4-D Evolution of the Maranhao Deepwater Fold Belt, Offshore NE Brasil

Abstract

The Maranhao deep-water fold belt is a gravity driven system of imbricated thrusts and fault-related folds that extends for more than 100 km on the passive margin of NE Brazil in water depths that range from 1 to 2.5 km. Several stacked thrust systems with overlapping detachments and 3D duplexes have been mapped within the fold belt using a 3D seismic volume over part of the system. The fold belt is formed by faulted detachment folds that deform Paleocene? to Oligocene? strata detached above the Late Cretaceous units. The Maranhao fold belt has a deformation front that curves from a N-S strike in the north to a NE-SW direction in center and to a N-S trend in the south. Individual thrusts within the fold belt extend for more than 15 km along strike, and their tip-line folds systems have present half-wavelengths than range from 0.5 to 2 km. In the south, thrust related folds have been rotated to adjust to the shape of the blocking seamount structure and are cut by localized oblique ramp accommodation structures. In center, the folds and thrusts are parallel to the NE-SW structural trend, but have been uplifted and tilted towards the basin by the development of an underlying duplex system that deforms the Late Cretaceous sequence below the imbricate detachment. To the north, the trend of the thrusts changes and coincides with a decrease in the spacing between the thrusts and with an increase in the displacement of the imbricate and the duplex systems. A lateral ramp that connects an upper and lower detachment permitted the transport of a duplex over the upper detachment to produce a structural high. In this region the thrusts are cut by later extensional faults that detach into the same level as the imbricate system. Mapping of the regional unconformities indicate that the imbricate system was developed during the Oligocene?, and was followed by sedimentation parallel to the regional palaeo-slope. This system was later tilted and folded by the underlying duplex systems during the Miocene?. Growth stratal patterns suggest a hinterland propagation for the duplex systems, with high sedimentation at the front and contemporaneous erosion in the internal part of the fold belt. The changes in the thrust fault/fold patterns of this part of the Maranhao deep-water fold belt are interpreted to be the result of the blocking effects of seamount structure combined with changes in the sedimentation/erosion patterns on this part of the passive margin.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015