DEEP TIME IN AN EPEIRIC SEA: A NEW PALEOSTRATIGRAPHIC UNDERSTANDING OF THE SILURIAN-DEVONIAN KEYSER FORMATION, APPALACHIAN BASIN (PENNSYLVANIA, USA)

The Silurian-Devonian carbonate sequence of the Appalachian Basin records transgressive-regressive cycle sedimentation across an epeiric ramp. An often studied, yet underutilized example within this interval is represented by the time-transgressive Keyser Formation. Keyser facies suggest deposition upon an exceedingly low gradient slope over a range of shallow marine environments. However, varying interpretation of these facies has led to inconsistencies within the lithostratigraphic framework. In west-central Pennsylvania, a unique package of strata occupies the lower Keyser, which differs remarkably from the established lithology currently in use for the state, the cause and extent of which has not yet been determined. This study reports on the mapped distribution of the lower Keyser with new sedimentologic, paleontologic, and SEM analysis data, from several outcrop exposures across central Pennsylvania, including one previously drilled core sample. The control on the stratum deposition presented herein is based on event correlation consistent with a symmetric epeiric model of basin geometry. Areal distribution appears to be concentrated within Blair County, Pennsylvania, where the strata represent evolving basin-margin facies during late Silurian sea level rise.