NERUCHEV, SERGEY, VNIGRI, St. Petersburg, Russia

Title: ABSTRACT: Oil Source Rocks in Sedimentary Basins of the CIS

Oil source rocks with dominant kerogen of types I or II and with a concentration of organic carbon of 6-7% are widely distributed at specific stratigraphic levels in the Phanerozoic section of the world. These source rocks control the petroleum richness of the main productive basins. Nineteen stratigraphic levels of source rock distribution are identified. These are (l) boundary strata between the Vendian and Cambrian, (2) between the Lower and Middle Cambrian, (3) between the Cambrian and Ordovician, (4) Middle Ordovician, (5, 6) Lower and Upper Silurian, (7) Upper Devonian, (8) boundary strata between the Devonian and the Carboniferous, (9) Upper Carboniferous, (10) Lower Permian (Artinskian), (11) Upper Permian, (12) Middle Triassic, (13) Lower Jurassic (Toarcian), (14) boundary st ata between the Jurassic and Cretaceous, (15) Aptian, (16) Turonian, (17) Maastrichtian, (18) Eocene, and (19) Miocene. Oil source rocks at almost all of these stratigraphic levels are known in basins of the Commonwealth of Independent States, and the paper contains a review of their distribution.

Black shales and oil shales enriched by P, U, V, Mo, and in places also by Ir, Os, and other metals, are found in the same stratigraphic intervals outside petroleum basins. High concentrations of uranium have been identified in terrestrial rocks at several of the stratigraphic levels. A high concentration of kerogen in oil source rocks is commonly explained by depositional conditions (anoxia and upwelling) that favor accumulation and preservation of organic matter. However, the main factor of enrichment of sediments by organic matter is the rifting activity and associated increase of supply with phosphorus, radioactive elements, and heavy metals. This results in the ecological crisis and global blossoming of plankton (cianobacteria, green algae, zooplankton in the Silurian, and diatom in the Miocene). Rocks with increased concentration of radioactive elements are present at the boundaries of large stratigraphic units that are identified based on paleontologic data. These rocks mark major events of fauna extinction and other important biotic events such as those that occur at the Vendian-Cambrian, Devonian-Carboniferous, and Permian-Triassic boundaries. The periodicity of the major global events is about 220 m.y., which corresponds to duration of the galactic year. Smaller periodicity of about 30 m.y. is identified inside the major periods. These regularities in the organic-rich rock distribution can be used to predict the presence of oil source rocks, oil shales, and shales enriched by metals.

AAPG Search and Discovery Article #90990©1993 AAPG International Conference and Exhibition, The Hague, Netherlands, October 17-20, 1993.