ABSTRACT

The type locality of the Oligocene Rosefield Marl Beds (Mosley Hill Formation, Catahoula Parish, Louisiana) has been collected since the early 1900's. However, no comprehensive faunal studies have been completed, and the marine vertebrate fauna is essentially unknown. This investigation describes both invertebrate and vertebrate fossil assemblages from the Rosefield Marl Beds and evaluates their biostratigraphical and paleoecological significance. Major invertebrate groups include foraminifera, ostracodes, and bivalves while vertebrates include cartilaginous and bony fishes. Bulk sampling and systematic surface collecting produced several thousand specimens.

The paleoecological parameters for the beds were determined independently by analyzing various fossil groups. These trends were compared and synthesized to produce a paleoenvironmental interpretation. Foraminiferal analysis of the coquina and overlying clay layers reveals a diverse assemblage of over 70 species including the macroscopic foraminifer Lepidocyclina supera that correlates the Rosefield with the Byram Formation of Mississippi. Comparison of both samples, each having deep inner to middle neritic taxa, indicates deepening during deposition of the clays. The ostracodes include forms typical of fully marine, warm-water environments from the middle to lower middle continental shelf. The bony fishes (based on skeletal remains and otoliths) indicate a neritic, tropical to temperate environment (inner shelf to shallow middle shelf) with a muddy substrate. The cartilaginous fishes (based on skeletal remains) signified a shallow marine environment with some indication of more openocean conditions. The utilization of multiple groups of invertebrate and vertebrate assemblages in paleoenvironmental determinations appears to be highly advantageous for increasing the reliability of the reconstructions.