Comparison of sedimentary paleoenvironment between coal and shale in Yan'an Formation——A case study of Lucun No.2 Mine in southern Ordos Basin
The bottom of the Yan'an Formation in the southern part of the Ordos Basin is characterized by the stable development of coal seams,with a thick layer of shale at the top.Although both coal and shale are organic-rich sedimentary rocks,the characteristics of depositional stage differences remain to be revealed.Eight coal samples and six shale samples from the roof of the No.2 Mine in Lucun were collected,and the major elements and trace elements of coal and shale were tested using an Inductively Coupled Plasma Emission Spectrometer and Inductively Coupled Plasma Mass Spectrometer to define their geochemical characteristics and to explore the depositional environments of different lithologies.The results show that:The coal and the shale have the highest Al2O3 content,followed by Fe2O3.Com-pared to the Upper Continental Crust(UCC),the coal exhibits relatively high enrichment of P2O5and Fe2O3,and the high concentration of K2O,Al2O3 and Fe2O3 in shale.In coal,Cr,Ni,Cu,Sr,Mo and U elements are obviously enriched,while in shale,only U elements are enriched and Ni,Cu,Sr and Mo elements are obviously depleted.The CIA values of the coal samples and the shale samples indicate a warm and humid climate in the depositional system and the climate condition is more favorable to the development of coal seam.The salinity of the coal varies greatly during the sedimentary period,and the sedimentary water is a brackish water environment.However,the salinity of water in shale deposition period is relatively stable,and the water in sedimentary period is brackish water environment.Com-pared to the shale,the coal formed in a shallow water-covered peat swamp environment,with the water body gradually deepening and productivity gradually weakening.The average(Fe+Mn)/Ti value of the coal samples is greater than 25,indicating that the coal seam was influenced by hydrothermal activity during the depositional period and experienced high-temperature baking.This paper provides a theoreti-cal basis for the exploration and development of coal seam in Yan'an Formation of Ordos Basin by ex-ploring the difference of paleoenvironment between coal and shale deposition periods.
coalshalemajor and trace elementsYan'an FormationLucun No.2 mine
国家科技期刊平台
NSTL
万方数据
