EVALUATING RIVER RESPONSE TO CLIMATE CHANGE USING CHANNEL-BAR RECONSTRUCTIONS IN THE WILLWOOD FORMATION, PALEOCENE-EOCENE, NORTHWESTERN BIGHORN BASIN, WYOMING, USA

Reconstructing ancient river dynamics from fluvial deposits is important for understanding how rivers responded to past climate change events. However, there are currently few tools that clearly connect stratigraphic observations to the types of river morphodynamics that are observable in modern systems. Here we leverage new approaches to identify avulsion-generated channel deposits to map internal channel-deposit architecture, with a specific emphasis on bar character, preservation, and stacking. We measure the scale, lateral continuity, intra-channel-belt stacking, and preservation of channel bar facies and clinoforms in channel-belt deposits of the Willwood Formation spanning the carbon-isotope excursion marking the Paleocene-Eocene Thermal Maximum (PETM). These measurements provide insight on the evolution of river planform, bar stability, channel mobility, and avulsion frequency before, during, and after the PETM. Results of this field study help differentiate between hypotheses that the large-scale sandbody architecture changes observed in the Willwood Formation resulted from discharge, sediment-supply, or land-cover changes during the PETM event. Preliminary results suggest increased lateral continuity and preservation of upper and lower channel-bar facies and a greater concentration of avulsion-generated channel-belt stories during the peak of the carbon-isotope excursion relative to before and after the PETM. These observations provide information on the relative mobility of ancient bars and channels, which may be compared to morphodynamic behavior of modern meandering rivers.