Geology of Saint Petersburg
St. Petersburg is located in the area between the Baltic Shield put by breeds of the crystal foundation and the Russian platform formed by ancient sedimentary breeds. The crystal foundation represented mostly by the granitoid complex, has a complex block structure and lies at the depth from 140 m on the western suburb of the Resort area up to 300 m at the southern borders of the city.
The section of the sedimentary cover in the foundation is represented by deposits of vendian complex (Redkinsky and Kotlinsky horizons) lying monoclinically on the crystal foundation. The Redkinsky horizon (Old Russian suite) in the lower part is represented mainly by the sandstones and the 10-30 m aleurolites blocked by argillitopodobny clays and aleurolites with power no more than 10-15 m. In the Kotlinsky horizon the lower and top subsuites are allocated. The Gdov layers with prevalence of sandstones and aleurolites with power up to 30 m are dated for the lower subsuite. The Gdov layers lie generally on deposits of the Redkinsky horizon, and in places of their wedging out directly on the crystal foundation breeds. The deposits of the top subsuite of Kotlinsky suite lying above are represented by powerful thickness (up to 150 m) of the interstratifying clays with rare pro-layers of sandstones.On the indistinct surface of deposits of the vendian complex sandstones and aleurolites of the Lomonosov suite of the lontovasky horizon of the lower Cambrian lie. Their power doesn't exceed 10-12 km. The suite comes to the pre-quaternary surface with a narrow strip 1-2 km wide in the southern districts of the city. Sandstones of the Lomonosov suite are blocked by powerful (115-120 km) thickness of bluish-gray clays of the Seversk suite of the Lontovassky horizon. Deposits of the Seversk suite come to the pre-quaternary surface with a wide strip 12-18 km along the southern coast of the Gulf of Finland. Above on the section locally developed sands and sandstones of average and top sectors of the Cambrian lie. Only in the south of Krasnoselsky and Pushkin districts in the section of the sedimentary cover there are carbonate deposits of ordovician complex with power up to 40 m containing interlay uranium-containing dictyonema oil shale.
The youngest pre-quaternary formations coming out to the pre-quaternary surface in the extreme South of the city and having very limited distribution are breeds of the Narovsky horizon of the Middle Devonian, represented by marl and dolomite with pro-layers of clays.
Quarternary deposits of various genesis almost completely cover the city area from the surface. Mostly their power doesn't exceed 20-30 m. Quarternary deposits differ in frequent lithologic variability, both in plan and in section. Most fully the section of quarternary deposits is represented in ancient buried valleys where their power increases up to 100-130 m. Here quarternary deposits contain 2-3 moraine sandy clayey horizons and sandy intermoraine layers dividing them are allocated.
The geological structure determines the nature of change of geological resources condition by area and depth, a possibility of their use and necessary restrictions of anthropogenic load on those.