Geochemical Fingerprinting of Rising Deep Endogenous Gases in an Active Hypogenic Karst System

Figure 9

Genetic zonation of CH₄ based on the isotopic composition of carbon (¹³C/¹²C) and hydrogen (²H/¹H). Proposed genetic zones of biotic CH₄ (grey zones): thermogenic, microbial from carbonate reduction, microbial from acetate fermentation, and microbial evaporitic, compared to the genetic zone for abiotic CH₄ (modified from [54]). Data pairs of δ¹³C_CH4 and δ²H_CH4 are plotted for the local atmosphere, soil air, and underground air of VC in comparison with other published data from hypogenic acid caves [7]. Arrows correspond to two potential postgenetic processes affecting the molecular and isotopic composition of CH₄ after its formation and during its migrations: [A] microbial oxidation and [B] gas diffusion.