Why do salt-floored minibasins subside? An almost universal explanation is that salt is forced from beneath the sinking basin by the weight of its sedimentary fill. This explanation is valid if the average density of the basin fill exceeds that of salt, which needs at least 1,600 meters of siliciclastic fill to ensure enough compaction. However, most minibasins start sinking when the fill is much thinner than this. Some mechanisms other than density inversion must explain the early subsidence history of these minibasins. Conventional understanding of minibasin subsidence is thus incomplete.

We identify five alternatives to density-driven subsidence of minibasins. During diapir shortening, the squeezed diapirs inflate, leaving the intervening minibasins as bathymetric depressions. In extensional diapir fall, stretching of a diapir causes it to sag, producing a minibasin above its subsiding crest. During decay of salt topography, a dynamic salt bulge subsides as upward flow of salt slows, which lowers the salt surface below the regional sediment surface. During sedimentary topographic loading, sediments accumulate as a bathymetric high above salt. Finally, subsalt deformation affecting the base of salt may produce relief at the top of salt. Each mechanism (including densitydr iven subs idence) produces a di f ferent bathymetry, which interacts with sediment transport to produce a different facies pattern in each type of minibasin. The particular mechanism for minibasin subsidence depends on the tectonic environment, regional bathymetry, and sedimentation rate. The spatial variation of minibasins on a continental margin creates provinces in which a given minibas in s tyle i s dominant . An appreciation of subsidence mechanisms should thus improve understanding of minibasin fill patterns and allow genetic comparisons between minibasins.

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