Biostratigraphy and Paleoecology of Diagnostic Invertebrates and Vertebrates from the Type Locality of the Oligocene Rosefield Marl Beds, Louisiana
G. L. Stringer1, S. Q. Breard2, and M. Kontrovitz1
1Department of Geosciences, The
University of Louisiana at Monroe, Monroe, LA
2Applied Biostratigraphix, Inc., Houston, TX
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 50 species, including the
macroscopic foraminifer Lepidocyclina supera, correlating 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 interpretational
reliability.
AAPG Search and Discovery Article #90901©2001 GCAGS, Annual Meeting, Shreveport, Louisiana