Salt Basin Seismic Sequences as a Signature of Near to Far Field Tectonics; Example: High Island, Northern Gulf of Mexico

John D. Pigott, Abdelazim A. Ibrahim

Seismic stratigraphic analysis of offshore High Island, Northern Gulf of Mexico, reveals Miocene to Pleistocene system tracts which record far-field (global), intermediate-field (regional), and near-field (local) tectonics. The respective tectonic controls are: 1. Global sea level excursions; 2. Regional basinal subsidence (thermal-mechanical and isostatic); and 3. Localized salt mobilization. Sequence analysis reveals deep water turbidites alternating with deltaics pulsed by global sea level fluctuations and exhibiting significant localized paleo-bathymetric influence from halokinetics. Salt bodies from north to south range from isolated salt swells to rootless salt bodies to attached diapirs.

Extensional faulting has three dominant signals: 1. Deeply originating, high to intermediate angle normal faults owing to thermal-mechanical subsidence of the Gulf of Mexico shelf; 2. Shallow-restricted local extensional faults associated with compaction and subsidence of loaded Pliocene muds; and 3. Halokinetic-associated: A. High angle faults extending to the surface and associated with salt diapiric intrusions; B. Intermediate to low-angle faults associated with broad salt swells or salt rollers and generally terminating or soling out against the salt, and C. High-angle faults associated with sagging intra-salt basins and peripheral sinks.

These near to far field sedimentologic-structural responses afford several hydrocarbon play types: 1. Sub-salt inclined strata (truncating against the salt base or weld); 2. Syn-salt growth lowstand system tracts out of phase with global sea level (asynchronous L.S.T.s) owing to halokinetics; 3. Syn-salt growth structures (turtle-back, drapes, etc.); and 4. Post-salt growth synchronous L.S.T.s.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995