DETRITAL ZIRCON GEOCHRONOLOGY, PROVENANCE, AND SEDIMENT DISPERSAL IN LATE CRETACEOUS STRATA WITH IMPLICATIONS FOR SEVIER AND LARAMIDE TECTONISM IN THE WESTERN INTERIOR BASIN, MONTANA AND WYOMING, NORTH AMERICAN CORDILLERA

The goal of this study is to better resolve depositional chronology of terrestrial strata and timing of sediment transport compartmentalization between Wyoming and Montana during the Late Cretaceous by using published U-Pb detrital zircon ages. However, due to the paucity of good biostratigraphic data in terrestrial deposits, constraining the timing of deposition and linking terrestrial deposits to their basinal equivalent is difficult. Previous models indicate large sediment dispersal systems in the North American Cordillera flowed parallel to the foreland basin with transversely draining small rivers in the Early Cretaceous. Between this time and the Paleocene, there was a shift in sediment transport splitting the Western Interior Basin between Wyoming and Montana into two separate drainage systems. Late Cretaceous stratigraphic units in the region also record the transition from Sevier to Laramide orogenesis which may play a role in drainage shift. This study builds on published and ongoing research of the tectonics and sedimentary history of this region and divides the Late Cretaceous into seven 5 Myr time slices from the early Cenomanian to late Maastrichtian. We evaluate several methods of determining Maximum depositional ages for terrestrial deposits using MATLAB AgeCalcML. Provenance analysis was conducted using non-negative matrix factorization modeling to identify potential sources (i.e., factorized sources) for basin samples. An optimal number of three to nine sources, depending on the time slice, was predicted using DZnmf segmented linear regression and sum of squared residuals graphs. Modeling indicates that sources with prominent peaks at approximately 500 Ma and 1700 Ma are dominant during the Cenomanian through Coniacian and development of additional minor 700 and 1000 Ma peaks with a Grenville signal from the Campanian to late Maastrichtian. These results support a model in which a drainage system parallel to the axis of the basin transported sediment from the Mesozoic eolianites from the south and passive margin from the south and west from the Cenomanian to Coniacian. A divide in drainage began to separate the Montana samples from the Wyoming samples starting in the Coniacian. Further uplift of the thrust belt and Laramide structures began to contribute additional sediment starting in the Campanian.