lithofacies deposited proximal to the Cordilleran fold and thrust

belt on the western side of the basin are composed of intertonguing non- and marginal

marine sandstone and marine shale, and those on the eastern platform of the basin are

dominated by marine limestones and shale.

The Western Interior basin is an excellent locale for understanding the coupled

relationships between tectonic factors and foreland basin development (Price, 1973;

Bond, 1976; Kauffman, 1977a; Cross and Pilger, 1978; Cross, 1986; Beaumont, 1981;

Jordan, 1981; Heller et al., 1986; Mitrovica et al., 1989; Gumis, 1990). There are two

important reasons for this. First, there are abundant biostratigraphic and lithostratigraphic

data for the Western Interior basin. These data have made the Western Interior basin a

fertile ground for the development and testing of many stratigraphic as well as

sedimentologic concepts (Kauffman and Caldwell, 1993). Secondly, the structures in the

Cordilleran fold and thrust belt are fairly well preserved for direct observational

information (Armstrong, 1968; Price, 1973; Royse et al., 1975). Therefore, information

on the styles of thrusting and amount of crustal shortening can be integrated into foreland

basin models.

Many plausible models bearing directly or indirectly on the Western Interior basin

have been proposed. In general, they emphasize in different manner the roles of tectonic

loading, sublithospheric processes, eustatic, and sedimentary factors. Figure 2 is a

generalized stratigraphic cross section accompanied by a simple illustration of a foreland

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LA -IOWA- 3 0 0 0 m Stable Eastern Platform □ Marineshale Limestoneand chalk NEBRASKA JCANSAS AND. ********** A kAAAAAAAAAA kAAAAAAAAAA A A] AAAAAAAAAAA AAAAAAAAAAA A] _6l sandstone Fox H illsss Marine/coastal "HingeZone": Moderate Subsidence i mudstone Non-marine -COLORADO- Zoneof High Subsidence Non-marine Conglomerate [Frontier Fi Foreland Basin Foreland Fill Flexural Subsidence Belt Zoneof Max. Subsidence ^_^.Thrust -UTAH- tectonic zones"" proposed by Kauffman (1985). 2 b: foreland basin subsidence model. Figure 2 a: Generalized stratigraphic cross section ofthe Western Interioirbasin by King (1977). Also shown are b a

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6

basin model. Price (1973) first hypothesized that the Western Interior foreland basin

resulted from isostatic flexural subsidence in response to the vertical loading of

supracrustal rocks tectonically thickened by thrusting. This mechanical linkage between

basin and thrust belt was subsequently tested in the framework of quantitative

lithospheric flexural models by Jordan (1981) and Beaumont (1981). Their models

demonstrated that the asymmetrical stratigraphic architecture observed within a few

hundred miles of the thrust belt can be explained by lithospheric flexure. Since then,

these models have served as a useful guide to understanding the tectonic control on

foreland basin stratigraphy in the Western Interior and other basins.

Despite the impact of these studies, a growing body of evidence suggests that the

Cretaceous Western Interior basin can only be partially described by flexural models. For

example, the basin is much wider than the flexural depressions predicted by any model.

This anomaly is reflected in nearly 1 km of Cretaceous rocks deposited in the cratonic

interior, as far as 1000 km away from the Sevier thrust belt (Fig. 2 a). Lithospheric

flexure under thrust loading, unaccompanied by additional mechanisms, can not explain

such a broad basin dimension. Finding a viable complementary tectonic mechanism has

not been an easy task. Furthermore, previous studies have essentially treated flexural

mechanisms of the Western Interior foreland basin as a two-dimensional case. Although

this generalization is a reasonable first order approximation, its usefulness beyond the site

of observational controls is questionable. Recent studies of foreland basins have

documented that spatial variations in the flexural subsidence may be the norm rather than

the exception (Waschbusch and Royden, 1992).

Drawing on the general lithofacies pattern of the observed basin fill and foreland

basin models, Kauffman (1985) proposed that spatial variations in basin subsidence

divided the Western Interior basin into a series of longitudinal zones (Fig. 2 a). These

zones occur from west to east in the following order: a western foredeep zone of

maximum subsidence, a west-median trough of high subsidence, an east-median hinge of

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7

moderate subsidence, and an eastern platform of low subsidence. Because of its

speculative nature, however, this characterization of the spatial subsidence pattern has yet

to be corroborated by quantitative subsidence and detailed stratigraphic data.

Cross (1986) provided a regional synthesis on the development of the Cretaceous

Western Interior basin in the context of Farallon Plate subduction beneath North America

Plate. He suggested that lithospheric flexure by thrust loading was most effective in the

early phase of the basin subsidence history during early Late Cretaceous. With the onset

of low-angle subduction of the Farallon Plate in the Late Cretaceous, Cross (1986)

argued, a broad downwarping centered in Wyoming and Colorado occurred in response

to sublithospheric loading and cooling, which dominated over the lithospheric flexure

caused by thrust loading.

Although these and other works collectively enhanced our understanding of the basin,

a coherent explanation of basin development that can accommodate separate facets of the

basin stratigraphy and tectonic setting remains elusive. The quest for such a

comprehensive model demands a thorough and accurate understanding of basin

subsidence history.

OBJECTIVES

The first objective of this dissertation is to provide an improved documentation of the

subsidence history of the Western Interior basin in both spatial extent and temporal

refinement, a step that is long overdue. To do this, two-dimensional flexural

backstripping techniques were applied to six regional stratigraphic cross sections

extending east-west across the basin from Montana and North Dakota to southern Utah

and New Mexico. These sections were constructed with subsurface data and

biostratigraphically calibrated with outcrop megafossil data. The approach and scope

taken here enables sampling of the temporal and spatial variations in basin subsidence on

many different scales.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8

The second objective of this dissertation is to explore the tectonic mechanisms of the

observed subsidence in the framework of foreland basin models. The objective consists

of two parts. First, tectonic subsidence observed in the foreland area is evaluated both

quantitatively in terms of an elastic lithospheric flexural model and qualitatively in the

context of basement tectonics. This provides a perspective on the spatial and temporal

significance of lithospheric flexure and thrust loading in the Western Interior basin.

Secondly, with the flexural subsidence identified and separated, th e" residual"

component of subsidence observed in the eastern cratonic interior can then be evaluated.

This regional subsidence component, indistinguishable from a eustatic sea level rise if

considered in isolation, has long been overlooked in previous studies. In view of this,

this study demonstrates its significance to the development of the Western Interior basin

and suggests that it may originate in the dynamic topographic effects of mantle convection

and subduction.

DISSERTATION STRUCTURE

This dissertation consists of seven chapters including this introductory chapter.

Chapter 2 provides a literature review of the tectonic history of the western North

American craton from the Precambrian to the Tertiary. Attention is focused on the tectonic

events and processes that shaped basement heterogeneity, and the styles and timing of

thrusting during the Cretaceous. This information is essential for discussion of flexural

subsidence and its relation to the basement and thrust tectonics. Chapter 3 describes the

stratigraphic data base as well as the procedures used in constructing the regional cross

sections. Chapter 4 discusses the concepts and application of backstripping techniques.

The procedures of two-dimensional flexural backstripping techniques are discussed with

reference to the Cretaceous stratigraphic data. Chapter 5 presents an analysis of the

flexural subsidence both in terms of lithospheric flexural models and in the context of the

basement and thrust tectonics. Chapter 6 discusses the pattern of the platform subsidence

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. and its probable causes. Conclusions are given in Chapter 7. The seven chapters

complement each other and present a coherent analysis of the subsidence history of the

Cretaceous Western Interior basin.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 10

CHAPTER 2

THE TECTONIC FRAMEWORK OF THE CRETACEOUS WESTERN INTERIOR BASIN, U.S.A.

INTRODUCTION

Prior to the development of the Cretaceous Western Interior basin, the western North

American continent had been shaped by a succession of distinct tectonic episodes dating

back to the Precambrian. In highly generalized terms, these include early Proterozoic

crustal accretion in southwestern U.S., late Proterozoic rifting, early Paleozoic passive

margin development, middle Paleozoic accretionary tectonics, Pennsylvanian-Permian

Ancestral Rocky Mountain deformation, and the early Mesozoic transformation into an

active margin. Each episode brought about profound changes in the tectonic regime and

depositional setting. Tectonic features acquired in an earlier episode commonly persisted

to exert influence on subsequent tectonic and sedimentary patterns.

Fundamentally, the Cretaceous Western Interior basin is a consequence of the

accelerated sea floor spreading and subduction in the late Mesozoic following the break­

up of Pangaea. Subduction of the Farallon Plate beneath the North American Plate

initiated a north-south trending orogenic belt, the Cordillera fold-thrust belt. The Western

Interior basin was formed in response to the crustal shortening and loading by this b elt.

Though a direct consequence of Mesozoic orogenic loading, the Western Interior

basin was also affected by older tectonic features such as the geometry of basement

trends and faults/lineaments inherited from the latest Proterozoic rifting. Therefore,

analysis of the Cretaceous subsidence history requires knowledge of the pre-existing

tectonic conditions. This chapter provides a literature review of the tectonic history of the

western North American continent as it evolved from Precambrian to the late Mesozoic.

In composing this review an effort was made to maintain the continuity of the tectonic

history as presented. However, emphasis was placed on those aspects thought to be of

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greatest relevance to the Cretaceous subsidence history. Essentially, they include

basement structural features that had persistent effects on Phanerozoic sedimentation and

the styles and timing of thrusting in different sectors of the Sevier belt.

Because of the enormous scope and intrinsic complexity of this subject, much of the

discussion is stripped to bare essentials and, inevitably, certain important views or

references on a particular issue may be overlooked. Limited as it is, this document

provides an independent source of constraints for subsequent analysis of subsidence

data.

PRECAMBRIAN PROVINCES AND BASINS

Archean Provinces

The Phanerozoic sedimentary cover of the North American Western Interior is

underlain by Precambrian metamorphic and plutonic rocks that comprise several

lithotectonic provinces (Fig. 3). The nuclei of these provinces are generally considered to

have been separate Archean microcontinents, which were gradually assembled into a

coherent craton during the Early Proterozoic by collisional orogens and by crustal

accretion along their margins (Bickford, 1988a; Hoffman, 1989; Reed et al., 1993). The

Wyoming Province, which includes parts of Wyoming, Montana, eastern Idaho, and

northernmost Utah, is one of the oldest and largest Precambrian provinces in the U.S. It

is bordered to the east by the Superior Province and to the north by the Heame Province.

The boundary between the Wyoming and Superior Provinces is an Early Proterozoic

collisional zone that extends across North and South Dakota. This boundary is known as

the Trans-Hudson orogen or the Dakota mobile belt (Bickford, 1988a). The boundary

between the Wyoming and Heame Provinces is concealed from direct observation, but it

is inferred to be a northeast-southwest trending Early Proterozoic crustal discontinuity

named the Great Falls tectonic zone (Hoffman, 1989). South of the Wyoming Province,

in Colorado, southern Nebraska, Kansas, and New Mexico, basement rocks are early

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. VN»

-GFi SUPERIOR^',/. * * t * **rmMS±t kr^

Archean greenstone 2.3-2.1 Ga 2.0-1.8 Ga 1.9-1.8 Ga granite-gneiss provinces Juvenile(?) crust thrust-fold belts Juvenile crust

2.0-1.8 Ga ].8-1.6Ga 1.3-1.0 1.1 Ga magmatic arcs Juvenile crust imbricated crust continental rift

Figure 3. Precambrian tectonic elements of the North American craton. BH, Black Hills inlier; CH, Cheyenne belt; GF, Great Falls tectonic zone; KR, Keweenawan rift; THO, Trans-Hudson orogen; VN, Vulcan tectonic zone. Archean rocks are undifferentiated. Modified from Hoffman (1989).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. //////✓✓////✓✓XX// //////////////////////// ////✓✓/////////////////////////✓ ✓///////✓////////////✓////////✓/////// ///////////////✓////✓/✓//./✓/✓//////// //// //////✓//////✓////////////✓✓/✓/////////// //////////////////////////////// ///////✓///////✓///✓/////// ////////////✓ ////// //////////// /////

N orth

American///i

~ ^ [ates

Craton

uinta Basin

Figure 4. Protrozoic basins along the Cordillera. Dashed patterns in northwest part of craton indicate possible extension of craton. From Harrison et al. (1974).

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Proterozoic in age. These rocks have been interpreted as arc-affiliated oceanic rocks

accreted to the Archean Wyoming Province during the early Proterozoic (Bickford,

1988b; Hoffman, 1989; Tonnsen, 1986). The boundary between the Wyoming Province

and these younger, accreted Proterozoic rocks is a major crustal discontinuity or suture

zone, named as the Cheyenne belt (Duebendorfer and Houston, 1986,1987).

Proterozoic basins

During the Middle Proterozoic, widespread extensional tectonics attenuated the crust

along the western margin of the Heame and Wyoming Provinces and resulted in several

large Proterozoic basins (Fig. 4; Harrison et al., 1974; Link, 1993; Hoffman, 1989;

Tonnsen, 1986). Strata deposited in these basins range in age from 1.8 Ga to 0.8 Ga,

including the Belt Supergroup, Big Cottonwood Formation, Uinta Mountain Group,

Grand Canyon Supergroup, and the Apache Group (Link et al., 1993).

The Belt basin, which extends from southern British Columbia to the Snake River

plain, accumulated some 18 km of fine-grained, quartz-rich, clastic sediments and

subordinate carbonates. These sediments are mostly Middle Proterozoic in age and are

collectively known as the Belt Supergroup. The southernmost part of the basin extended

inland into central Montana, forming the Helena embayment or rift system (Winston,

1986; Oldow, 1989). Southwest of the Belt basin in central Idaho was a major

Proterozoic landmass referred to as the Belt Island (Ruppel, 1986). The Belt basin has

been interpreted to have formed on attenuated Archean crust in an intracratonic rift

(Winston, 1986) or remnant back-arc basin setting (Hoffman, 1989).

In northern Utah, the Proterozoic Uinta Basin (Uinta trough or aulacogen) developed

in close contemporaneity with the Belt basin. The basin fill strata, named the Uinta

Mountain Group or Big Cottonwood Formation, are Middle or early Late Proterozoic in

age (Link, 1993; Hoffman, 1989). The Uinta Mountain Group is found only in

northeastern Utah, where it consists of up to 7 km of quartzites and shale and lies

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unconformably on the early Proterozoic metasediments. These quartzite-rich sediments

form the core of the Uinta Mountain today. Immediately to the west in the Wasatch

Mountains, the Big Cottonwood Formation consists of as much as 4 km of more

metamorphosed quartzites and shale. Sediments of the Uinta Mountain Group and Big

Cottonwood Formation outline a west-east trending aulacogen located near the western

extension of the Cheyenne belt (Fig. 3 and 4).

Late Proterozoic rifting

The Late Proterozoic marked a period of intensified continental rifting before the

development of a passive margin in the early Paleozoic. Sedimentary rocks of this age are

fairly extensive in Canada, as represented by the Windermere Group, but only

sporadically preserved in the U.S. (Stewart, 1972; Stewart and Poole, 1974; Hoffman,

1989; Link et al., 1993). These rocks consist mainly of immature glaciogenic elastics and

volcaniclastics marking episodic rifting events. They form a narrow, westward

thickening belt along the west margin of the North American craton (Fig. 5a).

Toward the end of the Proterozoic, a continental fragment was rifted away from the

western margin of the North American craton during the breakup of the Proterozoic

supercontinent (Stewart, 1972; Armin and Mayer, 1983; Bond and Kominz, 1984). This

rifting event resulted in a passive margin that persisted virtually uninterrupted until the

Devonian (Fig. 6). Figure 7 is a tectonic subsidence curve by Kominz and Bond (1991)

showing the subsidence history of the Western U.S. from Cambrian to Pennsylvanian

time. This curve depicts the thermal subsidence on a newly developed passive margin.

The boundary between the attenuated passive margin crust and the cratonic crust

defines an important tectonic feature, the Cordilleran hingeline (Fig. 6; Picha, 1986;

Picha and Gibson, 1985; Allmendinger et al., 1987,1986). The Cordilleran hingeline

largely coincides with the much younger Sevier thrust front in Utah (Allmendinger et al.,

1987,1986). West of the hingeline, late Proterozoic and Paleozoic strata thicken

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'-"V"

t—

-----1

j — 100 200 300 mi 300 Km

Figure 5. Isopach maps of: a, Precambrian and Lower Cambrian rocks; b, Cambrian, Ordovician, and Silurian rocks. Contours are in feet. From Stewart (1972).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. HINGELINE' '^CONTINENTALCRUST \\\ \ N\ NS\\\\\\S\\\ N\ \ \\\ Nevada WEDGE'~~~x~~ X v v v R I F T STAGE CRUST ,,S///////////mOGE

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. oo 250 PERM. 300400 350 450 ORDOVICIAN SEL. DEVONIAN MISS PENN. 500 CAMBRIAN 550 Ma “ - 5 0 0 - NorthAmerica. Thecurve is representative ofnorthern Utah. From Kominz andBond (1991). Figure 7. Tectonic subsidencecurve showing the early Paleozoic passive margin subsidence history ofwestern 1500 - 1000 2000 meters

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 19

markedly, whereas east of it, platform sedimentation accompanied by subdued tectonic

activities prevailed through much of the Phanerozoic (Fig. 5a and b).

Basement faults

The normal faults associated with the latest Proterozoic rifting and those associated

with the earlier Belt basin development shaped the geometry of the Precambrian basement

in the western North America. Most of these faults were formed at high angles to the

Cordilleran hingeline (Fig. 8), creating promontories and embayments along the passive

margin strike (Kulik and Schmidt, 1988). During the late Mesozoic Sevier orogeny, these

old passive margin promontories and embayments might have been an important factor

controlling the style and orientation of the thrust belt (Kulik and Schmidt, 1988;

Allmendinger et al., 1983). The faults themselves also served as long-lived crustal

fractures that were periodically reactivated during the Phanerozoic to affect the lithofacies

and thickness patterns of sediments deposited nearby.

A few such structures are particularly noteworthy. In Montana, the east-west trending

Perry (Willow Creek) and Garnet faults along the periphery of the Helena embayment

were periodically reactivated to influence not only Paleozoic and Mesozoic sedimentation,

but also the formation of lateral thrust ramps during the Sevier orogeny (Harrison et al.,

1974; Fryxell and Smith, 1986; Winston, 1986; Peterson, 1986; Kulik and Schmidt,

1988; Wallace et al., 1990). In northern Utah, the boundary-normal faults of the

Proterozoic Uinta trough marked the western extension of the Cheyenne belt. These

faults were intermittently active during the Proterozoic and Paleozoic, affecting the

sedimentation on opposite side of the faults (Bruhn et al., 1986; Bryant and Nichols,

1988). In the Tertiary, however, they were tectonically inversed into reverse faults

creating the Uinta Mountain (Gries, 1983). In central Utah, Picha and Gibson (1985) and

Picha (1986) identified not only a major north-south trending Precambrian normal fault,

the Ancient Ephraim Fault, but also four other northeast- and east-trending lineaments

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Lineaments or normal faults of probable Precambrian age

Lineaments or faults of Mesozoic age

100 200 miles

Figure 8. Normal faults and lineaments along the Sevier thrust front or the Cordilleran hingeline. Modified from Kulik and Schmidt (1988) and Picha and Gibson (1985). 1: Lemhi Arch; 2: Lewis & Clark lineament; 3: Transverse zone; 4: Ancestral Cache Creek fault; 5: Uinta trough margin faults; 6: Leamington lineament; 7: Scipio lineament; 8: Cove Fork lineament; 9: Paragona lineament; 10: Ancient Ephraim fault.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 21

(Fig. 8). These lineaments were interpreted to be zones of crustal weakness associated

with the latest Proterozoic rifting. They were reactivated as tear faults in the late Mesozoic

to sever the continuity of the Sevier thrust belt.

PALEOZOIC OROGENIES

The early Paleozoic passive margin

The passive margin setting initiated by the latest Proterozoic rifting became well

established in the early Paleozoic. From the Cambrian to the Devonian, sedimentation on

this passive margin proceeded largely uninterrupted with deposition of extensive clastic

and carbonate shelf sediments. These sediments assume the form of an elongated,

westward-thickening wedge subparallel to the Cordilleran hingeline (Fig. 5b; Peterson

and Smith, 1986). Contemporaneous tectonic activities in the cratonic interior were

insignificant; the only known large-scale structure is the Transcontinental Arch, a

northeast-southwest trending paleotopographic high that was most evident from the early

Paleozoic sedimentation patterns (Sloss, 1988).

The Antler orogeny

In Middle Devonian time, a volcanic arc formed offshore and migrated toward the

western North American passive margin (Speed et al., 1988). In Early Mississippian

time, oceanic rocks of the Roberts Mountains allochthon, derived from this arc, were

emplaced eastward over the continental shelf of the Paleozoic passive margin. This event,

widely known as the Antler orogeny, marked the advent of accretionary tectonics in

western North America (Poole, 1974; Dickinson, 1977; Nilsen and Stewart, 1980; Speed

and Sleep, 1982; Dorobek et al., 1991). In response to the tectonic loading of the

emplaced allochthon, an elongated foreland basin parallel with the Cordilleran hingeline

was formed by lithospheric flexure on the former passive margin (Speed and Sleep,

1982). On the gentle, eastern side of the foreland basin near the Cordilleran hingeline,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. to to EAST BASIN W1LLISTON Big Snowy Group 5;W 5;W o W Madison Ls gSfif 3 SHELF CRATONIC Mission Canyon Ls LOWER SHELFMARGIN Lodgepole Ls MIOGEOCLINE CORDILLERAN I 50 km White Knob & MonroeCanyon Ls M cGowanCreek Fm Middle Canyon Fm IDAHO I MONTANA 300 m Figure 9. A generalized stratigraphicModified fromcrosss Rose section (1976). ofthe Antler foreland basin. UPPER SHELF MARGIN ANTLER HIGHLAND WEST

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 23

fine-grained clastic and carbonate sediments dominated (Fig. 9). On the steep, western

part of the basin, coarse clastic sediments shed from the rising Antler highland rest on

outer shelf or slope facies of the early Paleozoic passive margin. Subsidence analysis by

Dorobek et al. (1991) indicates that the flexure across the Antler foreland basin was

complicated by differential subsidence associated with the reactivation of Precambrian

faults/lineaments. Specifically, isopach maps and sections across Idaho and western

Montana indicate that the subsidence across the basin was highly variable, exhibiting

apparent reversals of basement movement at different times. The locations of major

troughs in the Antler foreland coincide largely with the Precambrian faults/lineaments,

suggesting that the crustal heterogeneity inherited from Precambrian tectonics played an

important role in distorting the Antler flexural subsidence pattern.

The Ancestral Rocky Mountain deformation

From Late Mississippian through Pennsylvanian time, tectonic activities propagated

from the plate boundary into the cratonic interior. This intracratonic tectonic interval,

limited to the accreted early Proterozoic crusts in Colorado, Utah and adjacent areas, is

referred to as the Ancestral Rocky Mountains deformation (Fig. 10; Kluth, 1986). The

dominant tectonic elements are uplifts bounded by high-angle faults of both normal and

reverse types, some of which had Precambrian ancestry (Stevenson and Baars, 1986).

The main uplifts are the Uncompahgre and Front Range highlands, and the major basins

include the Paradox and Central Colorado troughs. The origin of the Ancestral Rocky

Mountains deformation has been difficult to decipher chiefly because much of the

evidence for its existence, severely overprinted by the Laramide orogeny, has been

derived from stratigraphic studies (Oldow et al., 1989). Eardley (1962) hypothesized that

the Ancestral Rocky Mountains deformation was related to the coeval collisional tectonics

in the Ouachita Mountains. Kluth and Coney (1981) and Kluth (1986) further suggested

that this tectonic episode probably took place in a transpressional tectonic regime driven

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m

Apishipa Highland

TOl w y . Arkose ^ » rafA

Evapontes 200 mi I I 200 km

Figure 10. Principal tectonic elements of the Ancestral Rocky Mountain orogeny during Middle and Late Pennsylvanian time. From Lindsey et al. (1986), modified from Mckee et al. (1975).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 25

by the continental collision between South and North American. Regardless of its exact

cause, there is little doubt that as a result of the Ancestral Rocky Mountains deformation

the basement rigidity was further weakened by its block faulting along pre-existing or

new faults/lineaments.

Transformation into an active margin

In Late Permian time, another volcanic arc was migrating from offshore toward the

North American plate. In Early Triassic time, arc-affiliated oceanic rocks of the Golconda

allochthon were emplaced eastward across the continental shelf of the Nevada continental

margin and onto the earlier Roberts Mountains allochthon. This is the so-called Sonoma

orogeny. Unlike the Antler orogeny, the Sonoma orogeny generated no conspicuous

foreland basin on the cratonic side (Speed and Sleep, 1982). Following the Sonoma

orogeny, the western margin of the North American continent began a dramatic

reorganization. An active margin was formed in Late Triassic time. From that time to the

Late Cretaceous, over a span of 100 m.y., east-dipping subduction proceeded along this

active margin in a manner analogous to many modem subduction zones (Atwater, 1989).

THE SEVIER OROGENY

Style of deformation

As a result of the convergence between the North American and Farallon plates in the

late Mesozoic, a north-south trending fold-thrust belt, the Cordilleran orogenic belt, was

formed inland of the Sierra Nevada-Klamath volcanic arc on the western margin of the

North American craton (Fig. 11). The U.S. part of the Cordillera is referred to as the

"Sevier orogenic belt" (Armstrong and Oriel, 1965; Armstrong, 1968; Beutner, 1977).

The eastern front of the Sevier belt follows closely the Cordilleran hingeline or "the

Wasatch Line" of Utah (Allmendinger et al., 1983; Cross, 1986; Picha, 1986; Kulik and

Schmidt, 1988).

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Laramide uplifts

500 km

Figure 11. Sketch map of the Cordilleran region showing the Cretaceous Sevier orogenic belt relative to the Laramide trend and other tectonic elements at the time of the Mesozoic/Cenozoic boundary. From Dickinson and Snyder (1978).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 27

The Sevier belt is characterized by east-vergent thrusting and folding in the Paleozoic and

Mesozoic sedimentary cover above gently west-dipping ddcollements in weak horizons

(Armstrong, 1968; Armstrong and Oriel, 1965; Royse et al., 1975; Royse, 1993;

Wiltschko and Dorr, 1983). Thrust sheets cut successively younger rocks as they moved

eastward along the dgcollements. Generally, the youngest thrust is structurally the lowest

and closest to the foreland. Multiple episodes of thrusting and folding led to progressive

eastward-directed crustal shortening in excess of 100 km in many places across the

orogenic belt (Elison, 1991). The shortening was accommodated entirely within the

sedimentaiy cover by displacement along stair-step thrust faults, by folding of thrust

plates, or by internal shortening in sedimentary rocks (Wiltschko and Dorr, 1983).

Because decollements separate the shortened sedimentary rocks above from the

undeformed crystalline basement below, this style of deformation has been widely

referred to as the 'thin-skinned' in contrast to the 'basement-involved' Laramide tectonic

style that characterized the latest Cretaceous-early Tertiary foreland (Cross, 1986).

Times o f Movement

Thrusting along the Sevier belt proceeded through time in a discrete, sequential

manner (Fig. 12). The initial thrusting probably occurred between latest Jurassic and

Early Cretaceous. A recent estimate by Heller et al. (1986) based on subsidence analysis

placed the initial thrusting as late as Aptian age. Despite this ambiguity, thrusting was

probably in full progress by Late Cretaceous time along the Sevier belt. Possible

exceptions may exist in western Montana, where no unequivocal evidence exists to

indicate so (Ruppel and Lopez, 1984). Overall, thrusting remained active throughout the

Late Cretaceous and well into the Tertiary, a period of more than 50 m.y.

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:fy/; w id e Pm North North £ w South £ [vGroup ;VvV [vGroup CodyShale W. WYOMING ...*.■ M esavetde Fra ,W.* %’• S**\\\',\ ,W.* %’• .jwGamet Thrusts Thrusts m m Limestone •. » • . : •. .*». shorn Fm sandstone and conglomerate Conglomerate Unconformity Q aggett Shale ’V* V* V*V«V» V»V*i*. V»V*i*. V*V«V» V* ’V* - .VA-.V.V.V.-.vT’ JudithRiver fin ^ North £ ^ South W. MONTANA Shale m nonmanne Marineand Nonmarine sandstone Silicious Thrusts Aptian Albian Turanian Barremian Coniacian Santonian Campanian Cenomanian Maastnchian SP=Sapphire, GH= Grasshopper, EH=Elkhom, P=Paris, M=Meade, C=Crawford, A=Absaroka, D=Darby, CR= Canyon thepossible duration ofthrustinga event. Generalizedbasin stratigraphy eachat segment is shownin west-east trending cross-sectional columns. Compiled from authors mentioned Abbreviationsthein text. for thrusts: ML= Medicine Lodge, Range, PI andP2=Pavant, P&G=Paxton and Gunnison. Figure 12. Chart showing the thrust chronology atthree segments ofthe Sevierbelt. The length the blockof barrepresents 80 90 70 120 110 Ma 100

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 29

Montana:

The fold and thrust belt in western Montana is broken up into three segments by the

east-west trending Lewis and Clark Lineament and the Transverse Zone (or the Perry

Line; the Willow Creek Fault) (Fig. 8 and 13; Schmidt et al., 1988; Eldredge et al.,

1988). These lineaments represent zones of crustal weakness inherited from the

Precambrian Belt Basin. They were reactivated intermittently since then and eventually

became tear faults during the development of the Sevier belt (Ruppel and Lopez, 1984;

Kulik and Schmidt, 1988). North of the Lewis and Clark Lineament is a series of thrust

faults collectively known as "Disturbed Belt" (Mudge, 1970). These thrusts were

emplaced from west to east in early Tertiary time, equivalent in age to the easternmost

thrust faults in the Idaho-Wyoming salient, such as the Darby thrust (Mudge and

Earhart, 1980). The cumulative horizontal displacement across the Disturbed Belt is

estimated at between 60 - 80 km (Mudge and Earhart, 1980).

Between the Lewis and Clark Lineament and the Transverse Zone is the Helena

Salient, where two major thrust systems are recognizable: the Sapphire to the west and

those curved thrusts in the Helena Salient to the east, such as the Lombard thrust (Fig.

13). Movement on the Sapphire thrust is estimated to be Santonian to early Campanian in

age, with a total displacement of 50 - 65 km (Ruppel et al. 1981; Ruppel and Lopez,

1984; Mudge and Earhart, 1980; Elison 1991). The Lombard thrust lying to the east of

the Sapphire thrust is dated roughly as Campanian to Maastrichtian (75-73 Ma) (Cross,

1986).

South of the Transverse Zone, structural relationships of the east-directed thrust faults

become even more complex. The added complexity stems from involvement of the

foreland basement (Kulik and Schmidt, 1988). Ruppel (1978) and Ruppel et al. (1981,

1984) mapped two major thrust systems and many associated imbricate thrust faults in

southwestern Montana: the Grasshopper thrust system, which is structurally lower and

younger, and the Medicine Lodge thrust system, which is structurally higher and much

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. o WYOMING HELENA EMBAYMENT TransverseZone Plate K Snake RiverPlai CANADA MONTANA Boulder Batholith^ J J > ite ite f Grassh Sapphire Idaho '%'Batholith Idaho Batholith too 50 km LO IDAHO Snowcrest Uplift. Modified from Schmidtet al. (1988) and Kulikand Schmidt (1988). Figure Schematic13. map showing the majorstructural features ofwestern Montana. BSU is Blacktail

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 31

larger (Fig. 13). Movements on individual thrusts of the two thrust systems are poorly

dated. According the postulated age of the synorogenic conglomerates of the Beaverhead

Formation presumably derived from these thrusts, Ruppel and Lopez (1984) inferred that

thrust movements could span the entire Late Cretaceous. However, a new palynological

study of the Beaverhead Formation suggests that thrusting in southwestern Montana did

not begin until early Campanian (Nichols et al., 1985, see the correlation chart by

Johnson and Sears, 1988, p. 232). Ruppel and Lopez (1984) considered the

Grasshopper thrust system to be partially equivalent to the Sapphire thrust system to the

north.

Wvominp-Idaho:

The timing of Sevier thrusting is better constrained in the Idaho and Wyoming salient,

where several discrete episodes of thrusting, ranging in age from Late Jurassic to early

Eocene, have been recognized and dated over the years (Fig. 12,14; Armstrong and

Oriel, 1965; Royse et al., 1975; Wiltschko and Dorr, 1983; Oriel and Armstrong, 1986;

Coogan, 1992; DeCelles et al., 1993).

The Sevier thrust belt in Idaho-Wyoming-Utah forms a broad, eastward-convex

salient that is 320 km long and 100 km wide (Fig. 15). From west to east, in order of

progressively younger ages, the major thrusts are: Paris, Meade-Crawford, Absaroka,

Hogsback- Darby, and Prospect. These thrusts have been studied in great details by

many authors with respect to the timing and the amount of crustal shortening (Armstrong

and Oriel, 1965; Jordan, 1981; Wiltschko et al., 1983; Oriel and Armstrong, 1986). As a

result, their movements are the best understood along the entire Sevier belt.

The Paris thrust of southeastern Idaho has the longest history of movement (Fig. 12,

13). Its initial movement is indicated by the synorogenic conglomerates in the late

Jurassic lower Ephraim Formation of the Gannet Group. Marine mollusks have been

reported in the lower, pre-orogenic Ephraim Formation. These, along with other evidence

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. to East West 120 140 100 80 40 ■60 Albian A ptian Eocene Santonian T uranian Paleocene C oniacian N eocom ian C am panian Maastrichtian C enom anian JURASSIC and fault in the adjacent foreland. Modified from Oriel and Armstrong (1986) and Craddock, Kopania, and Figure Timing14. ofmajor thrust faults in the Idaho-Wyoming salientand the contemporaneousuplift Wiltschko (1988). ! i

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7T77 ------VTeton Range £Snake ^River w (% Gros Ventre ^Plain Range \ \V (Jackson'4A/s‘\\

gj Quaternary and Tertiary volcanic rocks □ Precambrian rocks Thrust fault

SO km 'Kemmerer

Coalville

Salt Lake City

Figure 15. Generalized tectonic map of the Idaho-Wyoming salient showing the locations and extent of the major thrust faults. Modified from Oriel and Armstrong (1986).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 34

reviewed by Armstrong and Oriel (1965), date the initial movement of the Paris thrust as

latest Jurassic/early Cretaceous time. Subsequent movements on the Paris thrust are also

indicated by deposition of several other synorogenic clastic wedges described in their

paper. The Paris thrust dies out southward in northern Utah, where the Willard thrust has

been considered its equivalent (Royse et al., 1975). However, Bryant et al. (1988)

pointed out that the Willard thrust may connect with the younger Meade thrust. The

cessation of the Paris thrusting is poorly constrained because the oldest sedimentary

rocks above the Paris fault trace are of Pliocene age. Nevertheless, the major movements

on the Paris thrust probably occurred in the early Cretaceous (Wiltschko and Dorr,

1983).

Directly east of the Paris thrust are the Meade and the Crawford thrusts (Fig. 15). The

traces of the two thrusts occupy the same structural and stratigraphic position, and

therefore they have been considered as two segments of one thrust system (Royse et al.,

1975). Closely related as they were, however, estimates of their timing of movement

differ. Based on palynologic data and interpreted ages of the synorogenic clastic deposits,

the initial movement on the Meade thrust was estimated to be either of Albian (Oriel and

Armstrong, 1986) or Coniacian age (Wiltschko and Dorr, 1983), and that on the

Crawford thrust Coniacian or earliest Santonian age (Jacobson and Nichols, 1982;

Wiltschko and Dorr, 1983). Recently, a reexamination of the Meade and the Crawford

thrusts by DeCelles et al. (1993) suggests that the Meade thrust is part of the Paris thrust,

unrelated to the Crawford thrust. They argued that the initial Meade thrusting occurred in

Aptian time. Cessation of the Meade and the Crawford thrusting is less certain because

the oldest rocks overlying them are of Miocene-Pliocene age. Nevertheless, structural

analysis suggests that the Meade and Crawford thrusts were followed by the Absaroka

thrust, which is fairly well dated as late Campanian or earliest Maastrichtian in age

(Jacobson and Nichols, 1982). Given these data, it is reasonable to assume that the

Meade and Crawford thrusts spanned the Aptian to Santonian interval with little temporal

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 35

overlapping by immediately adjacent thrusts. This interpretation places the Meade and

Crawford thrust system largely contemporaneous with the Greenhorn and Niobrara

cycles (see Chapter 3).

Central Utah:

The Sevier thrust belt continues southwestward into Utah, where it displays structural

styles similar to those in the Idaho-Wyoming salient. In part because of erosion, post-

Cretaceous tectonic overprints, and burial by derivative sediments, the Sevier thrusts in

Utah were for a long time poorly documented and dated. As a result of subsurface

drilling, seismic profiling, coupled with surface mapping and detailed sedimentologic

analysis, a succession of major thrust faults have been recognized in west-central Utah

and occasionally dated (Royse, 1993; Villien and Kligfield, 1986; Lawton, 1985;

Allmendinger et al., 1986; Armstrong 1968; Heller et al.; 1986). Elsewhere in Utah,

much work is needed to identify and map the distribution of Sevier thrust faults.

The major thrust faults in west-central Utah, in progressive sequential order, are: the

Canyon Range, Pavant, Paxton, and Gunnison thrusts (Fig. 16). Total, cumulative

crustal shortening on these thrust faults is about 120 km (Royse, 1993). Because

structurally well-juxtaposed synorogenic clastic wedges are not abundant and reliable

paleontologic data are rare, most of these thrust faults are not well dated. Generally, they

range from Early Cretaceous (Albian) to middle Eocene (Heller et al., 1986).

In west-central Utah, the earliest and structurally highest thrust is the Canyon Range

thrust (Allmendinger, 1986; Royse, 1993). Its movement is recorded by the synorogenic

conglomerates in the Lower Cretaceous Cedar Mountain Formation (Lawton, 1986), or

the Canyon Range Fanglomerate (Armstrong, 1968). Palynomorphs collected from the

lower part of the Canyon Range Fanglomerate on the Gunnison Plateau yielded an age

between Neocomian and Albian (Standlee, 1982). This suggests that the Canyon Range

thrust was broadly contemporaneous with the Paris-Willard thrust to the north.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. n O Plateau Wasatch AncientEphraim A ult 20km TK TK P-TR : p z V i - l • ///////////////// Pavant Range R Hraore Arch u t :L_-PZ. PVT. Mountains Cricket .in'; CRX p z - l •■ Canyon Range P ts Figure 16. A structural cross section ofwest-central Utah. P' s= Proterozoic sediments; LPz= lowerPaleozoic; P-TR= upperPaleozoic and Triassic; J=Jurassic; K= Cretaceous; PVT=Pavant Range Thrust; PAX= Paxton thrust;the locationsG= Gunnison ofwells thrust. used Vertical in constructing lines are the cross section. Modified fromRoyce (1993). TK= lowerTertiary andUpper Cretaceous; UT= upperTertiary; CRT= Canyon RangeThrust; PEs UT House Range PCs L-PZ P-TK ‘ Range Confusion 10 k m Cross section Cross

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 37

According to the estimate by Royse (1993), displacement on the Canyon Range thrust is

about 50 km. East of the Canyon Range thrust is the Pavant thrust (Fig. 16), which Villien and

Kligfield (1986) inferred had two separate phases of movement. The early phase of the

Pavant thrust is recorded by synorogenic conglomerates equivalent to the Sanpete

Formation. Palynomorphs collected from these rocks suggest an age between late Albian

and Turanian time. The late phase of the Pavant thrust is recorded by synorogenic

conglomerates interpreted as being equivalent to the Sixmile Formation, which Fouch et

al. (1983) assigned a late Santonian to early Campanian age by correlations with better

dated strata in the distal foreland. The ages of the synorogenic conglomerates, though

somewhat tenuous, date the movements on the Pavant thrust roughly as Late Cretaceous.

The Paxton and Gunnison thrusts occurred in the latest Cretaceous (Royse, 1993).

Their movements were probably recorded by the widespread conglomerates of

Campanian to Maastrichtian age found throughout central Utah. However, because of

lack of precise age constraints, the initiation and cessation of their movements are

essentially uncertain.

Magnitude of thrust loads

Viewed as a single tectonic entity, the Sevier belt can be characterized as an east-

tapering wedge of sedimentary rocks migrating inland along the west-dipping

decollements above the passive basement crystalline rocks. Crustal shortening across the

thrust belt amounted to 200 km in the Canadian Rockies and 100 to 150 km in the U.S.,

where the smaller shortening may have been counterbalanced in the foreland by the

Laramide orogeny (Elison, 1991). Crustal shortening, and therefore vertical thickening,

generates supracrustal loads that require isostatic balance by lithospheric flexure in the

foreland (Barrell, 1914; Price, 1973).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 38

A useful reference for the magnitude of the supracrustal load is available from the

southern Canadian Rockies, where a supracrustal wedge more than 370 km wide and up

to 15 km thick was horizontally shortened by more than 50 percent (Price, 1973). More

detailed work on the crustal shortening was carried out by Jordan (1981) in the Idaho-

Wyoming salient. On the basis of seismically controlled structural cross sections (Royse

et al., 1975), she reconstructed the amount of excess mass associated with the Paris,

Meade-Crawford, and Absaroka thrusts, respectively. The Paris thrust amounted to a

relatively small and narrow crustal load, 30 km wide and 1.5 km thick. The Meade-

Crawford thrust system was a substantially larger thrust load. It is up to 100 km wide

and over 4 km thick.

BASEMENT CONTROLS ON THE SEVIER THRUSTING

The Overlap Province and buttressing

Toward the end of the Cretaceous and continuing into the early Tertiary, widespread

basement faulting occurred in the Western Interior foreland basin. This tectonic style,

named the Laramide orogeny, is characterized by deep-rooted reverse faults. The

Laramide orogeny ended the domination of the thin skinned Sevier thrusting and

eventually broke the Western Interior foreland basin into the Laramide structural basins

and intervening uplifts in their present form (Cross, 1986; Dickinson et al., 1988).

Initially, the Sevier and Laramide orogenies were considered as two contrasting styles

of deformation that were partitioned in two distinct provinces and succeeded each other in

time (Armstrong, 1968). Subsequently, however, it was found that the Laramide

deformation and Sevier thrusting partly overlapped in time (Armstrong, 1974; Wiltschko

and Dorr, 1983; Cross, 1986; Dickinson et al., 1988). Still later, it was found that in

addition to the temporal overlap, the two tectonic styles developed in tandem since at least

the middle Late Cretaceous in a so called "overlap province" (Fig. 17; Schmidt and Perry,

1988). Although the precise tectonic mechanisms of both the Sevier and Laramide

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. VO foreland RockyMountain Overlap Province .Sevier thrust belt. Figure a: 17. Location oftheoverlap province between Cordilleran the thrustbelt andthe Rocky Mountainb: foreland,Across section ofthe overlap province. Arrowscrustal indicate shortening. From Kulikand Schmidt (1988). 100 200 miles Major faults ofthe Rocky Mountain foreland ■Overlap Province Sevier thrust front ----- T

a

I I

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 40

orogenies still remain controversial, there is a growing consensus that they were not

mutually exclusive of each other in either spatial or temporal domains.

The overlap province refers to a north-south elongated region 100 to 150 km wide

along the Cordilleran hingeline, where zones of crustal weakness inherited from the

Precambrian were concentrated (Fig. 8,17; Kulik and Schmidt, 1988). The interactions

between the thin-skinned thrusting and coeval basement uplifting in this region took place

primarily in the form of buttressing (Schmidt and Perry, 1988). Buttressing involves

impingement of eastward-advancing thrust sheets against uplifted basement blocks or

other pre-existing basement irregularities, such as the inferred basement promontories

and embayments along the Cordilleran hingeline (Beutner, 1977, Schmidt et al., 1988,

Kulik and Schmidt, 1988). The complex alternating reentrants and salients along the

strike of the Sevier belt have been attributed to buttressing (Beutner, 1977, Couples and

Lewis, 1988). Perhaps more important, buttressing against pre-existing basement

irregularities could be an effective mechanism of generating along-strike variations in

crustal shortening, which may find expressions in the foreland basin subsidence patterns

(Craddock et al., 1988, Beutner, 1977). Below is a description of those structures that

have been mentioned as candidates for buttressing of coeval thrusting.

