Abstract: Paleontologic Techniques for Determining Growth History and Depositional Environments of Offshore Louisiana South Timbalier Block 54 Salt Dome

Gerald R. Stude

Foraminifer fossils from 34 wells of late Miocene-Pleistocene age were used with electric-log and seismic information in the geologic interpretation of the South Timbalier Block 54 salt dome of offshore Louisiana. A thick crestal graben overlies the deep-seated salt plug which has a thin near-flank section. Faulting is transverse, with older, buried faults farther away from the salt crest.

A detailed zonation based on index fossils, species diversity plots, and paleowater-depth curves resulted in (1) better correlation, (2) recognition of faults and unconformities, (3) elimination of excess log runs, and (4) determination of casing levels and total depths of drilling wells.

The construction of paleobathymetric maps aided in understanding depositional environments and growth history. This growth model can be used for interpreting growth history of other salt domes and may enhance the success in finding total hydrocarbon reserves.

The thicker graben system over the salt crest resulted from depositional filling of a topographic low which was created by lateral sediment breakaway. The breakaway void space was filled partly from below by an upward salt rise and from above by sediment deposition. Lateral tensional stress formed high horst blocks flanking the depression and salt crest. Regional subsidence and sediment overburden resulted in burial of the salt surface to present depths.

Application of paleontologic concepts contributed greatly to the addition of significant reserves and location of other hydrocarbon potential areas on this structure.

AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC