西秦岭南带中志留统的岩石学特征与沉积环境

PETROLOGY AND SEDIMENTARY ENVIRONMENT OF MIDDLE SILURIAN IN SOUTHERN REGION OF WEST QINLING

详细研究了西秦岭南带中志留统岩石学特征,对遭受重结晶作用的碳酸盐岩进行了结构成因分类。分析了该区中志留世的沉积环境及变化特征。在该区发现的层孔虫生物礁及其它“浅水”标志,表明志留纪时,为若尔盖微古陆北侧的边缘浅海环境。西部为局限陆棚环境,可分为:局限内陆棚、海湾、礁滩-泻湖-潮坪(孤立台地)等亚环境;东部为开阔陆棚环境,可分为浅海砂滩、内陆棚、外陆棚等亚环境。

This paper deals with the petrology of Middle Silurian in southern region of West Qinling. Various types of lightly metamophosed rocks have been recognized, especially the recystallized carbonate rocks have been classified in the light of texture and origin. The sedimentary environment of Middle Silurian is also involved. As a result of discovering of the Stromatopora organic reef and other ' shallow water 'criteria, the authors proposes a entirely new view of sedimentary environment of Middle Silurian in this area. In Silurian, it should belong to a marginal sheif environment in North of Roergai microcontinent, North-western margin of Yangtze Plate, instead of deep sea environment believed by earlier authors. In western region, it should be of restricted shelf environment. Because of the existence of Baiyi subaqueous uplift, an isolated platform was developed in the restricted inner shelf environment during the reef-forming period of Middle Silurian,and formed the special complex of organic reef/shl facies and tidal flat/lagoon facies. Eastwardly, there was a open shelf to sub-deep or deep marine environment in this period, and it can be subdivided into inner-outer shelf and neritic shoal environment.