Home – Home – Jornals – Russian Geology and Geophysics 2008 number 6

Distribution of hydrogen and carbon isotopes (D/H and ¹³C/¹²C) in the microbial systems CH₄-H₂O and CH₄-CO₂ was studied in different world's regions. According to the distribution of these isotopes in the above systems, two types of microbial methane are recognized in the Earth's crust: (1) resulting from CO₂ reduction and (2) produced through acetate fermentation. In the case of methane 1, the biologic distribution of hydrogen and carbon isotopes in the above systems corresponds to the thermodynamic isotope exchange equilibrium at a given temperature of the methane genesis medium. In the case of methane 2, the same systems show mainly a nonequilibrium distribution of these isotopes. We have revealed a linear relationship between the isotopic compositions of CH₄, H₂O, and CO₂: δD - CH₄ = α _D ^b δD - H₂ O + b and δ¹³ C - CH₄ = α _C ^b δ¹³ C - CO₂ + d, where α _D ^b