湖南桃江奥陶系磨刀溪组锰质岩的内碎屑结构和重力流沉积

湖南桃江一带的奥陶纪锰质碳酸盐岩,具有清晰的内碎屑结构和一些粒度递变沉积构造。锰质岩或锰矿层呈薄层或条带夹在含有笔石的黑色泥页岩中,表现出它们在成因或沉积环境方面的极不协调。以砂屑和藻屑为主组成的白色、灰白色锰质碳酸盐岩是清洁、浅水、碱性环境中的产物;以细粉砂级颗粒为主并含有硅质、碳质的泥页岩则是污浊、深水、酸性环境中的沉积。这种不协调的沉积组合是由于浅水锰质碳酸盐沉积物以重力流方式进入深水盆地与黑色泥质沉积物混合、交互沉积结果。

INTRACLASTIC STRUCTURE AND GRAVITY-FLOW SEDIMENTATION OF MANGANESE ROCK IN ORDOVICIAN MODAOXI FORMATION,TAOJIANG COUNTY,HUNAN PROVINCE

The intraclastic structure and gravity-flow sedimentation of the manganese rock in Taojiang manganese ore deposit, Hunan Province, are studied in this paper. The Taojiang manganese ore deposit is located on the slope of a transiion zone from Middle Ordovician shallow-water carbonate platform to deepwater muddy basin. The manganese-bearing series consists of manganese ore bed, manganiferous limestone and black carbonaceous mudrock. The manganese ore bed shows distinct intraclastic structure and has graded bed sequence. The intraclasts in manganese ore were formed from the fragments of several manganiferous carbonate deposits containing mineralized algae remains in shallow-water sedimentary environment. They flowed along the basin slopes into the deep-water basin, and deposited together with more or less amount of illite, chlorite, calcite, quartz and organic carbon to form the intraclastic manganese ore. The slope zone between the shallow-water carbonate platform and deepwater muddy basin was a favorable geologic setting for occurrence of the gravity-flow deposits.