Lithofacies-influenced ostracod associations in the middle Ordovician Bromide Formation, Oklahoma, USA

Abstract. The Bromide Formation of southern Oklahoma was deposited in a linear basin and on the adjoining platform during a marine transgressive-regressive event in the middle Ordovician. The formation displays wide lateral (platform-basin) and vertical (transgressive-regressive) sedimentary facies variation. From the prolific and diverse ostracod fauna present in the Bromide Formation two lithofaeies-related ostracod associations can be defined: a geographically and stratigraphically widespread Anisocyamus Association, occupying subtidally deposited marine sediments: and a Leperditella Association, which is restricted to marginal marine environments. The ostracods of the Bromide Formation demonstrate that the group can be utilized in the Ordovician as a tool to help establish palaeoenvironments and differentiate palaeoshoreline.