Post-rift salt tectonic evolution and key control factors of the Jequitinhonha deepwater fold belt, central Brazil passive margin: Insights from scaled physical experiments

摘要

This experiment study investigates the basin-scale salt tectonic processes and kinematic evolution of the gravity-driven deepwater fold belt in the offshore Jequitinhonha salt basin, central Brazil margin. Scaled analogue experiments, geologically constrained by 2D regional seismic interpretations, examine the salt tectonic processes and related depocentre evolution in the basin for variable margin tilt histories and depositional scenarios on appropriate time scales of post-rift basin evolution. The analogue experiments and derived 3D strain data demonstrate that early post-rift sedimentation patterns and margin tilt history were important control factors of the structural and kinematic evolution of the deepwater fold belt. The experiments produced different contractional structures varying from pinched short-wavelength synclines, via polyharmonic salt-cored folds, to thrust belts of variable widths. The salt-cored fold styles and Albian-Cenomanian minibasins characteristic of the Jequitinhonha deepwater fold belt were only reproduced in one experiment, which included isolated carbonate buildups in the seaward salt basin at the onset of post-salt deposition. Basin evolution and salt tectonics in the Jequitinhonha Basin were dominantly controlled by gravity-gliding of the post-rift sediment succession and formation of carbonate-dominated minibasins on a thick viscous salt substratum in the seaward basin. The subsiding minibasins determined the positions of future synclines and created intervening salt ridges, which became the cores of the long-wavelength anticlines. Experiment restoration utilising time-series strain data allowed estimation of early post-rift deformation showing that strain in the Albian—Cenomanian carbonates probably is six times higher than documented in seismic data. This discrepancy would have major implications for producing realistic palaeo-depositional reconstructions or fracture analysis in the deformed carbonate reservoirs potentially targeted in the salt-cored anticlines.