CATAGENESIS OF ORGANIC-MATTER OF PALEOZOI C DEPOSITS ON THE SOUTHEASTOF THE WEST-SIBERIAN PLATE

It is established that on the territory under study catagenesis of dis sipated organic matter (DOM) in the roof of Paleozoic deposits varies within stages MC2-AC(3) (R-vt(0) is 0.9-5.6%). The least-altered DOM i s in the terrigenous-carbonate deposits in the Nyurolka sedimentary ba sin (Mezhovsky median mass), the stage MC2 (R-vt(0) is 0.9-1.2%) being traceable to depths of about 4,000 m. The stage MC31 (R-vt(0) is 1.2- 1.6%) is of limited occurrence, chiefly, within the Azharma trough. Th e DOM is altered to the MC32-AC(1) stage (R-vt(0) is 1.6-2.5%) in sepa rate parts of the territory under consideration both locally and regio nally. A considerable part of the territory is occupied by Paleozoic s ediments subjected to strong near metamorphic alterations. The level o f DOM maturity there corresponds, chiefly, to gradation AC(3), more ra rely, AC(2). Thus, the Paleozoic deposits experiences significant cata genetic alterations and virtually left the primary zone of oil formati on. In the deposits with DOM altered to gradations MC2-MC32 (R-vt(0) i s 0.9-2.0%) accumulations of condensate gas and metamorphosed oils may be preserved. In the deposits exepienced nearly metamorphic alteratio ns (stages AC(2-3)) the possibility of occurrence of syngenetic deposi ts of not only oil but also gas is completely ruled out.