摘要
根据显微镜和扫描电镜的观察以及X射线衍射和能谱分析,在层状硅质岩中鉴定出最古老的海绵骨针和放射虫化石,提出古菌藻类微生物活动在硅质沉淀中起着重要的作用。这些微生物活动形成了一系列形状奇特的石英单晶和集合体,生物成因的单晶常呈球状、杆棒伏、板状、胶粒状和晶粒状。最常见的集合体是由密集分布的球形石英构成的菌群,被认为是典型的细菌成因。其它蜂巢状、双联球状、链球状和球状集合体可能是藻类细胞硅化的结果,它们主要为原生成因。该文还讨论了古海底热水沉积的碧玉岩以及交代、成岩重结晶硅质岩的超微组构特征和鉴别标志。
Upper Sinian bedded chert is widely distributed on the southeast continental margin of the Yangtze Platform. The vertical sequences and sedimentary environments of this type of siliceous deposits are described and ecological areas of ultramicroo-rganism associations in abyssal environments are established in this paper. Microscopic and SEM observations indicate that the activities of marine bacteria and algae were important during silica precipitation. Microbial processes resulted in the formation of single crystals and aggregates of crystals of varying sizes and forms. The biogenic single crystals occur in spherical, rod, tabular, colloidal and granular forms, which were confirmed to be quartz by X-ray diffraction and X-ray energy dispersive analyses. The most common aggregates are framboid ones composed of round- ed and ellipsoidal single quartz crystals 5-10μm in size. They are probably the product of bacterial activity. Other aggregates, such as cellular, double-spherical, chain-spherical and spherical aggregates, are interpreted to represent the remnants of silicified algal cells and communities. The oldest sponge spicules and radiolarians in geologic history have been found in some chert beds. This paper also briefly introduces the features of ultramicroscopic fabrics and diagnostic indications of jasper rocks formed by hot water precipitation on the ancient sea floor and chert formed by replacement and diagenetic recrystallization.It is concluded that the bedded chert deposited on the continental margin is of primary sedimentary origin and it is suggested that submarine hydrothermal water was the main source of silica.
出处
《地质学报》
EI
CAS
CSCD
北大核心
1994年第2期132-141,T002,共11页
Acta Geologica Sinica
基金
国家自然科学基金(编号 489700115)
关键词
硅质岩
超微组构
成因
菌藻
chert, ultramicropic fabric, algae-bacteria origin
