Differences in the thermal evolution of hopanes and steranes in free and bound fractions

A geochemical investigation of the free and carbonate-bound organic matter in the clay-sized fraction of argillaceous source rocks and its significance for biogenic interpretation

“…Thus, it is theoretically reasonable to deduce that the bound OM fraction has the potential to preserve additional geochemical information on the molecular level, which has already been verified by previous research (e.g. Li et al 2008a, b;Wu and Geng 2016). Therefore, it is meaningful to analyze the CM-bound fraction on the molecular level to reveal its geochemical significance.…”

“…Because of the steric protection provided by the macromolecular network and inorganic minerals, the bound fraction shows retarded responses to thermal evolution and biodegradation (Li et al 2008a, b;Glombitza et al 2016;Wu and Geng 2016). In addition, the free and bound OM fractions exhibit different OM preservation mechanisms, as the bonding interactions between minerals and associated OM alters the preservation conditions (Zonneveld et al 2010;Cai et al 2013;Makeen et al 2015;Zhu et al 2016).…”

“…Guan et al 1998;Xie et al 2000;Wang and Cheng 2000;Farrimond et al 2003;Cai et al 2013;Li et al 2014; Edited by Jie Hao & Jin-Gong Cai jgcai@tongji.edu.cn Snowdon et al 2016;Chen and Peng 2017), which have previously been overlooked in conventional geochemical studies. In addition to the free fraction of OM in source rocks, the remaining bound fraction could also preserve significant geochemical information concerning OM origin and maturity (Farrimond et al 2003;Ma et al 2008;Li et al 2014;Wu and Geng 2016). Because of the steric protection of inorganic minerals and kerogen/asphaltene macromolecular networks, the thermal evolution of bound OM shows retarded responses to ambient environmental changes when subjected to increased pressure and temperature during gradual burial, thus possessing the capability to better preserve the primitive features of OM compared to the free fraction.…”

“…Because of the steric protection of inorganic minerals and kerogen/asphaltene macromolecular networks, the thermal evolution of bound OM shows retarded responses to ambient environmental changes when subjected to increased pressure and temperature during gradual burial, thus possessing the capability to better preserve the primitive features of OM compared to the free fraction. This is of great significance for geochemical studies of highly matured or severely biodegraded samples (Ma et al 2008;Chen et al 2011;Li et al 2014;Wu and Geng 2016;Glombitza et al 2016). Various experimental procedures have been established to release the bound OM, which makes further geochemical characterization possible.…”

“…Generally, the mineral-bound OM could be released via chemical treatments, such as saponification and acid hydrolysis, after solvent extraction, which first removes the free OM (Zegouagh et al 2000;Warren and Ziegler 2017); the kerogen/asphaltene-bound OM could be released via oxidative or thermal degradation of kerogen/asphaltene, such as ruthenium-ion-catalyzed oxidation and pyrolysis GC/MS (Li et al 2004;Pan et al 2017). Based on previous studies of bound OM, it is generally accepted that the bound fraction is of relatively lower maturity and better authenticity compared to the free fraction (French et al 2015;Glombitza et al 2016;Wu and Geng 2016). The Dongying Sag in the Bohai Bay Basin is a petroleum-rich unit in North China, which has preserved abundant lacustrine fine-grained deposits of great thickness, among which the lower member 3 (Es 3 ) and upper member 4 (Es 4 ) of the Shahejie Formation are the two primary sets of source rocks contributing the most petroleum production (Pang et al 2005;Li et al 2008a, b;Zhang et al 2009;Guo et al 2011;Zhu and Jin 2015;Li et al 2017a;Ma et al 2017a).…”