PROVENANCE CHANGE IN FLUVIAL AND DELTAIC SANDSTONE BODIES ACROSS THE PALEOCENE-EOCENE BOUNDARY WITHIN THE HANNA BASIN

The Laramide Orogeny segmented the Sevier foreland basin of the United States into a series of intramontane basins during the latest Cretaceous into the Paleogene. Basement-involved uplifts caused the flexural subsidence of the adjacent crust and generated accommodation space that was then filled by sediment eroded off the evolving mountain ranges. This history of unroofing and uplift is recorded in provenance changes within alluvial strata in the adjacent sedimentary basins. The Hanna Basin in south-central Wyoming, U.S.A. preserves over 12,500m of Late Cretaceous to Early Paleogene terrestrial strata and provides a high resolution record of local tectonic activity. We collected 27 sandstone samples from fluvial, deltaic, and marginal lacustrine depositional environments in the Hanna Formation that span several hundred meters of stratigraphic thickness. Our samples date from the Paleocene to the Eocene and include samples from within the Paleocene-Eocene Thermal Maximum (PETM), a geologically abrupt perturbation to the global carbon cycle and the climate system.

Thin sections from these samples were point-counted (400 minerals per slide) documenting the relative abundance of mono- and poly-crystalline quartz, plagioclase, potassium feldpar, and lithic fragments (igneous, sedimentary, and metamorphic) as well as minor accessory minerals such as micas and minor amphiboles. Initial data sets indicate the different depositional environments display relative mineral abundances similar to one another and dominated by monocrystalline and polycrystalline quartz followed by feldspars and sedimentary lithic fragments. To complement the thin section work and provide additional information about sediment transport into the Hanna Basin, 284 paleoflow measurements were taken from strata before, during and after the PETM. These suggest dominant drainage to the east-southeast before the PETM and drainage to the northeast during and after the PETM; however, individual fluvial sandbodies and deltaic units display significant variation. Overall, these data are consistent with significant contributions from the eroded sedimentary cover of the surrounding Laramide uplifts and potentially more distal sediment sources.