Abstract The Purbeck-Wealden of the type areas in onshore southern Britain (Fig. 1 ) encompasses the Berria-sian-earliest Aptian stages of the Cretaceous, a time span of approximately 21 Ma. At least some of the lowest part of the succession belongs to the latest Jurassic (Portlandian); how much depends on where the Jurassic-Cretaceous boundary is placed. Ostracods are frequently diverse and abundant in the predominantly calcareous or argillaceous units (e.g. Purbeck Limestone Group, Wadhurst Clay Formation, Grinstead Clay Formation, Weald Clay Group), sometimes forming ostracod limestones, but in clays that have undergone pedogenesis and in arenaceous facies (e.g. Ashdown Beds Formation, Upper and Lower Tunbridge Wells Sand formations) they tend to be rare or poorly preserved. They are essentially non-marine faunas, with only a few convincing indicators of direct marine influence. Although their interpretation is difficult and has given rise to controversy, ostracods are undoubtedly the most useful biostratigraphical tool available in Purbeck-Wealden sequences. They have also been used with some success in correlations of the offshore ‘ Purbeck-Wealden’ facies of Portlandian-Barremian age found in the Celtic Sea and Fastnet basins between southern Ireland and SW England (Fig. 1 ).

Abstract Although their value as palaeoenvironmental and palaeoclimatic proxies is widely acknowledged, ostracods have traditionally been considered to be of only limited use in British Pleistocene biostrati-graphy. To some extent this is due to the patchy and fragmentary nature of most onshore Pleistocene deposits, precluding the establishment of long, continuous records on which to base species ranges. It is also a result of taxonomic continuity; the majority of British Pleistocene species are still alive today and relatively few extinct taxa, such as might provide stratigraphical markers, have been recognized. Examples of the latter were discussed by Griffiths (2001) in his review of the use of European freshwater ostracods as biostratigraphic indicators, including Scottia browniana (Jones, 1850), Ilyocy-pris quinculminata Sylvester-Bradley, 1973 and Amplocypris tonnensis Diebel & Pietrzeniuk, 1975. The presence or absence of species in any particular stratigraphical or geographical location is usually best explained, however, in terms of local environmental conditions and/or climate. This is true not only of Britain, but of the rest of the world in general. An excellent and comprehensive recent work, Holmes & Chivas’ (2002) The Ostracoda: Applications in Quaternary Research, covers palaeoceanography and palaeoenvironmen-tal analysis (including trace-element and stable-isotope techniques) in detail but has no chapter on biostratigraphy. Perceptions of the biostratigraphical value of Pleistocene ostracods are changing. Studies carried out on ostracod assemblages from new excavations of Pleistocene sites in Britain, coupled with taxo-nomic revisions, are revealing a growing number of taxa with limited chronostratigraphic ranges. At the same time, multidisciplinary