University of Montana ScholarWorks at University of Montana Graduate Student Theses, Dissertations, & Professional Papers Graduate School 2015 FACIES, ARCHITECTURE, AND SEQUENCE STRATIGRAPHY OF THE DEVONIAN-MISSISSIPPIAN SAPPINGTON FORMATION, BRIDGER RANGE, MONTANA Anna S. Phelps University of Montana - Missoula Follow this and additional works at: https://scholarworks.umt.edu/etd Part of the Geology Commons Let us know how access to this document benefits ou.y Recommended Citation Phelps, Anna S., "FACIES, ARCHITECTURE, AND SEQUENCE STRATIGRAPHY OF THE DEVONIAN- MISSISSIPPIAN SAPPINGTON FORMATION, BRIDGER RANGE, MONTANA" (2015). Graduate Student Theses, Dissertations, & Professional Papers. 4529. https://scholarworks.umt.edu/etd/4529 This Thesis is brought to you for free and open access by the Graduate School at ScholarWorks at University of Montana. It has been accepted for inclusion in Graduate Student Theses, Dissertations, & Professional Papers by an authorized administrator of ScholarWorks at University of Montana. For more information, please contact [email protected]. FACIES, ARCHITECTURE, AND SEQUENCE STRATIGRAPHY OF THE DEVONIAN- MISSISSIPPIAN SAPPINGTON FORMATION, BRIDGER RANGE, MONTANA By ANNA SHELDON PHELPS Bachelor of Arts, Colorado College, Colorado Springs, Colorado, 2010 Thesis presented in partial fulfillment of the requirements for the degree of Master of Science in Geology The University of Montana Missoula, MT August 2015 Approved by: Sandy Ross, Dean of The Graduate School Graduate School Marc S. Hendrix, Committee Chair Department of Geosciences Michael H. Hofmann Department of Geosciences Michael D. DeGrandpre, Department of Chemistry and Biochemistry © COPYRIGHT by Anna Sheldon Phelps 2015 All Rights Reserved ii Phelps, Anna, M.S., Summer 2015 Geology Facies, architecture, and sequence stratigraphy of the Devonian-Mississippian Sappington Formation, Bridger Range, Montana Chairperson: Marc S. Hendrix The Late Devonian-Early Mississippian Sappington Formation in Montana is a marine unit comprised of lower and upper organic-rich shale members and a middle calcareous siltstone member. The Sappington Formation was deposited during a period of complex paleogeography in Montana, characterized by deposition in sub-basins and onlap onto structural highs, and eustatically- and tectonically-driven transgressive-regressive cycles. Detailed outcrop analysis was conducted on the Sappington Formation across the Bridger Range in southwestern Montana to better understand the Sappington Formation depositional system and changing regional paleogeography. The Sappington Formation is further interpreted in a stratigraphic architectural framework to improve the ability to predict hydrocarbon reservoir heterogeneity within Late Devonian-Early Mississippian strata more regionally. Fourteen facies within the Sappington Formation are identified: 1) organic-rich mudstone and siltstone; 2) silty mudstone; 3) clay-rich, calcareous siltstone; 4) quartzose siltstone, 5) interlaminated siltstone and mudstone; 6) lenticular siltstone and mudstone; 7) wavy siltstone and mudstone; 8) combined flow siltstone; 9) ripple laminated siltstone; 10) convoluted siltstone; 11) tabular siltstone; 12) low-angle-stratified sandstone; 13) fossiliferous dolomite; and 14) oncoid-bearing floatstone. Genetically related facies are assigned to facies associations that generally represent deposition along a wave-storm-dominated prograding shoreface-shelf system sourced from the Beartooth Shelf to the south. Stratigraphic sequences, surfaces, and systems tracts are interpreted based on facies relationships, depositional processes, and regional stratal stacking patterns. The sequence stratigraphic framework includes two full depositional sequences, the oldest including a TST and HST, the second including a TST, HST and FSST, and a third sequence containing a TST and HST continuing into the overlying Lodgepole Formation. Depositional sequences are interpreted to be controlled by glacioeustatic, third-order sea level fluctuations, whereas basin geometry and configuration is inferred to be tectonic in origin. Analysis of facies stacking and stratigraphic architecture indicate significant lateral lithologic heterogeneity on the field and reservoir scale. Observed facies heterogeneity and architectural complexity of the Sappington Formation may help explain hydrocarbon production heterogeneity of the contemporaneous Bakken Formation in the Williston Basin and might have strong implications for new development and secondary recovery for the Bakken Formation in the Williston Basin. iii To the women of science in my family: Past, present, and future. iv ACKNOWLEDGEMENTS First and foremost, I’d like to express my deepest gratitude to my advisors Dr. Michael