Regional Controls from Syn-Halokinetic Carbonate Platforms from Extensional Basins

Steven L. Dorobek
Exploration and New Business, Maersk Oil & Gas, Copenhagen K, Denmark

Salt structures provide dynamic substrates for carbonate platforms in extensional basins. Salt structures in sag basins are dominated by salt diapirs and pillows; regional extension or contraction is limited. In rift basins and along passive margins, rift-related basement topography and original salt thickness influence styles of salt deformation, with gravity sliding/detachment becoming important along passive margins. Near the updip depositional limits of salt, small salt diapirs/pillows and minor withdrawal features are typical. Updip areas of limited salt deformation change downdip into an extensional province where typical syn-halokinetic carbonate platforms include: (1) isolated platforms on rotated fault blocks with internal growth strata that grossly mimic patterns observed in syn-rift carbonate platforms; (2) isolated platforms on turtle structures with internal growth strata that can record growth of the turtle; and (3) land-attached, mixed siliciclastic-carbonate ramps and shelves that form in fault-bounded withdrawal depocenters or over crests of late-stage turtle structures. Extensional deformation changes downdip into a transitional province, which is characterized by large salt diapirs, ridges, and some allochthonous salt bodies, and ultimately, a contractional province at the downdip limit of salt deformation. The seaward limit of syn-halokinetic platforms is generally found within the transitional province because water depths progressively increase basinward. Salt-related uplift of the seafloor can provide local shallow-water substrates for isolated carbonate-platform development, even far offshore. Syn-halokinetic carbonate-platform facies are rarely associated with allochthonous salt bodies because water depths in the zone of contraction are too great for shallow-marine carbonate sedimentation.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas