Dolomite cement carbon isotopic values

Carbon and oxygen isotope analyses of carbonate cements were performed on 20 samples. Each sample was reacted with 100% phosphoric acid at 25 °C for calcite and at 50°C for dolomite. The evolved gas for each carbonate fraction was analysed using a SIRA-12 mass spectrometer. The phosphoric acid fractionation factors used were 1.01025 for calcite (Friedman O Neil, 1977), and 1.01060 for dolomite (Rosenbaum Sheppard, 1986). Oxygen and carbon isotope data are presented in the normal 6 notation relative to pdb (Craig, 1957). Precision (1 o) was monitored through daily analysis of the NBS-20 calcite standard and was better than 0.05%o for both 6 C and 8 0. The isotopic data obtained are for bulk dolomite and calcite separately, and it is uncertain whether or not crystal-chemical zonations are accompanied by strong shifts in isotopic values. 

Chemical, carbon-isotopic, and oxygen-isotopic compositions from selected samples of the Latrobe dolomite cement are presented in Table 5(A and B). All of the values in Table 5B fall between —10 and —22%o (PDB, Peedee Formation Belemnite). values of the dolomite cement range from 22.7 to 25.2%o (SMOW, Standard Mean Ocean Water) with an... 

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