GRAIN-SIZE FEATURES OF QUATERNARY RED EARTH IN JINHUA-QUZHOU BASIN

Jinhua-Quzhou basin is one of the red earth regions in Zhejiang Province, which is an ideal area to study red earth sediments and global change. Grain size distribution in Tangxi section was measured, and the results are as follows:①It contains no gravel (>2 mm); low content of sand (>63 μm); and high content of both clay (<4 μm) and silt fraction (4~63 μm), which probably indicates aeolian characteristics from their parent materials and the pedogenic processes. The average contents of silt fraction, clay and sand are respectively 48.51%, 49.91% and less than 1.58%. The grain-size frequency curves of the red earth show the double-peak mode in the section-the 10~63 μm particle group and the one less than 4 μm are its "two dominating modes". ②The sedimentary environment for typical red clay unit and that for vermiculated red clay unit are similar. However, the probability accumulation curves of red earth suggest that sorting of the vermiculated red clay unit would be more complicated. ③The vertical changes of grain size in Tangxi section probably reflect the trend of dry-cold paleoclimate and the climatic variability since mid-Pleistocene in South China.