Testing the initial 230Th/232Th for “Known Age Carbonate” and its significance for 230Th dating and paleoclimate research

Abstract

The 230Th dating (238U–234U–230Th dating method) has become one of the most important dating methods for Quaternary research. However, the 230Th/232Th ratio of 4.4 ± 2.2ⅹ10−6 is widely used for age correction in 230Th dating method. Here, we collected active speleothems with exactly known age and zero-year-old calcium carbonate from caves and dated them by 230Th dating. Our data indicated that the initial 230Th/232Th ratio can be one order of magnitude higher than the ratio of 4.4 ± 2.2 × 10−6. High initial 230Th/232Th ratio may result in false and comparatively old calculated age than the real age of young samples with low 238U concentration. So, the accurate initial 230Th/232Th ratio of active speleothem deposited in the same cave, instead of the general initial 230Th/232Th ratio, is essential for the precise age correction of young speleothem samples of low 238U concentration. Finally, we proposed a procedure to correlate modern observation and speleothem based paleoclimate reconstruction, on the basis of precise 230Th age which corrected by the true initial 230Th/232Th ratio.