PRELIMINARY SEQUENCE AND EVENT STRATIGRAPHIC CORRELATIONS WITHIN THE HELDERBERG GROUP (SILURIAN – DEVONIAN) BETWEEN NEW YORK AND THE CENTRAL APPALACHIAN BASIN

Correlations of the Helderberg Group (Head, 1969, 1972, 1974) between the Appalachian Standard Succession of New York and the Central Appalachian Basin (CAB) were influenced by a model of migrating coeval facies in NY (Rickard 1962; Laporte 1969). Recognition of unconformities within the Helderberg Group of NY has prompted reconsideration of these correlations. Sequence and event stratigraphic correlations between NY and the CAB (PA, MD, WV, and VA) delineate five unconformity-bounded sequences, comprising two transgressive cycles rather than a single transgression as in previous correlations.

The first sequence commences with an unconformity at the base of the Keyser Fm. in the CAB and below the Manlius Fm. in NY. This lower Keyser-Thacher Mbr. sequence is terminated by a pyritic hardground at the base of the Big Mountain Shale (BMS) in the CAB and the Clockville Discontinuity beneath the Green Vedder Mbr. (GVM) of the Manlius Fm. in NY. The BMS-GVM interval records the peak of the first transgression. Widespread debris of the pelagic crinoid Scyphocrinites, found only in this siliciclastic-bearing sequence, suggests highstand connections with other basins (e.g., TN, MO, OK). The BMS-GVM sequence is capped by the Terrace Mountain Unconformity in NY and glauconitic sandstone in the CAB, which mark the base of the third sequence. Sequence 3 comprises the upper members of the Manlius Fm. (NY) and the upper Keyser Fm. (CAB).

The fourth sequence overlies the Howe Cave Unconformity, which is erosional throughout the basin. Icriodus woschmidti, a proxy for the Silurian-Devonian boundary, first appears immediately above this surface in NY and the CAB, though it occurs in the uppermost Keyser at some localities (Helfrich 1975). Sequence 4 comprises the Ravena/Deansboro members of the Coeymans Fm. (NY) and the New Creek Fm. (CAB). The Punch Kill Unconformity terminates sequence 4.

Sequence 5 commences with the Hannacroix Mbr. of the Kalkberg Fm. (NY) and the Corriganville Limestone (CAB), a correlation supported by the presence of the Bald Hill K-bentonites in both units. A maximum flooding surface (pyritized fossils, pyrite and phosphate nodules) at the base of the Broncks Lake Mbr. (Kalkberg Fm., NY) and the Mandata Shale (CAB) marks the beginning of a basin-wide anoxic event and records the peak of the second transgression.