Abstract: The Geometry and Development of the Salt Withdrawl Basin in Ship Shoal Block 318 and Vicinity

KULANDER, CHRIS
Texas A&M Geophysics, College Station, TX

The regional geology of the southwest Ship Shoal South additions is dominated by an oblong salt-withdrawl basin with axes 9 mi in the east-west direction and 6 mi in the north-south direction. Seismic reflection data shows that the bottom of this basin is at about 6.1 seconds two-way travel time (twt), or a maximum depth of 22,000-25,000 ft. The basin is flanked to the south by a group of diapirs and separated bulbs resulting from salt migration to the south. To the north, east and west, the basin is bounded by generally continuous salt ridges which rise locally to about 9,000 ft seubsea depth (1760 ms) and average about 15,000 ft subsea depth (2500 ms).

A series of arcuate normal faults separate the salt-withdrawl basin from the surrounding salt ridges to the north, east, and west. Dipping steeply into the basin, these faults coalesce at points where the basin edge changes direction to form a horseshoe-shaped fault system opening to the south. Maximum throw of these syndepositional faults is nearly 600 ft and generally occurs at around 12,000-14,000 ft depth subsea (about 2.5 seconds twt). Throw decreases to nearly zero both at the surface and at maximum basin depth.

Basin development began over 2.2 Ma, with allochthonous salt migration triggered by the prograding shelf margin. As subsidence continued, shelf progradation stalled and deposition of sediments reached a maximum rate of just under 2.0 mm/yr at 1.2 Ma. Primary accommodation space was filled by around 0.4 Ma. Secondary accommodation from compaction and subsidence provided space for up to an additional 400 ft of very recent (>0.4 Ma) sediments.

AAPG Search and Discovery Article #90932©1998 GCAGS/GCS-SEPM Meeting, Corpus Christi, Texas