A late Middle Pleistocene temperate-periglacial-temperate sequence (OxygenIsotope Stages 7-5e) near Marsworth, Buckinghamshire, UK

River-channel and colluvial deposits, near Marsworth, Buckinghamshire, reco rd a temperate-periglacial-temperate sequence during the late Middle Pleist ocene. The deposits of a lower channel contain tufa clasts bearing leaf imp ressions that include Acer sp., and Sorbus aucuparia and containing tempera te arboreal pollen attributed to ash-dominated woodland. The tufa probably formed at the mouth of a limestone spring before being redeposited in a sma ll river whose deposits contain plant remains, Mollusca, Coleoptera, Ostrac oda and vertebrate bones of temperate affinities. The sediments, sedimentar y structures and limited biological remains above the Lower Channel deposit s indicate that fluvial deposition preceded climatic cooling into periglaci al conditions. Fluvial deposition recurred during a later temperate episode , as shown by the mammalian bone assemblage in stratigraphically higher cha nnel deposits. The Upper Channel deposits are confidently attributed to Oxy gen Isotope Sub-stage 5e (Ipswichian) on the basis of their vertebrate rema ins. However, the age of the Lower Channel deposits is less clear. The mamm alian and coleopteran remains in the Lower Channel strongly suggest correla tion with oxygen isotope stage 7 on the basis of their similarities to othe r sites whose stratigraphy is better known and the clear difference of the Lower Channel assemblage from well-established faunas of Ipswichian or any other age. By contrast, U-Th dating of the tufa clasts suggests an age post 160 ka BP, while Aile/Ile ratios on Mollusca point to an Ipswichian age an d younger. Four ways of interpreting this age discrepancy are considered, t he preferred one correlating the Lower Channel deposits with Oxygen Isotope Stage 7. (C) 2001 Elsevier Science Ltd. All rights reserved.