Epen Formation DCGE

 

Premise Unit, defined by Van Adrichem Boogaert and Kouwe (1995), previously these deposits were referred to by some operators as ‘Namen Shale’.
Derivatio nominis Named after the village of Epen in the south of the province of Limburg. The name corresponds to a former stratigraphic unit Jongmans (1928) ; Jongmans (1940) representing the Namurian B. Several outcrops of this formation exist in the valley of the river Geul near Epen.
Type section Location map See figure (pdf)
  Well Nagele-1 (pdf)
  Location N 52°37’10.0
E 05°44’23.3
  Depth 2438 to 4303 m
  Length 1865 m along hole
Additional section Location map See figure (pdf)
  Well Rijsbergen-1 (pdf) (pdf)
  Location N 51°31’44.3
E 04°41’21.6
  Depth 2927 to NaN m
  Length NaN m along hole
  Well Geverik-1 (pdf)
  Location N 50°55’37.03
E 05°46’47.91
  Depth 672 to NaN m
  Length NaN m along hole
Definition Succession of dark-grey to black mudstones with a few intercalations of grey and buff, (sub-) angular, moderately - to well- sorted, very fine- to medium-grained sandstone. Coal seams are absent, but disperse carbonaceous matter is locally abundant. The interval consists of a number of stacked coarsening-upward sequences (with funnel-shaped GR-log patterns), arranged into several large-scale coarsening-upward trends. The sequences are between 50 and 300 metres thick. Sandstone sheets are intercalated at the tops of some sequences, especially in the upper part of the formation (Ubachsberg Member). Shaly mudstones, some containing marine fossils, dominate the basal and middle parts of each sequence. Locally, a black, bituminous, partially silicified and calcareous shale is found at the base of the formation (Geverik Member). In the area south of the Mid North Sea High some carbonate beds can be intercalated (e.g. well A14-01, Annex C-5).
Upper Boundary The upper boundary, with the Baarlo Formation (Caumer Subgroup), has been drawn at the base of the first prominent coal seam. This can occur up to 150 metres above or below the Namurian-Westphalian boundary (‘Sarnsbank’ or ‘G. subcrenatum’ marine band). In the northwestern Netherlands offshore and in the adjoining UK sector (quadrants 41 to 53; Cameron (1993) ), the formation is overlain by the Millstone Grit Formation. The boundary has been placed at the base of the lowermost thick sandstone bed of the sandstone-dominated Millstone Grit succession. It is a diachronous boundary, which becomes younger from north to south. Therefore these formations are also partial lateral equivalents.
Lower Boundary The base of this formation has been penetrated by only a few wells. Along the northern margin of the London-Brabant Massif, a basal bituminous shale (Geverik Member) rests on the carbonates of the Carboniferous Limestone Group (Dinantian). In well Geverik-1 (see pdf) this transition is gradual and apparently conformable, but elsewhere this contact can be unconformable, locally lacking the basal shale (well S02-02). Well A14-01 shows the Mid North Sea High succession. The Yoredale Formation (Farne Group) grades upwards into the Epen Formation. The boundary has been placed at the top of the uppermost carbonate-dominated sequence.
Distribution Present throughout the Netherlands on- and offshore territory, except for the northern flank of the London-Brabant Massif and the crest of the Elbow Spit High - Mid North Sea High.
Age Represents most of the Namurian, locally persisting into the Early Westphalian A. On the northern flank of the London-Brabant Massif, the base of the formation (roughly) coincides with the Visean-Namurian boundary. Near the Mid North Sea High, the transition of the Yoredale Formation (Farne Group) into the Limburg Group appears to be slightly younger. The top of the Epen Formation is a diachronous boundary. Depending on the geographic position in the basin, it can vary in age from Namurian B (South-Limburg) to Early Westphalian A (central onshore, well Nagele-1 (see pdf) ). In southern Limburg and neighbouring Germany, coal seams are developed in the Namurian B/C (well Geverik-1:Price () ; RGD (1987) . For the Aachen-Erkelenz and Ruhr coal districts, see Drozdzewski et al (1985) ; Wrede and Zeller (1988) ;Strack (1989) ).
Depositional Setting The stacked coarsening-upward sequences (funnel-shaped GR-log patterns) have been interpreted as cycles of repeated delta progradation into a predominantly lacustrine basin. Each cycle started with a brief, but basin-wide influx of marine conditions (goniatite-rich marine bands), followed by a period of deltaic progradation into the basin (Ramsbottom (1979) ; Collinson (1988) ; Holdsworth (1988) ; Leeder (1990) ; Cameron (1992) ; Collinson (1993) ). Towards the south the deposits get a more argillaceous, basinal character. This points to a predominantly northern sediment source. However, southern sediment sources have also been documented along the London-Brabant Massif (Langenaeker (1992) ). In some sequences, clays, silts and thin (very) fine-grained sand beds are clearly turbiditic delta-slope and prodelta deposits. Other cycles are capped by delta-front sheet sands (mouth bars and distributary channel fills). Therefore, Collinson (1988) distinguishes a turbidite-fronted and a sheet-delta sequence type for this period.
Subdivision In the formation two members are recognised. The (Geverik Member comprises the basal succession of bituminous shales which unconformably cover, or locally grade into, the Lower Carboniferous Limestone Group. The Ubachsberg Member is an interval containing one or more sheet sandstone beds. It is a diachronous unit, encompassing an interval of Namurian B - lowermost Westphalian A age. All deposits that belong to this formation, but are not attributed to one of the two members, can be referred to as the informal main Epen member (DCGEM). Where the Epen Formation is split in two by an intercalated Ubachsberg Member the claystone interval above that member may be called upper Epen member (DCGET). The interval underlying the Ubachsberg Member would be called main Epen member (DCGEM)
  DCGEU Ubachsberg Member
  DCGEG Geverik Member
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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