BREARD, S. Q., Biostratigraphix, Inc., Houston, TX; and GARY STRINGER*, Northeast Louisiana University, Monroe, LA
Abstract: Integrated Paleoecology and Marine Vertebrate Fauna of the Stone City Formation (Middle Eocene), Brazos River Section, Texas
Marine vertebrate faunas, including sharks, rays, teleosts, and reptiles, have been collected from two horizons in the Middle Eocene (Claiborne) Stone City Formation of southeast Texas. Extensive collecting and recent advances, especially in the study of otoliths and foraminifera, provide for additional evaluation of paleoecological parameters. Otolith-based teleosts are dominated by neritic taxa such as sciaenids and ophidiids, while skeletal-based teleosts include catfish, barracuda, mackerel, and gar. Selachians include sand, tiger, and catsharks as well as rays and sawfish. Least common are reptiles, represented by crocodiles and turtles. Vertebrate diversity is 50 taxa, the richest marine fauna yet recorded from the Gulf Coast Middle Eocene. Vertebrates were collected from the top of the Main Glauconite bed and a thin lag zone 3 m below. The lower fauna (Assemblage A) is rich in tiger and sand sharks, eagle rays, plus estuarine elements, such as catfish, sawfish, and softshell turtle. The mixture of estuarine vertebrates with abundant marine mollusks suggests a possible tidal channel emptying into nearshore marine. The upper fauna (Assemblage B) is dominated by a rich, moderately diverse fish fauna with scarce rays and sharks. An assemblage with sciaenids, ophidiids, and myripristids with abundant, diverse mollusks, especially infaunal pelecypods, suggests a fully marine, but nearshore setting of 25 m or less. Microfauna includes 33 benthic foraminifera and 15 ostracode species. The shallow nature of this assemblage, plus the lack of planktonic foraminifera, suggests an absence of open ocean currents. Macrofaunal and microfaunal paleoecology supports the shallow neritic to estuarine conditions suggested by vertebrate parameters. The Main Glauconite bed was deposited in an open marine bay or lagoon which was separated from ocean currents by some barrier, possibly an offshore marine sandbar complex.
AAPG Search and Discovery Article #90924©1999 GCAGS Annual Meeting Lafayette, Louisiana