Late Middle Pleistocene pollen biostratigraphy in Britain: pitfalls and possibilities in the separation of interglacial sequences

Abstract

Recent work on late Middle Pleistocene interglacials in Britain has shown that sites formerly attributed to the Hoxnian include representatives of two different interglacials, which have been correlated with Oxygen Isotope Stages 11 and 9. Palynology has long been used to characterize and correlate temperate sequences in Britain. However, the quality of the palynological record is considerably better in lacustrine sequences than in fluvial and estuarine sediments; the former have longer sequences and higher resolution, whereas more rapid deposition in fluvial and estuarine environments leads to sequences representing only fragments of interglacials. The latter type of site, however, is more likely to have multi-proxy evidence and to be readily fitted into a stratigraphical framework. The problems are reviewed in the light of new work in the West Midlands, where some of the most complete British late Middle Pleistocene lacustrine sequences are preserved. Lacustrine sites here have a strong affinity with ‘Hoxnian’ sites of the ‘type’ area in East Anglia. A critical question remains as to whether the two interglacials conflated under the term Hoxnian can be separately characterized in terms of their pollen assemblages. Details of lacustrine sequences in the North Birmingham area and East Anglia show remarkable similarities, perhaps suggesting that the same interglacial is recorded in all of them. As many of these sites are thought to be kettle holes or glacially overdeepened basins, the first interglacial following the Anglian glaciation is the most likely to be represented, suggesting that all the lacustrine ‘Hoxnian’ sites might date from OIS 11. In areas not glaciated since the Anglian, interglacials after OIS 11 are likely to be represented only by fragmentary, non-lacustrine sequences, difficult if not impossible to separate using palynology alone.