A SEM analysis of quartz grains in the sediments of the Lhasa karst areas, Tibet

Abstract

The quartz grains from the sediments of the Lhasa karst areas have been examined by scanning electron microscopy. As the quartz grains were chosen from newly-discovered sediments in caves and relict karst doline, the results show some differences from the sediments sampled by the author in 1987, which were examined by Bull and others (1990). The grains from cave alluvial deposits and doline sediments show many features that are only produced in high chemical and water energy environments. These include solution grooves, holes and V pits. The cave sediments were deposited in the Pleistocene, according to the U-series dating. The analysis, however, shows that the grains might come from the sediments of the Tertiary surface of the plateau, which were brought into the caves by water, mixed with fresh weathering materials and then redeposited. The destruction of this Tertiary surface by intensive erosion was induced by the fast uplift in the Quaternary. Alternatively, many features had also been modified in the chemically active periods during the Quaternary.