ABSTRACT

Structural and isopach mapping of 985 mi² (2,550 km²) of the Louisiana outer continental shelf was accomplished utilizing 41 electric logs and 635 mi (1,020 km) of 48-fold, digital, common-depth-point, seismic reflection data on a two-mile grid. This mapping has revealed a large, elongate, salt withdrawal basin surrounded by seven salt domes and three low-relief anticlines. Two salt-cored anticlines are separated from major sediment thicks by salt domes which align parallel to the margins of minor depositional basins. Another anticline, interpreted to be sediment-cored, is a turtle structure locating an earlier depositional trough beneath the northwestern basin rim. Progradation of a shelfal area underlain by thick salt initiated shallow-water domal growth. Processes attributable to salt flow including 1) local 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 occured from middle to late Pliocene time coinciding with maximum growth of the major, basin-bounding, down-to-the-north fault. Maximum growth of the largest salt dome occurred in earl Pleistocene time and thus lagged maximum basinal subsidence in time, indicating that the domes are later stage apophyses rising from a pre-existing salt ridge or rim surrounding the basin.

The study area is part of an extensive salt plateau which began structural maturation in early to middle Pliocene time as shelfal depositional systems prograded the upper continental slope and initiated a small depopod in relatively shallow water. Such late-stage depositional thicks are underlain by significant thicknesses of salt and have the potential of evolving into major shelf or deltaic depocenters. Significant exploration potential might exist for deep-water, slope sands concentrated in anastomosing depotroughs which segmented the salt plateau into smaller massifs.