辽东半岛南部金州湾拉树山剖面寒武系苗岭统徐庄组核形石沉积特征

Sedimentary features of oncoids from Xuzhuang Formation of Cambrian Miaoling Series in Lashushan Section, Jinzhou Bay, Southern Liaodong Peninsula

辽东半岛南部金州湾拉树山剖面寒武系苗岭统徐庄组顶部发育丰富的巨型泥晶核形石。基于野外描述和镜下观察资料,分析研究区核形石沉积特征及微观组构。结果表明:徐庄组产出的核形石与鲕粒共生且核形石灰岩与鲕粒灰岩具有明显分界,最典型的沉积特征为核形石的泥晶质组成和非纹层化结构,核形石内部致密泥晶中发育密集的丝状钙化蓝细菌鞘化石及不规则的窗格状组构;核形石可能形成于光合作用生物膜与“碱度发动机”和EPS紧密耦合的复杂的钙化作用,与以丝状钙化蓝细菌为主导的微生物膜沉积作用密切相关。核形石表现无纹层特征、白云石化现象及外来碎屑存在,可能形成于浅海正常浪基面附近的中高能水体环境。该结果为研究早古生代高能水体中微生物调节的沉淀作用形成碳酸盐颗粒提供典型实例。

There are abundant giant argillaceous nuclear stones on the top of Xuzhuang Formation of Cambrian Miaoling Series in Lashushan Section of Jinzhou Bay in the south of Liaodong Peninsula.Based on the field description and microscopic observation data,the sedimentary characteristics and microstructure of the study area are analyzed.The results show that the oncoid and oolite produced in Xuzhuang Formation are symbiotic,and the oncoid limestone and oolitic limestone have an obvious boundary.The most typical sedimentary characteristics are the composition and non laminar structure of nucleated stone argillaceous crystal.Dense filamentous calcified cyanobacteria sheath fossils and irregular pane fabric are developed in the dense argillaceous crystal in the oncoids.The oncoids of Xuzhuang Formation may be formed in the complex calcification of photosynthetic biofilm closely coupled with alkalinity engine and EPS,which is closely related to the deposition of microbial membrane dominated by filamentous calcified cyanobacteria.The non laminar characteristics,dolomitization and the existence of foreign debris of the core stone indicate that the core stone may be formed in the medium and high energy water environment near the normal wave base in the shallow sea.The results provide a typical example for the study of microbial regulated precipitation in Early Paleozoic high-energy water to form carbonate particles.