R. A. Fortey, 2000. "Definitions of chronostratigraphic subdivisions in the Ordovician System", A revised correlation of Ordovician Rocks in the British Isles, R. A. Fortey, D. A. T. Harpe, J. K. Ingham, A. W Owen, M. A. Parkes, A. W. A. Rushton, N. H. Woodcock
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The base of the Ordovician has in the past been taken at the base of the Arenig Series in the British Isles, not least because Lapworth (1879, p.14) defined it that way – he recognized the System as comprising ‘Strata included between the base of the Lower Llandovery Formation and that of the Lower Arenig’. The base of the Arenig Series was taken as the lower boundary of the Ordovician System by Williams et al. (1972); hence Tremadoc rocks were excluded from the Ordovician correlation charts, and included in the Cambrian correlation charts by Cowie et al. (1972).In other parts of the world, for example in Scandinavia and the United States, an horizon at or close to the base of the Tremadoc Series had usually been considered to mark the base of the Ordovician. Henningsmoen (1973) discussed the history of these different usages, and noted that Lapworth himself entertained several views on where the base of the Ordovician should be taken, and indeed by 1902 (in Groom 1902, p.148) was evidently prepared to accept at least some part of the Tremadoc within his system.
Figures & Tables
This Report is revised and expanded from the 1972 publication providing an up-to-the-minute account of the British Ordovician formations and their correlation nationally and internationally. It also includes the most comprehensive treatment of Ireland ever attempted. The reference list of a comprehensive bibliography of papers on the subject published since 1970.
The British sections are the type for the Ordovician System and classical in stratigraphical, tectonic and volcanic studies. The Charts bring together 30 years of research over the period in which plate tectonics has revolutionized our understanding of the Lower Palaeozoic rocks of the British Isles.
This Special Report will be a valuable reference for research and applied geoscientists working with rocks of Ordovician age. It will be of particular interest to those working in, or visiting, the Welsh mountains and the English Lake District.