Deformation of continental crust - the Legacy of Mike Coward Special Publication, Geological Society of London, in press

Geology and Tectonics of the South Atlantic Brazilian Salt Basins

Ian Davison
Earthmoves Ltd., Chartley House, 38-42 Upper Park Road, Camberley, Surrey, GU15 2EF, UK

Abstract

The South Atlantic salt province is a series of basins separated by basement highs and lows, later volcanic highs and sub-aerial ocean spreading ridges. The Brazilian salt basins (Santos-Campos-Espírito Santo, South Bahia (Cumuruxatiba, Jequitinhonha and Camamu), Sergipe-Alagoas and Ceará) are separated from the African salt basins of Angola-Congo-Gabon, Rio Muni and Doula.
The base salt horizon is offset by faults with up to 2 km of displacement in the Santos and Campos basins and the salt is thicker on the downthrown side of the faults. Fault scarps also controlled the thickness of the underlying ‘sag’ phase of sedimentation. Downslope sliding movement of overlying Albian strata occurred soon after salt deposition and listric faults developed which sole out in the salt horizon.

Sediment loading in the Santos Basin produced a landward-dipping base salt which has promoted development of counter-regional faults and enhanced later contractional effects due to either downslope sliding or regional tectonic compression. The narrow salt basins of South Bahia have a steeply-dipping base salt horizon (4°), and pronounced folding which begins at the oceanward pinch-out of the salt and propagates back up the slope. The topographic highs above the fold anticlines are rapidly eroded on narrow margins, which allows the folds to grow more easily to large amplitudes at the top salt horizon.