END-DEVONIAN (FAMENNIAN) EVENT-STRATIGRAPHY IN THE CLASSIC PENNSYLVANIA "OIL LANDS" : NEW DISCOVERIES IN THE RICEVILLE FORMATION-BEREA SANDSTONE SUCCESSION

Recent mapping of end-Devonian units in Crawford County, Pennsylvania has yielded important preliminary chronostratigraphic information. Compared to the end-Devonian succession in Ohio (Cleveland Shale, Bedford Shale, Berea Sandstone), corresponding units in northwest Pennsylvania are less well understood. The standard Ohio succession has generally been considered to change eastward into a mosaic of shale and sandstone units which have been difficult to correlate.

Using regional event-stratigraphic markers and sequence-stratigraphic principles, we have discovered that key Upper Devonian units (Cleveland Member, Bedford Member-equivalent succession), known to be absent near the PA/Ohio state line due to sub-Cussewago Sandstone erosion, progressively reappear eastward below the base-Cussewago contact from the French Creek Valley eastward to the meridian of Union City. A condensed unit (Cleveland Member?), characterized by dark, bioturbated siltstone and black shale partings and floored by a detrital pyrite/bone lag (probable Skinner Run Bed), is succeeded by a higher, discontinuity (“Syringothyris Bed”), which Caster (1934) interpreted as the base of the Bedford succession in Pennsylvania. Succeeding units (“Drake Well Formation”, “Tidioute Shale” sensu Harper, 1998), up to the Corry Sandstone, are herein believed to be Bedford Shale equivalents. These interpretations await confirmation pending conodont analysis. Strata yielding echinoids, the enigmatic taxon Titusvillia, glass sponges, and bone/conodont lags provide markers potentially useful in this correlation work.

Ongoing work, directed toward clarifying the temporal relationship of the Corry, Cussewago, and Berea sandstones, should help in the search for the regional signeture of the global Hangenberg mass-extinction and the end-Devonian eustatic lowstand event.