Yang Zhenqiang, Jiang Dehe, Zhao Shijiu. A NEW SEDIMENTOLOGICAL EXPLANTION OF STABLE ISOTOPIC COMPOSITIONS IN ORDOVICIAN AND SINIAN MANGANESE-BEARING BEDS IN CENTRAL HUNAN[J]. Sedimentary Geology and Tethyan Geology, 1993, 13(2): 25-36.
Citation:
Yang Zhenqiang, Jiang Dehe, Zhao Shijiu. A NEW SEDIMENTOLOGICAL EXPLANTION OF STABLE ISOTOPIC COMPOSITIONS IN ORDOVICIAN AND SINIAN MANGANESE-BEARING BEDS IN CENTRAL HUNAN[J]. Sedimentary Geology and Tethyan Geology, 1993, 13(2): 25-36.
Yang Zhenqiang, Jiang Dehe, Zhao Shijiu. A NEW SEDIMENTOLOGICAL EXPLANTION OF STABLE ISOTOPIC COMPOSITIONS IN ORDOVICIAN AND SINIAN MANGANESE-BEARING BEDS IN CENTRAL HUNAN[J]. Sedimentary Geology and Tethyan Geology, 1993, 13(2): 25-36.
Citation:
Yang Zhenqiang, Jiang Dehe, Zhao Shijiu. A NEW SEDIMENTOLOGICAL EXPLANTION OF STABLE ISOTOPIC COMPOSITIONS IN ORDOVICIAN AND SINIAN MANGANESE-BEARING BEDS IN CENTRAL HUNAN[J]. Sedimentary Geology and Tethyan Geology, 1993, 13(2): 25-36.
There are two important manganese carbonate horizons in the Middle Ordovician and Early Sinian strata in central Hunan Province. Manganese marl and manganese dolomite in the Xiangmeng Formation (Early Sinian) in the vicinity of Anhua County have carbon and oxygen isotope values ranging from -2.69 to -4.00‰ and from -6.87 to -14.04‰, respectively. MnCO3 in the Xiangmeng Formation yields δ13C values ranging from -7.4 4 to -13.00‰ and δ18O values from -2.65 to -13.03‰. Manganese marl in the black shale of the Modaoxi Formation (Middle Ordovician) shows negative δ18C values ranging between -1.70 and -6.56‰, and δ18O values between -11.67 and -14.00‰. Morever, crystalline manganese ores have highly negative δ13C values ranging between -4.70 and -17.79‰, and δ18O values between -11.67 and -17.27‰. There are three kinds of evolutionary trends for carbon and oxygen isotopes in the manganese carbonate rocks. (1)Stable δ13C trend in the manganese limestone of the Early Sinian strata in the Anhua district; (2) sympathetic trend of MnCO3 in black shale in the Xiangmeng Formation. and (3) strongly antipathetic trend of manganese ores in the Middle Ordovician black shale. Carbon diagenesis has an important effect on carbon and oxygen isotope compositions during the formation of manganese carbonates. Carbonate source in the Xiangmeng Formation probably comes from the inorganic marine CO2, and is related to the addition of organic carbon from sulphatereduction (SR) zone to methanogenesis (Me) zone. The carbonates in crystalline MnCO2 in the Modaoxi Formation are derived mainly from the decarboxylation (D) zone. δ34S, ranging from -8.00 to -27.49‰, also has an organic source. The manganese contents in the manganese ores show a negative correlation with δ13C values. The evidences here suggest that the manganese carbonate origin is closely linked to the anoxic events in the marine basin and submarine hydrothermal (exhalative) deposits.
DownLoad: