Relationship between sedimentation and red karst landform during the Ordovician in Hunan,Chongqing and Guizhou
The Ordovician red karst is a newly discovered geological landscape in Hunan,Chongqing and Guizhou.Its appearances,distributions and rhythms are distinctive.With the development of red stone forest parks in the study area,red karst landforms have attracted great attention in recent years.Researchers have analyzed red karst landforms from their appearance characteristics,geomorphological types,surface corrosion,geological structures,climatic and neo-tectonic movement.However,there is still lack of research on the relationship between formation of red karst landforms and sedimentation.Integrating the field geological survey,observation of thin sections,odontolite analysis and X-ray diffraction analysis,this study tried to discuss the inner connection between weathering and red karst landforms in the view of sedimentation.During the syndiagenetic stage,the increase of oxygen content in the atmosphere caused the oxidation at the bottom of shallow continental shelf.During this process,Fe2O3 that was formed by the oxidation of iron ions in terrigenous debris entered sedimentary strata,which contributed to red-colored landform.Controlled by the distribution of lithofacies in the early-to-mid Ordovician,karst landforms were only developed in the carbonate arc blet of the shallow continental shelf along the area of Wuhan-Songzi-Songtao-Huangping.Pore sizes and structures of carbonate rocks affected by sedimentary microfacies would influence weathering,and hence the differential weathering caused concave and convex terrains.The Milankovitch cycle resulted in the overlapping of argillaceous limestone and bioclastic micritic limestone in the Guniutan Formation,and the meter-scale cycle of circum-tidal flat caused the rhythms of karst landforms.Types and contents of clay minerals within the limestone indicate the differences in sediment sources and burial histories and also affects hydration expansion and weathering resistance of the formation.In summary,the sedimentation process that controls the rock formation and weathering is one controlling factor to the formation and distribution of red karst landforms.
red karst landformsedimentationsedimentary faciesoutcropsedimentary cycle
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