摘要:
为了揭示黔中地区埃迪卡拉系陡山沱组磷质岩系中白云石胶结物的成因，并评估磷质颗粒间白云石胶结物作为指示磷质颗粒沉积时期海水地球化学性质地质记录的可靠性。采用偏光显微镜、阴极发光显微镜及ICP-MS等分析手段对黔中瓮安地区穿岩洞剖面陡山沱组磷质岩系中胶结物的岩石学及地球化学特征进行研究。根据矿物类型，将陡山沱组磷质岩系中胶结物分为磷质和白云石两种类型。依据晶体大小和晶体表面干净程度，进一步将胶结物白云石划分为细晶干净白云石胶结物、细晶脏白云石胶结物、中-粗晶白云石胶结物三种类型。在阴极发光显微镜下，白云石胶结物整体发斑点状的红光。研究区陡山沱组磷质岩系中白云石胶结物的稀土元素配分模式与现代碳酸盐岩较为类似，即明显的Ce负异常、LREE相对HREE亏损、接近现代海水的Y/Ho。白云石胶结物主要形成于埋藏阶段的海源孔隙水，后期发生了较为强烈的重结晶作用。但研究区陡山沱组磷质岩系中白云石胶一定程度上可以作为表征磷质颗粒沉积时期海水氧化还原状态的地质记录，指示磷质颗粒沉积时期海水的氧化状态逐渐增强。
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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