Skylge Formation SGSK


Premise This new formation is included in the Scruff Group. It comprises all marine successions from the Terschelling and Vlieland basins in Sequence 2 sensu Abbink et al. (2006). Scattered occurrences are also recorded at the fringes of the Central Graben. Four members are recognised in the Skylge Formation: the Oyster Ground, Terschelling Sandstone, Noordvaarder and Lies members.
The Oyster Ground and Terschelling Sandstone members are transferred from the Friese Front Formation (mainly continental Schieland Group) to the new Skylge Formation, because of their restricted marine character.
The Noordvaarder Member includes the predominantly sandy part of the former Scruff Argillaceous Member and the underlying difficult to distinguish Scruff Basal Sandstone Member. The recognition of the Scruff Basal Sandstone Member as a separate unit is abandoned here.
The lateral clayey facies of the former Scruff Argillaceous is attributed to the Lies Member. In addition, the informal main Kimmeridge Clay Member sensu Van Adrichem Boogaert & Kouwe (1993) in the southern Central Graben, the Terschelling and Vlieland basins is also included in the Lies Member. The Kimmeridge Clay Formation (amended) is currently restricted to the northern Central Graben. The term Scruff Argillaceous Member is also abandoned here.
The stratigraphic interval from 2312 till 2565 m of well L06-02 is presented as the new type section for the Skylge Formation and its attributed members. Cores taken from within this interval enable the description of the type section in detail. A critical note on this type section is the occurrence of faults in the Terschelling Sandstone Member, which casts doubt on the assumption that the type section represents the true stratigraphic thickness. However, for definition of a sound lithological description this well seems appropriate, taking into account the surrounding wells where a similar succession can be observed.
Derivatio nominis Named after the Frysian name of the Wadden island Terschelling.
Type section Location map See figure (pdf)
  Well L06-02 (pdf)
  Location N 53°48’53.7"
E 04°59’19.97"
  Depth 2318 to 2565 m
  Length 247 m along hole
  Reference Munsterman et al. (2012)
Additional section Location map See figure (pdf)
  Well F18-02 (pdf)
  Location N 54°04’25.3
E 04°43’48.5
  Depth 2182 to 2512 m
  Length 330 m along hole
  Reference Munsterman et al. (2012)
Definition Succession of alternating slightly silty to sandy claystones, argillaceous and/or non-argillaceous glauconitic sandstones. Bioturbation is often present. Locally pyrite, lignite and/or shell fragments are present.
Upper Boundary The transition coincides with the Sequence 2 / Sequence 3 boundary sensu Abbink et al. (2006). In the southern Central Graben the formation is unconformably overlain by the Scruff Greensand Formation. The upper boundary with the Scruff Greensand Formation is recorded by a funnel- shaped GR-log pattern, resulting from the upward decreasing clay content. This change is also well shown on the porosity log. Sequences 2 and 3 are relatively thick in the Terschelling Basin as compared to the Central Graben. Deposition was continuous in the depocentre of the Terschelling Basin (Abbink et al., 2006).
Lower Boundary The Skylge Formation conformably overlies the Friese Front Formation (boundary: top of the first variegated or grey, non- marine clay-/siltstones or thick sand bed)..
Distribution The formation occurs at the fringes of the Central Graben (e.g. blocks B14, F11 and F12), the Terschelling and Vlieland basins (blocks F15, F17, F18, G16, L02, L03, L05, L06, L09, L12, L15, M01, M04 and M07-see Fig.). In the Terschelling Basin the basal part of the Skylge Formation may also interfinger with the top of the Friese Front Formation. The Kimmeridge Clay Formation in the northern part of the Central Graben is the open marine equivalent of the restricted to shallow marine Skylge  Formation (see pdf).
Age Sequence 2 sensu Abbink et al. (2006): Late Kimmeridgian – late Middle Volgian, eudoxus-anguiformis Ammonite zones. The base of the formation is associated with the late Early Kimmeridgian J63 MFS sensu Partington et al. (1993). The top coincides with the Sequence 2/Sequence 3 boundary sensu Abbink et al. (2006) in the anguiformis Ammonite Zone and is associated with the Middle Volgian J73 MFS sensu Partington et al. (1993).
Depositional Setting Restricted to shallow marine conditions.
Subdivision Four formal members are recognised in the Skylge Formation:
  SG Scruff Group
  SGSK Skylge Formation (new)
  SGSKL Lies Member (new)
  SGSKN Noordvaarder Member (new)
  SGSKT Terschelling Sandstone Member (revised)
  SGSKO Oyster Ground Member (revised)
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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