Fig. 9

a Modified “Bernard diagram” showing the methane carbon isotopic composition vs. dryness (modified after Bernard et al. 1978; Whiticar 1999) showing the composite biogenic and thermogenic composition of the gas retrieved from Satigny (this study). b Interpretation of gas origin using stable carbon and hydrogen isotopic composition of methane according to Whiticar (1999). c Stable carbon isotopic composition of methane and ethane from the Satigny gas sample. d Stable carbon isotopic composition of ethane and propane from the Satigny gas sample. The vitrinite reflectance ⁄ isotope composition lines (maturation lines) are obtained using the calibration data for Type II and III source rocks from Berner and Faber, (1996) and Type II source rock from Faber et al. (2015). Samples Sa (Sachseln), We (Wellenberg), Lö (Lötschberg), Sp (Spiez), La (Langenthal), Ob (Oberbauenstock), Wy (Wynau), Wi (Wilen), Gi (Giswil), MT (Mont Terri), Wa (Weiach), Sc (Schafisheim), Ro (Rothrist and Lättweg), Of (Oftringen) are synthesized from the Swiss Plateau (Wyss 2001; Etiope et al. 2010; Eichinger et al. 2011; Sachs and Schneider 2012). Dashed grey area show the geochemistry of gas samples from the Austrian Molasse Basin (Pytlak et al. 2017)