Stepwise chemical degradation of immature S-rich kerogens from Vena del Gesso (Italy)

Stepwise chemical degradation involving cleavage of ester bonds (KOH/MeOH), sulfide and remaining ester bonds (Li/EtNH₂), ether bonds (HI/LiAlH₄) and sub-units linked to aromatic moieties (RuO₄) has been carried out on the kerogens of two immature sulfur-rich marls (IV-1.4 and 1.8, TOC ca. 1.5%) from evaporitic cycle IV of the Gesosso-solfifera Formation (Messinian, Vena del Gesso, Italy). Up to 80% of the organic matter was converted to solvent-soluble material, with the greatest proportion released by Li/EtNH₂. The majority by far of the extracts comprises polar macromolecular material which is thought to correspond to high molecular weight sub-units of the kerogen. Quantification of the small amounts (<1%) of the released GC-amenable components indicates that diagenetic sulfurization was more important in the case of kerogen IV-1.4 but that the extent of oxygen sequestration was similar in both cases; the distributions of biomarkers released by ether cleavage of the desulfurized residue and polar fraction showed differences which reveal heterogeneity in the building blocks making up different macromolecular fractions.