Differential Fault-Related Early Miocene Sedimentation, Bayou Hebert Area, Southwestern Louisiana

Abstract

Well logs from the Bayou Hebert area in southwestern Louisiana show that most of the differential sedimentation associated with one zone of contemporaneous faults cannot be attributed to simple expansion. Rather, the lower Miocene sequence on the downthrown side of the fault zone has grown principally by the episodic deposition of sedimentary units that have no correlative counterparts on the upthrown side. Such units range up to about 2,000 ft (600 m) thick near faults, and most are laterally discontinuous over distances of several kilometers. The isolated downthrown intervals lie in different parts of the sequence at various places along the strike of the fault zone, indicating lateral and temporal variation in subsidence rates in the downthrown block. The intervals may represent times of erosion or sediment bypass updip of faults. Isolation of thick intervals on the downthrown block adds potential for unexpected reservoir units and may enhance the development of combination traps associated with contemporaneous faulting and deposition characteristic of growth faults. Overlapping of the tapered edges of multiple laterally adjacent intervals may also create potential for small flexural structures in the areas of overlap.