Episodic Salt Tectonics in the Northern North German Basin, Lolland–Falster Area, Denmark

Salt tectonics exerts a fundamental control on both the storage potential for CO 2 and hydrogen and the formation of hydrocarbon traps across numerous basins, including the North German Basin. Here, we investigate salt dynamics within the basin, uncovering a previously unrecognised link between deep‐seated and supra‐salt faulting and diapirism along its margin. Much of the North German Basin has a simple structural outline characterised by few faults and Zechstein salt mobilised into large salt pillows. In contrast, the northern basin rim is characterised by a complex fault belt and by salt diapirism. Seismic data show that the Lolland‐Falster Fault Zone is part of this fault belt. Detachment faulting over a decollement of Zechstein salt occurred here in the latest Middle to early Late Triassic triggered by mild deep‐seated faulting and furthered by gravitational gliding and local loading from infill of rift depressions. Contemporaneous diapirism took place locally within this fault zone utilising faults as conduits. While from ~300 m to +2 km thick Zechstein halite buffered deep‐seated fault break‐through, and thus hampered diapirism in the central part of the basin, the modest salt thicknesses of around 250–300 m at the outer basin margin permitted fault break‐through, such that diapirism became limited to the basin outskirts despite lesser salt volumes. These mechanisms are applicable in epicontinental salt basins elsewhere. Near basin centres, ductile deformation of thickly developed salt layers inhibits mechanical break‐through of deep‐seated faults into the overlying supra‐salt section. Triggering of salt diapirism here requires strong faulting. In contrast, salt attains a critical thickness on the outer basin margin bordering the basin centre, thin enough for small‐offset deep‐seated faulting to pierce through and thick enough for salt to mobilise into diapirs within fault zones. In Lolland‐Falster, following a pause in salt motion and faulting, renewed differential salt movement and faulting took place during the Mid‐Cimmerian uplift in Middle Jurassic through Early Cretaceous time reactivated by regional tectonism and instability. Salt motion and faulting ceased during the Early Cretaceous with tectonic tranquillity persisting into the Late Cretaceous. The most recent episode of salt motion and detachment faulting occurred sometime during the Cenozoic, deforming the Chalk Group and overlying Palaeocene sediments. Investigations of the near‐surface geology through shallow seismic interpretation, review of SkyTEM data and interpretation of the present‐day landscape based on DEM maps document surface and near‐surface expressions of deeper faults and salt structures caused by either differential erosion or very young salt motion.