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Post-Rift Basin Evolution and Kinematics of the Salt-Detached Deepwater Fold-Belt of the Jequitinhonha Basin, Central East Brazil Passive Margin

Adam, Jurgen *1; Zhiyuan, Ge 1; Sanchez, Marianela 2
(1) Earth Sciences, Royal Holloway, University of London, Egham, United Kingdom.
(2) WesternGeco, Gatwick, United Kingdom.

Salt structures in linked extensional-contractional systems of passive margin basins are important targets in deepwater exploration. The presented study investigates the basin-scale salt tectonic processes and kinematic evolution of the deepwater fold-belt in the Jequitinhonha salt basin, offshore the central Brazil margin. In the deepwater basin impressive salt-cored folds, salt walls and inflated salt massifs reach heights up to 4 km.

We applied analogue experiments and strain monitoring techniques to reproduce the salt dynamic processes and basin history of the Jequitinhonha Basin. The aim was to understand the interaction between margin subsidence, sedimentation and salt mobilization as well as the kinematics of the salt-cored fold and fault structures. 2D regional seismic interpretations provided the boundary conditions for the scaled analogue experiments.

The kinematic evolution of the experiments was characterized by three major stages, e.g. post-rift, drift, modern margin. Most of the total deformation was accumulated already during the early experiment stage followed by a drastic reduction of strain rates when continuous deposition in the deepwater basin impeded the deformation process because of the increased overburden strength. The experiments demonstrated that sedimentation patterns and margin tilt history in the early post-rift stage are the main factors controlling salt tectonics and basin architecture.

The best results to reproduce the poly-harmonic folds typical of the Jequitinhonha Basin were achieved in experiments simulating stable carbonate platform conditions in the landward shallow salt basin and an unstable patchwork of carbonate build-ups in the central deep salt basin during the early post-rift stage. Ongoing thermal subsidence transformed the isolated carbonate build-ups in a network of contractional minibasins and intervening salt ridges which later became the cores of the long-wavelength folds.

Kinematic analysis of experiment sections and time-series strain data provided the mechanical concepts for the sequential restoration of a representative regional seismic line. The restoration results demonstrated that horizontal strain in the Albian-Cenomanian carbonate sequence is twice as high as deduced from kinematic restoration of the seismic sections. This has implications for the reconstruction of basin-scale palaeo-depositional maps, reservoir characterisation, and fracture analysis in the deformed carbonate reservoirs.

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California