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

Abstract

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.