HYDROLOGIC CONDITIONS ACROSS THE K/PG BOUNDARY, DAWSON CREEK SECTION, BIG BEND NATIONAL PARK, TEXAS

The Dawson Creek section in Big Bend National Park, Texas consists of fluvial sandstones and pedogenically modified overbank deposits that span the K/Pg boundary. Previous work on this section has identified two hyperthermal events (Mid-Maastrichtian event (MME) and the Late-Maastrichtian event (LME)) that are characterized by increased temperature and atmospheric pCO2. This study further investigates environmental and hydrologic conditions associated with these greenhouse events as well as conditions following the K/Pg boundary using bulk-paleosol element concentrations as well as trace metal concentrations in coeval pedogenic calcite.

We reconstruct mean annual precipitation (MAP) in the Tornillo Basin using elemental data from both bulk paleosols and pedogenic carbonate nodules. Application of the PPM1.0 transfer function to bulk elemental chemistry of paleosol B-horizons indicates a range of MAP between 300 and 1200 mm spanning the study interval. The MME has a MAP of 1200 mm/year whereas the LME is distinctly dry with as little as 300 mm/year. MAP immediately following the K/Pg boundary is relatively wet with a maximum of 1200 mm/year. These hydrologic conditions are supported by the elemental chemistry of coeval pedogenic carbonates. Uranium concentrations in carbonate nodules are enriched in paleosols within the MME, depleted in the LME, and again enriched following the K/Pg boundary. This is consistent with the redox and substitution behavior of uranium in calcite. These results aid our understanding of potential long-term and extensive changes that CO₂ forcings can have on the hydrological cycle and constrain the climate sensitivity of environmental systems.