Major heterogeneity in evaporitic depositional systems: The genesis of kilometre-scale gypsum networks in the Zechstein Basin

Evaporite sequences typically exhibit uniform thickness and facies distribution during accumulation on a flat seafloor, facilitating stratigraphic regional correlation across vast distances. Understanding the evolution and variability of these authigenic formations is essential to addressing a range of geoenergy, geostorage, and geohazard challenges, making them a key focus of modern geoscience research. Here, this study reveals a significant departure from this typical layer-cake stratigraphy during gypsum precipitation in the Permian Basin of NW Europe. Focusing on the Zechstein main anhydrite (Z3a) cycle, the research demonstrates that this lowermost Z3 unit deviates from an isopachous distribution across the entire basin. While thickness anomalies of this layer were first observed in German mines in the 20th century, and were later visualised across the Dutch offshore sector, it is shown here that the Z3a thick zones form a basin-scale network of gypsiferous buildups, extending over 1000 km from the UK into Germany, Poland, and possibly beyond. Whereas some hypotheses suggest that these thicker deposits result from gypsum diapirism (during the gypsum-to-anhydrite transformation), this study proposes that these features developed progressively within hypersaline conditions during precipitation. Documenting a unique observation of basin-scale networks of sediment mounds, previously unreported in the stratigraphic record at this scale, this unveils a potentially distinct mode of gypsum accumulation in a major evaporitic basin, with broad implications for understanding evaporite variability on a global scale.