108 The Cretaceous-Paleogene (K-Pg) Boundary Interval: From Large-Scale Geological Events to Mass Extinction Mechanisms (Posters)

The Cretaceous-Paleogene boundary interval witnessed extreme geological events: the Chicxulub impact and Deccan Traps volcanism, and a biological catastrophe. New proxy-records, coupled with numerical modelling, unravel the mechanisms driving the environmental change and mass extinction.

Monday, 20 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1

JAWS! Ammonite Kill Layer Preserved in a K–Pg Event Deposit in Kemper County, Mississippi USA

Paper number: 108-2
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

The Chicxulub Impact (~66 Ma) is widely accepted as the main driver of the Cretaceous–Paleogene (K–Pg) mass extinction. At Wahalak Creek, northeastern Mississippi (~1500km from the crater), shallow‐marine deposits record a detailed response to this event. The uppermost Prairie Bluff Chalk formation represents quiet, below‐storm‐wave‐base conditions prior to impact, whereas the base of the overlying Clayton Formation preserves three distinct, impact‐related channels: (1) a rip‐up channel containing reworked pebble to cobble-sized chalk clasts indicative of a high energy event such as a tsunami, (2) a spherule‐rich bed formed by ejecta, and (3) a “jaw channel” packed with ammonite jaws (Eubaculites and Discoscaphites), chalk rip‐ups, fish bones and scales, oysters, and lignitic plant debris. The jaws are well preserved and retain delicate chitinous and calcitic layers. They are mostly articulated, oriented in folio rather than butterfly position, including at least one buccal mass with associated upper and lower jaws. There is a wide range of sizes (lengths range from 4mm to 12mm), comprising juveniles and adults. This suggests rapid burial following sudden death. The jaw channel contains granule-sized Prairie Bluff rip-up clasts and terrestrial lignite within the marine Clayton sediments. This further supports tsunami‐driven transport of sediment from both land and farther offshore. Thus, we interpret the ammonite‐rich jaw channel as a post‐impact marine kill layer, capturing a catastrophic die-off within a short period of time after the Chicxulub event.

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

doi: 10.1130/abs/2025AM-414410

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