INTENSE BASIC MAGMATISM IN THE TUNGUSKA PETROLEUM BASIN, EASTERN SIBERIA, RUSSIA

The Tunguska basin, eastern Siberia, contains 3.5-8 km of Late Precamb rian to Triassic sedimentary and igneous rocks. Source-reservoir-seal systems are present throughout the Upper Precambrian to Permo-Carbonif erous interval. Hydrocarbon generation and accumulation largely preced ed the formation of the Siberian traps, a Late Permian to Middle Trias sic association of effusive and explosive extrusives and intrusive dol erites. The intrusives occur mainly in Palaeozoic strata and have prof oundly affected hydrocarbon accumulation. The major process is of dest ruction of hydrocarbon accumulations, owing to the fact that substanti al volumes of the Palaeozoic basin fill has been heated to 150 degrees C plus. At lower temperatures experienced further from the contacts b etween the intrusions and the country rocks, organic matter thermal ma turation levels may significantly exceed those related to burial alone . Water-mineral-hydrocarbon interactions in association with magmatic heating have produced a range of effects, including the generation of hydrocarbons rich in sulphur compounds such as mercaptans.