ORGANIC CARBON ISOTOPE AND FLUVIAL-LACUSTRINE SEDIMENTATION RECORD OF PALEOCENE TO EARLY EOCENE WARMING EVENTS, WASATCH AND GREEN RIVER FORMATIONS, UINTA BASIN, UTAH

Previously published individual regional terrestrial and global marine carbon isotope records provide an archive of major climatic fluctuations including the Paleocene-Eocene Thermal Maximum (PETM) and at least five early Eocene hyperthermal events. Here we present a continuous fluvial-lacustrine record of sedimentation style changes that were associated with dispersed organic carbon isotope (δ¹³C_org ) excursions from the same succession in the Paleocene to Eocene Wasatch and Green River Formations, Uinta Basin, Utah. Negative δ¹³C_org excursions from floodplain mudstone units from two widely separated localities across the Uinta Basin capture at least five warming events, including the PETM and ETM2 (H1), H2, and I1. Additional more minor δ¹³C_org shifts are locally observed in Nine Mile Canyon that may record the I2, J, K(‘X’), and b and c hyperthermal events. δ¹³C_org excursions interpreted as hyperthermal events are concurrent with widespread, laterally correlative fluvial channel sandstone and mouthbar packages with distinct sedimentary characteristics. Specifically, fluvial channel bodies, ranging in thickness from 4 to 25 m and width from 200 m to 1 km, distinctly contain an abundance of upper flow regime structures that indicate a highly seasonal fluvial discharge regime characteristic of monsoonal climates. This is in contrast to the underlying Paleocene North Horn Formation and stratigraphically higher intervals of the Green River Formation that contain dominantly trough cross- stratified fluvial channels that are typical of traditional fluvial facies models developed from temperate less seasonal climate regions. Between hyperthermal events, preservation of lacustrine carbonates and organic rich oil shale with minor fluvial deposits indicate increased carbon burial and sequestration, thus providing a possible balancing mechanism for carbon release during hyperthermal events. In the neighboring Greater Green River Basin, similar fluvial-lacustrine cycles have been linked to 100 year period eccentricity cycles. This study provides evidence of increased seasonality, fluvial expansion, and increased continental source to sink sediment delivery during abrupt Paleocene to early Eocene global warming events.