Spatial and Temporal Variation of Fault Activity in the Terrebonne Salt Withdrawal Basin, Southeastern Louisiana: Response to Salt Evacuation and Sediment Loading

Abstract

The Terrebonne Salt Withdrawal Basin (TSWB) was formed during the Miocene due to high sediment influx on the Terrebonne salt canopy, which triggered salt evacuation, the formation of salt structures and faults. The major faults were active during the Miocene and Pliocene because the sedimentary depocenters coincide with the TSWB. However, little is known about Quaternary fault activity in the basin despite geomorphic evidence suggesting that the faults are still active. Previous studies using 2D seismic data and well logs interpreted relatively continuous E-W striking faults. Using proprietary 3D seismic data, well logs and biostratigraphic data, we mapped 10 stratal units ranging in age from Late Miocene through Late Pleistocene in the Lapeyrouse and nearby fields in Terrebonne Parish, LA. We interpret a more discontinuous and complex fault geometry that includes a large northwest striking fault, the Lake Boudreaux fault, and two E-W striking faults, the Montegut fault and the Isle de Jean Charles fault. The Montegut and Isle de Jean Charles faults are segments of the Golden Meadow fault zone, which defines the northern margin of the TSWB. The east-west striking faults interact with radial faults related to the Bully Camp salt dome to the east and intersect the Lake Boudreaux fault toward the west. Displacement on all three faults extends to the top of the 3D seismic volume. Fault kinematic techniques utilizing isopach maps, throw-depth plots and expansion indices show temporal and spatial variation in fault activity. Stratal units between the Latest Miocene and Middle Pleistocene show a decrease in expansion indices. This means the faults were slipping more slowly. In addition, the decrease in fault activity is due to the location of the Pliocene depocenter south of the TSWB. The average Quaternary throw rate, Middle Pleistocene to present, on these faults is 0.53 - 0.65 mm/yr and they are one order of magnitude larger than those of the Baton Rouge fault zone from Late Pleistocene to present. Projections of the fault surfaces coincide with the edge of a cypress swamp near Montegut, historical patterns of wetland loss near Isle de Jean Charles, and marsh edges and wetland loss within the Madison Bay subsidence hot-spot along the Lake Boudreaux fault. We interpret the long-lived patterns of fault activity to correspond primarily to sediment loading, salt evacuation and possible on-going salt deformation.

AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019