Geverik Member DCGEG

 

Premise Unit, defined by Van Adrichem Boogaert and Kouwe (1995). Analogous deposits are known from Belgium by Muchez (1988) , Muchez (1990) , Langenaeker (1992) , ‘Hot Shales’ and Paproth (1983) , ‘Ampelite’, and from Germany ‘Hangende Alaunschiefer’ by Richwien (1963) , Wolburg (1963) , Wolburg (1970) , Hedemann (1971) , Hedemann (1973) . In the Netherlands, the basal deposits of the Namurian were first described by Price (1987) and RGD (1987) .
Derivatio nominis Named after the village of Geverik in the south of the Dutch province of Limburg, where the type section is situated.
Type section Location map See figure (pdf)
  Well Geverik-1 (pdf)
  Location N 50°55’37.0
E 05°46’47.9
  Depth 926 to 992 m
  Length 66 m along hole
Definition Interval of dark-grey or black, bituminous, shaly claystones, with abundant intercalated laminae of graded siltstone and very fine-grained sandstone. In the type section, dark-grey to black limestone laminae are intercalated in the basal part. The tops of individual beds are frequently silicified. Tuffaceous bands of cm- to mm-thickness can occur. Because of its high uranium- and thorium-content, the unit stands out prominently on GR-logs (300-500 API units).
Upper Boundary The ‘hot shales’ pass upwards into the non-bituminous, dark-coloured mudstones of the main Epen member. The upper boundary is defined by the disappearance of the bituminous character, reflected by an abrupt upward shift to lower GR-log readings.
Lower Boundary In the type section a gradual transition can be observed from the limestone-shale alternation of the Carboniferous Limestone Group into the marly basal interval of the Geverik Member. Elsewhere, the member is usually found to rest unconformably on massive Dinantian carbonates.
Distribution Thusfar only reported along the northern flank of the London-Brabant Massif. Comparable deposits have been encountered in central Germany (Richwien (1963) ).
Age Alportian to Arnsbergian (Namurian A) ages have been reported for the member. The presence of the Pendleian in this member has not yet been confirmed (Langenaeker (1992) ). This might indicate the existence of a basal hiatus. This is not evident in the cores from the type section, but an unconformable contact is observed in other wells and exposures in Belgium (Boonen (1979) ; Langenaeker (1992) ).
Depositional Setting The black shales have been interpreted as having settled from suspension in an anoxic marine basin with restricted circulation. This has been confirmed by fossil assemblages, which lack in-situ benthic elements. The high organic-matter content points to very low clastic sedimentation rates. The intercalated graded silt-/sandstone and limestone laminae in the type section have been interpreted as distal turbidites.
References See References Upper Carboniferous

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