Foraminiferal isoleucine epimerization determinations from the Nar Valley Clay, Norfolk, UK: implications for Quaternary correlations in the southernNorth Sea basin

Fully temperate freshwater, brackish and marine sediments overlying Anglian till and glacilacustrine sediments in the Nar Valley area of northwest Nor folk, UK, have been attributed to the Middle Pleistocene Hoxnian temperate stage on palynological grounds, and basal peats associated with this sequen ce have been recently correlated with oxygen isotope stage 9 on the basis o f a series of Th-230/U-238 dates (mean 317 +/- 14 ka). At Tottenhill these sediments (Nar Valley Freshwater Beds, Nar Valley Clay) underlie a deltaic complex attributed to the Wolstonian ice margin. The lithostratigraphical r elations between the major formations in the Nar Valley, and the pollen str atigraphy of the fully temperate sequence, are very similar to the Pleistoc ene sequence in the Inner Silver Pit area of the southern North Sea, and co rrelation has been proposed between the successions described from these tw o localities. However, the Inner Silver Pit sequence has yielded aminostrat igraphic data consistent with isotopic stage 11. Benthic foraminiferal assemblages and foraminiferal amino-acid determinatio ns have been investigated from the Nar Valley Clay in order to test further the palaeoenvironmental setting of the sequence and to help resolve the ag e of the sequence and correlation with the Inner Silver Pit interglacial. T he foraminiferal assemblages support previous sedimentological and palaeont ological evidence for a transgressive tendency within this sequence. Multip le isoleucine epimerization determinations on Ammonia beccarii and Aubignyn a perlucida from five levels within the Nar Valley Clay give mean aIle/Ile ratios of 0.135 and 0.111, respectively. The A. beccarii ratios are much lo wer than mean aIle/Ile ratios on equivalent species from the interglacial s equence in the Inner Silver Pit (upper Sand Hole Formation), which are clos e to 0.2, and the two datasets fail to overlap at the lo level. The new ami nostratigraphic ratios indicate correlation of the Nar Valley Clay with oxy gen isotope stage 9, and therefore support the pre-existing Th-230/U-238 da ta. These results suggest that two temperate stages of Hoxnian palynological af finity are present in the Quaternary record of East Anglia and the southern North Sea basin, a conclusion consistent with independent new U-series dat a from other Hoxnian sites in East Anglia. An alternative model in which th e amino-acid ratios are explained as a function of different post-depositio nal thermal histories, related to length of cover by ice and water, is disc ussed but considered unlikely. The conclusions have important implications for the timing and number of glacial events in and around the southern Nort h Sea basin, and help to resolve discrepancies in relative sea-level histor ies and biogeography in temperate sequences hitherto accommodated within a single stage.