Brabant Formation ATBR

 

Premise Definition after NAM and RGD (1980) . The British term ‘Cornbrash’ has previously been used for the sandy limestone intercalations which are typical for this unit. In the Achterhoek (‘central eastern Netherlands’ of Haanstra (1963) ) the upper Dogger has been encountered in a few isolated locations which have been correlated with the Brabant Formation. Stratigraphic reconnaissance borehole D of the ‘Rijksdienst voor Opsporing van Delfstoffen’ revealed the presence of Upper Bajocian/Lower Bathonian marls and sandy limestones (Gerth (1955) ; Herngreen and de Boer (1974) ). Boreholes Klomps-3, -3a and -4 demonstrated the presence of more than 40 m of dark-grey to black, calcareous clay, which yielded a Middle to Late Callovian age Herngreen et al (1983) .. As a result of the intensely block-faulted, complex structure of the Achterhoek, the stratigraphic relationship between these two intervals, or with the Werkendam Formation, remains uncertain.
Derivatio nominis Named after the Dutch province of Noord-Brabant, where the most complete succession this formation is found.
Type section Location map See figure (pdf)
  Well Oisterwijk-1 (pdf)
  Location N 51°35’32.6
E 05°10’56.1
  Depth 1787 to 2154 m
  Length 367 m along hole
  Reference NAM and RGD (1980)
Additional section Location map See figure (pdf)
  Well Werkendam-2 (pdf)
  Location N 51°47’29.7
E 04°50’22.1
  Depth 1507 to 1746 m
  Length 239 m along hole
  Reference NAM and RGD (1980)
Definition Sequence of limestones, marls and claystones. The entire succession is generally sandy, and the sand content increases towards the top. In the West Netherlands Basin a calcareous sandstone bed is found at the top of the formation in the most complete successions. In the Roer Valley Graben the youngest deposits of the formation consist of oolitic, algal limestones. In the Achterhoek the youngest interval consists of dark-grey to black, calcareous claystones, following a succession of marly and sandy carbonates.
Upper Boundary In a complete succession the top of the formation is formed by the unconformable contact with the variegated siliciclastic deposits of the Nieuwerkerk Formation (Roer Valley Graben and West Netherlands Basin) or the Breeveertien Formation (Broad Fourteens Basin). In some inverted settings and in the Achterhoek the unit may be succeeded unconformably by the Chalk Group, the Lower North Sea Group or the Middle North Sea Group.
Lower Boundary The lower boundary has been placed at the base of the first limestone bed of a marly succession, resting on the claystones of the Werkendam Formation.
Distribution The unit is restricted to synclinal erosional remnants in the Roer Valley Graben, the West Netherlands Basin, the Broad Fourteens Basin, the Central Netherlands Basin and the Achterhoek, which represents the southwestern fringe of the Lower Saxony Basin. Its presence in the Central Netherlands Basin and Broad Fourteens Basin is inferred from seismic data, but has not yet been confirmed by wells (e.g. RGD (1993) ).
Age The formation generally yields palynofloras and rich microfaunas of Bathonian to Late Callovian age. In the most complete successions Oxfordian ages have been found in the uppermost interval of the formation (Upper Brabant Marl and Oisterwijk Limestone Limestone Members), which are locally overlain unconformably by lacustrine deposits of the Nieuwerkerk Formation with an Early Kimmeridgian age (see Fig. G.5 in Section G). Deposits of Late Bajocian to Bathonian age in the Achterhoek show a similar lithofacies, yielding identical palynomorph associations to the Brabant Formation in its type area, the Roer Valley Graben. The Callovian deposits found in the Achterhoek do not resemble the Roer Valley Graben succession in lithofacies or fossil association. These deposits do, however, show a strong affinity with the upper Dogger sequence found in northern Germany, on the eastern side of the Ems Low Herngreen et al (1983) ..
Depositional Setting .The fossils and lithofacies associations encountered in this formation indicate a shift towards periodic very shallow-marine conditions, separated by periods of shallow- to moderately deep-marine deposition. The open marine Callovian deposits of the Achterhoek suggest that this area, which had a development completely comparable to the Roer Valley Graben during the Bathonian, deepened considerably during this period. During the Callovian the fossil associations of the Roer Valley Graben province no longer extended as far as the Achterhoek. Instead, a connection formed between the latter area and the Lower Saxony Basin.
Subdivision  
  In its type area the alternation of marl and limestone intervals enable subdivision of the formation into seven members:
  AT Altena Group
  ATBR Brabant Formation
  ATBRO Oisterwijk Limestone Member
  ATBRU Upper Brabant Marl Member
  ATBR3 Upper Brabant Limestone Member
  ATBRM Middle Brabant Marl Member
  ATBR2 Middle Brabant Limestone Member
  ATBRL Lower Brabant Marl Member
  ATBR1 Lower Brabant Limestone Member
  The boundaries between the various members are based on the differences in carbonate/sand content, as expressed on wire-line logs, especially in sonic velocity and resistivity. As a result of local facies differences, these boundaries may not be synchronous. Owing to truncation and facies changes it is often not possible to recognise this subdivision outside the type area. The special development of the Middle Callovian deposits in the Achterhoek make it possible to distinguish this interval as a separate member. Since the areal distribution of these deposit
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.
Retrieved [Datum] from [url].