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Tectonic Evolution of a Mixed Salt-Shale-Detached Deepwater Fold and Thrust Belt in the Eastern Salina del Bravo Province, Western Gulf of Mexico


We analyse the regional tectonic evolution and stratigraphic framework of the eastern Salina del Bravo province in the Western Gulf of Mexico deep-water basin in order to establish a kinematic model of the unique fold-and-thrust belt system (FTB), which is developing on a shale detachment in front of basinward-advancing allochthnonous salt sheets. The fold-and-thrust belt is affected by thin-skinned shortening and is part of the deep-water contractional domain of a regional salt-detached gravity-driven linked extensional-contractional system that is characterized by a Mesozoic to Cenozoic sedimentary succession ranging from 10 to 13 km in thickness. A kinematic analysis has been conducted based on the structural-stratigraphic interpretation of a 3D survey and structural restoration of three regional 2D seismic lines, to determine the basin morphology, architecture and kinematic evolution of the FTB. The FTB detaches on Middle Eocene overpressured shales and incorporates Upper Eocene to Oligocene pre-kinematic deep-marine shales and sandstones, and Neogene syn- and post-kinematic sediments. The thin-skinned FTB has formed by regional shortening in response to gravitational sliding of shelf sediments and an interaction of the inflating and advancing salt sheets. Based on timing constraints from syn-kinematic sediments and structural restoration, the FTB developed in a basinward-breaking thrust sequence forming a proximal arcuate fold-thrust belt basinward of the salt sheet during the Late Oligocene to Early Miocene times, and a more distal faulted detachment fold belt in the basinal sequences from Early Miocene-to present time. The sequential restoration of the FTB documents an overall shortening of approximately 11.3 km (21%) in the northern part of the study area, 11 km (27%) in the central, and 10.8 km (26%) in the southern part. In relation to the petroleum system implications, we propose that the most prospective traps are the thrust-related folds because they developed earlier than the detachment folds, and were in place for the second stage of hydrocarbon charge that occurred during Pleistocene times. The derived kinematic model and tectono-stratigraphic information provides valuable insights into the evolution of mixed salt-shale systems and is useful to determine styles and timing of prospective hydrocarbon traps in this part of the Gulf of Mexico basin.