THE 'ULTIMATE' TACONIC THRUST SLICE - AN EXTENSION OF THE NORMANSKILL SEQUENCE (EARLY MEDIAL ORDOVICIAN), MID-HUDSON VALLEY, NEW YORK

A Taconic thrust slice, bordering the western margin of the Hudson River, extends 23 km (14 mi) south of Kingston, in Ulster County. Its width varies from 4 to 1 km (2.5 - 0.6 mi). To the north, in Kingston, the slice is overlain in angular unconformity by late Silurian carbonates. To the east, except where covered by the Hudson River, the slice appears overthrust by Austin Glen (Normanskill) strata of the Livingston Thrust slice. To the south and west, the new slice appears thrust against medial and late Ordovician Quassaic strata. Within the slice is a 3.4 km (2.1 mi) stratigraphic sequence folded into a NNW trending syncline with its overturned east limb dominately exposed. Strata are comprised of andesine-bearing laminated detritals (siltstones, subgreywackes, shales) formerly considered Austin Glen, Normanskill, Snake Hill or Martinsburg. Trilobite evidence (Bathyurus, Encrinuroides, Hemiarges) from the top to near the bottom of the sequence dates it as Kirkfieldian (slightly older than early Martinsburg (Shorehamian) and somewhat younger than Austin Glen (Lowvillian), all early medial Ordovician). Marked dissimilarity in thickness, lithology and continuity with the local autochthonous Kirkfieldian Balmville carbonates strongly suggests a thrust slice origin considerably removed from the Mid-Hudson region. Consequently, it is suggested the slice and its contents are allochthonous, similar to other, previously recognized Taconic Thrust slices. It is further suggested that the strata in the slice most likely are the stratigraphic conclusion to the allochtonous Normanskill sequence so widespread in several of the Taconic slices. Finally, it is suggested that the new structural slice is the westernmost (and possibly first formed) structural 'ultimate' of the Taconic Thrust slice sequence, the strata of which tend to 'young' westward.