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Wrench Fault Tectonics, Early Mesozoic Basins, Pennsylvania

Samuel Root

Contemporaneous Early Jurassic wrench faults are present in the Gettysburg and Newark half-graben rift basins. They are significant because wrench tectonics may produce hydrocarbon trapping folds.

The northeast-southwest-trending Gettysburg basin is dominated by extensional tectonics, principally normal faulting subparallel to the master normal fault at the northwest basin border. Two east-west-trending Paleozoic faults, reactivated during rifting, intersect the border fault. Within the basin, the northern fault forms a 15-km, east-west-trending right-lateral wrench fault with 3.5 km displacement but without associated folds. The southern fault forms a 20-km northwest-southeast-trending left-lateral wrench, splaying from the border fault, and generates the new folds in the basin.

In the nearly east-west-trending part of the Newark basin, significant en-echelon folding is produced by left-lateral wrenching of the border fault on the north basin margin. In the basin interior, a major conjugate set of antithetic and synthetic wrench faults is developed with some extending for 35 km.

Basin orientation was controlled by basement tectonic grain of the arc-shaped Pennsylvania reentrant but structures formed in a regionally invariant stress field. In the Gettysburg basin, oriented normal to regional extension, extensional structures dominate, with local wrenching only in unique situations. The western half of the Newark basin is oblique to the stress field and divergent wrenching is a significant deformational mode, forming during the rifting process to accommodate oblique extension. This tectonic framework allows prediction of the type of structural traps present in the rift basins of the western Atlantic margin.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.