FRACTURE MAPPING IN THE MARCELLUS FORMATION AND ONONDAGA LIMESTONE TO DETERMINE THE TECTONIC HISTORY OF THE APPALACHIAN PLATEAU AND SIGNIFICANCE OF THE SENECA STONE THRUST

In the Appalachian Plateau province of New York, the Seneca Stone thrust is an imbricate fault off the Salina decollement that cuts through Devonian Onondaga Limestone and the overlying Marcellus Formation. Detailed mapping of the fracture networks in Seneca Stone quarry on a range of scales shows how the fracture arrays vary in the hanging wall and footwall of the fault and in the various stratigraphic units. We have determined the deformation history of these units on the Appalachian Plateau by studying crosscutting relationships between the observed faults, folds, and fracture sets.

The Seneca Stone thrust is exposed in the quarry as a prominent E-W trending, gently south dipping fault with a dip separation of ~10m. The fault is sub-parallel to bedding within the lower-middle Onondaga limestone, and ramps up through the upper Onondaga members into the Marcellus Shale with a dip of 35° south. Fracture orientations in both the hanging wall and the footwall of the fault show similar patterns within limestone units. Sets of small N-S striking thrust faults, high angle E-W striking fractures, and conjugate sets of wrench faults indicate E-W shortening in both the hanging wall and footwall. These are overprinted by high angle fractures trending ~335° (Engelder’s J1 set) on both sides of the thrust that likely formed during later N-S shortening. The hanging wall also has E-W trending low angle thrust surfaces with calcite mineralization that indicate N-S shortening associated with the Seneca Stone thrust.

In the hanging wall, there are changes in the fracture patterns in successive members of the Marcellus. The Union Springs contains J1 and rare J2 joints, and numerous N-S trending low angle thrust faults and steeply dipping conjugate wrench faults indicating early E-W shortening. The Cherry Valley limestone and the Oatka Creek both contain the J1 and J2 joint sets, E-W trending low angle surfaces indicating N-S shortening, and one or more sets of possible conjugate wrench faults suggesting E-W shortening. The complex patterns in fracturing in the different units suggest controls on fracture network patterns by both the local structure and the stratigraphy.