CARADOC SERIES

also called Caradocian Series, the fifth of six subdivisions (in ascending order) of the Ordovician System, comprising all those rocks deposited worldwide during the Caradocian Age (458 to 448 million years ago). The series' name is derived from the hills called Caer Caradoc, near Church Stretton in Shropshire, England. The type section is located in the valley of the Onny River near Horderley, across the border in Wales, but the base of this section is unconformable and diachronous and thus unsuitable as a global stratotype section. The Caradoc strata of northern Wales reach a thickness of more than 2,000 m (6,000 feet) and are exposed as graywackes, mudstones, thin limestones, and fine-grained black shales. Silica-rich rhyolitic lavas and tuffs also occur and can be seen at Snowdon mountain. No global stratotype and point (GSSP) has yet been defined for the series by the International Commission on Stratigraphy. The base of the biozone of the graptolite Nemagraptus gracilis has been applied as the base of the Caradoc, but this fossil zone has been found to extend far down into the underlying Llandeilo Series. Thus, the base of the Caradoc Series is in urgent need of redefinition. The biozones of the conodonts Amorphognathus tvaerensis and A. superbus extend through the Caradoc Series. The Caradoc is overlain by the Ashgill Series.