Autogenic initiation of basin-scale salt tectonics

Jimmy Moneron, Giridas Maiti, Mads Huuse, Christopher Aiden-Lee Jackson , Alexandre Lethiers, Nevena Andrić-Tomašević

Salt structures typically form due to the post-depositional flow of salt triggered and maintained by allogenic drivers such as differential loading, gravity gliding, or shortening. Using ~26,000 km² of 3-D seismic reflection data and 34 wells from the Southern North Sea, we propose that the earliest regional deformation of the Southern Permian Basin salt giant (Zechstein Supergroup) was instead autogenic, being initiated by intra-salt diagenetic processes. The synclines of the earliest salt-cored folds overlie ridges of intrasalt gypsum that converted to anhydrite at the end of the Permian. Triassic onlap and truncation show that these folds formed immediately after salt deposition, long before regional Paleogene–Neogene shortening, and that the curvilinear, variably oriented hinges parallel neither the sub-salt fault network nor the dip of the detachment, as allogenic mechanisms would predict. Numerical experiments show that the density contrast created by intrasalt diagenesis may have caused the gypsum ridges to founder into the underlying halite, drawing down the depositional surface, forming depressions ultimately filled by Triassic sediment. A significant component of early-stage salt tectonics in the Southern Permian Basin may therefore be autogenic in origin, with the distribution of the much younger shortening structures being dictated by diagenetic reactions within the evaporite rather than by regional, plate-driven stresses. Regional tectonism subsequently amplified these structures, which nonetheless retain a record of key control on their distribution.