SURFACE STRUCTURAL EXPRESSION RELATED TO SUBSURFACE SALT THICKNESS, APPALACHIAN PLATEAU, BRADFORD AND TIOGA COUNTIES, PENNSYLVANIA

Folding in the Appalachian Plateau province of northern Pennsylvania is characterized by long wavelength, low amplitude anticlines and synclines, compared to the shorter wavelength/higher amplitude folding of the Valley and Ridge province. The limbs of Appalachian Plateau folds typically exhibit shallow dips, primarily from 3 to 6 degrees. Some anticlines are asymmetric, having slightly steeper-dipping southeast limbs. Geologic mapping has documented areas within the Plateau where dips are significantly steeper, often as much as 40 to 60 degrees. This deformation is observed on the southeast limbs of both the Wilmot and Towanda anticlines, resulting in strongly asymmetrical southeast-verging folds. The steeper-dipping successions are observed within strata of the Late Devonian-age Lock Haven and Catskill Formations.

The most extensive of these deformed zones lies along the southeast limb of the Towanda anticline. Here, we have recognized areas of steeper dips, covering along-strike distances exceeding 20 km, where dip magnitudes are in the 40- to 60-degree range. Across strike, the narrow band of steep dips is 1 to 2 km wide, then dips flatten out to the north approaching the axis of the Towanda anticline. The steeply dipping strata can be identified within LIDAR datasets and in some cases exhibit a flat-iron type geomorphology.

We hypothesize that these zones of steep dips are associated with areas where the Silurian-age Salina Group salt is thicker in the subsurface. Using isopach reconstructions of the Salina Group salt, the zones of steeper dips are associated with areas where salt thickness exceeds ~900 m. Areas where the salt is thinner show the more typical dips of 3 to 6 degrees.