MINERALOGICAL AND GEOCHEMICAL TRENDS ACROSS THE LOESS PLATEAU, NORTH CHINA

The mineralogy and major element geochemistry of Malan loess, the uppermost loess layer, were studied along two transects from the Baiyu Mountains in the north to the Wei River lowlands, 350 km to the south. The mineralogy of the coarse silt, fine silt and clay fractions is generally uniform across the Loess Plateau. However, in the coarse silt fraction there is a decrease in the weight percentage of heavy minerals and in the hornblende: epidote ratio southwards. Also, in the clay fraction, mica contents increase slightly southwards and smectite increases northwards along one transect. The major element geochemistry of Malan loess shows several clear trends. Silicon, sodium and magnesium generally 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 particle 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 from a desert source area to the north and northwest of the Loess Plateau.