湘西岩溶区风化壳的物源:石英粒度分布特征的指示

Taking a karst region of western Hunan Province as research area, and selecting four weathering profiles (of which, two are underlain by limestones, and other two by clastic rocks) as research object, through contrasting and surveying of characteristics of grain size distribution of quartz, this paper makes effort to unveil the formation of weathering crusts in the area. In the weathering profiles of WC1 and WC2, the bedrocks are limestones, the grain size frequency distribution curves of quartz show single, narrow peak, and their modes are 4. 9p and A respectively. The weathering profiles of WC3 and DBK are of clastic rocks, grain size frequency distribution curves of quartz show single, broad peak, and their modes are approximately 5. l and 6 respectively. Furthermore, the grain size frequency distribution curves of quartz for the 4 weathering profile and their bedrocks display good accordant relation. Such parameters as standard deviation, skewness, kurtosis, etc. revealed by scatter diagram of quartz grain size indicate that each profile basically plots in different area. From the evidence above, following conclusion can be drawn: (1) Characteristics of grain size distribution of quartz can be entirely inherited during weathering of mother rocks; (2) Profiles WC1 and WC2 are weathering crusts derived from carbonate rocks, indicating that the carbonate rocks may entirely form weathering crusts by way of weathering process in the favorable morphological units; (3) Characteristics of grain size distribution of quartz are distinct in different weathering profiles, suggesting that weathering crusts have no common provenance on a regional scale, and originating from the underlying mother rocks; (4) Characteristics grain size distribution of quartz is a good index for tracing the origin of weathering crusts in karst regions.