Graduate Theses, Dissertations, and Problem Reports 2019 STRUCTURAL STYLE AND STRATIGRAPHIC ARCHITECTURE OF THE NORTHEASTERN BROOKS RANGE, ALASKA Benjamin G. Johnson [email protected] Follow this and additional works at: https://researchrepository.wvu.edu/etd Part of the Geology Commons, Paleontology Commons, Stratigraphy Commons, and the Tectonics and Structure Commons Recommended Citation Johnson, Benjamin G., "STRUCTURAL STYLE AND STRATIGRAPHIC ARCHITECTURE OF THE NORTHEASTERN BROOKS RANGE, ALASKA" (2019). Graduate Theses, Dissertations, and Problem Reports. 3949. https://researchrepository.wvu.edu/etd/3949 This Dissertation is protected by copyright and/or related rights. It has been brought to you by the The Research Repository @ WVU with permission from the rights-holder(s). You are free to use this Dissertation in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you must obtain permission from the rights-holder(s) directly, unless additional rights are indicated by a Creative Commons license in the record and/ or on the work itself. This Dissertation has been accepted for inclusion in WVU Graduate Theses, Dissertations, and Problem Reports collection by an authorized administrator of The Research Repository @ WVU. For more information, please contact [email protected]. STRUCTURAL STYLE AND STRATIGRAPHIC ARCHITECTURE OF THE NORTHEASTERN BROOKS RANGE, ALASKA Benjamin G. Johnson A dissertation submitted to the Eberly College of Arts and Sciences at West Virginia University in partial fulfillment of requirements for the degree of Doctor of Philosophy in Geology Jaime, Toro, Ph.D., Chair Graham Andrews, Ph.D. Kathleen Benison, Ph.D. Amy Weislogel, Ph.D. Jeffrey Benowitz, Ph. D. Department of Geology and Geography Morgantown, West Virginia 2019 Keywords: Brooks Range, Alaska, Plate tectonics, Structural geology, Sedimentology, Whale Mountain allochthon Copyright 2018 Benjamin G. Johnson ABSTRACT STRUCTURAL STYLE AND STRATIGRAPHIC ARCHITECTURE OF THE NORTHEASTERN BROOKS RANGE, ALASKA Benjamin G. Johnson The Arctic Alaska–Chukotka microplate is a large Mesozoic–Cenozoic composite terrane that resides at the northern limit of the North American Cordillera. Although its Mesozoic origins are assuredly linked to the opening of the Amerasian Basin of the Arctic Ocean, its Paleozoic origins can be linked to at least three separate paleocontinents, including northern Laurentia, Baltica, and Siberia. Across the Arctic Alaska portion of the microplate, an internal, mid-Paleozoic suture zone presumably separates rocks of the North Slope subterrane (Laurentian affinity) from a collection of smaller subterranes in the southern Brooks Range and Seward Peninsula (Baltic affinity). The mountains of the northeastern Brooks Range expose a thick assemblage of Neoproterozoic–Lower Cretaceous rocks that belong to the North Slope subterrane. New data from geological mapping, coupled with zircon U-Pb and muscovite 40Ar/39Ar radiometric ages, reveal that the Neoproterozoic–Ordovician rocks in the NE Brooks Range, assigned to the Firth River Group, Neruokpuk Formation, and the informal Leffingwell formation, record deep-water, slope- to basin-floor sedimentation along the ancient passive margin of northern Laurentia. Stata of the Ordovician–Lower Devonian(?) Clarence River Group (new name) disconformably overlie these passive margin units and record a major shift in the sedimentary source. Detrital zircon U-Pb ages from Clarence River Group strata closely resemble the deep-water, syn- orogenic strata exposed in the Franklinian Basin of northern Ellesmere Island, and are interpreted to reflect erosion and transport of sediment sourced from the Caledonian orogen. A rootless thrust sheet places a Cambrian–Middle Ordovician structural complex of basalt, limestone and chert, herein named the Whale Mountain allochthon, above the upper strata of the Clarence River Group. Igneous geochemistry and trilobite paleontology suggest that the Whale Mountain allochthon formed as a series of remote volcanic islands or seamounts that established outboard the Laurentian margin. The emplacement of the allochthon occurred in concert with the locally-defined, Early–Middle Devonian Romanzof orogeny, and it may be linked to the closure of the Iapetus Ocean and the collision between Baltica and Laurentia in the Caledonian orogeny. This major collisional event is responsible for the assembly of the Arctic Alaska–Chukotka microplate, implicating the Whale Mountain allochthon as a potential relic to the suture zone that separates the North Slope subterrane from the rest of Arctic Alaska and Chukotka. ACKNOWLEDGEMENTS My time in the geology department a WVU is filled with many fond memories. Most notably, the relationship