Geochemical Characteristics And Coal-formation Environment Of Late Permian Coals In Xiaoniu Coalfield,Shuicheng County,Guizhou Province

In the Late Permian,Xiaoniu area was in the transitional facies,with transgression frequently.In the end of Late Permian,Paleoenvironment changed dramatically,ancient environmental information was saved in coal.Therefore,it is significant to foucus on coal in Palaeoenvironmental studies.Based on sedimentology,geochemistry,coal petrology,mathematical statistics and other aspects of knowledge,a total of more than 140 samples of 18 main coal seams from Late Permian were collected from the 12 boreholes,and the trace elements,major elements,basic coal quality of the samples were tested.organic carbon isotope of the top three coal seams from Songhe coal mine were tested.The vertical variations of trace elements,major elements and organic carbon isotope of coal samples are analyzed,the geochemical parameters are discussed.The purpose of this study is to understand the relation between coal-forming environment and trace elements,major elements,coal quality characteristics and organic carbon isotope of coal.After research and analysis,the following conclusions were reached:1.The coal quality were mainly controlled by coal-forming environment by analyzing sulfur content,ash yield.Medium ash,low volatile,medium-high sulfur coal are dominanted in the Xiaoniu coalfield.Total sulfur is mainly composed of pyrite sulfur,followed by organic sulfur.According to the proportion of sulfur in total sulfur and the proportion of organic sulfur to total sulfur,the formation-environment of coal seams should be mainly in tidal flat and delta environment.The total variation of total sulfur and ash in the coal seams can be clearly reversed two stages of transgressions and regressions cycles.Lower sulfur and higher ash yield coal are corresponding to regression,while higher sulfur and lower ash yield coal are corresponding to transgression.2.The enrichment of trace elements and major elements are correlated with coal-formation environment.The major elements contents of Xiaoniu coalfield are higher than the average ofChina coal.The content of V,B,Mo,Co,Cu,Ga,Ni in coal are enrichment.The enrichment of trace elements is largely controlled by the terrestrial clastic material provided by the Emeishan basalts,and the enrichment of the major elements is not only affected by terrestrial debris.The geochemical parameters of the elements indicate that the source region has moderate chemical weathering under warm and humid conditions,and peat is formed in the reducing environment.The enrichment of elements in the coal seams are affected by seawater to a certain extent.When the seawater is strong,the concentration increases,and the concentration decreases with the seawater decreases.The vertical variations of the major and trace elements in the coal can be reversed two stages of the transgressions and regressions.3.The maceral of Xiaoniu coalfield mainly composed by vitrinite,followed by inertinite.According to the V/I values,the formation of peat layer is extremely damp reduction environment.Organic carbon isotopic of coal near the P/T boundary negative fall significantly,which is familiar with the global organic carbon isotope variation.The volcanic sources of CO2 content may be very high,which lead to a significant negative fall of carbon isotope in the plant.The end Permian extinction might be related to this phenomenon.