Inferred buttresses and their consequences

Along the length of the Sevier belt from Montana to Utah, thrust sheets were

emplaced onto basement rocks that display different degrees of complexity (Fig. 8). In

the Idaho-Wyoming salient, Sevier thrusting progressed on a gently westward-dipping

stable platform established since Precambrian time (Picha, 1986). North and south of the

Idaho-Wyoming salient, in contrast, Sevier thrusting progressed across complexly

faulted margins of the North American craton inherited from Precambrian continental

rifting (Skipp, 1988; Picha, 1986). These basement variations determined to a large

extent the distribution of buttressing.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 41

The Blacktail-Snowcrest uplift in southwestern Montana provides a well documented

case of buttressing (Fig. 13). Structural as well as stratigraphic evidence suggests that

this basement-cored uplift, though spatially restricted, was active as early as Coniacian

time (Nichols et al., 1985; Ryder and Scholten, 1973). It has been suggested that because

of this and nearby buttresses, the contemporaneous eastward Sevier thrusting was

restrained, leading to the formation of the southwestern Montana reentrant (Beutner,

1977; Perry et al., 1988). Northeast of the Blacktail-Snowcrest uplift, the formation of

the Helena salient might also be the result of buttressing (Beutner, 1977; Kulik and

Schmidt, 1988; Schmidt et al., 1988). The Helena salient is connected to the reentrant to

the south by the Willow Creek fault zone or Transverse zone, which was probably the

southern boundary fault of the Proterozoic Belt basin. Schmidt et al. (1988) developed a

lateral thrust ramp model for the thrust styles in the Helena salient (Fig. 18). North of the

Transverse zone in the Helena salient, a ddcollement was developed deep within the

Proterozoic sedimentary rocks of the Belt basin and thrusts progressed to the east and up.

South of the Transverse zone, in contrast, the Archean crystalline rocks acted as a

buttress to thrust propagation. Paleomagnetic data obtained near the Helena salient have

documented local rotations of thrust sheets along the margin of the salient possibly due to

buttressing (Eldredge and Van der Voo, 1988).

Evidence for buttressing also exists in the ancestral Teton-Gros Ventre uplift in

northwestern Wyoming (Fig. 15). This tectonic feature was inferred to be uplifted along

the Cache Creek thrust contemporaneously with the early phase of Sevier thrusting

during Coniacian time (Kulik and Schmidt, 1988), or even Albian time (Craddock et al.,

1988). As thrust sheets approached from the west, buttressing by this uplift may have

caused the deflection of thrust sheets away from the uplift initiating rotations of frontal

thrusts (Craddock et al., 1988). Paleomagnetic data obtained near the Teton-Gros Ventre

uplift have documented rotations of rocks presumably in response to this buttressing

(Hunter, 1988; Eldredge and Van der Voo, 1988). Structural analysis by Craddock et al.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 18. An interpretative structural block diagram showing the inferred relationship between the Proterozoic Willow Creek fault, the transverse zone, and frontal ramps of the Helena salient. From Schmidt et al. (1988).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. (1988) also indicate that thrust displacements on the Paleocene-Eocene Prospect and

Darby thrusts increase toward the south, away from the Teton-Gros Ventre uplift.

Farther south, in northern Utah, deflections of thrusts around the western edge of the

Uinta Uplift has been interpreted as a result of buttressing by relatively rigid quartzites

deposited in the Proterozoic Uinta trough (Beutner, 1977). However, the same structural

pattern has been explained by post-thrusting bending effects (Crittenden, 1969). In other

words, the apparent deflection patterns of thrusts in question is due to subsequent erosion

following the doming of the Uinta Uplift in the Tertiary.

Because of these basement buttresses, eastward thrust translation along the Sevier

thrust belt was not uniform. In the case of the Idaho-Wyoming salient, more thrust

translation occurred between the Uinta trough in the south and the ancestral Teton-Gros

Ventre uplift and the uplifts in the southwestern Montana foreland to the north. As a

result, the Idaho-Wyoming salient was the site where disproportionally greater crustal

shortening was accommodated. The implication of this thrusting style to basin subsidence

is discussed in Chapter 5.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 3

STRATIGRAPHY OF THE UPPER CRETACEOUS ROCKS, THE U.S. WESTERN INTERIOR BASIN

INTRODUCTION

Cretaceous rocks comprise one of the most important systems in the North American

Western Interior. They represent highly diverse marine and nonmarine facies, many of

which contain a rich fossil record. They host many types of economically valuable

deposits such as coal, oil, gas, and uranium. During the Tertiary Laramide orogeny,

many areas in the Western Interior were uplifted, resulting in extensive outcrops across

the Rocky Mountains and many areas of the Great Plains (Fig. 19). Most Cretaceous

rocks, however, are buried in the subsurface of the Tertiary Laramide structural basins

that were once part of the much larger Cretaceous Western Interior foreland basin.

Because of economic and academic interest, Cretaceous rocks have been studied

extensively by generations of geologists with respect to their sedimentary characteristics,

paleontologic records, and regional stratigraphic relationships. These studies augmented

the exploration activities in the region, which in turn provided studies of the Cretaceous

rocks with a steady input of subsurface data. As a result of the extensive studies and

prolonged exploration activities, an enormously large body of stratigraphic data has

accumulated over time. This includes wireline logs, seismic sections, outcrop litho- and

biostratigraphic sections, subsurface cross sections, and numerous publications devoted

to the study of Cretaceous rocks. This body of data not only makes the Western Interior

basin a thoroughly explored region with respect to economic resources but also ranks it

as one of the world's best studied foreland basins that provides many textbook examples

for stratigraphic analysis.

The abundant litho- and biostratigraphic data available in the Western Interior basin

present an excellent opportunity for restoring basin subsidence history. This study

44

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Bismarck

[Hot Spings

Rawlins] K cm m crcr North Platte

• Denver

I G ran d ] Junction C edar C it'

0 100 200 300 km

Figure 19. Map showing the extent of the Cretaceous outcrops (shaded) in the U.S. Western Interior. Oblique hatches denote uplifted Precambrian basement rocks. From Cobban and Reeside (1952a).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 46

applied two-dimensional flexural backstripping techniques to six regional stratigraphic

cross sections crossing different parts of the basin, from Montana and the Dakotas to

Utah and New Mexico (Fig. 20). Each cross section, portraying lateral changes in stratal

thickness and lithofacies, was compiled by integrating subsurface and surface

stratigraphic data. The stratigraphic interval emphasized on the sections is the "middle

Cretaceous" or in more formal terms, the lower part of the Upper Cretaceous succession.

This chapter reviews the Cretaceous stratigraphy and describes the stratigraphic data

base that supports the subsequent flexural backstripping analysis. The first half of this

chapter provides a brief overview of the depositional setting, biostratigraphic framework,

and the transgressive-regressive cycles. Because of the scope of the subject, this review

is highly generalized and by no means complete. The second half of this chapter

describes the regional stratigraphic cross sections and the specific procedures and data

that were used to compile them. Discussion focuses on the major lithologic units

involved, age-diagnostic fossils, and chronostratigraphic correlations along the length of

the cross sections.

DEPOSITIONAL SETTING

Rapid sea floor spreading and subduction during the Cretaceous led to the flooding of

a sizable portion of the world’s continental areas (Hays and Pitman, 1973; Kominz,

1984). As part of this flooding, the North American craton underwent the largest marine

incursion since the Paleozoic and developed a large western interior epeiric seaway (Fig.

21). The Cretaceous Western Interior seaway, as it is commonly called, was confined

between the Cordilleran fold and thrust belt to the west and the drainage divide of the

low-relief cratonic interior to the east. At times of maximum flooding, it connected the

Arctic ocean and the Gulf of Mexico, a longitudinal distance of more than 5000 km, and

reached a width of 1000 km or more in many places (Williams and Stelck, 1975).

Toward the end of the Cretaceous, this marine basin was brought to an end by the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. — I— -T- 110 "TI5 100 95 -50

50-

^ T \ Willistoti M*"01 Devils Lake \ Great Falls

Bismarck -4 5 Billings

Livingston 4 5 -

heridan

•Hot Spmgs

Rawlins Kemmc North Platte

Lincoln . 4 0 -

Denve

Junction d arC it Wichita Pueblo Durango Trinidad

Flagstafr Santa Fc

0 100 200 300 km

110 105 190 — I— JL

Figure 20. Map showing the distribution of Laramide structural basins in the U.S. Western Interior. The east-west trending lines numbered from 1 to 6 are the locations of the regional stratigraphic cross sections compiled in this study.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. ARCTIC OCEAN

M£*lC0 \\cpj,

r ?

500 1000 miles

Sand and silt Dark gray muds: Pure carbonate Impure clayey deposits: nearshore offshore muds: offshore carbonate muds: offshore Figure 21. Generalized map of the Western Interior Seaway during the maximum transgression in the Late Cretaceous. From Kauffman (1977a).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 49

withdrawal of marine water and by the onset of the Laramide orogeny, which broke the

basin apart and created numerous uplifts and intervening structural basins (Dickinson and

Snyder, 1978; Cross, 1986).

Great quantities of clastic sediments were shed into the seaway from the rising

Cordilleran highlands and deposited in shallow marine and nonmarine environments

(Fig. 21). Easterly-derived clastic sediments are less significant and restricted to the

easternmost part of the cratonic platform and most has been removed by Tertiary erosion.

Lithofacies proximal to the Cordillera were composed of intertongued non/marginal-

marine sandstone and marine shale. Towards the east, these predominantly shallow

marine clastic deposits become finer and thinner, eventually grading into relatively

uniform calcareous shale or carbonate-dominated sediments deposited in open marine

environments on the broad cratonic platform. Overall, the basin fill thickness assumes a

distinctive asymmetrical foreland basin pattern, varying from as much as 5000 meters

proximal to the thrust belt to a few hundred meters or less in the Great Plains (Fig. 22).

In contrast to a passive continental margin setting, the Cretaceous Western Interior

seaway represents a foreland ramp type depositional setting (Nummedal et al., 1989),

where the bathymetry was shallow and gentle. In this depositional setting, sediments

deposited in the seaway are predominantly of shallow marine origin. However, partly

because of lack of a modem analog for such a basin, the precise water depth has been

difficult to determine. Attempts have been made to estimate water depth on the basis of

the distribution of benthic Foraminifera (Eicher, 1969), reconstruction of depositional

clinoform topography (Asquith, 1970), physical evidence for shelf, slope, and basin

models ( Weimer, 1983), and sedimentologic model (Kauffman, 1969; 1977a; Hattin,

1975). The consequent estimates of maximum water depth vary considerably, from a

high of 600 meters (Eicher, 1969; Asquith, 1970) to a low of 100 to 300 meters

(Kauffman, 1969, 1977a; Hattin, 1975; Weimer, 1983).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. o T - > 4 - n- outcrops Limitof UK 300 ml 300 km j ----- i andb: Campanian andMaastrichtian strata. Isopachcontours in 1000 ft interval. From Cross andPilger (1978). Figure 22. RestoredCretaceous isopachpatterns in theWestern Interior, a: Albian through Santonian strata ! i i !

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 51

Episodic contractions and expansions of the seaway left a cyclic stratigraphic record in

the basin. The cycles occur on varied temporal and spatial scales, ranging from those

major transgressive-regressive depositional cycles that are recognizable over much of the

basin to individual sandstone/mudstone tongues that represent episodes of local

strandplain progradation and retreat (Weimer, 1962; McGookey et al., 1975; Kauffman,

1977b; Peterson, 1977; Molenaar, 1983; Ryer, 1977,1993). The typical

lithostratigraphic units and the age-diagnostic fossils of the five major transgressive-

regressive cycles are discussed later in this chapter.

THE MOLLUSCAN BIOCHRONOSTRATIGRAPHIC SCALE

The Cretaceous rocks of the North American Western Interior have one of the most

refined biostratigraphic systems among the Mesozoic rocks around the world. This

system is based primarily on rapidly evolving molluscan lineages, in particular

ammonites and various groups of bivalves. Based on several decades of stratigraphic and

systematic paleontologic research by many workers, such as W. A. Cobban, over 70

thoroughly tested molluscan biozones have now been established for the Upper

Cretaceous series alone (Fig. 23; Cobban, 1993; Obradovich, 1993). These molluscan

biozones offer exceptional chronostratigraphic resolution and reliability. Moreover, the

Cretaceous rocks of the Western Interior contain numerous volcanic ash beds useful for

radiometric dating, and numerical ages have been assigned to many of these biozones.

Using single crystal Ar40 /Ar39 dating techniques, Obradovich (1993) obtained over 30

closely-spaced radiometric ages from volcanic ash beds in the Upper Cretaceous

sequence of the Western Interior. These radiometric age data, which commonly have an

analytical error bar of less than 0.5 m.y., allow the molluscan biozones of the Western

Interior to be calibrated quantitatively (Kauffman and Caldwell, 1993).

A standard reference sequence for the Upper Cretaceous rocks of the U.S. Western

Interior is shown on Figure 23. This particular sequence is largely based on rock

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reference Sequences, U. Cretaceous Ammonite zones Western Interior, U.S.A. Stages Eastern Colorado

-M — Scaphitcs Ic c i-

32 Desmoscaphites baaleri TT _33„Dcsmosc ophites erdmonni .Santonian 85- -Clioscaphitcs chotcaucnsis M 35 Clioscaphitcs vcrmiformis

Smoky Hill Shale Mbr 36 Clioscaphitcs saxitonianus

u 37 Scaphitcs dcprcssus

Coniacian- M- -48—Scaphitcs ventricosua- Corresponding bivalve 39 Scaphites preventricosus Fort Hays *40“ Forreslcria peruana ------39 Inoceramusdcformis Limestone Mbr 41 S. corvcnsis, P. germari “42™Scaphitcs nigricollensis" Unnamed Shale Mbr ^>Ir»occramus pciplexus 43 Scaphites whitfiddi -u- 4 ) “54” Scaphites fcrroncnsis *«3 Juana Lopez Mbr 45 Scaphitcs warreni 90 ^>Inoccram us dimidius CO 46 Prionocyclus macombi 4 6 ' £ ^ Codell Ss Mbr -47— Prionocyclus hyatli ------j^M ytiloides mytiloidci Blue Hill Shale Mbr 48 Prionocyclus pcrcarinatus <3 Turanian M' U Fairport Shale Mbr ,4a__ColIignoniccras woollgari

50 Mammites nodosoidcs i Bridge Creek 51 Vascoccras birchbyi 4 $Neocardioccrasjuddii- 52 Pscudaspidoccras flcxuosum R Limestone Mbr 53 Watinoccrasdcvoncnsc x: 5 4 "Nigcriccras 8 Vascoccras diartiamim 56 Burroccras clydenae u 57 Euomphaloccras septcmacriatum ^ ______Duvcnganoccras conaitum a Dunveganoccras aJbcrtcnsc Hartland Shale Mbr Dunveganoceras problcmaticum Dunveaanoceras oondi Lincoln Mbr Plctriacanthoccras wvomingcrc 95 Acamhoccrasbcucnse Acanthoccras muldooncnsc Acamnoccras grancroscnsc M Cenomanian Conlinoccrasgilbcrti _____ Graneros Shale

52 Watinoccrascoloradocnsc

55 v > Sciponoceras gracile 5 9 ' 69 Ncogastroplites macicami 55 ^ Pycnodontc ncwbcrryi 70 Ncogastroplitesamcricanu Mowry Shale 7T Ncogastroplites mucllcri ^M elolcoccras mosbyense „22,..Ncoga

J Sandstone 100 Albian

"74,MInoccramus bcllvucnsis

Skull Creek Shale 75 Inoccramuscomanchcanus Figure 23. Molluscan time scale and reference sequences of the Western Interior Basin. Based on Obradovich (1993), Cobban (1993), and Kauffman et al. (1993), Scott (1969), Gill and Cobban (1966b, 1973), McGookey et al. (1972). (figure con'd.)

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reference Sequences, U. Cretaceous Ammonite zones Western Interior, U.S.A. Stages N.E. Wyoming W. Montana South Dakota

Hell Creek / Lance Formation

U

3 Dtacoscapfcitea roaacrais, H. nicciJeti Fox Hills Sandstone

Maastrichtian 4 Hoploscaphiics spaff. H.nicollcli Elk Butte Mbr 5 Baculitesclinolobatus Upper Mobridge Mbr L 6 Baculilcs grandis unnamed shale unit 7 Baculitesbacuius Virgin Creek 8 Baculilcs cliasi Mbr

9 Bactiliicsjcnscni

10 Baculilcs reesidci Bearpaw Verendrye Mbr Shale 11 Baculilcs cuneatus Lower unnamed IT 12 Baculilcs compressus shale unit (Tepee Butte zone) DeGrey Mbr 14 Exitdocerasjcnncyi

IS Didymoccrasstevcnsoni Gow Creek Mbr 16 Didymoccras ncbrasccnsc

17 Baculitcsscolli Campanian 18 Baculilcs gregorycnsis, B. reduncus Judith River Red Bird Gregory Mbr Sandstone 19 Baculilcs perplexus(late form) Silty Mbr

M 20 Baculilcs gilhcni 21 Baculilcs perplexus (early form) ------Mitten Black

------Shale Mbr T\ Baculilcs aspcriformis Sharon

------Springs Mbr Sharon Claggett Shale Springs Mbr 26 Baculilcs sp. (weak flank ribs) 27 Baculilcs sp. (smooth 1) ....2R Scaphitcs hippocrcpis 111 Gammon 29 Scaphitcs hippocicpisll L Ferruginous Eagle Sandstone Mbr 30 Scaphites hlppocrcpisl 1 1 | Pierre Shale

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 54

formations exposed in the eastern and central part of the Western Interior basin,

particularly eastern Colorado and contiguous areas ( Cobban and Reeside, 1952; Gill and

Cobban, 1966 b; Kauffman, 1977b). In this part of the basin, Upper Cretaceous rocks

are highly fossiliferous and biostratigraphically better constrained than elsewhere.

Because of the distinctive, short-ranging, fossil assemblages these formations possess,

they have in practice been used as biostratigraphic or chronostratigraphic units in regional

stratigraphic correlations for many years. The Lower Cretaceous series is excluded in

Figure 5 because it is thin, poorly constrained and mostly nonmarine. For an updated

reference, a recent correlation chart of the Lower Cretaceous rocks compiled by Heller

and Paola (1989) is shown instead in Figure 24.

TRANSGRESSIVE-REGRESSIVE CYCLES

It is widely recognized among stratigraphers that the Cretaceous stratigraphy of the

North American Western Interior reflects a succession of major transgressive-regressive

depositional cycles. In the U.S. Western Interior, five transgressive-regressive

depositional cycles have long been recognized in Albian to Maastrichtian strata (Weimer,

1960; Kauffman, 1969,1977a and b; McGookey et al., 1972; Kauffman and Caldwell,

1993). They have been named in ascending order as: the Kiowa-Skull Creek, Greenhorn,

Niobrara, Claggett, and Bearpaw cycles (Fig. 25). Where fully developed, these cycles,

or cyclothems, generally consist of transgressive marine shales or limestones overlain by

subsequent regressive marine and marginal marine shales, siltstones, and sandstones.

These cycles are not periodic; their duration ranges from 5 to 10 m.y. Some cycles are

apparently provincial, confined to the Western Interior or only part of it, whereas others

such as the Greenhorn cycle can be correlated with most world-wide Cretaceous

transgression-regression records (Hancock and Kauffman, 1979; Matsumoto, 1980).

It should be noted that the current knowledge of these cycles is generalized and

heavily influenced by the stratigraphic records in the type areas where the cycles were

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LA CO ------Beaver Beaver 7TV1 Mines Fm Mines Cadomin Fm. Fm. Cadomin Gladstone Fm Gladstone Kootenay Group Mill Creek Fm Creek Mill CANADA m m Femie Gp SOUTHERN MONTANA WESTERN ColoradoSh KootenaiFm Swift Fm Morrison Fm Morrison CreekSh FusonFm Fall RiverSs cul S. DAKOTA NewcastleSs BLACK HILLS 999999999^ , r Sundance Fm Sundance Morrison Fm Morrison 11/ Rusty Beds Muddy Ss CENTRAL C]ove^ly_Fm Greybull Ss Mowry Sh. Mowry Sh. WYOMING r Thermopolis Sh ^— — Peterson Ls Ls Peterson U^phraim Lower Ephraim Draney Ls Ls Draney Fm Bechler congl. Smoot Sh Sh Smoot WEST Aspen Sh WYOMING BearRiver Ss South Lytle Fm PlatteFin Mowry Sh COLORADO COLORADO Ralston FmRalston Fm Stump N. FRONT RANGE FRONT N. Morrison Fm Morrison Fm cooel_ Plainview Ss Glencaim Sh ''Purgatoffe'’ CENTRAL MowiySh COLORADO 9793^9665190 Burro CanyonFn

l Morrison Fm Morrison Summerville Fm Summerville M _J L_ 1 Mbr ormation Buckhom UTAH UTAH COLORADO F Cedar CENTRAL WESTERN WESTERN CENTRAL 152 156 144 124 131 138 113 119 Ma 97 Barr. Bern Haul. Valan. Aptian Albian Kinun. Oxford Tithon. STAGE c o o .2 *5 55 TheMowry AspenShale Shale and arenow assigned Cretaceousthe Upperto Cenomanian) (lower (Cobban and Kennedy, 1989). Figure24. Late toJurassic Early correlation Cretaceous chartpartsfor of Western the InteriorPaolaHellerFrom basin. and (1989).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. REFERENCE SEQUENCE OF STUDY STAGES T-R CYCLES U.S. WESTERN INTERVAL M a INTERIOR

Fox Hills Sandstone/ Hell Creek Fm Maastrichtian Elk Butte Mbr. 70 - Bearpaw Virgin Creek Mbr.

Verendrye Mbr. -PsQrev MbL__ Crow Creek Mbr.

Campanian Gregory Mbr Claggett

80 - Sharon Springs Mbr Eagle Sandstone Telegraph Creek Fm

Santonian Niobrara Niobrara Fm. Coniacian

90 - Turonian Carlile Shale

Greenhorn Greenhorn Fm.

Graneros/Belle Cenomanian Fourche Shale

Mowry Shale

ioo - Newcastle Sandstone Regression

Skull Creek Shale Albian Kiowa-Skull Creek

Transgression Fall River Sandstone

Figure 25. Transgressive-regressive depositional cycles of the North American Cretaceous Western Interior. Selected stratigraphic intervals on the six regional cross sections of this study are shown by arrows. From McGookey et al., (1972); Kauffman (1977b, 1985). Time scale based on Obradovich (1993).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 57

first defined. The Kiowa-Skull Creek, Greenhorn, and Niobrara cycles were defined in

the eastern and central parts of the basin, including Colorado, western Kansas and

adjacent areas, whereas the Claggett and Bearpaw cycles were established in Montana

and South Dakota. The following is a generalized description of these cycles in terms of

their lithologic successions and associated fossils found in their type areas. No attempt is

made to compare systematically equivalent strata of these cycles in every part of the

Western Interior with those in the type areas.

Neocomian to Aptian

During much of Early Cretaceous time, the U.S. Western Interior was a broad fluvial

drainage basin, where the overall drainage direction was to the north and most sediments

were derived from the incipient Sevier orogenic belt (Fig. 26). Rocks of Neocomian to

Aptian age are distinguished by the presence of abundant and widespread nonmarine

conglomerates displaying rapid lateral changes in lithofacies, stratal thickness, and age.

Figure 24 summarizes the main Lower Cretaceous lithostratigraphic units from different

regions and their probable age relations (Heller and Paola, 1989). The nonmarine,

conglomeratic Lower Cretaceous rocks rest with a regional unconformity of uncertain

duration on the Morrison Formation of Late Jurassic age ( Peterson, 1994). These

conglomeratic units, including the Ephraim Conglomerate in western Wyoming, the

Cloverly Formation in central Wyoming, the Kootenai Formation in western Montana,

and the Lakota Sandstone in the Black Hills, form a 100-200 meter thick blanket of

conglomeratic sandstones and variegated mudstones over much of the Western Interior.

The Kiowa-Skull Creek cycle

The Kiowa-Skull Creek cycle, the first marine incursion into the U.S. Western

Interior in the Cretaceous, was Albian in age and lasted nearly 10 m.y. (Fig. 25). Strata

associated with the Kiowa-Skull Creek cycle are well described in the central-eastern part

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 110 105 100 95

Kootenai Fm

C loverly Fm

40

Lytle Fm

Burro Canyon Fm

35

0 1 0 0 200300 km

105

Figure 26. Early Cretaceous drainage pattern in the Western Interior. Modified after Young (1970).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 59

of the U.S. Western Interior (Haun and Weimer, 1959; Waage, 1959; Franks, 1975;

Young, 1970; MacKenzie, 1971).

The Kiowa-Skull Creek transgression was represented by the Fall River Sandstone

and its correlatives, including the Rusty Beds in central Wyoming and the Plainview

Sandstone in Colorado (Fig. 24). These rocks rest unconformably on the pre-Albian

fluvial deposits of the Cloverly Formation and its correlatives. They occur as an extensive

sheet of marine or marginal marine sandstones, siltstones, shales, and thin coals that

measure in thickness from a few meters to tens of meters. Other than plant remains and

trace fossils, few age-diagnostic fossils have been reported from these transgressive

deposits.

Conformably overlying the Fall River SaBdstone is the Skull Creek Shale and its

correlatives, the Kiowa Shale in Western Kansas and Nebraska, and the Thermopolis

Shale in Wyoming and Colorado. These rocks, deposited during the peak of the Kiowa-

Skull Creek transgression, consist of dark-gray marine shale and siltstone and are

generally less than 60 meters in thickness. Marine fossils, including mollusks (Waage,

1959; MacKenzie, 1971) and foraminifera (Eicher, 1960), have been widely reported

from these deposits, albeit with low diversity and abundance. Among them, lnoceramus

comancheanus Cragin has proved to be a very reliable late Albian guide fossil to date the

Kiowa-Skull Creek marine deposits throughout the U.S. Western Interior.

The Kiowa-Skull Creek regression in late Albian time was recorded by several

closely contemporaneous sandy units, including the Newcastle Sandstone in the Black

Hills, the Bear River Sandstone in western Wyoming, and the Muddy Sandstone in

central Wyoming and Colorado. These rocks consist of interbedded sandstone, siltstone,

and shale deposited in deltaic or estuarine environments. Their thickness is rarely in

excess of 50 meters. Fossil records from them are sparse and restricted to plant remains,

vertebrate fragments, and trace fossils.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 60

The Greenhorn cycle

The Greenhorn cycle spans the time interval from latest Albian-earliest Cenomanian

through middle Turanian time, a period of nearly 10 m.y. The standard section of the

Greenhorn cycle is located at Pueblo, Colorado (Fig. 27). Its lithostratigraphy and

biostratigraphy have been thoroughly described by Scott (1969), Cobban and Scott

(1972), and Kauffman (1977b). In western Kansas, complementary sections of the

Greenhorn cycle have also been described in great detail by Hattin (1962,1965a, 1969,

1971,1975b). In these places as well as many others, the Greenhorn cycle assumes a

more or less symmetrical sequence in terms of the duration of the transgressive phase and

the ensuing regressive phase. The transgressive phase consists of, in ascending order,

the Mowry Shale, Graneros Shale, and Greenhorn Formation; the regressive phase is

represented by the Carlile Shale and the Codell Sandstone.

The Mowry Shale

The Mowry Shale was deposited in a marine embayment during the initial Greenhorn

transgression as the sea advanced from the north in the early Cenomanian (Fig. 28a). It

occurs as an extensive blanket of siliceous shales and bentonite beds overlying the

Newcastle Sandstone and its correlatives (Fig. 24) in the northern and central parts of the

Western Interior. It grades laterally into marginal marine and nonmarine sandstones

towards the basin margins, such as the undifferentiated Cedar Mountain Formation and

the Dakota Sandstone in central and southern Utah (Molenaar and Cobban, 1991). The

thickness of the Mowry shale is usually less than 100 m in the central part of the basin

and diminishes towards the basin margin. Abundant fish remains exist in the Mowry, but

other fossils are scarce. Only a very limited early Cenomanian fauna, including

Neogastroplites americanus and Neogastroplites comutus, have been widely reported

from the Mowry (Reeside and Cobban, 1960).

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B a c u l i t e s o b tu s u s Thickness (meters)

Apache Creek Sandstone Mbr B a c u l i u s s p (w eak ribbed)

Pierre Shale

Transition M br

'B a c u I U e s s p (smooth)

-y uppercfMUc y — X illlit /

Ccncrctiotnry uboail

I n o c e r a m u s s im p s o n l

Upper chalk shale unit

Inoceramus piatinus CO I n o c e r a m u s cfJ. patootensis

Inoceramus cordiformis Niobrara Formation

Inoceramus undulatoplicatus

M iddle shate unit

11.6 Lower limestone unit

Lower shate unit Inoceramus invdutus 17.1 _ / Shale and 'Ss - limestone unit - 7 I n o c e r a m u s d e fo r m is Fort Hays I n o c e r a m u s e r e c tu s 12.2 Limestone Mbr " X ju a n a Lopez Mbc^" >*ssJScaphitfs whitfieldi Pionocyclus wyomingensis - V N / I VTodcll Sandstone/ I n o c e r a m u s h o w e lli Prionocyclus hyatti 30.8 Carlile Blue Hilt Shale Shale Mbr

Fairport chalky 30.2 shale M br Collignoniceras woollgari

Bridge Creek Inoceramus labiatus Limestone Mbr Sciponoccras gracile Greenhorn Haitland Shale Mbr Formation Inoceramus pictus

Lincoln Lim estone M b 11.4

Graneros Shale — Conlinoceras sp. 31.4

Dakota ' Sandstone

Figure 27. Generalized stratigraphic section for the Rock Canyon anticline area, northwestern Pueblo quadrangle, Colorado, showing principled lithologies and zonal fossils of the Dakota, Greenhorn, Carlile, Niobrara, and lower Pierre Shale. From Scott (1969).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. time .Embayment' 'Mississippi ; ] Scaphites. hippocrepis Early Early Campanian Seas is now consideredto be early Cenomanian time Watinoceras Early Early Turanian Seas (Neogastroplites comutus Late Late Albian Seas by Cobban and Kennedy, 1989) FromWilliams and Stelck (1975). Figure 28. Map showing the extent ofthe Cretaceous Western Interior SeaWays atthree differenttimes.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 63

In both outcrops and the subsurface, the Mowry Shale occurs as a distinct lithologic unit

that contrasts with both the overlying and underlying rocks. In eastern Montana and

Wyoming, a bentonite bed, the Clay Spur Bentonite, occurs near the top of the Mowry

Shale. Radiometric dating of this bentonite bed in the Black Hills yielded an age of 97

Ma, or early Cenomanian (Obradovich, 1993).

The Graneros Shale

The Mowry is succeeded without a depositional break by the Graneros Shale (Fig.

25). In Colorado and Western Kansas, the Graneros Shale is a dark, organic-rich shale

deposited in a open marine environment. Thickness of the Graneros Shale is variable,

ranging from around 10 m in western Kansas to 50 meters in much of Colorado. In the

Black Hills, near the junction of Montana, South Dakota, and Wyoming, the Belle

Fourche Shale overlies the Mowry shale as the lateral equivalent of the Graneros Shale.

Marine fossils are sparse in the lower part of the Graneros Shale and its correlatives, but

are comparatively abundant in the upper part, including ammonites and inoceramid

bivalves. Cobban and Scott (1972) established four middle Cenomanian ammonite zones

in the upper Graneros Shale, which, in ascending order, are Calycoceras gilberti,

Acanthoceras granerosense, Acanthoceras muldoonense, and Acanthoceras

amphibolum. Bentonite beds of varying thickness are common throughout the Graneros

Shale. The most prominent one, the X bentonite, occurs at the top of the Graneros Shale

and lies within the Acanthoceras amphibolum zone. It is nearly a meter in thickness and

can be traced northward into the Alberta foreland. Because of its extent, it has been

widely used as a marker bed in surface and subsurface correlation.

The Greenhorn Formation

In Colorado, Kansas, and adjacent areas, the Greenhorn Formation comprises three

distinct lithologic units which, in ascending order, are the Lincoln Limestone, Hartland

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 64

Shale, and Bridge Creek Limestone Members (Fig. 27). Their cumulative thickness is

usually less than 70 m. The Lincoln Limestone consists of calcareous shale, limestone,

and numerous thin bentonite beds. Its thickness varies from 10 m at the Pueblo to less

than 1 m in Bunker Hill, Kansas. Abundant ammonites and inoceramid bivalves have

been collected from the Lincoln Limestone. Late middle Cenomanian zonal fossil

Acanthoceras amphibolum occurs at its base, and the late Cenomanian zonal fossil

Dunveganoceras pondi is found at its top (Cobban and Scott, 1972; Sageman, 1985;

Sageman and Johnson, 1985). Overlying the Lincoln Limestone Member, the Hartland

Shale Member is composed of organic-rich, well-laminated calcareous shale and

numerous thin bentonite beds. At Pueblo, the Hartland Shale Member is 17 m thick and

contains Inoceramus pictus Sowerby, which ranges from the basal Lincoln Limestone

Member to the lower part of the Bridge Creek Limestone Member. In the northern part of

the Western Interior, the Hartland Shale and its correlatives encompass the early late

Cenomanian Dunveganoceras conditum and Dunveganoceras albertense zones

(Metoicoceras mosbyense zone; Cobban and Scott, 1972). The Hartland Shale Member

is succeeded by the Bridge Creek Limestone Member, which records the peak of the

Greenhorn transgression and the maximum areal extent reached by the Western Interior

seaway (Fig. 28b). At Pueblo, it is 15 m thick and consists of many rhythmic limestone-

shale couplets and laterally persistent bentonite beds. These lithofacies are widespread in

the eastern and central part of the Western Interior basin. In western Kansas, the Bridge

Creek Limestone is divided into a lower Jetmore Chalk Member and an upper Pfeifer

Shale Member (Hattin, 1971b). Marine fossils are abundant and diverse in the Bridge

Creek Limestone, and fossil zonations are well established. Four ammonite zones,

ranging in age from middle late Cenomanian to earliest middle Turanian, are defined in

the Bridge Creek Limestone by Cobban and Scott (1972). These are the Sciponoceras

gracile, Watinoceras coloradoense, Mammites nodosoides, and Collignoniceras

woollgari zones.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 65

The Cariile Shale

Conformably overlying the Bridge Creek Limestone Member of the Greenhorn

Formation is an upward coarsing succession of shale, siltstone, and sandstone that

comprise the Cariile Shale (Fig. 27). The Cariile Shale is divided into, in ascending

order, the Fairport Chalky Shale, Blue Hill Shale, Codell Sandstone, and Juana Lopez

Members (Hattin, 1971a; Hattin and Cobban, 1977). Its total thickness ranges from less

than 15 m to more than 60 m (Weimer, 1986). The Fairport Member is a calcareous shale

and siltstone unit (Scott, 1969; Glenister and Kauffman, 1985). Marine fossils in the

Fairport are low in diversity and poorly preserved. The early middle Turanian zonal

index fossil Collignoniceras woollgari, which is best documented in the Pool Creek

Member of the Cariile Shale in the Black Hills, occurs as flattened impressions (Cobban,

1984). The Blue Hill Member is composed of non-calcareous, silty shale. At Pueblo, the

Blue Hill is 30 m thick; the lower half consists of silty shale and the upper half of sandy

siltstone. Marine fossils are sparse and poorly preserved in the Blue Hill Shale Member.

In north-central Kansas, however, the Blue Hill contains many specimens of the

ammonite Prionocyclus hyatti (Cobban, 1984). The Codell Sandstone Member is a fine­

grained shallow marine sandstone unit deposited during the terminal regression of the

Greenhorn cycle (Glenister and Kauffman, 1985; Weimer, 1986). It occurs sporadically

on the eastern side of the basin and is usually less than 10 m thick. Its contact with the

Blue Hill Member is either conformable, as at Pueblo (Glenister and Kauffman, 1985),

or disconformable, as in parts of the Denver basin (Weimer, 1986). Its contact with the

overlying Juana Lopez Member, the basal transgressive deposits of the Niobrara cycle, is

disconformable. Marine fossils found in the Codell Sandstone Member include the

middle Turanian Prionocyclus hyatti and Inoceramus howelli (Scott, 1969).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 6

The Niobrara cycle

The Niobrara cycle spans the time interval from the latest Turonian to early

Campanian, a period of more than 9 m.y. (Fig. 25). Like the Greenhorn cycle, the

standard section of the Niobrara cycle is also located at Pueblo (Fig. 27; Scott and

Cobban, 1964; Scott, 1969). As defined by Kauffman et al. (1977b), strata deposited

during this period of time include the upper part of the Cariile Shale or Mancos Shale

{e.g., the Juana Lopez Member), the Niobrara Formation, and the Transition member and

the lower part of the Apache Creek Sandstone Member of the Pierre Shale. Similar to the

Greenhorn cycle, strata of the Niobrara cycle are distinguished by domination of

limestones and calcareous shales. The transgressive phase of the Niobrara cycle is thin;

the peak transgressive deposits rest unconformably on regressive facies of the Greenhorn

cycle (Codell Sandstone or Blue Hill Shale Members). The regressive phase, on the other

hand, has a long and well developed rock record.

The Juana Lopez Member

At Pueblo, Colorado, the initial transgression of the Niobrara cycle is represented by

three lithologic units, which, in ascending order, are: 1) a 25-cm-thick silty shale unit of

the upper Cariile Shale lying disconformably on the Codell Sandstone (not shown on

Fig. 23,27), 2) a calcarenite-calcareous shale unit of the Juana Lopez Member, and 3) a

shale unit equivalent to the Sage Breaks Member of the Cariile Shale in Wyoming (Fisher

et al., 1985). Among them, the Juana Lopez Member is the most laterally persistent and

lithologically distinct unit that records the initial transgression of the Niobrara cycle in

New Mexico, Colorado, and Utah. Time-equivalent rocks include part of the Turner

Sandy Member of the Cariile Shale in northeastern Wyoming and Montana, and the Wall

Creek Member of the Frontier Formation in central and southeastern Wyoming. The type

section of the Juana Lopez Member is located near Cerrillos, Santa Fe County, New

Mexico (Rankin, 1944). At a reference section in the southeastern part of the San Juan

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 67

basin, New Mexico, the Juana Lopez Member is 30 m thick and composed of

interbedded calcarenites, fine-grained sandstones, and shales (Dane et al., 1966; Hook

and Cobban, 1980; Molenaar, 1983). There, the Juana Lopez Member has a conformable

contact with both the overlying and underlying Mancos Shale. Its top has been

considered a time-parallel surface that can be traced over long distances in the subsurface

(Dane, 1960a; Molenaar, 1973). In the eastern part of the Western Interior basin, the

Juana Lopez Member occurs only locally. Where preserved, it is rarely more than 1 m

thick, and unconformably bounded between the underlying regressive deposits of the

Greenhorn cycle and the overlying transgressive deposits of the Niobrara cycle. The

Juana Lopez Member and its equivalents are generally fossiliferous, lying within the late

Turanian Inoceramus dimidius, Scaphites warreni , Prionocyclus wyomingensis, and

Prionocyclus macombi zones (Hook and Cobban, 1980).

The Niobrara Formation

The Niobrara Formation is a dominantly chalky unit that constitutes the bulk of the

Niobrara cycle in much of the Great Plains, from the North and South Dakotas to

Colorado and western Kansas (Fig. 27). It is best exposed in Colorado, western Kansas,

and neighboring areas. For this reason, the stratigraphy of the Niobrara Formation has

been studied in detail by Hattin (1981,1982) in western Kansas, by Scott and Cobban

(1964) at Pueblo, Colorado, and by Scott et al. (1986) in the Raton basin, New Mexico.

Kauffman (1977b) identified as many as four successive transgressive pulses, separated

by regressive episodes, in the Niobrara Formation at Pueblo, Colorado. In Colorado,

western Kansas, and adjacent areas, the Niobrara Formation comprises a lower Fort

Hays Limestone Member and an upper Smoky Hill Shale Member. These two members

are lithologically distinct and can be recognized either in outcrops or in the subsurface

over a large area.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 68

The Fort Hays Limestone unconformably overlies the Cariile Shale and records the

inception of the Niobrara transgression (Kauffman, 1977b; Scott and Cobban, 1964). It

consists of about 10 to 20 m of limestone beds and intervening shale. The limestone

beds are micritic and contain abundant inoceramids. Locally, the basal part of the Fort

Hays Limestone contains quartz sands reworked from the underlying Codell Sandstone.

The Fort Hays Limestone is laterally persistent and forms an excellent time-parallel

marker bed in the subsurface. In the western part of the basin, age-equivalent rocks

include the uppermost part of the Frontier Formation of Wyoming, and the upper part of

the Gallup Sandstone and the lower part of the Tocito Sandstone in New Mexico. To the

north and west, the Fort Hays Limestone thins and becomes shaly by facies changes. At

Pueblo, three latest Turonian-early Coniacian Inoceramus zones span the Fort Hays

Limestone, which, from the bottom to the top, are the Inoceramus perplexus,

Inoceramus erectus, Inoceramus deformis (Scott and Cobban, 1964). In the Raton

basin, only one latest Turanian ammonite zone, that of Prionocyclus germari, is present

(Scott et al., 1986).

The Smoky Hill Shale Member consists of alternating units of calcareous shale and

chalk or limestone (Scott and Cobban, 1964; Hattin, 1981,1982). In the northern Great

Plains, the equivalent of the Smoky Hill Shale is unnamed chalk and calcareous shale in

the Niobrara Formation (Shurr and Rice, 1986). At Pueblo, the Smoky Hill Shale is

about 212 m thick and is divided into seven lithologic units (Scott and Cobban, 1964).

These are, in ascending order, the shale and limestone unit; the lower shale unit; the

lower limestone unit; the middle shale unit; the middle chalk unit; the upper chalky shale

unit; and the upper chalk unit (Fig. 27). Kauffman (1977b) identified the lower limestone

unit, the middle chalk unit, and the upper chalk unit as the three additional transgressive

pulses of the Niobrara cycle. Throughout the section, marine fossils, particularly

inoceramids, are abundant and diverse. The section encompasses the following zonal

fossils ranging in age from middle Coniacian to lower Campanian; Inoceramus deformis,

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Inoceramus involutes, Scaphites depressus, Inoceramus undulatoplicatus-Clioscaphites

saxitonianus, Clioscaphites vermiformis , Clioscaphites choteauensis, Scaphites

hippocrepis, Baculites sp zones (smooth) (Scott and Cobban, 1964).

Pierre Shale

During the regressive phase of the Niobrara cycle, following the deposition of the

Smoky Hill Shale Member, the Western Interior seaway became greatly reduced in areal

extent (Fig. 28c). The regression of the Niobrara cycle is represented by the basal Pierre

Shale lying below the earliest middle Campanian zonal fossil Baculites obtusus

(Kauffman, 1977b). This interval includes the Transition member and the lower part of

the Apache Creek Sandstone Member of the Pierre Shale at Pueblo (Fig. 27), the

Gammon Member of the Pierre Shale in the Dakotas, and the Telegraph Creek Formation

and Eagle Sandstone in Montana (Fig. 23). The contact between the Pierre Shale and the

underlying Niobrara Formation at Pueblo and Raton basin is gradational, lying between

the fossil zones of Scaphites hippocrepis II and Scaphites hippocrepis III (Scott et al.,

1986). In the Denver basin and the Black Hills region, the contact has been inferred to be

a regional unconformity (LeRoy and Schultz, 1958; DeGraw, 1975; Weimer, 1983).

The Claggett cycle

The Claggett cycle spans the middle Campanian, a period of about 5 m.y. (Fig. 25).

The stratigraphic signature of the Claggett cycle is well defined in the northern part of the

U.S. Western Interior. However, in central and southern parts of the Western Interior,

the transgressive-regressive patterns in the contemporaneous rocks display complex and

diachronous relationships. The stratigraphy of the Claggett cycle and the trends of the

contemporaneous strandline movements have been described by Gill and Cobban (1973)

in the northern part of the basin. In that region, the Claggett cycle consists of a

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transgressive phase represented by the Claggett shale, and a regressive phase represented

by the Judith River Formation.

The Claggett Shale is a noncalcareous bentonic unit deposited during a period of

intensive volcanic activity. The basal part of the Claggett Shale contains the Ardmore

Bentonite, a bentonite bed that is locally one meter thick and can be traced throughout the

Dakotas, Montana, and Wyoming. This bentonite bed lies between the two successive

ammonite zones: the latest early Campanian Baculites sp. (weak flank ribs) and the

earliest middle Campanian Baculites obtusus. Radiometric dating of the Ardmore

Bentonite yielded an age of 80.5 Ma (Obradovich, 1993). The Claggett shale overlying

the Ardmore Bentonite Bed contains many early middle Campanian ammonites,

including, Baculites obtusus, Baculites macleami, and Baculites asperiformis (Gill and

Cobban, 1973).

