Sedimentary characteristics of microbialites influenced by volcanic eruption: a case study from the Lower Cretaceous Shipu Group in Zhejiang Province, East China

作者：Xiao-Fang Wang,Xiu-Cheng Tan,Shao-Nan Zhang,An-Jiang Shen,Chang Li,Guang Hu,Xin Wang,Zi-Liao Chen,Li-Yin Pan,Jie Zhang,Wei Chen

摘要：This study describes a sequence of microbialites and volcanics of the Lower Cretaceous Shipu Group, an example of microbialites influenced by volcanic activity. It is located at Shipu town in eastern Zhejiang Province on the coast of southeastern China. Based on macroscopic outcrop observations, microscopic examination of thin sections,electron probe microanalysis(EPMA), field emission scanning electron microscopy(FESEM) imaging analysis, and energy dispersive X-ray spectrometry(EDS) analysis, nine microbialite–tuffite assemblages have been recognized in the section. Their thickness increased gradually upwards as volcanism decreased. There are ooids, bioclastic grains,intraclasts and tuffaceous grains in the grain shoal with local dolomitization. Above the grain shoal, microbial reefs develop either individually or conjoining with adjacent ones, and consist of stromatolites and serpulid tubes with common recrystallization. Tubes of serpulids are calcified and the tube wall is micrite. The tube and intertube parts are filled by sparry calcite. Colonial serpulids are surrounded by microbes to form stromatolites. Black layers of stromatolites contain many calcite crystals with fan-shaped growth pattern and preserved organic matter. Microbes are so well preserved in crystal lattices that the original microstructure of the microbes can be clearly observed by FESEM imaging analysis. Microbial reefs develop at a local high point near or above fair-weather wave-base where waves removed fine volcanic ashes. Interreef deposits are coarse tuffite due to physical differentiation. Volcanic activity could provide rich nutrition for microbes, but too much fine volcanic ash inhibits microbial growth. As a result, a moderate supply of volcanic ash favors the development of microbialites.

发文机构：State Key Laboratory of Oil and Gas Geology and Exploitation School of Geoscience and Technology Key Laboratory of Carbonate Reservoirs PetroChina Hangzhou Research Institute of Geology

关键词：MICROBIALITESTROMATOLITESTuffiteLowerCretaceousShipuGroup

分类号： P588.14[天文地球—岩石学]P534.5[天文地球—地质学]