University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Dissertations & Theses in Earth and Earth and Atmospheric Sciences, Department Atmospheric Sciences of Spring 5-23-2010 Stratigraphy, Sedimentology, and Ichnology of the Upper Cretaceous Frontier Formation in the Alkali Anticline Region, Bighorn County, Wyoming Charles K. Clark University of Nebraska at Lincoln, [email protected] Follow this and additional works at: https://digitalcommons.unl.edu/geoscidiss Part of the Geology Commons Clark, Charles K., "Stratigraphy, Sedimentology, and Ichnology of the Upper Cretaceous Frontier Formation in the Alkali Anticline Region, Bighorn County, Wyoming" (2010). Dissertations & Theses in Earth and Atmospheric Sciences. 9. https://digitalcommons.unl.edu/geoscidiss/9 This Article is brought to you for free and open access by the Earth and Atmospheric Sciences, Department of at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Dissertations & Theses in Earth and Atmospheric Sciences by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. STRATIGRAPHY, SEDIMENTOLOGY, AND ICHNOLOGY OF THE UPPER CRETACEOUS FRONTIER FORMATION IN THE ALKALI ANTICLINE REGION, BIGHORN COUNTY, WYOMING. by C. Kittinger Clark A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science Major: Geosciences Under the Supervision of Professor Christopher R. Fielding Lincoln, Nebraska May, 2010 STRATIGRAPHY, SEDIMENTOLOGY, AND ICHNOLOGY OF THE UPPER CRETACEOUS FRONTIER FORMATION IN THE ALKALI ANTICLINE REGION, BIGHORN COUNTY, WYOMING. C. Kittinger Clark, M.S University of Nebraska, 2010 Adviser: Christopher R. Fielding The Upper Cretaceous Frontier Formation was studied along two strike-parallel cliff-lines in the Alkali Anticline region of the northeastern Bighorn Basin, Bighorn County, Wyoming. The unit comprises up to 145 m of mudrock, sandstone, conglomerate, and volcanic fallout sediments deposited along the western margin of the Cretaceous Western Interior Seaway (KWIS) in the mid- to late-Cenomanian. Eighteen facies, comprising six facies associations are identified from physical and biogenic sedimentary features. Sediments were deposited in open marine offshore to shoreface and subaqueous deltaic to delta platform environments. The observed trace fossil suites record departures from the archetypal ichnofacies. Such departures record environmental stresses associated with nearshore deltaic settings. Resolving the ichnological signature of these stressed nearshore settings was crucial to reconstructing the depositional environment. The Frontier Formation consists of multiple progradational and retrogradational sequences deposited during a low-frequency (high magnitude) lowstand characterized by lower-magnitude, higher- frequency fluctuations. This study reveals a complex succession of parasequences and deltaic coarsening upward successions deposited under low-accommodation conditions. Parasequence boundaries were the most useful for sub-regional correlation. Two sequence boundary candidates are identified in the Peay and Torchlight Members but they are not useful for correlating across the study area. This investigation provides new insights into the recognition and interpretation of the facies and stratigraphic architecture of nearshore sediments deposited in low accommodation settings, and provides a framework for future evaluations of similar deposits in the Western Interior Seaway. iii Copyright 2010 by Clark, C. Kittinger All rights reserved iv ACKNOWLEDGEMENTS Both the pursuit and completion of this thesis would not have been possible without the support and influence of countless educators, family, and friends. I could never compile a comprehensive list identifying these people for their numbers are too great. Nevertheless I want to convey my sincere gratitude to: my parents, Hilary and Richard Clark who never discouraged me from my pursuit of place and happiness; my siblings Chris and Hadley for their immeasurable support; the staff of the Raymond M. Alf Museum of Paleontology, namely Sadie Kingsbury, Dr. Don. Lofgren, Heather Moffat, & Kathy Sanders, for instilling within me a love for all things geology and an appreciation for the scientific method; the Colby College Geology Department for their invaluable education and research experience; the “Big Friggin Group” for providing me with unrelenting friendship and laughter; the University of Nebraska-Lincoln Geosciences Department, which afforded me countless opportunities to expand my knowledge and experience; my adviser Chris Fielding who led me in the field and was invaluable in the preparation of this work. I would additionally like to thank Dan Close at MiSwaco, and Mark Kirschbaum at