University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Dissertations & Theses in Earth and Atmospheric Earth and Atmospheric Sciences, Department of Sciences 5-2015 Stratigraphy and Depositional Environment of the Mesaverde Group in the Northern Bighorn Basin of Wyoming Gordon Adams University of Nebraska-Lincoln, [email protected] Follow this and additional works at: http://digitalcommons.unl.edu/geoscidiss Part of the Geology Commons, and the Sedimentology Commons Adams, Gordon, "Stratigraphy and Depositional Environment of the Mesaverde Group in the Northern Bighorn Basin of Wyoming" (2015). Dissertations & Theses in Earth and Atmospheric Sciences. 64. http://digitalcommons.unl.edu/geoscidiss/64 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 AND DEPOSITIONAL ENVIRONMENT OF THE MESAVERDE GROUP IN THE NORTHERN BIGHORN BASIN OF WYOMING by Gordon Adams 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: Earth and Atmospheric Sciences Under the Supervision of Professor Christopher R. Fielding Lincoln, Nebraska May, 2015 STRATIGRAPHY AND DEPOSITIONAL ENVIRONMENT OF THE MESAVERDE GROUP IN THE NORTHERN BIGHORN BASIN OF WYOMING Gordon Adams, M.S. University of Nebraska, 2015 Advisor: Christopher R. Fielding A sedimentological, stratigraphical and palynological study was conducted on the upper Cretaceous (Campanian) Mesaverde Group over 27.5 km of a north-south- orientated outcrop belt in the northern Bighorn Basin, Wyoming. During the Campanian, the study area lay in the western part of the Cretaceous Western Interior Seaway. The study aims to provide a stratigraphic and paleoenvironmental analysis of the Mesaverde Group and to integrate findings with data from outcrop belts to the south (southern Bighorn Basin), north (Montana) and east (Powder River Basin). The Mesaverde Group (371 - 515 m thick) comprises a succession of mainly coarsening-upward stratal cycles, with some anomalous, sharply-based sandstone bodies that are out of context with respect to underlying facies. The trace fossil assemblage is typically of low diversity with only a few ichnotaxa recurring throughout the succession. The palynofacies analysis shows predominantly low abundance of palynomorphs and dinoflagellates indicating a high energy environment. There is, however, a wide range in types and abundance of phytoclasts present. Paleocurrent data indicate a dominantly southeastward direction of sediment dispersal with bi-modal sediment dispersal patterns within individual facies. This study indicates a similar lithological assemblage to previous studies of the Mesaverde Group; however the interpretation of depositional environment from this study points towards a dominantly deltaic depositional environment, something that only a subset of previous studies has done. The depositional environment changes vertically throughout the section from distal to proximal, with facies associations ranging from basinal to coastal plain. The palynofacies analysis performed in this study is consistent with the lithofacies analysis but also reveals some flooding events that are not revealed by the lithology. Finally, four sequence stratigraphic cycles are interpreted throughout the Mesaverde Group identified by incised lithosome bases and major dislocation of facies. Overall this study provides a basis for future study on the Mesaverde Group and allows for a more detailed paleoenvironmental evaluation of the unit. Acknowledgements This thesis would not have been possible without the help of many people to whom I am forever grateful and indebted. First and foremost I want to thank Dr. Christopher Fielding who has been a source of invaluable assistance, information and advice since this project began. Without his patience, knowledge and mentorship I would not have gotten this far. I’d also like to thank my wife Kristen who has helped me with all the images in this document, and who worked tirelessly to assist me in the field. To my parents, family, and my closest friends in both Scotland and Nebraska for their guidance and support throughout this study, with a special thanks to Sebastian Blanchard for helping Dr. Fielding gather palynological samples for me. I’d also like to thank my colleague Andrew Hutsky for his advice and friendship. I want to thank Mr. and Mrs. Casey for allowing me access to their land and arranging access to their neighbors’ land which is part of the study area. I also thank Dr. Oboh-Ikuenobe and Mr. Robert Haselwander, at the University of Missouri, Rolla, without whom the palynological aspect of this study