CORE DRILLING THE ALLEGHENY PLATEAU IN THE PA WILDS AND ITS VALUE IN GEOLOGIC MAPPING

Since 2010, the Pennsylvania Geological Survey has drilled deep cores to assist geologic mapping. These cores are particularly useful for mapping where strata are near horizontal and coring can capture 50% or more of the quadrangle’s stratigraphy. One example is the work done for the Rich Valley 7.5-minute quadrangle, Cameron and McKean Counties, Pennsylvania. Two 1,100-foot cores were critical in identifying local marker beds and lateral changes of formation thickness, capturing fragile fossil specimens, determining lithology percentages per formation, and interpreting depositional environment.

The cores also tell the geologic story of the westward progradation of terrestrial deposits of the Catskill clastic wedge’s shoreline and the marine transgression that followed. The Catskill Formation’s distal setting from the Acadian Mountain source is evidenced by tongues of marine or brackish facies, thinness of the Catskill Formation (350 ± 25 feet), and a subsequent, marine transgression on the upper contact. Above the transgression, the core displays the dominance of the inland sea to approximately the Devonian-Mississippian boundary

Deep cores such as these provide the mapping geologist a distinct advantage when combined with traditional mapping methods. Advantages include providing a reference section to more accurately correlate field station observations to their stratigraphic position, confirm/deny the presence of key marker beds, and provide a more thorough characterization of the formations.