THE FOSSVOGUR MARINE-SEDIMENTS IN SW ICELAND - CONFINED TO THE ALLEROD YOUNGER DRYAS TRANSITION BY AMS C-14 DATING

An exhaustive C-14 dating programme of molluscs from the Fossvogur sed iments in Reykjavik, Iceland is presented. For the first time all the fossiliferous units of the sediments are dated. The results confirm ea rlier conclusions of a widespread occurrence of marine sediments of Al lerod age in Reykjavik. The set of dates from the Fossvogur sediments shows a narrow C-14 age distribution (standard deviation of +/- 235 ye ars) of molluscs from all localities and from successive marine units in vertical sections. The weighted mean conventional C-14 age is 11,40 0 BP. Assuming a reservoir effect of 400 years, this corresponds to a reservoir-corrected age of 11,000 BP, i.e. the Allerod-Younger Dryas t ransition for the sampled units. These new C-14 dates from Fossvogur c onfirm the need for a revision of the Upper Pleistocene chronology of the Reykjavik region. They also have a bearing on the Late Weichselian record of glacier readvances and sea-level changes in the area. The d ates suggest that the marine units in Fossvogur accumulated within a r estricted time-span of a few hundred years. The sediments in Fossvogur are of volcaniclastic origin and are extremely lithified, indicating local geothermal activity soon after their deposition. This may explai n anomalously high D/L amino acid ratios measured in molluscs from the Fossvogur sediments. deltaC-13 and deltaO-18 results suggest that tem peratures may have ranged up to 60-degrees-C.