MASS-SPECTROMETRIC TH-230-U-234-U-238 DATING OF THE DEVILS-HOLE CALCITE VEIN

The Devils Hole calcite vein contains a long-term climatic record, but requires accurate chronologic control for its interpretation. Mass-spectrometric U-series ages for samples from core DH-11 yielded Th-230 ages with precisions ranging from less than 1,000 years (2sigma) for samples younger than approximately 140 ka (thousands of years ago) to less than 50,000 years for the oldest samples (approximately 566 ka). The U-234/U-238 ages could be determined to a precision of approximately 20,000 years for all ages. Calcite accumulated continuously from 566 ka until approximately 60 ka at an average rate of 0.7 millimeter per 10(3) years. The precise agreement between replicate analyses and the concordance of the Th-230/U-238 and U-234/U-238 ages for the oldest samples indicate that the DH-11 samples were closed systems and validate the dating technique in general.