Possible Implications for Silurian Paleogeography from Phytoplankton Assemblages of the Rose Hill and Tuscarora Formations of Pennsylvania

Silurian phytoplankton and chitinozoans were found in great abundance in shales of the upper Lower Silurian Rose Hill Formation from an outcrop near Millers-town, Pennsylvania. Two new acritarch species and one new chitinozoan species are described. These are Baltisphaeridium maravillosum, B. monterrosae, and Conochitina? monterrosae.

When the composition of presently known, approximately mid-Silurian acritarch assemblages in the broad area bordering the Atlantic is plotted, two distinct phytoplankton provinces are conspicuous: (1) the Deunffia furcata province and (2) Veryhachium? carminae province. These two biofacies appear to be not directly controlled by lithofacies differences and not due to noncontemporaneity of the assemblages compared. It is suggested that they reflect differences in paleoclimate, the D. furcata province being characteristic of the warmer climate, and the V.? carminae province related to a cooler climate.