Abstract: Depositional Environments of Gulf of Mexico South Timbalier Block 54 Salt Dome and Salt Dome Growth Models

Gerald R. Stude

Techniques in using foraminiferal fossils provided a detailed zonation and interpretation of depositional environments of the offshore Louisiana South Timbalier 54 field. A crestal graben thick over the deep-seated salt dome resulted from depositional fill-in of a topographic low which was created by lateral sediment break-away. About 20,000 ft of late Miocene to Pleistocene sands and shales were deposited in water depths ranging from less than 100 ft to more than 3,000 ft during progradation of the field area.

Miocene to Pleistocene foraminiferal assemblages were used in interpreting the growth history of several other salt domes in South Louisiana and on the Louisiana shelf. Four salt dome growth models were recognized: (1) salt movement within a topographic low that was contemporaneous with sediment fill-in resulted in a graben "thick" over the salt crest, (2) salt piercement contemporaneous with deposition formed a topographic high of thinner beds over the salt crest, (3) rapid salt piercement after deposition displaced beds over salt crest, and (4) slow salt movement contemporaneous with deposition created a topographic high of thinner sediments over the salt crest. Formation of different models or the combination of two or more models was dependent on timing and rate of salt movement w ich was in response to depositional rate and local salt source. These models can be utilized in the search for hydrocarbons to predict structure of domes with limited well control or incoherent seismic data.

Salt domes of the study area developed through different stages as the deep-water basin was prograded over a thick layer of buried salt: (1) early salt movement was seaward with salt accumulations forming swells owing to an overburden of deep-water clays, (2) nonpiercement mounds extruded from the swells during periods of slow deposition, (3) continuous progradation with rapid sand deposition accelerated salt movement from the mounds into large piercement spines, and (4) salt then was rearranged into thin, elongate piercement spines during shallow-water deposition at the time of greatest basement subsidence.

AAPG Search and Discovery Article #90965©1978 GCAGS and GC Section SEPM, New Orleans, Louisiana