Characteristics And Formation Mechanism Of Microbolite In Xiaoerbulake Section, Tarim Basin

Microbialite is considered to be widely concerned in the art of sedimentology in past few years. Microbialite is developed in Upper Sinian-Lower Cambrian strata at Xiaoerbulake profile of Tarim Basin, the study of features and formation mechanisms about it is conducive to further understand and identify the microbialite.This article studied the texture and the material composition of the microbialite by incorporating microbialite macro features, the rock texture under the microscope and distributing characteristics of organic matters, the research also makes further efforts to analysis the rock texture under microscope of the microbialite by applying Field Emission Scanning Electron Microscopy(FESEM) and energy spectrum, the formation mechanism is also involved.Based on the various macro and micro features, Microbialite of Xiaoerbulake profile can be divided into four following types:(1) The microbialite with layer structure, which is founded interbedded with the Micritic dolomite composed dark layer and the dolosparite composed bright layer, organic matters mainly distributed in the dark layer.(2) The microbialite with lamellar structure, which lower grain size of cements of dolosparite and micritic dolomite can be observed by using microscope. The brown intermittent laminated texture within the microbialite is closely related to the distribution of organic matter.(3) The microbialite with spherulitic structure, which its structure can be observed under microscope. Boundaries of the microbialite are composed by the black or dark brown micritic dolomite. Cements of micritic dolomite are developed in intergranular spaces, whereas recrystallized dolomite is developed from within. Besides, organic matters is distributed on the boundaries.(4) The microbialite with compact structure, which presents as compact dolostone under microscope, is provided with a distinct recrystallization and metasomatic relict image feature. The distribution of a relatively small amount of organic matters is only founded in intergranular pores.Based on the analysis by utilizing FESEM and energy spectrum, the main microorganism affect microbialite formation in Qigbulake Formation at Xiaoerbulake profiles is considered to be bacteria, extra-cellular polymers of the bacteria cohere sediment particles, which enable the formation of nano spherulitic dolomite; the same process is also founded in the microbialite of Xiaoerbulake Formation, but the existence of algae and other organic matters shows that the formation process is not identical comparing to the Qigbulake. The nano spherulitic dolomite formed by the extra-cellular polymers of the bacteria, is distributed both in Cambrian system and simian system, and it also preserves significant environmental information which should be taken into consideration seriously in further research.