华北中元古代鱼骨状方解石:成因机制和古环境意义
发布时间：2018-10-09 15:57
【摘要】：鱼骨状方解石是一种特殊的碳酸盐沉积,由锯齿状亮暗交互的亚毫米级条带组成,主要见于太古宙。以往认为,鱼骨状方解石属无机化学沉淀成因,形成于水体缺氧、碳酸盐过饱和、富Fe~(2+)、Mn~(2+)等碳酸盐沉淀抑制剂的环境条件;在地质记录中其丰度随时间的减少反映了海洋的长期氧化趋势。文中首次在华北地台中元古界高于庄组四段微生物礁内发现了大量鱼骨状方解石。宏观观察表明,这些鱼骨状方解石主要以微生物礁孔洞充填物形式产出,明显区别于太古宙以海底沉淀形式直接产出在海底的鱼骨状方解石。显微研究发现,鱼骨状方解石晶体纤维具有沿晶体生长方向旋转消光特征,证明其内部亚晶的光学C轴从纤维底部的随机排列逐步旋转至上部垂直纤维生长方向。这符合球状晶体生长模式,需要方解石沉淀抑制剂的参与。鱼骨状方解石产出具有丰度随时间减少以及产出形式由海底沉淀向孔洞胶结物转变的特征。这些特征与海洋氧化逐渐增强以及具氧化还原敏感属性的碳酸盐沉淀抑制剂逐渐从水体中移除相吻合。笔者认为鱼骨状方解石的沉淀抑制剂为Fe~(2+)和Mn~(2+),这与微生物岩无明显Ce异常和Fe~(2+)极强的抑制能力相一致。因此,鱼骨状方解石可用于指示缺氧环境条件。此外,显微和超微研究也表明鱼骨状方解石晶体内存在有大量与其生长方向一致的菌丝体残余和与之密切伴生的有机矿物,表明微生物为鱼骨状方解石成核和初始沉淀提供了重要垫板。
[Abstract]:Fishbone calcite is a special carbonate deposit consisting of zigzag bright and dark interacting submillimeter bands mainly found in Archean. In the past, it was considered that fishbone calcite belongs to inorganic chemical precipitation, which was formed under the environmental conditions of anoxia, supersaturation of carbonate, rich in Fe~ (2) mn ~ (2) and so on. The decrease of abundance over time in geological records reflects the long-term oxidation trend of the ocean. In this paper, a large number of fishbone calcite was first found in the microbe reef of the Proterozoic in Taizhong, North China. Macroscopic observation shows that these fish bone calcite are mainly produced in the form of microorganism reef pore filling, which is obviously different from Archean fish bone calcite produced directly in the form of submarine sedimentation. Microscopic study shows that the fishbone calcite crystal fiber has the characteristics of rotation and extinction along the crystal growth direction. It is proved that the optical C axis of the inner subcrystal rotates gradually from the random arrangement at the bottom of the fiber to the vertical fiber growth direction in the upper part. This is in line with the growth pattern of spheroid crystals and requires the participation of calcite precipitation inhibitors. The fish bone calcite production is characterized by the decrease of abundance over time and the transition from seabed sedimentation to pore cementation. These characteristics are consistent with the gradual enhancement of marine oxidation and the gradual removal of carbonate precipitation inhibitors with redox sensitivity from water. The authors consider that the depressants of fishbone calcite are Fe~ (2) and Mn~ (2), which are consistent with the fact that there is no obvious Ce abnormality in microbe rock and the strong inhibition ability of Fe~ (2). Therefore, fishbone calcite can be used to indicate anoxic environmental conditions. In addition, microscopic and ultrastructural studies also showed that there are a large number of mycelium residues and organic minerals closely associated with the fishbone calcite crystal. The results show that the microorganism provides an important cushion for the nucleation and initial precipitation of fish bone calcite.
【作者单位】： 中国地质大学生物地质与环境地质国家重点实验室;中国地质大学(北京)科学研究院;中国地质大学(北京)地球科学与资源学院;中国地质调查局油气资源调查中心;
【基金】：国家自然科学基金项目(编号:41402024,41272039) 中央高校基本科研业务费专项资金项目(编号:2652014063)共同资助~~
【分类号】：P578.61
本文编号：2259916
[Abstract]:Fishbone calcite is a special carbonate deposit consisting of zigzag bright and dark interacting submillimeter bands mainly found in Archean. In the past, it was considered that fishbone calcite belongs to inorganic chemical precipitation, which was formed under the environmental conditions of anoxia, supersaturation of carbonate, rich in Fe~ (2) mn ~ (2) and so on. The decrease of abundance over time in geological records reflects the long-term oxidation trend of the ocean. In this paper, a large number of fishbone calcite was first found in the microbe reef of the Proterozoic in Taizhong, North China. Macroscopic observation shows that these fish bone calcite are mainly produced in the form of microorganism reef pore filling, which is obviously different from Archean fish bone calcite produced directly in the form of submarine sedimentation. Microscopic study shows that the fishbone calcite crystal fiber has the characteristics of rotation and extinction along the crystal growth direction. It is proved that the optical C axis of the inner subcrystal rotates gradually from the random arrangement at the bottom of the fiber to the vertical fiber growth direction in the upper part. This is in line with the growth pattern of spheroid crystals and requires the participation of calcite precipitation inhibitors. The fish bone calcite production is characterized by the decrease of abundance over time and the transition from seabed sedimentation to pore cementation. These characteristics are consistent with the gradual enhancement of marine oxidation and the gradual removal of carbonate precipitation inhibitors with redox sensitivity from water. The authors consider that the depressants of fishbone calcite are Fe~ (2) and Mn~ (2), which are consistent with the fact that there is no obvious Ce abnormality in microbe rock and the strong inhibition ability of Fe~ (2). Therefore, fishbone calcite can be used to indicate anoxic environmental conditions. In addition, microscopic and ultrastructural studies also showed that there are a large number of mycelium residues and organic minerals closely associated with the fishbone calcite crystal. The results show that the microorganism provides an important cushion for the nucleation and initial precipitation of fish bone calcite.
【作者单位】： 中国地质大学生物地质与环境地质国家重点实验室;中国地质大学(北京)科学研究院;中国地质大学(北京)地球科学与资源学院;中国地质调查局油气资源调查中心;
【基金】：国家自然科学基金项目(编号:41402024,41272039) 中央高校基本科研业务费专项资金项目(编号:2652014063)共同资助~~
【分类号】：P578.61
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