2014年6月英语四级作文真题附范文(第2套):A Beautiful City in China

According to Al-Fe-Mn trigonometry, Al/(Al Fe Mn) ratio and Babio-SiO2 correlation analysis, the siliceous rocks of Wufeng Formation in the study area is not related to hydrothermal solution, and affected by biological activity. Based on the distribution characteristics of rare earth elements and K2O-Rb, Zr/TiO2-(V Ni Cr)/Al2O3 analysis, it is finally determined that the siliceous source is terrigenous sedimentation, and the siliceous rock is normal sedimentary genetic siliceous rock affected by biological activity. According to the analysis of earth elements and carbon and oxygen isotopes, the dolomite in Guanyinqiao of Wufeng Formation is mainly composed of pyroclastic material. Dolomite is not affected by strong diagenetic alteration and chemical weathering, and belongs to the burial dolomite which is developed by anoxic oxidation of methane (AOM) and sulfate reducing bacteria (BSR).