Amino acid dating of a molluscan fauna from Bassingham Fen, Lincolnshire: implications for the chronology of the Trent Terraces

This paper re-examines the age of the Fulbeck Sand and Gravel and the chron ology of the Trent Terraces following amino acid dating of a molluscan faun a found within a basin at Bassingham Fen, incised c. 3 m below the Fulbeck deposit. Two species were dated and yielded different ratios, Lymnaea pereg ra 0.074 +/- 0.002 (2), and Valvata piscinalis 0.131 +/- 0.002 (2). It is a rgued that the V. piscinalis are derived and that the L. peregra indicate t he true age of the deposit. Currently available amino acid geochronologies suggest that the shells of L. peregra were deposited between sub-stage 5a a nd 4 of the early Devensian (c. 85-64 ka sp). Correlation with sub-stage 5a would suggest correlation with the Odderade Interstadial of continental Eu rope and with the only other known 5a site in England, at Cassington in the Upper Thames. Incision into the temperate sub-stage 5e deposits may perhap s have been associated with adjustment of base levels to the cold climate c onditions of the early Devensian and suggests unimpeded drainage through th e area to the North Sea. More problematic, is the interpretation of the V. piscinalis ratios; with assignment to either warm sub-stage 5e (c. 125-115 ka BP) or cold sub-stage 5d (c. 115-105 ka sp) using a younger amino acid g eochronology, or using an older geochronology, to cold stage 6 (c. 128-195 ka sp). The implications of the V. piscinalis ratios for the chronology of the Trent terraces is discussed.