Abstract: Structure and Stratigraphy of Small Pliocene-Pleistocene Depocenter, Louisiana Continental Shelf

William Mathais Spindler, III

Structural and isopach mapping of 2,550 sq km of the Louisiana outer continental shelf was accomplished utilizing 41 electric logs and 1,020 km of 48-fold, digital, common-depth-point, seismic-reflection data on a 2-mi grid. This mapping has revealed a large, elongate, salt-withdrawal basin surrounded by seven salt domes and three low-relief salt anticlines. These anticlinal structures are separated from major thick sedimentary sections by the salt domes which parallel the margins of the depositional basins. Stacking of depositional-thick axes adjacent to domes and a general lack of domeward convergence of seismic reflections indicate that progradation of an area of very thick salt initiated late-stage domal growth; that is, domes originated in relatively shallow water (l ss than 600 ft or 200 m) and were maintained near the sediment-water interface. Processes attributable to salt flow, including (1) basinal subsidence, (2) bending associated with subsidence, and (3) structural uplift, resulted in the elongation of rock sequences and, consequently, normal faulting.

Major deposition in the salt-withdrawal basin occurred from middle to late Pliocene time coinciding with maximum growth of the major, basin-bounding fault. Maximum growth of the largest salt dome occurred in early Pleistocene time and thus lagged maximum basinal subsidence, evidence that the domes are later stage apophyses rising from a preexisting salt ridge or rim surrounding the basin.

The study area possibly is part of an extensive salt massif which began structural maturation in early to middle Pliocene time when the upper continental slope and shelf prograded the area and initiated the small depopod. Such late-stage depositional "thicks" are underlain by significant thicknesses of salt and have the potential of evolving into major shelf or deltaic depocenters.

AAPG Search and Discovery Article #90967©1977 GCAGS and GC Section SEPM 27th Annual Meeting, Austin, Texas