Formal (NAM & RGD 1980). Amended (Van Adrichem Boogaert & Kouwe 1994).
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.
Definition of lower boundary
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.
Definition of upper boundary
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.
Extremely variable (up to 2900 m) as often eroded through inversion.
UK: West Sole Group & Lias Group; GER: Dogger Group & Lias Group; BEL: Aalburg Formation.
Rhaetian - early Oxfordian.
Origin of name
The Altena Group is named after ‘Het Land van Altena’, the northern part of the Dutch province of Noord-Brabant, where the most complete sequence of the group has been encountered in wells.
NAM & RGD 1980. Stratigraphic nomenclature of The Netherlands. Verhandelingen van het Koninklijk Nederlands Geologisch Mijnbouwkundig Genootschap 32, 77 p.
Van Adrichem Boogaert, H.A. & Kouwe, W.F.P. 1994. Stratigraphic nomenclature of The Netherlands; revision and update by RGD and NOGEPA, Section F, Lower and Middle Jurassic. Mededelingen Rijks Geologische Dienst, 50, 1-20.
TNO-GDN ([YEAR]). Altena Group. In: Stratigraphic Nomenclature of the Netherlands, TNO – Geological Survey of the Netherlands. Accessed on [DATE] from http://acc.dinoloket.nl/en/stratigraphic-nomenclature/altena-group.