Geochemical peculiarities of Pre-Cambrian source rocks in the East European Platform

Modern methods of organic geochemistry (GC-MS, Rock-Eval pyrolysis) were used to investigate insoluble organic matter (OM) and oils of Upper Pre-Cambrian (Riphean and Vendian) age from the East European Platform, mainly from the Moscow Syneclise, Ryasan-Saratov Depression and the Mesen Depression. Riphean deposits up to 3.5 km thick accumulate in narrow graben structures, while Vendian sediments up to 1.3 km thick are more widely distributed. Against a background of low concentrations of OM in the Pre-Cambrian successions there are some bands of clayey rocks with OM contents of significant percentage values. The genetic potential of the Upper Riphean source rocks is 4 kg t−1 in the Moscow Graben. The oil-source potential of Pre-Cambrian rocks has not been realized completely. According to the sterane hydrocarbon (HC) distributions, all the extract and oil samples studied can be divided into three groups. The first group is well known, with a strong prevalence of ethylcholestanes. A second group of samples, previously not known for Pre-Cambrian OM and oils, has a relatively equal distribution of C27-, C28- and C29-steranes; a third type of sterane distribution with distinct C27-prevalence was observed in solid bitumen in Riphean rocks. The composition and distribution of biomarkers (normal and isoprenoid alkanes, triterpanes, steranes) in Pre-Cambrian solid OM and oils is not distinguished by specific features from OM and oils of the Phanerozoic. The only biomarkers indicative of Pre-Cambrian derived organic matter, the 12- and 13-monomethyl-substituted alkanes, have not been observed in younger deposits.