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Early Evolution of Salt Structures in North Louisiana Salt Basin

Jeffrey J. Lobao, Rex H. Pilger, Jr.

Several salt diapirs and pillows in southern and central north Louisiana have been studied using approximately 355 mi (570 km) of seismic reflection data and information from 57 deep well holes. Using seismic profiles with deep well-hole data is the most advantageous method to document regional salt tectonism through time.

Three stages, pillow, diapir, and postdiapir, are required to explain salt stock growth through time in the North Louisiana Salt basin. The pillow stage and associated primary peripheral sinks exhibit 11-35% thinning over pillow crests and 50% overthickening in the primary peripheral sinks in the basin. Thinning values as great as 87%, and overthickening values as high as 400% are inferred for prediapiric (juvenile) salt pillows. The diapir stage and its associated secondary peripheral sinks exhibit 50-25% overthickening. This stage is characterized by piercement diapirism and withdrawal of large volumes of salt from the pillow flanks. The postdiapir stage and its associated peripheral sinks exhibit less than 45% overthickening. Moreover, in places, dome growth is in a steady state wi h sedimentation. Growth stages are generally confined to the following stratigraphic units: Smackover to Knowles (pillow stage), Calvin (diapir stage), and Winn and younger sediments (postdiapir stage).

These considerations lead to the following conclusions on diapirism in the North Louisiana Salt basin. (1) The diapiric event began early (early Coahuilan) in the southern and central part of the basin, and later (late Coahuilan to Comanchean) in the northern part. (2) The initial diapiric event is much more abrupt and intense in the southern and central diapirs when compared with the later diapiric event in the northern diapirs. (3) Regional depocenter shifting, relative sea level, local erosion with salt extrusion, and rapid depositional loading of sediments are the major controls on diapirism in the basin.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.