Hofmann and Dr. Marc Hendrix. I am so grateful to Michael for his tireless patience, mentoring, expertise, academic and professional support, and for opening so many doors for me. I am equally grateful to Marc, for his guidance, encouragement, good humor, and contagious passion for geology. It has been an honor and a privilege to work with two such brilliant geologists and I look forward to working together with them in the future. Thanks to Clayton Schultz, with whom I spent a summer hiking around the Bridger Range, hunting for Sappington outcrops and hanging out with mountain goats. I am thankful for his help in the field, but I am especially grateful for his feedback, our brainstorming sessions, and his friendship. I would like to thank Bruce Hart at Statoil for his support for and belief in this project, as well as his ideas, feedback, suggestions, and questions. Thanks to fellow research group member, John Zupanic, for his great sense of humor, friendship, support, and smooth dance moves. I would like to thank my third committee member, Michael DeGrandpre, for taking time out of his busy schedule to participate in my thesis committee. Thanks to the people behind the scenes of the Geosciences Department—Loreene Skeel, Christine Foster, Aaron Deskins—who make everything run smoothly and were so helpful and patient with me through this process. Thanks also to Matt Young for his geochemical analysis of samples. Thanks to Mark Taylor for expertly and safely piloting us around the Bridger Range and to Pat Moffitt for his additional field assistance. I would like to thank my greatest friend, Hilary Rice, for celebrating with me during the best times and making me laugh during the worst. There are good friends, there are best friends, and then there’s Hilary. Special thanks to my parents, Ames Sheldon and Gary Phelps, for their unwavering love, support, belief in me, and for always letting me sail my own boat. Finally, I gratefully acknowledge the funding sources that made this Master’s work possible. This research, and my academic career at the University of Montana, was supported primarily by Statoil with additional financial support from the University of Montana Department of Geosciences, the Apache Corporation, and the Geological Society of America. v TABLE OF CONTENTS 1. INTRODUCTION ................................................................................................................. 1 2. REGIONAL FRAMEWORK ............................................................................................... 4 3. METHODOLOGY ................................................................................................................ 6 4. FACIES ANALYSIS ............................................................................................................. 8 5. SEQUENCE STRATIGRAPHIC FRAMEWORK .......................................................... 24 5.1 Sequences ....................................................................................................................... 24 5.2 Surfaces .......................................................................................................................... 26 5.3 Systems Tracts ............................................................................................................... 29 6. CONTROLLING MECHANISMS .................................................................................... 36 6.1 Eustacy ........................................................................................................................... 36 6.2 Tectonics ........................................................................................................................ 37 6.3 Oceanography................................................................................................................. 38 7. IMPLICATIONS FOR THE BAKKEN FORMATION ................................................. 40 8. SUMMARY .......................................................................................................................... 43 9. REFERENCES CITED ....................................................................................................... 45 10. FIGURES AND TABLES ................................................................................................... 52 Figure 1: Study Area, Bridger Range, MT ............................................................................... 52 Figure 2: Stratigraphy and regional biostratigraphic correlation of the Sappington and Bakken Formations ................................................................................................................................ 53 Figure 3: Paleogeographic reconstruction during Devonian-Mississippian ............................