GRAIN SIZE DISTRIBUTION CHARACTERS OF THE RED WEATHERING CRUST AT XINPU,NORTH GUIZHOU:DISCUSSION ON PROVENANCE OF OVERLYING WEATHERING CRUSTS IN KARST AREAS
Feng Zhigang1, Wang Shijie1, Zhou Dequan2, Sun Chengxing1, Liu Xiuming1
1. State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550002; 2. Department of Resources and Environment, Guizhou Normal University, Guiyang 550001
To indicate the provenance of weathering crust by grain size analysis is a new attempt, which bears the feature of direct indication. Especially, it is difficult for routine methods of geochemistry and mineralogy to directly show the influence of inhomogenous bedrock on weathering crust, but grain size analysis of weathering profiles may establish relation of the both, and so may rationally indicate the relation of weathering crust to underlying bedrock. This paper analysized grain size distribution characters of acidic insoluable matter of continuous carbonatite and overlying red weathering crust, and showed the inhomogeneity of basement carbonatite in vertical direction resulting in the difference of grain size distribution characters of overlying red weathering crust. Moreover, it existed that the grain size frequency distribution curves of varied underlying bedrock acidic insoluable matter were similar to those of overlying weathering crust of the different depth, and indicated the carbonatite being parent rock of overlying weathering crust. The variation of chemical weathering indices with the depth also supported the result of grain size analysis, i.e. parent rock being inhomogenous. From the contribution amount of interlayered detrital rock and carbonatite in weathering crust respectively, the authors suggested acidic insoluable matter of underlying carbonatite being main provenance of overlying weathering crust. In the view of grain size parameters, further interprets residual weathering pedologic process of carbonatite was realistic, which provided a new study way for exactly understanding the genesis of red weathering crust of karst areas in southwest China. To synthesize various data, it was possible for carbonatite, especially continuous carbonatite, to become main provenance of red weathering crust in karst areas of southwest China.
Feng Zhigang,Wang Shijie,Zhou Dequan et al. GRAIN SIZE DISTRIBUTION CHARACTERS OF THE RED WEATHERING CRUST AT XINPU,NORTH GUIZHOU:DISCUSSION ON PROVENANCE OF OVERLYING WEATHERING CRUSTS IN KARST AREAS[J]. Chinese Journal of Geology, 2004, (3): 440-451.