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Part III: The Stratigraphic Record |
Exploration & Production Division, B.P. Research Centre, Chertsey Road, Sunbury-on-Thames, Middlesex, UK
The Marl Slate is the basal unit of the Upper Permian (Zechstein) in northeast England. A finely laminated, organic-rich, silty dolomite/dolomitic siltstone, it is equivalent to the Kupferschiefer of the Southern North Sea basin and northern Germany and Poland. Several lines of evidence indicate the Marl Slate/Kupferschiefer accumulated in the anoxic bottom waters of a shallow (< 200 m), stratified, epicontinental sea. The vertical succession of the first Zechstein cycle is explicable in terms of the effect on sedimentation of a stratified water column undergoing progressive evaporitic concentration.
Total organic contents of the Marl Slate generally fall in the range 5–15%, decreasing upwards. The kerogen is largely amorphous and oil-prone. Original pyrolysis yields approach 100 kg hydrocarbon/tonne rock. It is immature in northeast England but even where mature in the Southern North Sea basin and Northern Europe the unit is unlikely to have sourced commercially significant amounts of oil because of its limited thickness (generally <2 m).
