The Bridger Range of southwest Montana, USA, preserves one of the most temporally extensive sedimentary sections in North America, with strata ranging from Mesoproterozoic to Cretaceous in age. This study presents new detrital zircon geochronologic data from eight samples collected across this mountain range. Multidimensional scaling and non-negative matrix factorization statistical analyses are used to quantitatively unmix potential sediment sources from these and 54 samples compiled from previous studies on regional correlative strata. We interpret these sources based on reference data from preserved strata with detrital zircon signatures likely representative of ancient sediment sources. We link these sources to their sinks along sediment dispersal pathways interpreted using available paleogeographic constraints. Our results show that Mesoproterozoic strata in southwest Montana contain detritus derived from the nearby craton exposed along the southern margin of the fault-bounded Helena Embayment. Middle Cambrian strata were dominated by the recycling of local sources eroded during the development of the Great Unconformity. In Devonian−Pennsylvanian time, provenance in southwest Montana shifted to more distal sources along the northeastern to southeastern margins of Laurentia, but more western basins received detritus from outboard sources along a tectonically complicated margin. By the Late Jurassic, provenance in the developing retroarc foreland basin system was dominated by Cordilleran magmatic arcs and fold-thrust belt sources to the west. Eastward propagation of the fold-thrust belt caused recycling of Paleozoic and Jurassic detritus into the foreland basin to dominate by the Early Cretaceous.

Thank you, Miranda Grover, for being the most supportive person in the world. I would have certainly lost weight and likely sanity without your nurturing love, understanding, and latenight leftover deliveries. I am grateful to my friend Caden Howlett-every discussion with you leaves me with a renewed enthusiasm for the mysteries of the natural world. Thank you to Stuart Parker, Mariah Romero, Sophie Black, and other student researchers for serving as sources of geologic inspiration. I am indebted to my undergraduate and graduate professors for sharing their knowledge and excitement with me. I am grateful to Dr. Colleen Elliot, Katie McDonald, and others at the MBMG for sharing their knowledge of Montana geology. I am also thankful to Chris Kussmaul, Dom D'Amato, Chris Baird, and others who assisted me with field work. I express immense love and appreciation for my mother and father-Amby and Kyle Ronemus-to whom I owe the entirety of my curiosity. Thank you for your support, encouragement, and understanding unceasing since the day I was born. Finally, this project would not have been possible without financial support from Montana State University, the MSU Department of Earth Sciences and the Tobacco Root Geological Society.

No abstract

No abstract