Quasi-three-dimensional modelling of the Jurassic-Cretaceous sediments hydrogeochemical conditions in the central part of the West Siberian megabasin

Abstract

Abstract This paper presents the method and results of the hydrogeochemical spatial pattern modelling in the Cretaceous and Jurassic sediments of the Koltogor and Tolkin megatroughs and the surrounding areas of the West Siberian megabasin. The method is based on the preliminary calculation of two-dimensional radial profiles that provide the assessment of hydrogeochemical parameter changes with depth at the given points set within the study area. Using the results of the calculations, a model of hydrogeochemical conditions is constructed as a series of maps of the groundwater salinity in Formations, as well as NS and EW oriented cross-sections. The method is relatively simple, reliable and ensures result consistency. The analysis of the results indicates a significant variability of groundwater salinity both as a whole in the Jurassic-Cretaceous sediments, and within individual aquifer. On cross-sections, areas with relatively constant salinity appear both in the form of separate thin and inconsistent layers and in the form of thick extended zones. The geometry of the zones is not fully defined by the boundaries of the aquifers. Such variability is also reflected in the significant differences of hydrogeochemical conditions in different Formations and Subformations of the sedimentary cover of the West Siberian megabasin. The revealed substantial heterogeneity of hydrogeochemical conditions in the Jurassic-Cretaceous sediments indicates a complex genesis of the groundwater chemical composition and, in particular, the absence of a clear impact of the powerful pre-Jurassic tectonics, including those that have formed the regional vast Koltogor-Tolkin trough zone.