Middle Graben Formation SLCM


Premise The formation has been included in the Schieland Group (SL). Original definition by NAM & RGD (1980), as Middle Graben Shale Formation, but renamed and re-described as Middle Graben Formation by Van Adrichem Boogaert & Kouwe (1993). The type section of the ’Lower Kimmeridge Clay Member’ of NAM & RGD (1980) has been transferred to this formation by Herngreen & Wong (1989).
Derivatio nominis Named after the Central Graben
Type section Location map See figure (pdf)
  Well F03-03 (pdf)
  Location N 54°50’45.5
E 04°42’29.3
  Depth 2670 to 3090 m
  Length 420 m along hole
  Reference NAM and RGD (1980)
Definition Section of grey, locally very silty, carbonaceous claystones. In the northern part of the F-quadrant (e.g. F02, F03 and F05) one thick or locally two sandstone beds may be intercalated (Middle Graben Sandstone Member, SLCMS). At the base of the formation three thin but distinct coal seams occur. They are laterally very extensive and form important lithostratigraphic markers.
Upper Boundary The upper boundary of the formation is the conformable contact with the marine fines of the Kimmeridge Clay Formation (northern part of the F02 and F03 blocks) or barrier sands of the Upper Graben Formation (in the lower half of the F02 & F03 blocks and the greater part of the F05 and F06 blocks) in the northern part of the Dutch Central Graben. To the south it is overlain by the coal-bed dominated Puzzle  Hole  Formation (southernmost part of F05, F06 and in the F08, F11 and F14 blocks). The transition from the Middle Graben Formation to the Puzzle Hole Formation is gradual. Therefore, the upper part of the formation in e.g. F08 is equivalent to the basal Puzzle Hole Formation in F14. The basal coal beds with intercalated marine clays can be correlated with the lowermost Rifgronden Member of the Friese Front Formation (southern Dutch Central Graben).
Lower Boundary The lower boundary with the Lower Graben Formation is placed below the base of the lowermost distinct coal seam, immediately overlying thick sand beds (well F03-03 at 3090 m in Van Adrichem Boogaert & Kouwe, 1993, Annex G-2).
Distribution The distribution area is somewhat smaller than the Lower Graben Formation:  in  the northern  and  central  parts of  the Dutch Central Graben, Blocks B18, F3-F14 (see pdf).
Age Sequence 1 sensu Abbink et al. (2006): Early-Middle Oxfordian. Diagnostic dinoflagellates are: Liesbergia scarburghensis (LOD: M. Oxfordian), Leptodinium subtile (FOD: E. Oxfordian), Polystephanephorus paracalathus (LOD: E. Oxfordian), Scriniodinium crystallinum, Systematophora fasciculigera/penicillata (FOD: E. Oxfordian), S. valensii, S. spp., Wanaea fimbriata (LOD: E. Oxfordian), W. thysanota (LOD: E. Oxfordian). Among the sporomorphs the frequent presence of the Precicatricosisporites spp. complex can be noted and the top occurrence of Neoraistrickia gristhorpensis (LOD: E. Oxfordian). The formation is characterised by a typical ostracod assemblage consisting of  a number of yet undescribed species of Galliaecytheridea (see Herngreen & Wong, 1989). The Middle Graben Formation is age equivalent to the Oisterwijk Limestone Member and part of the Upper Brabant Marl Member of the Brabant Formation (Altena Group) in the Roer Valley Graben.
Depositional Setting Lacustrine to marginal marine embayment.
Subdivision The Middle Graben Formation can be subdivided into three units if the Middle Graben Sandstone Member is recognised. However, as stated by Herngreen and Wong (1989) , only the middle member merits a formal status.
  SL Schieland Group
  SLC Central Graben Subgroup
  SLCM Middle Graben Formation
  upper claystone member
  SLCMS Middle Graben Sandstone Member
  lower claystone member
References See References Upper Jurassic/ Lower Cretaceous

D.K. Munsterman, R.M.C.H. Verreussel, H.F. Mijnlieff, N. Witmans, S. Kerstholt-Boegehold & O.A, Abbink (2012), Revision and update of the Callovian-Ryazanian Stratigraphic Nomenclature in the northern Dutch Offshore, i.e. Central Graben Subgroup and Scruff Group. Netherlands Journal of Geosciences-Geologie en Mijnbouw, 91 (4):555-590.
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