Stratigraphy and paleoenvironmental analysis of the Frasnian-Famennian (Upper Devonian) boundary interval in Tioga, north-central Pennsylvania
Abstract Two pulses of extinction in the late Frasnian (Late Devonian), the Lower and Upper Kellwasser (LKW and UKW) events, coincided with the deposition of organic-rich strata in many parts of the world, including the Appalachian Basin. Here, we describe two stratigraphic sections from Tioga, north-central Pennsylvania, that span the Frasnian-Famennian (F-F) boundary interval. The F-F boundary and UKW-equivalent strata are probably located in the covered interval between the two sections, but the LKW-equivalent Pipe Creek Formation is well exposed. We propose several stratigraphic revisions, including raising the Lock Haven Formation to group status and dividing it into formations, as well as redefining the base of the Canaseraga Formation and subdividing it into members. Paleoenvironments at Tioga range from offshore/outer shelf to middle shoreface. A regression follows the LKW transgression, as evidenced by the sharp superposition of middle shoreface sands on outer-shelf mudstones, similar to large facies changes associated with the LKW in other settings. The LKW is typically interpreted as representing deposition under dysoxic-anoxic conditions, and trace and body fossil content suggest that the Pipe Creek Formation represents dysoxic but not permanently anoxic conditions. These stratigraphic revisions and records of environmental change will provide the framework for more detailed studies of the LKW and UKW extinction events in the Appalachian Basin.