“…, pyrolysis analysis (e.g., Seifert, 1978), carbon isotope measurements (e.g., McKirdy & Powell, 1974), infrared spectrometry (e.g., Ganz & Kalkreuth, 1987), and Raman spectrometry (e.g., Tuinstra & Koenig, 1970). Among these, Raman spectroscopy has become one of the most popular techniques of the past two decades (e.g., Aoya et al, 2010;Beyssac et al, 2002;Cheng et al, 2022;Guedes et al, 2012;Henry et al, 2019a;Jehlička et al, 2009;Kouketsu et al, 2014;Lahfid et al, 2010;Lünsdorf & Lünsdorf, 2016;Nakamura et al, 2020;Perraki et al, 2006;Rahl et al, 2005;Skrzypek, 2021;Yesiltas et al, 2018). Two characteristic spectral regions appear in a Raman spectrum of CM: the first-order region between 1000 and 1800 cm À1 (Tuinstra & Koenig, 1970), and the second-order region between 2200 and 3400 cm À1 (Nemanich & Solin, 1977).…”