Tectonic Origin of Montgomery Terrace Scarp of Southwestern Louisiana

Paul V. Heinrich

Harold Fisk and recent Louisiana State Geological publications have mapped the northern edge of the Prairie terrace at different positions within southwestern Louisiana. Fisk used a prominent 8-m high scarp within Calcasieu Parish for the depositional boundary of his Prairie terrace. However, this scarp lies well within the Intermediate terrace as mapped and recognized by the Louisiana Geological Survey.

Geomorphologic and subsurface data from the De Quincy, Louisiana, area demonstrate that the scarp used by Fisk as his Prairie-Montgomery terrace boundary within southwestern Louisiana is tectonic, not depositional, in origin. Initially, an earlier period of dip-slip movement occurred along a regional growth fault during the Oligocene (to middle Miocene?) Epoch. This movement formed the rollover structure associated with hydrocarbon production from the East Perkins and Perkins oil and gas fields. Reactivation of this fault during the Pleistocene displaced the Intermediate terrace by about 8 m. Later erosion considerably modified the original fault scarp to form the present scarp. The tectonic origin of this scarp is significant in terms of the structural evolution and the Pleistocene g ology of this area.

AAPG Search and Discovery Article #91036©1988 GCAGS and SEPM Gulf Coast Section Meeting; New Orleans, Louisiana, 19-21 October 1988.