Abstract

A late Wisconsinan ice advance into northwestern Long Island caused large-scale thrust faulting and folding of Cretaceous and glacial strata along the east side of Manhasset Neck. Several large thrust blocks of frozen Cretaceous sediments were pushed over an outwash-till-outwash sequence causing considerable disturbance of these beds. An unusually large fold, as well as rapid pinching and swelling, was observed in the Montauk(?) till, while the less cohesive outwash and Cretaceous strata show extensive lateral displacement due to thrust faulting. The magnitude of the glacial deformation of the local strata is greater than any heretofore recorded for Long Island, and an active Harbor Hill readvance of the Hudson River lobe is suggested as the cause.

Based on the excellent local stratigraphic section, renaming of two of the upper Wisconsinan glacial deposits on western Long Island is proposed. The tetms “Montauk(?) outwash” and “Roslyn out-wash” are used to replace Fuller's (1914) Herod gravel and Hempstead gravel. The new terms associate the outwash units with the corresponding tills — Montauk(?) and Roslyn, as named by Sirkin (1971). Additionally, Fuller's Manhasset formation is extended to include the Roslyn till.

Finally, grain size analysis of the Cretaceous sediments indicates an estuarine or deltaic environment of deposition for these layers. A horizon of quartz ventifacts appears to be the result of periglacial winds acting on surficial Cretaceous deposits; however, periglacial dunes previously noted for this area were not observed.

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