FINE SILT AND CLAY MINERALOGICAL CHANGES OF A SOIL CHRONOSEQUENCE IN THE LANGTANG VALLEY (CENTRAL NEPAL)

Chemical and mineralogical properties of a soil chronosequence in the high mountain zone between 3857 m and 4120 m a.s.l. in Central Nepal ( Langtang valley) are presented. The soils have been developed in morai ne deposits which consist of acid gneisses. They were classified as En tisols, and Spodosols. XRD analyses of the clay and fine silt fraction show increasing changes with distance from the recent Lirung glacier, depending on the time of deposition, resp. soil age. Alteration of il lite to interstratified minerals and to hydroxy-Al interlayered minera ls or pedogenic chlorite with increasing soil development could be obs erved. The interstratified minerals could be identified as random and regular illite-interlayered vermiculite mixed-layer minerals. Intensif ication of the X-ray signals of the fine silt fraction is given compar ed to the clay. With increasing soil development differences between t he clay and fine silt fraction seem to increase. Indications are given of interstratification of the mica-pedogenic chlorite and chlorite-in terlayered vermiculite type in the more intensively weathered soils.