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

Sylvester Q. Breard, Gary L. Stringer

A diverse assemblage of marine vertebrate fossils from the exposures of the Tullos Member, Yazoo Clay (Jackson Group, Late Eocene) from Caldwell Parish, Louisiana revealed 66 vertebrate species, including 11 shark and five ray species, 11 non-otolith teleosts, 34 otolith-based teleosts, three reptiles, and two mammals. Over 8000 specimens have been collected making it possible to discuss paleoenvironmental conditions.

The Copenhagen fauna, in comparison to previously described Jackson faunas in Louisiana, Arkansas, Mississippi, Alabama, and Georgia, has the greatest abundance and diversity of species. 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 suggest that the fauna accumulated in open marine conditions. Paleoecologic comparisons to extant species support an interpretation of an inner shelf low in the section, deepening to middle shelf (100 to 150 feet deep) upsection as the pelagics increase.

The Yazoo Clay, when compared to the Moodys Branch Formation, has an impoverished invertebrate macrofauna of oysters, corals, crabs, gooseneck barnacles, comatulid crinoids, and rare pelecypods and gastropods. However, the foraminiferal and ostracode microfaunas are more diverse and abundant in the Yazoo Clay, supporting an interpretation of deposition in deeper waters as suggested by vertebrate distribution. The Yazoo Clay vertebrate fauna 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.

AAPG Search and Discovery Article #90955©1995 GCAGS 45th Annual Meeting and Gulf Section SEPM, Baton Rouge, Louisiana