Friese Front Formation SLCF


Premise The formation is included in the Schieland Group. The formation has been defined and described by Van Adrichem Boogaert & Kouwe (1993). The definition is modified here: the restricted to shallow marine Oyster Ground Claystone and Terschelling members are transferred from the Friese Front to the new Skylge Formation (Scruff Group). One formal member is recognised in the Friese Front Formation: Rifgronden Member. Strata between the Rifgronden and Oyster Ground members are assigned to the undifferentiated Friese Front Formation and indicated informally as  ‘main Friese Front member’ in Van Adrichem Boogaert & Kouwe (1993).
Derivatio nominis Named after the Friese Front, a fisherman’s name for the shelf break area north of the Wadden Islands, near the type locality.
Type section Location map See figure (pdf)
  Well F18-02 (pdf)
  Location N 54°04’25.3
E 04°43’48.7
  Depth 2440 to 2734 m
  Length 294 m along hole
Additional section Location map See figure (pdf)
  Well L03-01 (pdf)
  Location N 53°56’55.4
E 04°40’22.0
  Depth 2542 to 2990 m
  Length 448m along hole
Definition The formation consists of alternating claystones, siltstones, sandstones and some minor coal. The siltstones and claystones are generally grey or variegated and become increasingly reddish-mottled towards the south in the L blocks. Siderite spherulites and concretions are common. The sands have been described as sheets, isolated and amalgamated channels (Van Adrichem Boogaert & Kouwe, 1993). The GR-log pattern shows a change from predominantly funnel-shaped in the north (F17 block) to predominantly bell-shaped in the south (L blocks). Several intervals of dark-grey to black silty, carbonaceous, fossiliferous claystone with intercalated calcareous beds can be encountered in the formation.
Upper Boundary Normally, the Skylge Formation (new formation) overlies the Friese Front Formation conformably. The Rijnland Group (Vlieland Sandstone Formation or Vlieland Claystone Formation) or the Scruff Greensand Formation (Stortemelk Member) occasionally rest unconformably on this formation if a prominent Late Kimmerian II unconformity is developed.
Lower Boundary The Friese Front Formation rests with an unconformity on the marine claystones and carbonates of the Altena Group or on older Triassic or Permian units.
Distribution he Friese Front Formation is restricted to the southern Dutch Central Graben and Terschelling Basin (blocks F17, F18, L01, L02, L03, L05, L06, M01, M04 and M07-see Fig.). In the upper parts the formation interfingers with the marine Scruff Group. It is a lateral equivalent of the Lower, the Middle Graben and the Puzzle Hole formations in the northern part of the Central Graben. The fault-controlled transition to the Puzzle Hole is located near the northern margin of the Terschelling Basin, in the F15-F17 blocks and is characterised by a sharp increase in the number of coal beds (from a few to 10-20/100 m), which can easily be discerned on logs (highly serrate in the Puzzle Hole Formation) and on seismic lines (see pdf).
Age Sequence 1 and 2 sensu Abbink et al., 2006: Late Callovian – Early Volgian. In the Terschelling Basin the Friese Front Formation is younger (Sequence 2) than in the Central Graben area (Sequence 1 and 2). In the southern part of the Dutch Central Graben the age is latest Callovian to Kimmeridgian. The top occurrence of Couperisporites jurassicus, Rotverrusporites granularis and Varirugosisporites granituberosus (LODs: E. Volgian, hudlestoni Ammonite Zone) fall within the formation.
Depositional Setting Non-marine (coastal) delta plain to lagoonal deposits.
Subdivision One formal member isrecognised in the Friese Front Formation:
  SL Schieland Group
  SLC Central Graben Subgroup
  SLCF Friese Front Formation
  SLCFR Rifgronden 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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