Jimmy Moneron, Christopher Aiden-Lee Jackson 

Across buried sedimentary basins, the dissolution-prone nature of evaporite sequences drives the formation of collapse structures (e.g., sinkholes), fundamentally transforming landscapes at large scales. Understanding where, why, and how such structures form is crucial, given they pose geological hazards that may threaten human safety and infrastructure stability, or may affect subsurface resource extraction and geological storage. Here, we use 3D seismic reflection and borehole data from the Southern North Sea Basin to document giant (km-wide and several hundred-metres deep) collapse structures within the upper part of the evaporite-dominated, Zechstein Supergroup (Permian). We show that these features, which form both isolated, sub-circular sinkholes and polygonal, valley-like networks, are developed at the basin-scale (>10,000km2). Critically, these structures invariably overlie gypsum buildups capped by thick halite deposits (100–300m), with seismic-stratigraphic relationships enabling precise dating and facilitating accurate modelling. We propose that the transformation of gypsum to anhydrite during early burial initiated the extrusion of NaCl-undersaturated water, which provoked hypogenic dissolution of the capping halite, leading to collapse at the depositional surface. The resulting Permian landscape was buried and thus preserved by a potash infilling unit. To the best of our knowledge, the basin-wide development of this type of giant salt dissolution-induced collapse structure has not previously been described in the stratigraphic record.