Westphalian Volcanism at the Horizon of the Black Rake in Derbyshire and Nottinghamshire

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.

Mineralogy and Chemistry of Tonsteins From Carboniferous Sequences in Great Britain

“…TREWIN (1968) invoked contemporaneous volcanism to account for the presence within the Namurian of the Southern Pennines of certain, hitherto unsuspected, extensive bentonite horizons. SABINE (1963) andFRANCIS et al (1968) showed that Westphalian volcanicity took place in the immediate area of deposition of some of our samples. Evidence of contemporaneous, rather than nearby contemporaneous, volcanicity is the important point here, of course, as there is abundant proof in recent times of the vast distances volcanic ash can travel (e. g., LARSSON, 1937).…”

A geochemical and mineralogical investigation of some British and other European tonsteins

“…The evidence for this is as follows. (a) Basic lavas and pyroclastics are important in the East Midlands and vents are known (Francis, Smart & Raisbeck, 1968). (b) It is thought that the volcanic activity was dominantly explosive and emanated from centres only briefly active, which is comparable with the Midland Valley of Scotland, and kaolinized tuffs (or tonsteins) of limited lateral extent are therefore also to be expected.…”