Study of the Holocene sediments of Lake Beloe (West Siberia) in the depth range 0-137 cm gave an insight into the transformation of organic matter (OM) at the early stages of diagenesis. Analysis of OM was performed by pyrolytic methods (Rock Eval and pyrolysis + chromato-mass spectrometry). It showed that the macromolecular aliphatic structure of the kerogen and the precursors of sterane and hopane geomoleculessterenes and hopenesform at the early stages of diagenesis. We suggest that macrophytes and bacteria are the main sources of OM for the lacustrine sediments.
