Structural Development of Some Shallow Salt Domes in Louisiana Miocene Productive Belt

Six shallow salt domes in the Miocene productive belt of coastal Louisiana were studied to attain an understanding of the structural history during the time of deposition of the sediments penetrated by drilling. The domes were Clovelly, Cote Blanche, Lake Washington, Napoleonville, Weeks Island, and White Castle. Structural growth of the salt domes was contemporaneous with the deposition of sediments. The known stratigraphic section at the domes consists of about 15,000 ft of interbedded sandstone and shale underlain by a predominantly shale section with abnormally high pore pressures. The physical properties and differences in physical properties of the sandstone and shale sequence, predominantly shale section, and salt of these salt dome structures are partly responsible for the geometry of the structures. Structural details and features which were studied in an effort to understand the history of the salt structures were the "sheath" configuration, indications of uplift and differential subsidence, development of rim synclines, and faulting and fault patterns. Most of the flanking sedimentary rocks were either deposited against the core of the structure or "pierced" by the core shortly after deposition. The core of the structures consists of salt or a combination of salt with shale from the high-pore-pressure section underlying the shallower sandstone and shale sequence. The shale of the core moved and was emplaced in its present position as "sheath" by folding or by a combination of folding and faulting. The shape of the core exerted a control on the radius and rate of divergence of sedimentary intervals away from the core. If the side of the core dips at an angle of up to about 60°, the contours on the major faults in the flanking sedimentary rocks curve in tangentially to the core.