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Abstract Numerous geochemical anomalies exist at the K-Pg boundary that indicate the addition of extraterrestrial materials; however, none fingerprint volatilization, a key process that occurs during large bolide impacts. Stable Zn isotopes are an exceptional indicator of volatility-related processes, where partial vaporization of Zn leaves the residuum enriched in its heavy isotopes. Here, we present Zn isotope data for sedimentary rock layers of the K-Pg boundary, which display heavier Zn isotope compositions and lower Zn concentrations relative to surrounding sedimentary rocks, the carbonate platform at the impact site, and most carbonaceous chondrites. Neither volcanic events nor secondary alteration during weathering and diagenesis can explain the Zn concentration and isotope signatures present. The systematically higher Zn isotope values within the boundary layer sediments provide an isotopic fingerprint of partially evaporated material within the K-Pg boundary layer, thus earmarking Zn volatilization during impact and subsequent ejecta transport associated with an impact at the K-Pg.
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Filling in the Gaps: Paleosols as Regional Recorders of East Asian Hydroclimate Response to the Cretaceous-Paleogene
The stable isotopic composition of soil-formed carbonate, and bulk geochemistry of preserved soil matrix, can provide regionally constrained records of hydroclimatic change throughout deep-time. The SK cores, spanning over 10 km of sediment drilled from the Songliao Basin in Northeast China, represent near continuous terrestrial deposition across the late Jurassic to early Paleogene. In this study we analyze SK-1n paleosol core samples spanning late Maastrichtian to early Danian to interpret the regional hydroclimate response to global climate change, concurrent with Deccan Traps volcanism and the Chicxulub impact. Building on numerous paleosol carbonate datasets from the Sifangtai and Mingshui formations, we present ~40 new carbonate clumped isotope measurements at ca. 10 – 20 kyr resolution between 66.3 to 65.5 Ma. We produce a new kernel-smoothed temperature record and estimate the δ18O of soil porewater (δ18Opw), and δ13C of soil CO2 (δ13Cs) from new and previously published datasets. Molecular weathering ratios, derived from bulk geochemistry, are used to reconstruct weathering (CIA-K), clay formation (Al/Si), soil drainage (Ba/Sr), and calculate mean annual precipitation (MAP) via established transfer functions. Preliminary results suggest elevated K-Pg boundary temperatures, averaging ~30 °C, that decline by ~10 °C over the following 500 kyr. Post-impact cooling may contribute to a negative δ18Ocarb excursion (-2.5‰) at ~65.8 Ma. Further, stable subhumid MAP (~1100 mm/yr) across the dataset suggests negligible amount effect influence. Mean δ18Opw (-6.9‰) is largely stable, and does not reflect regional monsoon seasonality. Instead, stable δ18Opw indicates a consistent moisture source, a potential persistent seasonal bias in carbonate formation. Binning all compiled δ18Opw by soil profile depth reveals statistically significant enrichment in the upper 60 cm of soil profiles, and accounts for variability in the δ18Opw (σ = 1.16‰). Soil respiration, modeled from δ13Cs, increases from ca. 700 to 2000 gC/m2/year across the K-Pg boundary, indicating increased productivity despite declining pCO2 and available phosphorus. Future work will expand the temporal range of isotopic measurements (~72 to 65 Ma) and contextualize our latest Cretaceous results within a spatial framework across Asia.
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- Award ID(s):
- 2316733
- PAR ID:
- 10517581
- Publisher / Repository:
- American Geophysical Union
- Date Published:
- Format(s):
- Medium: X
- Location:
- San Francisco, CA
- Sponsoring Org:
- National Science Foundation
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