STRATIGRAPHIC, SEDIMENTOLOGIC, AND TAPHONOMIC INSIGHTS FROM SCHOHARIE, NY: GREEN VEDDER MEMBER, MANLIUS FORMATION (UPPER PRÍDOLÍ, HELDERBERG GROUP)

Large road cuts along I-88 near Schoharie, NY provide nearly continuous exposure of the Helderberg Group (U. Sil. - L. Dev.). The easternmost outcrop has yielded new insights regarding the Green Vedder Member (GVM, informal, i.e. upper, thin-bedded Thacher) of the Manlius Formation.

The GVM rests on the Clockville Discontinuity, which is marked by a coarse, intraclastic lag with numerous stromatoporoids. Large clasts (up to 6.5 cm) are similar in lithology to the topmost Thacher bed below. Semi-exotic clasts of dolostone may be derived from deeper exhumation associated with channels in the uppermost Thacher. The Clockville bed, which records initial transgressive flooding, is capped by a pyritic hardground and thin black shale recording sediment starvation during early highstand.

The GVM comprises tempestitic wackestones and packstones that alternate with “background” sediments comprised of dark, carbonaceous shales. GVM shales yield a sparse shelly fauna of ostracods, brachiopods, and skeletal debris of the pelagic crinoid Scyphocrinites. Tentaculites conches occur rarely in specific beds. Matteson, Natel and Ebert (1996) reported a distinctive carbonized biota from these shales. Articulated assemblages of scolecodont elements and preservation of soft tissues are common. Most of the fauna is restricted to the basal and/or upper few millimeters of the shales; medial portions are barren.

Fauna in the limestones is dominated by ostracods and valves of Stropheodonta varistriata with some bryozoans and gastropods. Skeletal debris of Scyphocrinites is common and rare plate loboliths (Camarocrinus stellatus) occur as well. The soles of many GVM limestones display obrution-type preservation of the delicate crinoid Lasiocrinus scoparius, which supports the interpretation of the GVM limestones as tempestites. Post-storm colonization of the substrate is represented by in situ monospecific clusters of Howellella vanuxemi.