Grain size analysis and origin of the Chengdu clay from the Chengdu Plain, Sichuan

The grain size analysis is carried out for the representative samples of the Chengdu clay taken from the Quaternary sections in the Chengdu Plain, Sichuan. The Chengdu clay consists essentially of silty grains of 5 to 50 μm in size, with an average grain diameter of 7.1 to 7.3 φ(i. e., 7.4 to 6.6μm in size) and also a small amount of more than 63μm fraction, and in the diagram, tends to display the bimodal patterns of distribution. The grain size parameters, mean square deviation values and kurtosis values for the Chengdu clay are strikingly similar to those of the northern China loess and Garze loess, but quite different from those of the fluvial deposits. The abovementioned aspects suggest that the Chengdu clay is a kind of aeolian soil. According the results of optically stimulated luminescence(OSL), the Chengdu clay from the Chengdu Plain should be originated from the latest glacial sediments in the middle to late stages of the late Pleistocene. The bulk of the Chengdu clay is distal.