Salt-structural styles and kinematic evolution of the Jequitinhonha deepwater fold belt, central Brazil passive margin
摘要
Salt structures in linked extensional–contractional systems of passive margin sedimentary basins and deepwater fold belts play an important role in the evolution of rifted continental margins. The 100 km wide Jequitinhonha Basin with its salt-detached deepwater fold belt provides insight in the post-rift salt deformation processes in deepwater fold belts of the central Brazilian continental margin. Seismic interpretation and kinematic analysis of basin-scale 2D sections provide insights into the salt tectonic processes, related depositional systems, salt basin geometry, and kinematic evolution of the deepwater fold belt. Several salt kinematic domains have been identified; the most evident is the long-term contractional domain in the distal basin, which formed impressive salt-cored anticlines, salt walls and salt massifs reaching 4 km in thickness. The post-rift basin evolution was dominated by thin-skinned deformation and was initiated by differential loading of early post-rift shallow marine carbonates. Subsequently, the system was mainly driven by gravity-gliding of the overburden on the Aptian salt detachment. The depocenters were controlled by early post-rift salt mobilization and ranged from asymmetric grabens and rollovers to minibasins with vertically-stacked or shifting depocenters and formed the basis of the deepwater fold belt architecture in the Jequitinhonha Basin. The structural styles and kinematic evolution of the deepwater fold belt were strongly controlled by the original salt thickness, the distribution of Albian–Campanian depocenters and thickness variations in the overburden sediments. Early Cretaceous short-wavelength folds have been overprinted by long-wavelength folding owing to increased strength and thickness of the overburden since Paleogene times. Large-amplitude salt-cored folds developed in the deepwater basin due to contraction of pre-existing salt walls and formed margin-parallel, NNW–SSE trending narrow structural highs separated by wide depocenters. Ongoing uplift with reduced sediment accumulation over contractional diapirs or crestal erosion of the deepwater anticlines supported long-term strain localization and positive feedback in the active deepwater contractional deformation.
