GEOCHEMICAL-PECULIARITIES OF PRECAMBRIAN SOURCE ROCKS IN THE EAST EUROPEAN PLATFORM

Modern methods of organic geochemistry (GC-MS, Rock-Eval pyrolysis) we re used to investigate insoluble organic matter (OM) and oils of Upper Pre-Cambrian (Riphean and Vendian) age from the East European Platfor m, mainly from the Moscow Syneclise, Ryasan-Saratov Depression and the Mesen Depression. Riphean deposits up to 3.5 km thick accumulate in n arrow graben structures, while Vendian sediments up to 1.3 km thick ar e more widely distributed. Against a background of low concentrations of OM in the Pre-Cambrian successions there are some bands of clayey r ocks with OM contents of significant percentage values. The genetic po tential 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 re alized completely. According to the sterane hydrocarbon (HC) distribut ions, all the extract and oil samples studied can be divided into thre e groups. The first group is well known, with a strong prevalence of e thylcholestanes. A second group of samples, previously not known for P re-Cambrian OM and oils, has a relatively equal distribution of C27-, C28- and C-29-steranes; a third type of sterane distribution with dist inct C-27-prevalence was observed in solid bitumen in Riphean rocks. T he composition and distribution of biomarkers (normal and isoprenoid a lkanes, triterpanes, steranes) in Pre-Cambrian solid OM and oils is no t distinguished by specific features from OM and oils of the Phanerozo ic. The only biomarkers indicative of Pre-Cambrian derived organic mat ter, the 12- and 13-monomethyl-substituted alkanes, have not been obse rved in younger deposits. (C) 1997 Elsevier Science Ltd.