STRATIGRAPHIC REVISION AND FACIES ANALYSES OF THE FRASNIAN-FAMENNIAN BOUNDARY INTERVAL (UPPER DEVONIAN) IN NEW YORK AND PENNSYLVANIA

Two extinction pulses in the late Frasnian, the Lower and Upper Kellwasser events (LKW and UKW), coincided in many locations with the deposition of organic-rich sediments. In this study, we describe facies changes through multiple stratigraphic sections from the upper Frasnian-lower Famennian in north-central Pennsylvania and the southern tier of New York State. We have recently revised the stratigraphy of these strata, and we discuss several additional changes that will facilitate the recognition and comparison of the KW events across the northern-central Appalachian Basin.

The Pennsylvania and New York sections record paleoenvironments that range from offshore/outer shelf up to middle shoreface. The LKW interval represents the culmination of a transgression, as evidenced by the transition from shallower-water facies to the distal outer-shelf deposits of the Pipe Creek Formation (the temporal equivalent of the LKW). Fossil data suggest that the LKW represents a dysoxic, but not permanently anoxic, paleoenvironment. The LKW transgression is terminated by regression that juxtaposes middle shoreface sands directly on top of the outer shelf shales of the Pipe Creek at our most proximal location (Tioga, Pennsylvania). These facies changes are unusually large and abrupt relative to those observed in the rest of the sections; for example, facies fluctuations between the LKW and UKW are more muted. The UKW is not exposed at any of our sections, but the overlying strata are. The post-UKW interval shows a brief return to the middle shoreface settings before the transgression that culminated in the deposition of the offshore Dunkirk Formation. This transgression was eventually followed by a substantial regression that resulted in deposition of the terrestrial Catskill Formation in the more proximal portions of the study area. The stratigraphic revisions and facies analysis discussed here will provide a stronger framework from which to study the Kellwasser events in the Appalachian Basin.