TAPHONOMY OF THE SUN RIVER BONEBED, LATE CRETACEOUS (CAMPANIAN) TWO MEDICINE FORMATION OF MONTANA by Benjamin Andrew Scherzer A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Earth Sciences MONTANA STATE UNIVERSITY-BOZEMAN Bozeman, Montana April 2008 © COPYRIGHT by Benjamin Andrew Scherzer 2008 All Rights Reserved ii APPROVAL of a thesis submitted by Benjamin Andrew Scherzer This thesis has been read by each member of the thesis committee and has been found to be satisfactory regarding content, English usage, format, citations, bibliographic style, and consistency, and is ready for submission to the Division of Graduate Education. Dr. David J. Varricchio Approved for the Department of Earth Sciences Dr. Stephan G. Custer Approved for the Division of Graduate Education Dr. Carl A. Fox iii STATEMENT OF PERMISSION TO USE In presenting this thesis in partial fulfillment for the requirements for a master’s degree at Montana State University, I agree that the Library shall make it available to borrowers under rules of the Library. If I have indicated my intention to copyright this thesis by including a copyright notice page, copying is allowed only for scholarly purposes, consistent with “fair use” as prescribed in the U.S. Copyright Law. Request for permission for extended quotation from or reproduction of this thesis in whole or in parts may be granted only by the copyright holder. Benjamin Andrew Scherzer April 2008 iv ACKNOWLEDGEMENTS This thesis would not have come to completion without the help of each member of my committee: Dave Varricchio, Jack Horner, and Jim Schmitt. Field work would have been impossible if not for the work of my field assistants: Josh Bonde, Pete Bucholz, Jennifer Krey, John Plummer, Anne Teppo, and Eric Williams. The Museum of the Rockies was generous in both providing me office space and sharing field equipment. Additional academic assistance came from Mic Jackson (Earlham College), Anthony Martin (Emory University), Greg Retallack (University of Oregon), Eric Roberts (Southern Utah University). Finally, my family, as always, was patient, supportive, and occasionally blunt. Field work was possible thanks to permission from the State of Montana and the BLM. This project was funded by the Jurassic Foundation and The American Museum of Natural History’s Theodore Roosevelt Memorial Fund. IN MEMORIAM, 1988-2004 v TABLE OF CONTENTS 1. INTRODUCTION ..........................................................................................................1 2. LOCATION AND GEOLOGIC SETTING ...................................................................4 3. METHODS .....................................................................................................................7 4. LITHOFACIES .............................................................................................................11 Matrix-Supported Massive Conglomerate (Gms) ........................................................11 Description ............................................................................................................11 Interpretation .........................................................................................................13 Trough Cross-Bedded Sandstone (St) ..........................................................................14 Description ...........................................................................................................14 Interpretation ........................................................................................................14 Ripple Cross-Laminated Sandstone (Sr) ......................................................................17 Description ............................................................................................................17 Interpretation .........................................................................................................17 Horizontally Laminated Sandstone (Sh) .....................................................................17 Description ............................................................................................................17 Interpretation .........................................................................................................21 Massive Sandstone (Sm) ..............................................................................................22 Description ............................................................................................................22 Interpretation .........................................................................................................22 Massive Mudrock (Fm) ................................................................................................25 Description ............................................................................................................25 Interpretation .........................................................................................................26 Bentonite (Fb) ..............................................................................................................27 Description ............................................................................................................27 Interpretation .........................................................................................................27 5. BONEBED LITHOLOGY ............................................................................................29 6. LITHOFACIES ASSOCIATIONS ...............................................................................37 Massive Mudrock..........................................................................................................37 Description ............................................................................................................37 Interpretation .........................................................................................................38 Major Tabular Sandstone..............................................................................................38 Description ............................................................................................................38 Interpretation .........................................................................................................38 vi TABLE OF CONTENTS – CONTINUED Minor tabular sandstone................................................................................................39 Description ............................................................................................................39 Interpretation .........................................................................................................40 Alternating Mudrock and Sandstone ............................................................................40 Description ............................................................................................................40 Interpretation .........................................................................................................41 Gradational Sandstone and Mudrock............................................................................41 Description ............................................................................................................41 Interpretation .........................................................................................................42 Gradational Conglomerate and Sandstone....................................................................42 Description ............................................................................................................42 Interpretation .........................................................................................................43 Summary.......................................................................................................................43 Interpretation of Depositional Environment .........................................................43 Comparison to Previous Interpretations ................................................................45 7. TAPHONOMIC DATA ...............................................................................................46 Taxonomic Composition of SRB .................................................................................46 Orientation of Elements ...............................................................................................49 Spatial Distribution of Elements ..................................................................................52 Element Representation ...............................................................................................52 Weathering and Abrasion ............................................................................................56 Bone Breakage and Fracturing .....................................................................................62 “Wet Rot” ....................................................................................................................67 8. DISCUSSION ...............................................................................................................71 SRB Deposition and Comparison to other Two Medicine Bonebeds ..........................71 Debris Flow Genesis ....................................................................................................77 The Debris Flow ...........................................................................................................81