Abstract

We used three- and two-dimensional seismic data, well and biostratigraphic constraints, and structural restorations to evaluate the evolution of the Mahogany salt body and surrounding strata on the central Louisiana outer shelf of the northern Gulf of Mexico. The history of emplacement and subsequent modification of the Mahogany salt body is divided into six stages: (1) growth of a basinward-leaning salt ridge sourced from a deep allochthonous salt sheet prior to 7.5 Ma; (2) loading-induced evacuation of a large volume of salt from the sheet and ridge through a narrow feeder, resulting in rapid salt flow and consequent radial growth of a bulb-shaped salt stock beteen 7.5 and 4.3 Ma; (3) gravitational collapse of the inflated salt stock after depletion of the deep source layer, leading to basinward extrusion of a subhorizontal salt tongue and its rafted overburden between 4.3 and 3.65 Ma; (4) burial of the composite salt body during a period of slow sedimentation between 3.65 and 1.95 Ma; (5) basinward translation of the overburden resulting from gravity gliding/spreading on the upper slope between 1.95 and 0.5 Ma, causing extension, reactive diapirism, and matching contraction; and (6) cessation of lateral translation once the shelf margin prograded past the salt body, and subsequent loading of the salt driving active diapirism in the footwalls of normal faults. The Mahogany salt body provides an excellent case study that illustrates both the value and limitations of published simple models for allochthonous salt, and the reconstructed evolution yields insights into the complex interactions between salt deformation and sedimentation. The results also suggest that the Mahogany salt body did not influence the trap style of the subsalt Mahogany field or hydrocarbon migration into the pay sands but that it did affect sediment transport pathways and, to a lesser degree, reservoir facies distribution.

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