NAUTILOIDS FROM NORTHERN NEW JERSEY GLACIAL ERRATICS: EVIDENCE FOR LAG DEPOSIT FORMATION IN THE RICKARD HILL FACIES (LOWER DEVONIAN-LATE EMSIAN), HELDERBERG MOUNTAIN REGION, NEW YORK

Glacial erratics belonging to the Rickard Hill facies (RHf) of the Saugerties Member of the Schoharie Formation occur scattered throughout the northern New Jersey Piedmont. These erratics are most similar to lithologies exposed ~200km north in the Helderberg Mountain Region of New York. The RHf erratics contain an assemblage of exceptionally well-preserved nautiloids dominated by large orthoconic and gyroconic taxa. These taxa are exposed along bedding planes by a complex sequence of physical and chemical weathering during transport within the Hudson-Champlain Lobe of the Laurentide Ice Sheet and deposition within acidic soils of regional ground moraines. Weathering also reveals taphonomic details within phragmocones and body chambers of these nautiloids that are not readily observable in outcrop exposures of the RHf. Phragmocones and body chambers display preferred orientations on bedding surfaces and contain casts and molds of numerous invertebrates including trilobites, brachiopods and corals. Original taphonomic conditions indicate that the RHf nautiloids represent a post-mortem, localized lag assemblage transported by wave and current activity prior to final burial and fossilization. Sequence stratigraphic analysis indicates that this lag deposit occurs at the boundary between third order eustatic sea level cycles Emsian 5 and Eifelian 1 and accumulated as part of a shallowing upward cycle bounded below and above by the sub-Aquetuck and sub-Edgecliff unconformities. Nautiloids and other invertebrate fauna would have been concentrated during multiple exhumation and reburial events where localized wave base was capable of eroding into the shallow shelf platform in this area of eastern New York.