江西玉山祝宅晚奥陶世地层、沉积特征及环境初探

<正> 江西玉山县城东南约15km处的祝宅,出露着富含壳相化石、以碳酸盐岩相为主的奥陶纪地层。这一地层最早为张利民等于1977年发现,1980年韩乃仁、李罗照等测制剖面,写了“江西玉山祝宅奥陶系剖面”初稿。1985年,陈旭、戎嘉余、李守军在前人工作的基础上进行野外调查,室内研究后草成本文。 本文珊瑚、藻类和层孔虫由邓占球、穆西南和董得源鉴定。刘云做了红外曲线分析,杨荣庆清绘插图,毛继良摄制沉积岩薄片,李懋摄制高岭石的扫描电镜照片,均一并致谢。

Prelimiary investigation of the Late Ordovician Strata of Zhuzhai in Yushan of Jiangxi,their depositional features and environment

The Sanjushan Formation in this area consists of four sedimentary cycles characterized by the shallow water limestone and mudstone with paraconformity in their contact relations. Two brachiopod communities, Tcherskidium and Sowerbyella-Zygospira communities are herein recognized. The former occurs in micrite or biostrome and the latter in mudstone and shale. They indicate a mid-Ashgillian in age and Benthic Assemblage 2-3 in their depth zonation.The abundance of the algae in the micrite may indicate the source of the lime. The development of the calcareous algae, reef and carbonate mud mound indicate a warm water environment within a low latitude region. The patch reefs consist of the tabulnte corals and stromatoporoids as the frameworks and some gastropods, brachiopods, calcareous algae and trilobites as the attached-reef organism. At the fore-reef, the floatstone, a kind of talus or reef-derived breccia occur.The kaolinite mudstone at the top of the Sanjushan Formation there is recognized as a weathering front during the mid-late Ashgillian. Thus, the area uplifted and had been a part of the Cathaysian Land which expanded during the eustatic sea level lowering in the late Ashgillian.