Paleoenvironment of a Diverse Marine Vertebrate Fauna from the Yazoo Clay (Late Eocene) at Copenhagen, Caldwell Parish, Louisiana: ABSTRACT

Abstract

ABSTRACT The vertebrate fauna from the exposures of the Tullos Member, Yazoo Clay (Jackson Group, Late Eocene) at Copenhagen represents the most diverse assemblage documented from Louisiana and is one of the richest faunas known from the Tertiary of the Gulf coastal plain. Studies of the diverse assemblage of marine vertebrates revealed 70 vertebrate species, including 14 sharks, 5 rays, 46 teleosts (34 based on otoliths), 3 reptiles, and 2 mammals. Over 8,000 specimens have been collected making paleoenvironmental interpretations possible. The Copenhagen fauna has the greatest abundance and diversity of vertebrate species in comparison to previously described Jackson faunas in Louisiana, Texas, Arkansas, Mississippi, Alabama, Georgia, and Florida. Open marine conditions are suggested by the occurrence and variety of open-water and pelagic species such as the sharks Isurus, Abdounia, and Alopias, teleosts such as Bregmaceros, Cylindracanthus, Myripristis, Sphyraena, and Xiphiorhynchus, and cetaceans. Paleoecologic comparisons to extant species support an interpretation of an inner shelf deepening to middle shelf upsection as pelagics increase. The Yazoo Clay's invertebrate macrofauna which consisted mainly of oysters, corals, crabs, gooseneck barnacles, comatulid crinoids, and other rare bivalves and gastropods is not especially helpful for paleoecologic comparisons to the vertebrate fauna. However, diverse and abundant foraminiferal and ostracode microfaunas in the Yazoo Clay support an interpretation of deposition in middle shelf waters as suggested by the vertebrate distribution.