扬子克拉通北缘中元古界神农架群乱石沟组叠层石类型及其沉积学意义*
Types of stromatolites of the Mesoproterozoic Shennongjia Group in northern margin of Yangtze Craton and their sedimentary significance

扬子克拉通北缘神农架地区中元古界神农架群叠层石十分发育。该群下部乱石沟组中叠层石类型丰富,根据形态可分为柱状、穹状、层状叠层石以及锥状、层柱状、包心菜状、墙状叠层石和叠层石丘等。研究区叠层石以中小型为主,少数为大型和巨型;多数无壁,部分具单层壁;对称性和继承性由好到一般,部分较差。研究表明,叠层石的形态和规模,与水动力条件、水体深度及陆源组分含量关系密切,其中层状叠层石主要发育于潮间带上部,柱状叠层石产于潮间带下部和浅潮下带,穹状叠层石出现在潮间带和潮下带,锥状叠层石多见于潮间带下部和潮下带,层柱状、锥柱状叠层石则集中于潮间带,叠层石丘位于潮间带和潮下带。依据各类型叠层石宏观和微观特征、垂向组合类型、沉积构造及沉积岩相相互关系,并结合碳、氧同位素测试结果,综合研究认为: 虽然叠层石的形成受生物和环境等多重因素影响,但生物因素主要影响叠层石的微观组构,水动力条件则控制叠层石的宏观形态类型,水体深度影响叠层石的规模;另外,生物繁盛、陆源物质供给少的环境更有利于叠层石发育。
Stromatolites of the Luanshigou Formation of Mesoproterozoic Shennongjia Group were developed very well in the northern margin of Yangtze Craton. Their types are abundant. The forms of the stromatolites include colonnella,domal,stratiform,conophyton,strati-columnar,cabbage-like stromatolites and stromatolite bioherm. They are mainly small-medium sized,with some of them large- or huge-sized. Most of them have no walls, and some of them have a single wall. Their symmetry and inheritance are mainly good. The study shows that the morphology and size of stromatolites are closely related to the corresponding hydrodynamic conditions,water depth and the content of terrestrial components. Stratiform stromatolites grew up primarily in the intertidal;columnar stromatolites were found in the intertidal and the subtidal environment. Domal stromatolites were formed in the intertidal zone and the subtidal zone. Conophyton stromatolites were often seen in the subtidal zone and the intertidal zone. Strati-columnar and cone-columnar stromatolites were developed dominantly in the intertidal zone. Stromatolites bioherm were located in the intertidal zone and the subtidal zone. The combinations of macro and micro characteristics of different types of stromatolites, the vertical supperpositions of different stromatolites, the relationship between their sedimentary structure and their corresponding facies, as well as the carbon and oxygen isotopes, all infer that the formation of stromatolites was mainly influenced by the content of microbacteria and sedimentary environment. Biological factors affected the microscopic constitution of stromatolites;hydrodynamic condition controlled the types of stromatolites,and the water depth affected their size. The environment with biological prosperity and less terrigenous materials was favorable for the development of stromatolites