Abstract
The lower Clayton Limestone Unit of the Midway Group (Paleocene) has been exposed as a result of highway stabilization in response to soft-sediment slumping near Malvern, Arkansas. This exposure contains phosphatic, sandy-pebble lag deposits with an abundance of chondrichthyan microteeth (<0.5cm) and occurs directly adjacent and updip from a previously identified K-Pg boundary section exposed in the Ouachita River. Chondrichthyan teeth in this assemblage belong to at least 10 taxa including: Odontaspis winkleri, Carcharias cf. C. whitei, Carcharias sp., Palaeohypotodus rutori, Palaeogaleus vincenti, Pseudoginglymostoma sp., Hypolophites hutchinsi, Dasyatis cf. D. hexagonalis, Myliodasyatis sp., and Raja sp. Only three of these species have been previously reported higher in the stratigraphic section of the Clayton Limestone Unit of the Midway Group in the Gulf Coastal Plain of Arkansas. These chondrichthyans co-occur with remains of osteichthyans, gharials, crabs, oysters, foraminifera, and Thalassinoides burrows that are indicative of marginal-shallow marine environments. The remains of large, pelagic chondrichthyans, taxa with deep water affinities, and Maastrichtian species are noticeably absent and further support the presence of a marginal-shallow marine paleoenvironment near Malvern, Arkansas, during the Paleocene. Taxa from this lower Clayton Limestone Unit exposure provide a means to: 1) assess chondrichthyan diversity across a continuous K-Pg boundary section in the Malvern region and Gulf Coastal Plain of southwestern Arkansas, 2) compare this Gulf Coastal Plain assemblage to those seen in continuous and composite K-Pg stratigraphic sections at local, regional, and global scales, and 3) evaluate marginal-shallow marine chondrichthyan extinction and faunal turnover at a proximal location nearly equal 1500km from the Chicxulub, Mexico, K-Pg impact site.