SCHULTZ-ELA, DANIEL D. and RYAN J. MANN
Bureau of Economic Geology, The University of Texas at Austin, Austin, TX

Abstract: Numerical Models of Salt Sheet Deformation Driven by Various Rates and Patterns of Sedimentation

Two-dimensional numerical modeling illustrates how the rate and pattern of sedimentary loading largely determines the structures that develop above salt sheets.

A sediment wedge prograded across a salt sheet and aggraded at 1 mm/yr to maintain a 1° slope. A depocenter initially developed above a basinward-dipping fault at the proximal salt margin. This pattern represents the early stages of a roho system. Fault slip ceased, however, when the sediment wedge prograded to the distal sheet margin. Basinward migration of the depocenter signaled transition to a counterregional system. Layers were truncated and lapout relations changed, independently of any eustatic changes. Salt flow from an inclined feeder prolonged the roho phase.

Slower aggradation (0.5 mm/yr) allowed more time for basinward salt flow away from the load, which deepened the depocenter and perpetuated the proximal fault. The exposed distal salt then inflated and slowed the progradation. Both effects tended to maintain a roho system. Conversely, a steeper 3° depositional slope thickened and strengthened the proximal wedge, which inhibited faulting there. The distal depocenter near the wedge tip typified a counterregional system. Undercompacted sediment intensified this effect.

A sediment lens deposited at the center of the sheet created a bathymetric high because the lens was less dense than underlying salt. If deposition continually shifted to an adjoining bathymetric low, sediment eventually covered the salt uniformly. If deposition remained fixed, the growing pile developed a deep keel and onlapped outward from the depocenter high.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas