BITUMOIDS IN CAMBRIAN DEPOSITS OF THE CIS-YENISEI SUB-BASIN: FORMATION CONDITIONS, DIAGNOSTIC CRITERIA

The history of development of the Cis-Yenisei sedimentary sub-basin, the presence of several stratigraphic levels in the section of organic-rich Cambrian rocks, and high level of catagenetic transformations (i.e. high maturity level) of the organic matter suggest intensive hydrocarbon generation processes in these deposits in the geological past. The migration processes are shown to be responsible for high variability of bitumoids (chloroform-extractable part of organic matter), both in terms of their content and group/hydrocarbon composition. This is evidenced by three variety of bitumoids (allochthonous, autochthonous, and sedentary autochthonous) defined according to the Uspenskii-Vassoevich regularity. In order to attain more precise differentiation between these bitumoids, we propose here their classification by group and hydrocarbon composition, into seven classes. Allochthonous bitumoids (class VII) are described as hydrocarbon-dominated and migration-prone accounts for about 30% of the total amount of bitumoids, another (mixed) group (6%) is made up by autochthonous-allochthones bitumoids (classes V, VI), while the last group includes autochthonous and sedentary autochthonous bitumoids, with their composition dominated by asphaltenes and resins. Results of the molecular analysis of the composition of bitumoids generally attest to the genetic unity of autochthonous and allochthonous bitumoids. For allochthonous bitumoids, however, there is a wider range of values for molecular indicators, which evidence the influence of migration processes on their composition.