Rupel Formation

Heavy, dark brown-grey silty clays, rich in pyrite and relatively glauconite-poor. Towards both base and top, the clays grade into silts and rather abruptly into sands along the southern basin margin (Vis et al. 2016). The sands are moderately fine-grained (150-210 µm) to coarse-grained (150-300 µm) and glauconitic. Flint pebbles and phosphorite nodules commonly occur at the base. The formation is expected to contain septarian carbonate concretions which are well documented from Belgian quarries (De Craen et al. 1999).

Middle to outer neritic marine setting (water depths of up to 500 m). The sands are of a shallow-marine origin with intercalated lagoonal sediments.

Unconformably overlies the Tongeren Formation, the Dongen Formation or older sediments. In those areas where the sandy development at the base is missing, the clays of the Rupel Formation rest directly on the Asse or Engelsche Hoek members, which complicates definition of the boundary. However, on wire-line logs, the Rupel clays show a somewhat higher gamma-ray response compared to the clays of the Lower North Sea Group. Biostratigraphic data may assist in establishing this boundary.

Conformably or mildly unconformably overlain in the central and eastern Netherlands, and part of the northeastern offshore by the sands and silty shales of the Veldhoven Formation. In the southern Netherlands the latter has a typical, thin clay interval at its base. The upper limit is usually sharp in those parts of the Netherlands where the Rupel Formation is partly eroded (in the early Kenozoic on the high between Nijmegen and Leiden) and is overlain by the Breda Formation or the Naaldwijk Formation. The Breda Formation often is richer in glauconitic sands and clays. The upper boundary is arbitrary in areas where the macroscopic characteristics of the covering clays are the same as those of the Boom Member.