T109 Impact Cratering in the Solar System: Remembering Nadine Barlow and H. Jay Melosh

Monday, 11 October 2021
1:30 PM - 5:30 PM
Portland Ballroom 252 (Hybrid Room)

ECOLOGICAL STATUS AT THE TIME OF IMPACT: EVIDENCE OF DINOSAURIA AT THE KPG BOUNDARY, HELL CREEK FORMATION, NORTH DAKOTA

Paper number: T109-16
Program: Technical Sessions
Time: 5:00 PM – 5:15 PM

Authors

Abstract

The intensity and tempo of the massive ecological failure post-Chicxulub impact has been the subject of much debate. While there is little question that ~75% of species were driven to extinction, it has been proposed that the Dinosauria, the terrestrial megafauna of the Mesozoic, were already in decline. The absence of reported dinosaur fossils in the uppermost Cretaceous strata of the U.S. Western Interior, the so-called “3-meter gap”, has led to the suggestion that dinosaurs were in major decline or extinct prior to the impact event. Precise reconstruction of these terminal-Cretaceous ecosystems, including the dinosaurs, is critical if we are to ascertain the severity, abruptness, and timing of the mass-extinction at (or near) the Cretaceous-Paleogene boundary. Here, we report new evidence from Tanis, a Chicxulub impact-triggered surge deposit in the Hell Creek Formation, U.S.A., that supports a thriving ecology up to the last minutes of the Cretaceous. The rapidly emplaced sediment package constitutes a “bioclastic time-capsule” that preserves a condensed association of flora and fauna from the first hours after the impact event. The deposit therefore provides an unparalleled assessment of Hell Creek life that comprises abundant fragile or soft-bodied remains that are typically not preserved in the Hell Creek Formation sediments. Ceratopsian remains, including fossilized osseous and soft-tissue, indicate the presence of Dinosauria until immediately prior to impact. Feathery integument from within the deposit (c.f. Theropoda), and a diverse assemblage of trackways (both theropod and ornithischian dinosaur) in the paleosurface immediately underlying the surge deposit, further suggest an abundant and speciose terminal-Cretaceous biome. Additional fossils from the underlying paleosurface include an abundance of flowering plants and invertebrate burrow morphologies, supporting robust ecological fitness immediately prior to the Chicxulub impact. The examination of the plant and animal assemblage at Tanis will enable an important gap to be filled in understanding the terminal-Cretaceous biodiversity of the uppermost Hell Creek Formation at the moment of impact. Ultimately, Tanis will provide a more complete understanding of the complex interplay between the Chicxulub impact event and the resulting mass-extinction that decimated Earth’s biomes.

Geological Society of America Abstracts with Programs. Vol. 53, No. 6

doi: 10.1130/abs/2021AM-368267

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