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Abstract: Salt Geometry and Evolution in the Vicinity the Mahogany Subsalt Discovery, Offshore Louisiana

ROWAN, MARK G., and BRUCE D. TRUDGILL, University of Colorado at Boulder

A 3-D seismic survey is used to illustrate the variety of salt body geometries in a 55-block area in the Ship Shoal South, Ewing Bank, and Green Canyon protraction areas. The survey is centered around the Mahogany subsalt discovery in Ship Shoal 349/359. Both the Mahogany salt body and a similar feature immediately to the east are composite salt bodies: they consist of bulb-shaped salt stocks with subhorizontal tongues that extend to the south and southeast. In each case, basinward translation of the tongue overburden created extensional faults and reactive diapirs at the boundary between the stock and tongue segments and thrust faults at the basinward toe. The western margin of the survey covers the eastern edge of a composite salt body of uncertain origin. The areas south and southwest of Mahogany are dominated by several stepped counter-regional systems with deep welds connected landward to the autochthonous Louann salt and basinward to shallow salt bodies. The cylindrical Green Canyon 18 stock was formed by salt extruding from a deep sheet (now evacuated) in a counter-clockwise manner, first landward and then basinward.

A pseudo-depth map of the base salt and weld surfaces enable the time and nature of salt emplacement to be estimated. Five stages of salt growth can be identified in the Mahogany area: (1) Jurassic to Paleogene (?) diapir growth; (2) lateral extrusion in the Paleogene (?); (3) sheet evacuation and secondary diapir growth during the Paleogene (?) to late Miocene; (4) a second phase of lateral extrusion in the latest Miocene to early Pliocene; and (5) further evacuation and diapir growth in the Plio-Pleistocene.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah