Abstract Explanations for the thermal decomposition of ethane and propane in sedimentary basins have long been conceptual without quantitative evidence. This work bridges the gap between 13C depletion and the conversion of ethane and propane, and confirms their thermal decomposition during the late catagenesis stage. Isotopic fractionation was rigorously investigated in a partly reversible reaction scheme for ethane and propane decompositions. Analytical solutions under isothermal conditions were derived. Non-monotonic isotopic fractionation with respect to conversion is demonstrated, which may be ignored if a steady-state approximation is applied. The results imply that depletion of 13C in ethane and propane as their molar fractions decrease (isotopic inverse with respect to thermal maturity) results from the reversible conversion from alkane to alkyl groups. Kinetic parameters were obtained for ethane and propane decomposition in sedimentary basins, and the chemical kinetic method applies to different isotopic fractionation systems. The results help to better understand the chemical form of deep carbon and the thermal conversion of gaseous hydrocarbons in the geochemical carbon cycle.

中文翻译：

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沉积盆地中残余乙烷和丙烷热分解过程中 13C 的消耗

摘要 长期以来，对沉积盆地中乙烷和丙烷热分解的解释一直是概念性的，没有定量证据。这项工作弥合了 13C 消耗与乙烷和丙烷转化之间的差距，并证实了它们在后期催化阶段的热分解。在乙烷和丙烷分解的部分可逆反应方案中，对同位素分馏进行了严格的研究。得到等温条件下的分析溶液。证明了与转化相关的非单调同位素分馏，如果应用稳态近似，则可以忽略。结果表明，乙烷和丙烷中 13C 的消耗随着它们摩尔分数的降低（同位素与热成熟度相反）是由烷烃向烷基的可逆转化造成的。获得了沉积盆地中乙烷和丙烷分解的动力学参数，化学动力学方法适用于不同的同位素分馏系统。研究结果有助于更好地了解深层碳的化学形式和地球化学碳循环中气态烃的热转化。