The paper considers the paleohydrogeochemistry of the Upper Jurassic sediments of the Arctic regions of Western Siberia. On the territory under investigation during the late Jurassic marine sedimentation was predominate, the sea depths reached 400 m in the Volga time. Under these conditions, syngenetic sodium thalassogenic chloride waters were buried, in some places with a high content of magnesium, the salinity of which reached 35-40 g/dm3. A comparative analysis of the buried syngenetic waters of the Oxford basin and data on the modern hydrogeochemistry of groundwater of the Upper Jurassic aquiferous complex revealed very significant differences. The analysis of distribution value the total mineralization allowed to establish areas of positive and negative anomalies. In the first case, most of the anomalies are associated with the processes of vertical discharge of groundwater of the Lower Middle Jurassic and Paleozoic aquifers in the zones of tectonic disturbances. Negative anomalies regularly trace the clay boundary of the Oxford regional reservoir, expanding significantly in the north-east direction. Their nature is associated with the development of processes of elision water exchange and thermal dehydration of clay minerals.