GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 8-6
Presentation Time: 9:15 AM


IRIZARRY, Kayla M.1, WITTS, James D.2, GARB, Matthew P.3, LANDMAN, Neil H.4 and DANILOVA, Anastasia3, (1)Geosciences, Pennsylvania State University, 201 Old Main, University Park, PA 16802, (2)Earth and Planetary Sciences, University of New Mexico, Northrop Hall, 221 Yale Blvd NE, Albuquerque, NM 87131, (3)Earth and Environmental Sciences, Brooklyn College, 2900 Bedford Ave, Brooklyn, NY 11210, (4)Division of Paleontology (Invertebrates), American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024-5192

Approximately 66 million years ago the Chicxulub bolide impact triggered global environmental perturbations, leading to a mass extinction event at the Cretaceous-Paleogene (K-Pg) boundary. Proximal to the crater in the Gulf of Mexico, the impact likely caused mass wasting due to shelf collapse and/or seismic activity, tsunamis, storms, and rapid deposition and reworking of ejecta. K-Pg boundary outcrops on the U.S Gulf Coastal Plain may thus provide a detailed record of depositional environments and the effects of impact-related processes on marine biota. Along the Brazos River, Texas, the K-Pg boundary occurs between the fossiliferous late Maastrichtian Corsicana Formation and Danian Kincaid Formation. Previous authors have described an event deposit composed of three units coincident with the K-Pg transition. Unit A is composed of shell hash in a muddy matrix with mudstone rip-ups. The overlying Unit B is a semi-laminated shell hash, containing impact ejecta, in a clay matrix. Both units are fossiliferous and contain well-preserved mollusks, the subject of this study. The uppermost Unit C is represented by unfossiliferous cross-bedded sandstones and interbedded siltstones. We conducted a faunal analysis to elucidate depositional processes of these units using bulk sediment and systematically collected fossil samples. Faunal data from Unit A, Unit B and the Corsicana Formation were evaluated relative to one another using multivariate analysis (non-parametric multidimensional scaling – NMDS), diversity estimates, and quantitative analyses of molluscan modes of life. High-resolution stratigraphic logs, grain size analysis, and point counts provide additional paleoenvironmental information. Data suggest that Units 1 and 2 represent allochthonous deposition, with faunal distributions different to the underlying Corsicana Formation, such as the sudden appearance and abundance of the bivalve Vetericardiella webbervillensis. A two-fold increase in gastropod species richness in Unit 2 also suggests derivation from a distinctly different paleoenvironment. Unit 1 is considered to be the result of localized mass flows related to seismic activity following the Chicxulub impact. Unit 2 may be the result of higher energy depositional process, such as a tsunami or the effects of large post-impact storms.