Faulting in Triassic Gettysburg Basin, Pennsylvania and Maryland: ABSTRACT

Abstract

End_Page 1446------------------------------The structural framework of the Gettysburg basin is defined by three parallel, northeast-southwest-trending, southeast-dipping, postdepositional (Sinemurian?) normal faults into which originally horizontal Triassic strata now dip 20°-30° northwest. The faults are controlled by the earlier Alleghanian structural grain. The main portion of the Gettysburg basin extends 120 km from its termination near Frederick, Maryland, to an arbitrary cutoff near Palmyra, Pennsylvania. The basin is bounded on the northwest by a normal fault with a probable maximum displacement of several thousand meters. Inliers of basement, surrounded by Triassic strata, occur adjacent to the border fault, indicating that the deepest part of the basin is not necessarily at the border fault as in a simple ha f-graben model. At York Springs, Pennsylvania, basement and Triassic strata occur in a fault sliver on the major east-west, older Transylvania fault, which was reactivated with 3.5 km of right-lateral wrenching. Extensive normal faults in the Blue Ridge and Great Valley are associated with development of the Gettysburg basin. Southeast, near Keymar, Maryland, two normal faults with an aggregate displacement of 1,350 m partially separate a subbasin 20 × 5 km from the main basin. These faults extend 40 km south along the Martic Line into the Triassic Culpeper basin. Farther southeast, near Tyrone, Maryland, a normal fault with 800 m of displacement totally separates a small (4 × 0.6 km) Triassic basin from the main basin on the northwest. Dip reversals are rare and develop on a minor scale only adjacent to faults. Therefore, petroleum plays based on surface structural closure are not viable. End_of_Article - Last_Page 1447------------