THE DEVELOPMENT OF CHERT BETWEEN THE MAIN AND CROW LIMESTONES IN NORTH YORKSHIRE

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Abstract
Summary: The Carboniferous Cherts of Swaledale and Wensleydale include two series, the Main Chert overlying the Main Limestone and the Richmond Chert Series overlying the Little Limestone. The stratigraphical relations of these are traced, and a minor but widespread unconformity is deduced between the Main and Little limestones. Rapid variations in lithological type ranging from pure limestone to pure chert within these series are thought to be largely due to local fluctuations in rates of deposition. Most of the cherts can be explained by simultaneous primary precipitation of calcium carbonate and silica, and a method by which this could have taken place is suggested. There is evidence of small-scale secondary silicification at most horizons in the chert series, and this is thought to have taken place penecontemporaneously with deposition. The structure of the “cauda-galli” markings on the parting surfaces of some of the cherts is demonstrated, but their primary origin remains unknown.

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