Chemical properties of the graptolite periderm from the Holy Cross Mountains (Central Poland)

indices of thermal maturity of pre-Upper Silurian rocks, in which vitrinite does not appear (e.g. Goodarzi 1984, 1985; Goodarzi & Norford 1985, 1987, 1989; Link et al. 1990; Cole 1994; Petersen et al. 2013; Luo et al. 2020). It is commonly employed in the recognition of the unconventional hydrocarbon deposits, which frequently occur in the Cambrian–Silurian organic-rich shales (e.g. Więcław et al. 2010, Schovsbo et al. 2011, Jarvie 2012, Petersen et al. 2013). However, the chemical structure of the graptolite periderm (or fusellum sensu Maletz et al. 2014) is still not fully resolved. Periderm of living graptolites was composed of collagen-like fibrils but their corresponding fossil counterparts lack protein and they underwent the coalification process similar to plant remains (Towe & Urbanek 1972, Link et al. 1990). Deep insight into graptolite paleobiology was given by Maletz et al. (2017). Research on the chemistry of the fossilized graptolite periderm (Bustin et al. 1989; Suchý et al. 2002, 2004; Caricchi et al. 2016; Morga & Kamińska 2018; Luo et al. 2020) were mostly performed on graptolite specimens, reflectance (Rr) of which exceeded values of 0.8–1%, and still little is known about chemistry of low reflectance graptolites. The purpose of this investigation is to determine, for the first time, chemical properties of the graptolite periderms from the Holy Cross Mountains (Rr < 0.8%), and compare them to those known from the previous studies. The research is a continuation of the microstructural examination performed on the same samples (Morga 2019).