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Salt-Related Deformation Recorded by Allochthonous Salt Rather than Growth Strata
Subsidence of minibasins into salt is typically recorded by growth strata that thin onto topographic highs over diapirs or inflated salt. Typical patterns of stratal convergence, onlap, overlap, and offlap develop depending on the interplay between sediment-accumulation rate and salt-related subsidence/uplift rates.
Allochthonous salt may take the place of growth strata in recording deformation above a deeper salt level, whether an older canopy or the autochthonous salt. Salt sheets advance on thrust faults linking the tip of the sheet to the sea floor, with salt moving from beneath topographic highs into topographic lows, generally carrying a thin carapace over the salt. The base of the sheet sinks as underlying salt evacuation continues. If there is an adequate supply of shallow salt, the sheet thickens as its base subsides and the record of deep salt evacuation is hidden in the shallow salt. When the lateral supply of salt can no longer keep up with subsidence, the top of the shallow salt also sinks, thereby triggering the growth of a new suprasalt minibasin.
We illustrate these concepts with examples from the northern Gulf of Mexico. These include allochthonous sheets emplaced above inflated autochthonous salt that subsequently collapses, as well as secondary minibasins that become encapsulated within allochthonous salt when a shallower sheet is emplaced during ongoing minibasin subsidence.
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