Estimation of atmospheric pCO_2 in the geologic time based on stable carbon isotope ratios of higher plant biomarkers

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Carbon isotope fractionation by photosynthesis of higher land plant is mainly controlled by the growth rate of plants, which is partly related to partial pressure of atmospheric carbon dioxide. Compound specific stable carbon isotope ratio of higher plant biomarkers in the terrigenous sedimentary rocks can be one of parameters for estimation of paleo-patial pressure of atmospheric carbon dioxide. The variation of stable carbon isotope ratio of higher plant biomarkers in the Tertiary non-marine organic-rich sedimentary rocks such as coal and coaly mudstones in Japan and Sakhalin were investigated in the present study. The following results were consequently obtained.(1) Tertiary non-marine terrigenous sedimentary rocks commonly contain diterpanes and aromatic diterpenoids such as diaromatic totarane and retene.(2) Abundance of retene is positively correlated to that of abietane type diterpenoid aromatic hydrocarbons, suggesting their genetic relationship.(3) Abundance of retene and abie … More tane type compounds is negatively correlated to that of oleanane which is derived from angiosperms, suggesting that retene is mainly derived from gymnosperm.(4) Abundance of dibenzofuran is positively correlated to that of oleanane, suggesting that dibenzofuran is also derived from angiosperms.(5) Carbon isotope ratios of n-alkanes tend to decrease with increasing carbon numbers of n-alkane, showing higher molecular weight n-alkanes are mainly derived from higher land plants.(6) Carbon isotope ratios of n-alkanes, β-norisopimarane, diaromatic totarane, and retene in Eocene coal and coaly mudstones are enriched in ^<13>C compared to those of Miocene coal and coaly mudstones.(7) High-pressure liquid chromatography is useful method for aromatic hydrocarbon fractionation for gas chromatography combustion isotope ratio mass spectrometry.(8) Variation of carbon isotope ratio of higher plant biomarker with geologic age is consistent with the possible geologic change of atmospheric carbon dioxide partial pressure.Compound specific stable carbon isotope ratio of higher plant biomarkers can be a useful parameter to estimate the atmospheric pCO_2 in the geologic time. However, other environmental condition, which affect growth rate of higher plant, may be influential to the isotope ratio of higher plant biomarkers. Less