The Claggett Shale is overlain by the eastward-thinning regressive clastic wedge of

the Judith River Formation. The basal part of the Judith River Formation is a shallow

marine sandstone unit named the Parkman Sandstone Member. Overlying the Parkman

Sandstone are non-marine deposits rich in coarse volcanic material. The proportion of

volcanic material in the Judith River Formation increases towards the western source

areas in the Elkhom Mountains. The Judith River regression took place during the span

of six ammonite zones. In ascending order, they are: the Baculites sp. (smooth),

Baculites perplexus (early), Baculites gilberti, Baculites perplexus (late), Baculites

gregoryensis, and Baculites scotti (Gill and Cobban, 1973).

The Bearpaw cycle

The Bearpaw cycle marks the conclusion of marine sedimentation in the Cretaceous

Western Interior basin. Like the preceding Claggett cycle, the Bearpaw cycle is well

developed in the northern part of the U.S. Western Interior, where it is bounded by the

Judith River Formation at the base and the Fox Hills Sandstone at the top. The Bearpaw

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 71

Shale overlies the Judith River Formation to form the transgressive phase of the Bearpaw

cycle. It spans about six late Campanian ammonite zones, ranging, in ascending order,

from the Didymoceras nebrascense, Didymoceras stevensoni, Exiteloceras jenneyi,

Didymoceras cheyennense, Baculites compressus, to Baculites cuneatus. Marine water

finally withdrew from the Western Interior during the succeeding Fox Hills regression.

The withdrawal began in the late Campanian during zones of Baculites compressus and

Baculites cuneatus.

STRATIGRAPHIC CORRELATIONS

Data

The regional stratigraphic cross sections of this study were constructed with data

available in the public domain. These data consist of wireline logs and various reports of

outcrop fossil collections. Within most Laramide structural basins and across much of the

Great Plains, such data are readily available. Over 300 well logs were collected from

different parts of the basin for the purpose of subsurface correlation. In addition, many

subsurface log cross sections in Laramide basins were also collected from various

publications. They were either referred to or incorporated selectively in the present

stratigraphic cross sections with or without modifications. The names and locations of the

wells incorporated in the cross sections are given in the Appendix.

The most common and valuable biostratigraphic data in the Cretaceous Western

Interior are the ammonite and bivalve collections made by geologists of the U.S.

Geological Survey, most notably W. A. Cobban and his colleagues. Over the decades,

these collections have been made at many fossil-bearing outcrops in the Western Interior.

As a result, an extremely large body of age-diagnostic fossil data are available for

stratigraphic correlations. This constitutes a significant advantage for constraining the

chronostratigraphic relationships of Cretaceous rocks in widely separated areas.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 72

One particular problem in handling subsurface data is the variance in the nomenclature

attached to the Cretaceous rocks. In some cases, multiple names, dictated by local

lithofacies, were applied to single rock units in different places (e.g., Cody, Hilliard,

Baxter Shales); in others, a formation name was extended to an unrelated rock unit in

different areas (e.g., the Emery Sandstone in central and southern Utah). Yet, a more

serious problem is produced by differences in the designation of lithologic subdivisions

in different areas based on local lithofacies patterns. These problems are more annoying

than serious, but they highlight the importance of proper biostratigraphic data in

chronostratigraphic correlations.

Correlation method

Chronostratigraphic correlations in the Upper Cretaceous series can be carried out by

two complementary methods. Regional correlations are best carried out with the support

of ammonite and bivalve fossil data. This is particularly important across areas where

Cretaceous rocks have been stripped away by uplift and erosion due to the Laramide

orogeny. The other method is based on the physical continuity of certain time-parallel

marker beds, such as limestone and bentonite beds. Such marker beds generate

distinctive log patterns that can be traced laterally for tens or hundreds of miles. In some

places, the log patterns are so laterally persistent that they can be correlated from one

Laramide basin to the next.

In planning each cross section, care was taken to maximize the integration of outcrop

fossil data and wireline log correlations. To achieve this, the location of the cross sections

in Figure 2 was dictated to a large extent by the availability and distribution of the fossil-

bearing outcrops. In selecting wireline logs, priority was given to those located as close

as possible to the outcrop sections where age-diagnostic fossils have been reported. In

many places, logs can be found from wells within a few to tens of miles of the outcrops.

Because Cretaceous fossil-bearing rocks are invariably marine, the lithofacies change

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 73

little over this distance. Therefore, prominent lithologic units or marker beds can readily

be correlated to the log sections. By matching prominent lithologic units between outcrop

sections and log sections, fossil occurrences on outcrop sections can then be projected

into the subsurface and allow wireline log correlations to be biostratigraphically

constrained and dated. Because of the widespread fossil-bearing outcrops, each cross

section usually contains multiple wireline logs tied to outcrop sections.

Between the foredeep and the cratonic interior, 12 to 33 wireline logs were selected as

individual stratigraphic columns along each cross section. In many cases, however,

correlations on each cross section are supported by additional logs not listed in the

Appendix. The selected logs are usually spaced tens of miles or less in Laramide basins,

and up to hundreds of miles across Laramide uplifts. Such large spacings between logs

may not be suited for detailed lithostratigraphic analysis, but because correlations are

performed at the formation or larger scale and supported by biostratigraphic data they are

well-suited to this study.

Study interval

Strata presented on the six cross sections encompass the lower and middle part of the

Upper Cretaceous Series, ranging in age from middle Cenomanian to early Campanian.

This time interval corresponds to the Greenhorn and Niobrara cycles (Fig. 25). Selection

of this stratigraphic interval carries several advantages as far as correlations are

concerned. First, strata of this interval are better preserved than younger ones. Therefore,

correlations can be made over wider areas and with more data points. Second, unlike the

overlying complexly intertongued marine and nonmarine formations, this interval

consists of predominantly marine rocks distinguished by exceptional lateral lithofacies

consistency. Third, rocks of this interval contain many marker beds recognizable over

large areas. For example, the Mowry Shale, the 'X' and Ardmore Bentonite Beds, the

Juan Lopez Member, and many of the limestone beds of the Greenhorn and Niobrara

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 74

Formations can be traced continuously for several hundreds of miles ( Zelt, 1985;

Kirkland, 1991; Elder et al., 1994). These and other beds serve as ideal markers for

chronostratigraphic correlations. Fourth, strata of the Greenhorn and the Niobrara cycles

are highly fossiliferous. A large body of ammonite and bivalve data have been collected

from this interval throughout the Western Interior. They can be readily integrated into

subsurface correlations. Finally, although spanning a period of 16 m.y., this interval

represents more than half of the preserved Upper Cretaceous series in many places.

A note on the cross sections

The six regional litho-stratigraphic cross sections show stratal thickness, lithofacies,

and age relationships across different parts of the U.S. Western Interior, from Montana

and the Dakotas to southern Utah, New Mexico, Colorado, and Western Kansas. Each

litho-stratigraphic cross section is accompanied by a generalized chronostratigraphic

section crossing approximately the same segment of the Western Interior basin. Such

sections show generalized lateral stratigraphic relationships between individual Laramide

basins and include younger Cretaceous rocks. The remainder of this chapter is devoted to

the discussion of the litho-stratigraphic cross sections. Several procedural remarks need

to be made in advance. First, discussion extends only to the formations within the range

of the cross sections of this study; age-equivalent formations that exist in the thrust belt,

where they assume different lithofacies and different nomenclature, are not considered.

Second, the following discussion will focus on strata deposited in the western part of the

basin Inasmuch as those in the central and eastern parts have been described to some

extent in the preceding section on the stratigraphy of the cycles. In addition, the

Cretaceous lithofacies and fossil records in the central and eastern part of the basin are

fairly consistent, whereas those in the western part of the basin show great variations and

therefore deserve special attention. Finally, the terms "Greenhorn" and "Niobrara" cycles

were used in a chronostratigraphic sense in the following discussions of the cross

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 75

sections. This usage was adopted merely for the purpose of organizing age-equivalent

strata from widely separated regions. Apart from the convenience provided by the two

chronostratigraphic units, the time they represent may be discrete periods of time possibly

related to the ultimate tectonic forces that also drive basin subsidence.

REGIONAL STRATIGRAPHIC CROSS SECTIONS

Cross sections 1 and 2: west Montana to North and South Dakotas

Upper Cretaceous rocks are not as fully exposed in Montana and the Dakotas as

farther south because of lack of major Laramide uplifts. However, for the same reason,

these rocks are better preserved in the subsurface. Because subsurface data are abundant,

closely spaced wells logs can be used in stratigraphic correlations.

Upper Cretaceous rocks in western Montana consist of, in ascending order, the

Marias River Formation/Cody Shale, the Telegraph Creek Formation, the Eagle

Sandstone, the Claggett Shale, the Judith River Formation, the Bearpaw Shale, the Fox

Hills Sandstone, and the latest Cretaceous nonmarine formations that overly the Fox Hills

Sandstone (Figs, 29,31; Cobban and Reeside, 1952a; Cobban, 1955a; Gill et al., 1972a;

Gill and Cobban, 1973; Rice and Shurr, 1983; Roberts, 1972). These formations

generally amount to less than 2000 meters in total thickness. In contrast, equivalent beds

in western Wyoming and central Utah can be twice as thick. The lower part of the Upper

Cretaceous succession, including the Marias River Formation/Cody Shale, and the

Telegraph Creek Formation, is conspicuously dominated by marine shale. The upper part

of the Upper Cretaceous succession, from the Eagle Sandstone to the Fox Hills Sand­

stone, comprises intertongued marine/nonmarine sandstone and shale. Towards the east,

the Upper Cretaceous succession as a whole thins and grades into marine shales by facies

changes. In eastern Montana and the Dakotas, this succession is a monotonously uniform

marine shale sequence composed of, in ascending order, the Belle Fourche Shale, the

Greenhorn Formation, the Cariile Shale, the Niobrara Formation, and the Pierre Shale.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. -j ON ' -1 , 29 unconformity North Dakota North marine sandstone Mowiy Shale GreenhornF m .u '223^23 mmmm nonmarinerocks coastal and N.Montana E. t : it j . ^ <* - x " , If- - -1 r ,-T---1-- , I Tir . v vrjk'«rr -4' P manne limestone tv ~ ir 7 i

- 1 gg»m»Mosby Ss gg»m»Mosby Montana N. Central * -* — tt” -' n ; ffiw n j: |lr \ . ‘S< . 11 I,*'' ' ■ ■ ^ ir ^ ir - ' 023 Arch interbeddedlimestone shale Sweetgrass Montanato North Dakota. Figure Generalized 29. time-stratigraphic correlation chartUpperfor Cretaceous strata from northwestern Albian Turanian Coniacian Santonian Campanian Cenomanian marine shale calcareous shale with siliceousmarine Maastrichtian

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. MONTANA— Swettgrass Havre Glasgow Arch 6 7 Ardmore Bentonite Bed r ^vvV^A;VvV'-;ivV^ meters • */• m* * • * 5 j ? 5 3 ? 5 J 5 3 5 3 E » *•*■ ♦+ *»+ *•«**• * * * + «► ■*■ «► **T*•►«4» • ♦ 4* 4t^.+ ♦♦♦♦ + * N id ra n ! ilcS ha Si^**.1 7 nternFB ;^.jg elfnFoiirc

Howcrec^^T 33,35,38,39,49,57.58,60: Mhr ^ : Cobban, 1951a; Cobbanetal., 1958,1959

Marine calcareous Undifferentiated marine and Marine shale 1000 - shale or limestone nonmarine sandstone

Figure 30. Regional stratigraphic cross section 1 of lower Upper Cretaceous rocks from northwestern P (see Appendix for name and location). Projected fossil occurrences are marked by small triangles follo\ section is shown in Figure 20.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. f------NORTH DAKOTA Glasgow ------Williston Basin ------* Cavalier 10 11 12 13 14 15 16

0 100 200 km ■ i n e a n d , ______i______,

> n e

;ks from northwestern Montana to North Dakota. Vertical lines and the numbers above represent individual wells by small triangles followed by numbers that correspond to the ammonite zones in Figure 23. Location of the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 00 Central N. Dakota m m Black Hills ibraraFra. *1 m C C immonShale G G eenbomFm. Ci Shale rltle B< leFourcbeS Mowry Shale Montana S-central W m m m . tamSDEEB -Ji tamSDEEB ’.FrootierF Livingston area Figure 31. Generalized time-stratigraphiccorrelation chartfor Upper Cretaceous stratafrom southwestern Montanato South Dakota. Albian Turanian Coniacian Santonian Campanian Cenomanian Maastrichtian

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. MONTANA

Bozeman Roundup Boyes

?&%?I 1 *•••.*.• *.* .**• .*.• .*.• *.*»•.*„• /.• Sandstone •.%•/.•/.**,*.•/.♦.*.».*.♦.*.»•-»•*- • *. ,* • ,• \ • * .. . *. . • . . *Ty

- yfyfy^.....

^Niobrara!

29: Cobban (1969) 35: Cobban (1951b)55* 39- 49, and 60 were projected from the column 34 on cross section C of Rice (1976, 1977) 1000

37: Robert (1972)

Figure 32. Regional stratigraphic cross section 2 of lower Upper Cretaceous rocks from southweste individual wells (see Appendix A for name and location). Projected fossil occurrences are marked b in Figure 23. Location of the section is shown in Figure 20. See Figure 30 for legends.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. SOUTH DAKOTA -Williston Basin- N. Black Hills Pierre

Ardmore

Niobrara Fmj

The age of the Clay Spur Bentonite is dated as 97 Ma, ourchc Sha and that of the Ardmore Bentonite 50: Cobban (1951a) 35 80 5 Ma (obdoroch>1993) jrojected from the on C of Rice (1976, 1977) 25,27,45: Rice (1976), Robinson et al. (1964) 29: Cobban (1969)

100 2 0 0 km

jtaceous rocks from southwestern Montana to South Dakota. Vertical lines and the numbers above represent fossil occurrences are marked by small triangles followed by numbers that correspond to the ammonite zones ire 30 for legends.

Reproduced w«h p e n n o n of .he copyright owner Further reproduction prohibited whhout permission Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 80

Cross sections 1 and 2 extend from western Montana to the Dakotas (Figs. 30,32). They

were composed by combining and modifying four different subsurface cross sections

from Montana and the Dakotas that were originally compiled by Rice (1976,1977).

Where possible, molluscan fossil data collected within short distances of these two cross

sections were projected in to constrain correlations. Strata included on the two cross

sections are those of the Greenhorn and the Niobrara cycles, bounded below by the

Mowry Shale and above by the Ardmore Bentonite Bed. This interval encloses many

distinct marker beds whose log patterns can be traced continuously along the length of the

entire cross sections. Based on the fossil data available, four time lines were drawn on

the two cross sections for the purpose of backstripping. Inasmuch as the lithofacies and

stratigraphic architecture of Upper Cretaceous rocks along the two cross sections are

nearly identical, their discussion is combined.

Greenhorn age

The Mowry Shale consists of marine and nearshore marine shale and siltstone

deposited during the initial Greenhorn transgression. It measures up to 150 meters in

thickness in central Montana and decreases to less than 50 meters in much of the Dakotas.

The relatively high siliceous content gives the Mowry Shale a distinct log response

recognizable over much of the Western Interior (Reeside and Cobban, 1960; McGookey

et al., 1972; Vuke, 1984; Molenaar and Cobban, 1991). For this reason, the top of the

Mowry Shale, where recognizable, was chosen as the oldest horizon in subsequent

backstripping analysis. In northwestern Montana, the correlative of the Mowry Shale

consists of 30 m of interbedded sandstone and shale assigned to the Bootlegger Member

of the Blackleaf Formation (Cobban et al., 1976; Rice, 1976; Rice and Cobban, 1977).

In northwestern Montana, the Mowry Shale is overlain conformably by the Marias

River Formation, a predominantly marine shale and siltstone unit that averages about 200

m in thickness (Figs. 29,30). The Marias River Formation is divided into the Floweree,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 81

Cone, Ferdig, and Kevin Members (Cobban et al., 1976). The Floweree Member, the

Cone Member, and the lower part of the Ferdig Member are of Greenhorn age, whereas

the upper part of the Ferdig Member, and the Kevin Member fall into Niobrara age. The

Marias River Formation as a whole passes eastward into calcareous and noncalcareous

shale assigned to the Belle Fourche Shale, Greenhorn Formation, Carlile Shale, and

Niobrara Formation. Many molluscan zonal fossils have been collected in members of the

Marias River Formation. On the Sweetgrass Arch, the late Cenomanian zonal fossil

Metoicoceras mosbyense occurs in the upper part of the Floweree Member, and another

younger late Cenomanian zonal fossil Sciponoceras gracile in the overlying Cone

Member (Cobban et al., 1976). The former is a guide fossil of the Hartland Shale and the

latter is a guide fossil of the basal part of the Bridge Creek Limestone in Colorado and

western Kansas. In the overlying Ferdig Member, middle Turanian ammonites

Prionocyclus hyatti, and, perhaps, Collignoniceras woollgari are present (Cobban et al.,

1976).

In southwestern Montana, the Mowry Shale is overlain by the Frontier Formation

(Figs. 31,32; Roberts, 1972; Rice, 1976). An eastward-thinning sandstone wedge of

limited extent, the Frontier Formation is composed of marine and nonmarine sandstone

and is less than 100 meters thick. It grades eastward rapidly into the marine Belle

Fourche Shale by facies changes. Overlying the Frontier Formation is the Cody Shale, a

silty shale interval that correlates with the Greenhorn Formation, Carlile Shale, and

Niobrara Formation in eastern Montana and the Dakotas. The lower part of the Cody

Shale falls into the Greenhorn cycle. Fossils from both the Frontier Formation and the

lower Cody Shale are sparse.

In eastern Montana and the Dakotas, strata of the Greenhorn cycle consists of the

Belle Fourche Shale, Greenhorn Formation, and lower part of the Carlile Shale. The

Belle Fourche Shale is a noncalcareous shale unit and averages about 30-100 meters in

thickness. It is in gradational contact with both the underlying Mowry Shale and the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8 2

overlying Greenhorn Formation. Unlike its equivalent, the Graneros Shale in Colorado,

the Belle Fourche Shale is barren of age-diagnostic fossils. The overlying Greenhorn

Formation is a calcareous shale unit containing locally interbedded thin limestone units,

and averaging 40 meters in thickness. In central Montana, the lower 10 m of the

Greenhorn Formation is a fossiliferous sandstone unit named the Mosby Sandstone

member (Cobban, 1951a; Rice, 1976). The Mosby contains late Cenomanian ammonites

Dunveganoceras albertense and Metoicoceras mosbyense (Cobban, 1951a, 1953b).

These fossils are guide fossils found in the Hartland Shale Member of Colorado and

western Kansas. In the northern Black Hills, the Greenhorn Formation contains

Inoceramus fragilis (?) at the base and Inoceramus labiatus (early Turanian) at the top

(Cobban, 1951a). Overlying the Greenhorn Formation, the Carlile Shale is a

noncalcareous shale unit. It represents the transition between the Greenhorn regression

and the Niobrara transgression. In South Dakota, a sandy unit of limited extent, named

the Codell Sandstone, occurs in the middle of the Carlile Shale and passes into shales to

the west (Fig. 32; Rice, 1977). A second sandy unit named the Turner Sandy Member

also occurs in the Carlile Shale. The ages of these sandy units are uncertain because of

lack of age-diagnostic fossils. Possibly, they are correlatives of the Codell Sandstone of

Colorado and record the final regression of the Greenhorn cycle.

Niobrara age

In northwestern Montana, strata of the Niobrara cycle consists of the upper part of the

Ferdig Member and the Kevin Member of the Marias River Formation, the Telegraph

Creek, and the Eagle Sandstone Formations (Figs. 29,30). The Kevin Member of the

Marias River Formation is composed of marine shales. It grades eastward into the

calcareous shales in the Niobrara Formation and southward into the upper Cody Shale.

Many molluscan zonal fossils of Niobrara age have been found in the Kevin Member. On

the Sweetgrass Arch, early and middle Coniacian zonal fossil Inoceramus erectus,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 83

middle Coniacian Scaphites preventricosus, and Inoceramus deformis occur at its base,

and late Coniacian Inoceramus involutus, Scaphites ventricosus, and Scaphites

depressus occur in its middle part, and Santonian Clioscaphites choteauensis,

Desmoscaphites erdmanni, Desmoscaphites bassleri, and Scaphites lee are found in its

upper part (Cobban, 1955a and b; Cobban et al., 1976). These are all guide fossils of the

Niobrara Formation in Colorado.

In southwestern Montana, the equivalent of the Kevin Member is the upper part of the

Cody Shale (Figs. 31,32). To the east, the upper part of the Cody Shale becomes

increasingly calcareous and grades into the Niobrara Formation. The Niobrara Formation

in Montana and the Dakotas is generally barren of age-diagnostic fossils, but the Cody

Shale has yielded a few molluscan zonal fossils in the Livingston area of southwestern

Montana. These fossils include the latest Coniacian-earliest Santonian Inoceramus

involutus, and Scaphites depressus in a sandy unit in the middle of the Cody Shale

(Roberts, 1972; Cobban et al., 1958), and middle Santonian ammonite Clioscaphites

vermiformis in the upper part of the Cody Shale (Cobban, 1951b).

The Telegraph Creek Formation is a upward-coarsing succession of shale, siltstone,

and sandstone in western and central Montana. It is transitional from the underlying

Kevin Member of the Marias River Formation or the Cody Shale to the overlying Eagle

Sandstone. To the east, it grades into the Gammon Shale. Fossils are sparse and poorly

preserved in the Telegraph Creek Formation, but on the Kevin-Sunburst dome (Column

1, Fig. 30), the late Santonian zonal fossil Desmoscaphites bassleri and the early

Campanian Scaphites hippocrepis (DeKay) have been reported from it (Cobban, 1951a,

1955a, 1955b; Cobban et al., 1976). These are guide fossils for the uppermost part of the

Niobrara Formation in Colorado.

The Eagle Sandstone is a major wedge of regressive marine and nonmarine sandstone

that mark the end of the Niobrara cycle. Its lower part is a marine sandstone bed called

the Virgelle Sandstone. Its upper part consists of predominantly nonmarine sandstone.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 84

The contact between the Eagle Sandstone and the overlying Claggett Shale is a sharp

surface that lies within meters of the Ardmore Bentonite Bed. To the east, the Eagle

Sandstone thins and grades into marine, noncalcareous shale in the Gammon Shale. The

Eagle Sandstone is sparsely fossiliferous, but Scaphites hippocrepis II was reported from

the Virgelle Sandstone at its base (Cobban 1955a, b). In the northern Black Hills the

upper part of the Gammon Shale yielded early Campanian zonal fossils Scaphites

hippocrepis and Scaphites sp. (smooth) (Cobban, 1951a, 1969).

Cross sections 3 and 4: western Wyoming to south Dakota and Nebraska

The Upper Cretaceous series in Wyoming has a greater average thickness than almost

anywhere else in the Western Interior basin. In western Wyoming, over 4000 meters of

Upper Cretaceous rocks accumulated, composing a complexly intertongued succession of

marine and nonmarine strata. The major lithostratigraphic units include the Frontier, the

Cody/Hilliard, and the Mesaverde Formations (Figs. 33, 35). To varying degrees, these

formations demonstrate lateral changes in stratal thickness, lithology, and age. In eastern

Wyoming and adjacent states, Upper Cretaceous rocks are comprised predominantly of

shale. In ascending order this succession consists of: the Belle Fourche Shale, Greenhorn

Formation, Carlile Shale, Niobrara Formation, and Pierre Shale (Gill and Cobban,

1966a, 1966b, 1973; Merewether, 1972,1980; Merewether et al., 1977). Because the

Upper Cretaceous stratigraphic succession is similar over much of Wyoming, discussion

of the two cross sections is combined (Figs. 34,36).

The northern cross section extends from the Jackson Hole area across the southern

rim of the Bighorn basin, the Powder River basin, the Black Hills, and ends in central

South Dakota (Fig. 34). As on the Montana sections, strata represented here encompass

the Greenhorn and the Niobrara cycles, bounded below by the top of the Mowry Shale

and above by the Ardmore Bentonite Bed. Included are the Frontier Formation and the

Cody Shale in the Jackson Hole area and the Bighorn basin. East of the Powder River

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 00 Central S. Dakota Black Hills V 7 7 7 7 7 7 7 , Buffalo WallCreek Thermopolis Jackson Hole Figure Generalized 33. time-stratigraphic correlation chart forUpperCretaceous fromstrata northwestern Wyoming to SouthDakota. Albian Turom an Coniacian Santonian Campanian Cenomanian Maastrichtian

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. S. BIGHORN BASIN- -POWDER RIVER BASIN-

Jackson Hole Thermopolis Bighom Mts Buffalo N.W 1 10 11

meters Shannon Ss sry<-j mm /* Cody Shale r/OAVV;^v*vy

I

Colui 23,2 Mere

Column 8: 25,27,39, *14-43,49,52,62,64: Merewether etal. (1977) Column S: •V;..;.: 30: Cobbari (1969) 24,25, 27,37: Keefer (1972) ontier Pm* 39: Merewether etal. (1975) 27: Gill and Cobban (1966a) Column 3: 30: Cobban (1969) 39: Keefer (1972) Column 2: Column 6: 37: Cobban (195lb) 43,62: Merewether et al. (1975) Column 7: | Column 1: 25,27: Keefer (1972) ! 39,49: Cobban and Reeside 2000 - (1952b) and Love (1956)

Figure 34. Regional stratigraphic cross section 3 of lower Upper Cretaceous rocks from northwestern > represent individual wells (see Appendix for name and location). Projected fossil occurrences are mark to the ammonite zones in Figure 23. Location of the section is shown in Figure 20. See Figure 30 for le

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. POWDER RIVER BASIN— «------S. DAKOTA

Its Buffalo N.W. Black Hills

12 13 141516

t! ! ! ! L , ?Ardmore Bentonite;

‘Shannon Sa]

.Niobrara Fr

iCarlile Shale* ysmmm v v v

■Belle Fourche Shal

Colum n 16: 23,26,30,40 44,62,65: Merewether et al. (1977), Robinson et al. (1964)

Column 8: 25,27,39, <14-43,49,52,62,64: Merewethe r et al. (1977) 30: Cobban (1969) 72) 75) a)

1.(1975)

>er Cretaceous rocks from northwestern Wyoming to South Dakota. Vertical lines and the numbers above n). Projected fossil occurrences are marked by small triangles followed by numbers that correspond shown in Figure 20. See Figure 30 for legends.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 00 cSieenbornn Nebraska Medicine Bow Rawlins W T |l IlHlflililll m m m m m U plift Rock Springs M M Pii! Thrust B ek Figure 35. Generalized time-stratigraphic correlation chartforUpper Cretaceous fromstrata southwesternWyoming to Nebraska. Albian Santonian Coniacian Turoman Campanian Maastrichtian Cenomanian

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. GREATER GREEN LARAP RIVER BASIN BASH Moxa Rock Springs Rawlins Medicine Lararr Arch Uplift Bow

|<»or Jl 7 8 9 1 0 11 1 1 'li '.B ail Blair si-V'-V'/vV-V. meters

; A

j** *■ ' ‘ • ; ’ f, Hilliard Shale •* c* r ^ ’irPl* 't - . I - , ' Column 13: s m t a 42,43: Merewethe V v--V ’» M erewether and C

HM j Colum n 11: ' 39,43,47,62: Cobban (1951b] 1000- Colum n 10: 39,43,47,63: Merewether (1983b)

Column 9: (composite): 30,32,35: Smith (1965)

VjToniicrFnr Column Smith Column Merewether .•Aspen

Column 1 2000-1 40: Merewether (1983b)

Figure 36. Regional stratigraphic cross section 4 of lower Upper Cretaceous rocks from so represent individual wells (see Appendix for name and location). Projected fossil occurrenc to the ammonite zones in Figure 23. Location of the section is shown in Figure 20. See Figi

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. LARAMIE DENVER TO NEBRASKA BASIN BASIN Medicine Laramie Cheyenne Bow 18 15i 16i 17i

<2?*v V 4 { .*. .- + '- ^ -t I i i i I i i—I i i i I i i i i I i i jj-.i- • L .-r ~*~t t t t t + ti-t -t- -f- ■*■ t ^ ^ ■

Front er Belle Fourche Soil

Column 16: 25: Kitely (1978)

Column 13: 42,43: Merewether et al. (1979) Merewether and Cobban (1972) I Column 11: ' 39,43,47,62: Cobban (1951b) 100 200 km mn 10: 3,47,63: Merewether (1983b)

(composite): Smith (1965)

pper Cretaceous rocks from southwestern Wyoming to Nebraska. Vertical lines and the numbers above on). Projected fossil occurrences are marked by small triangles followed by numbers that correspond s shown in Figure 20. See Figure 30 for legends.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 89

basin, equivalent strata consist of the Belle Fourche Shale, Greenhorn Formation, Carlile

Shale, Niobrara Formation, and lower part of the Steele Shale. Four time lines are drawn

on the basis of fossil data and lithologic marker beds.

The southern cross section begins near Kemmerer, crosses the Rock Springs Uplift,

and ends near the northeast margin of the Denver basin (Fig. 36). Strata included here are

late Cenomanian to Santonian in age; early Campanian strata in the upper part of the

Niobrara cycle are excluded because of insufficient age-diagnostic fossil data. In

lithostratigraphic terms, this interval consists of the Frontier Formation and the Hilliard

Shale in the Kemmerer area; the Frontier Formation and the lower part of the Baxter

Shale in the Rock Springs Uplift area; the Frontier Formation and the Niobrara Formation

in Laramie and Denver basins; and the Graneros/Belle Fourche Shale, Greenhorn

Formation, Carlile Shale, and Niobrara Formation in Nebraska. Three time lines are

drawn on the cross section on the basis of fossil data and lithologic marker beds.

Greenhorn age

The Frontier Formation and its temporal equivalents elsewhere, such as the Ferron

Sandstone of central Utah, represent a major regressive clastic wedge along the western

part of the Western Interior basin (Cobban and Reeside, 1952b). As defined in western

Wyoming, the Frontier Formation consists of those strata that lie between the top of the

hard siliceous marine shale of the Aspen or Mowry Shale, and the top of the highest

sandstone below the soft black marine shale of the Cody/Hilliard Shale. The Frontier

Formation, of both marine and nonmarine origin, comprises an alternating succession of

sandstone and shale with minor amounts of bentonite and coal beds. The thickness of the

Frontier Formation ranges from less than 50 meters on the Rock Springs uplift to more

than 700 meters near the thrust belt (Figs. 34,36). Inasmuch as the sandstone that

defines the top of the formation intertongues and passes into shale to the east, the

lithological boundaries of the Frontier Formation become progressively older in that

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 90

direction. The Frontier Formation is gradational with both the underlying Mowry Shale

and the overlying Cody/Hilliard Shale. However, internally, the Frontier Formation is

punctuated by several unconformities (Merewether and Cobban, 1986).

The Frontier Formation is in excess of 300 meters thick in Jackson Hole area, about

150 meters on the southern flank of the Bighorn basin, and nearly 180 meters in the

Powder River basin (Fig. 34). Its lithofacies changes laterally from interbedded marine

and nonmarine sandstone and shale in Jackson Hole area to fully marine shale and

sandstone in the Powder River basin, where it is divided into the Belle Fourche Shale,

the Wall Creek Sandstone, and the intervening "unnamed Member" (Merewether et al.,

1977,1979). In the Black Hills, the correlative of the Frontier Formation consists of the

Belle Fourche Shale, the Greenhorn Formation, and the Carlile Shale. Ammonites and

bivalves have been found in the upper part of the Frontier Formation; they are sparse to

absent at most other horizons. The reported collections of zonal fossils include:

Collignoniceras woollgari from the Jackson Hole area (Cobban and Reeside, 1952b;

Love, 1956), Dunveganoceras pondi from the eastern flank of the Bighorn Mountains

(Merewether et al., 1975), and Dunveganoceras pondi and Collignoniceras woollgari

from the western flank (Merewether et al., 1977). These are late Cenomanian to early

Turonian guide fossils of the Greenhorn Formation in Colorado. In and east of the

Powder River basin, late Turonian-early Coniacian molluscan zonal fossils

Dunveganoceras pondi through Inoceramus erectus have been found in abundance in the

Frontier Formation or its equivalent (Merewether and Cobban, 1986; Cobban, 1958a).

At its type locality at Cumberland (about 30 miles southwest of Column 1, Fig. 36),

the Frontier Formation consists of 700 meters of sandstone, siltstone, mudstone, and

minor amounts of coal and bentonite beds (Cobban and Reeside, 1952b). The lower half

of the Frontier Formation consists of nonmarine sandstone and mudstone, whereas the

upper half consists of interbedded, predominantly marine sandstone and shale. The

Frontier Formation thins to the east and grades into increasingly marine rocks with fewer

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 91

and thinner sandstones beds. Near Rawlins, the Frontier Formation is a fully marine

succession totaling 150 to 200 meters in thickness. It comprises the Belle Fourche Shale,

the Wall Creek Sandstone, and the intervening "unnamed Member" (Merewether and

Cobban, 1972; Merewether et al., 1979). Fossils are generally sparse in the Frontier

Formation. However, the early-middle Turonian zonal fossils Mammites nodosoides

and Collignoniceras woollgari have been reported from the upper part of the Frontier

Formation (Allen Hollow Member and the Oyster Ridge Sandstone) in the Kemmerer

area (Merewether, 1983b; Merewether and Cobban, 1986). In southeastern Wyoming,

late Turonian to early Coniacian zonal fossils Scaphites whitfieldi, Inceramus erectus,

and Prionocyclus quadratus have been collected from the Wall Creek Sandstone

(Merewether et al., 1979).

The Frontier Formation in western Wyoming spans much of the Greenhorn cycle.

The transgressive phase of the Greenhorn cycle was recorded by the regressive sandstone

and interbedded siltstone in the lower part of the Frontier Formation in western and

central Wyoming, and by the lower part of the Belle Fourche Shale in eastern Wyoming

and beyond. The Greenhorn regression is recorded by one or more unconformities in the

Frontier Formation. According to Merewether (1983b), Merewether et al. (1975,1976,

1984), and Merewether and Cobban (1973,1985,1986), a regional unconformity may

be found in the upper Frontier Formation throughout Wyoming, separating the upper

predominantly marine sandstones (Wall Creek) from the lower marine and nonmarine

sandstones and shales.

Niobrara age

In western Wyoming, strata of the Niobrara cycle are represented by the uppermost

marine and nonmarine Frontier sandstone, the overlying marine shale, and the lower part

of the Mesaverde Formation (Figs. 33,35). Many names have been given to this marine

shale unit (Gill et al., 1970). In southwestern Wyoming, it is named the Hilliard or

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 92

Baxter Shale. In the remainder of Wyoming and Montana, it is called the Cody Shale.

Where the Niobrara limestone beds can be recognized, the marine shale above the

Niobrara Formation is named the Steele Shale, as in eastern Wyoming, or the Pierre

Shale, as in eastern Colorado, Nebraska, and western Kansas.

The Cody/Hilliard Shale consists of shale and minor amounts of thin bentonitic,

calcareous, and fine-grained sandstones and siltstone beds. It intertongues extensively

with the overlying marine and nonmarine sandstones of the Mesaverde Formation. As a

result, the upper boundary of the Cody/Hilliard Shale rises stratigraphically eastward as

successively younger Mesaverde sandstone tongues pass into shales (Figs. 33,34,35).

The Ardmore Bentonite Bed can be recognized on wireline logs in northern Wyoming,

but its lithologic identity becomes lost in southern Wyoming. The Cody/Hilliard Shale is

moderately fossiliferous at some horizons. These fossils permit stratigraphic correlations

in this otherwise nondescript shale unit. Reported collections of molluscan zonal fossils

include: the late Coniacian Scaphites depressus from the flanks of the Bighorn basin

(Cobban, 1951b, Keefer, 1972), the middle Santonian Clioscaphites vermiformis and

late Santonian Desmoscaphites bassleri in the Rock Springs Uplift and Rawlins area

(Smith, 1961,1965; Cobban and Reeside, 1951; Gill et al., 1970), the early Campanian

Scaphites hippocrepis and Baculites sp. (weak flank ribs) in the Black Hills (Cobban,

1969; Robinson et al., 1964).

Cross sections 5: central Utah to Denver Basin

Upper Cretaceous rocks are well exposed in central Utah and northern Colorado.

Regionally, they display similar intertonguing facies relationships to those in Wyoming.

However, a different set of lithostratigraphic nomenclature has been applied (Fisher et

al., 1960; Fouch et al., 1983; Molenaar and Rice, 1988). Near the Sevier thrust belt in

central Utah, the bulk of the Upper Cretaceous rocks are composed of synorogenic

conglomerates of the Indianola Group. The Indianola Group, aggregating over 4000

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 93

meters locally, grades rapidly eastward into a series of sandstone beds that intertongue

with the marine Mancos Shale farther to the east. The Mancos Shale consists of marine

shale and siltstone and correlates broadly to the Hilliard/Cody Shale in Wyoming. It

attains a thickness over 1 km in many areas of eastern Utah and western Colorado. In

eastern-central Utah, the major sandstone units intertonguing with the Mancos Shale are

the Ferron Sandstone, Emery Sandstone, Star Point Sandstone, Blackhawk Formation,

and Castlegate Sandstone (Fig. 37). These sandstone tongues break the Mancos Shale

into the Tununk Shale, lower Blue Gate Shale, and upper Blue Gate Shale members.

Most of these coastal sandstones pinch out in northwestern Colorado. There, the Mancos

Shale is a monotonously uniform shale succession containing only the Juana Lopez

siltstone bed near its base and the sandy Mancos B zone in its upper part. Farther east, in

the Denver basin, the Upper Cretaceous rocks are distinguished by abundant calcareous

marine shale and limestone beds much like those in the Pueblo area in terms of lithology

and nomenclature.

This cross section (Fig. 38) extends across three Laramide basins: the Uinta,

Piceance Creek, and Denver basins (Fig. 20). Strata selected on this cross section span

not only the Greenhorn and Niobrara cycles, but also the early phase of the Claggett

cycle. This package is bounded by the Mowry Shale and the top of the Castlegate

Sandstone or its correlative strata to the east (within the Baculites gilberti or Baculites

perplexus zones). Correlations of these rocks between basins are reasonably well

constrained owing to the available subsurface as well as surface data. Six time lines were

established along the cross section by using lithologic marker beds and fossil data where

available.

Greenhorn age

The Mowry Shale deposited during the initial Greenhorn transgression is confined to

areas north of northeastern Utah and central Colorado (Fig. 28 a). Rocks in eastern Utah

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4^ VO F m V * V A W GreenhornFm Niobrara ' t ' i 'w * *- * £r« .miner kRid and K«» I I DenverBasin irfox'fflllsSs'- «.> irfox'fflllsSs'- /Hygiene as/Hygiene Kremling Front Range Kremlu s MancosShale fuahaLopez Mbr Douglas Arch BuckTong l*kkhi*k I m Emery Ss, egatess. UintaBasin Figure 37. Generalized time-stratigraphic correlation chartUpperfor Cretaceous fromstrata Uinta to Denver Basins. Albian Turonian Coniacian Santonian Campanian Cenomanian Maastrichtian

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. —PICEANCE CREEK-*. _N. PA UINTA BASIN- BASIN BAS Salina Sunnyside Douglas Arch Meeker Kremlin 7 8 9 10 12 1314 15 16 171819 2021 22

unu a*

meters

erreS ht

"v Mancos S lu le -o r/ 'V-1 *

1000 -

2 1 ,2 3 ,2 4 Izett et al. 39 and 43- i3 7 an d 4 6 : 40,44: Iz< P 24, and 26 Cullins (1969) ^ B lu c G itc S Gill and Hail (1975) | 21 and 23: ! i i i i i i i Gill and Hail (1975)| i i i i ! 29,' 3 2 ,3 5 ,3 7 ,3 8 ,4 4 ,4 6 ,4 7 , 21,24,25, and i 49, and 63: Fisher et al. (1960) 26: Hail (1974) 63: Katich (1954)

2000H

i29 and 35: Cobban (1976) i 44 and 47: Esher et al. (1960) Tununk Shale

55-56: Zelt (1985) M m -

Figure 38. Regional stratigraphic cross section 5 of lower Upper Cretaceous rocks from central Utah to western IS (see Appendix for name and location). Projected fossil occurrences are marked by small triangles followed by nun section is shown in Figure 20. See Figure 30 for legends.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. NCE CREEK — _N. PARK DENVER BASIN- \SIN BASIN Meeker Kremling Boulder 16 17>8 19 2021 22 23 24 25 26 28 29 30 31

Kremling .Ss

£ N io b ram F CSrlfleSha Orccnboro F m IM owrySna

Ptenr Shale

20 (21?), 2 3 ,2 4 , and 25 Scotland Cobban (1965) 34,39, and 43: Scott (1963) * 62: Scott (i9 6 2 )

21,23,24,25, and 26: Izett etal. (1971) 39 and 43-45: Hail (1968) 40,44: Izett (1968) 200 km fail (1975) • 21,24,25, and 26: Hail (1974)

i rocks from central Utah to western Nebraska. Vertical lines and the numbers above represent individual wells ;ed by small triangles followed by numbers that correspond to the ammonite zones in Figure 23. Location of the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 96

that are correlative with the Mowry Shale include the nonmarine sandstones in the upper

part of the undifferentiated Dakota Sandstone and the Cedar Mountain Formation of

Aptian to early Cenomanian age (Molenaar and Cobban, 1991). In much of northern

Colorado and northeastern Utah, the Mowry Shale retains its distinct lithology and log

patterns, but it is only about 20 meters thick, considerably thinner than to the north.

In east-central Utah, the oldest fully marine unit resulting from the Greenhorn

transgression is the Tununk Shale Member of the Mancos Shale. The Tununk Shale

consists of shale, siltstone, and minor amounts of bentonite beds. Many bentonite beds

can be traced laterally over long distances (Zelt, 1985). Its contact with the underlying

Dakota Sandstone is conformable. The contact with the overlying Ferron Sandstone is

also gradational. The thickness of the Tununk Shale decreases rapidly to the northeast,

from over 200 m on the Wasatch Plateau to only 30 m near the Utah-Colorado state line

(Ryer and McPhilips, 1983). Molluscan fossils are fairly abundant in the Tununk Shale.

In eastern Utah, the late Cenomanian bivalve Pycnodonte newberryi (formerly Gryphaea

newberryi) has been widely reported in beds a few meters above its base (Dane, 1935;

Katich, 1954; Young, 1960; Fisher and others, 1960); the middle Turonian zonal fossil

Collignoniceras woollgari has been found in a sandy unit (Coon Spring Sandstone) in

the middle of the Tununk Shale (Molenaar and Cobban, 1991); and the late middle

Turonian zonal fossil Prionocyclus hyatti in the basal beds of the overlying Ferron

Sandstone (Cobban, 1976; Cobban and Hook, 1980; Molenaar and Cobban, 1991). Near

the Colorado state line, the slightly older late Cenomanian zonal fossil Duvenganocems

albertense has been found in the basal part of the Mancos Shale (Fouch et al., 1983). In

central Utah, Collignoniceras woollgari was also found in the basal beds of the Ferron-

equivalent strata of the Funk valley Formation (Ryer and McPhilips, 1983). These fossils

indicate that the base of the Tununk Shale becomes progressively younger and its top

progressively older to the west. In general terms, the total Tununk Shale is approximately

correlative with the Bridge Creek Limestone and the Carlile Shale of Colorado.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 97

The regressive phase of the Greenhorn cycle is represented in eastern Utah by the

lower Ferron Sandstone Member, an eastward-thinning sandstone wedge

contemporaneous with the upper part of the Frontier Formation in Wyoming. The Ferron

Member is nearly 300 m thick on the Wasatch Plateau, but pinches out rapidly eastward.

The upper part of the Ferron grades into the marine siltstone and shale of the Juana Lopez

Member (Molenaar and Cobban, 1991). The Ferron Sandstone Member consists of

sandstones interbedded with minor amount of shales, and coal beds. The basal Ferron

Sandstone is a coastal sandstone unit gradationally overlying the Tununk Shale. The

upper Ferron Sandstone, sharply overlain by the main body of the Mancos Shale and

confined west of Price, consists of interbedded deltaic/fluvial sandstone and shale that

thin and become increasingly marine to the east (Molenaar and Cobban, 1991; Ryer and

McPhilips, 1983). Many ammonites and bivalves have been collected from the marine

beds in the Ferron Sandstone Member and from its correlative to the east, the Juana

Lopez Member. They span three or four molluscan fossil zones, ranging from the middle

Turanian Prionocyclus hyatti to late Turanian Inocemmus perplexus (Fisher et al., 1960;

Molenaar and Cobban, 1991). These fossils indicate partial equivalence of the Ferron

Sandstone to the Codell Sandstone and Juana Lopez Member in eastern Colorado and

western Kansas (Fig. 37).

Niobrara age

Strata of the Niobrara cycle are represented by the upper part of the Ferron

Sandstone, Blue Gate Shale Member of the Mancos Shale, the Star Point Sandstone, and

the Blackhawk Formation in central and eastern Utah; by the main body of the Mancos

Shale in northwestern Colorado; and by the Niobrara Formation and the lower part of the

Pierre Shale in northeastern Colorado.

