Lithostratigraphy and depositional history of the late Toarcian sequence at Ravenscar, Yorkshire

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Abstract
SUMMARY: A detailed examination of the late Toarcian beds of Ravenscar has shown that the traditional lithostratigraphical subdivisions do not adequately reflect the lithological sequence. A new subdivision is therefore proposed that is based on grain size and other lithological characters. At the formation level, the Blea Wyke Beds are renamed the Blea Wyke Sandstone Formation, and the base redefined to correspond to an upward increase in silt and sand content that separates dominantly silty beds below from dominantly sandy beds above. The underlying siltstones and mudstones are placed within the previously defined Whitby Mudstone Formation. At member level, the following units are proposed. The Peak Mudstone Member, whose base is defined by a sharp upward increase in silt and mica content, takes the place of the upper part of the Peak Shales and the lower part of the Striatulum Shales of previous authors. The Fox Cliff Siltstone Member (new name), whose base is defined by a sharp upward increase in coarse silt and fine sand content, takes the place of the upper part of the Striatulum Shales and the basal part of the Grey Beds of previous authors. The Grey Sandstone Member is equivalent to the middle and upper part of the Grey Beds, and the Yellow Sandstone Member is exactly equivalent to the Yellow Beds. Other lithological characters discussed in the text include the distribution and mineralogy of carbonate concretions, and the distribution of phosphate nodules.

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