The West Siberian basin is underlain by an extensive basalt layer of end-Permian age, coeval to the large igneous province of the Siberian traps. Very little is known about its lateral extent and thickness, which is an important element to the thermal evolution of the basin. The top basalt has been imaged in several seismic sections, but the bottom of the layer has not been resolved by seismic studies. Interpretation of gravity and magnetic data helps to investigate the basalt, as basaltic rocks generate in general, due to the high density and magnetic susceptibility contrast with respect to the sediments, a strong signal. In our study we interpret the newest satellite gravity fields, the magnetic field, and the published seismic lines to define the geometry of the basalt layer. We first characterize the expected gravity and magnetic signal for the basalt. We then consider what the contribution of the ongoing satellite gravity GOCE mission will be for a better understanding of the West Siberian basin. Afterwards we build 2D models along the Ob rift in the western part of the basin. We find considerable depth and thickness variations of the basalt layer. It is interesting that the depth and thickness variations correlate with the transition zone from oil to gas fields.
