Coeval changes in grain size and sedimentation rate of eolian loess, the Chinese loess plateau

Abstract

To determine the temporal-spatial relationship between strength of the winds transporting the Chinese loess and aridity conditions of the loess source area, six loess sections located respectively in the northern, middle, and southern Loess Plateau were studied. Grain size distributions were analyzed on loess-paleosol samples that are closely spaced in the sections. Time scales were established by tuning each of the grain size records to theoretical changes in the Earth's orbital parameters. Results obtained show that during the last two glacial cycles, particle size of the loess co-varies with apparent sedimentation rates, suggesting that variations in winter monsoon intensity and the aridity of the loess source area are tightly coupled. This proximal relationship is in striking contrast with the observation of distal eolian clays in North Pacific sediments. We propose that this phenomenon may result from the proximity of the Loess Plateau to the source area and from the significant control of the winter monsoon on the expansion-retreat changes of the deserts in the northern and northwestern China.