Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1993 Stratigraphy, paleotectonics and paleoenvironments of the Morrison Formation in the Bighorn Basin of Wyoming and Montana Dibakar Goswami Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Geology Commons Recommended Citation Goswami, Dibakar, "Stratigraphy, paleotectonics and paleoenvironments of the Morrison Formation in the Bighorn Basin of Wyoming and Montana " (1993). Retrospective Theses and Dissertations. 10434. https://lib.dr.iastate.edu/rtd/10434 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. 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ZeebRA Ann Aibor, MI 48106 stratigraphy, paleotectonics and paleoenvironments of the Morrison Formation in the Bighorn Basin of Wyoming and Montana by Dibakar Goswami A dissertation Submitted to the Graduate Faculty in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY Department: Geological and Atmospheric Sciences Major: Geology ipprovi Signature was redacted for privacy. Charg^^f Major Work Signature was redacted for privacy. Signature was redacted for privacy. For the Graduate College Iowa State University Ames, Iowa 1993 ii TABLE OF CONTENTS Page GENERAL INTRODUCTION 1 Statement of the Problem 1 Research Objectives 6 Explanation of Format 7 Methods of Study 7 PAPER I. REGIONAL STRATIGRAPHY AND PALEOTECTONICS OF THE MORRISON FORMATION IN THE BIGHORN BASIN OF WYOMING AND MONTANA 10 ABSTRACT 11 INTRODUCTION 13 GEOLOGIC SETTING 15 REGIONAL STRATIGRAPHY OF THE MORRISON FORMATION 20 Upper Contact 2 0 Lower Contact 27 Subsurface Contact 28 Interpretation of Subsurface Geophysical Data 30 Stratigraphy 37 PALEOTECTONICS 61 CONCLUSIONS 69 REFERENCES 71 APPENDIX A. LOCATION OF STRATIGRAPHIC SECTIONS 83 APPENDIX B. GRAPHIC STRATIGRAPHIC SECTION 86 APPENDIX C. SUBSURFACE WELL LOG DATA OF THE MORRISON FORMATION IN THE BIGHORN BASIN OF WYOMING AND MONTANA 102 iii PAPER II. FACIES AND DEPOSITIONAL ENVIRONMENTS OF THE MORRISON FORMATION IN THE BIGHORN BASIN OF WYOMING AND MONTANA 107 ABSTRACT 108 INTRODUCTION 110 LOWER MORRISON 112 Quartzarenite Lithofacies Association 112 Interbedded Silty Claystone and Sandstone Lithofacies Association 126 UPPER MORRISON 136 REGIONAL SYNTHESIS OF THE PALEOGEOGRAPHY AND DEPOSITIONAL ENVIRONMENTS 150 CONCLUSIONS 154 REFERENCES 156 GENERAL CONCLUSIONS 166 ACKNOWLEDGEMENTS 169 iv LIST OF FIGURES Page GENERAL INTRODUCTION Figure 1. Location map of the study area 2 Figure 2. Geological map of north-central Wyoming 3 PAPER I Figure 1. Map showing generalized paleotectonic framework of the western United States during the Late Jurassic 16 Figure 2. East-west 1ithostratigraphic correlation of the Morrison, Cloverly, Ephraim Conglomerate of the Gannet Group, and the overlying formations across the state of Wyoming 18 Figure 3. Pre 1973 correlations and age inter­ pretations 21 Figure 4. Identification of the Morrison-Cloverly contact from electrical logs 29 Figure 5. Quantitative log analysis showing the use of both porosity and V-clay in the interpretation of thin sandstone beds 33 Figure 6. Quantitative log analysis of thin sandstone beds 35 Figure 7. Idealized section of the Morrison Formation showing the vertical distribution of environment, associated lithology, sandstone geometry, and architecture 38 Figure 8. North-south cross-section of the Morrison and Cloverly formations across the Bighorn Basin of Wyoming 39 Figure 9. East-west cross-section of the Morrison and Cloverly formations across the Bighorn Basin of Wyoming 41 V Figure 10. Isopach map of the Morrison Formation in the Bighorn Basin of Wyoming 44 Figure 11. Sand-Shale ratio map of the Morrison Formation in the Bighorn basin of Wyoming 47 Figure 12. Photograph showing the quartzarenite