A REVISION OF ORDOVICIAN SERIES AND STAGES FROM THE HISTORICAL TYPE AREA

This paper is a revision of the standard chronostratigraphy of the Ord ovician of the historical type area in England and Wales. The revision is a response to the need for more precise definitions of series and stages, especially for practical international correlation. In some ca ses this has entailed moving horizons for Series bases away from those in the classical sections. The scheme will be used as the standard fo r a forthcoming revision of the Correlation Chart of the British Ordov ician System. The Ordovician is divided into five series: Tremadoc, Ar enig, Llanvirn, Caradoc and Ashgill. The Llanvirn is extended to inclu de part of the classical Llandeilo Series, which is included within it as a stage. Where stage subdivisions of standard series have not yet been defined, as in the Tremadoc, they are proposed in this paper. How ever, Bancroft's fine stadial divisions of the Caradoc, which have bee n criticized for their brevity and local utility, are combined into fo ur new stages, which will have wider application. The former Caradoc s ubdivisions are retained as substages for the purposes of regional cor relation.