Knowledge Bank

A study of the molluscan fauna of the Sunbeam Prairie lacustrine deposit of Darke County, OH combined with palynologic data from an earlier study provide an interpretation of the Late Wisconsinan history. Early Sunbeam Prairie Lake had a molluscan fauna dominated by Gyraulus parvus and Valvata lewisi. Valvata tricarinata, Fossaria obrussa, Gyraulus parvus, and Pisidium casertanum were dominant members of the diverse molluscan assemblage that existed during marl deposition, suggesting changing littoral conditions. The appearance of amnicolids and scattered terrestrial gastropods in the upper part of the marl section indicates a shallowing of water and an increase in aquatic vegetation. The latest stage of Sunbeam Prairie Lake was characterized by gradual infilling with humic sediments, reduction of the aquatic molluscan fauna, and an increase in the terrestrial gastropod fauna. A comparison of our molluscan data to earlier pollen data for the deposit provides inconclusive support for the recognition of the Two Creeks interval in pollen diagrams of central Indiana and Ohio.