The Upper Permian in the Netherlands

The Upper Permian in the Netherlands, as known from borehole data, is deposited in a mainly evaporitic facies north of the Brabant and Rhenish Massifs. In the extreme south (Belgian Campine, de Peel) a near-shore facies of reef dolomites and elastics occurs. In the western and central Netherlands the Upper Permian is represented by a thin sequence of anhydrite and dolomite with some elastics (anhydrite facies). The rock salt facies, developed in the northeastern part of the country, is subdivided into 4 evaporation cycles. Each cycle, when complete, consists of a series of claystone, dolomite, anhydrite, rock salt, bitter salts, laid down under conditions of increasing basin salinity followed by a thin series of rocksalt and anhydrite, deposited under decreasing salinity. The depositional rhythm of the deposits in the rock salt facies is caused by periodic northward shifts of the area of greatest subsidence. Owing to tectonic movements, initiating these shifts, changes occurred in the physiographic conditions relating to entrance channel and basin causing the basin salinity to decrease. Only during periods of relatively low salinity did euxinic conditions exist which gave rise to bituminous deposits. From the distribution of dolomites and bituminous deposits the presence of an east-west striking swell, the Cocvorden Swell, has been inferred, showing that this was a higher and more slowly subsiding tract in the Upper Permian basin. The transition of marine Upper Permian to continental Bunter cannot be regarded as a time boundary; nor are time and rock units within the Upper Permian basin necessarily identical.