Abstract: The Mohe Basin in northeastern China possesses the potential for gas hydrate accumulation and exploration in the permafrost zone of China. During a recent investigation of wells used for gas hydrate testing and gas source exploration, we discovered significant negative shifts in stable carbon and hydrogen isotopes of methane in the Mohe Basin. The measured δ13CCH4 and δDCH4 values commonly ranged from -60‰ to -82.9‰ and from -350‰ to -450‰, respectively. We also observed that at burial depth of approximately less than 1500 m, δ13CCH4 value generally increased with depth, whereas δDCH4 value decreased; however, both values increased synchronously with burial depth at greater than 1500 m. We believe that the negative shifts of stable carbon isotope are associated with the microbial origin of methane; whilst the negative shifts of stable hydrogen isotope are the results of a combined effect of Rayleigh distillation during the evaporation of surface water or atmospheric condensation process driven by basin‘s unique climate at higher latitude, and methane production through acetate fermentation.

Key words: Mohe Basin, Northeast China, high latitude, methane, stable isotope, Rayleigh distillation