QUANTITATIVE ASSESSMENT OF MONOSULFIDE-LINKED AND POLYSULFIDE-LINKED CARBON SKELETONS IN SULFUR-RICH MACROMOLECULAR AGGREGATES PRESENT IN BITUMENS AND OILS

Polar fractions of three immature sulphur-rich sediments and four sulphur-rich oils, all of Miocene age, were studied using two selective chemolytic methods, namely methyl lithium/methyl iodide, which selectively cleaves polysulphide bonds, and Raney nickel or nickel boride which cleave both mono- and polysulphide bonds. In this way the amount of polysulphide-linked vs mono- and polysulphide-linked carbon skeletons was assessed. Steranes, phytane and gammacerane are bound by polysulphide linkages in large amounts (30% or more) in the immature Vena del Gesso sediment whereas squalane, isorenieratane and C-35 hopane carbon skeletons are hardly bound at al by polysulphide-bonds only. The amounts of polysulphide-bound carbon skeletons are much lower in samples from the Northern Apennines and the Monterey Formation acid consist predominantly of n-alkanes. Phytane and steranes are relatively more polysulphide-linked than beta-carotane and n-alkanes in the oils. This phenomenon may be explained in part by the number of carbon-sulphur bonds by which they are bound to the macromolecular moieties, since it is statistically unlikely that moieties bound by several sulphur-bonds are linked exclusively by polysulphide-bonds, Other explanations, however, such as differences in the timing and nature of the sulphur incorporation processes have also to be considered.