微量元素在沉积环境中的应用--以柴西英西地区下干柴沟组上段为例

Application of Trace Elements in Sedimentary Environment--Case Study of Upper Member of Lower Ganchaigou Formation in Yingxi Area,Western Qaidam Basin

对英西地区下干柴沟组上段27件混积型碳酸盐岩样品进行微量元素测试,经校正陆源碎屑对元素含量影响后,取对沉积环境反应敏感的B含量、w(Sr)/w(Ba)、w(Sr)/w(Cu)、w(Rb)/w(Sr)、δU、w(Th)/w(U)、w(V)/[w(V)+w(Ni)]作为判别沉积环境的指标,并且结合测井的Th、U含量数据,对英西地区下干柴沟组上段古气候、古盐度、古水深、氧化还原环境进行了研究。结果表明:(1)B元素含量为(47.68~159.38)×10(-6),平均值为88×10(-6),平均值为88×10^(-6);B法计算古盐度为3.49‰~15.99‰,均值12.08‰,Sr元素含量为(150.76~3989.92)×10(-6);B法计算古盐度为3.49‰~15.99‰,均值12.08‰,Sr元素含量为(150.76~3989.92)×10^(-6),平均值为952.10×10^(-6),平均值为952.10×10^(-6);w(Sr)/w(Ba)范围为0.30~3.28,平均值为1.20,B含量、Sr含量以及w(Sr)/w(Ba)值均指示为咸水环境。(2)w(Sr)/w(Cu)范围为2.15~74.75,平均值为19.03;w(Rb)/w(Sr)为0.01~1.10,平均值为0.55,指示为干热气候。(3)δU范围为0.87~1.31,平均值为1.08;w(V)/[w(V)+w(Ni)]范围为0.37~0.71,平均值为0.65,w(U)/w(Th)范围为0.23~0.73,平均值为0.39;w(Th)/w(U)范围为1.38~4.44,平均值为2.68;各判别指标综合表明为还原缺氧沉积环境。沉积地球化学进一步佐证了该沉积时期为较深水、咸水且强烈蒸发、干热气候、还原缺氧、半开放—半封闭的半深湖、深湖沉积环境,间伴有少量温湿气候、水体淡化环境。

Trace elements in twenty-seven hybrid-sedimentary carbonate rocks samples in Upper Member of Lower Ganchaigou Formation in Yingxi area,Western Qaidam Basin were tested.After the influence of terrigenous clastics on element content was corrected,B content,w (Sr)/w (Ba),w (Sr)/w (Cu),w (Rb)/w (Sr),δU,w (Th)/w(U),w(V)/[w(V)+w(Ni)]sensitive to the sedimentary environment were selected as identification indexes of sedimentary environment.Paleoclimate,paleo-salinity,paleo-water depth,oxidation-reduction environment of the Upper Member of Xiaganchaigou Formation in Yingxi area were studied combined with Th and U content by logging.The results show that:(1)The content of element B is 47.68×10^(-6)-159.38×10^(-6),with an average of 88×10^(-6);the paleosalinity calculated by method B is 3.49‰-15.99‰,with an average of 12.08‰,and the Sr content is 150.76×10^(-6)-3989.92×10^(-6),with an average of 952.10×10^(-6);the w(Sr)/w(Ba) ranges from 0.30 to3.28,with an average of 1.20;the B content,Sr content and w (Sr)/w (Ba) values all indicate the saltwater environment.(2) w (Sr)/w (Cu) ranges from 2.15 to 74.75,with an average of 19.03;w (Rb)/w (Sr) ranges from0.01 to 1.10,with an average of 0.55,it indicates dry hot climate.(3)δU ranges from 0.87 to 1.31,with an average of 1.08;w (V)/[w (V)+w (Ni)]is 0.37-0.71,with an average of 0.65,w (U)/w (Th) is 0.23-0.73,with an average of 0.39;w(Th)/w(U) ranges from 1.38 to 4.44,with an average of 2.68;the discriminant indexes indicate the reduction and anoxic sedimentary environment.Sedimentary geochemistry further proves that its sedimentary environment is reductive,anoxic,semi-open and semi-closed semi-deep and deep lake with relatively deep and salty water under intense evaporation in dry hot climate,accompanied by less water desalination environment in warm and humid climate.