Bimode Grain － Size Distribution of Chinese Loess and Its Paleoclimate Implication

SUN Dong huai; LU Hua yu; DAVID Rea; SUN You bin; WU Sheng guan

Grain-size distribution of Chinese loess consistently shows bimode spectrum, which is composed of two distinct components. The main component is coarse grain size with, large kurtosis and narrow distribution range,makes up main part of loess material. This main component is likely produced in the season when winter monsoon dominate the paleoclimate of loess plateau, and therefore its grain size indicates East Asia winter monsoon strength. The other grain size component has a wide distribution range, lower kurtosis and fine average grain size. This fine component probably represents the general dust base level of atmosphere over loess plateau, which prevails in most of the season. In some extension, it is genetically connected to the Northern Hemisphere westerly. Grain size distribution function of Chinese loess can be expressed with a sum of two Weibull distribution functions that represent two components of loess grain size. By fitting measured grain-size data to proposed distribution function, all parameters of the function can be estimated. Meanwhile, distribution function as well as the ratio of the two components can also be obtained.

1 Xi'an Laboratory of Loess and Quaternary Geology, Chinese Academy of Science Xi'an 710054;

2 Department of Geological Science,University of Michigan USA

Received Date: 1999-05-11

Rev Recd Date: 1999-10-27

Publish Date: 2000-09-10

Key words:

loess /
grain size /
winter monsoon /
westerly

Abstract: Grain-size distribution of Chinese loess consistently shows bimode spectrum, which is composed of two distinct components. The main component is coarse grain size with, large kurtosis and narrow distribution range,makes up main part of loess material. This main component is likely produced in the season when winter monsoon dominate the paleoclimate of loess plateau, and therefore its grain size indicates East Asia winter monsoon strength. The other grain size component has a wide distribution range, lower kurtosis and fine average grain size. This fine component probably represents the general dust base level of atmosphere over loess plateau, which prevails in most of the season. In some extension, it is genetically connected to the Northern Hemisphere westerly. Grain size distribution function of Chinese loess can be expressed with a sum of two Weibull distribution functions that represent two components of loess grain size. By fitting measured grain-size data to proposed distribution function, all parameters of the function can be estimated. Meanwhile, distribution function as well as the ratio of the two components can also be obtained.

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Reference (26)

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Bimode Grain － Size Distribution of Chinese Loess and Its Paleoclimate Implication

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