Geochemistry, composition, and structure of protoasphaltenes in organic matter of recent lacustrine sediments

Asphaltenes and asphaltogene acids of organic matter (OM) of lacustrine sediments in the Novosibirsk and Tomsk Regions of West Siberia have been investigated by applying physical and physicochemical methods (elemental and X-ray diffraction analyses, IR, NMR, and EPR spectroscopy, Rock Eval pyrolysis, and electron microscopy). Compared with asphaltenes of dispersed OM at the early catagenesis stages, asphaltenes of OM at the diagenesis stage have a high number of hydrogen atoms and heteroatoms, a low degree of aromaticity, a low concentration of paramagnetic centers, a large number of carbon atoms in the long paraffin chains and oxygen-containing groups. Tetravalent vanadium is absent from asphaltenes of recent lacustrine sediments, and only complex compounds of copper have been identified. The sediments contain not asphaltenes but their precursors, protoasphaltenes. These are less condensed compounds with a looser nongraphite structure and a rather high petroleum potential. At the diagenesis stage, protoasphaltenes are immature protokerogen blocks.