Paleoenvironments and their Control of Acritarch Distribution: Silurian of East-Central Pennsylvania

Abstract

ABSTRACT Analyses of lithologic and stratigraphic relations in certain Lower and Middle Silurian units of eastern and central Pennsylvania have led to a subdivision of these rocks into four principal environmental facies: open marine, barrier bar, tidal flat-lagoonal (all in the Clinton), and fluvial (Tuscarora-Shawangunk). The distribution of acritarchs (a group of acid-insoluble microfossils with unknown affinities) in fine-grained deposits of these facies supports the following conclusions: (1) The acritarchs are confined to depositional areas continuously or intermittently open to marine waters and do not occur in the fluvial deposits. (2) The degree of preservation reflects the depositional environment--forms from deeper open marine sediments are generally well preserved, while those in n ar-shore and transitional facies are usually fragmentary and abraded. (3) Acritarch distribution is in part controlled by directions of prevailing currents. These relations suggest that acritarchs might be exploited more by sedimentary geologists in reconstructing ancient depositional environments, especially in areas where outcrops are poorly exposed, scarce in macrofossils, or lacking other criteria ordinarily used in interpreting paleoenvironments.