An Analysis of the Thickness and Emplacement of a Shallow Salt Sheet in the Northeastern East Breaks Area, Gulf of Mexico
J. E. Desantis and P. F. Gabbard
An analysis of the thickness and emplacement of a shallow salt sheet is presented for a 20 square mile salt sheet in the area around East Breaks blocks 215, 216, and 260 in the Gulf of Mexico. The top of salt is very rugose and lies at depths between 2500 and 6000 feet subsea in upper Pleistocene sediments.
Attempts to define the obscure base of salt sheet by reprocessing the 2D seismic data were complicated by pervasive interbed multiples and primary multiples from top of salt. A 3D gravity model was developed for the area using shipborne gravity data. The best fit model constrained by 2D seismic data showed a rooted salt body in the north with a thin sheet extending south from the root. Minimum thickness of the salt sheet could not be ascertained from the gravity alone because of shallow salt-sediment density crossover depths. Maximum thickness for the southern salt sheet section was established by iteration of the geological model with various salt thickness until there was a divergence in the slope of the curves of the modeled gravity field from the observed field. A regional 3D seismic survey was subsequently acquired and shows considerable overhang of salt around steep dipping sediments. The base of the salt on the 3D seismic, however, was obscured by the same multiple events as seen on the 2D data.
A geological reconstruction shows initial salt diapir intrusion from lower to upper Pleistocene time with salt sheet flow beginning in Sangamon to recent. A model for salt thickness and emplacement history is shown. Mechanisms for emplacement and predicting subsalt sediments will be discussed.
AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California