Localization of carbonate platforms in ordovician formations of West-Siberian geosyneclise

The relevance of the research lies in the need to increase facilities for searching oil and gas fields, one of which is a carbonate platform in the pre-Jurassic formation of West Siberia. The discovery of a number of oil and gas fields: Urmanskoye, Archinskoye and several others, are related to carbonate platforms on the territory of West Siberian geosyneclise (WSG). The aim of the research is to consider the conditions of formation of the Ordovician depositions of West Siberian geosyneclise for establishing in its territory the sites for the formation of carbonate rocks (carbonate platforms), which are transformed into rock-collectors at the appropriate studying by hydrothermal leaching and hydrothermal dolomitization. The fissure-metasomatic zones of hydrothermal study of carbonate rocks are formed. They underlie the area zones of formation of reservoir rocks in the regions of the Paleozoic formations discharge on the pre-Jurassic surface, or zones of oil and gas horizon of the contact zone, contact areas of Paleozoic (pre-Jurassic) and Mesozoic deposits. Research methods: lithological, paleontological, paleogeographic, tectonic. On the basis of complexity of the research methods by the previous researchers, the WSG territory is divided into 23 structural-facial districts (SFD), with a characteristic set of lithostratigraphic units (sweet, thick) and paleontological substantiation of the age. By the results of the study the authors have reconstructed the paleo-geographic conditions, conditions of accumulation and distribution of precipitation in the early and middle-late Ordovician time. The greatest attention is paid to the establishment of formation areas of carbonate rocks prospective for forming reservoir rocks. The tectonic analysis allowed comparing the phases of development of carbonate platforms of early and middle-late Ordovician age for determining the tectonic movements that promote the increase or reduction of carbonate platforms. Results. The paper introduces the information on distribution of lower-, middle-upper Ordovician deposits in the territory of WSG. The authors reconstructed the conditions of sedimentation during the Ordovician period, built schematic paleogeographic maps of early and middle-late Ordovician age, and a complex map of distribution of the identified carbonate platforms of early and middle-late Ordovician age. The conclusions were made on the tectonic history of WSG during the Ordovician, in particular the manifestation of the transgressive phases in the zone of formation of the carbonate platforms of the Ordovician age.