ABSTRACT

The regional geology of the southwest Ship Shoal South additions is dominated by an oblong salt-withdrawal basin with axes 10 km in the east-west direction and 15 km 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 7300-7800 m. 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 locally rise to about 2000 m subsea depth (1760 ms) and average about 3000 m subsea depth (2500 ms).

A series of arcuate normal faults separate the salt-withdrawal 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 200 m and generally occurs at around 3000 m depth subsea, (about 2.5 second 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 south 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 150 m of very recent ( >0.4 Ma) sediments.