Altena Group

Predominantly fine-grained mudstones with occasional silt- and sandstones. Incidentally organic-carbon concentrations are substantially elevated.

Neritic environment in a generally open-marine basin. Occasionally basin circulation stagnated. With periods of lower sea level and/or tectonic activity.

Conformably overlies the red-brown, variegated, anhydritic beds of the Keuper Formation. Locally, unconformably upon this unit, or on the underlying Muschelkalk Formation or on older units of the Upper Germanic Trias Group, locally even on Zechstein deposits.

Unconformably by the, generally variegated, siliciclastic deposits of the Schieland Group or the shallow-marine sediments of the Rijnland Group. In inverted parts of the West Netherlands Basin, the Roer Valley Graben, the Broad Fourteens Basin and the Central Netherlands Basin the group is often overlain unconformably by the Chalk Group, the Lower North Sea Group or the Middle North Sea Group.