PRELIMINARY STRATIGRAPHY AND STRUCTURE OF A MEDIAL ORDOVICIAN MOUNT MERINO INLIER WITHIN THE LIVINGSTON TACONIC TECTONIC THRUST SLICE IN WEST-CENTRAL DUTCHESS COUNTY, MID-HUDSON VALLEY, NEW YORK

Within the allochthonous Livingston Taconic slice in a 7.43 square km. (2.88 square mi.) mapped area centering on (41^o 44' 45.5" N, 73^o 55' 00" W), several north-south trending railroad cuts reveal a continuous stratigraphic sequence comprised of lower Austin Glen and upper Mount Merino strata (middle Ordovician Normanskill Group). The sequence aggregates 349 meters (1,145 feet) stratigraphically and consists, north to south, of massive sandstones underlain by 224 meters (735 feet) of subgraywackes and interbedded shales bearing graptolites at two new localities [Nemograptus gracilis zone]. This unit (lower Austin Glen) may rest disconformably on an intermediate sequence of 24-37 meters (80-120 feet) of argillaceous siltstones, which, in turn, overlies 6 meters (20 feet) of quartzose siltstone. The latter rests disconformably on typical Mount Merino strata. The Mount Merino is represented by an incomplete, 113-meter (370 feet) sequence of intercalated shales, siltstones, conglomeratic carbonates, and thin lenticular carbonates with the Hudson River covering the base. Approximately 0.42 kilometers (0.25 miles) to the east of the railroad cuts at the west end of West Dorsey Lane (41^o 44' 39.1" N, 073^o 55' 49.8" W), at an undetermined stratigraphic position lower in the Mount Merino, a second set of lithologies is exposed in a 91-meter (300 feet) sequence apparently grading towards the underlying Indian River facies: green and black shales, chert layers, and red weathering siltstones.

Within the north-south aligned Livingston slice, a modified antiformal structure trends east-west across the map area for more than 2.0 kilometers (1.3 miles), exposing an inlier of east-dipping Mount Merino strata bounded on the north and south by Austin Glen strata. In the core of the antiform, in the western side of the map area along the Austin Glen-Mount Merino disconformity, the Mount Merino increases in thickness southward. In addition, at least 67 meters (220 feet) of stratigraphic truncation occurs in the Mount Merino below the disconformity. Further, in the map area, strata previously assigned to the Poughkeepsie Mélange appear confined to the lowest unit of the Austin Glen and seem to be tectonically disturbed. Consequently, the Poughkeepsie Mélange appears to be a structural rather than a stratigraphic unit.