Organic-walled Microphytoplankton Abundance and Strategraphic Distribution from the Middle Devonian Columbus and Delaware Limestones of the Hamilton Quarry, Marion County, Ohio

Author Institution: Department of Geology, Central Michigan University ; Cities Service Company, Research LaboratoryForty-three species representing 25 genera of organic-walled microphytoplankton were recovered from a 28.04—m thick section of the Middle Devonian Columbus and Delaware Limestones of central Ohio, USA. This assemblage compares closely with other Middle Devonian microphytoplankton assemblages from North America, indicating their potential use as biostratigraphic guides. Their stratigraphic distribution is probably related in part, to the Columbus-Delaware carbonate lithofacies. The organic-walled microfossils are neither abundant nor well-preserved in the porous dolomite near the bottom of the Columbus Limestone. This poor preservation is probably a consequence of dolomitization, while their paucity may reflect an original shallowwater environment of restricted circulation. Such an environment may not have been conducive to plankton growth. The microphytoplankton assemblage increases in numerical abundance and diversity in the overlying non-dolomitized carbonates, particularly the finer-grained limestones