Basin-scale development of giant collapse structures induced by gypsum diagenesis

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 Zechstein Supergroup (Permian) that developed at the basin-scale (>10,000km²). Critically, these structures invariably overlie gypsum buildups capped by thick halite, 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 dissolution of the capping halite, leading to collapse at the depositional surface. The resulting 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 structures has not previously been described in the stratigraphic record.