|Premise||The formation is included in the Schieland Group (SL), into which the former Central Graben Group has been placed as a subgroup (SLC). Originally defined by NAM & RGD (1980), as Lower Graben Sand Formation. Amended by Herngreen & Wong (1989), since the formation does not always consist of sand- stone alone, the lithological affix has been dropped.|
|Derivatio nominis||Named after the Central Graben|
|Type section||Location map||See figure (pdf)|
|Depth||3090 to 3652 m|
|Length||562 m along hole|
|Definition||Section of greyish brown, very fine to fine-grained, well-sorted sandstones, occurring in beds generally less than 10 m thick, with intercalations of thin greyish brown silty to sandy claystones. The formation is generally carbonaceous with some distinct coal layers. The individual sandstone bodies have a rather restricted lateral extent. Especially in the upper parts of this unit the GR-log pattern of these beds tends to show a coarsening-upward trend.|
|Upper Boundary||The top of the formation is conformable and formed by the base of the Middle Graben Formation. This boundary is defined at the first distinct coal-bed recognised over most of the studied area.|
|Lower Boundary||The base of the formation disconformably overlies Lower-Middle Jurassic formations (Werkendam Formation, the Posidonia Formation, the Aalburg Formation), or formations from the Upper Germanic Triassic Group. Occasionally, the underlying Werkendam Formation may be developed in a coarse-grained oolitic facies, which makes the boundary between the two formations difficult to pick on logs alone.|
|Distribution||The formation is restricted to the northern-central parts of the Dutch Central Graben (Blocks F03, F05, F06, F08, F09, F11, F12 and F14 (see pdf)) in Sequence 1 sensu Abbink et al. (2006). It shows a wide range in thickness (40-562 m), with the thickest accumulation in the fault-bounded south-western corner of block F03. In the Danish part of the Central Graben similar strata have also been recognised and are referred to as the Lulu Formation (Koch, 1983; Herngreen & Wong, 1989; Michelsen & Wong, 1991; Michelsen et al., 2003).|
|Age||Sequence 1 sensu Abbink et al. (2006): Middle-Late Callovian. Significant dinoflagellate species, from which this interpretation is derived, are: Liesbergia scarburghensis (First Occurrence Datum, ‘FOD’: M. Callovian), Ctenidodinium spp. (a.o. C. continuum, C. gochtii-kettonense group, C. sellwoodii-stauromatos group), Energlynia acollaris, Lithodinia jurassica (Last Occurrence Datum, ‘LOD’: Callovian), Meiourogonyaulax borealis, Pareodinia prolongata (LOD: Callovian), Rigaudella aemula, Scriniodinium galeritum, Stephanelytron spp., Systematophora spp., Wanaea fimbriata, and W. thysanota (FOD: M. Callovian). There is a consistent presence of a characteristic sporomorph association with Precicatricosisporites spp. (FOD: M. Callovian). The ostracods Lophocythere interrupta interrupta, L. bipartita, Fuhrbergiella horrida horrida, Pseudohutsonia tuberosa and Lophocythere interrupta are rare, but characteristic elements in this formation (e.g. wells F17-03 and F14-01).|
|Depositional Setting||Fluvial to delta- and coastal plain.|
|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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