Abstract:

In the forced regressive system at the top of the Cambrian Zhangxia Formation in the Zhucaoying section of Qinhuangdao, Hebei Province, a set of leiolitic bioherms with a thickness of tens of meters were intensively developed, indicating that these leiolitic bioherms formed in shallow sea and high energy environment. Field investigation and microscopic observation, the formation mechanism and sedimentary environment of leiolitic bioherms are analyzed.The results show that the leiolitic bioherms  dense and homogeneous massive micritic limestone,  obvious macro fabric and directly the lower stromatolite bioherms.Under the microscope, the leiolite is composed of dense micrite and a small amount of sparry. The dense micrite contains a variety of calcified cyanobacteria sheath fossils, including Hedstroemia, Epiphyton, Renalcis,   and Girvanella. The results showed that the leiolite was formed by the complex metabolism of microbes and  in-situ. More specifically, oolith and dolomite crystals, indicating that the microtexture related to the calcification of globular microbial film and the selective expression of dolomite in the process of leiolite production under eutrophic conditions. There are not many related examples of leiolite since its, therefore the leiolitic bioherms in Zhangxia Formation of Qinhuangdao provide a typical example for understanding the formation mechanism and depositional environment of leiolite.

Key words: leiolitic bioherm, Qinhuangdao City, Hebei Province, Zhangxia Formation, microbial carbonate, calcified cyanobacteria