THE DOUBLE PEAKS OF THE FREQUENCY CURVE OF SAND GRAIN SIZE IN THE SOUTHEASTERN PART OF THE BADAIN JARAN DESERT, INNER MONGOLIA, CHINA

Particle size analysis of the samples of dunes from the southeastern Badain Jaran Desert, western Inner Mongolei is undertaken by dry sieving in order to study the relationship between the grain size variations of the aeolian deposits and wind intensity. The frequency curves of the grain size distributions of all samples show similar double peaks. It is found that the first peak takes place at the ca 2.3§ f (0.2mm), and the other at ca 3§ f (about 0.125mm). The first peak is to a large extent consistent with the mean grain size of the samples (ca 2§ f). However, the characteristics of the second peak cannot be reflected in mean grain size. We suggest that the first peak is formed by sand transported by winter monsoon. But the second peak should originate from sand fraction blown by summer monsoon. For the paleoenvironmental studies in the northwestern China, one needs to pay attention not only to the mean grain size but also to the feature of the frequency curve of the aeolian deposits.