Aalburg Formation ATAL

 

Premise Definition after NAM and RGD (1980) . The lithological affix has been dropped.
Derivatio nominis Named after the municipality of Aalburg in ‘Het Land van Altena’ (northern part of the Dutch province of Noord-Brabant).
Type section Location map See figure (pdf)
  Well Werkendam-2 (pdf)
  Location N 51°47’29.7
E 04°50’22.1
  Depth 2228 to 2803 m
  Length 575 m along hole
  Reference NAM and RGD (1980)
Definition Sequence of dark-grey, calcareous, locally silty or sandy, claystones containing occasional thin argillaceous limestone (fossil hash) beds. At the base, a distinct argillaceous limestone interval is found. Pyrite, carbonaceous matter, macrofossils (ammonites, belemnites, gastropods, etc., frequently pyritised), iron oolites and up to dm-size ferruginous siderite nodules can be common.
Upper Boundary The top of the formation has been placed at the base of the bituminous, shaly claystone interval of the Posidonia Shale Formation.
Lower Boundary The basal argillaceous limestone interval marks the transition from the brown claystones of the underlying Sleen Formation.
Distribution Distribution of the unit practically coincides with that of the entire Altena Group. Only in very few localities has the complete Aalburg Formation been removed by later erosion, while the thin Sleen Formation has been preserved.
Age The formation yields palynofloras and microfaunas of Hettangian to Pliensbachian (Lias-~ to -d) age.
Depositional Setting The fossils and lithofacies associations encountered in this formation indicate deposition in a shallow to fairly deep, open-marine, neritic environment. The thickness distribution of the formation illustrates differential subsidence rates during its deposition. Seismic data demonstrate growth fault activity associated with extension tectonics and considerable thinning towards the southern basin margin against the London-Brabant Massif. Particularly thick sequences of this formation can be encountered in the Dutch Central Graben, associated with halokinetic structures.
Subdivision On the basis of wire-line log characteristics, subdivision would be possible in some areas, but there are hardly any grounds for a formal, lithologically based, subdivision, as already stated by NAM and RGD (1980) .
References See References Lower and Middle Jurassic

Van Adrichem Boogaert, H.A. & Kouwe, W.F.P., 1993-1997. [Stratigraphic unit]. In: Stratigraphic Nomenclature of the Netherlands.
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