Abstract

An onshore-offshore model for the distribution of microfossils (foraminifers, ostracodes, conodonts, and radiolarians) is presented for Late Carboniferous-Lower Permian cyclothemic sedimentary sequences of the North American Mid-Continent. Nearshore marginal marine strata are characterized by the low diversity of microfossil assemblages dominated by Geisina ostracodes, no conodonts, and rare Thurammina foraminifers. Nearshore normal marine strata contain the Cavellina ostracode biofacies, Adetognathus conodont biofacies, and encrusting foraminifers along with Ammodiscus cf. A. semiconstrictus var. regularis. Intermediate depth (open mid-shelf) strata contain the Amphissites ostracode biofacies, Idiognathodus-Streptognathodus conodont biofacies, Tetrataxis, Globivalvulina, large paleotextularids (Climacammina, Deckerella), endothyranellids (Endothyra, Endothyranella), Ammobaculites, and fusulinaceans. Deep-shelf marine strata contain a high-diversity pelagic microfossil assemblage but a reduced diversity benthic microfossil assemblage containing the Mammoides and Healdia ostracode biofacies, Gondolella-Idioprioniodus conodont biofacies, Ammodiscus-Reophax foraminiferal biofacies, and abundant radiolarians.