Consists of brownish- grey to black bituminous claystones (Clay Deep Member). South of blocks F11/F12 the colour changes into olive-grey to grey-brown and the clays become more silty to very fine sandy and less bituminous (Schill Grund Member).
Basin circulation stagnated in the northernmost part of the basin, which resulted in dysoxic to anoxic basin-floor conditions and in the deposition and preservation of bituminous claystones. To the south relatively shallower, open marine circumstances occurred with (near) normal basin-floor ventilation. Overall the claystones are more silty or finely sandy and only slightly bituminous.
In the northern Central Graben unconformably on the Scruff Greensand or Kimmeridge Clay formations. May interfinger with the Scruff Greensand Formation. The bituminous shales show a less spiky appearance on the wire-logs, and higher values on the GR and resistivity readings than the underlying Kimmeridge Clay Formation. The boundary with the glauconitic Scruff Greensand Formation in the southern part of the Central Graben and Terschelling Basin is conformable.
Coincides with the Berriasian-Valanginian-boundary. It is associated with the Late Kimmerian unconformity. The formation is unconformably overlain by the Rijnland, Chalk or Lower North Sea groups.
