Abstract A shallow marine carbonate rock sequence with shale and evaporate developed in the Lower Triassic Feixianguan Formation in northeastern Sichuan Province.The edge of carbonate platform commonly developed some oolitic banks，which are dolomitized.The Feixianguan Formation which are formed by oolitic bank dolostone is the most important gas reservoir in northeastern Sichuan Province. Some researchers considered them as the origin of mixing for fresh water and sea water，the others make up them into model for dolomitization by seepage-reflux.The Feixianguan oolitic bank dolostone included stable isotopic oxygen composition of -6.73‰～-3.65‰(PDB)（-10.81‰ in Luojiazhai area），the average is -4.89‰(PDB)，stable isotopic carbon composition of +0.57‰～+3.00‰(PDB)，for matrix and vug-filling saddle dolomite and bright dolomite cement，stable isotopic strontium composition of 0.70735～0.70800 for 87Sr/86Sr rate.These data about oolitic bank dolostone indicate that the dolomitization was formed in the buried condition.After measuring fluid inclusion homogenization temperature，dolomitization temperature and isotopic oxygen of dolomite are known，and then the isotopic oxygen composition of dolomitizing fluid can be calculated(δ18Odol-δ18Owater=［3.2×106T-2］-1.5，from Friedman and ONeil (1977)). The average is about +4‰ (SMOW).According to the positive covariance between fluid isotopic oxygen and carbon composition and fluid salinity during evaporation of seawater，fluid δD can be calculated.It is about +25‰(SMOW).The measurement of fluid inclusion salinity suggest that dolomitizing fluid is a brines，which is about several times of seawater.Dolomitizing temperature changes from 90 ℃ to 130 ℃.As far as our knowledge goes，stable isotopic O and C composition of the Lower Triassic oolitic bank dolostone is similar to these of the uppermost Permian reef dolostone.Therefore，it is possible that their dolomitizing fluids are identified source.However，the reason for this conclusion needs to be perfected in the future.
About author: Qiang Zitong，born in 1937，is a professor of Southwest Petroleum University，and is engaged in teaching of sedimentary geology.E-mail: John-ba@126.com.
Cite this article:
. Isotopic geochemical characteristics of oolitic bank dolostones in the Lower Triassic Feixianguan Formation in northeastern Sichuan Province[J]. JOURNAL OF PALAEOGEOGRAPHY, 2012, 14(1): 13-20.
. Isotopic geochemical characteristics of oolitic bank dolostones in the Lower Triassic Feixianguan Formation in northeastern Sichuan Province[J]. JOPC, 2012, 14(1): 13-20.
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