THE LOWER KELLWASSER EVENT IN NEW YORK AND PENNSYLVANIA: FACIES CHANGES AND EXTINCTION

The Lower Kellwasser Event was the first pulse of the globally recognized Frasnian-Famennian extinction (Late Devonian), and it corresponds with the Pipe Creek Shale in the Northern Appalachian Basin. Bush et al. (2015; Palaeogeography, Palaeoclimatology, Palaeoecology) revised the correlation of the Pipe Creek in shallow marine, “Chemung” paleoenvironments of New York and northern Pennsylvania. Here, we examine facies changes during the Lower Kellwasser interval and compare them to patterns of extinction (or apparent extinction) in the shelly macroinvertebrate fauna. The uppermost Wiscoy Formation records a transition from amalgamated hummocky and swaley bedded fine sands into increasingly offshore facies, culminating in the dark silty shales of the Pipe Creek Formation (~ 4 m thick). At Tioga, Pennsylvania, the Pipe Creek is abruptly overlain by the informally named “Hammond” Member (~ 5 m thick), interpreted as representing a pair of forced regressions overlain by transgressive lag deposits. Facies changes in the immediately overlying strata are more muted. Thus, the Lower Kellwasser appears to fall within an interval of dramatic, high-frequency changes in water depth that are consistent with global observations. The “Hammond” is also present in other sections in the outcrop belt, and carbon isotope stratigraphy (in progress) should assist in detailed correlations. Brachiopods and rugose corals are abundant in the upper Wiscoy, and numerous species appear to go extinct by the base of the Pipe Creek Shale. However, at least two species of brachiopod reappear above the Pipe Creek, in the “Hammond”, when shallower paleoenvironments return. Thus, the extinction of these two species does not appear to be related to low oxygen conditions associated with organic-rich shale deposition. Further collecting may reveal whether additional species persist above the Pipe Creek Shale.