Amir Joffe, Christopher Aiden-Lee Jackson , Leonardo Muniz Pichel

Salt tectonics is typically caused by the flow of mobile evaporites in response to post-depositional gravity gliding and/or differential loading by overburden sediments. This situation is considerably more complex near the margins of salt basins, where carbonate and clastic rocks may be deposited at the same time and interbedded with more mobile evaporitic strata. In these cases, syn-depositional salt flow may occur due to density differences in the deposited lithologies, although our understanding of this and related processes is relatively poor. We here use 3D seismic reflection and borehole data from the Devil’s Hole Horst, West Central Shelf, offshore UK to understand the genesis, geometry and kinematic evolution of intra-Zechstein Supergroup (Lopingian) minibasins and their effect on post-depositional salt deformation. We show that immobile, pinnacle-to-barrier-like, carbonate build-ups and anhydrite are largely restricted to intra-basin highs, whereas mobile halite, which flowed to form large diapirs, dominates in the deep basin. At the transition between the intra-basin highs and the deep basin, a belt of intra-Zechstein minibasins occur, forming due to the subsidence of relatively dense anhydrite into underlying halite. Depending on primary halite thickness, these intra-Zechstein minibasins created topographic lows, dictating the position for nucleation and subsequent down-building of Triassic minibasins. Our study refines the original depositional model for the Zechstein Supergroup in the Central North Sea, with the results also helping us better understand the style and distribution of syn-depositional salt flow on other layered evaporitic sequences and the role intra-salt heterogeneity and related deformation may have in the associated petroleum plays.