In a collaborative effort with the University of Saskatchewan, we reported one of the largest observed carbon isotope effects caused by diffusional fractionation from a site in southern Saskatchewan.
The literature provides no clear explanation for large, well-defined changes in the δ13C values of methane (>5‰) with depth [Xia and Tang, 2012]. Some authors attribute the changes to the effects of methane transport in the subsurface [Prinzhofer and Huc, 1995; Prinzhofer and Pernaton, 1997; Zhang and Krooss, 2001] while others invoke biological mechanisms and discount the effects of migration on the δ13C values of methane [Fuex, 1980]. Using geochemical profiles from drilling programs, this work demonstrated that a large carbon isotope fractionation for methane likely originated from long-term diffusional processes through the tight shale formations.
Find the article in Water Resources Research at: http://onlinelibrary.wiley.com/doi/10.1002/2016WR019047/full