The Blue Gate Shale Member conformably overlies the Ferron Sandstone Member

and underlies the Star Point Sandstone and the Blackhawk Formation. It is separated into

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 98

a lower tongue and an upper tongue (or the Masuk Shale) by an eastward thinning

sandstone wedge, the Emery Sandstone. Where the Emery Sandstone pinches out, the

marine shale equivalent to the Blue Gate Shale is called the Mancos Shale. The total

thickness of the Blue Gate Shale Member, including that of the intervening Emery

Sandstone, averages about 1 km in central Utah. Toward the thrust belt, the Blue Gate

decreases in thickness as it grades to the sandstone and conglomerate of the Funk Valley

Formation (Molenaar and Rice, 1988). The upper boundary of the Blue Gate rises

stratigraphically eastward with the pinchout of successively younger sandstone beds in

the Star Point Sandstone and the Blackhawk Formation. On the Douglas Arch and in the

western Piceance Creek basin, the Mancos Shale contains in its upper part a regionally

extensive sandy unit locally called the "Mancos B" (Kellogg, 1977; Cole and Young,

1991). This sandy interval was formerly correlated with the Emery Sandstone in central

Utah (Fouch et al., 1983), but correlations of this study suggest that it correlates with the

younger Star Point Sandstone. Molluscan fossils are moderately abundant in the Blue

Gate Shale Member. In central Utah, early Coniacian Scaphites preventricosus and

middle Coniacian Inoceramus deformis have been reported in the basal Blue Gate Shale

Member; middle Santonian Clioscaphites vermiformis and late Santonian

Desmoscaphites bassleri in the basal Emery Sandstone; and early Campanian Scaphites

hippocrepis in the upper Blue Gate Shale Member (Fisher et al., 1960; Cobban, 1976).

These limited fossil collections indicate that the Blue Gate and the intervening Emery

Sandstone are the temporal equivalent of the Niobrara Formation in eastern Colorado and

western Kansas.

The Star Point Sandstone is the oldest sandstone tongue overlying the Blue Gate

Shale. It is less than 100 m thick on the Wasatch Plateau and pinches out rapidly to the

east. No age-diagnostic fossils have been collected from the Star Point Sandstone, but

Fouch et al. (1983) assigned the Star Point Sandstone to the latest Santonian and early

Campanian through correlation to ammonite bearing beds along the Book Cliffs.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 99

Overlying the Star Point Sandstone, the Blackhawk Formation is a succession of

nonmarine and marine sandstones comprising as many as six eastward-thinning

sandstone tongues or members (Young, 1955). Each tongue thins and becomes

increasingly marine to the east. Together, successively younger tongues step farther

basinward. The contact between the Blackhawk Formation and the overlying Castlegate

Sandstone is a major unconformity in Utah but becomes conformable towards the

Colorado state line, where the youngest Blackhawk sandstones pinch out.

The Castlegate Sandstone is areally the most extensive sandstone tongue in the

Mancos Shale. It thins and becomes increasingly marine to the east. It pinches out east of

the Colorado State line in the Piceance Creek basin. Its contact with the overlying Mancos

Shale is a sharp but conformable surface. Because of sufficient wireline log control and a

fair amount of fossil data, this surface has been correlated as far east as the Denver basin.

The Castlegate Sandstone and the shale immediately below and above have yielded many

ammonite zonal fossils, particularly along the Book Cliffs (Gill and Hail, 1975). These

include lower middle Campanian Baculites macleami and Baculites asperiformis in the

Castlegate Sandstone and the underlying shale, and the middle Campanian Baculites

perplexus at the base of the overlying Buck Tongue of the Mancos Shale.

Cross section 6: Kaiparowits region-San Juan Basin-Raton Basin-Pueblo

Upper Cretaceous rocks are only sporadically preserved in the southern part of the

Western Interior basin as a result of widespread post-Cretaceous uplift and erosion.

Areas with extensive Upper Cretaceous deposits include: the Kaiparowits Plateau, the

Henry Mountains region, the Black Mesa, San Juan, and Raton basins (Fig. 20). Upper

Cretaceous rocks vary with location in thickness, lithofacies, and stratigraphic

nomenclature (Fig. 39). On the Kaiparowits Plateau, the Upper Cretaceous series is

about 2350 m in total preserved thickness. Its lower 600 meters is a predominantly

marine unit composed of the Dakota Sandstone and the Tropic Shale, and the remainder

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. r 8 Vc rroc Vc Raton Basin ^ |♦ ... » QitlaodFm/yy San Juan Basin SW U plift M onum ent Henry region M ountains rowitsFm Drip TankDrip Mbr S.W. Kaiparowits Kaiparowits regionto Raton Basin. Figure Generalized 39. time-stratigraphic correlation chartUpperfor Cretaceous from strata Albian Turanian Coniacian Santonian Campanian Cenomanian Maastrichtian

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. KAIPAROWITS HENRY MTS SAN Jl REGION REGION BASI] Cedar City Hatch Mt Ellen Ship Rock 1 2

0

meters \\i'\lA•*.% i:y:y.y •* *.*•’> AV^V^V*‘V*.V*.' John Henry M b r\ •*.*.•>. •'/.•*. y.Sinujjju CIilT»Fn>\%;’.V

^ v T j 7 . » 7 ; |.;,'.1,'.Ferron&>.*.■ ■ f .

^ *' '« ^46n,<7 Br d jc Creek La Turn nk V p a k o to & \j< ......

32,35,39,44-47: Reeside (1924) 32,35,37,46-47,51, and 55- 44-47: Dane et al. (1966), SVM* Peterson and Ryder (1975) Hook and Cohhan ( 19801 59,62: Cobban et al. (198‘

1000 - * 58-60: Cobban and Hook (1984) 38,46-47: Peterson (1969)

49 and 55-58: Lawrence (1965), Peterson and Kirk (1977), Zelt (1985) 49: Lessard (1973) 55-58: Moir (1974)

Figure 40. Regional stratigraphic cross section 6 of lower Upper Cretaceous rocks from southern Utah to (see Appendix for name and location). Projected fossil occurrences are marked by srnall triangles folio wet section is shown in Figure 20. See Figure 30 for legends.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. SAN JUAN RATON BASIN BASIN Ship Rock El Vado Trinidad 10 11 To Alwood, KS *

Mancos

* v «44-47 CanileSba f ' Juana LopezK

33,35,38,41,42: Scott et al. (1986) 50,62: Kauffman et al. (1969) ...... i t 'i ‘ I i i ^ 32,35,39,44-47: 25: Cobban, Landis, and Dane (1974) Reeside (1924) 30: Cobban (1969) 44-47: Dane et al. (1966), 38,39,44: King (1974) and Dane (1960) Hnok and Cobban (10801 59,62: Cobban et al. (1989) 50,59: Landis et al. (1973)

100 200 km . i..

:eous rocks from southern Utah to western Kansas. Vertical lines and the numbers above represent individual wells marked by small triangles followed by numbers that correspond to the ammonite zones in Figure 23. Location of the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 0 2

of the section is a predominantly nonmarine unit comprising the Straight Cliffs and the

Wahweap Formations (Peterson, 1969). In the Henry Mountains region, Upper

Cretaceous rocks were more deeply eroded, preserving only the lower 1300 meters. The

section here comprises the Dakota Sandstone, Tununk Shale, Ferron Sandstone, and

Mancos Shale. In the San Juan basin, over 2000 meters of Upper Cretaceous rocks are

preserved (Molenaar, 1983). In the southwest part of the basin, rocks are predominantly

nonmarine sandstone and shale. To the northeast, they pass into the marine shale of the

Mancos and Lewis Shales by facies changes (Molenaar et al., in press). Because of the

complex intertonguing marine and nonmarine formations across the basin, stratigraphic

nomenclature varies with location. In the Raton basin, the lithofacies and stratigraphic

nomenclature of the Upper Cretaceous rocks are similar to those at Pueblo, Colorado

(Kauffman et al., 1969; Scott et al., 1986).

This cross section begins in the Kaiparowits Plateau, crosses the Henry Mountains,

San Juan and Raton basins, and ends in western Kansas (Fig. 40). The interval selected

is that of the Greenhorn cycle and the early and middle part of the Niobrara cycle.

Because of the absence of Mowry Shale, the initial Greenhorn transgressive surface at the

top of the Dakota Sandstone was chosen as the oldest horizon in the subsequent

backstripping analysis. Four time lines were established along the cross section on the

basis of lithologic marker beds and fossil records. These lines are well constrained by

fossil data in and east of the San Juan basin. However, uncertainties exist in correlations

of strata of the Niobrara age in the Kaiparowits Plateau and the Henry Mountains region

because of erosion, increased amount of nonmarine strata, and the scarcity of age-

diagnostic fossils.

Greenhorn age

The Greenhorn sea did not flood the southwestern part of the Western Interior basin

until near its peak transgression in the late Cenomanian-early Turanian. Therefore, in the

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 103

Kaiparowits, Henry, and much of the San Juan basins, early transgressive deposits of

the Greenhorn cycle equivalent to the Mowry Shale are absent. The oldest rocks of the

Greenhorn age are probably the Dakota Sandstone of late Cenomanian age. The Dakota

Sandstone in these basins is commonly less than 100 meters thick and consists of

nearshore marine sandstone in its uppermost part and nonmarine sandstone and shale in

the rest of the section. It unconformably overlies the Lower Cretaceous Cedar Mountain

and Burro Canyon Formations or older rocks, and is overlain conformably by the marine

Mancos Shale. In the Kaiparowits Plateau and Henry Mountains region, the late

Cenomanian zonal fossil Pycnodonte newberryi has been found at the top of the Dakota

Sandstone or the base of the overlying shale (Peterson and Ryder, 1975; Moir, 1974;

Lawrence 1965). In the San Juan basin, where a greater part of the Dakota is of marine

origin, middle and late Cenomanian zonal fossils, from Acanthoceras amphibolum to

Dunveganoceras pondi, have been reported (Molenaar et al., in press). These fossils

indicate that the Dakota Sandstone in these areas is approximately contemporaneous with

the Belle Fourche/Graneros Shale and the lower part of the Greenhorn Formation at

Pueblo. On the cross section in Fig. 40, the oldest time line follows the top of the Dakota

Sandstone in the Kaiparowits, Henry, and much of the San Juan basins. In and east of

the Raton basin, this line follows the top of the Graneros Shale; the Dakota Sandstone

here is Albian-early Cenomanian in age and much older than to the west.

The marine shale overlying the Dakota Sandstone is called the Tropic Shale in the

Kaiparowits Plateau region and the Tununk Shale in the Henry Mountains region

(Peterson, 1969; Peterson et al., 1980; Peterson and Ryder, 1975; Zelt, 1985). The

Tropic/Tununk Shale thins eastward from over 300 meters in the Kaiparowits Plateau

region to less than 200 meters in the Henry Mountains region. In the San Juan basin,

equivalent rocks are the basal Mancos Shale sandwiched between the Dakota Sandstone

and the Juana Lopez Member, including the Bridge Creek Limestone Member and the

Gallup Sandstone (Molenaar, 1983 ; Molenaar et al., in press). The average thickness of

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this interval is about 200 meters. Molluscan zonal fossils are fairly abundant at many

horizons in the Tropic/Tununk Shale and their equivalents. The lower part of the Tropic

Shale in the Kaiparowits Plateau has yielded the late Cenomanian Sciponceras gracile

and the middle Turanian Collignoniceras woollgari (Lawrence, 1965; Moir, 1964; Zelt,

1985). In the Henry Mountains region, the Tununk Shale yielded the early Turanian

Mytiloides mytiloides in its lower middle part, the middle Turanian Collignoniceras

woollgari in its middle part, and the early late Turanian Prionocyclus macombi in its

upper part (Peterson and Ryder, 1975). In the San Juan basin, molluscan zonal fossils

Sciponceras gracile through Collignoniceras woollgari have been collected in the

correlative interval (Molenaar et al., in press). Bentonite beds ranging in thickness from

centimeters to tens of centimeters are quite abundant in the Tropic Shale and its lateral

equivalents to allow correlations between basins. On this cross section, correlations in the

Kaiparowits Plateau region relied on the work of bentonite correlations by Zelt (1985).

Overlying the Tropic Shale in the Kaiparowits Plateau is the Straight Cliffs

Formation, a predominantly nonmarine succession of sandstone, mudstone, and coal

with an aggregate thickness of over 500 meters. The Straight Cliffs Formation

comprises, in ascending order, the Tibbet Canyon, Smoky Hollow, John Henry, and

Drip Tank Members (Peterson, 1969; Peterson and Kirk, 1977). The Tibbet Canyon

Member is a nearshore marine sandstone unit transitional between the underlying marine

Tropic Shale and the overlying nonmarine Smoky Hollow Member. It averages about 30

meters in thickness and contains the early middle Turanian bivalve Inoceramus howelli of

thePrionocyclus hyatti zone (Peterson, 1969). The Smoky Hollow Member is a unit

composed of nonmarine sandstone, mudstone, and coal. Its thickness is highly variable,

from 30 meters in southern Kaiparowits Plateau to 300 meters in northern Kaiparowits

Plateau. No age-diagnostic fossils have been found in the Smoky Hollow Member, but

because it is conformable with the underlying Tibbet Canyon Member, it is probably only

slightly younger. The Smoky Hollow Member is unconformably overlain by the John

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Henry Member, a succession of intertongued marine and nonmarine rocks. Above the

unconformity, the late Coniacian bivalve Inoceramus stantoni or kleini has been found in

the lower westward-thinning marine shale tongue of the John Henry Member (Peterson,

1969). This fossil and the Inoceramus howelli from the Tibbet Canyon Member suggest

that this unconformity could span late Turanian to middle Coniacian. It probably

correlates with the regional unconformity of lesser magnitude near the top of the Frontier

Formation in Wyoming.

In the Henry Mountains region, strata equivalent to the Tibbet Canyon and Smoky

Hollow Members are represented by the Ferron Sandstone, the lateral extension of the

Ferron Sandstone in central-eastern Utah. The Ferron Sandstone averages about 80

meters and consists of marine sandstones in the lower part and nonmarine sandstones,

mudstones, and coals in the upper part. It is in gradational contact with the Tununk Shale

below but separated from the Blue Gate Shale by an unconformity (Peterson and Ryder,

1975). Below the unconformity, the lower marine part of the Ferron Sandstone has

yielded the middle Turanian zonal fossil Inoceramus howelli. Above the unconformity,

the basal part of the Blue Gate Shale contains the late Coniacian inoceramids, either

Inoceramus stantoni or 7. kleini. This unconformity correlates with the one separating the

Smoky Hollow Member from the John Henry Member in the Kaiparowits Plateau

(Peterson and Kirk, 1977).

In the southwestern San Juan Basin, strata correlative with the Ferron Sandstone are

the Tres Hermanos Formation, a northeast-thinning wedge of nonmarine and nearshore

marine sandstones. Middle to late Turanian fossils such as Collignoniceras woollgari

and Lopha lugubris have been reported from the Tres Hermanos Formation (Molenaar et

al., in press). Because the cross section in Fig. 40 crosses the San Juan Basin farther

north, it does not include the Tres Hermanos Formation. Instead, only its offshore

equivalent Mancos Shale is shown.

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The Niobrara age

Initial transgressive strata of the Niobrara cycle, such as the Juana Lopez Member of

the Mancos Shale and the Fort Hayes Limestone Member of the Niobrara Formation in

Colorado, are not present in the Kaiparowits Plateau and Henry Mountains region (Fig.

39). This period of time was probably recorded by the predominantly regressive,

nonmarine deposits of the Smoky Hollow Member, the upper nonmarine Ferron

Sandstone, and the unconformities above them. In the Kaiparowits Plateau, strata

deposited during the remainder of the Niobrara include the John Henry and Drip Tank

Members of the Straight Cliffs Formation, and possibly part or all of the overlying

Wahweap Formation (Peterson and Kirk, 1977). These rocks are predominantly

nonmarine sandstones, mudstones and coals. Their total thickness averages about 600

meters. Owing to the scarcity of age-diagnostic fossils, considerable uncertainties exist

with respect to their ages. In the Henry Mountains region, strata of the Niobrara cycle

includes the Mancos Shale and the Muley Canyon Sandstone. The Mancos Shale in that

area averages about 450 meters in thickness. It has yielded several Coniacian and

Santonian molluscan zonal fossils, including Scaphites depressus, Clioscaphites

vermiformis, and Desmoscaphites bassleri (Peterson and Ryder, 1975). Conformably

overlying the Mancos Shale, the Muley Canyon Sandstone is a regressive sandstone unit

and averages about 90 meters in thickness. Its lower part consists of nearshore marine

sandstone and the upper part is composed of nonmarine sandstone. The Muley Canyon

Sandstone here is stratigraphically unrelated to the Emery Sandstone in central Utah.

According to Peterson et al. (1980) and Maxfield (1976), the Muley Canyon Sandstone

in the Henry Mountains region is of early Campanian age and correlate with the Star

Point Sandstone and the lower Blackhawk Formation in east-central Utah (Fig. 37).

Unlike in the Kaiparowits Plateau and the Henry Mountains region, strata of the

Niobrara age are well preserved in the San Juan basin and contain molluscan fossils (Fig.

40). However, considerable difference exists between the local stratal stacking pattern

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and the transgressive-regressive trends observed elsewhere (Fig. 39). On the western

side of the San Juan basin, the early phase of the Niobrara cycle is recorded by the Juana

Lopez Member and the predominantly regressive nearshore marine sandstones of the

Gallup Sandstone. It is noteworthy that the Gallup Sandstone has no lateral correlatives

in the Kaiparowits Plateau and Henry Mountains region (Molenaar, 1983; Peterson and

Kirk, 1977). The remainder of the Niobrara cycle in the western San Juan basin was

recorded by the northeast-thinning wedges of the Crevasse Canyon Formation, the Point

Lookout Sandstone, and the intervening southwest-thinning Mulatto and Satan Tongues

of the Mancos Shale (Molenaar et al., in press). On the cross section in Fig. 40, which is

seaward of these intertonguing units, these formations are represented by their offshore

equivalents in the Mancos Shale. In the northeastern San Juan basin, strata of the

Niobrara cycle consists of the Juana Lopez Member and the overlying Mancos Shale.

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INTRODUCTION

With few exceptions, stratigraphic successions attaining significant thickness reflect

continued tectonic subsidence. Determination of tectonic subsidence from basin

stratigraphy constitutes an important aspect of basin analysis. Early studies generally

relied on isopach maps or rock thickness-time diagrams to portray the trends of tectonic

subsidence. Although fairly effective in portraying the long term trends and dominant

patterns of tectonic subsidence, raw sediment thickness is not an accurate measure of

tectonic subsidence for detailed quantitative subsidence analysis. Sleep (1971) discussed

the complicating effects on subsidence analysis due to such factors as isostasy of

sedimentation, compaction, eustatic changes, and differences in sedimentary facies.

These concepts were later integrated into what is now known as the backstripping

techniques. The quantitative procedures of backstripping techniques were formulated by

Watts and Ryan (1976). Since then, they have been widely used as a powerful means of

extracting tectonic subsidence from stratigraphic records in many sedimentary basins

around the world (e.g., Steckler and Watts, 1978; Sclater and Christie, 1980; Bond and

Kominz, 1984).

Compared to the use of gross rock thickness, backstripping techniques provide a

more rigorous quantity that relates to with calculations of various basin models.

Furthermore, backstripping analysis facilitates comparison of results from different areas,

or basins. Indeed, since it was first formulated a little more than a decade ago, the

backstripping technique has been instrumental to the improved understanding of many

sedimentary basins.

This chapter briefly outlines the principles of backstripping and discusses step by step

the procedures of flexural backstripping as applied in the Cretaceous Western Interior

108

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basin. These procedures include flexural unloading of sediments, decompaction, and

correction for water depths. At the end of this chapter, a brief discussion is given of the

errors arising from various possible sources.

AIRY BACKSTRIPPING

Backstripping techniques were invented to extract tectonic subsidence from

stratigraphic records, i.e., that part of subsidence not attributable to sediment loading,

compaction, sea level changes, and paleowater depths. According to the types of isostasy

taken to calculate sediment loading (Airy, 1855; Barrell, 1914), two types of

backstripping analysis are generally recognized in the literature: Airy backstripping and

flexural backstripping (Fig. 41). Following Steckler and Watts (1978), the general

formula of Airy backstripping is:

Y = s pm1pi+W d_ ASL_P=_ (1) pm - pw pm - p«

where S is the decompacted sediment thickness, Wd is the water depth, ASL is

eustatic sea level change (positive for a rise), and p m , p s , and p * are the mantle, bulk

sediment, and water densities respectively. The above Airy backstripping scheme applies

to individual stratigraphic columns. It requires that a stratigraphic column, either an

outcrop or wireline log section, be broken down into a succession of stratigraphic units

or intervals according to faunal data, radiometric ages, or by correlation with a well-

established section. In calculations, stratigraphic units are successively stripped off,

causing the basement to rise isostatically and the underlying units to expand or decompact

to the original thickness in the absence of overburden. This procedure is repeated until the

oldest unit is removed.

Airy backstripping simplifies lithospheric response to sediment loading by assuming

that lithosphere has no lateral strength (Fig. 41). Although unsupported by geophysical

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Loaded Unloaded a. ______ASL Water column W

Sediment column S

Fully compacted sedimentary rocks 4 Mantle

Sediment load

Lithosphere

Sediment C. load >Ps

/ / < / / t / / » Lithosphere N N ' NX ✓ / i' NX*/ / XX f \ / X / ' / X ✓ X✓

Figure 41. Illustration and comparison of Airy and flexural backstripping schemes. Steckler and Watts's (1978) backstripping diagram includes an uncorrected geologic column and "backstripped" (unloaded) column (a.). Airy isostasy assumes no lateral strength for lithosphere (b.). In contrast, flexural isostasy recognizes lithosphere's lateral strength (c.). From Angevine et al. (1990)

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evidence, the simplifying assumption is often necessary and, in certain circumstances,

justifiable. For example, Airy backstripping can be applied with little hesitation in fault

dominated basins, especially those supported by a young and less rigid lithosphere

marking the early phase of rifting. In these situations, because flexural effects tend to be

spatially limited, Airy backstripping could provide adequate approximation to the actual

sediment loading. Also, Airy backstripping can be considered a viable method in cratonic

basins where strata extend for hundreds of kilometers without significant thickness

variation. Inasmuch as the dimension of such a spatially uniform sediment load can

greatly exceed the flexural wavelength of the lithosphere, sediments can be considered in

Airy isostatic compensation except at basin margins.

In practice, however, Airy backstripping has often been used indiscriminately with

respect to the size of the basin, stratal geometry, and the nature of the lithosphere. This is

partly due to the fact that the stratigraphic data it requires can be easily compiled and

calculations are quite simple and fast. As a potential hazardous consequence, however,

the resultant tectonic subsidence may be exaggerated, such as near basin flanks where

little has actually occurred, or underestimated, such as in the basin interior where certain

amount of tectonic subsidence is incorrectly attributed to sediment loading by Airy

isostasy (Angevine et al., 1990). Because of these limitations, flexural backstripping

schemes generally produce better estimates of regional tectonic subsidence patterns

(Watts, 1988; Watts and Thome, 1992; Steckler et al., 1988; Zhou, 1993).

FLEXURAL UNLOADING OF SEDIMENT

The Cretaceous Western Interior basin is a highly asymmetrical foreland basin, the

stratal geometry of which is a westward-thickening wedge (see Chapter 3). From a

theoretical point of view, this stratal geometry invalidates Airy backstripping. Despite

this, most workers resorted to Airy backstripping to calculate tectonic subsidence history

in the Cretaceous Western Interior basin (Cross, 1986; Heller et al., 1986; Steidtmann et

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al., 1991; Devlin et al., 1993; Johnson, 1992). This approach, though not unreasonable

considering the purposes of these works, fail to account for the potentially significant

flexural effects of sediment loading. In view of the shortcoming of Airy backstripping,

this study therefore adopted a two-dimensional flexural backstripping scheme.

Flexural backstripping calculates and removes sediment loading from the

decompacted sediment thickness according to lithospheric flexure theory instead of Airy

isostasy (Fig. 41). The data format required is regional stratigraphic cross sections,

composed of a series of individual stratigraphic columns of wireline logs, or

alternatively, high quality seismic profiles. The stratigraphic data for this study consists

of six biostratigraphically calibrated subsurface cross sections. Strata bounded by time

lines comprise a succession of discrete sediment sheet or wedge loads. On each cross

section, the interval thickness, lithology, age range, and water depth were specified for

each stratal layer and at each control point.

The flexural subsidence in response to sediment loads were calculated using the same

mathematical procedures as those used in lithospheric flexure modeling (e.g., Turcotte,

1979; Watts 1982; Jordan, 1981; Beaumont, 1978). For simplicity, an elastic flexural

model with constant flexural rigidity is used in this study. As described in Turcotte

(1979), the flexural deflection, w(x), of an infinite, elastic thin beam overlying a fluid

medium in response to loading in two dimensions is described by the differential

equation:

(2)

where D is flexural rigidity, N is horizontal stress, Ap are density contrast between

mantle and the basin fill, g is gravitational acceleration, and p(x) is the load function.

Elastic thickness T is related to the flexural rigidity D by:

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where E is Young's modulus, and v is Poisson's ratio.

Because only sediment loading is considered, the horizontal stress N is ignored.

Unless necessitated by geologic evidence, the flexural rigidity D can be held as a constant

so that the level of mathematical involvement is greatly reduced. The simplified equation

is:

+ Ap • g • w = p(x) (4) dx

where p(x) is the thrust load function in foreland basin modeling and is the sediment load

function in flexural backstripping.

Analytical solutions of this equation for certain geometrically simple loads can be

found in Nadai (1963) and Turcotte (1979). Generally, transform methods are applied to

express flexure in the frequency domain. To calculate flexure, the Fourier transform can

be taken to yield a solution for (4) in the frequency domain (Watts et al., 1983; Banks et

al., 1977):

w(k) = 0 (k L p(k) (5) A p g

f Dk4 '"' o = 1+- (6) Ap

where k is wave number, p(k) is the Fourier transform of p(x) or load spectrum, and

4>is basement response function. Then, the flexural deflection, w(x), can be calculated

by inverse Fourier transform of w(k) in (5).

The flexural backstripping scheme of this study adopts a hybrid finite-difference

method previously used in the literature (Jordan 1981; Flemings and Jordan, 1989). This

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scheme discretizes the sediment layers into evenly spaced line loads, and then uses an

efficient algorithm in Angevine et al. (1990) for solving flexure under line loads to

calculate the flexural deflection due to each load element. Sediment thickness between

control points is calculated by piecewise-linear interpolation of the decompacted

thicknesses. To account for lateral changes in lithologies along the cross sections, a

stepwise interpolation was used to assign sediment densities for each interval according

to the decompacted mean bulk sediment density at control points. At each point, flexure

due to sediment loading is obtained by summing the contributions from each individual

line load. To reduce the flexural edge effect at basin margins, the cross section was

extended for an additional 50 to 100 kilometers on both ends. The flexural rigidity used

in calculation is lxlO24 Nm, a typical value for continental lithosphere (Watts, 1992).

Figure 42 compares the amount of sediment loading calculated by applying Airy and

flexural backstripping schemes respectively to one of the cross sections used in this study

(cross section 5, Chapter 3). Airy isostasy predicts that the basement subsidence in

response to a sediment wedge (Fig. 42 a) assumes a similar but subdued form to that of

the original sediment geometry (Fig. 42 b). In contrast, flexural isostasy predicts a rather

different basement subsidence profile from that of the original sediment geometry (Fig.

42 c). As a result of this difference, the tectonic subsidence patterns calculated by the two

schemes differ significantly, as demonstrated in Figure 43. This demonstration highlights

the inadequacy of Airy backstripping in foreland basins like the U.S. Western Interior.

The Cretaceous rocks exhibit gross thickness variations not only across the basin but

also along the basin axis. However, a two-dimensional flexural backstripping scheme

considers only the flexural effects arising from changes in sediment thickness across the

basin. Apparently, even though the flexural effects across the basin are likely to be far

greater than along the basin axis, a two-dimensional scheme is inherently unsatisfactory.

A still better approach would be a three-dimensional flexural backstripping scheme. A

three-dimensional scheme, though conceptually desirable, is difficult to implement. The

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a. Original strata thickness pattern (cross section 5)

2000

b. Airy sediment unloading

C. Flexural sediment unloading

Figure 42. Subsidence profiles (b and c) in response to the loading of a sedimentary wedge (a). The wedge represents the real geometry of strata on the regional stratigraphic cross section 5 of this study.

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a.

0 km 200 400 600 800 1000 JT,

500

1000

b .

0 km 200 400 600 800 1000

/ ' s *

500 / s ' f /// // 1000

Figure 43. Tectonic subsidence profiles resulting from different backstripping schemes: a. Airy backstripping; b. flexural backstripping. The profiles are derived by subtracting the sediment loading (Fig. 42) from the decompacted thickness. Dashed lines, To to Ts, show progressive subsidence of an original horizontal datum (top of Mowry Shale) during successively deeper burial. Underlying strata was decompacted.

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main difficulty lies in the preparation of a suitable data base, which would take the form

of a series of isochron maps over the entire basin. Until the Cretaceous rocks are

systematically correlated along closely spaced grids to generate such maps, the

mathematical merit of a three-dimensional flexural backstripping scheme will be

undermined by the added difficulties and uncertainties that come with its numerical

implementation. As the stratigraphic data of the Cretaceous Western Interior steadily

accumulates and improves, however, a three-dimensional scheme may be employed in

future studies.

DECOMPACTION OF SEDIMENT

Decompaction restores a rock column to its original, depositional thickness in the

absence of overburden according to certain porosity-depth relationships presumably

followed by sediments. Given a porosity-depth relationship and the assumption that the

rock grain volume is conserved during compaction, decompaction is a rather

straightforward process (Sclater and Christie, 1980; Angevine et al., 1990). The relation

between sediment thickness and porosity is as follows:

So(l — (po) = Sn(l — (pn) (7)

where So and cpo denote the original sediment thickness and porosity respectively, and

Sn and

Given the porosity value of sediments at a certain depth, the decompacted thickness

can easily be calculated. To decompact a stratigraphic section composed of multiple

lithologies, the porosity-depth relationship for each lithology needs to be specified.

However, determination of meaningful porosity-depth relationships for different

lithologies found in a specific basin is seldom if ever an easy task. What is needed is

porosity data for each lithology obtained over a wide range of burial depths. Because this

is not the case in most basins, empirical porosity-depth relationships are commonly used

as a first order approximation. The empirical porosity-depth relationships obtained by

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Sclater and Christie (1980) from the North Sea are among the most widely used. These

empirical relationships assume an exponential form:

where

determined compaction constant, and z is the burial depth corresponding to the porosity

value cpn (Table 1). The porosity-depth relationships for these lithologies are shown

graphically in Figure 44.

Decompaction is usually performed only on the stratal interval under investigation. In

reality, compaction was not just limited to these strata; rather it could occur over the entire

sedimentary cover above the crystalline basement. Unless the underlying strata are thin or

had been sufficiently compacted, failure to take the underlying strata into consideration

results in overestimation of tectonic subsidence. Stated explicitly, compaction of the

underlying strata in response to the overburden of younger sediments leads to greater

depositional thickness than attributable to tectonic mechanisms. The additional thickness

resulting from this compaction is otherwise indistinguishable from the flexural

subsidence driven by supracrustal loading. In the Western Interior basin, the additional

step of including the lower Mesozoic and Paleozoic strata in decompaction is particularly

called for because of their great thickness. More important, because the overall thickness

of the Pre-Cretaceous strata increases westward, their compaction may have contributed

to the asymmetrical geometry displayed by the Cretaceous rocks (Sloss, 1988). To

decompact the Pre-Cretaceous strata, published Phanerozoic isopach maps for the U.S.

Western Interior were used to obtain their thickness (McGookey et al., 1972; Peterson

and Smith, 1986) and a siltstone lithology was used. This choice of lithology may not be

a good representation of these older strata, many of which have a high percentage of

carbonate rocks. Nevertheless, it provides an upper bound on the effect of their

compaction under the overburden of the Cretaceous rocks. Figure 45 compares

subsidence profiles obtained by including and excluding the underlying strata during

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Table 1. Empirical constants in the exponential porosity-depth relationships

cpo C x10'5 p s fcnr1) (a/cm3) Shale .63 .51 2.72

Sand .49 .27 2.65

Chalk .70 .71 2.71

Shaly sand .56 .39 2.68

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. without prohibited reproduction Further owner. copyright the of permission with Reproduced

-10000 Depth (meters) Cretaceous rocks of the Western Interior basin. From Sclater and Christie (1980). Sclater andChristie basin. From Interior Western of the rocks Cretaceous the in used decompacting relationships -depth porosity Exponential 44. Figure -8000- -6000- -4000- - 2000 2 4 6 8 100 80 60 40 20 0 - Silt Sand ooiy%) Porosity(% Shale Chalk 0 2 1 to 1000 '7 7 . 600 800 400 200 siltsone lithology usedwas in calculations. Flexural rigidity D=l.E+24 Nm. Basedon the regional cross section 5. ignoringthe compaction oftheunderlying strata;profile b by decompactingtheunderlying strata. A Figure45. Effectsofthe underlying rocks on resultsof flexural backstripping. Profilea was obtained by 0 0 Km 2000 1000

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 2 2

decompaction, respectively. By ignoring the underlying strata, a greater amount of

tectonic subsidence is predicted than if they are taken into account (Fig. 45 a and b).

Clearly, the compaction of underlying strata during deposition of the Cretaceous rocks

could potentially contribute to their accommodation and asymmetrical geometry.

Although the decompaction procedure is mathematically precise, the geologic

database has several uncertainties and errors. Among the uncertainties pertaining to

decompaction are the porosity-depth relationships, the complicating factors such as

cementation, and the present burial depth of tectonically elevated rocks. First and

foremost, it is important not to lose sight of the fact that the current porosity-depth

relationships are empirical by nature. They may not accurately represent the actual

compaction process in the Western Interior basin. As more precise depth-porosity data

become available for the Cretaceous rocks in the future, decompaction may be improved

accordingly.

The decompaction procedure applied here assumes that reduction of sediment

porosity is due only to mechanical compaction. This assumption certainly is a simplistic

approximation chosen more out of convenience than thoughtful considerations. Sediment

porosity is dependent not only on its burial depth, but also diagenesis. However, little is

known about the quantitative details of the interactions between chemical cementation and

mechanical compaction in the Western Interior basin. Consequently, chemical

cementation can not be easily incorporated into decompaction procedures. For this

reason, this decompaction procedure implicitly assumes that sediment porosity reduction

during burial is depth dependent and controlled by mechanical compaction alone. By

attributing the present thickness to compaction alone, the decompacted sediment thickness

is certainly greater than the original, depositional sediment thickness if chemical

cementation played an important role. Nevertheless, the errors introduced by this

assumption are systematic and distributed evenly over the rock columns where

backstripping is conducted.

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Finally, added to the above complexities is the fact that during Laramide tectonics and

ensuing erosion, Cretaceous rocks in many places were tectonically elevated or exposed

while retaining their low porosity and high density indicative of the previous burial depth

at which they were fully compacted and lithified. Therefore, the present day burial depth

of these rocks needs to be adjusted before decompaction can be carried out. By

comparing outcrop sections with adjacent subsurface ones, it is found that the difference

between subsurface thickness and adjacent outcrop thickness of the same stratigraphic

unit is usually less than 5% -10 %. This suggests that once Cretaceous rocks were fully

compacted and lithified at maximum burial depth, they did not incur significant thickness

expansion during subsequent uplift. In light of this, the present day burial depth of the

strata preserved near uplift areas is corrected according to the average burial depth of the

same strata in adjacent areas where a relatively complete sequence of Cretaceous rocks are

preserved.

SEA LEVEL CORRECTIONS AND THE MEANING OF SUBSIDENCE

As shown in equation (1), the backstripping technique was designed to determine

tectonic subsidence from the stratigraphic record. This goal requires that both water depth

and eustatic sea level changes through time can be independently determined. Uninhibited

by this requirement, many have made attempts towards this straightforward use of

backstripping technique to obtain "tectonic subsidence". Under the scrutiny of the

cautious, however, the fragility of this approach betrays itself. The main reason lies in the

difficulty and complexity of the subject of eustatic sea level changes. Although some

highly commendable results of eustatic sea level estimates, including the Exxon cycle

chart (Haq et al., 1988), have been published, their acceptance is not without skepticism

and reservations (Watts et al., 1982; Burton et al., 1987; Miall 1992). Given the

difficulties and controversies concerning the subject, it is hardly justifiable to consider the

current sea level curves as a known variable in backstripping analysis. With no solution

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of these controversies in sight, this study made no attempt to correct for eustatic sea level

changes. To circumvent this step, equation (1) was rearranged by combining the tectonic

subsidence and eustatic sea level terms to form a composite unknown term R l: R1 = Y + ASL——— = + Wd (9) pm - pw pm - p«r

This approach has been taken previously by Bond and Kominz (1988). Although

referred to as "subsidence" in the discussion, the resulting quantity is actually a

composite of tectonic subsidence, contemporaneous eustatic sea level change, and the

consequent effects of water loading.

WATER DEPTH CORRECTIONS

Tectonic subsidence is recorded by deposition of sediments as well as by changes in

water depth. Correction for changes in water depth is therefore an important step in

backstripping analysis. In general, water depth estimation is difficult for deep marine

deposits, much less so for shelf sediments, and quite accurate for deltaic and nonmarine

deposits. The commonly used criteria for estimating water depth range from sedimentary

facies characteristics, fossil assemblages indicative of certain water depths, to the

reconstruction of depositional topography or bathymetry. These criteria are rarely

quantitatively definitive, however.

The Cretaceous Western Interior Basin has been commonly referred to as an epeiric

sea way or a ramp setting, with the connotation that it lacked deep marine environments

analogous to a continental slope or deep sea basin. From west to east, strata of the

Greenhorn and Niobrara cycles were deposited in environments ranging from nonmarine

and deltaic to offshore. The western part of the basin shows predominance of shallow

marine and nonmarine deposits and water depths in this region probably remained fairly

shallow, possibly no greater than that of a typical shelf environment. For example,

Lessard (1973) studied the paleowater depth of the Tununk Shale in Henry Mountains

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region on the basis of microfauna and sediment characteristics. His analysis suggested

that the water depths of the seaway extending from central Utah to eastern Colorado were

no more than 150 to 200 meters (300-600 feet). Zelt (1985) arrived at the same water

depth range for the marine Tropic Shale of southern Utah by using Asquith's (1970)

model of depositional topography.

Towards the east, the predominantly deltaic deposits become finer and thinner,

eventually grading into fully marine shales interbedded with siltstones and limestones.

Through detailed subsurface stratigraphic correlation of clinoform geometry exhibited by

rocks of the Mesaverde Formation in Wyoming, Asquith (1970) constructed the

depositional topography assumed by these rocks at the time of deposition. On the basis of

his depositional topography model, Asquith estimated that these rocks were deposited a

water depth as high as 600 meters. Unlike the younger, coarse grained rocks in the

Mesaverde Formation, however, strata of the Greenhorn and Niobrara cycles display

greater lateral constancy in thickness and lithofacies, and therefore more subdued

depositional topography. For example, Hattin (1971), Kauffman (1977a, 1985), and

Weimer (1983) suggested that maximum depths experienced by the Cretaceous strata in

the central and eastern part of the basin were as shallow as 100 to 300 meters.

The water depth correction in backstripping analysis is a measure of how much the

water depths may have changed at each location since deposition of the Mowry Shale.

This variation certainly cannot be greater than the maximum water depth of the seaway,

and probably was less. For convenience, 100 meters was used as the upper limit for net

changes in local water depth and the actual values assigned to each lithofacies were scaled

accordingly.

A NOTE ON ERROR SOURCES

The potential sources of errors in the backstripping analysis of this study are mainly

two types: those arising from the backstripping techniques, such as the decompaction and

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flexural unloading procedures, and those inherited from input stratigraphic data, such as

age determination, stratigraphic correlation, water depth estimation, and lithology.

A rigorous evaluation of the total error is difficult because the magnitudes of

individual types of errors involved are essentially quantitatively unknown. Nevertheless,

those errors stemming from the backstripping procedures are systematic rather than

random. Such errors have been discussed in several case studies and their results provide

a reference. For example, Sawyer et al. (1982) and Steckler et al. (1988) examined the

error bars of backstripping techniques in studying the U.S. Atlantic continental margin.

By using extreme values for physical parameters and by comparing results of different

backstripping calculations, they suggested an error bar of 5% and 10% respectively. In a

particular study like this, the specific error could of course differ from this reference

because errors inherited from input stratigraphic data vary from case to case. Of such

errors, correlation is probably the single most important source. Although many distinct

stratigraphic intervals can be correlated accurately over long distances, correlation errors

on the order of tens of meters or more are quite possible on some less distinctive and

sparsely fossiliferous intervals, particularly in areas where wireline log control is poor.

Likewise, errors on the same order of magnitude are also quite possible for water depth

correction. In the final analysis, however, results of this study represent a significant

quantitative improvement over the earlier ones because of the heavy reliance on

biostratigraphic data and the use of two-dimensional backstripping scheme.

RESULTS

By applying flexural backstripping techniques to the six regional stratigraphic cross

sections, six subsidence profiles are obtained (See Chapter 5). These profiles show the

amount of tectonic subsidence taking place across the basin at different times since the

deposition of the Mowry Shale. These subsidence profiles along with their corresponding

subsidence curves will be analyzed in the following two chapters.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 5

FLEXURAL SUBSIDENCE AND BASEMENT TECTONICS

INTRODUCTION

The Western Interior basin is a retro-arc foreland basin developed in the late Mesozoic

on the western North American craton (Dickinson, 1974). It provides a potentially

decipherable record of nearly 100 m.y. of interactions between thrust loading,

lithospheric flexure, basement block movements, and eustatic sea level changes. Efforts

to unravel this record in the past have led to the development of quantitative foreland

basin models (Price, 1973; Jordan, 1981; Beaumont, 1981). In recent years, these efforts

have been succeeded by those devoted to the isolation of tectonic factors and sea level

signals recorded in the stratigraphy of the Western Interior basin, either using

backstripping techniques (e.g., Heller et al., 1986; Cross, 1986), through field

observations (e.g., Nummedal, 1990; Ryer, 1993; DeCelles, 1986) or relying on

numerical simulation techniques (e.g., Jordan and Flemings, 1991; Jervey, 1992). These

works have provided valuable insights into evolution of the Cretaceous Western Interior

basin.

Further progress in understanding the Cretaceous Western Interior basin is now

hampered by an inadequate knowledge of its subsidence history. Many site-specific

subsidence analyses based on Airy backstripping have been conducted, but no efforts

went beyond this limitation to document the variations in flexural subsidence in space and

time on a broad basis. As a result, many attributes of the flexural mechanism, such as the

role of certain long-lived basement structures, thrust load distribution along the Sevier

belt etc., remain poorly known.

The flexural backstripping analysis of this study documents the subsidence history on

a broad spatial and refined temporal scales. Through a window of 16 m.y., this chapter

127

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intends to show that flexural subsidence in the U.S. Cretaceous Western Interior was

characterized by spatial segmentation as well as temporal discordance. These variations in

flexural subsidence have not been documented in previous studies. Following this

discussion, an elastic flexural model is applied to two backstripped subsidence profiles

across the Wyoming foreland to evaluate the role of lithospheric flexure during basin

development. This modeling, though limited by its two-dimensional nature, provides a

quantitative assessment of the spatial extent of the flexural subsidence and its control on

sedimentation. Finally, the observed subsidence patterns are discussed in the context of

the structural elements of the basement and the thrust belt. This leads to a qualitative basin

subsidence model that reconciles observations from two independent sources: basin

stratigraphy and the tectonic record.

PREVIOUS WORK

In studying the coupled Cordillera fold-thrust belt and foreland basin in the southern

Canadian Rockies, Price (1973) intuitively recognized the physical analogy between

foreland basins coupled with orogenic highlands and the well-known peripheral flexural

depressions caused by ice sheets. He proposed that the North American Western Interior

foreland basin resulted from flexural isostatic response to the excess mass in the

Cordillera. Viewed from this perspective, he stated, "the record of fluctuating rates of

sedimentation and of intermittent erosion in the clastic wedge deposits of the foredeep is a

sensitive gauge of variations in the intensity of deformation within the whole of the

orogenic belt." (p. 50, Price, 1973). Elaborating further on the stratigraphic implications

of this model he went to say that "unconformities in the clastic wedge sequence of the

foredeep do not mark the times of most intense deformation within the orogenic belt but

instead reflect anorogenic intervals." (p. 50-51, Price, 1973). These unpopular but

insightful thoughts went unnoticed until very recently with the publication of a series of

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papers arguing that conglomerates in proximal foreland basins should be vestiges of

tectonic quiescence rather than indicators of thrusting events (e.g., Burbank et al., 1988).

