|Premise||Definition modified after Herngreen, Smit and Wong (1991) . Formerly contained in the Niedersachsen Group NAM and RGD (1980) . Described most extensively by Perrot and Van der Poel (1987).|
|Derivatio nominis||Named after the Petroland Zuidwal gas discovery in the Dutch Waddenzee.|
|Type section||Location map||See figure (pdf)|
|Depth||1944 to 3002 m|
|Length||1058 m along hole|
|Reference||NAM and RGD (1980)|
|Definition||The formation consists of massive volcanic (lava) rocks and brecciated volcanic agglomerates. Thusfar these have only been encountered in the volcanic plug drilled by the Zuidwal-1 well. For details on the composition of the agglomerates the reader is referred to Jeans (1977) , Harrison et al (1979) and Dixon et al (1981) . The ’tuffs’ mentioned in the original definition by NAM and RGD (1980) are not included in the Zuidwal Volcanic Formation, but have been assigned to the Wadden Volcaniclastic Member of the Zurich Formation (Delfland Subgroup of the Schieland Group).|
|Upper Boundary||The top is formed by the onlap of the Vlieland Sandstone Formation (Friesland Member) of the Rijnland Group.|
|Lower Boundary||The base of the formation has not yet been penetrated.|
|Distribution||The core of the Zuidwal volcanic dome in the centre of the Dutch Waddenzee.|
|Age||Radiometric datings of the Zuidwal-1 volcanic breccias are given by various authors. Jeans (1977) present-ed four datings, ranging from 119 ± 2 to 92 ± 2 Ma, which should be considered as minimum ages because of apparent considerable Ar losses. Harrison et al (1979) reported a 145 Ma K/Ar date, while Dixon et al (1981) published a virtually identical 144 ± 1 Ma Ar/Ar age. More recently an additional dating of 152 ± 3 Ma was published in Perrot and Van der Poel (1987). This is the oldest age for the volcanic breccias published thus far. Depending on the advocated time scale, the period of apparent volcanic activity, 155 to 143 Ma, should be considered as Oxfordian to Early Ryazanian Harland et al (1990) or Callovian to Early Kimmeridgian Haq et al (1988) . In this publication the former is preferred.|
|Depositional Setting||The volcanic rocks are referred to as of an ’alkaline intra-plate’ type by Perrot and Van der Poel (1987). Herngreen, Smit and Wong (1991) attribute the formation of the Zuidwal volcanic dome to the Mid Kimmerian tectonic phase. If the formation of the volcanics is placed in the Oxfordian to Early Ryazanian, it would be related to Late Kimmerian tectonism. Palaeogeographic reconstructions indicate that the dome formed a positive relief during the deposition of the Upper Jurassic and earliest Cretaceous in the Vlieland Basin (see pdf) (Late Kimmeridgian to Ryazanian|
|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.
Retrieved [Datum] from [url].