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Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

Salt Deposition, Loading and Gravity Drainage in the Campos and Santos Salt Basin, Southern Brazil

Ian Davison1; Lee Anderson1; Peter Nuttall2

(1) GEO International Ltd., Camberley, United Kingdom.

(2) ION/GXT, Houston, TX.

The southern Brazilian salt basin, comprised of three sub basins Santos, Campos and Espirito Santo, and was deposited over a pre-existing rifted basin with approximately 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.