ABSTRACT

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 ccreated by lateral sediment break-away. Some 20000 feet of Late Miocene to Pleistocene sands and shales were deposited in water depths ranging from less than 100 feet to greater than 3000 feet during progradation of the field area.

Miocene to Pleistocene foraminiferal assemblages were used in interpreting the growth history of several other salt domes located 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 which were in response to depositional rate and local salt source. These models can be utilized to predict structure of domes with limited well control or incoherent seismic data in the search for hydrocarbons.

Salt domes of the study area developed from a thick layer of buried salt that was displaced by overburden of a progradational clastic wedge: (1) early salt movement was seaward with salt accumulations forming swells due to an overburden of deep water clays, (2) non-piercement 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 was then rearranged into thin, elongate piercement spines during shallow water deposition at the time of greatest basement subsidence.