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 driven by differential loading, gravity gliding, or shortening, with the internal architecture of the evaporite treated as a passive strain marker. Using ~26,000 km² of 3-D seismic reflection data and 34 wells from the Southern North Sea, we show that the earliest regional deformation of the Southern Permian Basin salt giant (Zechstein Supergroup) was instead autogenic. The synclines of the first salt-cored folds overlie ridges of intrasalt gypsum that converted to anhydrite at the end of the Lopingian. Triassic onlap and truncation show that these folds formed immediately after salt deposition, long before Paleogene–Neogene shortening, and their curvilinear, unoriented pattern follows neither the sub-salt fault grid nor the dip of the detachment, as allogenic mechanisms would predict. Numerical experiments show that the density contrast created by the conversion suffices to make the ridges founder into the underlying halite, depressing the depositional surface above them into lows that Triassic sediments then filled. A significant component of Southern Permian Basin salt tectonics may therefore be autogenic in origin, with the distribution of the related structures being fixed by depositional mounding and diagenetic reactions within the evaporite rather than by regional, plate-driven stresses. Regional tectonism subsequently amplified these structures, which nonetheless retain the distribution imposed within the evaporite.