Carbonate Pb-Pb ages of the Wittenoom Formation and Carawine Dolomite, Hamersley Basin, Western Australia (with implications for their correlation with the Transvaal Dolomite of South Africa)


Pb isotopic analyses of carbonates from the Hamersley Group, Western Australia, yield the following results. (1) A late Archean (minimum) age of 2.5 Ga is definitely established for the deposition of both the deeper-water basinal Wittenoom Formation and the shallow-water Carawine Dolomite. Stratigraphic correlation of the Transvaal Dolomite (South Africa) with these two formations is supported by the present Pb isotope age data. (2) A Pb-Pb isochron age of 2505 ± 37 Ma for the Paraburdoo Member (lower part) of the Wittenoom Formation is best interpreted as a late diagenetic event, which took place ~ 100 Ma after the initial deposition. (3) A Pb-Pb isochron age of 2346 ± 38 Ma for the Bee Gorge Member most likely represents a still later local event of calcite replacement in fractures and veins. (4) A Pb-Pb isochron age of 2541 ± 32 Ma for Carawine Dolomite could represent a regional diagenesis slightly earlier than the Paraburdoo carbonates if the Carawine carbonates were deposited contemporaneously with the Wittenoom Formation. Alternatively, it may represent the time of early diagenesis which closely followed the initial sedimentation. A study of trace element abundances and stable isotope compositions has revealed a major difference in Fe and Mn contents and δ18O values between the Wittenoom and Carawine dolomite samples. This suggests that the two suites of dolomites have undergone separate diagenetic histories with different chemical and oxygen isotopic modifications.



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Precambrian Research



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