Cambrian Limestone Dolomite Mechanism in the Bachu Area,Tarim Basin,China

Bo, Zhou; Ming, Li; Shufu, Duan
Tarim branch institute, Research Institute of Petroleum Exploration&development (Petrochina), Beijing, China.

Geochemical characteristics of the Cambrian Shayilike Group carbonate rock in Bachu area of Tarim basin are studied through geochemical analysis after systematic sampling.Basing on that three kinds of carbonate rock dolomitization mechanisms are investigated by using comparative study among the limestone between gypsum and salt beds,the dolomites above and below the gypsum and salt bed. The δ¹⁸O values of dolomite in the limestone between salt beds are larger than-6‰, The δ¹³C values are normally larger than -1‰, the ⁸⁷Sr/⁸⁶Sr values are smaller than ancient sea water plus Mn and Na element enrichment. All these features illustrate that dolomites developed due to early sabakha dolomitization. To the medium and coarse grained dolomite above the upper salt bed,the δ¹³C values of samples are lower than zero, the δ¹⁸O values normally distribute between -9‰-0, the ⁸⁷Sr/⁸⁶Sr values are close to ancient sea water plus Fe and Sr element enrichment. All these features show that dolomites developed within the burial environment. To the powdered and finely dolomite below the lower salt bed, the δ¹³C values of samples are larger than 0‰, 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. All these features indicate that dolomites developed within the evaporitic environment on the restricted platform. The carbonate rock experienced the penecontemporaneous penetration reflux dolomitization firstly, and was affected by the deep burial hyperthermal environment lately.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012