A seismically induced onshore surge deposit at the KPg boundary, North Dakota
DePalma, R.A.; Smit, J.; Burnham, D.A.; Kuiper, K.; Manning, P.L.; Oleinik, A.; Larson, P.; Maurrasse, F.J.; Vellekoop, J.; Richards, M.A.; Gurche, L.; Alvarez, W. (2019). A seismically induced onshore surge deposit at the KPg boundary, North Dakota. Proc. Natl. Acad. Sci. U.S.A. 116(17): 8190-8199. https://dx.doi.org/10.1073/pnas.1817407116 In: Proceedings of the National Academy of Sciences of the United States of America. The Academy: Washington, D.C.. ISSN 0027-8424; e-ISSN 1091-6490, more |   |
| Keyword | | | Author keywords | KPg extinction; Chicxulub; Hell Creek Formation; tsunami; impact |
| Authors | | Top | - DePalma, R.A.
- Smit, J.
- Burnham, D.A.
- Kuiper, K.
| - Manning, P.L.
- Oleinik, A.
- Larson, P.
- Maurrasse, F.J.
| - Vellekoop, J., more
- Richards, M.A.
- Gurche, L.
- Alvarez, W.
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| Abstract | The most immediate effects of the terminal-Cretaceous Chicxulub impact, essential to understanding the global-scale environmental and biotic collapses that mark the Cretaceous-Paleogene extinction, are poorly resolved despite extensive previous work. Here, we help to resolve this by describing a rapidly emplaced, highenergy onshore surge deposit from the terrestrial Hell Creek Formation in Montana. Associated ejecta and a cap of iridium-rich impactite reveal that its emplacement coincided with the Chicxulub event. Acipenseriform fish, densely packed in the deposit, contain ejecta spherules in their gills and were buried by an inland-directed surge that inundated a deeply incised river channel before accretion of the fine-grained impactite. Although this deposit displays all of the physical characteristics of a tsunami runup, the timing (<1 hour postimpact) is instead consistent with the arrival of strong seismic waves from the magnitude M-w similar to 10 to 11 earthquake generated by the Chicxulub impact, identifying a seismically coupled seiche inundation as the likely cause. Our findings present high-resolution chronology of the immediate aftereffects of the Chicxulub impact event in the Western Interior, and report an impact-triggered onshore mix of marine and terrestrial sedimentation-potentially a significant advancement for eventually resolving both the complex dynamics of debris ejection and the full nature and extent of biotic disruptions that took place in the first moments postimpact. |
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