河北省秦皇岛市寒武系张夏组顶部均一石主导的微生物礁

Microbial Reefs Predominated by Leiolites in the Zhanxia Formation of Cambrian from Qinhuangdao City,Hebei Province

叠层石、凝块石、均一石以及树形石被并列划分为典型微生物碳酸盐岩, 其中均一石以隐晶质岩性、凝块结构不发育且无明显宏观构造为特征。自从均一石1995年被命名以来, 在地层中很少得到观察与识别, 而且现代类比物也十分缺乏, 因此使得研究均一石具有极其重要的意义。为了解华北地台寒武系的均一石的特征, 选取河北秦皇岛寒武系张夏组构成三级层序的强迫型海退体系域顶部集中发育的一套由均一石主导的、数十米厚的微生物礁, 采取野外采样及室内镜下微观特征观察相结合的方法进行研究。均一石由致密泥晶和少量微亮晶构成, 构成均一石的致密泥晶中可见类似于现代织线菌 (Plectonema) 的丝状体葛万菌 (Girvanella) , 局部可见灌木丛状的附枝菌 (Epiphyton) 以及基座菌 (Hedstroemia) 。研究结果表明, 均一石主导的微生物礁的形成受复杂的有机矿化过程影响或受早期的蓝细菌主导的、发生微生物膜或微生物席内的石化作用影响。因此在了解古老微生物礁的形成过程中, 受蓝细菌主导、经微生物席钙化作用而形成的秦皇岛寒武系张夏组均一石所主导的微生物礁是一个重要的窗口。

Stromatolites, thrombolites, leiolites and dendrites are juxtaposed and classified as typical microbial carbonates, with leiolite characterized by cryptocrystalline lithology, undeveloped agglomerate structure, lacking obvious macroscopic structure and clot. Since its designation in 1995, leiolites have been rarely observed and recognized in strata and modern analogies are scarce, whoch makes the report of a leiolite example extremely important. In order to research the characteristics of leiolites in Cambrian of North China Platform, combine the methods of field sampling observation and observation of indoor microscopic characteristics under the microscope and selected microbial reefs predominated by leiolites with thickness of tens of meters develop intensively at the top of the Forced Regression system domain of the Cambrian Zhangxia Formation in Qinhuangdao, Hebei Province was selected, which constitutes a three-order sequence as research object. Leiolite consists of dense mud crystals and a small amount of microlithophores, and the Filamental Girvanella similar to the modern Plectonema is visible in the dense mud crystals that make up leiolites, while Epiphyton and Hedstroemia can be seen locally in the bushy mud crystals. It is indicated that microbial reefs predominated by leiolites are influenced by complex organic mineralization processes or by early cyanobacteria-dominated lithification occurring within microbial membranes or microbial mats. Therefore, in understanding the formation of ancient microbial reefs, the microbial reef predominated by leiolites at the Cambrian Zhangxia Formation in Qinhuangdao, formed by the calcification of microbial mats, are an important window.