Faunal and stratigraphic analysis of the basal Cretaceous-Paleogene (K-Pg) boundary event deposits, Brazos River, Texas, USA

Kayla Irizarry*, James D Witts, M.P. Garb, Anastasia Rashkova, Neil H Landman, Mark E. Patzkowsky

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

1 Citation (Scopus)


A bolide impact ~66 million years ago near Chicxulub, Yucatan Peninsula, Mexico triggered environmental perturbations on a global scale, leading to mass extinction at the Cretaceous-Paleogene (K-Pg) boundary. Outcrops on the U.S Gulf Coastal Plain that contain the K-Pg boundary provide a detailed record of environments across this critical transition, but questions remain about the nature and timing of depositional processes that affected the region at the time of impact and mass extinction. We present a new study of coarse-grained K-Pg ‘event deposits’ located at the contact between the fossiliferous Cretaceous Corsicana Formation and the Danian Kincaid Formation, and which outcrop in tributaries along the Brazos River, Falls County, Texas. A generalized succession can be recognized in these deposits. We sampled the basal-most unconsolidated units, Unit I and Unit II, and the Corsicana Formation for macrofaunal and sedimentological data. Unit I is interpreted as a debrite, deposited by a medium – high strength cohesive debris flow initiated by ground shaking and intense seismic activity after the Chicxulub impact. Macrofossil analysis shows a mostly locally derived assemblage. Grain size analysis of non‑carbonate portions of the matrix indicates an identical mean grain size to that of the underlying Corsicana Formation. The chaotic fabric, boulder sized clasts, and muddy matrix support the interpretation of deposition via cohesive debris flow. Unit II is also interpreted as a debrite, deposited by a low-medium strength cohesive debris flow. We propose that this unit was initiated by wave energy from a tsunami or local shelf collapse immediately following impact. Macrofossil analysis of Unit II shows an increase in fauna with a predatory/carnivorous lifestyle, which are interpreted as allochthonous elements derived from shoreward environments and transported across the shelf. The high mud content of the matrix and abrupt pinching out on topographic highs support the interpretation of deposition via a cohesive debris flow for Unit II. Our results indicate that sediment flows were a major driver of mass sediment transport in proximal locations directly following the Chicxulub impact.
Original languageEnglish
Article number111334
Number of pages64
JournalPalaeogeography, Palaeoclimatology, Palaeoecology
Early online date1 Dec 2022
Publication statusPublished - 15 Jan 2023

Bibliographical note

Funding Information:
We are hugely grateful to Mr. and Mrs. Ronnie and Jackie Mullinax (Brazos Rose Ranch) for allowing access to their property for fieldwork, and their generous hospitality. We thank Tom Yancey, Carlie Pietsch, Ekaterina Larina, Remy Rovelli, Paul Renne, Isabel Fendley, Linda Ivany, Chris Junium, Ben Uveges, and Shibajyoti Das for useful discussions and assistance in the field. At the AMNH, we thank Mariah Slovacek for assistance with specimen preparation and SEM analysis, and Steve Thurston for assistance with figures. At Brooklyn College we thank Shannon Brophy, Jone Naujokaityte for useful discussions, and Natalie Dastas for her mentorship and access to petrographic microscopes. At Penn State we thank Claire Cleveland and Heather Jones for their feedback on preliminary figures and interpretations. This research was funded by the Louis Stokes Alliance for Minority Participation and the National Science Foundation , the Rosen Fellowship at Brooklyn College , and a Lerner-Gray Postdoctoral Research Fellowship at the American Museum of Natural History and Richard Gilder Graduate School awarded to James Witts . Additional funding was provided by the Norman Newell Fund (AMNH).

Publisher Copyright:
© 2022 Elsevier B.V.


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