Salt deposition, loading and gravity drainage in the Campos and Santos salt basins

Abstract

AbstractThe southern Brazilian salt basin, comprising the three sub-basins Santos, Campos and Espirito Santo, was deposited over a pre-existing rifted basin with c. 1–2 km of relief bordered by an outer basin high that separated the basin from the conjugate African margin. The evaporites are interpreted to have been deposited very rapidly (<1 Ma) during the waning of extension. Deposition of salt caused rapid loading of the basin, so that further basin subsidence occurred and mobile salt drained from structurally higher zones into the subsiding basins. Seismic evidence indicates that downslope salt drainage occurred before any sediment overburden accumulated. Withdrawal synclines within salt units developed adjacent to diapirs, which have intruded the evaporite sequence, and salt extrusions are observed which were buried by later salts. The early movement of the salt probably contributed to significant fault reactivation and redistribution of salt load, so that the final half-graben salt fill reached up to 4.5 km thick where only 1–2 km of salt was originally deposited.