西藏伦坡拉盆地丁青湖组油页岩地球化学特征及其地质意义

Geochemical characteristics of oil shale member of Dingqinghu Formation in Lunpola Basin of Tibet and their geological implications

对伦坡拉盆地丁青湖组油页岩进行了系统采样和地球化学分析,结果显示该地区油页岩SiO2含量整体较低,K2O/Na2O值较高,Al2O3＋ Fe2O3为6.43％ ～10.28％,Al2O3/（Na2O＋ K2O）为1.7～4.91,含有一定的铁镁质组分和较多的稳定组分;化学蚀变指数CIA为65～85,Th/U值多集中在0.97～3.38,表明油页岩源区经历了相对中等的风化作用,反映温暖、湿润的气候条件;Sr/Ba值为0.45 ～0.82,V/（V＋ Ni）值为0.46～0.68,Th/U平均值为0.59,表明丁青湖组油页岩形成于淡水缺氧的湖泊之中.温暖湿润的气候、丰富的生物来源及淡水缺氧的沉积环境是伦坡拉盆地丁青湖组油页岩形成的重要条件.

Systematic sampling and geochemical analysis of the oil shale member of Dingqinghu Formation show that SiO2 are low,K2O/Na2O ratios are relatively high,Al2O3 ＋ Fe2O3 are in the range of 6.43 % ～ 10.28 %,and Al2O3/（Na2O ＋ K2O） values are between 1.7 and 4.91,indicating that the oil shale contains mafic components and more stable components.Chemical indexes of alteration （CIA） are between 65 and 85,and Th/U ratios are concentrated in the range of 0.97～3.38,suggesting that the provenances of oil shale had experienced relatively moderate weathering and were in a warm and humid climate environment.Sr/Ba ratios are between 0.45 and 0.82,V/（V＋ Ni） ratios are between 0.46 and 0.68,and Th/U ratios have an average of 0.59,indicating that the oil shale was formed in a fresh water and anoxic lacustrine environment.Warm and humid climatic conditions,abundant biological sources,fresh water and anoxic environment were important for the formation of Lunpola oil shale.