巴楚地区寒武系碳酸盐岩白云石化机制

Dolomitization mechanism of Cambrian carbonates in the Bachu area, Tarim Basin, NW China

通过系统取样进行地球化学分析,研究塔里木盆地巴楚地区寒武系碳酸盐岩地球化学特征,在此基础上对盐上白云岩、盐间灰岩及盐下白云岩的白云石化成因进行对比研究。盐间灰岩中的白云石δ18O值大于6‰,δ13C值一般大于1‰,87Sr/86Sr值略低于古海水,Mn和Na元素富集,表明白云石化作用发生在沉积早期,系萨布哈成因;盐上白云岩以中—粗晶白云岩为主,δ13C值偏负,δ18O值偏负但均大于9‰,87Sr/86Sr值趋同于古海水,反映形成于浅埋藏环境;盐下白云岩以粉—细晶白云岩为主,δ13C值偏正,δ18O值偏负,87Sr/86Sr值大,Fe和Sr元素富集,形成于局限台地的超盐度蒸发环境中,系渗透-回流成因,并受后期深埋藏高温环境影响。

Geochemical characteristics of the Cambrian carbonates are studied through systematic sampling in the Bachu area of the Tarim Basin.The dolomitization mechanisms are compared and analyzed of the dolomites above and below salt beds and limestone between the salt beds.The δ 18O values of dolomites in the limestone between salt beds are larger than 6‰,the δ13C values are normally larger than 1‰,the87Sr/86Sr values are smaller than ancient sea water plus Mn and Na element enrichment.All these features suggest that the dolomites are developed due to early sabakha dolomitization.For the dominantly medium-and coarse-grained dolomites above the uppper salt bed,the δ13C values of samples are lower than zero,the δ 18O values are normally –9‰ – 0,the 87Sr/86Sr values are close to ancient sea water.These features show that the dolomites are developed in a shallow burial environment.For the dominantly powdered and fine dolomites below the lower salt bed,the δ13C values of samples are larger than zero,the δ18O values are normally lower than zero,the 87Sr/86Sr values are larger than the above mentioned dolomites,plus Fe and Sr element enrichment.These features indicate that the dolomites are developed within an evaporate environment on a restricted platform,and they are of penetration reflux dolomitization and affected by the deep burial hyperthermal environment later.