Extent and variability of Mesozoic-Cenozoic multi-stage salt diapirs in the Southern Permian Basin, Southern North Sea

Abstract

Salt structures can be used as an archive for tectonic and depositional processes as all salt structures respond distinctively. Few salt tectonic studies have investigated the evolution of multi-stage salt structures, nevertheless, no previous study had systematically identified, mapped, nor classified, the evolution of multi-stage salt structures in a regional study. Decades of hydrocarbon exploration and the heavily dense 3D seismic data available, make the Southern North Sea one of the best natural laboratories to investigate the evolution of salt structures. The Southern North Sea salt basin is a Late Permian Zechstein salt mega-basin containing a myriad of salt structures. The complex tectonic evolution of the Southern North Sea created diverse Mesozoic structural sub-basins with different tectonostratigraphic evolutions. We defined a nomenclature, linked to the mega-stratigraphic sequences, for the classification of salt structures. We used a Two-Way-Travel-Time 3D seismic reflection dataset and time-thickness variations around salt structures to systematically analyse the evolution of salt structures across the diverse structural sub-basins of the Southern North Sea. Multi-stage salt diapirs were triggered halokinetically in the Early Triassic and are linked to regional palaeo-depocentres controlled by the sub-Zechstein structural configuration. Multi-stage salt diapirs in the different sub-basins evolved through three different regional phases and up to five distinctive local stages. The most complex salt diapirs developed in the Central Graben, Sole Pit High and Silver Pit Basin, where multi-stage salt diapirs showed 4–5 local stages of salt diapirism. The multi-stage evolution of salt structures should be thoroughly investigated to reduce risks and uncertainties in the energy sector and net zero projects, such as in carbon capturing and storage projects, and energy storage in man-made salt caverns.