The foreland basin model proposed by Price (1973) was subsequently tested

quantitatively in the North American Western Interior basin by Jordan (1981) and

Beaumont (1981). Jordan (1981) applied an elastic flexural model to evaluate the effect of

Sevier thrust loading on the Cretaceous stratigraphic architecture observed near the Idaho-

Wyoming thrust belt. Beaumont (1981), on the other hand, adopted a viscoelastic

flexural model to simulate subsidence and large scale stratigraphic stacking pattern of

Mesozoic rocks in the Alberta foreland basin. Figure 46 graphically illustrates the

mechanics of the foreland basin model. Curve 1 depicts the lithospheric flexural

subsidence profile as a load is applied to an originally undeformed lithosphere. Given an

elastic assumption (Jordan, 1981), the basin geometry will be maintained until the load

changes. If, however, viscoelastic flexure is dominant (Beaumont, 1981), the basin

geometry will evolve through time in accordance with the predictions highlighted by

curves 2 and 3. Although supported by stratigraphic data from different parts of the

basin, both Jordan's and Beaumont's work demonstrated that lithospheric flexure exerted

first order control on the stratigraphic architecture observed within a few hundred

kilometers of the thrust belt. This finding not only provided a theoretical framework for

understanding the relationships between basin sedimentation and tectonics but also served

as a model guiding studies of other foreland basins around the world.

Following these early works, many others continued to search for more

comprehensive and representative foreland basin models (Schedl and Wiltschko, 1984;

Stockmal and Beaumont, 1987; Cant and Stockmal, 1989). Recognizing that many

cratonic interior foreland basins developed on the attenuated passive margin crust,

Stockmal et al. (1986) and Stockmal and Beaumont (1987) developed a flexural model

that takes into account the inherited thermal subsidence of the passive margin as well as

effects of pre-existing basement topography on thrust motion. Their model, constrained

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. OJ o Load — 3— r I_i involving viscous relaxationunder aconstant load. FromQuinlan andBeaumont (1984). resulting from initial emplacementof aload, oran elastic response. Curves 2 and 3 dipict flexure Figure46. Qualitative representation ofthe flexural responses to loading. Curve depicts1 flexure

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by the Alberta and the Alpine Molasse foreland basins, enabled them to predict the

evolution of thrust wedge topography through time. In an effort to further test this model,

Cant and Stockmal (1989) related this model to the sedimentary record of the Alberta

foreland basin and to the terrane accretion history in the Canadian Cordillera. Their work

suggested that the clastic wedges in the foreland might record the terrane accretion history

on the older passive margin.

Cross (1986) provided a regional synthesis of the development of the U.S.

Cretaceous Western Interior basin in the context of plate tectonics. Drawing on the gross

isopach trends, he suggested that lithospheric flexure by thrust loading was most

effective in the early phase of basin subsidence history during early Late Cretaceous.

With the inferred onset of the low-angle subduction of the Farallon Plate in late Late

Cretaceous, he inferred that sublithospheric loading and cooling resulted in a broad

downwarping centered in Wyoming and Colorado. This subsidence mechanism therefore

complicated the lithospheric flexure by thrust loading.

In the past few years, several workers have developed quantitative foreland basin

stratigraphic models with particular reference to the North American Western Interior

basin (Jordan and Flemings, 1991, Pepper, 1993; Jervey, 1992). The recent model by

Jordan and Flemings (1992) is perhaps the most refined and rigorous. In this model,

flexural subsidence, sea level changes, and sediment supply were approximated with

empirical relationships and treated as independent variables. Given certain initial and

boundary conditions, the model can be executed to simulate evolution of basin

stratigraphic architecture through time.

The works selectively summarized here greatly enhanced our understanding of the

Western Interior basin. In particular, the advent of increasingly sophisticated quantitative

models has defined a common ground for multidisplinary research to unravel the

relationships between the many factors involved in foreland basin development. These

models can potentially be a useful analytic tool to predict the amount of flexural

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subsidence in the foreland basin, infer tectonic loading history, and constrain lithospheric

rheology from the stratigraphic record. However, as shown in paragraphs below, the

subsidence pattern in the Cretaceous Western Interior basin is highly complex. Therefore,

development of future foreland basin models should be accompanied by more realistic

constraints, particularly accurate documentations of the actual basin subsidence history.

SUBSIDENCE PATTERNS IN SPACE AND TIME

Subsidence profiles

The six subsidence profiles calculated by flexural backstripping across different

segments of the U.S. Western Interior basin are shown in Figure 47. Their locations are

shown in Figure 20 in chapter 3. These profiles portray the subsidence as it varies

spatially both across and along the basin axis. Clearly, the pattern of cumulative

subsidence over the 16 m.y. of the Greenhorn and Niobrara cycles reveals two spatially

distinct components. On the eastern cratonic platform, basin subsidence is essentially

uniform. In areas within a few hundred kilometers of the thrust belt, in contrast, basin

subsidence increases westward, although the rate of increase varies significantly from

western Montana to southwestern Utah. Because of its spatial proximity to the thrust belt

to the west, this subsidence pattern is interpreted as the flexural response to thrust

loading, as has been demonstrated by Jordan (1981). This part of the basin is hence

considered the foreland basin proper.

The geometry of the flexural subsidence pattern, or the shape of the foreland basin, is

highly variable both in amplitude and in wavelength along the Sevier belt. In western

Montana, flexural subsidence just barely exceeds the platform subsidence (Fig. 47,

profiles 1 and 2). Viewed in isolation, this subdued flexural subsidence pattern is hardly

consistent with the assertion that the Cretaceous Western Interior basin is a typical

foreland basin. This observation suggests that thrust loading near this part of the foreland

was rather insignificant, at least during the time interval of this study. Farther south,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. M etres 0 200 400 km k ■ - 1

Figure 47. Flexurally backstripped subsidence profiles across basin. Light shading marks amount of subsidence from 96 (94 on e and f) to 90 Ma, and dark shading marks amount of subsidence from 90 to 80 (83 on c and d) Ma. Vertical scale is tectonic subsidence in metres. Triangles indicate locations of subsidence curves discussed next. DCA is Douglas Creek Arch.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 134

however, in Wyoming and northern Utah, the flexural subsidence pattern is far more

distinctive. On both profiles across Wyoming, the amplitude of the flexural subsidence

near the thrust front is several times greater than the platform subsidence, and its half

wavelength is on the order o f400 km, reaching as far east as the Laramie and Powder

River Basins (Fig. 47, profiles 3 and 4). This flexural subsidence pattern here defines a

broad and deep foreland basin that requires significant thrust loading coupled with a

strong basement foundation. Southward across the Uinta Mountain, the flexural

subsidence in central Utah has even greater amplitude, but shorter half wavelength (Fig.

47, profile 5). Towards the east, the flexural subsidence pattern was strongly influenced

by the differential subsidence on the Douglas Creek Arch, a persistent structural high

throughout the Phanerozoic, particularly during the Tertiary Laramide orogeny (Johnson

and Finn, 1986). Notwithstanding this structural complication, this particular flexural

subsidence pattern in central Utah implies a relatively weak basement crust. In southern

Utah, some 200 kilometers or so farther south, the flexural subsidence is again relatively

small, implying that local thrust loading was minor (Fig. 47, profile 6).

Subsidence curves

To complement this analysis of spatial variations in basin subsidence, a series of site-

specific subsidence curves were constructed by plotting flexurally backstripped

subsidence against time (Fig. 48). These sites are chosen 100 to 150 kilometers east of

the Sevier belt depending on the local flexural wavelength.

The six curves show that the temporal changes in subsidence vary with location along

the strike of the thrust belt. From the middle Cenomanian to late Turanian (96 to 90 Ma),

or the Greenhorn cycle, subsidence rates were high in Utah (Fig. 48, curves 5 and 6) and

much lower in Wyoming and Montana (Fig. 48, curves 1,2,3, and 4). In contrast,

during the Coniacian and Santonian stages (90 to 85 Ma), or the Niobrara cycle,

subsidence accelerated rapidly in Wyoming, increased slightly in Montana, and decreased

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Cen.- L. Tur. i Con.- E. Camp. 100 80 (Ma)

•3

1500 Metres

Figure 48. Temporal subsidence trends at six locations 100-150 km east of the thrust belt. Hatched areas represent cumulative tectonic subsidence through time. Solid lines below represent total (uncorrected) subsidence.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 136

in Utah. At the end of the Santonian and into the early Campanian, rates of subsidence

appear to have slowed everywhere. The temporal trends in subsidence as described above

differentiate the Utah province from the rest of the foredeep area.

MODELING FLEXURAL SUBSIDENCE

Model description

Since the pioneering work by Jordan (1981) and Beaumont (1981), there have been

substantial improvements in both the quality and quantity of the stratigraphic data in the

Western Interior basin. However, no attempts were taken to further test the lithospheric

flexural mechanism with this improved stratigraphic database. In view of this, this

chapter includes a quantitative test of the lithospheric flexure model on the basis of two

subsidence profiles across the Wyoming foreland. The decision to limit the modeling

effort to this area was made in part because thrust loading history in the Idaho-Wyoming

salient is better understood, and in part because this area depicts the most pronounced

flexural depression. By comparison, the remainder of the profiles are either less

pronounced or complicated by intrabasinal differential subsidence.

Models describing the evolution of foreland basins approximate the flexural deflection

with either elastic or viscoelastic thin plate theory (Nadai, 1963; Turcotte, 1979). In most

models, flexural deflection is treated in two-dimensions because orogenic belts are large-

scale linear features on earth's surface. This study selected a two-dimensional elastic

flexural model to evaluate the documented subsidence patterns. In such a model, the half­

wavelength of flexure is governed by the lithospheric strength and the amplitude by the

applied load in addition to lithospheric strength (Fig. 49).

In addition to its mathematical simplicity, an elastic flexural model is chosen because

it has been applied to approximate flexural deflections in many different tectonic settings

with satisfying results. Furthermore, because the duration of the stratigraphic interval to

be examined is relatively short, an elastic flexural model is an adequate first order

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 100 km Te=25 km Te=110 km - 0- Figure 49. Flexural halfwave-length as afunction ofthe of loadlithospheric shape, elasticTe controls thickness the Te. flexural Irrespective halfwave-length and, to alesser extent, the depth offlexure. 1000 2000 J m eters

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approximation. In adopting such a model, however, one should remember a potentially

more serious problem: the errors introduced by using a two-dimensional approximation

of the three-dimensional problem of flexural subsidence. Structural evidence reviewed in

Chapter 2 suggests not only a heterogeneous crustal fabric beneath the sedimentary cover

of the U.S. Western Interior but also along-strike variations in thrust loads. These

complicating factors are ignored in this model, but their implications will be discussed

later in this chapter.

Method

The spatial pattern of cumulative subsidence on the two backstripped subsidence

profiles across Wyoming provide observational constraints for flexural modeling.

Flexural subsidence in response to a thrust load was calculated by using the same

mathematical procedures as described in Chapter 4 for flexural sediment unloading. In the

calculations, a trial and error method was used to search for a best-fitting theoretical

profile. This consisted of iteratively calculating flexural deflection profiles by

systematically varying the applied load and elastic thickness independently. If a particular

theoretical profile matched the geometry of the backstripped subsidence profile, and if the

applied load and elastic thickness lies within their accepted range, then it can be

considered as a best-fitting profile. If, however, the flexural model is unable to generate a

subsidence profile that matches the geometry of the backstripped profile, the conclusion

would be that either subsidence mechanisms other than flexure played an important role

during basin development, or the model itself is an inadequate approximation of the actual

flexural subsidence.

Model results

The best-fitting theoretical flexural profiles and their corresponding backstripped

profiles are shown in Figure 50. These two profiles were obtained by using an elastic

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 139

S. BIGHORN POWDER RIVER W. NORTH DAKOTA

b. t

GREEN RIVER HANNA W. NEBRASKA

5 km

meters 100 km

Figure 50. Best-fitting flexural profiles for the backstripped subsidence profiles across the Wyoming foreland, a: model match for subsidence profile 3; b: model match for subsidence profile 4. Solid lines are backstripped subsidence profiles and dashed lines are best-fitting model profiles. Flexural rigidity D=4 x 1024 Nm.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 140

thickness of 80 + 10 km and crustal loads 100 km wide and 3 to 5 km high, respectively.

The elastic thickness value is considerably greater than previously suggested for the

Cretaceous Western Interior basin (Jordan, 1981), but not unusual in cratonic interior

foreland basins (McNutt et al. 1988; Watts, 1992). The model thrust loads are

comparable to the size of the Meade-Crawford thrust system as reconstructed by Jordan

(1981) (see Chapter 2).

To a first approximation, the theoretical flexural profiles yield a reasonable match to

the westward-deepening trends in the subsidence profiles. The overall agreement between

model results and observations, though not quite unexpected, support the conclusion

reached in previous studies that the observed asymmetric basin geometry can be

generated entirely by lithospheric flexure in response to Sevier thrust loading (Beaumont,

1981; Jordan, 1981). Without such a model, it is not certain how much of the asymmetric

subsidence can be attributed to lithospheric flexure or what are the required loads and

lithospheric strength. Notwithstanding this general agreement, the details of the flexural

mechanisms predicted in this model differ from those in Jordan's model (1981). The

flexural half wavelength of the Wyoming foredeep is about 400 km, encompassing the

Bighorn Basin, the Green River Basin, and their contiguous areas to the east. This basin

width suggests that in the Cretaceous the lithosphere beneath Wyoming was strong,

comparable to those in other broad foreland basins such as that in front of the late

Paleozoic Appalachian and the Ganges (McNutt et al., 1988; Watts, 1992; Watts et al.,

1982). The predicted outer flexural bulge is located slightly east of the Powder River and

Hanna basins (Fig 50 a and b), not near the Moxa Arch as previously suggested by

several people. Further to the east, basin subsidence was not affected by lithospheric

flexure under Sevier thrust loading.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 141

A note on the lithosphere's elastic thickness

Because lithospheric elastic thickness is an important determinant of the foreland

basin geometry, the value required for the best-fitting flexural subsidence profiles

warrants an explanation.

Studies of continental lithospheric flexure in a wide variety of tectonic settings

demonstrate that continental elastic thickness varies over a range from 10 km to 100 km

or more (McNutt et al., 1988; Watts, 1992). According to Watts (1992), the distribution

of continental lithospheric elastic thickness is strongly 'bi-modal' (Fig. 51). The mode

with small elastic thickness corresponds to narrow and deep foreland basins, such as the

Alpine foreland basin. The other mode represented by a large elastic thickness

corresponds to wide foreland basins, such as the Appalachian and Ganges foreland

basins. Examined with this reference, the elastic thickness from Jordan's (1981) model,

which is in the neighborhood of 30-40 km, places the U.S. Western Interior basin into

the first mode, whereas results of this study put it in the second mode. Because this study

applied a similar flexural model to that of Jordan, the discrepancy in elastic thickness

reflects the disparity in the quality of the stratigraphic data between the two.

In light of the current understanding of the variations in continental lithospheric elastic

thickness, the value obtained in this study is not unreasonable. According to Kamer et

al. (1983), one of the most important factors dictating lithospheric strength is the secular

cooling of the basement crust since its formation. As shown in Figure 52, continental

elastic thickness generally increases with the age of the basement crust, much like oceanic

lithosphere. As described in Chapter 2, the Wyoming foreland region is underlain by

Archean crusts of the Wyoming Province. If secular cooling has been a dominant factor

controlling the lithospheric strength, the Wyoming foreland basement should be cold and

strong.

In addition to secular cooling, McNutt et al. (1988) suggested that another possible

factor controlling lithospheric strength is the state of stress and strain in the lithosphere.

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Frequency (%) 20 -

Jordan's study (1981)

Figure 51. Bi-modal distribution of continental lithospheric elastic thickness (Te). Te is based on foreland basin and glacial rebound studies. Number of estimated Te values N=28. From Watts (1992). Arrows indicate Te for the Wyoming foreland derived from Jordan's (1981) and this study, respectively.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. l_ 3000 __ Wyoming foreland ______2000 ♦ Caucasus + Z a g ro s ♦ U rals + Carpathians ♦ Fennoscandia X G anges

^ Sub-Andean Lake A lgonquin4 X 1000 ♦ ♦Appalachians Lake Agassiz Age of Lithosphere at time of loading (m.y.) S. Tienshan T a r im +

E. E. Alps ♦ i • ♦ g W. Alps g Lake Bonneville N xienshan < J - 150 100 y u c (A O S 50 5 H *•*3 ^ 4 Solid circlesestimates are from glacial studies anddiamonds from foreland basin studies. Tefor the Wyoming forelandderived from this study shownis in square (with errorbars). ModifiedfromWatts (1992). Figure 52. Distribution ofcontinental elastic thickness Te versus age oflithosphere atthe timeofloading.

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She argued that orogenic belts that appear highly arcuate are associated with low values

of elastic thickness, whereas long, linear orogenic belts are supported by strong plates.

By the same token, steeply dipping plates, having been bent at a greater angle, appear

weaker than shallowly dipping plates because of inelastic yielding. The Western Interior

basin was coupled with a linear thrust belt and accompanied by insignificant bending of

the continental plate during its development. Therefore, the lithosphere in the Wyoming

foreland should be strong. This inference, however, does not exclude the possibility that

the lithosphere beneath other parts of the U.S. Western Interior might be weakened by

basement faults/lineaments. As discussed next, variations in basement strength with

location are quite significant.

DISCUSSION

Complexities offoreland basin subsidence

The six subsidence profiles in Figure 47, supplemented by the above flexural

modeling, clearly suggest that lithospheric flexure in response to the Sevier thrust

loading played a major role in the basin history. However, rather than a spatially

invariant flexural depression coaxial with the thrust belt, as occasionally implied in

some stratigraphic studies, the Western Interior foreland was characterized by

considerable spatial and temporal variations in the flexural subsidence over the chosen

16 m.y. time interval. Spatially, the magnitude and half wavelength of the flexural

subsidence varied with location in the Western Interior foreland. In Wyoming and

northern Utah, flexural subsidence resulted in a deep and wide foreland basin. In

contrast, flexural subsidence in southern Utah and western Montana was

insignificant. These spatial variations imply that the gross crustal shortening over the

16 m.y. was centered in the Idaho-Wyoming salient rather than evenly distributed

along the Sevier belt. They also imply that the Western Interior foreland basement

was segmented, consisting of the Wyoming, Montana, and Utah blocks. Each block

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responded to thrust loading with flexural subsidence of different magnitude and half

wavelength as observed.

Temporally, flexural subsidence was rapid in the Utah foreland and slower in

Wyoming and Montana foreland during the Greenhorn cycle. During the succeeding

Niobrara cycle, in contrast, flexural subsidence accelerated rapidly in Wyoming,

increased slightly in Montana, and decreased in Utah. This implies that thrusting was not

synchronous along the length of the Sevier belt. Specifically, the thrust load was first

emplaced in Utah. Late on, as thrusting decreased there, the Wyoming-Idaho salient

experienced rapid thrusting. As shown below, these temporally discordant and spatially

non-uniform thrusting activities are not inconsistent with geologic evidence residing in

the styles of thrusting and basement structures of the Western Interior.

Basement structures and their influences on lithospheric flexure

This study proposes that the above described spatial and temporal variations in the

flexural subsidence were controlled by zones of crustal weakness oriented at high angles

to the Cordillera hingeline. As described in Chapter 2, these zones of crustal weakness

were mostly faults and lineaments inherited from Precambrian rifting and early Paleozoic

passive margin development. They persistently influenced Phanerozoic sedimentation.

During the development of the Western Interior basin, these basement structures

influenced the Cretaceous flexural subsidence in the following manners. First, basement

irregularities due to these zones of crustal weakness affected spatial distribution of crustal

shortening through buttressing. Secondly, the east-west trending normal faults inherited

from the Proterozoic Belt Basin and the Uinta aulacogen probably dissected the foreland

lithosphere into more or less mechanically independent blocks. Thirdly, each basement

block had different mechanical strength depending on the internal zones of crustal

weakness.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 146

The thin-skinned Sevier thrusting interacted with coeval basement uplifts in many

places in a so called overlap province. The interactions between the two contrasting

tectonic styles took place primarily in the form of buttressing (Schmidt and Perry, 1988).

Buttressing not only led to local deflections in thrust sheet propagation but also created

nonuniform crustal shortening along the thrust belt. Specifically, in response to the

buttresses located in the Uinta aulacogen and northwest Wyoming and southwestern

Montana, the Sevier thrust sheets preferably moved to the east along the less resistant

course between them. Therefore, disaproportionally greater crustal shortening was

probably accommodated in the Idaho-Wyoming salient through time. The cartoon in

Figure 53 is drawn to illustrate this effect. Coupled with a segmented lithosphere, such a

crustal shortening pattern could cause greater cumulative flexural subsidence in the

adjacent southwestern Wyoming foreland than in Montana or southern Utah during the

Greenhorn and Niobrara cycles, as documented in this study.

The east-west trending normal faults in west-central Montana associated with the

Proterozoic Belt basin and boundary faults of the Proterozoic Uinta aulacogen represent

major zones of crustal weakness. According to Tonnsen (1986), these basement

structures partitioned the crust underlying the Rocky Mountain region into three large

paleotectonic blocks: the Montana, Wyoming, and Utah-Colorado blocks (Fig. 54).

These blocks correlate well with the Cretaceous flexural subsidence pattern. Under thrust

loading during the Cretaceous, these blocks probably behaved as more or less

mechanically independent regions. It is conceivable that during the Greenhorn cycle, in

response to the loading of thrust sheets concentrated in Utah, possibly the Pavant thrusts,

the Uinta foreland experienced greater subsidence while the Wyoming foreland remained

unaffected. By the same token, once the locus of thrusting activities shifted to the

Wyoming-Idaho salient during the succeeding Niobrara cycle, possibly on the Meade and

Crowford thrusts, the Wyoming block underwent greater flexural subsidence than the

neighboring foreland areas. Lack of pronounced flexural subsidence in Montana was

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 147 buttressing buttressing near Uinta Mt. and in southwestern Montana. Figure 53. Interpretative diagram Figure 53. Interpretative diagram showing differential crustal shortening result as a of

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4^ 00 Continental crust Colorado 'yoming IMontana Attenuatedcrust Oceaniccrust time. Theunderwent blocks recurrent movements during the Phanerozoic. FromTonnsen (1986). Figure Diagramatic 54. sketch ofthe paleotectonic blocks during the middleProterozoic i Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 149

probably due to insignificant thrusting throughout the Greenhorn and Niobrara cycles.

This inferred complex lithospheric flexure mechanism is not unique to the Cretaceous

Western Interior Basin; similar observations have been made in the late Paleozoic Antler

foreland basin (Dorobek et al., 1991), and elsewhere (Royden, 1988; Waschbusch and

Royden, 1992).

In addition to foreland basement segmentation, the internal basement strength of each

block was also different from each other. The Wyoming block, composed of Archean

rocks of the Wyoming Province, was probably the strongest, as evidenced by its large

elastic thickness value derived from this study. In contrast, the Utah block was much

weaker than the Wyoming block, as indicated by its deep and narrow flexural subsidence

pattern. The weak mechanical strength of the Utah block was probably a long-lived

feature caused by zones of weakness inherited from the Precambrian rifting. According to

Picha and Gibson (1985), the major zones of crustal weakness in the Utah basement

block consist of a north-south trending normal fault called the Ancient Ephraim Fault and

a series of northeast trending lineaments that offset the thrust belt. It is possible that the

observed weak mechanical strength in the Utah foreland was just a consequence of these

faults.

The contrast in the mechanical strength between the Wyoming and the Utah blocks

has persisted today despite the Tertiary Laramide orogeny and the Basin and Range

extension. By numerical inversion of modem gravity and topography data, Lowry and

Smith (1994) calculated and mapped the lithospheric strength in the middle and southern

Rocky Mountain region. Their work documented that the modem elastic thickness in this

region varies from as low as 5 km in the Basin and Range to as high as 77 km in

Wyoming. This latter value is essentially identical to the one derived from this study on

the basis of flexural backstripping of the Cretaceous rocks. More importantly, as shown

in Figure 55, the spatial variations in the mechanical strength from Utah to Wyoming

correlate well with those inferred from the subsidence profiles derived from this study

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 150

Elastic thickness (km)

Uinta Mt.

Sevier thrust faults

Figure 55. Spatial variations in the present day lithospheric elastic thickness across parts of Idaho, Wyoming, and Utah. The elastic thickness is derived from inversion of gravity and topography data. Modified from Lowry and Smith (1994).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 151

(Fig. 47). North of the Uinta Mountain, the Archean crust in Wyoming has an elastic

thickness ranging from 40 km to 77 km, whereas in central Utah, the elastic thickness

lies within 15 km to 20 km. The transition from a strong crust in Wyoming to a weak

crust in Utah occurs close to and parallel with the Uinta aulacogen. The subsidence

profiles derived from this study clearly show a similar pattern in the lithospheric strength

as it varied from Wyoming to Utah during the Cretaceous (Fig. 47). One might therefore

argue that the correlation between the Cretaceous subsidence pattern and the modem

lithospheric strength is not simply a coincident. Rather, it reflects the long-lived nature of

the Precambrian basement tectonics, particularly the zones of crustal weakness.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 6

RESIDUAL SUBSIDENCE AND SPECULATIONS ON ITS CAUSES

INTRODUCTION

The flexural subsidence resulting from thrust loading takes a fairly distinct

pattern so that it can be easily identified (Fig. 56). If this component is separated

from the composite subsidence profiles and the intrabasinal differential

subsidence ignored, the Western Interior basin is left with a residual or

"background" subsidence component. This residual component measures about

200 meters over much of the eastern platform of the basin. Extrapolated to the

foreland area towards the thrust belt, it is superimposed on the flexural

component. Locally, such as in western Montana, the residual subsidence plays a

dominant role even close to the thrust belt.

Unlike the westward-increasing subsidence pattern, which signifies a tectonic

mechanism such as lithospheric flexure, the cause of the observed residual

subsidence component cannot be easily determined. In theory, it could be caused

by a eustatic sea level rise, an episode of regional tectonic subsidence, or a

combination of both. This ambiguity exists because the backstripping techniques

as implemented do not allow for differentiation between the two (see Chapter 4).

Deposition of marine Cretaceous strata on the eastern platform has long been

attributed to eustatic sea level changes and tectonic subsidence was rarely the

subject of discussion. For example, many authors considered the cratonic

platform part of the Western Interior basin to be tectonically stable and therefore

have tried to determine the elevation of the Cretaceous eustatic sea level

presumably preserved in these platform strata (Sleep et al., 1980; Haq et al.,

1988; Sahagian, 1987; McDonough and Cross, 1991). Likewise, in other studies

152

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Cratonic platform forebulge

across southern Wyoming (subsidenceprofile 4). flexural subsidence tothe west andresidual subsidence overdie entire basin. The frontal view is Figure 56. Diagram illustrating the two main subsidence components in theWestern Interiorbasin: ! Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 154

concerned with flexural modeling or its applications, strata deposited beyond the

flexural effect were either ignored or simply attributed to a eustatic sea level rise

and associated sediment loading (e.g., Jordan, 1981). However, as demonstrated

by Bond (1976) almost two decades ago, the development of the Cretaceous

Western Interior basin requires regional tectonic subsidence in addition to the

eustatic factors. This chapter intends to show that the residual subsidence

calculated above can not be explained by eustasy. This is followed by a review of

several recent hypotheses that relate subsidence in the Cretaceous Western Interior

basin to coeval plate tectonics in the subduction zone between the Farallon and

North American plates. This review shows that although the exact cause of the

residual subsidence remains elusive, the concept of mantle dynamic topography

driven by subduction and mantle convection provides a plausible explanation that

deserves special attention in future studies.

NATURE OF THE RESIDUAL SUBSIDENCE

It is widely believed that sedimentation on the eastern cratonic platform of the

Western Interior basin was subjected to domination by eustatic sea level changes

(e.g., Kauffman, 1985; Weimer, 1983). Observations that led to this assumption

can be summarized as follows. First, unlike tectonically active areas where

eustasy, lithospheric deformation, and thermal subsidence are all inscripted into

the sedimentary records, this portion of the basin lacked conspicuous tectonic

activities throughout the Phanerozoic. The only known structural feature active

during the Cretaceous is the Transcontinental Arch, which, according to Weimer

(1983) and others, influenced Cretaceous sedimentation by subtle vertical

movements in the basement. Secondly, Upper Cretaceous strata deposited in this

platform region consist of marine shales and limestones that display remarkable

lateral continuity in lithofacies and consistency in thickness. This is in sharp

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 155

contrast to those deposited in the tectonically active foredeep region, where

complexly intertongued marine and nonmarine strata dominate. Perhaps more

important, the Cretaceous strata are distinguished by regionally correlative

transgressive and regressive cycles. The major cycles such as the Greenhorn and

Niobrara have generally been interpreted as the result of eustatic sea level

fluctuations. Thirdly, it is well documented that the Cretaceous is a period of

global transgression when many continental interiors were flooded. Hays and

Pitman (1973) first proposed that this transgression resulted from a eustatic sea

level rise caused by changes in spreading rates and mid-ocean ridge length, a

mechanism subsequently known as tectonoeustasy. Using global spreading rates

as a data base, Kominz (1984) demonstrated that the long term eustatic sea level

fluctuations driven by tectonoeustasy amounted to 230 m (±100) over the last 80

m.y.

In the absence of any direct evidence for a viable tectonic mechanism, it

stands to reason that the residual "subsidence" perhaps record the long term

Cretaceous eustatic sea level rise. Intuitively appealing as it may be, this view can

be discounted simply because the required eustatic sea level rise proves

unrealistic, at least according to current understanding of tectonoeustasy

(Kominz, 1984; Engebretson et al., 1992). The first important step in this

direction was made by Bond (1978), who demonstrated that eustasy alone can not

explain the size of the Cretaceous Western Interior basin. He calculated the

amount of sea level rise required to accommodate the extensive Cretaceous

deposits under the assumption that no tectonic subsidence other than sediment

loading occurred. His results indicate that given an unusually large sea level rise

of 310 meters during the Cretaceous, sedimentation in nearly half of the Western

Interior basin still remains unaccounted for.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 156

Since Bond's work, progress has been made in understanding and

documenting Cretaceous eustasy. A widely accepted document marking this

progress, though not without controversies, is the detailed eustatic sea level curve

by Haq et al. (1988), which is presumably based on a synthesis of seismic,

borehole, geochronologic, and biostratigraphic data from around the world.

Figure 57 shows the Cretaceous and Tertiary eustatic sea level curve by Haq and

others (1988). The curve has been smoothed with a 10 m.y. running window so

that short term sea level fluctuations can be filtered out. These short term

fluctuations, at time scales of 10 m.y. or less, may be recorded in the Cretaceous

strata, but they are irrelevant here because this analysis focuses only on the long

term sea level trends. The modified sea level curve by Haq and others (1988) is

superimposed on a group of theoretical sea level curves Engebretson et al. (1992)

calculated on the basis of global spreading rates. From middle Cenomanian to

early Campanian (96 to 80 Ma), the time interval of study in this paper, the long

term eustatic sea level trend shows a net lowering instead of a rise. Apparently, if

this trend is a true representation of the Cretaceous eustatic sea level history, then

the residual subsidence of the Western Interior basin must reflect tectonic

mechanisms.

In addition to the difficulty presented by the timing of the eustatic sea level

changes, the amplitude of the sea level rise required to account for the residual

subsidence documented in this study is equally problematic. It can easily be

calculated on isostatic grounds that 200 meters of residual subsidence is in effect

equivalent to a sea level rise of 150 m. Such a sea level rise almost equals Haq et

al's documented rise for the previous 90 m.y. Granted that eustatic sea level

fluctuations on time scales of 10 m.y. or less may be an important control on the

varied cyclicities in the Cretaceous strata of the Western Interior basin, the net,

long term sea level rise enough to account for the residual subsidence seems

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 157

300

’\ 200 /M / / > o \ Eustatic (:urve I C'\W " - - o ' ; Si * /fj& \ % o 1 / /// \\ V ^ V \, a y H '///// / II \\\\\* « 100 1,11 ’/ii v > \ \ «V u 1,1 1, A \ w \ > tflt/i1,1 if '/! JO ' \W ' * * *iini / Pre

x — - II ___ / -100 I i f f 180 150 120 90 60 30 Time (Ma) Figure 57. Eustatic sea level curve (heavy line) of Haq et al. (1988) and predicted sea level curves by Engebreston et al. (1992) using global spreading rate data (dashed lines). Shaded column represents the time span of this study.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. improbable. From this simple test, the inescapable conclusion is that the residual

subsidence resulted from mechanism(s) other than eustatic sea level changes.

EPEIROGENIC SUBSIDENCE MECHANISMS

Many Phanerozoic cratonic platforms are characterized by laterally extensive

strata punctuated by unconformities of various durations. These settings have

been the preferred areas for measuring eustatic sea level changes (Hancock and

Kauffman, 1979; Sleep et al., 1980; McDonough and Cross, 1991; Sahagian et

al. 1992). Despite this, there is quite unequivocal evidence from continents

around the world for long term epeirogenic movements (Fig. 58. Harrison,

1990). An expanding body of data suggests that such epeirogenic movements,

after correction for possible eustatic sea level changes, could occur on time scales

of tens or hundreds of millions of years and amount to several hundred meters in

amplitude (Sloss, 1974, 1991; Bond, 1978; Harrison, 1988, 1990; Bond and

Kominz, 1992). Such movements have been advocated as an alternative to

eustasy as a control on platform sedimentation. Sloss (1991) even argued that the

synchronous vertical motions observed in some widely separated Paleozoic

cratonic basins may not necessarily be indicators of eustatic control. He suggested

that such motions can be the product of secular variations in radial heat flow,

which result in alternate episodes of inflation and deflation of continental

lithosphere. This mechanism is an early form of the concept of mantle-driven

dynamic topography. In the following paragraphs, several recent hypotheses

proposed with specific reference to the Western Interior basin are briefly

reviewed, including sublithospheric loading and cooling, continental tilting, and

mantle dynamic topography.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. VO 100

80 Time (Ma) N. America Australia X Asia +■ Africa A S. Am erica ▼ Europe Figure 58. Vertical continental movements during the past Ma. 180 FromHarisson (1990), partlybased on Bond (1978).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Sublithospheric loading and cooling

Subduction at convergent margins can be identified as the ultimate cause for

many crustal and surface processes. Following this tenet of plate tectonics,

attempts have been made to relate the subsidence recorded in the Cretaceous strata

to the subduction of the Farallon Plate beneath the North American craton (Cross,

1986; Mitrovica et al. 1989).

On the basis of Cretaceous isopach patterns, Cross and Pilger (1978) and

Cross (1986) inferred that two modes of subsidence succeeded each other in the

Western Interior basin. During early Late Cretaceous time (100-80 Ma), basin

subsidence was mostly confined to the thrust front and insignificant on the

cratonic interior. Because the foredeep’ outlined on the isopach map is fairly

distinct, lithospheric flexure under thrust loading affords a reasonable

explanation. During late Late Cretaceous time (80-70 Ma), basin subsidence

assumed a different and more complicated mode: flexural subsidence gave way to

a broad down warping centered in Wyoming and Colorado. Cross (1986)

proposed the sublithospheric loading and cooling occurred in the later period of

time and caused the downwarping.

Several lines of geologic evidence, including plate convergence rates and

Cordilleran magmatism, suggest that subduction of the Farallon Plate changed

from "normal" to "low angle" in middle Late Cretaceous (80 Ma) (Dickinson and

Snyder, 1978, Cross and Pilger, 1978, Cross, 1986). According to Cross

(1986), the timing of the postulated low angle subduction coincided with the

transition between the two subsidence modes described above. Inspired by this

coincidence, Cross (1986) proposed that as the Farallon Plate was placed in

virtual contact with the overlying North American Plate, it acted as a

sublithospheric load causing a broad downwarping in Wyoming and Colorado. In

addition, because the subducting Farallon Plate was colder than the mantle it

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. replaced, thermal cooling also occurred to further enhance subsidence due to

sublithospheric loading mechanism.

This hypothesis represents one of the earliest attempts to find a tectonic

mechanism for deposition of the widespread Cretaceous strata beyond the

influence of thrust loading. However, the physics of sublithospheric loading and

cooling as a subsidence mechanism is highly problematic. In fact, many workers

have interpreted the formation of widespread Laramide uplifts and intervening

basins as the result of the flat subduction (Dickinson and Snyder, 1978;

Hamilton, 1988,1989). Also, the broad downwarping cited by Cross (1986)

appears to coincide in time with the break-up of the Western Interior basin into

isolated Laramide structural basins. Therefore, it is possible that the inferred

"downwarping" may be an artifact of the nature of stratigraphic correlations

between individual Laramide basins.

Continental tilting

More recently, Mitrovica et al. (1989) used numerical simulation techniques in

a study of the dynamic effects of plate subduction on the surface topography of

cratonic platform basins. By comparing the Cretaceous isopach and present day.

topography of the U.S. Western Interior, Mitrovica et al. (1989) reconstructed the

history of vertical movements western North America was subjected from

Cretaceous to Tertiary (Fig. 59, A.). The Cretaceous-Tertiary vertical movements

consist of a regional subsidence during the Cretaceous, and a rebound during the

Tertiary. They attributed the vertical movements experienced by western North

America to "continental tilt".

Mitrovica et al. (1989) proposed that the continental tilt resulted from large

scale lithospheric deflection dynamically coupled with the subduction of the

Farallon Plate. The lithospheric deflections induced by subduction can be a

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Black Hills

Thrust / belt edge

2 km 500 km

Cretaceous

Fold-Thrust Foredeep Platform

Active subduction

Tertiary

Inactive subduction

Figure 59. Continental tilt model by Mitrovica et al. (1989). A. Schematic illustration of the net effect of Late Cretaceous subsidence and Tertiary uplift across Wyoming. The base of the Cretaceous series is shown in by a. During subsequent uplift in Tertiary, a moved to b. The surface of the uplift is c. B. The proposed tilting mechanism resulting from subduction and mantle convection. Active subduction during the Cretaceous leads to a continental tilt, or regional subsidence (top of B). Cessation of subduction brings the the tilting mechanism to an end. Therefore the platform rebounds (below).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. kilometer in amplitude and up to 1000 km in wavelength, depending on the angle

of subduction as well as on lithospheric rigidity. Specifically, this mechanism

predicts that broad lithospheric deflection or epeirogenic subsidence occurred

across much of the Western Interior during Cretaceous time when subduction

remained active (Fig. 59 B). During the Tertiary, in contrast, as subduction

slowed down and eventually ceased when the East Pacific spreading center

reached the Californian coast, the cratonic margin began to rebound, creating

much of the present day topography in the Western Interior.

Although the observation that led to this model may be an oversimplification

of the tectonic evolution of the western North America, the physics underlying the

"continental tilt" mechanism is derived from some well established concepts of

mantle convection model. In a study of the relationships between active

subduction zones and surface topography, Gumis (1993b) documented that many

modem coastal plains inland of subduction zones display gently depressed

topography after corrections were made for surface processes. This finding lends

support to the concept of continental tilt as a mechanism for the vertical movement

patterns western North America was subjected to during the Cretaceous and

Tertiary. The limitation of this mechanism, however, is that it does entail very

shallow subduction and a strong lithosphere for the deflection to reach far enough

into the cratonic interior. For example, if "continental tilt" is invoked to explain

the residual subsidence documented in this study, one would expect a "tilted"

subsidence profile similar to curve a in Fig 59 A. Clearly, this is not the case.

Nevertheless, this mechanism deserves further testing in future studies,

particularly in the rock record. The ideal settings to test this mechanism would be

cratonic interior basins bordering subduction zones. Specifically, the approach

taken in this study can be applied to make corrections for tectonic subsidence

originating in crustal processes, such as thrust loading. If "continental tilt" is a

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. valid mechanism, then predictably the regional subsidence patterns, once

corrected for other subsidence mechanisms, should always increases slowly

towards the subduction zones.

Mantle dynamic topography

Over the years, epeirogenic movements have been hypothesized to be a

consequence of secular variations in the mantle thermal regimes (Sloss, 1974).

However, it is not until recently, owing to progress in studies of mantle

convection, that the relationships between the dynamics of mantle convection and

vertical movements of continents has begun to be understood (Gumis, 1990,

1988).

Using sophisticated numerical modeling techniques and drawing on the latest

findings in tomographic mapping of the mantle, Gumis (1988,1990) and others

have demonstrated that significant changes in dynamic topography and the geoid

can occur as plates move from regions of upwelling to downwelling (Fig. 60).

With respect to individual plates in motion, such changes are reflected in episodic

vertical movements that measure up to several hundreds of meters. Although

contemporaneous tectonoeustatic fluctuations brought about by ridge volume

changes also are important, the epeirogenic movements are continent-specific,

depending on the rate and path of plate motion. Gumis (1988) suggested that the

epeirogenic movements documented in cratonic basins around the world may be

the records of continental vertical movements caused by dynamic topography.

Gumis (1990,1993a) interpreted the widespread Cretaceous shallow marine

deposits in the Western Interior basin as the result of this mechanism.

Specifically, this model can be expanded as follows. As seen in Figure 60,

following the break-up of Pangaea in the early Mesozoic, the North American

plate became separated from Africa plate. Since then, it has been moving

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Downwelling CRETACEOUS Sea surface Seasurface [Pangaea; Upwelling TRIASSIC 1111! Distance Distance 1 1 1 I I (North Americaduring the Cretaceous) moving towards downwellings has alower topography and reduced free a. Aplate (Pangaeaduring the Triassic) positioned overupwellings has ahigh topography; b. a fragmentof the plate board area. Modified fromGumis (1990). Figure 60. Diagram showing changes in continental topography relative to sea surface during continental breakup,

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. northwestward and away from regions of mantle upwelling (Engebretson et al.,

1985). Based on this plate motion history, the model for dynamic topography

predicts that the western the North America should experience a decrease in the

dynamic topography or a gradual reduction in the freeboard. The changes in the

dynamic topography therefore should lead to epeirogenic subsidence in the

Western Interior.

The "residual" subsidence documented in this study, which has so far been

difficult to explain either in terms of eustasy factors or using other known tectonic

mechanisms, may be the evidence of changes in the dynamic topography. Until a

more refined model arrives, the model for dynamic topography at least provides a

plausible explanation for the residual subsidence documented in this study.

The concept of dynamic topography is based on recent breakthroughs in solid

earth geophysics. To stratigraphers, it provides a powerful conceptual framework

within which to investigate epeirogenic movements and their relationships to

contemporaneous eustatic sea level changes. However, because much of this

model is based on modem plate tectonics data, it remains unclear what

stratigraphic signatures it would leave in the rock record. Compelling evidence in

support of it has been found in many Phanerozoic cratonic platform basins

(Gumis, 1993a), but the challenge of unequivocally documenting its role in

sedimentary basins around the world has not been met.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. CHAPTER 7

CONCLUSIONS

The abundant litho- and biostratigraphic data in the Cretaceous Western Interior basin

are superbly suited to flexural backstripping and foreland basin modeling. To document

basin subsidence history, a major effort of this study went into compiling a regional

stratigraphic data base by integrating subsurface and outcrop stratigraphic data from

various sources. The result is a set of six regional stratigraphic sections showing middle

Cenomanian to early Campanian (96 to 80 Ma) stratal thickness, lithofacies, and

chronostratigraphic relationships across different segments of the U.S. Western Interior.

Application of the two-dimensional flexural backstripping techniques to this stratigraphic

data base resulted in six regional subsidence profiles. These profiles document a

subsidence pattern that is spatially and temporally much more complex than previously

recognized. Analysis of the observed subsidence pattern in terms of foreland basin

models and in the context of basement tectonics furnished significant new insights into

the Cretaceous subsidence history and its probable causes. The main conclusions follow:

1. The subsidence profiles, supplemented by a flexural model, document that the

cumulative subsidence across the Western Interior over the 16 m.y. study interval

consists of two distinct components: a westward-increasing flexural subsidence confined

within a few hundred kilometers of the thrust belt, and a spatially uniform "residual"

subsidence that affected the entire basin. The flexural subsidence generally exceeds the

residual subsidence in magnitude along the thrust belt. However, in western Montana the

residual subsidence actually exceeded flexural subsidence in this time interval. This

observation implies that subsidence trends observed in the foreland of the Western

Interior basin can not be all attributed to orogenic loading.

