Methane sources and sinks in continental sedimentary systems: New insights from paired clumped isotopologues <SUP>13</SUP>CH₃D and <SUP>12</SUP>CH₂D₂

Stable isotope compositions of methane (delta C-13 and delta D) and of short-chain alkanes are commonly used to trace the origin and fate of carbon in the continental crust. In continental sedimentary systems, methane is typically produced through thermogenic cracking of organic matter and/or through microbial methanogenesis. However, secondary processes such as mixing, migration or biodegradation can alter the original isotopic and composition of the gas, making the identification and the quantification of primary sources challenging. The recently resolved methane 'clumped' isotopologues Delta(CH3D)-C-13 and Delta(CH2D2)-C-12 are unique indicators of whether methane is at thermodynamic isotopic equilibrium or not, thereby providing insights into formation temperatures and/or into kinetic processes controlling methane generation processes, including microbial methanogenesis.