137-4 Sedimentary Fingerprints of Extreme Precipitation during the PETM in the Eastern Tethys

Session: Joint SGD-SEPM-IAS Focus on the Sedimentary Record of Climate Change

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The Paleocene–Eocene Thermal Maximum (PETM, ~56 million years ago) is arguably the best geological analogue for future warming driven by anthropogenic CO₂; however, direct field evidence for the predicted surge in rainfall extremes remains limited. Here, we track hydroclimatic changes from the pre-onset excursion (POE) through the PETM and its aftermath in the subtropical eastern Tethys based on sedimentary and geochemical evidence from the Kuzigongsu section in northwestern China, deposited in a shallow-water carbonate setting. Our multi-proxy approach—combining laser-diffraction granulometry and X-ray fluorescence bulk-element analyses—shows that coarse-fraction pulses, when coupled with terrigenous-to-marine elemental shifts, form a sensitive archive of precipitation intensity. During the ~150 kyr of the POE-to-PETM transition, sediment input is dominated by silt and clay except for a single sand-rich pulse. Because this sand peak is unaccompanied by shifts in K/Al, Ti/Al, C/N, or K/Ti, we attribute it to a hydrological extreme—such as tropical storm landings that lofted coastal sand into deeper settings without large increases in continental runoff, consistent with the absence of any major river nearby. The PETM interval records a step-change: mean grain size and sand content rise sharply, with three prominent sand peaks. Each peak coincides with spikes in K/Al, Ti/Al, C/N, and K/Ti ratios, signaling episodes of extreme terrestrial precipitation, which facilitated the transport of chemical-weathering products to the ocean, delivering nutrients that fueled the coastal primary productivity documented previously. High-resolution cyclostratigraphy and carbon-isotope stratigraphy suggest that each sand maxima lasts <10 kyr following peak negative δ¹³C excursions, indicating a rapid sedimentary response to changes in atmospheric–hydrological processes. Grain size analysis supports short-distance fluvial delivery rather than aeolian input, underscoring storm-driven runoff as the dominant transport pathway. These coupled mineralogical and chemical changes reveal an "overcharged" hydrological cycle in the eastern Tethys, with storms strong enough to transport coarse sediments far offshore. Post-PETM strata show a rapid shift toward finer textures and lower elemental ratios, indicating a weakened hydrological cycle and diminished terrestrial discharge as global temperatures declined. Our study provides direct sedimentary evidence for heightened extreme-precipitation frequency during the PETM and offers critical constraints for assessing hydroclimatic risk under anthropogenic warming.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8802

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