Botney Member DCCKB

 

Premise The Lower Westphalian B interval of this member, which frequently consists of massive sandstones, constitutes the reservoir interval in the Murdoch and Caister gas fields in the UK offshore (blocks 44/22, resp. 43/23). That specific interval has informally been named ‘Caister Sandstone unit’ by Cameron (1993) , and is described by Ritchie (1993) . For the Netherlands, use of this unit as a member is not encouraged.
Derivatio nominis Named after the Botney Ground, a fishing ground in the central North Sea.
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 4297 m
  Length 411 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 stacked, sheet-like, amalgamated channel fill sandstone bodies, mudstone intervals and coal seams. Sandstone intervals show thicknesses of 3 to 25 m, with an average around 10 m. On logs they commonly display a bell shape. The sand is cream to pink, fine- to very coarse-grained, locally conglomeratic and/or carbonaceous, rounded to subangular, well- to poorly-sorted and well-cemented. Sandy mudstone intercalations can reach 25 m in thickness, and locally account for 50% or more of the bulk volume. Coal seams can constitute up to 5% of the member. In many wells they constitute less than 1%, or are absent. The member can be discriminated from the sometimes similar Hospital Ground Formation (Dinkel Subgroup) by the scarcity of coal seams and the widespread occurrence of primary red-bed facies in the latter. But especially the stratigraphic position of the Botney Member beneath the Maurits Formation is diagnostic.
Upper Boundary The transition into the overlying Maurits Formation is marked by the abrupt transition of thick-bedded (pebbly) sandstones into a thick succession of dark-coloured mudstones with abundant coal seams.
Lower Boundary At the base of the member the stacked coarsening-upward sequences of the main Klaverbank Formation change into combined fining-coarsening sequences. This is accompanied by an abrupt upward increase in sand content. The boundary has been placed at the base of the lowermost thick sandstone bed of the sandstone-dominated interval. This bed truncates the uppermost clear coarsening-upward cycle.
Correlation The Ruurlo Formation is a finer-grained age equivalent of the member, which is found in the southern and eastern offshore and in the onshore. The stacked massive sandstone beds of the Klaverbank Formation grade into a mudstone-dominated facies of the Ruurlo Formation in the southern J- and K-quadrants.
Distribution Restricted to the area between the Cleaver Bank High and the Mid North Sea High (northwestern offshore).
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 This formation was deposited in a poorly- to moderately-drained fluvial-plain setting. Sandstones were mainly deposited by braided fluvial channel systems, entering the basin from the north. Individual channel fills frequently amalgamated into sheets. Some fluvial systems were structurally confined, resulting in multistorey sands. This system was intermittently replaced by poorly-drained flood-plain, swamp or lake systems. Meandering and anastomosing river systems formed isolated sandstone bodies during such stages of higher base level. Marine influence was restricted to short-term incursions. The Lower Westphalian B interval in the northwestern offshore is remarkably thin in comparison to the development in the rest of the country (i.e. Lower Westphalian B interval of the Ruurlo Formation). In the UK it can even consist of a single, thick sandstone bed (Cameron (1992) ; Ritchie (1993) ; Collinson (1993) ; ‘Caister Sandstone unit’ of Cameron (1993) ).
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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