ABSTRACT

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

Three stages, pillow, diapir and post-diapir stages are required to explain salt stock growth through time in the North Louisiana Salt Basin. The pillow stage, and its associated primary peripheral sinks, exhibit 11-34% thinning over pillow crests and 12-50% 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 pre-diapiric (juvenile) salt pillows. The diapir stage, and its associated secondary peripheral sinks, exhibit 50-250% overthickening. This stage is characterized by piercement diapirisin and the withdrawal of large volumes of salt from the flanks of the pillow. The post-diapir stage, and its associated peripheral sinks, exhibit less than 45% overthickening. Moreover, in some instances, dome growth is in a steady-state with sedimentation. Growth stages are generally confined to the following stratigraphic units: Smackover to Knowles (pillow stage), Calvin (diapir stage), and Winn and younger sediments (post-diapir stage).

The above considerations lead to the following conclusions on diapirism in the North Louisiana Salt Basin: (1) Onset of the diapiric event was early (Late Jurassic) in the southern and central portion of the basin, and later (Early Cretaceous) in the northern portion. (2) The initial diapiric event is much more rapid 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.