MINERALOGICAL AND GEOCHEMICAL TRENDS ACROSS THE LOESS PLATEAU, NORTH CHINA

The mineralogy and major element geochemistry of Malan loess, the uppe rmost loess layer, were studied along two transects from the Baiyu Mou ntains in the north to the Wei River lowlands, 350 km to the south. Th e mineralogy of the coarse silt, fine silt and clay fractions is gener ally uniform across the Loess Plateau. However, in the coarse silt fra ction there is a decrease in the weight percentage of heavy minerals a nd in the hornblende: epidote ratio southwards. Also, in the clay frac tion, mica contents increase slightly southwards and smectite increase s northwards along one transect. The major element geochemistry of Mal an loess shows several clear trends. Silicon, sodium and magnesium gen erally decrease from north to south while aluminium, iron, potassium, titanium and manganese generally increase. The observed mineralogical and chemical patterns appear to be mainly related to the changing part icle size from sandy loess in the north to clayey loess in the south. Slightly higher potassium and phosphorus contents in the clayey loess suggest that this loess has a greater natural fertility. Overall, the results confirm particle size evidence that Malan loess was derived fr om a desert source area to the north and northwest of the Loess Platea u.