ABSTRACT: Origin and Structural Development of the LaSalle Arch, Louisiana

Paul N. Lawless

The LaSalle arch is a basement high separating the Louisiana and Mississippi interior salt basins. Using reflection seismic data, an area located on the southern end of the LaSalle arch was shown to be composed of relict Paleozoic continental crust that was left behind and partially rifted during the breakup of Pangea during the Triassic. Rifting preferentially occurred to the north of a Paleozoic thrust fault nose, and crustal extension took place in a northeast-southwest direction.

The LaSalle arch, as seen in post-Triassic stratigraphy, formed by a two-part process. The western limb developed syndepositionally due to differential subsidence, and the eastern limb developed due to relative regional tilting to the east after deposition of the Claibornian Sparta Formation. The LaSalle arch acted as only a minor impediment to sediment transport with a very low relief except during the Tayloran Stage of the Upper Cretaceous.

A single truncational unconformity in post-Triassic stratigraphy is present in the Taylora Demopolis Formation, indicating a period of relatively major uplift by the LaSalle arch. This contrasts with the Sabine arch in eastern Texas; the Sabine arch experienced uplift during the Eagle Fordian and Sabinian stages. A recently proposed hypothesis calling for overthrusting in the Western Cordillera as the mechanism for uplift on the Sabine arch cannot explain movement of the LaSalle arch because horizontal stress would predict synchronous uplift of basement highs. A more satisfactory uplift mechanism calls upon lateral heat flow from the mantle as the driving force for uplift.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990