Variations in the aeolian sequence Zr/Rb ratios in the Mu Us Desert during the Holocene and their implications for the East Asian monsoon

Abstract

Situated in the Salawusu River Valley in the southeast of China’s Mu Us Desert, the Milanggouwan stratigraphical section MGS1 has recorded 11 sedimentary cycles, consisting of alternations between dune sands and fluvial or lacustrine facies. This paper analyzed the distribution of grain-size and Zr/Rb ratios in the MGS1, which is located in the arid and semi-arid areas of North China, and grain-size and Zr/Rb ratios are good proxy indicators of East Asian winter and summer monsoons. Results determined the age of the top of MGS1 to be 11.6 ± 0.9 ka BP, and Mz and σ values in the dune sands to be lower than those in the corresponding fluviolacustrine or paleosols. Furthermore, Zr/Rb also exhibited low values in the dune sands and a relatively high content in the fluviolacustrine and paleosols. Both grain-size and Zr/Rb ratios displayed 11 cycles similar to the sedimentation changes, while the Zr/Rb ratios were observed to correlate with Mz and σ. The results suggested that the cycles resulted from the fluctuations between cold-dry and warm-humid climates, and the MGS1 segment experienced at least 11 cold-dry and warm-humid climatic fluctuations. This type of high-frequency climatic fluctuation on a millennial time-scale is related to variations in the strength of the East Asian winter and summer monsoons during the Holocene Period. The dominant periods of the winter monsoon corresponded to the cold events of 8200, 5000, 4000, 2700 and 1400a BP reported in the North Atlantic and other regions in China.