Abstract
To elucidate the genesis of dolomite cement in the phosphorite series of the Doushantuo Formation of the Ediacaran System in central Guizhou and assess the reliability of dolomite cement between phosphorite particles as a geological record indicating the geochemical properties of seawater during the deposition period of phosphorite particles, petrological and geochemical characteristics of the cement in the phosphorite series of the Doushantuo Formation at the Chuanyan Cave section in Weng'an, central Guizhou, were studied using polarizing microscopy, cathodoluminescence microscopy, and ICP-MS analysis. Based on mineral types, the cement in the phosphorite series of the Doushantuo Formation is classified into two types: phosphate and dolomite. According to crystal size and cleanliness of crystal surfaces, the dolomite cement is further divided into three types: fine-grained clean dolomite cement, fine-grained dirty dolomite cement, and medium-to-coarse-grained dolomite cement. Under cathodoluminescence microscopy, the dolomite cement generally emits spotty red light. The rare earth element patterns of dolomite cement in the phosphorite series of the Doushantuo Formation in the study area are similar to modern carbonate rocks, characterized by a significant negative Ce anomaly, relative depletion of LREE compared to HREE, and a Y/Ho ratio close to modern seawater. The dolomite cement was mainly formed in marine-derived pore water during the burial stage, and later underwent intense recrystallization. However, to a certain extent, the dolomite cement in the phosphorite series of the Doushantuo Formation in the study area can serve as a geological record indicating the redox state of seawater during the deposition period of phosphorite particles, suggesting a gradual increase in the oxidation state of seawater during the deposition of phosphorite particles.
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