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Abstract

Stratigraphic correlations from wells tied to high resolution seismic data offer specific constraints for interpreting tectonic events. Paleogeographic models based on these interpretations can be used to define the paleobathymetry of a basin at specific points in time and space, providing critical constraints on the rifting and subsidence history that are not available from regional structural interpretations.

Based on detailed work undertaken to define the play characteristics of the Campos basin, we propose a new subsidence history for the critical presalt to salt transition time. Mapping of the “synrift” to “sag” transitional stratigraphy indicates a significant erosional unconformity at the base salt level across the outer Campos hinge in the southern Campos basin that results in the removal of the uppermost presalt section and portions of the underlying coquina section. We propose that this erosional unconformity truncates presalt stratigraphy where the basin has undergone short wavelength differential subsidence due to ductile extension within the lower crust. The uppermost presalt interval is therefore a late synrift deposit, as opposed to postrift “sag” infill of accommodation created by thermal relaxation of thinned crust.

Well correlation within a sequence stratigraphic framework has identified three regionally correlative flooding surfaces and corresponding sequences within the coquina section that can be mapped with good confidence on 3D PSDM data, and extend across the hinge. These indicate a broad, shallow-water lacustrine depositional environment for the coquina and provide an upper limit on the age of differential subsidence. Halokinetic sequences seen in the postsalt section in the Campos basin imply that the original salt thickness was significantly greater downdip of the hinge, which required that enhanced subsidence occurred no later than the end of salt deposition, providing a lower limit on the age of differential subsidence.

Our interpretation of subsidence localized at the Campos hinge by extension expressed within the ductile lower crust of the Campos basin is supported by deep seismic imaging that places the zone of maximum crustal thinning, defined by an abrupt shallowing of the Moho reflection, beneath the hinge zone. The localization of extension and subsidence creates a monocline that is subject to erosion just prior to evaporite deposition in the Campos basin. The differential subsidence across the hinge provides the accommodation for thick evaporites in the outer Campos basin, while the inner Campos basin has only thin evaporite deposits due to the lack of accommodation.

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