The Plio-Miocene subsurface geology of Belle Isle dome in coastal Louisiana was studied using electrical logs. The pattern of syndepositional folding, faulting, and sand distribution at this shallow-piercement salt structure reflects variations with time in the configuration of the paleotopographic mound and indicates contemporaneous intrusive movement and sedimentation. Intrusive growth proceeded from an elongate shale and salt mass (ridge stage) to a buried cylindrical salt plug (deep-plug stage) to a plug which maintained a near-surface position (shallow-plug stage).

Each growth stage has a particular style of folding and normal growth faulting that is related to the shape and burial history of the intrusive. The ridge stage is characterized by movement on tangential faults and intrusive-coincident peripheral faults. The highly convergent beds of the deep-plug stage record the main episode of radial faulting. Shallow-plug-stage sediments are rarely faulted, and have low-sedimentary convergence rates. During both plug stages the salt-sediment interface acted as a vertical circular fault.

The shallow-plug stage is associated with slowly deposited nonmarine sediments, whereas the deep-plug stage is associated with rapidly deposited deltaic sediments. It is postulated that deposition rates largely determined burial depth of plug and that changes in absolute rate of salt movement during plug stages were minor.

Because of the large topographic mound present during the ridge stage and deep-plug stage, sandstones grade to shale near the salt, thereby creating numerous stratigraphic traps.

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