167

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 168

2. The regional flexural subsidence was characterized by spatial segmentation and

temporal discordance. Spatially, the westward-increasing flexural subsidence shows

great variations along the strike of the thrust belt. In Wyoming, flexural subsidence

generated a deep and wide foreland basin. In contrast, flexural subsidence in southern

Utah and western Montana was insignificant. In these areas, total subsidence was

dominated by the residual subsidence component which extended eastward far beyond

the effect of lithospheric flexure due to thrust loading.

Temporally, the rates of subsidence also vary with location along the thrust belt.

From middle Cenomanian to late Turonian (96 to 90 Ma), subsidence rates were high in

Utah and much lower in Wyoming and Montana. In contrast, during the Coniacian and

Santonian stages (90 to 85 Ma) subsidence accelerated rapidly in Wyoming, increased

slightly in Montana, and decreased in Utah. At the end of the Santonian and into the early

Campanian, rates of subsidence appear to have slowed everywhere.

3. The observed variations in flexural subsidence may be manifestations of basement

structures, particularly those zones of weakness inherited from Precambrian rifting and

early Paleozoic passive margin development. Three different mechanisms are proposed

concerning this basement control on the Cretaceous flexural subsidence. First, basement

directly affected the emplacement of thrust loads through the formation of buttresses that

inhibited the eastward advance of the Sevier thrust sheets. Buttressing by basement

structures may have controlled discrete, diachronous thrusting along the thrust belt,

causing variations in subsidence trends with location. Moreover, buttresses such as those

in southwestern Montana and northwestern Wyoming could lead to differential crustal

shortening, creating spatially concentrated crustal loads. Second, basement faults or

lineaments at high angle to the Cordilleran hingeline probably partitioned the crust

underlying the Rocky Mountain region into tectonic blocks. During loading by the Sevier

thrust sheets these separate blocks may have responded more or less independently.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 169

Third, the internal mechanical strength of the tectonic blocks differed from each other,

depending on the nature of the Precambrian crust and the distribution of the zones of

crustal weakness. Therefore, considerable variations in half flexural wavelength occurred

along the basin strike.

4. A two-dimensional flexural model of the two subsidence profiles across the

Wyoming foreland suggests that the westward-increasing flexural subsidence can be

satisfactorily accounted for by flexure of a lithosphere with an elastic thickness of 80 ±

10 km and under a crustal load measuring 100 km in width and 3 to 5 km in height.

These dimensions compare to earlier estimates for the size of the Meade-Crawford thrust

system. The flexural half wavelength of the Wyoming foredeep is about 400 km. The

predicted flexural forebulge is located slightly east of the Powder River and Hanna

basins.

5. The "residual" subsidence documented in this study probably reflects epeirogenic

movements specific to the North American Western Interior rather than eustatic sea level

changes. Tectonic mechanism(s) to explain the residual subsidence remains controversial.

Dynamic topography, driven by mantle convection, provides a plausible explanation.

6. The approach taken in this study of the tectonic subsidence history presents several

distinct advantages over site-specific studies or those based on gross lithostratigraphic

data. First, the broad stratigraphic data base of this study permits adequate sampling of

the temporal and spatial variations in basin subsidence on different scales. Second, the

large amount of outcrop biostratigraphy integrated into this data base improves the

temporal resolution and precision of the results. Third, compared to Airy backstripping

techniques, flexural backstripping techniques provide a superior means of calculating

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. basin subsidence history by accounting for both the flexural effects of sediment loading

and the compaction of the Pre-Cretaceous strata.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. REFERENCES

Abbott, W. O., and Liscomb, R. L., 1956, Stratigraphy of the Book Cliffs in east central Utah: Intermountain Association of Petroleum Geologists 7th Field Conference Guidebook, p. 120-123.

Airy, G. B., 1855, On the computation of the attraction of mountain masses as disturbing the apparent astronomical latitude of stations of geodetic surveys, Philosophical Transactions of the Royal Society, v. 145, p. 101-104.

Allmendinger, R. W., Farmer, H„ Hauser, E. C., Sharp, J. W., Potter, C. J., Klemperer, S. L., Nelson, K. D .,, P., and Oliver, J., 1987, Overview of the COCORP 40° N Transect, western United States; Fabrics of an orogenic belt: Geological Society of America Bulletin, v. 98, p. 308-319.

Allmendinger, R. W., Hauge, T. A., Hauser, E. C., Von Tish, D., Oliver, J., and Kaufman, S., 1986, Phanerozoic tectonics of the Basin and Range-Colorado Plateau transition from COCORP data and geologic data: A review: in Barazangi, M., and Brown, L., eds., Reflection seismology; The continental crust: American Geophysical Union Geodynamics Series, v. 14, p. 257-268.

Allmendinger, R. W., Sharp, J. W., Von Tish, D., Serpa, L., Kaufman, S., Oliver, J., and Smith, R. B., 1983, Cenozoic and Mesozoic structure of the eastern Basin and Range province, Utah, from COCORP seismic-reflection data: Geology, v. 11, p. 532-536.

Angevine, C. L., Heller, P. L., Paola, C., 1990, Quantitative sedimentary basin modeling, American Association of Petroleum Geologists Continuing Education Course Note Series 32.

Anna, L. O., 1986, Structural influences on Cretaceous sedimentation, Northern Great Plains, in Peterson, J. A., ed., Paleotectonics and sedimentation in the Rocky Mountain region, United States: American Association of Petroleum Geologists Memoir 41, p. 173-192.

Armin, R., and Mayer, L., 1983, Subsidence analysis of the Cordilleran miogeocline: implications for timing of Proterozoic rifting and amount of extension: Geology, v. 11, p. 702-705.

Armstrong, F. C. and Oriel, S. S., 1965, Tectonic development of Idaho-Wyoming thrust belt: American Association of Petroleum Geologists Bulletin, v. 49, p. 1847- 1866.

Armstrong, R. L., 1968, The Sevier orogenic belt in Nevada and Utah: Geological Society of American Bulletin, v. 79, p. 429-458.

Armstrong, R. L., 1974, Magmatism, orogenic timing, and orogenic diachronism in the Cordillera from Mexico to Canada: Nature, v. 247, p. 344-351.

171

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 172

Asquith, D. O., 1970, Depositional topography and major marine environments, Late Cretaceous, Wyoming: American Association of Petroleum Geologists Bulletin, v. 54, p. 1184-1224.

Asquith, D. O., 1974, Sedimentary models, cycles, and deltas, Upper Cretaceous, Wyoming: American Association of Petroleum Geologists Bulletin, v. 58, p. 2274- 2283.

Atwater, T., 1989, Plate tectonic history of the northeast Pacific and western North America: in Winterer, E. L., Hussong, D. M., Decher, R. W., eds., The Eastern Pacific Ocean and Hawaii: Geological Society of America, The Geology of North America, v. N, p. 21-72.

Averitt, P., 1962, Geology and coal resources of the Cedar Mountain Quadrangle, Iron County, Utah: U.S. Geological Survey Professional Paper 389.

Baars, D. L., and Stevenson, G. M., 1982, Subtle stratigraphic traps in Paleozoic rocks of Paradox basin, in Halbouty, M. T., ed., Deliberate search for the subtle traps: American Association of Petroleum Geologists Memoir 32, p. 131-158.

Baars, D. L., Bartleson, C. E., Chapin, C. E., Curtis, B. F., De Voto, R. H., Everett, J. R., Johnson, R. C., Molenaar, C. M., Peterson, F., Schenk, C. J., Love, J. D., Merin, I. S., Rose, P. R., Ryder, R. T., Waechter, N. B., Woodward, L. A., 1988, Basins of the Rocky Mountain region, in Sloss, L. L., ed., Sedimentary cover-North American Craton: U.S.: Geological Society of America, The Geology of North America, v. D-2, p. 109-220.

Banks, R. J., Parker, R. L„ and Huestis, S. P., 1977, Isostatic compensation on a continental scale: local versus regional mechanisms: Geophysical Journal of Royal Astronomical Society, v. 51, p. 431-452.

Barlow, J. A., Jr., and Haun. J. D., 1966, Regional stratigraphy of the Frontier Formation and relation to St. Creek Field, Wyoming: American Association of Petroleum Geologists Bulletin, v. 50, p. 2185-2196.

Barlow, L. K., and Kauffman, E. G., 1985, Depositional cycles in the Niobrara Formation, Colorado Front Range, in: Pratt, L. M., Kauffman, E. G., and Zelt, F. B., eds., Fine-grained deposits and biofacies of the Cretaceous Western Interior Seaway: Evidence of cyclic sedimentary processes, Society of Economic Paleontologists and Mineralogists Guidebook No. 4, p. 199-208.

Barrell, J., 1914, The strength of earth's crust, 8, Physical conditions controlling the nature of lithosphere and asthenosphere: Journal of Geology, v. 22, p. 425-433.

Barwin, J. R., 1961, Stratigraphy of the Mesaverde Formation in the southern part of the Wind River basin, Wyoming: Symposium on Late Cretaceous rocks, Wyoming and adjacent areas: Wyoming Geological Association 11th Field Conference Guidebook, p. 171-179.

Beaumont, C., 1978, The evolution of sedimentary basins on a viscoelastic lithosphere: theory and examples: Geophysical Journal of Royal Astronomical Society, v. 55, p. 471-497.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 173

Beaumont, C., 1981, Foreland basins: Geophysical Journal of Royal Astronomical Society, v. 65, p. 291-329.

Beaumont, C., Quinlan, G. M., and Hamilton, J., 1987, The Alleghenian orogeny and its relationship to the evolution of the Eastern Interior, North America, in Beaumont, C., and Tankard, A.J., eds., Sedimentary Basins and Basin-forming Mechanisms: Canadian Society of Petroleum Geologists Memoir 12, p. 425-445.

Beaumont, C., Quinlan, G. M., and Hamilton, J., 1988, Orogeny and stratigraphy: Numerical models of the Paleozoic in the Eastern Interior of North America: Tectonics, v. 7, p. 389-416.

Beaumont, C., Quinlan, G. M„ and Stockmal, G. S., 1993, The evolution of the Western Interior Basin: Causes, consequences and unsolved problems, in Caldwell, W. G. E., and Kauffman, E. G., eds., Evolution of the Western Interior Basin, Geological Association of Canada Special Paper 39, p. 97-117.

Beutner, E. C., 1977, Causes and consequences of curvature in the Sevier orogenic belt, in Heisey, E. L., ed., Rocky Mountain thrust belt geology and resources: Casper, Wyoming Geological Association, p. 353-366.

Bickford, M. E., 1988a, The formation of continental crust; part 1, A review of some principles; Part 2, An application to the Proterozoic evolution of southern North America: Geological Society of America Bulletin, v. 100, p. 1357-1391.

Bickford, M. E., 1988b, The accretion of Proterozoic crust in Colorado: igneous, sedimentary, deformation, and metamorphic history: in Ernst, W. G., ed., Metamorphism and crustal evolution of the western United States, Ruby Volume 7: Englewood Cliffs, New Jersey, Prentice Hall, p. 412-430.

Bird, P., 1984, Laramide crustal thickening event in the Rocky Mountain foreland and Great Plains: Tectonics, v. 3, p. 741-758.

Bond, G. C., 1976, Evidence for continental subsidence in North America during the Late Cretaceous global submergence: Geology, v. 4, p. 557-560.

Bond, G. C., 1978, Speculations on real sea-level changes, and vertical motions of continents at selected times in the Cretaceous and Tertiary periods: Geology, v. 6, p. 247-250.

Bond, G. C., and Kominz, M., 1984, Construction of tectonic subsidence curves for early Paleozoic miogeocline, southern Canadian Rocky Mountains: implications for subsidence mechanisms, age of breakup, and crustal thinning: Geological Society of America Bulletin, v. 95, p. 155-173.

Bond, G. C., and Kominz, M., 1991, Disentangling middle Paleozoic sea level and tectonic events in cratonic margins and cratonic basins of North America: Journal of Geophysical Research, v. 96, p. 6619-6639.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 174

Bond, G. C., Kominz, M., and Grotzinger, J. P., 1988, Cambro-Ordovician Eustasy: Evidence from Geophysical Modelling of Subsidence in Cordilleran and Appalachian Passive Margins, in Kleinspehn, K. L. and Paola, C., eds., New Perspectives in Basin Analysis: New York, Springer-Verlag, p. 129-160.

Bradley, M. D., and Bruhn, R. L., 1988, Structural interactions between the Uinta arch and the overthrust belt, north-central Utah; Implications of strain trajectories and displacement modeling, in Schmidt, C. J. and Perry, W. J. eds., Interaction of the Rocky Mountain Foreland and the Cordilleran Thrust Belt, Geological Society of America, Inc., p. 447-464.

Bruhn, R. L., Picard, M. D., and Isby, J. S., 1986, Tectonics and sedimentology of Uinta Arch, western Uinta Mountains, and Uinta Basin: in Peterson, J. A., ed., Paleotectonics and Sedimentation in the Rocky Mountain Region, United States: American Association of Petroleum Geologists Memoir 41, p. 333-352.

Bryant, B., 1988, Evolution and early Proterozoic history of the margin of the Archean continent in Utah: in Ernst, W. G., ed., Metamorphism and crustal evolution of the western United States, Ruby Volume 7: Englewood Cliffs, New Jersey, Prentice Hall, p. 432-445.

Bryant, B., Nichols, D. J., 1988, Late Mesozoic and early Tertiary reactivation of an ancient crustal boundary along the Uinta trend and its interaction with the Sevier orogenic belt, in Schmidt, C. J., and Perry, W. J., eds., Interaction of the Rocky Mountain Foreland and the Cordilleran Thrust Belt, Geological Society of America, p. 411-430.

Burbank, D. W., Beck, R. A., Raynold, R. G. H., Hobbs, R., and Tahirkheli, R. A. K., 1988, Thrusting and gravel progradation in foreland basins: A test of post- thrusting gravel dispersal: Geology, v. 16, p. 1143-1146.

Burchfiel, B. C. and Davis, G. A., 1975, Nature and controls of Cordilleran orogenesis, western United States: Extensions of an earlier synthesis: American Journal of Science, v. 275A, p. 363-396.

Burton, R., Kendall, C., and Lerche, I., 1987, Out of Our Depth: on the impossibility of fathoming eustasy from the stratigraphic record: Earth-Science Reviews, v. 24, p. 237-277.

Cant, D. J., and Stockmal, G. S., 1989, The Alberta foreland basin: relationship between stratigraphy and Cordilleran terrane-accretion events: Canadian Journal of Earth Science, v. 26, p. 1964-1975.

Cobban, W. A., 1951a, Colorado shale of central and northwestern Montana and equivalent rocks of Black Hills: American Association of Petroleum Geologists Bulletin, v. 35, p. 2170-2198.

Cobban, W. A., 1951b, Scaphitoid Cephalopods of the Colorado Group: U.S. Geological Survey Professional Paper 239,42 p.

Cobban, W. A., 1953a, A new species of Prionocyclus from Upper Cretaceous Carlile Shale: Journal of Paleontology, v. 27, p. 353-355.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 175

Cobban, W. A., 1953b, An Upper Cretaceous section near Mosby, Montana: Billings Geological Society 4th Annual Field Conference Guidebook, p. 98-101.

Cobban, W. A., 1955a, Cretaceous rocks of northwestern Montana: Billings Geological Society 6th Annual Field Conference Guidebook, p. 107-119.

Cobban, W. A., 1955b, Some guide fossils from the Colorado shale and telegraph Creek Formation, northwestern Montana: Billings Geological Society 6th Annual Field Conference Guidebook, p. 198-207.

Cobban, W. A., 1956, Cretaceous rocks along part of the southeast boundary of Glacier National Park, Montana: American Association of Petroleum Geologists Bulletin, v. 40, p. 1001-1004.

Cobban, W. A., 1958a, Late Cretaceous fossil zones of the Powder River Basin, Wyoming and Montana: Wyoming Geological Association 13th Annual Field Conference Guidebook, p. 114-119.

Cobban, W. A., 1958b, Two new species of Baculites from the Western Interior region: Journal of Paleontology, v. 32, p. 704-718.

Cobban, W. A., 1962, Baculites from the lower part of the Pierre Shale and equivalent rocks in the Western Interior: Journal of Paleontology, v. 36, p. 704-718.

Cobban, W. A., 1963, Occurrence of the Late Cretaceous ammonite Hoplitopiocsnticcror in Wyoming, in Shorter Papers in the Geological Sciences: U.S. Geological Survey Professional Paper 475-C, p. 60-62.

Cobban, W. A., 1969, The Late Cretaceous Ammonites Scaphites Leei and Scaphites hippocrepis (DeKay) in the Western Interior of the United States: U.S. Geological Survey Professional Paper 619,29 p.

Cobban, W. A., 1976, Ammonite record from Mancos Shale of the Castle Valley-Price Woodside area, east-central Utah: Brigham Young University Geology Studies, v. 22, p. 117-126.

Cobban, W. A., 1977a, Characteristic Mesozoic molluscan fossils from the Dakota Sandstone and Intertongued Mancos shale, west central New Mexico: U.S. Geological Survey Professional Paper 1009,309 p.

Cobban, W. A., 1977b, Fossil Mollusks of the Dakota sandstone and intertongued Mancos shale of west-central New Mexico: New Mexico Geological Society 28th Field Conference Guidebook, p. 213-220.

Cobban, W. A., 1983, Molluscan fossil record from the northeastern part of the Upper Cretaceous seaway, Western Interior: Stratigraphy and Paleontology of Mid Cretaceous rocks in Minnesota and Contiguous Areas, U.S. Geological Survey Professional Paper 1253 A, p. 1-23.

Cobban, W. A., 1984, Mid Cretaceous ammonite zones, Western Interior, United States: Bulletin of the Geological Society of Denmark, v. 33, p. 71-89.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 176

Cobban, W. A., 1987, A new ammonite from the Upper Cretaceous of Kansas: U.S. Geological Survey Bulletin 1690-B, p. 1-3.

Cobban, W. A., 1993, Diversity and distribution of Late Cretaceous Ammonites, Western Interior, United States, in Caldwell, W. G. E., and Kauffman, E. G., eds., Evolution of the Western Interior Basin, Geological Association of Canada Special Paper 39, p. 435-451.

Cobban, W. A., and Hook, S. C., 1984, Mid Cretaceous molluscan biostratigraphy and paleogeography of southwestern part of Western Interior, United States, in Westermann, C. E. C., ed., Jurassic-Cretaceous Biochronology and Paleogeography of North America: Geological Association of Canada Special Paper 27, p. 257-271.

Cobban, W. A., and Hook., S. C., 1980, The Upper Cretaceous (Turonian) Ammonite Family Coilopoceratidae Hyatti in the Western Interior of the United States: U.S. Geological Survey Professional Paper 1192.

Cobban, W. A., and Hook., S. C„ 1983, Mid-Cretaceous (Turonian) ammonite fauna from Fence Lake area of west-central New Mexico: New Mexico Bureau of Mines and Mineral Resources Memoir 41.

Cobban, W. A., and Hook., S. C., 1989, Mid-Cretaceous Molluscan record from the west-central New Mexico: New Mexico Geological Society 40th Field Conference Guidebook, p. 247-264.

Cobban, W. A., and Jeletzky, J. A., 1985, A new Scaphite from the Campanian rocks of the Western Interior of North America: Journal of Paleontology, v. 39, p. 794- 801.

Cobban, W. A., and Kennedy, W. J., 1989, The ammonite Metengonoceras Hyatt, 1903, from the Mowry Shale (Cretaceous) of Montana and Wyoming: U.S. Geological Survey Bulletin 1787-L, lip.

Cobban, W. A., and Reeside J. B., Jr., 1951, Frontier Formation near Sinclair, Carbon County, Wyoming: Wyoming Geological Association 6th Annual Field Conference Guidebook, p. 60-65.

Cobban, W. A., and Reeside, J. T., 1952a, Correlation of the Cretaceous formations of the Western Interior of the United States: American Association of Petroleum Geologists Bulletin, v. 63, p. 1011-1044.

Cobban, W. A., and Reeside, J. T., 1952b, Frontier Formation, Wyoming and adjacent areas: American Association of Petroleum Geologists Bulletin, v. 36, p. 1913-1961.

Cobban, W. A., and Scott, C. R., 1964, Multinodose scaphitid cephalopods from the lower part of the Pierre Shale and equivalent rocks in the conterminous United States: U.S. Geological Survey Professional Paper 483 E, p. 1-13.

Cobban, W. A., and Scott, C. R., 1972, Stratigraphy and ammonite fauna of the Graneros Shale and Greenhorn Limestone near Pueblo, Colorado: U.S. Geological Survey Professional Paper 645,108 p.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 177

Cobban, W. A., Erdmann, C. E., Alto, B.R., and Clark, C. H., 1958, Scaphites depressus Zone (Cretaceous) in northwestern Montana: American Association of Petroleum Geologists Bulletin, v. 42, p. 656-660.

Cobban, W. A., Erdmann, C. E., Lemke, R. W., and Maughan, E. K., 1959, Revision of Colorado Group on Sweetgrass Arch, Montana: American Association of Petroleum Geologists Bulletin, v. 43, p. 2786-2796.

Cobban, W. A., Erdmann, C. E., Lemke, R. W., and Maughan, E. K., 1976, Type sections and stratigraphy of the Blackleaf and Marias River Formations (Cretaceous) of the Sweetgrass Arch, Montana: U.S. Geological Survey Professional Paper 974.

Cobban, W. A., Hook., S. C, and Kennedy, W. J., 1989, Upper Cretaceous rocks and ammonite faunas of southwestern New Mexico, New Mexico Bureau of Mines and Mineral Resources Memoir 45.

Cobban, W. A., Landis, E. R., and Dane, C. H., 1974, Age relations of upper part of Lewis Shale on east side of San Juan Basin, New Mexico: New Mexico Geological Society 25th Annual Field Conference Guidebook, p. 279-282.

Cole, R. D., and Young, R. G., 1991, Facies characterization and architecture of a muddy shelf-sandstone complex: Mancos B interval of Upper Cretaceous Mancos Shale, northwest Colorado and northeast Utah, in Miall, A. D., and Tyler, N., eds., Three-dimensional facies architecture of clastic sediments: Society of Economic Paleontologists and Mineralogists Concepts in Sedimentology Series, p. 277-287.

Coletingh, S., McQueen, H., and Lambeck, K., 1985, On a tectonic mechanism for regional sea level variations: Earth and Planetary Science Letters, v. 75, p. 157-166

Coogan, J. C., 1992, Thrust systems and displacement transfer in the Wyoming-Idaho- Utah thrust belt; University of Wyoming Ph.D. dissertation, 229 p.

Cotter, E., 1975, Late Cretaceous sedimentation in a low-energy coastal zone: the Ferron Sandstone of Utah: Journal of Sedimentary Petrology, v. 45, p. 69-87.

Cotter, E., 1976, The role of deltas in the evolution of the Ferron Sandstone and its coals, Castle Valley, Utah: Brigham Young University Geology Studies, v. 22, p. 15-41.

Cotter, E.,1975, Deltaic deposits in the Upper Cretaceous Ferron Sandstone in Utah, in Broussard, M. L. S., ed., Deltas, models for exploration: Houston Geological Society, p. 471-484.

Couples, G. D., and Lewis, H., 1988, "Thrust belt" structures with "foreland" influences; The interaction of tectonic styles, in Schmidt, C. J., and Perry, W. J., eds., Interactions of the Rocky Mountain Foreland and the Cordilleran Thrust Belt: Geological Society of America Memoir 171, p. 99-110.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 178

Craddock, J. P., Kopania, A. A., and Wiltschko, D. V., 1988, Interaction between the northern Idaho-Wyoming thrust belt and bounding basement blocks, central western Wyoming: in Schmidt, C. J., and Perry, W. J., eds., Interactions of the Rocky Mountain Foreland and the Cordilleran Thrust Belt: Geological Society of America Memoir 171, p. 333-351.

Craig, L. C., 1981, Lower Cretaceous rocks, southwestern Colorado and southeastern Utah, in Wiegand, D. L., ed., Geology of the Paradox basin: Rocky Mountain Association Geologists 1981 Field Conference Guidebook, p. 195-200.

Crittenden, M. D., Jr., 1969, Interaction between Sevier orogenic belt and Uinta structures near Salt Lake City, Utah: Geological Society of American Abstracts with Programs, v. 1, p. 18.

Cross, T. A., 1986, Tectonic controls of foreland basin subsidence and Laramide style deformation, western United States, in: Allen, P., and Homewood, P., eds., Foreland Basins, Special Publication Number 8 of the International Association of Sedimentologists: Blackwell Scientific Publications, p. 15-39.

Cross, T. A., 1988, Controls on coal distribution in transgressive-regressive cycles, Upper Cretaceous, Western Interior, U.S.A., in Posamentier, H. W., Summerhayes, C. P., Haq, B. U., and Allen, G. P., eds., Sea-level Changes-An Integrated Approach, Society of Economic Paleontologists and Mineralogist Special Publication 42, p. 371-380.

Cross, T. A., and Pilger, R. 1978, Tectonic controls of late Cretaceous sedimentation, western interior, USA: Nature, v. 274, p. 653-657.

Cullins, H. L., 1968, Geologic map of the Banty Point Quadrangle, Rio Blanco County, Colorado: U.S. Geological Survey Map GQ-703.

Cullins, H. L., 1969, Geologic map of the Mellen Hill Quadrangle, Rio Blanco and Moffat counties, Colorado: U.S. Geological Survey Map GQ-835.

Cumella, S. P., 1983, Relation of Upper Cretaceous regressive sandstone units of the San Juan Basin to source area tectonics, in Reynolds, M. W„ and Dolly, E. D., eds., Mesozoic paleogeography of the west-central United States: Society of Economic Paleontologists and Mineralogist, Rocky Mountain Section, Rocky Mountain Paleogeography symposium 2, p. 189-199.

Curry, III, W. H., 1986, Subtle middle Cretaceous paleotectonic deformation of Frontier and lower Cody rocks in Wyoming, in Peterson, J. A., ed., Paleotectonics and sedimentation in the Rocky Mountain region, United States, American Association of Petroleum Geologists Memoir 41, p. 469-479.

Custason, E. R., Ryer, T. A., and Odland, S. K.,1988, Stratigraphy and depositional environments of the Muddy Sandstone, northwestern Black Hills, Wyoming: Wyoming Geological Association Earth Science Bulletin, v. 20, p. 49-60.

Dane, C. H., 1935, Geology of the Salt Valley anticline and adjacent areas, Grand County, Utah: U.S. Geological Survey Bulletin 863,184 p.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 179

Dane, C. H., 1960a, The boundary between rocks of Carlile, and Niobrara age in San Juan Basin, New Mexico and Colorado: American Journal of Science, Bradley Volume, v. 258-A, p. 46-56.

Dane, C. H., 1960b, The Dakota Sandstone and Mancos shale of the eastern side of San Juan Basin, New Mexico: New Mexico Geological Society 11th Field Conference Guidebook, p. 63-74.

Dane, C. H., Bachman, G. O., and Reeside, J. B., Jr., 1957, The Gallup sandstone, its age and stratigraphic relationships, south and east of the type locality: Four Comers Geological Society 2nd Field Conference Guidebook, p. 99-113.

Dane, C. H., Cobban, W. A., and Kauffman, E. G., 1966, Stratigraphy and regional relationships of a reference station for the Juana Lopez Member, Mancos Shale, in the San Juan Basin, New Mexico: U.S. Geological Survey Bulletin 1224-H, 15 p.

Dane, C. H., Wanek, A. A., and Reeside, J. B., Jr., 1957, Reinterpretation of section of Cretaceous rocks in Alamosa Creek Valley area, Catron and Socorro counties, New Mexico: American Association of Petroleum Geologists Bulletin, v. 41, p. 181-196.

Dane, C. R., Kauffman, E. G., and Cobban, W. A., 1968, Semilla Sandstone, a new member of the Mancos Shale in the southeastern part of the San Juan Basin, New Mexico: U.S. Geological Survey Bulletin 1254-F, 21 p.

Davis, T. L. 1985, Seismic evidence of the tectonic influence on development of Cretaceous listric-normal faults, Boulder-Wattenberg-Greeley Area, Denver basin, Colorado: Mountain Geologist, v. 22, p. 47-54.

Davis, T. L., 1983, Influence of Transcontinental arch on Cretaceous listric-normal faulting, west flank, Denver basin: American Association of Petroleum Geologists Bulletin, v. 67, p. 1333.

De Chadenes, J. F., 1975, Frontier deltas of the western Green River Basin, Wyoming: Deep Drilling frontiers of the central Rocky Mountains, Rocky Mountain Association of Geologists Symposium, 1975, Denver, Colorado, p. 149-157.

DeCelles, P. G., 1986, Sedimentation in a tectonically partitioned, nonmarine foreland basin: The lower Cretaceous Kootenai Formation, southwestern Montana: Geological Society of America Bulletin, v. 97, p. 911-931.

DeCelles, P. G., 1994, Late Cretaceous-Paleocene synorogenic sedimentation and kinematic history of the Sevier thrust belt, northeast Utah and southwest Wyoming: Geological Society of America Bulletin, v. 106, p. 32-56.

DeCelles, P. G., Pile, H. T., and Coogan, J. C., 1993, Kinematic history of the Meade thrust based on provenance of the Bachler Conglomerate at Red Mountain, Idaho, Sevier thrust belt: Tectonics, v. 12, p. 1436-1450.

DeGraw, H. M., 1975, The Pierre-Niobrara unconformity in western Nebraska, in W. G. E. Caldwell, ed., Cretaceous system in the western interior of North America, p. 589-606

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 180

DeRito, R. F., Cozzarelli, F. A., and Hodge, D. S., 1983, Mechanism of subsidence of ancient cratonic rift basins: Tectonophysics, v. 94, p. 141-168.

Devlin, W. J., Rudolph, K. W., Shaw, C. A., and Ehman, K. D., 1993, The effect of tectonic and eustatic cycles on accommodation and sequence-stratigraphic framework in the Upper Cretaceous foreland basin of southwestern Wyoming, in Posamentier, H. W., Summerhayes, C. P., Haq, B. U., and Allen, G. P., eds., Sequence Stratigraphy and Facies Associations, Special publications number 18 of the International Association of Sedimentologists, Blackwell Scientific Publications, p. 501-520.

Dickinson, W. R., 1974, Plate tectonics and sedimentation, in Dickinson, W. R., ed., Tectonics and Sedimentation, Society of Economic Paleontologists and Mineralogist Special publication 22, p. 1-27.

Dickinson, W. R., 1977, Paleozoic plate tectonics and the evolution of the Cordillera continental margin: in Stewart, J. H., Stevens, C. H., and Fritsche, A. E., eds., Paleozoic Paleogeography of the Western United States: Pacific Section, Society of Economic Paleontologists and Mineralogists, Pacific Coast Paleogeography Symposium 1, p. 137-155.

Dickinson, W. R., and Snyder, W. S., 1978, Plate tectonics of the Laramide orogeny: in Mathews, V., ed., Laramide folding associated basement block faulting in the western United States: Geological Society of America Memoir 151, p. 355-366.

Dickinson, W. R., Klute, M. A., Hayes, M. J., Janecke, S. U., Lundin, E. R., Mckittrick, M. A. and Olivares, M. D., 1988, Paleogeographic and paleotectonic setting of Laramide sedimentary basins in the central Rocky Mountain region: Geological Society of America Bulletin, v. 100, p. 1023-1039.

Doelling, H. H., and Graham. R. L., 1972, Eastern and northern Utah coal fields: Utah Geological and Mineralogical Survey Monograph 2. p. 97-190.

Doelling, H.H., 1975. Geology and mineral resources of Garfield County, Utah: Utah Geological and Mineral Survey Bulletin, p. 107-175.

Doelling, H.H., 1985, Geologic map of Arches National Park and vicinity, Grand County, Utah: Utah Geological and Mineralogical Survey Map 74.

Dorobek, S. L., Reid, S. K., Elrick, M., Bond, G. C., and Kominz, M. A., 1991, Subsidence across the Antler foreland of Montana and Idaho: Tectonic versus eustatic effects, in Franseen, E. K., Watney, W. L., Kendall, C. G., St. C., and Ross, W., eds., Sedimentary modeling: computer simulations and methods for improved parameter definition, Kansas Geological Survey Bulletin 233, p. 231-272.

Duebendorfer, E. M., and Houston, R. S., 1986, Kinematic history of the Cheyenne belt: A Proterozoic suture in southeastern Wyoming: Geology, v. 14, p. 171-174.

Duebendorfer, E. M., and Houston, R. S., 1987, Proterozoic accretionary tectonics at the southern margin of the Archean Wyoming craton: Geological Society of America Bulletin, v. 98, p. 554-568.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 181

Duke, W. C., 1965, Turonian (Cretaceous) stratigraphy and micropaleontology, Cumberland Gap, Wyoming - Woodside, Utah: Boulder, University of Colorado, Master's Thesis, 103 p.

Dumitru, T. A., Gans, P. B., Foster, D. A., and Miller, E. L., 1991, Refrigeration of the western Cordilleran lithosphere during Laramide shallow-angle subduction: Geology, v. 19, p. 1145-1148.

Dyman, T. S., Perry, W. J., Jr., Nichols, D. J., Davis, L. E., and Haley, 1989, Stratigraphy, petrology, and provenance of die Cenomanian to Turonian Frontier Formation near Lima, southwestern Montana, in French, D. E., and Grabb, R. F., eds., Geologic resources of Montana: Montana Geological Society Field Conference Guidebook, p. 103-114.

Dyni, J. R, and Cullins, H. J., 1965, Meeker and Lloyd sandstone members of the Mancos Shale, Moffat and Blanco counties, Colorado: U.S. Geological Survey Bulletin 1194-J, p. 1-7.

Dyni, J. R., 1966, Geologic map of the Thornburg oil and gas field and vicinity, Moffat and Rio Blanco counties, Colorado: U.S. Geological Survey Oil and Gas Investigations Map OM-216.

Dyni, J. R., 1968, Geologic map of the Elk Springs Quadrangle, Moffat County, Colorado: U.S. Geological Survey Map GQ-702.

Eardley, A. J., 1962, Structural geology of North America: New York, Harper and Row, 743 p.

Eaton, J. G., Kirkland, J. I., and Kauffman, E. G., 1990, Evidence and dating of mid- Cretaceous tectonic activity in the San Rafael swell, Emery County, Utah: Mountain Geologist, v. 27, p. 39-45.

Eaton, J. G., Kirkland, J. I., Gustason, E. R., Nations, J. D., Franczyk, K. J., Ryer, T. A., Carr, D. A., 1987, Stratigraphy, Correlation, and tectonic setting of Late Cretaceous Rocks in the Kaiparowits and Black Mesa Basins, in New Mexico Geological Society 25th Annual Field Conference Guidebook, p. 225-230.

Eicher, D. L., 1960, Stratigraphy and micropaleontology of the Thermopolis Shale: Yale University Peabody Museum of Natural History Bulletin, v. 5,126 p.

Eicher, D. L., 1969, Paleobathymetry of Cretaceous Greenhorn sea in eastern Colorado: American Association of Petroleum Geologists Bulletin, v. 53, p. 1075-1090.

Elder, W. P., 1991, Molluscan paleoecology and sedimentation patterns of the Cenomanian-Turonian extinction interval in the southern Colorado Plateau region, in Nations J. D., and Eaton, J. G„ eds., Stratigraphy, depositional environments, and sedimentary tectonics of the western margin, Cretaceous Western Interior seaway, Geological Society of America Special Paper 260, p. 113-138.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. I

182

Elder* W. P., and Kirkland, J. I., 1985, Stratigraphy and depositional environments of the Bridge Creek Member of the Greenhorn Limestone at Rock Canyon Anticline near Pueblo, Colorado, in: Pratt, L. M., Kauffman, E. G., and Zelt, F. B., eds., Fine­ grained deposits and biofacies of the Cretaceous Western Interior Seaway: Evidence of cyclic sedimentary processes, Society of Economic Paleontologists and Mineralogists Guidebook No. 4, p. 122-134.

Elder, W. P., Gustason, E. R., and Sageman, B. B., 1994, Correlation of basinal carbonate cycles to nearshore parasequences in the Late Cretaceous Greenhorn seaway, Western Interior U.S.A.: Geological Society of American Bulletin, v. 106, p. 892-902.

Eldredge, S., and Van der Voo, R., 1988, Paleomagnetic study of thrust sheet rotations in the Helena and Wyoming salients of the northern Rocky Mountains: in Schmidt, C. J., and Perry, W. J., eds., Interactions of the Rocky Mountain Foreland and the Cordilleran Thrust Belt: Geological Society of America Memoir 171, p. 319-332.

Elison, M. W., 1991, Intracontinental contraction in western North America: continuity and episodicity: Geological Society of American Bulletin, v. 103, p. 1226-1238.

Ellis, M. S., 1987, Cross sections showing stratigraphic framework of Upper Cretaceous Dakota Sandstone, Mancos Shale, Mesaverde Group, and Mesaverde Formation, and lower Tertiary Wasatch Formation, west-central Piceance Basin, Garfield County, Colorado: U.S. Geological Survey Map MF-2008-A.

Engebretson, D. C, Kelley, K. P., Cashman, H. J., Richards, M. A., 1992, 180 million years of subduction: GSA Today, Geological Society of America, v. 2, p. 93-100.

Engebretson, D. C., Cox, A. and Gordon, R. G.,1985, Relative Motions Between Oceanic and Continental Plates in the Pacific Basin: Geological Society of America Special Paper 206,59 p.

Evetts, M. J., 1976, Microfossil biostratigraphy of the sage breaks shale (Upper Cretaceous) in northeastern Wyoming: Mountain Geologist, v. 13, p. 115-134.

Fassett, J. E, 1976, What happened during Late Cretaceous time in the Raton and San Juan Basins- with some thoughts about the area in between: New Mexico Geological Society 27th Field Conference Guidebook, p. 185-190.

Fassett, J. E., 1974, Cretaceous and Tertiary rocks of the eastern San Juan basin, New Mexico and Colorado: New Mexico Geological Society 25th Field Conference Guidebook, p. 225-230.

Fassett, J. E., 1977, Geology of the Point lookout, Cliff House and Pictured Cliffs Sandstone of the San Juan Basin, New Mexico and Colorado: New Mexico Geological Society 28th Field Conference Guidebook, p. 193-195.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 183

Fisher, C. G., Kauffman, E. G., and Wilhelm, L. V. H., 1985, The Niobrara transgressive hemicyclothem in central and eastern Colorado: The anatomy of a multiple disconformity, in: Pratt, L. M., Kauffman, E. G., and Zelt, F. B., eds., Fine-grained deposits and biofacies of the Cretaceous Western Interior Seaway: Evidence of cyclic sedimentary processes, Society of Economic Paleontologists and Mineralogists Guidebook No. 4, p. 184-198.

Fisher, D. J., Erdmann, C. E. and Reeside, J. B., Jr., 1960, Cretaceous and Tertiary formations of the Book Cliffs, Carbon, Emery and Grand Counties, Utah, and Garfield and Mesa Counties, Colorado: U.S. Geological Survey Professional Paper 332, 80 p.

Fleming, T. F., 1989, New reference sections for the Semilla Sandstone Member of the Mancos shale and their genetic implications: New Mexico Geology, v. 11, pl-7.

Flemings, P. B., and Jordan, T. E., 1990, Stratigraphic modelling of foreland basins: interpreting thrust deformation and lithosphere rheology: Geology, v. 18, p. 430- 434.

Fouch, T. D., Lawton, T. F„ Nichols, D. J., Cashion, W. D., and Cobban, W. A., 1983, Patterns and timing of synorogenic sedimentation in Upper Cretaceous rocks of central and northeastern Utah, in Reynolds, M. W., and Dolly, E. D., eds., Mesozoic paleogeography of the west-central United States: Rocky Mountain Section, Society of Economic Paleontologists and Mineralogists, Rocky Mountain Paleogeography Symposium 2, p. 305-336.

Franczyk, K. J., 1987, Stratigraphic revision and depositional environments of the Upper Cretaceous Toreva Formation in the northern Black Mesa area, Navajo and Apache Counties, Arizona: U.S. Geological Survey Bulletin 1685.

Franks, P. C., 1975, The transgressive-regressive sequence of the Cretaceous Cheyenne, Kiowa, and Dakota formations of Kansas: in Caldwell, W. G. E., ed., The Cretaceous System in the Western Interior of North America: Geological Association of Canada Special Paper 13, p. 469-521.

Fryxell, J. C., and Smith, D. L., 1986; Paleotectonic implications of arkos beds in Park Shale (Middle Cambrian), Bridger Range, South-central Montana: in Peterson, J. A., ed., Paleotectonics and Sedimentation in the Rocky Mountain Region, United States: American Association of Petroleum Geologists Memoir 41, p. 159-171.

Gallagher, K., 1989, An examination of some uncertainties associated with estimates of sedimentation rates and tectonic subsidence: Basin Research, v. 2, p. 97-114.

Gill, J. R., and Cobban, W. A., 1961, Stratigraphy of lower and Middle parts of the Pierre Shale, northern Great Plains: U.S. Geological Survey Short Papers in the Geological and Hydrologic Sciences 293-435, p. D185-D191.

Gill, J. R., and Cobban, W. A., 1966a, Regional unconformity in late Cretaceous, Wyoming: U.S. Geological Survey Professional Paper 550-B, p. 20-27.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 184

Gill, J. R., and Cobban, W. A., 1966b, The Red Bird section of the Upper Cretaceous Pierre Shale in Wyoming, with a section on a new Echinoid from the Cretaceous Pierre Shale of eastern Wyoming by P. M. Kier,: U.S. Geological Survey Professional Paper 393-A, 73 p.

Gill, J. R., and Cobban, W. A., 1973, Stratigraphy and geologic history of the Montana Group and equivalent rocks, Montana, Wyoming, and North and south Dakota: U.S. Geological Survey Professional Paper 776,37 p.

Gill, J. R., and Hail, W. J., 1975, Stratigraphic sections across Upper Cretaceous Mancos Shale-Mesaverde Group boundary, eastern Utah and western Colorado: U.S. Geological Survey Oil and Gas Investigations Chart OC-68.

Gill, J. R., Cobban, W. A., and Schultz, L. C., 1972a, Correlation, ammonite zonation, and a reference section for the Montana Group, central Montana: Montana Geological Society 21st Annual Field Conference Guidebook, The Crazy Mountains Basin, p. 91-97.

Gill, J. R., Cobban, W. A., and Schultz, L. G., 1972b, Stratigraphy and composition of the Sharon Spring Member of the Pierre Shale in Western Kansas: U.S. Geological Survey Professional Paper 728.

Gill, J. R., Merewether, E. A., and Cobban, W. A., 1970, Stratigraphy and nomenclature of some Upper Cretaceous and Lower Tertiary rocks in south-central Wyoming: U.S. Geological Survey Professional Paper 667,50 p.

Glenister, L. M., and Kauffman, E. G., 1985, High resolution stratigraphy and depositional history of the Greenhorn regressive hemicyclothem, Rock Canyon anticline, Pueblo, Colorado, in: Pratt, L. M., Kauffman, E. G., and Zelt, F. B., eds., Fine-grained deposits and biofacies of the Cretaceous Western Interior Seaway: Evidence of cyclic sedimentary processes, Society of Economic Paleontologists and Mineralogists Guidebook No. 4, p. 170-183.

Goodell, H. G., 1962, The stratigraphy and petrology of the Frontier Formation of Wyoming: Symposium on Early Cretaceous rocks of Wyoming and adjacent areas, Wyoming Geologic Association 17th Annual Field Conference Guidebook, p. 173- 210.

Gregory, H. E., 1950, Geology and geography of the Zion Park region, Utah and Arizona: U.S. Geological Survey Professional Paper 220.

Gregory, H. E., 1951, The geology and geography of the Paunsaugunt region, Utah: U.S. Geological Survey Professional Paper 1-226, 16 p.

Gregory, H. E., and Moore, R. C., 1931, The Kaiparowits region, A geographic and geological reconnaissance of parts of Utah and Arizona: U.S. Geological Survey Professional Paper 164,161p.

Gries, R. R., 1983, North-south compression of Rocky Mountain foreland structures, in Lowell, J. D., and Gries, R. R., eds., Rocky Mountain foreland and uplifts, Rocky Mountain Association of Geologists, p. 9-32.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 185

Gries, R. R., Dyer, R. C., eds., 1985, Seismic exploration of the Rocky Mountain region: Denver, Colorado, Rocky Mountain Association of Geologists and the Denver Geophysical Society, 298 p.

Griffitts, M. O., 1949, Zones of Pierre Formation of Colorado: American Association of Petroleum Geologists Bulletin, v. 33, p. 2011-2028.

Gumis, M., 1988, Large-scale mantle convection and the aggregation and dispersal of supercontinents: Nature, v. 332, p. 695-699.

Gumis, M., 1990, Bounds on global dynamic topography from Phanerozoic flooding of continental platforms: Nature, v. 344, p. 754-756.

