Calibration of the 14C time scale to >40 ka by 234U-230Th dating of Lake Lisan sediments (last glacial Dead Sea)

A new comparison of C-14 dates with U-234-Th-230 ages is presented of aragonites from Lake Lisan, the last Glacial Dead Sea, between similar to 20-52 cal-ka-BP. The Lisan data are coincident with the coral based C-14-calendar age calibration through the continuous portion of the curve to 23.5 cal-ka-BP, and with the additional 'checkpoints' at similar to 30 and similar to 40 cal-ka-BP. The agreement with the corals provides evidence for the accuracy of the U-Th and C-14 ages, and indicates that Lisan aragonites can potentially be used to generate a nearly continuous record of the atmospheric C-14 variations through this crucial time interval. The Lisan data are compared with other records older than 25 cal-ka-BP from Lake Suigetsu, Japan, North Atlantic foraminifera, South African cave deposits and tufa from Spain. Over some age intervals the records show broad agreement, over other intervals they diverge. All agree that C-14 ages were similar to 2.5 +/- 0.5 ka younger than calendar ages between 20-32 cal-ka-BP. For ages > 32 cal-ka-BP, the Lake Suigetsu data indicate small differences between C-14 ages and calendar ages of less than 1.5 ka. The other records broadly agree that C-14 ages are too young by similar to 3 +/- 1 ka from 32-39 cal-ka-BP. At similar to 40 cal-ka-BP, the foraminifera show equal C-14 and calendar ages, while the corals, Lisan aragonites and the Spanish tufa indicate a large age difference of 4-5 ka. A recent paleomagnetic study of the Lisan Formation indicates that the high calendar-C-14 age difference at similar to 40 cal-ka-BP may be associated with the Laschamp paleomagnetic excursion. (C) 2000 Elsevier Science B.V. All rights reserved.