震旦纪大塘坡期锰矿的内碎屑结构和重力流沉积

INTRACLASTIC STRUCTURES AND GRAVITY FLOW SEDIM-ENTATION OF RHODOCHROSITE ORE IN SINIAN DATANGPO FORMATION

大塘坡组锰矿石由菱锰矿内碎屑和碳泥质基质组成。菱锰矿内碎屑是浅水沉积环境中的锰质沉积物破碎而成。它们沿着盆地斜坡流入深水地区与碳、粘土和粉砂沉积在一起形成内碎屑菱锰矿。一部分矿石有递变层理,具有浊流沉积特征。

The manganese deposits of Sinian Datangpo formation are mainly distributed in the northeastern Guizhou, southeastern Sichuan, western Hunan and northwestern Hubei provinces. The manganese-bearing series consists of lithic sandstone, black carbonaceous mudstone containing manganese ore bed, yellowish-brown mudstone and sandstone in ascending order. The manganese deposits occurred always in the large or small deep-water sedimentary basins.The manganese ore consists of the rhodochrosite intraclasts and carbonaceous pelitic matrix. The intraclasts were formed from the fragments of manganese deposits containing mineralized algae remains in shallow-water sedimentary environments. The matrix or adjoining rocks composed of organic carbon, clay and silt were precipitated in deep-water, reducing sedimentary environments. Therefore, the rhodochrosite intraclasts have probably come from the shallow-water zones on basin slopes. They flowed along the basin slopes into the deep-water area, and deposited together with more or less amount of carbon, clay and silt to form the intraclastic rhodochrosite ores. Some part of the ores show their graded bedding formed from intraclasts, and hence is characterized by turbidity current deposition.