THE EVOLUTION FEATURE OF WEATHERED CRUST DEVELOPED BY INHOMOGENEOUS LIMESTONE BEDROCK AT HUAXI PROFILE IN GUIYANG CITY: IMPLICATION FROM GRAIN-SIZE DISTRIBUTION

Research on the development characteristics of weathered crust is generally based on uni- member weathered parent rock. But few researchers have discussed the evolution feature of weathered profile developed by inhomogeneous bedrock, especially, on carbonate rock intercalated with clastic rocks. Through researching grain size distribution characteristics of weathered profile of limestone intercalated with argillous sheet in Huaxi, Guiyang City, and integrating with its mineral components, the development characteristics of weathered crust of inhomogeneous limestone are showed as follows:Limestone, as main weathered parent rock at early stage, is characterized of intense solution of carbonate materials and remains of acidic insoluble matter. Meanwhile, solution of calcite also retards weathering process of acidic insoluble matter. At late stage, with the absence of soluble minerals within weathered crust, acidic insoluble matter acts as main weathering matter, and develops weathered crust similar to other kinds of rocks. Argillous sheets, interlayers in limestone, as accessory ingredient of the weathered crust, are dislocated and enveloped by weathered residuals of limestone owing to huge volume shrinkage during weathering process of the parent limestone and this postpones weathering of argillous sheets. So, on account of its being situated in different microenvironment and its discrepant influenced level by weathering solution, every end- member is weathered and evolves in their own way. With gradual intensity of weathering degree, enveloping matter of argillous sheets is decomposed, end- members are gradually mixed, tend to convergence, weathered crust tends to become homogeneity and transform to supergene stable minerals in manner of uniform weathering action.