189 Paleontology, Paleoecology/Taphonomy (Posters)

Tuesday, 21 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1

The Nature of the Jurassic-Cretaceous Boundary Transition: Palaeoecological Change within the Stony Creek Formation of the Great Valley Sequence (California, USA)

Paper number: 189-9
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

Abstract

The Jurassic-Cretaceous (JK) boundary may denote an interval of significant extinction; however, a lack of available stratigraphic sections has made this boundary challenging to study. The JK boundary is recorded in the Stony Creek Formation (Great Valley Sequence). Outcrops are comprised of shales punctuated by more resistant beds of shale, sandstone, and conglomerate representative of a forearc basin with gradual background sedimentation punctuated by abrupt sediment flows. For this study, we examined outcrops along several kilometers of McCarty Creek in Tehama County. Based on prior work and our field identification of species of the bivalve Buchia, this interval represents the transition through the JK boundary. We sampled a relatively fossiliferous 30-m section in which we found late Tithonian Buchia species. Samples were taken at half-meter intervals as well as at every resistant bed. Preliminary observations indicate an uneven distribution of fossils with some intervals being extraordinarily fossiliferous. Fossils of Buchia are by far the most abundant, although belemnites, ammonites, burrows, and plant material were all observed in our surveys of the creek outcrops. Further processing of the samples will elucidate changes in species compositions and relationships with environmental factors. Identification of Buchia species will determine where and how the sampled section crosses the JK boundary. We plan to return to sample more in the coming months with the goal of creating a composite section with high resolution biostratigraphic data to further interpret paleoecological change across the JK boundary.

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

doi: 10.1130/abs/2025AM-412327

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