Thorium-230 dating of carbonates: current technical capabilities and major applications

Abstract:

Uranium-thorium or Th-230 dating has proven to be an important tool in determining the timing of events in the late Quaternary. Among the major applications are: the timing of sea level change, the timing of continental climate change as preserved in cave archives, the timing of climate change in marine and ice core archives through correlation to Th-230 – dated cave records, and calibration of the radiocarbon timescale. The success of these applications has been driven by continuing technical advances in the measurement of the rare actinide isotopes, U-234 and Th-230. The advances have improved the precision, sensitivity, and accuracy of the measurements. The main factor in measurement improvement has been an increase of about 5 orders of magnitude (over the past 30 years) in the fraction of the sample that can be detected, dramatically improving counting statistics, as well as measurement sensitivity. The 5-order of magnitude improvement, comes largely from the shift to mass spectrometric measurement techniques, but also has resulted from subsequent improvement in ionization plus transmission efficiency. While additional improvement above the 5-order of magnitude figure may be possible, current efforts are focused on improving the accuracy of the measurements, standardizing gravimetric standards among laboratories, and shortening measurement times. These efforts will be discussed along with summary results of some of the major applications.