WESTPHALIAN VOLCANISM AT THE HORIZON OF THE BLACK RAKE IN DERBYSHIRE AND NOTTINGHAMSHIRE

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Abstract
Summary: The Black Rake, some 7 to 15 metres below the Clay Cross Marine Band, contains an interbedded tuffaceous siltstone over much of the Derby-Nottingham Coalfield. This siltstone is up to 38 centimetres thick and comprises forty or fifty graded layers most of which include basaltic glass shards and pumice. At most localities the bed has been dolomitized, resulting in increased thickness and better preservation of the included basaltic material. The bed is formed of fall-out dust from at least three vents centred to the east and north-east of Nottingham; its distribution suggests the influence of prevailing easterly winds. The lateral equivalents of the siltstone near the vents include basaltic tuffs and accretionary lapilli tuffs. The lithology and field relationships of all these pyroclastic rocks are matched in the Namurian and Westphalian volcanic fields of Scotland.