Gumis, M., 1993a, Phanerozoic marine inundation of continents driven by dynamic topography above subducting slabs: Nature, v. 364, p. 589-593.

Gumis, M., 1993b, Depressed continental hypsometiy behind oceanic trenches: A clue to subduction controls on sea level change: Geology, v. 21, p. 29-32.

Gustason, E. R., and Kauffman, E. G., 1985, The Dakota Group and the Kiowa-Skull Creek Cyclothem in the Canyon City- Pueblo Area, Colorado, in: Pratt, L. M., Kauffman, E. G., and Zelt, F. B., eds., Fine-grained deposits and biofacies of the Cretaceous Western Interior Seaway: Evidence of cyclic sedimentary processes, Society of Economic Paleontologists and Mineralogists Guidebook No. 4, p. 72-99.

Hail, W. J., Jr., 1965, Geology of northwestern North Park, Colorado: U.S. Geological Survey Bulletin 1188.

Hail, W. J., Jr., 1968, Geology of southwestern North Park and vicinity Colorado: U.S. Geological Survey Bulletin 1257.

Hail, W. J., Jr., 1974, Geologic map of the Rough Gulch Quadrangle, Rio Blanco and Moffat counties, Colorado: U.S. Geological Survey Map GQ-1195.

Hale, L. A., 1955, Stratigraphy and facies relationship of the Montana Group in south central Wyoming, northeastern Utah and northwestern Colorado: Wyoming Geological Association 10th Annual field Conference Guidebook, p. 89-94.

Hale, L. A., 1959, Intertonguing Upper Cretaceous sediments of northeastern Utah- northwestern Colorado: Symposium on Cretaceous rocks of Colorado and adjacent areas, Rocky Mountain Association of Geologists 11th Annual Field Conference Guidebook, p. 55-66.

Hale, L. A., 1964, Cretaceous stratigraphy and facies pattems-northeastem Utah and adjacent areas: Intermountain Association of Petroleum Geologists 13th Annual Field Conference Guidebook, p. 115-138.

Hale, L. A., 1972, Depositional history of the Ferron Formation, central Utah, in Baer, J. L., and Callaghan, eds., Plateau-Basin and Range transition zone, central Utah 1972: Utah Geological Association Publication 2, p. 29-40.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 186

Hale, L. A., and Van de Graaff, F. R., 1964, Cretaceous stratigraphy and facies patterns; northeast Utah and adjacent areas; Intermountain Association of Petroleum Geologists 13th Annual Field Conference Guidebook, p. 115-138.

Hallam, A.,1984, Pre-Quaternary sea-level changes. Annual Reviews Earth and Planetary Science v. 12, p. 205-243.

Hallam, A., 1992, Phanerozoic sea-level changes, Columbia University Press, New York, 266 p.

Hamilton, W. A., 1988, Laramide crustal shortening, in Schmidt, C. J., and Perry, W. J., eds., Interactions of the Rocky Mountain Foreland and the Cordilleran Thrust Belt: Geological Society of America Memoir 171, p. 27-39.

Hamilton, W. A., 1989, Crustal geologic processes of the United States, in Pakiser, L. C., and Mooney, W. D., eds., Geophysical framework of the continental United States: Geological Society of America Memoir 172, p. 743-781.

Hancock, J. M., and Kauffman, E.G., 1979, The great transgressions of the Late Cretaceous: Journal of the Geological Society of London, v. 136, p. 175-186.

Hancock, J. M.,1975, The sequence of facies in the Upper Cretaceous of northern Europe compared with that in the Western Interior, in Caldwell, W. G. E., ed., The Cretaceous system in the Western Interior of North America: Geological Association of Canada, Special Paper 13, p. 83-118.

Haq, B. U., Hardenbol, J., and Vail, P. R., 1988, Mesozoic and Cenozoic chronostratigraphy and cycles of sea-level changes, in Wilgus, C.K., and others, eds., Sea-level Palentologists and Mineralogists Special Publication 42, p. 71-108.

Harrison, C. G. A., 1988, Eustasy and epeirogeny of continents on time scales between about 1 and 100 m.y.: Paleoceanography, v. 3, p. 671-684.

Harrison, C. G. A., 1990, Long term eustasy and epeirogeny in continents: in Revelle, R., ed., Sea level change, National Research Council Study, Committee on Geophysics, National Academy Press, p. 141-157.

Harrison, J. E., Griggs, A.B., and Wells, J. D., 1974, Tectonic features of the Precambrian Belt basin and their influence on the post-Belt structures: U.S. Geological Survey Professional Paper 866,15 p.

Haskett, G. I., 1959, Niobrara Formation of Northwestern Colorado: Symposium on Cretaceous rocks of Colorado and adjacent areas, Rocky Mountain Association of Geologists 11th Annual Field Conference Guidebook, p. 46-49.

Hattin, D. E., 1962, Stratigraphy of the Carlile Shale (Upper Cretaceous) in Kansas: Kansas Geological Survey Bulletin 156, 155 p.

Hattin, D. E., 1965a, Stratigraphy of the Graneros Shale (Upper Cretaceous) in central Kansas: Kansas Geological Survey Bulletin 178,83 p.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 187

Hattin, D. E., 1965b, Upper Cretaceous stratigraphy, paleontology, and paleoecology of western Kansas: Geological Society of America Annual Meeting, Kansas City, Kansas, Field Conference Guidebook, p. 69.

Hattin, D. E., 1967, Stratigraphic and paleoecologic significance of macroinvertebrate fossils in the Dakota Formation (Upper Cretaceous) of Kansas, in Essays in Paleontology and Stratigraphy - R.C. Moore Commemorative Volume, University of Kansas Department of Geology Special Publication 2, p. 570-589.

Hattin, D. E„ 1969, Reference section for Lincoln Limestone Member, Greenhorn Limestone (Upper Cretaceous), Lincoln County, Kansas: Kansas Geological Survey Bulletin 194, p. 29-33.

Hattin, D. E., 1971, Widespread, synchronously deposited, burrow-mottled limestone beds in Greenhorn limestone(upper Cretaceous) of Kansas and southeastern Colorado: American Association of Petroleum Geologists Bulletin, v. 55, p. 412- 431.

Hattin, D. E., 1975a, Stratigraphic study of the Carlile-Niobrara (Upper Cretaceous) unconformity in Kansas and northeastern Nebraska, in Caldwell, W. G. E., ed., The Cretaceous System in the Western Interior of North America: Geological Association of Canada Special Paper 13, p. 195-210.

Hattin, D. E., 1975b, Stratigraphy and depositional environment of Greenhorn limestone (upper Cretaceous) of Kansas: Kansas Geological Survey Bulletin 209, p. 1-128.

Hattin, D. E., 1981, Petrology of the Smoky Hill Chalk Member, Niobrara Chalk (Upper Cretaceous) in the type area, western Kansas: American Association of Petroleum Geologists Bulletin, v. 65, p. 831-849.

Hattin, D. E., 1982, Stratigraphy and depositional environment of Smoky Hill Chalk Member, Niobrara Chalk (Upper Cretaceous) of the type area, western Kansas: Kansas Geological Survey Bulletin 225, p. 1-108.

Hattin, D. E., and Cobban, W. A., 1977, Upper Cretaceous stratigraphy, paleontology and paleoecology of western Kansas: Mountain Geologist, v. 14, p. 175-217.

Haun, J. D., 1958, Early Upper Cretaceous stratigraphy, Powder River Basin, Wyoming: Powder River Basin, Wyoming Geological Association 13th Annual Field Conference Guidebook, p. 84-89.

Haun, J. D., 1961, Stratigraphy of post-Mesaverde Cretaceous rocks, Sand Wash basin and vicinity, Colorado and Wyoming: Green River, Washakie, Wind River, and Powder River basins, Wyoming Geological Association 16th Annual Field Conference Guidebook, p. 116-124.

Haun, J. D., and Weimer, R. J., 1959, Cretaceous stratigraphy of Colorado: Symposium on Cretaceous rocks of Colorado and adjacent areas, Rocky Mountain Association of Geologists 11th Annual Field Conference, p. 58-65.

Hays, J. D., and Pitman, W. C., 1973, Lithospheric plate motions, sea level changes and climatic and ecological consequences: Nature, v. 246, p. 18-22.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 188

Hegarty, K. A., Weissel, J. K., and Mutter, J. C., 1987, Subsidence history of Australia’s southern margin: constraints on basin models: American Association of Petroleum Geologists Bulletin, v. 72, p. 615-633

Heller, P. L., and Angevine, C. L„ Winslow, N. S., and Paola, C., 1988, Two-phase model of foreland basin sequences: Geology, v. 16, p. 501-504.

Heller, P. L., and Paola, C., 1989, The paradox of Lower Cretaceous gravels and the initiation of thrusting in the Sevier orogenic belt, United States Western Interior: Geological Society of American Bulletin, v. 101, p. 864-875.

Heller, P. L„ Bowdler, S. S., Chambers, H. P., Coogan, J. C., Hagen, E. S., Shuster, M. W., Winslow, N. S., and Lawton, T. F., 1986, Time of initial thrusting in the Sevier orogenic belt, Idaho-Wyoming and Utah: Geology, v. 14, p. 388-391.

Heller, P. L., Wentworth, C. M., and Poag, C. W., 1982, Episodic post-rift subsidence of the United States Atlantic continental margin: Geological Society of America Bulletin, v. 93, p. 379-390

Henderson, L. J., and Gordon, R. G., 1984, Mesozoic aseismic ridges on the Farallon Plate and southward migration of shallow subduction during the Laramide orogeny: Tectonics, v. 3, p. 121-132.

Hoffman, P. E., 1989, Precambrian geology and tectonic history of North America, in Bally, A. W., Palmer, A. R., eds., The Geology of North America, An overview: Boulder, Colorado, Geological Society of America, v. A, p. 447-512.

Hook, S. C., 1983, Stratigraphy, paleontology, depositional framework, and nomenclature of marine Upper Cretaceous rocks, Socorro County, New Mexico: New Mexico Geological Society 34th Field Conference Guidebook, p. 165-172.

Hook, S. C., 1984, Evolution of stratigraphic nomenclature of the Upper Cretaceous of Socorro County, New Mexico: New Mexico Geology, p. 28-33.

Hook, S. C., and Cobban, W. A., 1980, Reinterpretation of type section of Juana Lopez Member of Mancos Shale: New Mexico Geology, v. 2, p. 17-22.

Hook, S. C., and Cobban, W. A., 1981, Late Greenhorn (mid-Cretaceous) discontinuity surfaces, southwest New Mexico, in Hook, S. C., compiler, Contributions to mid- Cretaceous paleontology and stratigraphy of New Mexico: New Mexico Bureau of Mines and Mineral Resources Circular 180, p. 5-21.

Hook, S. C., Cobban, W. A., and Landis, E. R., 1980, Extension of the intertongued Dakota Sandstone-Mancos Shale terminology into the southern Zuni Basin: New Mexico Geology, v. 2, p. 42-46.

Izett, G.A., 1968, Geology of the Kassler Quadrangle, Jefferson and Douglas counties, Colorado: U.S. Geological Survey Professional Paper XXX, p.71-122

Izett, C. A., Cobban, W. A., and Gill, J. R., 1971, The Pierre Shale near Kremmling, Colorado, and its correlation to the east and the west: U.S. Geological Survey Professional Paper 684-A, 19 p.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 189

Jacobson, S. R., and Nichols, D. J., 1982, Palynological dating of syntectonic units in the Utah-Wyoming thrust belt: The Evanston Muddy Creek Conglomerate: Geologic studies of the Cordilleran thrust belt, Rocky Mountain Association of Geologists Symposium, v. II, p. 735-750.

Jensen, F. S., and Vamea, H. D., 1964, Geology of the Fort Peck area, Garfield. McCone, and Valley counties, Montana: U.S. Geological Survey Professional Paper 414-F, 49 p.

Jervey, M. T., 1992, Siliciclastic sequence development in foreland basins, with examples from die Western Canada foreland basin, in Macqueen, R. W., and Leckie, D. A., eds., Foreland Basins and Fold Belts, American Association of Petroleum Geologists Memoir 55, p. 47-80.

Johnson, L. M., and Sears, J. W., 1988, Cordilleran thrust belt-Rocky Mountain foreland interaction near Bannack, Montana, in Schmidt, C. J., and Perry, W. J., eds., Interactions of the Rocky Mountain foreland and the Cordilleran thrust belt: Geological Society of America Memoir 171, p. 229-236.

Johnson, R. B., and Wood, G.H., Jr., 1956, Stratigraphy of upper Cretaceous and Tertiary rocks of Raton Basin, Colorado and New Mexico: American Association of Petroleum Geologists Bulletin, v. 40, p. 707-721.

Johnson, R. C., 1986a, Cretaceous through Holocene history of the Douglas Creek arch, Colorado and Utah, in Stone, D. S., ed., New interpretations of northwestern Colorado Geology: Rocky Mountain Association of Geologists, p.75-77.

Johnson, R. C., 1986b, Structure contour map of the top of the Castlegate Sandstone, eastern part of the Uinta Basin and the western part of the Piceance Creek Basin, Utah and Colorado: U.S. Geological Survey Map MF-1826.

Johnson, R. C., 1989a, Detailed cross sections correlating Upper Cretaceous and Lower Tertiary rocks between the Uinta Basin and the Piceance Basin of western Colorado: U.S. Geological Survey Miscellaneous Investigations Map 1-1974.

Johnson, R. C., 1989b, Geologic history and Hydrocarbon potential of Late Cretaceous- age, low permeability reservoirs, Piceance Basin, western Colorado: U.S. Geological Survey Bulletin 1787-E.

Johnson, R. C., and Finn, T. M., 1985, Age of the Douglas Creek arch, Colorado and Utah (abs.): American Association of Petroleum Geologists Bulletin, v. 69, p. 270.

Johnson, R. C., and Finn, T. M., 1986, Cretaceous through Holocene history of the Douglas Creek arch, Colorado and Utah, in Stone, D.S., ed., New interpretations of northwestern Colorado Geology: Rocky Mountain Association of Geologists Symposium, p. 77-95.

Johnson, R. C., and Johnson, S. Y., 1991, Stratigraphic and time-stratigraphic cross sections of Phanerozoic rocks along line B-B', Uinta and Piceance Basin, west- central Uinta Basin, Utah to eastern Piceance Basin, Colorado: U.S. Geological Survey Miscellaneous Investigations Map I-1284-B.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 190

Johnson, S. Y., 1992, Phanerozoic evolution of sedimentary basins in the Uinta- Piceance Basin region, northwestern Colorado and northeastern Utah: U.S. Geological Survey Bulletin 1787-FF.

Johnson, S. Y., and Johnson, R. C., 1991, Stratigraphic and time-stratigraphic cross sections of Phanerozoic rocks along line A-A', Uinta and Piceance Basin area-Eagle Basin, Colorado, to eastern Basin and Range area, Utah: U.S. Geological Survey Miscellaneous Investigations Map I-1284-A.

Jordan, T. E., 1981, Thrust loads and foreland basin evolution, Cretaceous, western United States: American Association of Petroleum Geologists Bulletin, v. 65, p. 2506-2520.

Jordan, T. E., 1988, Dating thrust -fault by use of foreland-basin strata, in Kleinspehn, K.L., and Paola, C., eds., New Perspective in Basin Analysis. New York, Springer- Verlag, p.307-330.

Jordan, T. E., and Flemings, P. B., 1991, Large-scale stratigraphic architecture, eustatic variation, and unsteady tectonism: a theoretical evaluation: Journal of Geophysical Research, v. 96, No. B4, p.6681-6699.

Kamer, G. D., and Watts, A. B., 1983, Gravity anomalies and flexure of the lithosphere at mountain ranges: Journal of Geophysical Research, v. 88, p. 10449-10477.

Kamer, G. D., Steckler, M. S., and Thome, J. A., 1983, Long-term thermal mechanical properties of the continental lithosphere: Nature, v. 316, p. 138-142.

Katich, P. J., 1956, Some notes on the Cretaceous faunas of eastern Utah and western Colorado, in Peterson, J. A., ed., Geology and economic deposits of east-central Utah: Intermountain Association of Petroleum Geologists 7th Annual Field Conference Guidebook, p. 11-19.

Katich, P. J., Jr., 1953, Source direction of Ferron Sandstone in Utah: American Association of Petroleum Geologists Bulletin, v. 37, p. 858-861.

Katich, P. J., Jr., 1954, Cretaceous and early Tertiary stratigraphy of central and south- central Utah with emphasis on the Wasatch Plateau area: Intermountain Association of Petroleum Geologists 5th Annual Field Conference Guidebook, p. 42-54.

Katich, P. J., Jr., 1959, Late Cretaceous faunal zones, western Colorado: Symposium on Cretaceous rocks of Colorado and adjacent areas, Rocky Mountain Association of Geologists 11th Annual Field Conference Guidebook, p. 26-29.

Kauffman, E. G., 1969, Cretaceous marine cycles of the Western Interior: Mountain Geologist, v. 4, p. 227-245.

Kauffman, E. G., 1977a, Geological and biological overview: Western Interior Cretaceous Basin: Mountain Geologists, v. 14, p. 75-99.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 191

Kauffman, E. G., 1977b, Upper Cretaceous cyclothems, hiatus and environments, Rock Canyon Anticline, Pueblo, Colorado, in Kauffman, E. G., ed., Cretaceous facies, faunas and paleoenvironments across the Western Interior Basin: Mountain Geologist, v. 14, p. 129-152.

Kauffman, E. G., 1985, Cretaceous evolution of the Western Interior basin of the United States, in: Pratt, L. M., Kauffman, E. G., and Zelt, F. B., eds., Finegrained deposits and biofacies of the Cretaceous Western Interior Seaway: Evidence of cyclic sedimentary processes, Society of Economic Paleontologists and Mineralogists Guidebook No. 4, p. iv-xiii.

Kauffman, E. G., and Caldwell, W. G. E., 1993, The Western Interior Basin in space and time, in Caldwell, W. G. E., and Kauffman, E. G., eds., Evolution of the Western Interior Basin, Geological Association of Canada Special Paper 39, p. 1-30.

Kauffman, E. G., Powell, J. D., and Hattin, D. E., 1969, Cenomanian-Turonian facies across the Raton Basin: Mountain Geologist, v. 6, p. 93-118.

Kauffman, E. G., Sageman, B. B., Kirkland, J. J., Elder, W. P., Harries, P. J., and Villamil, T., 1993, Molluscan biostratigraphy of the Cretaceous Western Interior Basin, North America, in Caldwell, W. G. E., and Kauffman, E. G., eds., Evolution of the Western Interior Basin, Geological Association of Canada Special Paper 39, p. 397-434.

Keefer, W. R., 1972, Frontier, Cody, and Mesaverde Formations in the Wind River and southern Big-hom Basins, Wyoming: U.S. Geological Survey Professional Paper 495-E, p E1-E23.

Keen, C. E., and Barrett, D. L., 1981, Thinned and subsided continental crust on the rifted margin of eastern Canada: crustal structure, thermal evolution and subsidence history: Geophysical Journal of Royal Astronomical Society, v. 65, p. 443-465.

Kellogg, H. E., 1977, Geology and petroleum of the Mancos B Formation, Douglas Creek arch area Colorado and Utah: Exploration Frontiers of the Central and Southern Rockies, Rocky Mountain Association of Geologists Symposium, p. 167- 179.

King, P. B., 1977, The Evolution of North America: revised edition, Princeton University Press, Princeton, New Jersey, 197 p.

King, N. R., 1974, The Carlile-Niobrara contact and lower Niobrara strata near El Vado, New Mexico: New Mexico Geological Society 25th Field Conference Guidebook, p. 259-266.

Kinney, D. M., and Hail, W. J., Jr., 1959, Upper Cretaceous rocks in North Park, Jackson County, Colorado: Rocky Mountain Association of Geologists 11th Annual Field Conference Guidebook, Symposium on Cretaceous rocks of Colorado and adjacent areas, p. 105-109.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 192

Kirkland, J. I., 1991, Lithostratigraphic and biostratigraphic framework for the Mancos Shale (Late Cenomanian to Middle Turonian) at Black Mesa, northeastern Arizona, in Nations J. D., and Eaton, J. G., eds., Stratigraphy, depositional environments, and sedimentary tectonics of the western margin, Cretaceous Western Interior seaway, Geological Society of America Special Paper 260, p. 85-112.

Kiteley, L. W., 1977, Shallow marine deposits in the Upper Cretaceous Pierre Shale of the northern Denver Basin and their relation to hydrocarbon accumulation: Rocky Mountain Association of Geologists Symposium, p. 197-222.

Kiteley, L. W., 1978, Stratigraphic sections of Cretaceous rocks of the northern Denver basin, northeastern Colorado and southeastern Wyoming: U.S. Geological Survey Oil and Gas Investigations Chart OC-78.

Kiteley, L. W., 1983, Paleography and eustatic-tectonic model of late Campanian Cretaceous sedimentation, southwestern Wyoming and northwestern Colorado, in Reynolds, M. W., and Dolly, E. D., eds., Mesozoic paleogeography of the west- central United States: Society of Economic Paleontologists and Mineralogist, Rocky Mountain Section, Rocky Mountain Paleogeography symposium 2, p. 273-303

Kluth, C. F., 1986, Plate tectonics of the ancestral Rocky Mountains: in Peterson, J. A., ed., Paleotectonics and Sedimentation in the Rocky Mountain Region, United States: American Association of Petroleum Geologists Memoir 41, p. 353-369.

Kluth, C. F., and Coney, P., 1981, Plate tectonics of the ancestral Rocky Mountains: Geology, v. 9, p. 10-15.

Kominz, M. A., 1984, Oceanic ridge volumes and sea level change-an error analysis, in Schlee, J. S., ed., Interregional unconformities and hydrocarbon accumulation: American Association of Petroleum Geologists Memoir 36, p. 109-127.

Kominz, M. A., and Bond G. C., 1986, Geophysical modelling of the thermal history of foreland basins: Nature, v. 320, p. 252-256.

Kominz, M. A., and Bond, G. C.,1991, Unusually large subsidence and sea-level events during middle Paleozoic time: new evidence supporting mantle convection models for supercontinent assembly: Geology, v. 19, p. 56-60

Konishi, K., 1959, Stratigraphy of Dakota Sandstone, northwestern Colorado: Symposium on Cretaceous rocks of Colorado and adjacent areas, Rocky Mountain Association of Geologists 11th Annual Field Conference Guidebook, p. 30-32.

Konishi, K., 1959, Upper Cretaceous surface stratigraphy, Axial Basin and Williams Fork area, Moffat and Routt counties, Colorado: Symposium on Cretaceous rocks of Colorado and adjacent areas, Rocky Mountain Association of Geologists 11th Annual Field Conference Guidebook, p. 67-73.

Kucera, R. E., 1959, Cretaceous stratigraphy of the Yampa district, northwest Colorado: Symposium on Cretaceous rocks of Colorado and adjacent areas, Rocky Mountain Association of Geologists 11th Annual Field Conference Guidebook, p. 37-45.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 193

Kulik, D. M., and Schmidt, C. J., 1988, Region of overlap and styles of interaction of Cordilleran thrust belt and Rocky Mountain foreland, in Schmidt, C. J., and Perry, W. J., eds., Interactions of the Rocky Mountain foreland and the Cordilleran thrust belt: Geological Society of America Memoir 171, p. 75-98.

Lamb, G. M., 1968, Stratigraphy of the lower Mancos Shale in the San Juan basin: American Association of Petroleum Geologists Bulletin, v. 79, p. 827-854.

Landis, E. R., Dane, C. H., and Cobban, W. A., 1973, Stratigraphic terminology of the Dakota Sandstone and Mancos shale, west-central New Mexico: U.S. Geological Survey Professional Paper 1372-J.

Lawrence, J. C., 1965, Stratigraphy of the Dakota and Tropic Formations of Cretaceous age in southern Utah: Utah Geological Society Guidebook to Geology of Utah, v. 19, p. 71-91.

Lawton, T. F., 1982, Lithofacies correlations within the Upper Cretaceous Indianola Group, central Utah, in Nielsen, D. L., ed., Overthrust Belt of Utah: Utah Geological Association Publication 10, p. 199-213.

Lawton, T. F., 1985, Style and timing of frontal structures, thrust belt, central Utah: American Association of Petroleum Geologists Bulletin, v. 69, p. 1145-1159.

Lawton, T. F., Boyer, S. E., and Schmidt, J. G., 1994, Influence of inherited taper on structural variability and conglomerate distribution, Cordilleran fold and thrust belt, western United States: Geology, v. 22, p. 339-342.

Leithold, E. L., 1994, Stratigraphical architecture at the muddy margin of the Cretaceous Western Interior Seaway, southern Utah: Sedimentology, v. 41, p. 521-542.

LeRoy, L. W., and Schultz, N. C., 1958, Niobrara-Pierre boundary along Front Range, Colorado: American Association of Petroleum Geologists Bulletin, v. 42, p. 2444- 2464.

Lessard, R. H., 1973, Micropaleontology and paleoecology of the Tununk Member of the Mancos Shale: Utah Geological and Mineralogical Survey Special Studies 45,28 P- Lessentine, R. H., 1965, Kaiparowits and Black Mesa basins-stratigraphic synthesis: American Association of Petroleum Geologist Bulletin, v. 49, p. 1997-2019.

Link, P. K„ Christie-Blick, N., Delvin, W. J., Elston, D. P., Horodyski, R. J., Levy, M., Miller, J. M. G., Pearson, R. C., Prave, A, Stewart, J. H., Winston, D., Wright, L. A., and Wrucke, C. T., 1993, Middle and Late Proterozoic stratified rocks of the western U.S. Cordillera, Colorado Plateau, and Basin and Range province: in Reed, J. C., Jr., Bickford, M. E., Houston, R. S., Link, P. K., Rankin, D. W., Sims, P. K., and Van Schmus, W. R., eds., Precambrian : Conterminous U.S.: Boulder, Colorado, Geological Society of America, The Geology of North America, v. C-2, p. 463-595.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 194

Lipman, P. W., 1980, Cenozoic volcanism in the western United States: implications for continental tectonics, in Continental Tectonics, National Research Council Geophysics Study Committee, Washington D. C., p. 161-174.

Livaccari, R. F., 1991, Role of crustal thickening and extensional collapse in the tectonic evolution of the Sevier-Laramide orogeny, western United States: Geology, v. 19, p. 1104-1107.

Livaccari, R. F., Burke, K., and Sengor, A. M. C., 1981, Was the Laramide orogeny related to subduction of an oceanic plateau?: Nature, v. 289, p. 276-278.

Love, J. D., 1956, Cretaceous and Tertiary stratigraphy of the, Jackson Hole area, northwestern Wyoming: Wyoming Geological Association 11th Annual Field Conference Guidebook, p. 76-94.

Lowry, A. R., and Smith, R. B., 1994, Flexural rigidity of the Basin and Range- Colorado Plateau-Rocky Mountain transition from coherence analysis of gravity and topography: Journal of Geophysical Research, v. 99, p. 20123-20140.

Lyon-Caen, H., and Molnar, P., 1983, Constraints on the structure of the Himalayas from an analysis of gravity anomalies and a flexural model of the lithosphere: Journal of Geophysical Research, v. 88, p. 8171-8191.

MacKenzie, D. B., 1971, Post Lytle Dakota Group on west flank of Denver Basin: Mountain Geologist, v. 8, p. 91-131.

MacKenzie, D. B., and Poole, D. M., 1962, Provenance of Dakota Group sandstones of the Western Interior: Symposium on Early Cretaceous rocks of Wyoming and adjacent areas, Wyoming Geological Association 17th Annual Field Conference Guidebook, p. 44-61.

Maione, S. J., 1971, Stratigraphy of the Frontier sandstone Member of the Mancos shale (Upper Cretaceous) on the south flank of the eastern Uinta Mountains, Utah and Colorado: Wyoming Geological Association Earth Science Bulletin, v. 4, p. 27-58

Margaret, S. E., and Kelso, B. S., 1987, Cross sections showing stratigraphic framework of Upper Cretaceous Dakota Sandstone, Mancos Shale, Mesaverde Group, and Mesaverde Formation, and Lower Tertiary Wasatch Formation, west- central Piceance Basin, Garfield County, Colorado: U.S. Geological Survey Miscellaneous Field Studies Map MF-2008-A.

Masters, C. D., 1959, Correlation of the Post-Mancos Upper Cretaceous sediments of the Sand Wash and Piceance basins: Rocky Mountain Association of Geologists 11th Annual Field Conference Guidebook, Symposium on Cretaceous rocks of Colorado and adjacent areas, p. 78-80.

Matheny, J. P., and Picard, M. D., 1985, Sedimentology and depositional environments of the Emery Sandstone Member of the Mancos Shade, Emery and Sevier Counties, Utah: Mountain Geologist, v. 22, p. 94-109.

Matsumoto, T., 1980, Inter-regional correlation of transgressions and regressions in the Cretaceous Period: Cretaceous Research, v. 1, p. 359-373.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 195

Maughan, E. K., and Perry, W. J, 1986, Lineaments and their tectonic implications in the Rocky Mountains and adjacent Plains Region, in Peterson, J. A., ed., Paleotectonics and sedimentation in the Rocky Mountain region, United States: American Association of Petroleum Geologists Memoir 41, p. 41-52.

Maxfield, E. B., 1976, Foraminifera from the Mancos Shale of east central Utah: Brigham Young University, Geology Studies, v. 23, p. 67-162.

McDonough, K. J., and Cross, T. A., 1991, Late Cretaceous sea level from a paleoshoreline: Journal of Geophysical Research, v. 96, p. 6591-6607.

McGookey, D. P., Haun, J. D., Hale, L. A., McCubbin, D. G., Weimer. R. J. and Wolf, G. R., 1972, Cretaceous System, in Mallory, W. W., ed., Geologic Atlas of the Rocky Mountain Region, U.S.A.: Rocky Mountain Association of Geologists, Denver, p. 190-228.

McLane, M., 1982, Upper Cretaceous coastal deposits in south-central Colorado-Codell and Juan Lopez Members of Carlile Shale: American Association of Petroleum Geologists Bulletin, v. 66, p. 71-90

McNutt, M. K., Diament, M., and Kogan, M. G., 1988, Variations of elastic plate thickness at continental thrust belts: Journal of Geophysical Research, v. 93, p. 8825-8838.

McPeek, L. A., 1965, Dakota-Niobrara (Cretaceous) stratigraphy and regional relationships, El Vado area, Rio Arriba County, New Mexico: Mountain Geologist, v. 2 ,, p. 23-34.

Menard, H. W., and Smith S. M., 1966, Hypsometry of ocean basin provinces: Journal of Geophysical Research, v. 71, p. 4305-4325.

Merewether, E. A., 1972, Geologic map of the Rawlins NW quadrangle, Carbon County, Wyoming: U.S. Geological Survey Geologic Quadrangle Map GQ-1010.

Merewether, E. A., 1980, Stratigraphy of Mid-Cretaceous Fomtier at drilling sites in Weston and Johnson Counties, northeastern Wyoming: United States Geological Survey Professional Paper 1186-A, p. 1-25.

Merewether, E. A., 1983a, Lower Upper Cretaceous strata in Minnesota and adjacent areas - Time-stratigraphic correlations and structural attitudes: U.S. Geological Survey Professional Paper 1253-B, p. 27-52.

Merewether, E. A., 1983b, The Frontier Formation and Mid-Cretaceous orogeny in the foreland of southwestern Wyoming: Mountain Geologist, v. 20, p. 121-138.

Merewether, E. A., and Cobban, W. A., 1972, Unconformities within the Frontier Formation, northwestern Carbon County, Wyoming: U.S. Geological Survey Professional Paper 800-D, p. 57-66.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 196

Merewether, E. A., and Cobban, W. A., 1985, Tectonism in the Mid-Cretaceous foreland, southeastern Wyoming and adjoining areas, in Nelson, G. E., ed., The Cretaceous geology of Wyoming: Wyoming Geological Association 36th Annual Field Conference Guidebook, p. 67-73.

Merewether, E. A., and Cobban, W. A., 1986, Biostratigraphic units and tectonism in the mid-Cretaceous foreland of Wyoming, Colorado, and adjoining areas, in Peterson, J. A., ed., Paleotectonics and sedimentation in the Rocky Mountain region, United States, American Association of Petroleum Geologists Memoir 41, p. 443- 468.

Merewether, E. A., and Cobban, W. A., and Ryder, R. T., 1975, Lower Upper Cretaceous strata, Bighorn Basin, Wyoming and Montana: Wyoming Geological Association 27th Annual Field Conference Guidebook, p. 73-84.

Merewether, E. A., and Cobban, W. A.. 1973, Stratigraphic sections of the Upper Cretaceous Frontier Formation near Casper and Douglas, Wyoming: Wyoming Geological Association Earth Science Bulletin, Guidebook Issue, v. 6, p. 38-39.

Merewether, E. A., Blackman, P. D., and Webb, J. C., 1984, The Mid-Cretaceous Frontier Formation near the Moxa arch, southwestern Wyoming: U.S. Geological Survey Professional Paper 1290.

Merewether, E. A., Cobban W. A., and Spencer. C. W., 1976, The Upper Cretaceous Frontier Formation in the Kaycee Tisdale Mountain area, Johnson County, Wyoming: Geology and energy resources of the Powder River Basin, Wyoming Geological Association 28th Annual Field Conference Guidebook, p. 33-44.

Merewether, E. A., Cobban, W. A., and Cavanaugh, E. T., 1979, Frontier Formation and equivalent rocks in eastern Wyoming: Mountain Geologist, v. 6, p. 67-102.

Merewether, E. A., Cobban, W. A., Mataon. R. M., and Magatha, W. J., 1977, Stratigraphic diagrams with electric logs of Upper Cretaceous rocks, Powder River Basin, Johnson, Campbell and Crook Counties, Wyoming, section A-A's: U.S. Geological Survey Oil and Gas Investigations Map OC-73.

Miall, A. D., 1986, Eustatic sea level changes interpreted from Seismic stratigraphy: A critique of the methodology with particular reference to the North Sea Jurassic Record: American Association of Petroleum Geologists Bulletin, v. 70, p. 131-137.

Miall, A. D., 1992, Exxon global cycle chart: An event for every occasion ?: Geology, v. 20, p. 787-790.

Miller, D. N., Jr., Barlow, J. A., and Haun, J. D., 1965, Stratigraphy and petroleum potential of latest Cretaceous rocks, Bighorn Basin, Wyoming: American Association of Petroleum Geologists Bulletin, v. 49, p. 277-285.

Miller, H. W., 1968, Invertebrate fauna and environment of deposition of the Niobrara Formation (Cretaceous) of Kansas: Fort Hays Studies, New series, No. 8,90 p.

Miller, H. W., 1970, Additions to the fauna of the Niobrara Formation of Kansas: Transactions of the Kansas Academy of Science, v. 72, p. 533-546.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 197

Mitrovica, J. X., Beaumont, C. and Jarvis, J. T., 1989, Tilting of continental interiors by the dynamic effects of subduction, Tectonics, v. 8, p. 1079-1094.

Moir, G. J., 1974, Depositional environments and stratigraphy of the Cretaceous rocks, southwestern Utah: Los Angeles, University of California Ph.D. dissertation, 427 p.

Molenaar, C. M., 1973, Sedimentary facies and correlation of the Gallup Sandstone and associated formations, northwestern New Mexico, in Fassett, J.E., ed., Cretaceous and Tertiary rocks of the Colorado Plateau: Four Comers Geological Society Memoir, p. 85-110.

Molenaar, C. M., 1974, Correlation of the Gallup Sandstone and associated formations, upper Cretaceous, eastern San Juan and Acoma Basins New Mexico: New Mexico Geological Society 25th Field Conference Guidebook, p. 251-258.

Molenaar, C. M., 1977, Stratigraphy and depositional history of Upper Cretaceous rocks of the San Juan basin area, New Mexico and Colorado, with a note on economic resources: San Juan Basin HI, New Mexico Geological Society 28th Field Conference Guidebook, p.

Molenaar, C. M., 1983, Major depositional cycles and regional correlations of upper Cretaceous rocks southern Colorado Plateau and adjacent areas, in Reynolds, M. W., and Dolly, E. D., eds., Mesozoic paleogeography of the west-central United States: Society of Economic Paleontologists and Mineralogist, Rocky Mountain Section, Rocky Mountain Paleogeography symposium 2, p. 201-224.

Molenaar, C. M., and Baird, J. K., 1989, North-south stratigraphic cross sections of Upper Cretaceous rocks, northwestern New Mexico and southwestern Colorado: U.S. Geological Survey Miscellaneous Field Studies Map MF-2068.

Molenaar, C. M., and Baird, J. K., 1991, Stratigraphic cross sections of Upper Cretaceous rocks in the northern San Juan Basin, Southern Utah Indian Reservation, southwestern Colorado, in Zech, R.S., ed., Geologic framework and stratigraphy of Cretaceous and Tertiary rocks of the Southern Ute Indian Reservation, southwestern Colorado: U.S. Geological Survey Professional Paper 1505-C, p. C1-C12 and 3 plates.

Molenaar, C. M., and Baird, J. K., 1992, Regional stratigraphic cross sections of Upper Cretaceous Rocks across the San Juan basin, northwestern New Mexico and southwestern Colorado: U.S. Geological Survey Open File Report 92-257, 3 sheets.

Molenaar, C. M., and Cobban, 1991, Middle Cretaceous stratigraphy on the south and east sides of the Uinta Basin, northeastern Utah and northwestern Colorado: U.S. Geological Survey Bulletin 1787-P.

Molenaar, C. M., and Wilson, B. W., 1990, The Frontier Formation and associated rocks of northeastern Utah and northwestern Colorado: U.S. Geological Survey Bulletin 1787-M,21 p.

Molenaar, C. M, Cobban, W. A., Phillmore, C. L., Wolfe, D. G., and Holbrook, Regional stratigraphic section of Cretaceous rocks from east-central Arizona to the OOOklahoma Panhandle (in press).

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 198

Mudge, M. R., 1970, Origin of the disturbed belt in northwestern Montana: Geological Society of America Bulletin, v. 81, p. 377-392.

Mudge, M. R., and Earhart, R. L., 1980, The Lewis thrust fault and related structures in the disturbed belt, northwestern Montana: U.S. Geological Survey Professional Paper 1174,18 p.

Munger, M. R., 1965, Subsurface exploration mapping, southern Uinta basin, CasUegate and Dakota-Cedar Mountain Formations: Mountain Geologist, v. 2, p. 141-166.

Myers, R. C., 1977, Stratigraphy of the Frontier Formation (Upper Cretaceous), Kemmerer area, Lincoln County, Wyoming: Wyoming Geological Association 29th Annual Field Conference Guidebook, p. 271-311.

Nadai, A., 1963, Theory of flow and fracture of solids, v. 2, McGraw-Hill, New York, 705 p.

Nichols, D. J., Perry, W. J., Haley, J. C., 1985, Reinterpretation of the palynology and age of Laramide syntectonic deposits, southwestern Montana, and revision of the Beaverhead Group: Geology, v. 13, p. 149-153.

Nilsen, T. H., and Stewart, J. H., 1980, The Antler orogeny-Mid-Paleozoic tectonism in western North America: Geology, v. 8, p. 298-302.

North, B. R., and Caldwell, W. G. E.,1975, Foraminiferal faunas in the Cretaceous System of Saskatchewan, in Caldwell, W. G. E., ed., The Cretaceous System in the Western Interior of North America: Geological Association of Canada Special Paper 13, p. 303.331.

Nummedal, D., 1990, Sequence stratigraphic analysis of upper Turanian and Coniacian strata in the San Juan basin, New Mexico, U.S.A., in Ginsburg, R. N., and Beaudoin, B., eds., Cretaceous resources, events and rhythms: Kluwer Publishing, p. 33-46.

Nummedal, D., and Remy, R. R., eds., 1989, Cretaceous shelf sandstones and shelf depositional sequences, Western Interior basin, Utah, Colorado and New Mexico: Field Trip Guidebook T119,28th International Geological Congress; American Geophysical Union, 87 p.

Nummedal, D., and Riley, G.W., 1991, Origin of late Turanian and Coniacian unconformities in the San Juan basin, in, Van Wagoner, J.C., Jones, C .R., Taylor, D.R., Jennette, D.C., Nummedal, D., and Riley, G.W., eds., Sequence stratigraphy applications to shelf sandstone reservoirs - outcrop to subsurface examples: American Association of Petroleum Geologists Field Conference Guidebook.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 199

O'Sullivan, R. B., Repenning, C. A., Beaumont, E. C., and Page, H. G., 1972, Stratigraphy of the Cretaceous Rocks and the Tertiary Ojo Alamo Sandstone, Navajo and Hopi Indian Reservations, Arizona, New Mexico and Utah: U.S. Geological Survey Professional Paper 521-E, 65 p.

Obradovich, J. D., and Cobban, W. A., 1975, A time scale for the Late Cretaceous of Western interior of North America, in Caldwell, W. G. E., ed., The Cretaceous System in the Western Interior of North America: Geological Association of Canada Special Paper 13, p. 31-54.

Obradovich, J., 1993, A Cretaceous Time Scale, in Caldwell, W. G. E., and Kauffman, E. G., eds., Evolution of the Western Interior Basin, Geological Association of Canada Special Paper 39, p. 379-396.

Oldow, J. S., Bally, A. W., Lallemant, H. G. A., and Leeman, W. P., 1989, Phanerozoic evolution of the North American Cordillera; United States and Canada, in Bally, A.W., and Palmer, A.R., eds., The Geology of North America, An overview: Boulder, Colorado, Geological Society of America, v. A, p. 139-232.

Oriel, S. S., and Armstrong, F. C., Tectonic development of the Idaho-Wyoming thrust belt: author's commentary, in Peterson, J. A., ed., Paleotectonics and sedimentation in the Rocky Mountain region, United States, American Association of Petroleum Geologists Memoir 41, p. 267-279.

Penttila, W. C., 1964, Evidence for the Pre-Niobrara unconformity in the northwestern part of the San Juan Basin: Mountain Geologist, v. 1, p. 3-14.

Peper, T., 1994, Tectonic and eustatic control on Albian shallowing (Viking and Paddy Formations) in the western Canada foreland basin: Geological Society of America Bulletin, v. 106, p. 253-264.

Peterson, F., 1969, Four new members of the Upper Cretaceous Straight Cliffs Formation in the southeastern Kaiparowits region, Kane County, Utah: U.S. Geological Survey Professional Paper 1274-J.

Peterson, F., and Kirk. A.R., 1977, Correlation of the Cretaceous rocks in the San Juan. Black Mesa. Kaiparowits and Henry Basins, southern Colorado Plateau, in Fasset. J. E., ed., San Juan Basin, northwestern New Mexico: New Mexico Geological Society 28th Field Conference Guidebook, p. 167-178.

Peterson, F., and Ryder, R. T., 1975, Cretaceous rocks in the Henry Mountains region, Utah and their relation to neighboring regions, in Fassett, J. E., ed., Canyonlands country: Four Comers Geological Society 8th Field Conference Guidebook, p. 167- 189.

Peterson, F., Ryder, R. T., and Law, B., 1980, Stratigraphy sedimentology and regional relationships of the Cretaceous System in the Henry Mountains region: Henry Mountains Symposium, Utah Geological Society Guidebook, p. 151-170.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 0 0

Peterson, J. A., and Smith, D. L., 1986, Rocky Mountain paleogeography through geologic time, in Peterson, J. A., ed., Paleotectonics and sedimentation in the Rocky Mountain region, United States: American Association of Petroleum Geologists Memoir 41, p. 3-19.

Picha, F., 1986, The influence of preexisting tectonic trends on geometries of the Sevier orogenic belt and its foreland in Utah, in Peterson, J. A., ed., Paleotectonics and sedimentation in the Rocky Mountain region, United States: American Association of Petroleum Geologists Memoir 41, p. 309-320.

Picha, F., and Gibson, R. I., 1985, Cordilleran hingeline: Late Precambrian rifted margin of the North American craton and its impact on depositional and structural history, Utah and Nevada: Geology, v. 13, p. 465-468.

Poole, F. G., 1974, Flysch deposits of Antler foreland basin, western United States, in Dickinson, W. R., ed., Tectonics and Sedimentation, Society of Economic Paleontologists and Mineralogist Special publication 22, p. 58-82.

Price, R. A., 1973, Large scale gravitational flow of the supra-crustal rocks, southern Canadian Rockies, in De Jong, K. A., and Scholten, R., eds., Gravity and Tectonics: New York, John Wiley & Sons, p. 491-502.

Quinlan, G. and Beaumont, C., 1984, Appalachian thrusting, lithospheric flexure and the Paleozoic stratigraphy of the eastern interior of North America: Canadian Journal of Earth Sciences, v. 21, p. 973-996.

Rankin, G. H., 1944, Stratigraphy of the Colorado group, Upper Cretaceous, in northern New Mexico: New Mexico School of Mines Bulletin, v. 20,27 p.