and mentorship I built with my advisor, Jaime Toro. He is a superb field geologist and outdoorsmen, but it is his sense of humor, his positive attitude, and his genuine curiosity that I admire most. At the end of our first field campaign together, after we had floated for 40 km down the Kongakut River in northern Alaska, I was utterly exhausted. While I was looking for an easy way to cross the river to reach our final take-out point, he told me to never take shortcuts and to embrace the hardships of life. We took the long way home, and this work is a testament to that. Aside from the influence of Jaime, there are many other people at WVU that I am thankful to have known. My thesis committee members, Graham Andrews, Kathy Benison, and Amy Weislogel, provided a lot of helpful feedback to my research, and I enjoyed learning from them in the classroom. There are several other faculty members within the department that I need to acknowledge: Ryan Shackleton taught me more than I could ever know about structural geology; the late Helen Lang helped me distinguish between clinopyroxene and olivine in thin section; and Joe Donovan introduced me to the wonderful game of squash. I am also grateful to have been a member of a vibrant graduate student body, many of whom I spent countless Friday evenings with at the Brew Pub, resuscitating our soles with cold beer. My officemates, Patrick Frier, Greg Hammond, and Chantelle Parrish were my closest companions, serving as an initial sounding board to my early ideas. There is an ever-growing list of coauthors, collaborators, and funding sources that I owe many thanks to. Sadly, I do not have the space to acknowledge them all here (see the acknowledgment sections at the end of Chapters 2, 3, and 4). There are a few, however, whose contributions are too great to go unmentioned. Jeff Benowitz, from the University of Alaska Fairbanks, served as an external member of my thesis committee. Not only did he let me borrow his truck in Fairbanks to help prepare for field work, but he provided radiometric ages in a timely fashion and helped me with their interpretation. John Taylor, from Indiana University of Pennsylvania, diligently identified and described all the trilobite specimens that field partners and I hauled from the mountains. His emails still make me smile. Tom Moore, from the iii USGS in Menlo Park, California, is probably more critical of my research than anyone else I know. His insistent review of my first published manuscript, however, profoundly impacted my approach to science, and his >30 years of research serves as a foundation to my understanding of Brooks Range geology. And then there is my dear friend and closest collaborator Justin Strauss, who is now an assistant professor at Dartmouth College. Together, we waded through frigid rivers, climbed rugged mountains, and embraced the hardships of life in the Brooks Range, all in an effort to reconstruct our former world. Above all others, I need to thank my wife, Patricia. She has been by my side since I started this journey. Through my greatest achievements and my biggest shortcomings, it was her adventurous spirit, her patience, and her unconditional support that kept me motivated to finish. Without her, none of this was possible. iv TABLE OF CONTENTS LIST OF FIGURES…………..…………………………………………………………………vi LIST OF TABLES……………………………………………………………………………...xv LIST OF PLATES…………………………………………………………………………..…xvi CHAPTER 1: Death of an ocean—birth of an orogen: An introduction to the tectonic history of the North Slope subterrane and its role in the assembly of the Arctic Alaska–Chukotka microplate……………………………………................................................................................1 CHAPTER 2: Detrital geochronology of pre-Mississippian strata in the northeastern Brooks Range, Alaska: Insights into the tectonic evolution of northern Laurentia.....…………………..14 CHAPTER 3: The Whale Mountain allochthon: A relic of the Iapetus Ocean preserved in the northeastern Brooks Range of Alaska and Yukon ………..……………………………………..81 CHAPTER 4: Geological mapping in the Arctic National Wildlife Refuge (ANWR) of the northeastern Brooks Range, Alaska ……..……………………………………………………..178 SUPLEMENTAL MATERIALS……………………………………………………………..243 v LIST OF FIGURES CHAPTER 1 Figure 1.1: Simplified map of pertinent Proterozoic and Paleozoic orogenic belts, terranes, and cratons mapped onto the modern circum-Arctic continental margins and modified from Colpron and Nelson (2011) and Miller et al. (2011). Star indicates field area of this study……………………………..2 Figure 1.2: Simplified tectono-stratigraphic map of the composite Arctic Alaska– Chukotka microplate (AACM) after Mull (1982), Miller et al. (2006; 2011), Amato et al. (2009), Moore