LITHOFACIES-INFLUENCED OSTRACOD ASSOCIATIONS IN THE MIDDLE ORDOVICIANBROMIDE FORMATION, OKLAHOMA, USA

The Bromide Formation of southern Oklahoma was deposited in a linear b asin and on the adjoining platform during a marine transgressive-regre ssive event in the middle Ordovician. The Formation displays wide late ral (platform-basin) and vertical (transgressive-regressive) sedimenta ry Facies variation. From the prolific and diverse ostracod fauna pres ent in the Bromide Formation two lithofacies-related ostracod associat ions can be defined: a geographically and stratigraphically widespread Anisocyamus Association, occupying subtidally deposited marine sedime nts; and a Leperditella Association, which is restricted to marginal m arine environments. The ostracods oi the Bromide Formation demonstrate that the group can be utilized in the Ordovician as a tool to help es tablish palaeoenvironments and differentiate palaeoshoreline.