黔北新蒲红色风化壳剖面的粒度分布特征--兼论岩溶区上覆土层的物质来源

粒度分析在风化壳物源示踪方面是一种新的尝试,具有指示直接的特点。尤其当常规的地球化学、矿物学等方法难以直观反映母岩的不均一性对风化壳的影响时,粒度分布特征却可以建立两者的对应关系,从而更为合理地指示风化壳和下伏基岩的关系。黔北新蒲剖面的下伏基岩为局部夹碎屑岩薄层的连续型碳酸盐岩,本文通过对其酸不溶物及上覆红色风化壳粒度分布特征的研究,表明基岩的垂向不均一,导致上覆风化壳粒度分布特征的差异性,同时存在与下伏不同基岩酸不溶物粒度分布特征相对应的风化壳,指示了碳酸盐岩为其上覆风化壳的成土母岩。化学风化指标在剖面的变化也支持了粒度分析结果,即风化壳母岩的不均一性。从碎屑岩夹层和碳酸盐岩对风化壳提供物源的相对份额中指出碳酸盐岩的酸不溶物对上覆风化壳的优势贡献。从粒度参数角度进一步诠释了连续型碳酸盐岩风化残积成土的现实性,为正确理解中国西南岩溶区红色风化壳的成因提供了新的探索手段。综合资料显示,碳酸盐岩特别是连续型碳酸盐岩酸不溶物构成中国西南岩溶区上覆红色风化壳的主要物质来源也是可能的。

GRAIN SIZE DISTRIBUTION CHARACTERS OF THE RED WEATHERING CRUST AT XINPU, NORTH GUIZHOU:DISCUSSION ON PROVENANCE OF OVERLYING WEATHERING CRUSTS IN KARST AREAS

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.