East Asian monsoon variations on millennial scale during 35,000-25,000 a BP from records of grain size, CaCO3 and organic matter in the Badain Jaran Desert, China

摘要

The CGS3a segment of the Chagelebulu section in the southeastern Badain Jaran Desert in China records five and a half sedimentary cycles consisting of aeolian dune sands or loess alternating with overlying fluviolacustrine during 35,000-25,000 a BP. Based on the analyses of grain size, calcium carbonate (CaCO3) and organic matter (OM) for 139 samples in the CGS3a segment, we found that the values of mean particle size (Mz) (I center dot) and standard deviation (sigma), CaCO3, and OM from the lacustrine facies generally tended to be higher than those of the underlying dune sands or loess. These data indicate that the grain size was fine and poorly sorted with high values of CaCO3 and OM in the lacustrine facies, and grain size was coarse and well sorted with low values of CaCO3 and OM in the dune sands and loess. A graph of these values showed five and a half oscillations between layers, which were generally similar to the sedimentary cycles. A sedimentary cycle between the dune sands or loess and lacustrine facies in the CGS3a segment represents a cold-dry and warm-humid climate cycle. Therefore, we suggest that the CGS3a segment experienced at least five and a half climate cycles (five cold-dry climates and six warm-humid climates) during 35,000-25,000 a BP. Of these, the warm climate fluctuations correspond well to the Dansgaard-Oeschger events (D/O3-D/O8) recorded in the Greenland Ice Core Project (GRIP). Moreover, the cold period 28D (30,600 +/- 2,900 a BP) correlates well with the Heinrich Event H3 (approximately between 29,000 and 31,000 a BP). These results suggest that the driving forces of the East Asian monsoon in China's deserts are probably as the same as the Dansgaard-Oeschger events and Heinrich oscillations in the Northern Hemisphere during that period. This study reveals the East Asian monsoonal climatic fluctuations on millennial scale in China's deserts during 35,000-25,000 a BP.