Raman spectral parameters of pyrolyzed samples for three types of graptolites

A series of gold tube pyrolysis experiments (72 hrs, 300–600 °C) conducted on a graptolite-rich lower Paleozoic marine shale generated pyrolysis residues for a comprehensive evaluation of the molecular and structural variability of three types of graptolite periderm, namely granular, non-granular, and nodular graptolite. Raman spectroscopy in combination with organic petrology and field emission scanning electron microscopy (FE-SEM) was used to evaluate the thermal evolution process. The three types of graptolite periderm were analyzed by Raman spectroscopy wherein point measurements were obtained after the maceral was identified and the location verified by organic petrology. Raman spectroscopy, a non-destructive and rapid microstructural analysis technique, has recently emerged as a powerful tool for assessing the thermal maturity of source rocks (Ferralis et al., 2016; Kelemen and Fang, 2001). Applicability of these Raman thermal proxies has been extended to various OM types by correlating the Raman spectral parameters with traditional thermal maturity proxies, such as reflectance and pyrolysis Tmax (Liu et al., 2013; Wilkins et al., 2014; Morga and Pawlyta, 2018), and has thus proven to be useful in determining thermal maturity.