Reed, J. C., Jr., Ball, T. T., Farmer, G. L., and Hamilton, W. B., 1993, A Broad View: in Reed, J. C., Jr., Bickford, M. E., Houston, R.S., Link, P. K., Rankin, D. W., Sims, P. K., and Van Schmus, W. R., eds., Precambrian : Conterminous U.S.: Boulder, Colorado, Geological Society of America, The Geology of North America, v. C-2, p. 597-636.

Reeside, J. B., Jr., 1923a, A new fauna from the Colorado Group of southern Montana: U.S. Geological Survey Professional Paper 132-B, p. 25-33.

Reeside, J. B., Jr., 1923b, The fauna of the so-called Dakota formation of northern central Colorado and its equivalent in southeastern Wyoming: U.S. Geological Survey Professional Paper 131-H, p. 199-205.

Reeside, J. B., Jr., 1924, Upper Cretaceous and Tertiary formations of the western part of the San Juan Basin, Colorado and New Mexico: U.S. Geological Survey Professional Paper 134.

Reeside, J. B., Jr., 1927a, Cephalopods from the lower part of the Cody shale of Oregon Basin, Wyoming: U.S. Geological Survey Professional Paper 105-A, 19 p.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 0 1

Reeside, J. B., Jr., 1927b, The cephalopods of the Eagle Sandstone and related formations in the Western Interior of the United States: U.S. Geological Survey Professional Paper 151, 87 p.

Reeside, J. B., Jr., 1944, Map showing thickness and general character of the Cretaceous deposits in the Western Interior of the United States: U.S. Geological Survey Oil and Gas Investigations Map OM-10.

Reeside, J. B., Jr., 1955, Revised interpretation of the Cretaceous section on Vermilion Creek, Moffat County, Colorado: Green River Basin: Wyoming geological Association 10th Annual Field Conference Guidebook, p. 85-88.

Reeside, J. B., Jr., 1957, Paleoecology of the Cretaceous seas of the Western Interior of the United States, in Ladd, H. S., ed., Paleoecology: Geological Society of America Memoir 67, v. 2, p. 505-541.

Reeside, J. B., Jr., and Baker, A. A., 1929, The Cretaceous section in Black Mesa, northeastern Arizona: Journal of the Washington Academy of Sciences, v. 19, p. 30- 37

Reeside, J. B., Jr., and Cobban, W. A., 1960, Studies of the Mowry Shale (Cretaceous) and contemporary formations in the United States and Canada: U.S. Geological Survey Professional Paper 355,126 p.

Repenning, C. A., and Page, H. G., 1956, Late Cretaceous stratigraphy of Black Mesa, Navajo and Hopi Indian Reservations, Arizona: American Association of Petroleum Geologists Bulletin, v. 40, p. 255-294.

Reynolds, M. W., 1966, Stratigraphic relations of Upper Cretaceous rocks, Lamont- Bairoil area, south-central Wyoming: U.S. Geological Survey Professional Paper 550-B, p. B69-B76.

Rice, D. D., 1976, Stratigraphic sections from well logs and outcrops of Cretaceous and Paleocene rocks, northern Great Plains, Montana: U.S. Geological Survey Oil and Gas Investigations Chart OC-71.

Rice, D. D., 1977, Stratigraphic sections from well logs and outcrops of Cretaceous and Paleocene rocks, northern Great Plains, North Dakota and South Dakota: U.S. Geological Survey Oil and Gas Investigations Chart OC-72.

Rice, D. D., and Cobban, W. A., 1977, Cretaceous stratigraphy of the Glacier National Park area, northwestern Montana: Canadian Petroleum Geology Bulletin, v. 25, p. 828-841.

Rice, D. D., and Shurr, G. W., 1983, Patterns of sedimentation and paleogeography across the Western Interior Seaway during time of deposition of Upper Cretaceous Eagle Sandstone and equivalent rocks Northern Great Plains, in Reynolds, M. W., and Dolly, E. D., eds., Mesozoic paleogeography of the west-central United States: Rocky Mountain Section Society of Economic Paleontologists and Mineralogists, Rocky Mountain Paleogeography Symposium 2, p. 337-358.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 0 2

Rich, E. I., 1958, Stratigraphic relation of Latest Cretaceous rocks in parts of Powder River, Winder, and Bighorn basins, Wyoming: American Association of Petroleum Geologists Bulletin, v. 42, p. 2424-2443.

Ritzma, H. R., 1959, The Morapos Sandstone member of the Mancos Shale, Axial Basin vicinity, northwest Colorado: Rocky Mountain Association of Geologists 11th Annual Field Conference Guidebook, Symposium on Cretaceous rocks of Colorado and adjacent areas, p. 50-54.

Roberts, A. E., 1972, Cretaceous and early Tertiary depositional and tectonic history of the Livingston area, southwestern Montana: U.S. Geological Survey Professional Paper 526-C.

Robinson, C. S., Mapel, W. J. and Bergendahl, M. H., 1964, Stratigraphy and structure of the northern and western flanks of the Black Hills uplift, Wyoming, Montana and South Dakota: U.S. Geological Survey Professional Paper 404,134 p.

Roehler, H. W., 1990, Stratigraphy of the Mesaverde Group in the central and eastern Greater Green River Basin, Wyoming, Colorado, and Utah: U.S. Geological Survey Professional Paper 1508.

Ross, P. R., 1976, Mississippian carbonate shelf margins, western United States, in Hill, J. G., Symposium on Geology of the Cordilleran Hingeline: Rocky Mountain Association of Geologists, p. 135-152.

Royden, L., 1988, Flexural behavior of the continental lithosphere in Italy: constraints imposed by gravity and deflection data: Journal of Geophysical Research, v. 93, p. 6419-6431.

Royden, L., and Kamer, G. D., 1984, Flexure of lithosphere beneath Apennine and Carpathian foredeep basins: evidence for an insufficient topographic load: American Association of Petroleum Geologists Bulletin, v. 68, p. 704-712.

Royse, F., Jr., 1993, Case of the Phantom foredeep: early Cretaceous in west-central Utah: Geology, v.21, p. 133-136.

Royse, F., Jr., Warner, M. A., and Reese, D. L., 1975, Thrust structural geometry and related stratigraphic problems, in Bolyard, D. W., ed., Deep drilling frontiers in the central Rocky Mountains, Denver, Colorado, Rocky Mountain Association of Geologists, p. 41-54.

Rubey, W. W., 1930, Lithologic studies of the fine grained Upper Cretaceous rocks of the Black Hills region: U.S. Geological Survey Professional Paper 165-A, p. 1-54.

Rubey, W. W., Oriel, S. S., and Tracey, J. I., Jr., 1975, Geology of the Sage and Kemmerer 15-Minute Quadrangles, Lincoln County, Wyoming: U.S. Geological Survey Professional Paper 855.

Ruppel, E. T., 1978, The Medicine Lodge thrust system, east-central Idaho and southwestern Montana: U.S. Geological Survey Professional Paper 1031.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 203

Ruppel, E. T., 1986, The Lemhi arch; A Late Proterozoic and early Paleozoic landmass in central Idaho, in Peterson, J. A., ed., Paleotectonics and Sedimentation in the Rocky Mountain Region, United States: American Association of Petroleum Geologists Memoir 41, p. 119-130.

Ruppel, E. T., and Lopez, D. A., 1984, The thrust belt in southwestern Montana and east-central Idaho: U.S. Geological Survey Professional Paper 1287.

Ruppel, E. T., Wallace, C. A., Schmidt, R. G., and Lopez, D. A., 1981, Preliminary interpretation of the thrust belt in southwestern and west-central Montana and east- central Idaho: Southwest Montana Field Conference and Symposium Guidebook, Montana Geological Society, p. 139-159.

Ryder, R. T., and Scholten, R., 1973, Syntectonic conglomerates in southwestern Montana: Their nature, origin, and tectonic significance (with an Update), in Peterson, J. A., ed., Paleotectonics and sedimentation in the Rocky Mountain region, United States, American Association of Petroleum Geologists Memoir 41, p. 131- 157.

Ryer, T. A., 1976, Cretaceous stratigraphy of the Coalville and Rockport areas, Utah: Utah Geology, v. 3, p. 71-83.

Ryer, T. A., 1977a, Age of Frontier Formation in north-central Utah: American Association of Petroleum Geologists Bulletin, v. 61, p. 112-116.

Ryer, T. A., 1977b, Coalville and Rockport areas, Utah, in Kauffman, E. G., ed., Cretaceous facies, faunas and paleoenvironments across the Western Interior Basin: Mountain Geologist, v. 14, p. 105-128.

Ryer, T. A., 1977c, Patterns of Cretaceous shallow marine sedimentation, Coalville and Rockport areas, Utah: Geological Society of America Bulletin, v. 88, p. 177-188.

Ryer, T. A., 1981, Deltaic coals of Ferron Sandstone Member of Mancos Shale- Predictive model for Cretaceous coal bearing strata of Western Interior: American Association of Petroleum Geologists Bulletin, v. 65, p. 2323-2340.

Ryer, T. A., 1993, Speculations on the origin of Mid-Cretaceous clastic wedges, central Rocky Mountain region, United States, in Caldwell, W. G. E., and Kauffman, E. G., eds., Evolution of the Western Interior Basin, Geological Association of Canada Special Paper 39, p. 189-198.

Ryer, T. A., and Lovekin, J. R., 1986, The Upper Cretaceous Vernal delta of Utah; depositional or paleotectonic featured, in Peterson, J. A., ed., Paleotectonics and sedimentation in the Rocky Mountain region, United States, American Association of Petroleum Geologists Memoir 41, p. 497-510.

Ryer, T. A., and McPhillips, M., 1983, Early Late Cretaceous paleogeography of east- central Utah, in Reynolds, M. W., and Dolly, E. D., eds., Mesozoic paleogeography of the west-central United States: Rocky Mountain Section, Society of Economic Paleontologists and Mineralogists, Rocky Mountain Paleogeography Symposium 2, p. 253-272.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 204

Ryer, T. A., McClurg, J. J., and Muller, M. M., 1987, Dakota, Bear River paleoenvironments, depositional history, and shoreline trends - Implications for foreland basin paleotectonics, southwestern Green River Basin and southern Wyoming Overthrust Belt: Wyoming Geological Association 38th Annual Field Conference Guidebook, p. 179-206.

Sageman, B. B., 1985, High resolution stratigraphy and paleobiology of the Hartland Shale Member; Analysis of an oxygen-deficient epicontinental sea, in: Pratt, L. M., Kauffman, E. G., and Zelt, F. B., eds., Finegrained deposits and biofacies of the Cretaceous Western Interior Seaway: Evidence of cyclic sedimentary processes, Society of Economic Paleontologists and Mineralogists Guidebook No. 4, p. 110- 121.

Sageman, B. B., and Johnson, C. C., 1985, Stratigraphy and paleobiology of the Lincoln Limestone Member, Greenhorn Limestone, Rock Canyon anticline, Colorado, in: Pratt, L. M., Kauffman, E. G., and Zelt, F. B., eds., Finegrained deposits and biofacies of the Cretaceous Western Interior Seaway: Evidence of cyclic sedimentary processes, Society of Economic Paleontologists and Mineralogists Guidebook No. 4, p. 100-109.

Sahagian, D., 1987, Epeirogeny and eustatic sea level changes as inferred from Cretaceous shoreline deposits: Applications to the central and western United States: Journal of Geophysical Research, v. 92, p. 4895-4904.

Sahagian, D., and Jones, M., 1993, Quantified Middle Jurassic to Paleocene eustatic variations based on Russian platform stratigraphy: state level resolution: Geological Society of America Bulletin, v. 105, p. 1109-1118.

Sawyer, D. S., 1985, Total tectonic subsidence: a parameter for distinguishing crust type at the U.S. Atlantic continental margin: Journal of Geophysical Research, v. 90, p. 7751-7769.

Sawyer, D. S., Swift, B. A., Sclater, J. G., and Toksoz, M. N., 1982, Extensional model for the subsidence of the northern United States Atlantic continental margin: Geology, v.10, p. 134-140.

Schedl, A., and Wiltschko, D. V., 1984, Sedimentological effects of a moving terrain: Journal of Geology, v. 92, p. 273-287.

Schlanger, S. O., 1986, High frequency sea-level fluctuations in Cretaceous time: an emerging geophysical problem: Geodynamics Series 15, Mesozoic and Cenozoic oceans, p. 61-74.

Schmidt, C. J., O'Neill, J. M., and Brandon, W. C., 1988, Influence of Rocky Mountain foreland uplifts on the development of the frontal fold and thrust belt, southwestern Montana, in Schmidt, C. J., and Perry, W. J., eds., Interactions of the Rocky Mountain foreland and the Cordilleran thrust belt: Geological Society of America Memoir 171, p. 171-201.

Schmidt, C. J., and Perry, W. J., eds., 1988, Interaction of the Rocky Mountain Foreland and the Cordilleran Thrust Belt: Geological Society of America Memoir 171, 582 p.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 205

Schoff, S. L., 1951, Geology of the Cedar Hills, Utah: Geological Society of America Bulletin, v. 62, p. 619-646.

Schwartz, R. K., and DeCelles, P. G, 1988, Cordilleran Foreland Basin evolution in response to interactive Cretaceous thrusting and foreland partitioning, southwestern Montana, in Schmidt, C. J., and Perry, W. J., eds., Interaction of the Rocky Mountain Foreland and the Cordilleran Thrust Belt, Geological Society of America, Inc., p. 489-514.

Sclater, J. G., and Christie, P. A. F., 1980, Continental stretching: An explanation of the post-mid-Cretaceous subsidence of the central North Sea basin: Journal of Geophysical Research, v. 85, p. 3711-3739.

Scott, G. R., 1961, Preliminary geologic map of the Indian Hills quadrangle, Jefferson County, Colorado: U.S. Geological Survey Miscellaneous Geologic Investigations Map 1-333.

Scott, G. R., 1962, Geology of the Littleton Quadrangle, Jefferson, Douglas, and Arapahoe, counties, Colorado: U.S. Geological Survey Bulletin 1121-L, p. 1-53.

Scott, G. R., 1963, Bed rock geology of the Kassler Quadrangle, Colorado: U.S. Geological Survey Professional Paper 421-B, p. 71-125.

Scott, G. R., 1964, Geology of the Northwest and Northeast Pueblo quadrangles, Colorado: U.S. Geological Survey Miscellaneous Investigations Series Map 1-408, scale 1:24,000.

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., and Cobban, W. A., 1959, So-called hygiene group of northeastern Colorado and Wyoming: Washakie, Sand Wash, and Piceance Basins: Rocky Mountain Association of Geologists 11th Annual Field Conference Guidebook, p. 124-131.

Scott, G. R., and Cobban, W. A., 1964, Stratigraphy of the Niobrara Formation at Pueblo, Colorado: U.S. Geological Survey Professional Paper 454-L, 30 p.

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 Geological Investigations Map 1-439.

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 Geological Investigations Map 1-1700.

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.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 206

Scott, R. W., 1970, Paleoecology and paleontology of the Lower Cretaceous Kiowa Formation, Kansas: University of Kansas Paleontological Contributions Article 52 (Cretaceous 1), 94 p.

Shanely, K. W., and McCabe, P. J., 1991, Predicting facies architecture through sequence stratigraphy-An example from the Kaiparowits Plateau, Utah: Geology, v. 19, p. 742-745.

Shurr, G. W., and Rice, D. D., 1986, Paleotectonic control on deposition of the Niobrara Formation, Eagle Sandstone, and equivalent rocks(upper Cretaceous), Montana and South Dakota, in Peterson, J. A., ed., Paleotectonics and sedimentation in the Rocky Mountain region, United States: American Association of Petroleum Geologists Memoir 41, p. 193-212.

Siemers, C. T., and King, N. R., 1974, Macroinvertebrate paleoecology of a transgressive marine sandstone, Cliff House sandstone ( Upper Cretaceous), Chaco Canyon, northwestern New Mexico: New Mexico Geological Society 25th Field Conference Guidebook, p. 267-277.

Sinclair, H. D., Coakley, B. J., Allen, P. A., and Watts, A. B., 1991, Simulation of foreland basin stratigraphy using a diffusion model of mountain belt and erosion: an example from the Central Alps, Switzerland: Tectonics, v.10, p.599-620.

Skipp, B., 1988, Cordilleran thrust belt and faulted foreland in the Beaverhead Mountains, Idaho and Montana, in Schmidt, C. J., and Perry, W. J., eds., Interactions of the Rocky Mountain foreland and the Cordilleran thrust belt: Geological Society of America Memoir 171, p. 237-266.

Slack, P. B., 1981, Paleotectonics and hydrocarbon accumulation, Powder River Basin, Wyoming: American Association of Petroleum Geologists Bulletin, v. 65, p. 7 30- 743.

Sleep, N. H„ 1971, Thermal effects of the formation of Atlantic continental margins by continental break up: Geophysical Journal of Royal Astronomical Society, v. 24, p. 325-350

Sleep, N. H., 1976, Platform subsidence mechanisms and "eustatic" sea level changes: Tectonophysics, v. 36, p. 45-56.

Sleep, N. H., Nunn, J, A., and Chou, L., 1980, Platform basins: Annual Reviews Earth and Planetary Science, v. 8, p. 17-34.

Sloss, L. L., 1988, Tectonic evolution of the craton in Phanerozoic time, in Sloss, L.L., ed., Sedimentary cover-North American Craton: U.S.: Geological Society of America, The Geology of North America, v. D-2, p. 25-51.

Sloss, L. L., 1991, The tectonic factor in sea level change: a countervailing view: Journal of Geophysical Research, v. 96, p. 46609-6617.

Sloss, L. L., and Speed, R. C., 1974, Relationships of cratonic and continental-margin tectonic episodes, in Dickinson, W. R., ed., Tectonics and Sedimentation, Society of Economic Paleontologists and Mineralogist Special publication 22, p.98-119.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 207

Smith, J. H., 1961, A summary of stratigraphy and paleontology, upper Colorado and Montana Groups, south-central Wyoming, northeastern Utah, and northwestern Colorado: Symposium on Late Cretaceous rocks, Wyoming and adjacent areas: Wyoming Geological Association 16th Annual Conference Guidebook, p. 101-112.

Smith, J. H., 1964, Geology of the sedimentary rocks of the Morrison Quadrangle, Colorado: U.S. Geological Survey Map 1-428.

Smith, J. H., 1965, A summary of stratigraphy and paleontology, upper Colorado and Montana Groups, south-central Wyoming, northeastern Utah, and northwestern Colorado: Sedimentation of Late Cretaceous and Tertiary outcrops, Rock Springs uplift: Wyoming Geological Association 19th Annual Conference Guidebook, p. 13- 26.

Sonnenberg, S. A., and Weimer, R. J., 1981, Tectonics, sedimentation and petroleum potential, northern Denver basin, Colorado, Wyoming, and Nebraska: Colorado School of Mines Quarterly, v. 76,45 p.

Spearing, D. R., 1976, Upper Cretaceous Shannon Sandstone: an offshore shallow- marine sand body: Wyoming Geological Association 28th Annual Field Conference Guidebook, p. 65-72.

Speed, R. C., and Sleep, N. H., 1982, Antler orogeny and foreland basin: A model: Geological Society of America Bulletin, v. 93, p. 815-828.

Speed, R. C., Elison, M. W., and Heck, F. R., 1988, Phanerozoic tectonic evolution of the Great Basin: in Ernst, W. G., ed., Metamorphism and crustal evolution of the western United States, Ruby Volume 7: Englewood Cliffs, New Jersey, Prentice Hall, p. 573-605.

Spieker, E. M., 1926, Upper Cretaceous shoreline in Utah: Geological Society of America Bulletin, v. 37. p. 429-438.

Spieker, E. M., 1946, Late Mesozoic and early Cenozoic history of central Utah: U.S. Geological Survey Professional Paper 205-D.

Spieker, E. M., 1949, Sedimentary facies and associated diastrophism in the Upper Cretaceous of central and eastern Utah: Geological Society of America Memoir 39, p. 15-81.

Spieker, E. M., and Reeside, J. B., Jr., 1925, Cretaceous and Tertiary formations of the Wasatch Plateau Utah: Geological Society of America Bulletin, v. 36. p. 435-454.

Spieker, E. M., and Reeside, J.B., Jr., 1926, Upper Cretaceous shoreline in Utah: Geological Society of America Bulletin, v. 37, p. 429-438.

Standlee, L. A., 1982, Structure and stratigraphy of Jurassic rocks in central Utah; Their Influence on tectonic development of the Cordilleran foreland thrust belt: in Power, R. B., ed., Geologic studies of the Cordilleran thrust belt, Denver, Colorado, Rocky Mountain Association of Geologists, p. 357-382.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 208

Steckler, M. S., and Watts, A. B., 1978, Subsidence of the Atlantic-type continental margin off New York: Earth and Planetary Science Letters, v. 41, p.1-13.

Steckler, M. S., Watts, A. B., and Thome, J. A., 1988, Subsidence and basin modeling at the U.S. Atlantic passive margin, in Sheridan, R. E., and Grow, J. A., eds., The Geology of North America; The Atlantic Continental Margin: Boulder, Colorado, Geological Society of American, v. 1-2, p. 399-416.

Steidtmann, J. R., and Middleton, L. T., 1991, Fault chronology and uplift history of the southern Wind River Range, Wyoming: Implications for Laramide and post- Laramide deformation in the Rocky Mountain foreland: Geological Society of America Bulletin, v. 103, p. 472-485.

Stem, T. A., Quinlan, G. M., and Holt, W. E., 1992, Basin formation behind an active subduction zone: three-dimensional flexural modelling of Wanganui Basin, New Zealand: Basin Research, v. 4, p. 197-214.

Stevenson, G. M., and Baars, D. L., 1986, The Paradox: A pull-apart basin of Pennsylvanian age, in Peterson, J. A., ed., Paleotectonics and sedimentation in the Rocky Mountain region, United States: American Association of Petroleum Geologists Memoir 41, p. 513-539.

Stewart, J. H., 1972, Initial deposits in the Cordilleran geosyncline; Evidence of a Late Precambrian (<850 m.y.) continental separation: Geological Society of America Bulletin, v. 83, p. 1345-1360.

Stewart, J. H., and Poole, F. G., 1974, Lower Paleozoic and uppermost Precambrian Cordilleran miogeocline, Great Basin, western United States, in Dickinson, W. R., ed., Tectonics and Sedimentation, Society of Economic Paleontologists and Mineralogist Special publication 22, p. 28-57.

Stockmal, G. S. and Beaumont, C., 1987, Geodynamic models of convergent margin tectonics: The southern Canadian Cordillera and the Swiss Alps, in Beaumont, C., and Tankard, A. J., eds., Sedimentary Basins and Basin-forming Mechanisms: Canadian Society of Petroleum Geologists Memoir 12, p. 393-411.

Stockmal, G. S., Beaumont, C., and Boutilier, R., 1986, Geodynamic models of convergent margin tectonics: Transition from rifted margin to overthrust belt and consequences for foreland-basin development: American Association of Petroleum Geologists Bulletin, v. 70, p. 181-190.

Sweeney, J. F., 1977, Subsidence of the Sverdrup Basin, Canadian Arctic Islands: Geological Society of America Bulletin, v. 88, p. 41-48.

Swift, D. J. P., Thome, J. A., and Nummedal, D., 1985, Sequence stratigraphy in foreland basin: inference from the Cretaceous Western Interior, 17Th Annual OTC, p. 47-54.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 209

Tankard, A. J., 1986, On the depositional response to thrusting and lithospheric flexure: examples from the Appalachian and Rocky Mountain basins, in Allen, P.A., and Homewood, P. eds., Foreland Basins, Special Publication Number 8 of the International Association of Sedimentologists, p. 369-392.

Thomas, G. E., 1974, Lineament block tectonics: Williston -Blood Creek Basin: American Association of Petroleum Geologists Bulletin, v. 58, p. 1305-1320.

Thomas, H. D., 1936, Frontier-Niobrara contact in the Laramie Basin, Wyoming: American Association of Petroleum Geologists Bulletin, v. 20, p. 1189-1197.

Thome, J. A., and Watts, A. B., 1989, Quantitative analysis of North Sea subsidence: American Association of Petroleum Geologists Bulletin, v. 73, p. 88-116.

Tonnsen, J. J., 1986, Influence of tectonic terranes adjacent to the Precambrian Wyoming Province on Phanerozoic stratigraphy in the Rocky Mountain region, in Peterson, J. A., ed., Paleotectonics and sedimentation in the Rocky Mountain region, United States: American Association of Petroleum Geologists Memoir 41, p. 21-39.

Tourtelot, H. A., 1962, Preliminary investigation of the geologic setting and chemical composition of the Pierre Shale, Great Plains region: U.S. Geological Survey Professional Paper 390.

Towse, D., 1952, Frontier Formation, southwest Powder River Basin, Wyoming: American Association of Petroleum Geologists Bulletin, v. 36, p. 1982-2010.

Turcotte, D. L., 1979, Flexure: Advances in Geophysics, v. 21, Academic Press, Inc.

Tweto, O., and Sims, P. K., 1963, Precambrian ancestry of the Colorado mineral belt: Geological Society of American Bulletin, v. 74, p. 991-1014.

Vail, P. R., Audemard, F., Bowman, S. A., Eisner, P. N., and Perez-Cruz, C., 1991, The stratigraphic signatures of tectonics, eustasy and sedimentology-an overview, in Einsele, G., Ricken, W., and Seilacher, A., eds., Cycles and events in stratigraphy, Springer-Verlag.

Van De Graaff, F. R., 1963, Upper Cretaceous stratigraphy of southwestern Utah: Intermountain Association of Petroleum Geologists 12th Annual Field Conference Guidebook, Geology of Southwestern Utah, p. 65-70.

Van Hinte, J. E., 1878, Geohistory analysis—application of micropaleontology in exploration geology: American Association of Petroleum Geologists Bulletin, v. 62, p. 1-14.

Van Horn, R., 1972, Surficial and bedrock geologic map of the Golden Quadrangle, Jefferson County, Colorado: U.S. Geological Survey Map I-761-A.

Van Houten, F. B., 1962, Frontier Formation, Bighorn Basin: Wyoming Geological Association 17th Annual Field Conference Guidebook, p. 221-231.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 1 0

Vames, D. J., and Scott, G. R., 1967, General and engineering geology of the United States Air Force Academy Site, Colorado: U.S. Geological Survey Professional Paper 551.

Villien, A., and Kligfield, R. M., 1986; Thrusting and synorogenic sedimentation in central Utah, in Peterson, J. A., ed., Paleotectonics and Sedimentation in the Rocky Mountain Region, United States: American Association of Petroleum Geologists Memoir 41, p. 119-130.

Vuke, S. M., 1984, Depositional environments of the Early Cretaceous Western Interior seaway in southwestern Montana and northern United States, in Stott, D. F., and Glass, D. J., eds., The Mesozoic of middle North America, Canadian Society of Petroleum Geologists Memoir 9, p. 127-144.

Waage, K. M., 1955, Dakota Group in northern Front Range foothills, Colorado: U.S. Geological Survey Professional Paper 274-B, p. 15-51.

Waage, K. M., 1959, Stratigraphy of the Inyan Kara Group in the Black Hills: U.S. Geological Survey Bulletin 1081-B, p. 11-90.

Walcott, R. I., 1970, Flexural rigidity, thickness and viscosity of the lithosphere: Journal of Geophysical Research, v. 75, p. 3941-3954.

Wallace, C. A., Lidke, D. J., and Schmidt, R. G., 1990, Faults of the central part of the Lewis and Clark line and fragmentation of the Late Cretaceous foreland basin in west- central Montana: Geological Society of America Bulletin, v. 102, p. 1021-1037.

Warner, D. L., 1964, Mancos-Mesaverde (Upper Cretaceous) intertonguing relations, southeast Piceance Basin, Colorado: American Association of Petroleum Geologists Bulletin, v. 48, p. 1091-1107.

Warner, L. A., 1978, The Colorado Lineament: a Middle Precambrian wench fault system: Geological Society of America Bulletin, v. 89, p. 161-171.

Waschbusch, P. J., and Royden, L. H., 1992, Spatial and temporal evolution of foredeep basins: lateral strength variations and inelastic yielding in continental lithosphere: Basin Research, v. 4, p. 179-196.

Watts, A. B., 1982, Tectonic subsidence, flexure and global changes of sea level: Nature, v. 297, p. 469-474.

Watts, A. B., 1988, Gravity anomalies, crustal structure and flexure of the lithosphere at the Baltimore Canyon Trough: Earth and Planetary Science Letters, v. 89, p. 221- 238.

Watts, A. B., 1992, The effective elastic thickness of the lithosphere and evolution of foreland basins: Basin Research, v. 4, p. 169-178.

Watts, A. B., and Ryan, W. B. F., 1976, Flexure of the lithosphere and continental margin basins: Tectonophysics, v. 36, p. 25-44.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 1 1

Watts, A. B., and Tomd, M., 1992, Crustal structure and the mechanical properties of extended continental lithosphere in the Valencia trough (western Mediterranean): Journal of Geological Society London, v. 149, p. 813-827.

Watts, A. B., Kamer, G. D., and Steckler, M. S., 1982, Lithospheric flexure and the evolution of sedimentary basins: Philosophical Transactions of the Royal Society of London, A: 305, p. 249-281.

Weimer, R. J., 1960, Upper Cretaceous stratigraphy, Rock Mountain area: American Association of Petroleum Geologists Bulletin, v. 44, p. 1-20.

Weimer, R. J., 1966, Time-stratigraphic analysis and petroleum accumulations, Patric Draw field, Sweetward County, Wyoming: American Association of Petroleum Geologists Bulletin, v. 50, p. 2150-2175.

Weimer, R. J., 1970, Rates of deltaic sedimentation and intrabasin deformation, Upper Cretaceous of Rocky Mountain region, in Morgan, J. P., ed., Deltaic sedimentation, modem and ancient: Society of Economic Paleontology and Mineralogy Special Publication 15, p. 211-222.

Weimer, R. J., 1980, Recurrent movement on basement faults, a tectonic style for Colorado and adjacent areas, in Kent, H. C., and Porter, K., eds., Colorado Geology: Rocky Mountain Association Geological Guidebook, p. 23-35.

Weimer, R. J., 1983, Relations of unconformities, tectonics and sea level changes, Cretaceous of the Denver Basin and adjacent areas, in Reynolds, M. W., and Dolly, E. D., eds., Mesozoic paleogeography of the west-central United States: Rocky Mountain Section, Society of Economic Paleontologists and Mineralogists, Special Paper, p. 359-376.

Weimer, R. J., 1984, Relation of unconformities, tectonics and sea level changes, Cretaceous of Western Interior, U.S.A., in Schlee, J. S., ed., Interregional Unconformities and Hydrocarbon Accumulation: American Association of Petroleum Geologists Memoir 38, p. 7-35.

Weimer, R. J., 1986, Relation of unconformities, tectonics and sea level changes in the Cretaceous of the Western Interior, United States, in Peterson, J. A., ed., Paleotectonics and sedimentation in the Rocky Mountain region, United States, American Association of Petroleum Geologists Memoir 41, p. 397-422.

Weimer, R. J., and Flarer, A., 1985, Deposition patterns and unconformities, Upper Cretaceous, eastern Powder River Basin, Wyoming: Wyoming Geological Association 38th Annual Field Conference Guidebook, p. 131-148.

Williams, G. D., and Stelck, C. R., 1975, Speculations on the Cretaceous paleogeography of North America, in Caldwell, W. G. E., ed., The Cretaceous System in the Western Interior of North America: Geological Association of Canada Special Paper 13, p. 1-20.

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 1 2

Williams. P. L., and Hackman, R. J., 1971, Geology, structure and uranium deposit of the Salina quadrangle, Utah: U.S. Geological Survey Miscellaneous Geologic Investigations Map 1591.

Wiltschko, D. V., and Dorr, J. A., Jr., 1983, Timing of deformation in overthrust belt and foreland of Idaho, Wyoming, and Utah: American Association of Petroleum Geologists Bulletin, v. 67, p. 1304-1322.

Winston, D., 1986, Sedimentation and tectonics of the Middle Proterozoic Belt basin and their influence on Phanerozoic compression and extension in western Montana and northern Idaho, in Peterson, J. A., ed., Paleotectonics and sedimentation in the Rocky Mountain region: American Association of Petroleum Geologists Memoir 41, p. 87-118.

Witze, B. J., Ludvigson, G. A., Poppe, J. R., Ravn, R. L., 1983, Cretaceous paleogeography along the eastern margin of the western interior seaway, Iowa, southern Minnesota, and eastern Nebraska and south Dakota, in Reynolds, M. W., and Dolly, E. D., eds., Mesozoic paleogeography of the west-central United States: Society of Economic Paleontologists and Mineralogist, Rocky Mountain Section, Rocky Mountain Paleogeography symposium 2, p. 225-252.

Wright, R.,1986, Cycle stratigraphy as a paleogeographic tool: Point Lookout Sandstone, southeastern San Juan basin, New Mexico: Geological Society of America Bulletin, v. 96, p. 661-673.

Yenne, K. A., and Piringos, G. N., 1954, Stratigraphic sections of Cody Shale and younp°r Cretaceous and Paleocene rocks in the Wind River Basin, Fremont County, Wyoming: U.S. Geological Survey Oil and Gas Investigations Chart OC-49.

Yingling, V. L., and Heller, P. L., 1992, Timing and record of foreland sedimentation during the initiation of the Sevier orogenic belt in central Utah: Basin Research, v. 4, p. 279-290.

Young, R. G., 1955, Sedimentary facies and intertonguing in the Upper Cretaceous of the Book Cliffs, Utah-Colorado: Geological Society of American Bulletin, v. 66, p. 177-202.

Young, R. G., 1960, Dakota Group of Colorado Plateau: American Association of Petroleum Geologists Bulletin, v. 44, p. 156-194.

Young, R. G., 1970, Lower Cretaceous of Wyoming and the southern Rockies: Mountain Geologist, v. 7, p. 105-121.

Zapp, A. D., and Cobban, W. A., 1960, Some Late Cretaceous strand lines in Northwestern Colorado and northeastern Utah: U.S. Geological Survey Professional Paper 400-B, p. 246-249.

Zapp, A. D., and Cobban, W. A., 1962, Some Late Cretaceous strand lines in southern Wyoming: U.S. Geological Survey Professional Paper 450-D, p. 52-55.

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Zelt, F. B., 1985, Natural gamma-ray spectrometry, lithofacies, and depositional environments of selected Upper Cretaceous marine mudrocks, western United States, including Tropic Shale and Tununk Member of Mancos Shale (unpublished Ph.D. dissertation): Princeton, N. J., Princeton University, 340 p.

Zhou, Shaohua, 1993, A 3-D backstripping method and its application to the Eromanga Basin in central and eastern Australia: Geophysical Journal International, v. 112, p. 225-243.

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Wireline logs used in the stratigraphic cross-sections 1 to 6.

Operator Well Name Location State

Cross-section #1 (based on USGS Chart OC-71 and 72 by R ice): 1. Montalban 1 Don Wilson 27-36N-9W Montana 2. Johnston Petroleum Co. 1 Humes 21-36N-6W do 3. Grannell Sands 1 Fey 23-37N-2E do 4. Buttes Petroleum Co. Van Dessel 1 17-36N-7E do 5. Webb Resources Inc. 18-16-Lipp 18-32N-11E do 6. Gordon Hurd 1 James W.Davey 23-32N-17E do 7. Honolulu Oil 29-3 Thieltges 29-33N-23E do 8. Champlin Oil 1 Fed.-Kaufman 20-33N-27E do 9. W.A. Moncrief 1 Federal 22-33N-31E do 10. Seaboard & Honolulu Oil 1 Loberg 26-30N-36E do 11. Phillips Petrol. Co. 1-AUnruh 23-31N-45E do 12. J. P. Johnson 1 Blair 6-30N-50E do 13. Maxwell Oil Ostby 1 1-30N-58E N. Dakota 14. H.L. Hunt Marvin Nylander 1 15-156N-95W do 15. Pel-Tex and Conoco Haaland 26-159N-86W do 16. Midwest Gunning 22-159N-82W do 17. Pubco Petrol. Anklam 7-159-72W do 18. Mclaughlin Wolfe Fed. Land Bank 1 33-158-62W do

Cross-section #2 (based on USGS Chart OC-71 and 72 by Rice): 1. Composite outcrop section by Roberts (1972). Livingston area Montana 2. Naftzer-Barker 1 Glennie 20-6N-14E do 3. Occidental I Gov't -Hall 2-8N-24E do 4. Sumatra 1 Hougan-Whelan 7-9N-32E do 5. Champlin Oil 1 Treasure County 12-7N-35E do 6. Texaco Texaco 1 State-’F 32-7N-39E do 7. George J. Greer 1 N. P. 15-3N-44E do 8. Gulf Oil Co. 1 State 16-1S-48E do

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9. Davis Oil Co. 1 Federal 35-7S-50E do 10. Sinclair Oil and Gas 6-1 Espy 6-8S-55E do 11. Superior Oil Campbell Gov't 14-9 9-8S-60E S. Dakota 12. Mobil Mickelson 1 7-9N-9E do 13. Amerada Meade-Corwin 1 18-6N-13E do 14. F.E. Pohle May 1 21-4N-18E do 15. Gulf Oil C. E. Harry 1 4-3N-23E do 16. Tenneco Herman Estate 1 10-1N-29E do 17. Gulf Oil Hutchinson 1 4-103N-77W do

Cross-section #3: 1. Texaco Spread Creek Unit 1 31-44N-112W Wyoming 2. Kingwood Oil Dicke 3 22-45N-101W do 3. R.L. Manning Cottonwood Land company 1 15-45N-97W do 4. Continental Oil Boulder Gulch 27-1 27-45N-95W do 5. The California Company Neiber Unit 3 14-45N-93W do 6. Amoco USA-Dale D Ozman 1 10-45N-91W do 7. Mapco 1-8 Gov't 8-45N-89W do 8. Mapco 1-30 Fed. 30-50N-82W do 9. Davis Oil Co. Healy-Fed. 1 8-51N-80W do 10. Webb Resources Inc. Fed. 12-13 12-51N-78W do 11. R.L. Manning Gov't Hawks 1 22-52N-76W do 12. Davis Oil Co. Smith-Fed. 2 12-53N-74W do 13. Stuarco Oil Co. Herrington Fed. 19-11 19-54N-72W do 14. Jerry Enkich and Ass. Co. Enkich Gov't Norfolk 1 19-54N-71W do 15. C.E Brehm Co. Gov’t 13-2 2-54N-70W do 16. William Ham, Jr., Co. Heald Gov't 1 27-55N-69W do 17. Gulf Oil C. E. Harry 1 4-3N-23E do

Cross-section #4: 1. Amoco Dry Muddy Creek unit 1 16-20N-114W Wyoming 2. Carter Oil Co. Opal 1 34-22N-112W do 3. Davis Oil Co. East Storm Shelter 1 6-23N-110W do 4. Wolf Energy Sandy Bend 1 14-23N-108W do 5. Davis Oil Co. Dines Unit 1 7-20N-105W do

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6. Texaco Delaney Rim Unit 1 30-18N-97W do 7. U.S. Natural Gas Co. Cow Creek unit 22-13 13-16N-92W do 8. Tenneco Sugar Creek Unit 3 11-18N-90W do 9. Tesoro Tesoro-Skyline Fed. 1 28-19N-88W do 10. Sinclair Oil and Gas Fed. 12-22-87 1 12-22N-87W do 11. Composite log: upper part: Union 1 Gov't 22-20N-84W do lower part: (Skelly Oil) U.P.R.R-Maden 1 29-21-N-85W do 12. The Texas Company Hill Creek Unit 1 14-20N-81W do 13. R.G. Berry Fed. 1-24 24-21N-78W do 14. True Oil Company Schmale 11-1 1-19N-75W do 15. Phillips Petrol. Co. U. P. A. 6-23 23-16N-73W do 16. Apache Coip. 1 Polo Ranch 14-14N-68W do 17. M.L. Goodston Hutchinson 1 18-17N-62W do 18. Superior Oil Emers 33-5 5-5N-20W Nebraska

Cross-section #5: 1. Phillips Petrol. Co. Wasatch Plateau 1 24-2 IS-IE Utah 2. Tennessee Gas Transmission Irons 1 16-15S-3E do 3. Three States Natural Gas Joe's Valley Unit 2 23-16S-5E do 4. Composite log: upper: Pacific Western Oil Gordan Creek Unit 1 24-14S-7E do lower: Three States-Morgan-Walton Mary D Kearns 1 27-16S-6E do 5. Occidental Gordan Creek 1 19-14S-8E do 6. Amerada USA Abbott 1 29-14S-9E do 7. Forest Oil Co. Gov't Arnold 25-1 25-16S-14E do 8. Gulf Oil Co. US Norris Fed. 1 8-18S-16E do 9. Tenneco Butter Canyon USA 33-12 33-19S-17E do 10. Tenneco Rattle Snake Canyon 16-4 16-19S-19E do 11. Pacific Natural Gas Segundo Canyon 23-4 4-17S-21E do 12. Mountain Fuel & Supply Main Canyon 1 28-15S-23E do 13. Raymond Oil Company Government 1 17-13S-25E do 14. Coseka Resources USA Arco Fed. 11-4-5-103 4-5S-103W Colorado 15. Nucorp Energy Inc. Turner 1-27 27-6S-99W do 16. Phillips Petrol. Co. Mannel 1 27-1N-95W do

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17. Seaboard Oil Co. Kritsas 2 32-2N-93W do 18. California Oil Co. California Gov't 1 7-2N-92W do 19. The Texas Company Knolton 14 6-4N-91W do 20. Miami Oil Producers O'brien 1 14-4N-90W do 21. McCulIoch Oil Corp Skeeter 1 8-5N-89W do 22. Havenstrite Oil Company Pretiss 3 2-3N-86W do 23. Aztec Oil & Gas Company Carter Creek 1 7-3N-80W do 24. Great Lakes Natural Gas Underwood 54-B-’B' 31-2N-76W do 25. National Assoc. Petrol. Martin 1-33 33-2N-69W do 26. Equitable Petroleum Co. Hawkins 1 22-5N-67W do 27. The Ohio Oil Co. Eva S. Nordloh 1 20-5N-63W do 28. GEM Oil Company Redman 1 25-6-61W do 29. National Assoc. Petrol. Bomhart 1 14-4N-58W do 30. M.P. Gilbert Ebsack-State 16-33 16-1N-51W do 31. R.E. Hibbert Vorce 1 28-1S-49W do 32. LION Oil Company Earl 1 1-4N-41W Nebraska 33. Superior Oil Emers 33-5 5-5N-20W do

Cross-section #6 1. Phillips Petrol. Co. Hatch 16-37S-6W Utah 2. Tenneco Griffin Point USA 1 22-33S-1W do 3. Sam Gary & West Henry Mt. Co. Fed. Apple 22-7 22-31S-9E do 4. British Petrol. Fed. Cronigan 1 23-30N-16W New Mexico 5. Southland Royalty Comp. Locke 1 3-29N-14W do 6. Union Texas Petrol. Helh's Fed. 1-E 22-30N-10W do 7. Northwest Pipeline Co. San Juan 29-6-62-A 4-29N-6W do 8. Phillips Petrol. Co. Jicarilla 28-3 #1 6-28N-3W do 9, Texota Fed. 1-A 17-26N-1E do 10. Continental Oil Colorado Fuel & Iron 1 13-34S-66W Colorado 11. Coronado Co. Bohart 1 19-15S-62W do

12. Sinclair-Prairie Robbins 1 32-4S-35W Kansas

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. VITA

Ming Pang was bom and grew up in Hami, Xinjiang, a province in the northwestern

part of the People's Republic of China. In 1978, he was enrolled into the Chengdu

College of Geology to study petroleum geology. In 1982, he graduated with a Bachelor’s

degree in geology. After graduation from college, he attended graduate school at the

China University of Geosciences at Beijing, where he studied sedimentary geology and

its applications to petroleum explorations. He graduated in 1985 with a thesis on the

diagenesis of the coal-bearing Permian and Carboniferous rocks in north-central China.

After the graduate study, he joined the faculty of the Department of Petroleum Geology at

the China University of Geosciences at Beijing. In 1988, he came to the Department of

Geology and Geophysics of the Louisiana State University to pursue a Ph.D. degree.

While at the Louisiana State University, he directed his interest to stratigraphy and

geophysics. His Ph.D. dissertation is a regional stratigraphic and tectonic analysis of the

U.S. Cretaceous Western Interior basin.

218

Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. DOCTORAL EXAMINATION AND DISSERTATION REPORT

Candidate: Ming Pang

Major Pield: Geology

Title of Dissertation: Tectonic Subsidence of the Cretaceous Western Interior Basin, United States

EXAMINING COMMITTEE:

MM- ■J M

Date of Examination:

November 30. 1994

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