C-O,Sr isotope composition of the carbonate in Ordovician in Tarim Basin and implication on fluid origin

Carbonate reservoir in Ordovician is an important hydrocarbon reservoir.Determining the carbon and oxygen isotopic rations of the hydrothermal minerals in Tarim Basin,and the result shows that,δ18O value of calcite is negative,hence the main factor of the oxygen isotopic value due to the CO2 derived from the wallrock which was corroded by the hydrothermal fluid.The δ13C value of the authigenic carbonate implying two carbon source during diagenesis,13C-rich carbon source are attributed to early carbonate in Permian,deposit or recrystallization during early to late stage authigenic carbonate formation related to 12C-rich CO2 produced by organic matter degradation as fluid going throw the fracture system;87Sr/86Sr value(0.708~0.718) is higher than the seawater at the same stage,which implys the local hydrothermal fluid are in 87Sr-rich.