Klaverbank Formation DCCK


Premise Unit, defined by Van Adrichem Boogaert and Kouwe (1995). Thusfar, no released well in the Netherlands has penetrated this unit completely. Only a few wells from the adjoining UK offshore have yielded a complete succession.
Derivatio nominis Named after the Klaverbank (= Cleaver Bank) High, where this member is found. The Dutch name has been applied here, since the English name is in use in Quaternary lithostratigraphy.
Type section Location map See figure (pdf)
  Well K01-02 (pdf)
  Location N 53°54’28.2
E 03°12’41.0
  Depth 3886 to 4565 m
  Length 679 m along hole
Additional section Location map See figure (pdf)
  Well E13-01 (pdf)
  Location N 54°17’26.1
E 03°08’22.2
  Depth 3950 to 4277 m
  Length 327 m along hole
  Well K05-02 (pdf)
  Location N 53°47’57.7
E 03°24’41.7
  Depth 3738 to 4273 m
  Length 535 m along hole
Definition Alternation of white, light-grey or pink, massive, carbonaceous sandstones, dark- (brownish) grey to black silt- and mudstones and frequent coal seams. In the basal interval the formation displays a characteristic pattern of stacked coarsening-upward sequences of up to 120 m thick. In the UK, cycles of more than 300 m thick have been observed (Caister Coal Formation: Cameron (1993) ). In the younger part, this pattern changes into combined fining- and coarsening-upward sequences (Botney Member). Sandstones are stacked channel fills, forming sheets of 3 to 25 m thick. These are concentrated in the tops and bases of the depositional cycles. The sandstones largely consist of argillaceous, subangular, moderately- to well-sorted, very fine- to coarse-grained sand. At some intervals, the sands are conglomeratic and devoid of argillaceous matrix. Sandstones usually represent 30 to 50% of the bulk formation volume, but intervals containing only 15% sandstones can occur. Mudstone intervals are silty or very fine-grained sandy and carbonaceous. Fines make up more than 50% of the formations, with argillaceous intervals of up to 100 m thick. Cored intervals have revealed small-scale coarsening-upward cycles, capped by sand/ siltstone beds, coal seams or seat earths. Coal seams are rarely up to 3 m thick, and constitute 1 to 5% of the formation.
Upper Boundary The formation is overlain conformably by the Maurits Formation. At this boundary the succession changes abruptly to a thick mudstone interval, generally with abundant intercalated coal seams.
Lower Boundary The basal boundary has been defined as the base of the sandstone bed underlying the deepest coal seam, or the lowermost coal seam if no sandstone is developed. The deposits of the underlying Millstone Grit Formation are similar, but lack the coal seams.
Correlation The Baarlo and Ruurlo Formations are age equivalents in the southern and eastern offshore and the onshore. The Klaverbank Formation can be discriminated by its basin position (northwestern offshore) and higher sand/shale ratio (approx. 30% sand). The lateral transition is situated in the southern J- and adjoining K-quadrant.
Distribution Restricted to the vicinity of the Cleaver Bank High and Silverpit Basin, northwestern Dutch offshore. In the UK the equivalent unit is called Caister Coal Formation (Cameron (1993) ).
Age The base of the formation is diachronous, depending on the timing of the first peat (coal) deposition, varying between Namurian B/C (UK Quadrant 41) and Early Westphalian A (UK quadrant 48). The top of the formation practically coincides with the Early-Late Westphalian B boundary (‘Domina’ marine band).
Depositional Setting The depositional setting alternated between poorly-drained delta plain and lacustrine basin, with occasional marine incursions (Guion (1988) ; Cowan (1989) ; Collinson (1993) ). Sediments were mainly derived from a northern source. In the lower part of the formation, each coarsening-upward cycle was formed by a marine or lacustrine transgression, followed by delta progradation. Prodelta and delta-front mudstones grade upwards into a sheet-like delta top, consisting of an amalgamation of distributary-channel fills (sheet deltas of Collinson (1988) ; Collinson (1993) ). The sequence is capped by deposits of the delta plain. This developed either in sandstone-dominated fluvial-plain setting or in fine-grained flood-plain or interdistributary-bay setting. Coal seams are practically restricted to the latter. During deposition of the Botney Member, the ongoing overall regression changed the depositional cycles. In this unit they display alternations between upper and lower fluvial plain or delta plain. The sandstones are fluvial channel fills, formed by a combination of braided, anastomosing, and meandering fluvial systems. Locally, the structural setting formed valleys, filled with stacked braided channel fills (e.g. locally in the ‘Caister Sandstone unit’ of Cameron (1993) ). Coal seams in the Botney Member are concentrated in the fine-grained mid-cycle intervals.
Subdivision In the Klaverbank Formation one formal member has been recognised.Deposits placed in the Klaverbank Formation, but not belonging to the Botney Member, may informally be referred to as main Klaverbank member (DCCKM). In some wells a massive sandstone interval of over 100 m thick can be developed in the uppermost part of the Klaverbank Formation. This interval can be correlated with the Caister Sandstone unit of Cameron (1993) .
  DCCKB Botney 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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