Cephalopods from the Cretaceous-Paleogene (K-Pg) Boundary Interval on the Brazos River, Texas, and Extinction of the Ammonites

Abstract

We report on new collections of cephalopods (ammonites and nautilids) from the Cretaceous-Paleogene (K-Pg) successions of the Corsicana and Kincaid formations exposed along the Brazos River in Falls County, Texas. An abundant fauna of eight species comprising four genera of ammonites is described from the Corsicana Formation, including Discoscaphites mullinaxorum n. sp. The presence of abundant aptychi (probably lower jaws) of Discoscaphites and Eubaculites, as well as juvenile specimens, indicates a living population that experienced little postmortem drift. The lytoceratid genus Gaudryceras is also reported for the first time from the Brazos River area. Presence of the index taxon Discoscaphites iris (Conrad, 1858) indicates that the fauna belongs to the D. iris Range Zone, the highest ammonite range zone in North America. Correlation with new and existing microfossil data indicates that the fauna represents the uppermost Maastrichtian, and comparison with published records further suggests that this is the most diverse D. iris Zone fauna yet reported from the

Geographic and temporal morphological stasis in the latest Cretaceous ammonoid Discoscaphites iris from the U.S. Gulf and Atlantic Coastal Plains

“…It also coincides with planktonic foraminiferal zones CF1 (Plummerita hantkeninoides), CF2, and possibly the upper part of CF3 (Pseudoguembelina hariaensis) (Abramovich et al 2011;Witts et al 2021). These biostratigraphic markers all overlap with the upper part of magnetochron C30N and overlying chron C29R (Landman et al 2004a;Abramovich et al 2011;Larina et al 2016;Witts et al 2021), the base of which is currently dated at ∼340-400 ka before the K/Pg boundary (66.04 Ma) (Fig. 2) (Batenburg et al 2012;Thibault 2018;Ogg 2020).…”

“…To date, Discoscaphites iris has been recorded from >15 localities across the ACP and GCP (see summary in Witts et al 2021). The abundance of specimens at each locality varies due to local differences in preservation and differing sampling intensities.…”

“…Specimens are reposited in the collections of the American Museum of Natural History (Division of Paleontology) (AMNH), Department of Earth and Planetary Sciences, University of New Mexico (UNM), U.S. Geological Survey (USGS), Monmouth County Amateur Paleontological Society (MAPS), and the Museum at the Black Hills Institute of Geological Research (MBHI) (full details for each specimen are available in Supplementary Dataset 1). The stratigraphy of most of the localities these specimens are derived from is detailed in the literature (e.g., Landman et al 2004bLandman et al , 2007Larina et al 2016;Witts et al 2018Witts et al , 2021 and briefly reviewed in the following sections; a summary of locality information is provided in Table 1.…”

“…Texas.-Material comes from outcrops along the Brazos River and its tributaries in Falls County that preserve a continuous and expanded record across the K/Pg boundary (Witts et al 2021). Discoscaphites iris were collected from AMNH localities 3620 (Darting Minnow Creek) and 3621 (Cottonmouth Creek), which both contain 1.5to 2-m-thick outcrops of the upper Corsicana Formation, a fossiliferous dark mudstone.…”

Massive perturbations to atmospheric sulfur in the aftermath of the Chicxulub impact

“…The S-MIF signal is archived in rocks of the US Gulf Coastal Plain, ∼1,300 km from the impact site. Upper Cretaceous and lower Paleogene sediments exposed along the Brazos River and its tributaries in Falls County, Texas, comprise an exceptionally well-preserved and continuous succession across the K–Pg boundary ( 24 – 27 ), reflecting open marine deposition ∼100 km from shore ( 28 ) and close to the mouth of the remnant Western Interior Seaway. Marine muds of the Cretaceous Corsicana Formation are capped by clastic deposits interpreted to be the result of postimpact seismicity, tsunami activity, storms, and atmospheric fallout and contain abundant carbonate lapilli and ejecta spherules ( 28 , 29 ).…”