Cambrian

Abstract

Abstract Aspects of the history of the Cambrian System, and especially its usage in the British Isles, are discussed by Holland (1974). Rushton (1974), Cowie (1974) and Dhonau & Holland (1974) give general accounts of Cambrian stratigraphy in the British Isles, with extensive bibliographies, and the correlation is discussed by Cowie et al. (1972) The limits of the Cambrian System are still unsettled. The Precambrian/ Cambrian boundary has been the subject of much recent research, concentrated especially on strata of Tommotian and Meishucunian age (Cowie & Brasier 1989). These stages are characterized by faunas of small shelly fossils but biostratigraphical correlation based on them is still rather insecure and a consensus on the basal Cambrian stratotype has yet to be reached (Brasier 19896) The upper limit of the Cambrian (the base of the Ordovician System) is likewise unsettled. Cowie et al. (1972) took the base of the Ordovician at the base of the Arenig Series, thereby including the Tremadoc Series in the Cambrian. Nowadays a level at the base of the Tremadoc, for long adopted in continental Europe and elsewhere, is more widely accepted in Britain, and is employed here. However, the exact horizon for the base of the Ordovician, and the locality at which it is to be defined, are still under debate. There are no standard series defined in the Cambrian System. It has long been customary to speak of Lower, Middle and Upper Cambrian, and treat these as series, but they are employed in different senses in different