GLACIAL LAKE SCHOHARIE: AN INVESTIGATIVE STUDY OF GLACIOLACUSTRINE LITHOFACIES IN CAVES, HELDERBERG PLATEAU, CENTRAL NEW YORK

摘要

The glacially deranged karst topography of the Helderberg Plateau, central New York, contains glaciolacustrine lithofacies deposited at the end of the Wisconsin glaciation. Eight pre-glacial caves (Barrack Zourie Cave, McFail's Cave, Howe Caverns, Secret Caverns, Bensons Cave,Gage Caverns, Schoharie Caverns, and Caboose Cave), containing a unique sediment section, are located within the footprint of Glacial Lake Schoharie, Schoharie County. The lithofacies consist of three individual facies, stratigraphically uniform, with the middle facies in sharp contact with the facies directly above and below. This assemblage displays a similar stratigraphic sequence from bottom to top: tan/white to light-grey, very thinly bedded, silts and clays, rich in calcite, overlain by poorly sorted, matrix-supported gravels, in turn overlain by dark-brown very thinly bedded silts and clays. A post-glacial cave within the lake's footprint (Westfall Spring Cave) and a nearby pre-glacial cave outside the footprint (Knox Cave) were found to lack these lithofacies. The tan/white to light-grey sediment facies is interpreted to be a glacial rock flour deposited under stagnant lake conditions that limited fine-grained calcite particle dissolution. The overlying gravel facies were emplaced during lake termination and reestablishment of turbulent epigenic flow in the eight stream caves. The more recent dark-brown facies is perhaps soil-loss deposition following European settlement. Initial interpretations hypothesized that the deposits were laid down under ice-cover conditions, but similar deposits were not found in other glaciated cave settings in New York. The results presented here explain why the unusual tan/white and light-grey glaciolacustrine facies are not found in other caves in the glaciated central New York region, as those areas were not subject to inundation by glacial lake water.