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Abstract

In northern England Ordovician rocks crop out in the main Lake District inlier and in smaller inliers at Cross Fell, Cautley, Austwick and Teesdale (Fig.1), where they are brought up along the Pennine, Dent and Craven fault systems. The Lake District has a thick lower Ordovician sedimentary succession, the Skiddaw Group, and comparable strata make up much of the Isle of Man. Since the publication of the previous Correlation Chart (Williams et al.1972) fossiliferous Tremadoc rocks have been discovered in the Skiddaw Group (Rushton 1985, 1988).In both the Lake District and Cross Fell the Skiddaw Group successions are followed unconformably by thick arc volcanics, the Eycott and Borrowdale volcanic groups, of possible late Llanvirn to early Caradoc age (Molyneux 1988; Millward & Molyneux 1992).These are overlain, again unconformably, by the Dent Group, neritic marine sediments of mid-Caradoc to Ashgillage. Palaeogeographically, the lower Ordovician rocks of northern England were deposited in a deep shelf or ocean-facing setting, on the SE margin of Iapetus (Bevins et al.1992), and generally they represent a more distal facies than the rocks of the Welsh Basin. The Skiddaw Group is of particular importance as it represents the most complete graptolitic succession in the Arenig, not only in Britain, but anywhere in high palaeogeographical latitudes. It provides a graptolitic zonal standard for the Arenig Series in England and Wales.

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