Geological And Geochemical Characteristics Of Oil Shale In Permafrost Zone Of Qilian Mountain,Qinghai

In the year 2008,our country drilled the actual samples of gas hydrate in Qilian Mountain permafrost zone for the first time,which is also the first time to get the actual samples of gas hydrate in low-latitude plateau permafrost areas,and it is of great scientific,economic and environmental significance.With the discovery of gas hydrate,there are a lot of oil shale beds in the strata,the oil shale is a kind of source rock,It has some connection with gas hydrates in the spatial distribution,Therefore,the study on the geological and geochemical characteristics of the oil shale has great significance.In this paper,geochemical methods(main and trace element contents and ratios)are mainly used,combined with the drilling data and petromineralogy information,to study the elemental geochemistry and formation environment of oil shale in Muli DK2?DK3 drilling.The Muli oil shale has high content of clay mineral,mainly illite,kaolinite and mixed-layer minerals.In the plane,the oil shale's distribution is controlled by structures(faults)obviously,In the vertical,the oil shale mainly distributed in the up group of Jiang Cang in Middle Jurassic.The main elements of Muli oil shale are Si02?A1203,rich in Fe203,poor in FeO andthere is high content of CaO in some depth.In the oil shale,V,Ti and Cr has the good positive correlation;Sr andTi has the good negative correlation,it indicates that the elements V,Ti,Cr are source of terrigenous clastic;and the element Sr comes mainly from the biological itself.The study on the REE geochemistry of Muli oil shale shows that,the differentiation of REE is obviously,LREE/HREE=4.08,LREE relative rich and HREE relatve loss.The REE's distribution patterns(NASC)is slightly right-wing type.The average ratio of Sr/Ba in Muli oil shale is 0.36;Fe2+/Fe3+>>1,the average ratio of Ni/Co is 2.37;the average ratio of Ni/V is 0.34;the average ratio of V/(V+Ni)is 0.75;the average ratio of Sr/Cu is less than 4,it indicates that the oil shale was formated in the warm and humid climatic conditions in the reducing environment of freshwater.