would not have been possible. To Dr. Tracy Frank and Dr. David Watkins for agreeing to be my committee members and for providing me with abundant help over the course of this project. Finally, I’d like to acknowledge the Department of Earth and Atmospheric Sciences at the University of Nebraska Lincoln for the opportunity to carry out graduate research and for the funding it provided me through a TA position and a fellowship to allow me to follow my dream. Table of Contents Introduction 1 Geologic Setting 3 Previous Research 4 Methods 8 Facies Associations 11 Basinal Facies Associations 12 Facies B1 12 Facies B2 13 Facies B3 14 Delta Front Facies 14 Facies D1 14 Facies D2 15 Facies D3 17 Coastal Platform Facies 20 Facies C1 20 Facies C2 21 Facies C3 22 Incised Estuary Facies 23 Facies I1 23 Lithostratigraphy 24 Palynofacies Assemblages 29 Principal Components Analysis 32 Factor Analysis 34 Tyson Ternary Analysis 36 Initial Environmental Interpretations 38 Synthesis and Depositional Environment 42 Synthesis of Lithofacies and Palynofacies 42 Sequence Stratigraphy 43 Conclusions 51 1 Introduction The Mesaverde Group has been studied in detail throughout the western United States and Canada but has not been documented in detail in the northern Bighorn Basin of Wyoming; this study will investigate these poorly studied outcrops. The purpose of this study is threefold. First, a stratigraphical and lithological analysis of the poorly studied Mesaverde Group of the northern Bighorn Basin in Wyoming will be conducted in order to produce both a paleoenvironmental and stratigraphical analysis of the Mesaverde that can be compared against previous studies. Second, a palynofacies analysis of the group will be integrated into the paleo-environmental analysis to achieve a higher resolution evaluation of depositional environments. Finally, the results will be compared to previous studies on contemporary formations in Wyoming’s southern Bighorn Basin and the Powder River Basin in eastern Wyoming for a more comprehensive overview of the Mesaverde Group. This study will facilitate a fuller understanding of Mesaverde Group stratigraphy to inform future studies. The Mesaverde Group in the Western Cordilleran Foreland Basin of North America is an important stratigraphic unit because of its resource potential. Component formations are known to host not only coal deposits, which have been extensively mined, but also large quantities of shallow biogenic gas which has become of interest in hydrocarbon exploration in recent years (Condon 2000). The Mesaverde Group has been studied in detail in many regions of the United States, but the unit in the northern Bighorn Basin of north central Wyoming has not been studied in the modern era. There have been a few localized studies of the formation (e.g., Johnson et al. 1998); however no study has considered the outcrop belt as a whole. There have been a number of stratigraphic studies 2 in adjacent areas. In Montana, studies by Condon (2000), Rice (1980), and Roehler (1990) have been published. Studies in the southern Bighorn Basin include Severn (1961) and Fitzsimmons & Johnson (2000) and to the east in the Powder River Basin, Purcell (1960), Rich (1958) and Crews et al. (1976). The most commonly accepted stratigraphic division is into four members, from base to top: the Eagle Formation, the Claggett Shale Member, the Judith River Formation and the Teapot Sandstone Member. The Mesaverde Group is underlain by the Cody Shale and overlain by the Meeteetse Formation (Fig.1). The range of depositional environments represented within the Mesaverde Group has been discussed in previous studies; interpretations range from offshore marine, through deltaic, to multistory coastal platform fluvial/tidal channels (Fitzsimmons & Johnson 2000), and also include barrier islands and protected lagoons (Kieft et al. 2011). Figure 1: Regional stratigraphic frame work of the Campanian strata of Wyoming. Fm stands for formation, SS for sandstone, and Mbr for member. Sandstones are shaded in yellow. Modified from Swift et al. (2008) & Martinsen et al. (1995). 3 Geologic Setting The Mesaverde Group accumulated within the Cretaceous Western Interior Seaway during the late Cretaceous (Campanian to Maastrichtian), approximately 83 -76 Ma (Gill & Cobban 1966). The timing of Mesaverde Group accumulation is constrained by the presence of temporally significant ammonite marker species. The base of the Mesaverde Group fall within a biozone defined by Scaphites hippocrepis (82.7 Ma) and the top by Baculites cuneatus