Acritarchs of Llandeilo and Caradoo age from classic localities in Britain.

The last two decades have seen the publication of a large number of papers dealing with Palaeozoic acritarchs including many devoted to the description of Ordovician assemblages. It has become clear that, these microfossils have considerable potential for correlation and that they are frequently recovered From sequences otherwise devoid of fossil material. In Britain, acritarchs have been described in detail from the Cambrian (Potter 1974 M. S.); Tremadoc (Rasul 1971 M. S., 1974, 1977a, l977b) and from the Silurian (Lister 1966 M. S., 1970; Hill 1974 M. S.) Until the recent work of Booth (l979 M. S.) dealing with Arenig-Llanvirn assemblages, no detailed systematic investigation of British Ordovician acritarchs had been attempted. The primary objective of the present study is to provide a comprehensive description of acritarchs from the Middle and Upper Ordovician of Britain, with particular emphasis on the type-areas of the Llandeilo and Caradoc. In conjunction with the work of Booth it is hoped that this account will go some way towards providing a biostratigraphical framework which will facilitate the use of these microfossils for the purposes of correlation in the Ordovician.