Deep structure of the Danilovskii graben in Western Siberia: A geological interpretation of the density models

Gravimetric modeling is conducted for the Triassic Danilovskii graben. The model region may be an etalon for all of Western Siberia because of the nearby Danilovskoe and Severo-Danilovskoe oil deposits and representative geophysical and drilling data. The correctness of the gravitation model was checked by the magnetic model of the graben constructed on the basis of the gravitation model; the difference between the measured and model anomalous magnetic fields is less than 5%. The density models of the graben have shown that rocks with a significantly excess density of 0.3 g/cm(3) and higher, which probably represent the Triassic mantle diapir, should be located under the axial part of the graben. Rhyolites, forming small irregular bodies on the geological map of the basement, are combined into the common lopolith-like subvolcanic body at depths. The graben is flattened toward the north, which explains the previously unclear presence of Carboniferous shales among the Triassic rocks.