EVOLUTION OF HYDROGEOCHEMICAL FIELD OF NORTH AND ARCTIC REGIONS OF THE WEST SIBERIAN SEDIMENTARY BASIN IN THE MESOZOIC
The relevance of the work is in identification of fundamental role of paleohydrogeological factors in the evolution of the hydrogeochemical field in the Mesozoic of the West Siberian sedimentary basin northern and arctic regions. For the first time, the paper proposes the mechanism explaining their contribution to formation of hydrogeochemical anomalies in the Oxford reservoir (Upper Jurassic aquiferous complex) of the studied region, where hydrogeochemical inversion is widely developed. The aim of the research is to identify the features of composition of syngenetic waters disposed together with the sediment in the expelled and infiltration stages of a sedimentary basin on the basis of established cycling hydrogeological history of the West Siberian sedimentary basin northern and arctic regions; to carry out the comparative analysis of the current and syngenetic waters and determine the nature of hydrogeochemical anomalies. Methods. The methods developed by A.A. Kartseva, S.B. Vagina, E.A. Baskov and other researchers on paleohydrogeological reconstructions of sedimentary basins were used. The periodization of hydrogeological history was carried out, with identification of the main hydrogeological cycles (with the infiltration and elizion stages). Paleohydrogeochemical studies on the Arctic regions of the West Siberian sedimentary basin were carried out for the Jurassic-Cretaceous section using the methodology for reconstructing the salt composition of the waters of ancient marine and alluvial basins, paleogeographic maps and hydrogeochemical database of Siberian sedimentary basins. Results. The paper introduces the results of paleohydrogeological reconstructions of the West Siberian sedimentary basin northern and arctic regions. It was established that sedimentary waters dominate in the hydrogeological section of the studied region, in some cases diluted with infiltrogenic waters that have penetrated during the regression of the sea basin. A comparative analysis of buried syngenetic waters of the Oxford basin and data on modern hydrogeochemistry of groundwater revealed a number of negative and positive anomalies. Negative anomalies naturally trace the clay boundary of the Oxford regional reservoir and are associated with the development of water exchange elision. The geostatic (lithostatic) water-pressure system at a depth of 2-2,5 km goes into thermo-dehydration, which is accompanied by abnormally high reservoir pressure and the appearance of fresh chemically-bound water in the water-pressure system. Most of the positive anomalies are confined to the structures of the South Nadym and Predisenyskoy mega-monoclise, where the processes of vertical unloading of groundwater of the Lower Middle Jurassic and Paleozoic aquiferous complexes in the zones of tectonic disturbances are widely manifested. The water-rock-gas-organic matter system plays a key role in formation of groundwater chemical composition in oil and gas deposits.