Deep epigenesis of riftogenic-sedimentary series: key to gas and gas condensate fields prediction in the Arctic part of Western Siberia
Occurrence of juxta-epigenesis induced by structural transformation of the region is typical for West Siberian territory. Its features were greatly influenced by the buried continental rifts. Juxtaposed processes differ considerably in southern and northern regions. Ob-Irtyshsky interfluve (south of the West Siberian Plate) is a territory that has not been practically transformed by rifting. There, in the environment of lower temperatures and abnormally high concentrations of deep CO2 (an indicator of unexhausted mantle), the interconnected and interdependent processes of kaolinization and carbonation are present on a large scale along the faults transverse to sedimentary cover and basement. The West Siberian Plate is most complicated by rifting in its north (the Tazovsky Bay, Gydan Peninsula, etc.). In the environment of higher temperature and CO2 deficiency (due to mantle depletion), zeolite facies (the indicator mineral is laumontite) is widely developed along the deep faults cross-cutting the basement rocks (transitional sequence) and sedimentary cover, and sporadically - the Transylvanian facies (typical mineral is calcite). Both facies are part of low-temperature propylites. Juxta-epigenesis controlled by deep-seated faults and fault fissures resulted in formation of unusual vertical non-facies column-shaped zones; they are laumontite in the north, kaolinite and carbonate (mainly calcite) in the south. Regionally occurring zeolite propylites are usually productive. They must therefore be considered to be the prospective reservoirs for gas condensate and/or natural gas