Characteristic And Geological Significance Of Dendrolite From Zhangxia Formation, Cambrian, Jiulongshan Section Of Laiwu

Recently, studies of microbialite is becoming more and more popular, especially for the stromatolite which is biogenetic sedimentary rock and still exist in the current environment. As an important type of microbialite, because of its limitations of distribution, dendrolite has rarely been treated as a study Key Components.There are lots of microbialite in the lower limestone member of Zhangxia formation, Cambrian in Jiulongshan section of Laiwu, including dendrolite and thrombolite. According the detailed field measurement and observation, we find the precise position of the dendrolite bed and describe the morphology and dendroid structure of dendrolite in the field. According to the variation of the morphology and dendroid structure, and combining with the oolite, we interpret the sedimentary environment of lower limestone member as a subtidal zone. We analyze the component of the dendrolite with microscope, and find that there were a lot of bioclasts with few quartz and glauconite in the first dendrolite bed, while many bioclasts, few ooids, and sometimes quartz in the second to sixth dendrolite bed. Therefore according to the component of dendrolite, there are two types of dendrilite:quartz-bioclast dendrolite and ooid-bioclast dendrolite in the Zhangxia formation of Cambrian, Jiulongshan section of Laiwu. Through the observation of microscope, we find the microorganism to form dendrolite was cyanobacteria, including Girvanella and Epiphyton, while the Girvanella community in the lower bed and Epiphyton community in the upper bed. Therefore according to the cyanobacteria type, there are two types of dendrolite:Girvanella dendrolite and Epiphyton dendrolite in the Zhangxia formation of Cambrian, Jiulongshan section of Laiwu.The forming environment of microbialite is not identical, and there are mainly oolite beach facies and tidal-flat facies. There are a lot of microbial bioherms. Although it has certain resistance to wave ability, the slender dendroid structure formed by the cyanobacteria is easy to be destroyed, so usually it is in the low-energy environment.