Wadden Volcaniclastic Member SLDZV

 

Premise Defined by Herngreen, Smit and Wong (1991) . This member is not the same as the Zuidwal Volcanic Formation NAM and RGD (1980) , which is restricted to pure igneous rocks and volcanic agglomerates, and which is defined in section 6.1.
Derivatio nominis Named after the Wadden Sea.
Type section Location map See figure (pdf)
  Well Slenk-1 (pdf)
  Location N 53°13’48.0
E 05°17’42.3
  Depth 2274.5 to 2352.5 m
  Length 78 m along hole
Additional section Location map See figure (pdf)
  Well Zuidwal-2 (pdf)
  Location N 53°09’36.1
E 05°12’05.3
  Depth 2167 to 2189 m
  Length 22 m along hole
Definition Volcaniclast-bearing detrital layers, locally intercalated in reddish-brown, green, and grey clays and siltstones of the Zurich Formation The volcaniclasts are opaque, green, red, and brown, fine to coarse grained, predominantly angular to subangular with a greyish, tuffaceous matrix. It is not clear whether the various occurrences are part of one and the same continuous unit (e.g. in Slenk-1, Zuidwal-2, and Zuidwal-3). The reference section in Slenk-1, with significant claystone intercalations, suggests that several volcaniclast-bearing layers may be present.
Upper Boundary Strata of this member cannot be defined unambiguously on logs, although both GR readings and transit times appear to be somewhat lower than the conformably under- and overlying sediments of the Zurich Formation (Zuidwal-2). The upper boundary, with the upper member of the Zurich Formation, is characterised by a conformable, sudden transition into coaly, varicoloured mudstones with rare sand and abundant coal-bed intercalations.
Lower Boundary The lower boundary, with the lower member of the Zurich Formation, is characterised by a conformable, sudden transition into calcareous to dolomitic, vari-coloured mudstones with rare sand and coal bed intercalations.
Correlation The deposition of the Scruff Group (Scruff Greensand and Kimmeridge Clay Formation, e.g. L15-FA-101) is considered to be approximately coeval with the deposition of the Wadden Volcaniclastic Member
Distribution Restricted to the Vlieland Basin (see pdf) , in the immediate vicinity of the Zuidwal volcanic dome.
Age Approximately Portlandian-Early Ryazanian Herngreen, Smit and Wong (1991) . In the type section, Galliaecythe-ridea postsinuata, an ostracod indicative for the Jurassic/ Cretaceous boundary, was encountered. Depending on the advocated geological time scale, a considerable or negligible age difference may exist with radiometric datings of the volcanics of the Zuidwal Volcanics Formation (section 6.1): approx. 155-143 Ma in Zuidwal-1; Callovian to Early Kimmeridgian according to Odin and Odin (1990) and Haq (1988) , but Kimmeridgian to Ryazanian according to Harland et al. (1990).
Depositional Setting Herngreen, Smit and Wong (1991) concluded that the Wadden Volcaniclastic Member was not formed contemporaneously with the activity of the Zuidwal volcanic dome, but considerably later. This was based on the discrepancy between the paleontological age datings of the Wadden Volcaniclastic Member and the radiometric datings of the Zuidwal Volcanic Formation on the time scale applied by them Kennedy and Odin (1982) . Since the absolute age of the Late Jurassic and Early Cretaceous is still a matter of debate, it seems premature to decide whether this is true or not. According to the time scale preferred here, Harland et al. (1990), the two could very well be contemporaneous. The weathered appearance of the volcaniclasts suggests that this member was formed by erosion of the nearby Zuidwal volcano, instead of by primary volcanic deposition (see Herngreen, Smit and Wong (1991) for discussion).
Sequence Stratigraphy This member is intercalated between the lower and the upper member of the Zurich Formation. The basal upper member and the uppermost part of the lower member of the Zurich Formation are absent if the Wadden Volca-niclastic Member is found. The Scruff Greensand Formation incursion, found at this interface in other wells, is also absent. The deposits are roughly correlated to the transition of subsequence LZB 1.5a to 1.5b.
References See References Upper Jurassic/ Lower Cretaceous

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