Micro-tephra in the West Runton Freshwater Bed: Preliminary results

A volcanic mineral assemblage is present throughout the 20-120 μm size fraction of the Middle Pleistocene West Runton Freshwater Bed, Norfolk, UK. Glass shards are extremely rare but are present mainly at one horizon. This micro-tephra assemblage is indicative of a potassic mineral suite, possibly from an evolved phonolitic or trachytic melt. Mineralogical and electron microprobe data are inconsistent with a tephra source from mid Atlantic ridge sites and the amphibole and alkali feldspar components are more evolved than early Quaternary mineral assemblages from West Eifel volcanism in Germany. The mineral assemblage and geochemical compositions are most similar to those from the Mont Dore area (Massif Central, France) and the Italian volcanic complex of Mount Vulture in the southern Apennines. Taken alone these preliminary data are not strong enough to infer a deposit age. However, the age ranges for volcanism at both Mont Dore and Mount Vulture are similar (500-800 ka); the presence of micro-tephra from either of these sources is wholly consistent with other age estimates for the West Runton Freshwater Bed (>500 ka and <780 ka) supporting deposition during either the interglacials of marine isotope stages 15 or 17.