Changes in sand content of loess deposits along a north-south transect of the Chinese Loess Plateau and the implications for desert variations

Geological records have shown that the deserts east of the Helan Mountains in northern China were covered by grass during the Holocene Optimum, wherea s during marine oxygen isotope stages 2 and 4 distribution of the deserts w as almost the same as at present. The wide advance-retreat cycles of the de serts may have exerted an important control on gram-size changes in the loe ss of the Loess Plateau by altering the distance between the source and the accumulation zone of the loess. This challenges the widely accepted model that winter monsoon winds were the sole factor responsible for spatial and temporal changes in loess texture. To observe spatial changes in sedimentol ogical characteristics of loess during the last glacial-interglacial cycle, the texture of loess was measured along a north-south transect of the Loes s Plateau, This transect consists of nine loess sections, starting at Yulin in the transitional region between the Loess Plateau and the Mu Us Desert and ending at Weinan in the southernmost part of the Loess Plateau. Southwa rd changes in sand (>63 pm) content along the transect suggest that variati ons in desert extent have indeed played a significant role in loess grain-s ize distributions, particularly in the northern part of the Loess Plateau. It is proposed that sand content (>63 mu m%) of loess in the loess-desert t ransitional zone may be used as a proxy indicator for proximity to the dese rt margin, (C) 1999 University of Washington.