the USGS for their input. Lastly, I want to acknowledge Professors David Watkins and David Loope for serving on my masters committee. v TABLE OF CONTENTS CHAPTER TITLE/SECTION PG Preface Title Page i Abstract ii Copyright iii Acknowledgements iv Table of Contents v List of Figures ix List of Tables x 1 Introduction 1 Accommodation as a Depositional Control 1 Shoreline-Detached, Linear Sand Bodies in the 2 Cretaceous Western Interior Seaway Geologic Setting 3 2 The Frontier Formation in Wyoming 6 Regional Correlation 6 Moxa Arch 6 SW Powder River Basin 8 NE Bighorn Basin 8 Geochronologic Control for the Bighorn Basin 9 Biostratigraphic Control 9 Bentonites 12 Clay Spur Bentonite 12 X-Bentonite 13 3 Introduction to Ichnology 13 vi Sedimentological and Ichnological Signatures of 14 Brackish Water Settings 4 Methods 16 5 Facies Analysis 16 Mowry Facies Association 18 Facies Mo1 18 Description 18 Interpretation 18 Facies Mo2 19 Description 19 Interpretation 19 Facies Mo3 20 Description 20 Interpretation 20 Frontier- Peay Facies Association 24 Facies P1 24 Description 24 Interpretation 25 Facies P2 26 Description 26 Interpretation 26 Facies P3 28 Description 28 Interpretation 28 Facies P4 29 Description 29 Interpretation 29 Facies P5 30 Description 30 vii Interpretation 30 Frontier- Sub-X Facies Association 31 Facies SX1 31 Description 31 Interpretation 32 Frontier- Alkali Facies Association 34 Facies A1 34 Description 34 Interpretation 35 Facies A2 35 Description 35 Interpretation 36 Facies A3 37 Description 37 Interpretation 37 Facies A4 38 Description 38 Interpretation 38 Frontier- Torchlight Facies Association 39 Facies T1 39 Description 39 Interpretation 41 Facies T2 41 Description 41 Interpretation 42 Facies T3 42 Description 42 Interpretation 42 Frontier- Recurring Facies Association 43 viii Facies F1 43 Description 43 Interpretation 43 Facies F2 43 Description 44 Interpretation 44 Depositional Systems Overview 44 6 Stratigraphy 45 Key Surfaces 46 Transgressive Surfaces of Erosion 46 Parasequences and Flooding Surfaces 46 Regressive Surfaces of Marine Erosion 47 Sequence Boundaries 48 Discussion of Stratigraphy 49 7 Conclusions 50 8 References 59 end 65 ix LIST OF FIGURES CHAPTER TITLE/SECTION PG 1 Introduction 1 Figure1: Paleogeography Map of the KWIS 4 Figure 2: Regional Map of Wyoming 5 2 The Frontier Formation in Wyoming Figure 3: Regional Stratigraphy of the Frontier 7 Formation Figure 4: Stratigraphy of the Frontier Formation in the 10 Bighorn basin Figure 5: Typical outcrop exposure of the Frontier 11 Formation 3 Introduction to Ichnology 13 4 Methods 16 5 Facies Analysis 16 Figure 6: Photos of Mowry Facies Association 17 Figure 7: Photos of Peay Facies Association 21 Figure 8: Photo of Clinoforms in Peay Member 22 Figure 9: Photos of Peay Facies Association 23 Figure 10: Photos of Sub-X & Alkali Facies Association 33 Figure 11: Torchlight Facies Association 40 6 Stratigraphy 45 Figure 12: Sequence Stratigraphic Interpretation 58 x LIST OF TABLES CHAPTER TITLE/SECTION PG 5 Facies Analysis Table 1: Mowry Facies Association 54 Table 2: Peay Facies Association 55 Table 3: Sub-X Facies Association 55 Table 4: Alkali Facies Association 56 Table 5: Torchlight Facies Association 56 Table 6: Reoccurring Facies Association 57 1 INTRODUCTION Increasingly, sequence stratigraphic studies recognize accommodation as a significant depositional control in continental margin successions (Bhattacharya & Willis 2001; Fielding et al. 2008; Sadeque et al. 2007). Current stratigraphic models are largely biased toward successions where accommodation is not a limiting factor. Sequences formed under low accommodation regimes are generally thinner and less complete than their high accommodation counterparts (Van Wagoner et al. 1990; Mitchum & Wagoner 1991). The frequency and magnitude of changes in accommodation along continental margins strongly controls preservation potential and stratigraphic architecture of sediments deposited in nearshore environments (Porębski & Steel 2006). Facies relationships associated with limited accommodation directly influence reservoir character. Accommodation as a Depositional Control Sediment deposition in continental margin systems can be categorized as either supply- or accommodation limited (Porębski & Steel 2006). Shoreline trajectory and sediment dispersal patterns are directly impacted by the balance between accommodation and sediment supply (Steel et al. 2008; Porębski & Steel 2006). Shallow-marine sediments, deposited in accommodation limited settings, are commonly truncated by transgressive surfaces of erosion (TSE) and sequence boundaries. Ultimately, the extent of lateral progradation is a function