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1 March 2012 Notes on the Geology of the Shawangunk Ridge on the Mohonk Preserve and Environs
Howard R. Feldman, John A. Smoliga, Brian A. Feldman
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The Shawangunk Formation, a quartz pebble conglomerate of Middle Silurian age, extends from the lower mid-Hudson Valley through New Jersey and into Pennsylvania. It overlies the Ordovician Martinsburg Formation, which is composed of shales and graywackes. The Martinsburg crops out on the Shawangunk Ridge and is quarried by Mohonk Mountain House in New Paltz, NY, in order to prevent erosion and provide good footing on the trails. The quarry, locally known as the “Shale Bank”, contains a diverse marine fauna of brachiopods, crinoids, bivalves, ostracods, corals, trilobites, and conulariids. In this community, the partition of feeding niches results in a reduced competitive trophic structure and therefore increased community stability. Within the Shawangunk Formation, there are rare “pods”, domelike structures that are filled with a gray matrix of rounded quartz grains supported by a clay matrix. The pods appeared to have formed along cleavage surfaces. A previously unrecognized metal sulfide deposit has been discovered in the conglomerate along Eagle Cliff. This deposit consists of the Fe-sulfide phases pyrite and marcasite, lesser amounts of the Cu-Fe sulfide chalcopyrite, and trace amounts of anglesite (Pb-sulfate). An outcrop of the Middle Devonian Onondaga Limestone in the Port Jervis Trough contains large crinoid columnals, the coral Amplexiphyllum, trilobite fragments, and the brachiopod Levenea subcarinata. The Onondaga in this area is part of a carbonate ramp that was a shallow carbonate shelf in the Helderberg-Coxsackie area, a thick accumulation of shelf-margin bryozoan bafflestone between Leeds and Saugerties, and an even thicker accumulation of sparse to packed biocalcisiltites deposited on a carbonate ramp dipping southward into the Port Jervis area.

Howard R. Feldman, John A. Smoliga, and Brian A. Feldman "Notes on the Geology of the Shawangunk Ridge on the Mohonk Preserve and Environs," Northeastern Naturalist 19(sp6), 3-12, (1 March 2012).
Published: 1 March 2012
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