Stable isotopic response to late Eocene extraterrestrial impacts

Pusz, Aimee E.; Miller, Kenneth G.; Wright, James D.; Katz, Miriam E.; Cramer, Benjamin S.; Kent, Dennis V.

We evaluated the age of two Upper Eocene impact ejecta layers (North American microtektites linked to the Chesapeake Bay impact structure and clinopyroxene [cpx] spherules from the Popigai crater) and the global effects of the associated impact events. The reported occurrence of cpx spherules from the Popigai impact structure at South Atlantic ODP Site 1090 within the middle of magnetochron C16n.1n yields a magnetochronologic age of 35.4 Ma. We generated high-resolution stable isotope records at Sites 1090, 612 (New Jersey slope), and Caribbean core RC9-58 that show: (1) a 0.5‰ δ^13C decrease in bulk-carbonate at Site 1090 coincident with the Popigai cpx spherule layer, and (2) a 0.4‰-0.5‰ decrease in deep-water benthic foraminiferal δ^13C values across the Popigai impact ejecta layer at Site 612 and core RC9-58. We conclude that the δ^13C excursion associated with Popigai was a global event throughout the marine realm that can be correlated to magnetochron C16n.1n. The amplitude of this excursion (~0.5‰) is within the limits of natural variability, suggesting it was caused by a decrease in carbon export productivity, potentially triggered by the impact event(s). North American microtektites associated with the Chesapeake Bay impact occur stratigraphically above the Popigai cpx spherules at Site 612 and core RC9-58. We found no definite evidence of a δ^13C anomaly associated with the North American microtektite layer, though further studies are warranted. High-resolution bulk-carbonate and benthic foraminiferal δ^18O records show no global temperature change associated with the cpx spherule or North American microtektite layers.

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The Late Eocene Earth—Hothouse, Icehouse, and Impacts
Geological Society of America

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