lithofacies association of the lower Morrison in the southern part of the Bighorn Basin of Wyoming. Location: near Thermopolis, Wyoming 51 Figure 13. Isopach map of the eolian sandstone (quartzarenite lithofacies) of the Morrison Formation 53 Figure 14. Photograph of the channel sandstone lithofacies association of the Morrison Formation showing lateral accretion surfaces. Location: One mile south of Brock Ranch, Mayoworth 57 Figure 15. Photograph of the interbedded siItstone and claystone lithofacies association of the upper Morrison. The contact (person standing) between the Morrison and Cloverly formations is on top of the salmon colored unit below the white ash bed. Location: Coyote Basin 57 PAPER II Figure 1. Graphs comparing cumulative probability curves of grain size analysis of the eolian sandstones (quartzarenite lithofacies) of the Morrison Formation with modern dune sand 114 Figure 2. Figure showing the paleowind directions for lower Morrison eolian sandstones (quartzarenite lithofacies) at various locations. Number of foreset dip directions measured is represented by n. The mean paleowind direction is represented by the arrow 116 Figure 3. Photograph showing flat-bedded quartz­ arenite subfacies of the lower Morrison in the southern part of the Bighorn Basin, Wyoming. Location: Thermopolis 118 vi Figure 4. Photograph showing crossbedded quartz- arenite subfacies of the lower Morrison in the western flank of the Powder River Basin. Location: Kaycee 118 Figure 5. Photograph showing silicified tree trunk in the crossbedded quartzarenite subfacies of eolian origin, lower Morrison. Location: SE Baker Cabin Road 125 Figure 6. A typical electric log response of the quartzarenite lithofacies interpreted to represent an eolian deposit. The high resistivity with sharp base is very typical of a clean eolian sandstone 127 Figure 7. Photograph showing burrows ("skolithos" trace fossil) in the interbedded claystone and sandstone lithofacies association of the lower Morrison Formation. Location: Coyote Basin 129 igure 8. Photograph showing escape burrows in the interbedded claystone and sandstone lithofacies association of the lower Morrison Formation. Location: Fox Mesa 129 Figure 9. Photograph showing lateral accretion surfaces in the channel sandstone lithofacies. Location: Coyote Basin 139 Figure 10. Channel sandstone lithofacies of the upper Morrison showing gradual decrease in the cross bed set thickness upward and multi-story channel sandstone deposits. Location: Fox Mesa 143 Figure 11. Figure showing the mean paleocurrent directions of the upper Morrison fluvial sandstones in the Bighorn Basin of Wyoming and Montana. The number of directions measured is represented by n. Mean paleocurrent direction is represented by the arrow 144 Figure 12. Electric log of a sandstone interpreted to represent a braided stream channel deposit in the upper part of the Morrison Formation. Note the cylindrical shape of the log 147 vii figure 13. Electric log of a sandstone interpreted to represent a meandering stream channel deposit in the Morrison Formation, Bighorn Basin, Wyoming. Note the fining upward sequence shown by the gradual decrease in resistivity curve 148 1 GENERAL INTRODUCTION Statement of the Problem The Morrison Formation is one of the most widespread units in the Western Interior. Figure 1 shows the location of the present study area. Figure 2 shows the outcrops of the Upper Jurassic and Lower Cretaceous Morrison and Cloverly formations in the Bighorn Basin and along the western flank of the Powder River Basin of Wyoming and Montana. Geologic investigations of the Upper Jurassic nonmarine Morrison Formation in the Western Interior date back to the end of the last century.