Snake Hill — reconstructing eastern Taconic foreland basin litho- and biofacies from a giant mélange block in eastern New York, USA

Exotic lithofacies and faunas have long been known from Snake Hill, eastern New York, USA. The faunally diverse, sandstone-dominated Upper Ordovician succession at Snake Hill sharply contrasts with surrounding tectonized sparsely fossiliferous distal shale. Re-examination of the Snake Hill section shows that it is a storm- and wave-dominated near-shore facies with a benthic fauna analogous to that of the younger Lorraine Group (Ashgillian) of central New York, and to that of the upper Martinsburg Group (upper Caradocian) of eastern Pennsylvania. Orthograptus ruedemanni Chron graptolites indicate that the Snake Hill succession is older than the surrounding tectonized, deep-water shale (Climacograptus spiniferous Chron). Snake Hill is best interpreted as a parautochthonous block in mélange originally deposited close to the shoreline of the emergent Taconic accretionary prism. Because the Snake Hill succession is sandstone-dominated, it is inappropriate to refer mudstone-dominated facies that underlie the western margin of the Taconic allochthon in the Hudson River valley region to the Snake Hill “Shale,” as has been done in the past. The thick (ca. 150 m), lithologically distinct succession at Snake Hill is therefore referred to as the “Snake Hill Formation.” The Snake Hill Formation is the only known example of proximal, near-shore facies deposited on the western side of the outer Taconic arc, and represents easternmost deposition in the Taconic foreland basin. The Snake Hill Formation is a unique occurrence, and thus is restricted to its type locality at Snake Hill, New York.