AMS RADIOCARBON DATING AND VARVE CHRONOLOGY OF LAKE SOPPENSEE - 6000 TO 12000 C-14 YEARS BP

For the extension of the radiocarbon calibration curve beyond 10000 C-14 y BP, laminated sediment from Lake Soppensee (central Switzerland) was dated. The radiocarbon time scale was obtained using accelarator mass spectrometry (AMS) dating of terrestrial macrofossils selected from the Soppensee sediment. Because of an unlaminated sediment section during the Younger Dryas (10000-11000 C-14 y BP), the absolute time scale, based on counting annual layers (varves), had to be corrected for missing varves. The Soppensee radiocarbon-varve chronology covers the time period from 6000 to 12000 C-14 y BP on the radiocarbon time scale and 7000 to 13000 calendar y BP on the absolute time scale. The good agreement with the tree ring curve in the interval from 7000 to 11450 cal y BP (cal y indicates calendar year) proves the annual character of the laminations. The ash layer of the Vasset/Killian Tephra (Massif Central, France) is dated at 8230 +/- 140 C-14 y BP and 9407 +/- 44 cal y BP. The boundaries of the Younger Dryas biozone are placed at 10986 +/- 69 cal y BP (Younger Dryas/Preboreal) and 12125 +/- 86 cal y BP (Allerod/Younger Dryas) on the absolute time scale. The absolute age of the Laacher See Tephra layer, dated with the radiocarbon method at 10800 to 11200 C-14 y BP, is estimated at 12350 +/- 135 cal y BP. The oldest radiocarbon age of 14190 +/- 120 C-14 y BP was obtained on macrofossils of pioneer vegetation which were found in the lowermost part of the sediment profile. For the late Glacial, the offset between the radiocarbon (10000-12000 C-14 y BP) and the absolute time scale (11400-13000 cal y BP) in the Soppensee chronology is not greater than 1000 years, which differs from the trend of the U/th-radiocarbon curve derived from corals.