A study of a 1.2 Ga kerogen using Ru ion-catalyzed oxidation and pyrolysis–gas chromatography–mass spectrometry: structural features and possible source

This manuscript reports the structural features of a 1.2 Ga kerogen from the Hongshuizhuang Formation of the Jixian Group at a stratigraphic type section in north China, observed from Ru ion-catalyzed oxidation (RICO) and pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS). The results show that low aliphaticity, short polymethylenic chains and the presence of the latter mostly as terminal alkyl groups are the most striking structural features of this old kerogen. No obvious sterane-, hopane- or isoprenoid-type compounds were detected in the degradation products with both techniques, as was the case for the extractable bitumen from the host shale. Considering the age of 1.2 Ga for the kerogen, the absence of steroidal compounds precludes a source input from eukaryotic algae, tentatively suggesting a source from cyanobacteria. This is supported by a comparison between the RICO and Py–GC–MS data obtained from the kerogen Phanerazoic macromolecular materials derived from eukaryotic algae; indicates that eukaryotic algae are less likely to have been an important source for the kerogen. Moreover, The structural similarities between the kerogen and the so-called cyanobacterial resistant material (CRM) are also consistent with cyanobacteria being the most likely source of the 1.2 Ga kerogen.