Geochemical behavior of chemical elements is studied in a dolomitite weathering profile in upland of karst terrain in northern Guizhou. Two stages can be recognized during the process of in situ weathering of dolomiti...Geochemical behavior of chemical elements is studied in a dolomitite weathering profile in upland of karst terrain in northern Guizhou. Two stages can be recognized during the process of in situ weathering of dolomitite: the stage of sedentary accumulation of leaching residue of dolomitite and the stage of chemical weathering evolution of sedentary soil. Ni, Cr, Mo, W and Ti are the least mobile elements with reference to Al. The geochemical behavior of REE is similar to that observed in weathering of other types of rocks. Fractionation of REE is noticed during weathering, and the two layers of REE enrichments are thought to result from downward movement of the weathering front in response to changes in the environment. It is considered that the chemistry of the upper part of the profile, which was more intensively weathered, is representative of the mobile components of the upper curst at the time the dolomitite was formed, while the less weathered lower profile is chemically representative of the immobile constitution. Like glacial till and loess, the 'insoluble' materials in carbonate rocks originating from chemical sedimentation may also provide valuable information about the average chemical composition of the upper continental crust.展开更多
Tectonic uplift at the end of Sinian resulted in the denudation of the Dengying （灯影） Formation on a different scale and the development of a great number of secondary dissolution vugs beneath the unconformity betw...Tectonic uplift at the end of Sinian resulted in the denudation of the Dengying （灯影） Formation on a different scale and the development of a great number of secondary dissolution vugs beneath the unconformity between Sinian and Cambrian.Geological and geochemical characteristics such as the development of caves,sinkholes,karst tubes and weathering crust,abrupt depletion and negative deflection of δ13C and δ18O in country rock and vug filling toward unconformity surface suggest that subaerial karstification is responsible for the development of secondary karst vugs within 150 m or so beneath the unconformity surface.This kind of secondary dissolution vug was partially or completely filled by different stage dolomite,calcite,quartz and bitumen during the later deep burial and uplift.Facts such as the obvious difference in δ13C and δ18O of the filling in the subaerial karst vug from the country rock and the value of δ13C and δ18O of the filling increasing or decreasing with that of the country rocks,suggest that the hydrothermal fluid charged in vugs is allogenic fluid.Subaerial karstification vug acted as a conduit for allogenic corrosive fluid which can create new secondary vugs and enlarge previous karst vugs.The dissolution,precipitant and recrystallization produced by allogenic corrosive fluid introduction and petroleum thermal cracking,caused contraction or enlargement of the subaerial karstification vugs and the development of new secondary vugs during the deep burial and uplift.The ultimate vug of deep burial dolomitite is determined not only by fluid charge,dissolution,mineral precipitant,and petroleum thermal cracking during the deep burial and tectonic uplift,but also by the amount of initial secondary dissolution vugs created by subaerial karstification.展开更多
文摘Geochemical behavior of chemical elements is studied in a dolomitite weathering profile in upland of karst terrain in northern Guizhou. Two stages can be recognized during the process of in situ weathering of dolomitite: the stage of sedentary accumulation of leaching residue of dolomitite and the stage of chemical weathering evolution of sedentary soil. Ni, Cr, Mo, W and Ti are the least mobile elements with reference to Al. The geochemical behavior of REE is similar to that observed in weathering of other types of rocks. Fractionation of REE is noticed during weathering, and the two layers of REE enrichments are thought to result from downward movement of the weathering front in response to changes in the environment. It is considered that the chemistry of the upper part of the profile, which was more intensively weathered, is representative of the mobile components of the upper curst at the time the dolomitite was formed, while the less weathered lower profile is chemically representative of the immobile constitution. Like glacial till and loess, the 'insoluble' materials in carbonate rocks originating from chemical sedimentation may also provide valuable information about the average chemical composition of the upper continental crust.
基金supported by the National Basic Research Program of China (No. 2005CB422106)
文摘Tectonic uplift at the end of Sinian resulted in the denudation of the Dengying （灯影） Formation on a different scale and the development of a great number of secondary dissolution vugs beneath the unconformity between Sinian and Cambrian.Geological and geochemical characteristics such as the development of caves,sinkholes,karst tubes and weathering crust,abrupt depletion and negative deflection of δ13C and δ18O in country rock and vug filling toward unconformity surface suggest that subaerial karstification is responsible for the development of secondary karst vugs within 150 m or so beneath the unconformity surface.This kind of secondary dissolution vug was partially or completely filled by different stage dolomite,calcite,quartz and bitumen during the later deep burial and uplift.Facts such as the obvious difference in δ13C and δ18O of the filling in the subaerial karst vug from the country rock and the value of δ13C and δ18O of the filling increasing or decreasing with that of the country rocks,suggest that the hydrothermal fluid charged in vugs is allogenic fluid.Subaerial karstification vug acted as a conduit for allogenic corrosive fluid which can create new secondary vugs and enlarge previous karst vugs.The dissolution,precipitant and recrystallization produced by allogenic corrosive fluid introduction and petroleum thermal cracking,caused contraction or enlargement of the subaerial karstification vugs and the development of new secondary vugs during the deep burial and uplift.The ultimate vug of deep burial dolomitite is determined not only by fluid charge,dissolution,mineral precipitant,and petroleum thermal cracking during the deep burial and tectonic uplift,but also by the amount of initial secondary dissolution vugs created by subaerial karstification.
