Lower Germanic Trias Group RB

 

Derivatio nominis The name Lower Germanic Trias Group was introduced in NAM and RGD (1980) . In the present classification the lowest part of that succession (claystones between highest Zechstein evaporite and the base of the ‘Upper Br√∂ckelschiefer’ is assigned to the Zechstein (Zechstein Upper Claystone Formation). The former Bunter Group (basin-margin development) of NAM and RGD (1980) is incorporated in the redefined Lower Germanic Trias Group. Detailed correlation permitted the identification of the formations of the basinal realm in the fringe area. The name has been derived from the German stratigraphic nomenclature, where it is commonly applied to denominate the entire sedimentary sequence between the Zechstein Group and the Jurassic claystones . The prefix ‘Lower’ applies to the part of the Germanic Trias which occurs below the Base Solling Unconformity (= Spathian Unconformity) of late Scythian (Spathian) age.
Type section Location map See figure (pdf)
  Well Blijham-1 (pdf)
  Location N 53°05’40.9
E 07°04’40.0
  Depth 2736 to 3255 m
  Length 519 m along hole
  Reference (amended after NAM and RGD (1980) ).
Definition Group of formations composed mainly of red-bed-type sandstones, siltstones and claystones, situated between the top of the Zechstein Group and the Base Solling Unconformity (= Spathian Unconformity), which marks the base of the Upper Germanic Trias Group. .
Upper Boundary The upper boundary of the group is formed by the unconformity at the base of the Upper Germanic Trias Group. It is placed at the base of the Solling Sandstone Member, which is generally distinguished by higher acoustic velocities (indicating a higher degree of cementation) than the underlying sandstones.
Lower Boundary The lower boundary is placed at the base of a thin, but distinct sandstone bed forming the basal unit of a gradual fining-upwards trend, which overlies the topmost claystones or carbonates of the Zechstein Group. On wireline logs, this sandstone bed commonly displays relatively low gamma-ray values and high acoustic velocities suggesting anhydrite cementation.
Distribution The group has a very wide distribution and is found over large areas of the Dutch onshore and offshore. It is absent on the Texel-IJsselmeer High (see pdf) , Brabant Massif and most of the Cleaver Bank and Mid North Sea Highs as a result of later erosion related to, amongst others, the Late Kimmerian uplift.
Age Latest Permian to Scythian. Hardly any palynomorphs have been found in the sediments of the Lower Germanic Trias Group in the Netherlands up to now. An exception is well America (R.O.v.D. nr. 11), where a typical Late Permian sporomorph assemblage was found in part of the section which is attributed to the lower part of the Lower Buntsandstein Formation RGD (1993) .
Depositional Setting The Lower Germanic Trias Group comprises mainly clastic sediments, deposited in a lacustrine and fluvial setting with local aeolian influences.
Subdivision The subdivision of the Lower Germanic Trias Group essentially follows the German subdivision. The group can be subdivided as follows:
  RB Lower Germanic Trias Group
  RBM Buntsandstein Subgroup
  RBMH Hardegsen Formation
  RBMD Detfurth Formation
  RBMV Volpriehausen Formation
  RBSH Lower Buntsandstein Formation
References See References Triassic

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