Title

N.YU. NIKULOVA (Institute of Geology Komi SC UB RAS)

Lythological and chemical composition and depositional conditions of basal uralides deposits in the basin of Malaya Usa River (Polar Urals)

The results of the investigations of geochemistry of Late Cambrian – Early Ordovician khoidyshorskaya (Є₃–O₁hd) suite sandstones at the base of the Paleozoic section in the Polar Urals are generalized in the article. We attributed the sandstones of khoidyshorskaya suite to sedimentary continental, coastal-­marine and marine volcanic­sedimentary facies. It was shown that the chemical composition of khoidyshorskaya suite sandstones reflects different paleogeodynamic situation. The high­alumina sandstones (including gold­bearing ones) containing material of ancient metamorphosed weathering crust are formed at continental conditions. Tufogenic character of the sandstones is revealed by using diagrams demonstrating their consanguinity with the riftogenic volcanites in the continental crust. Coastal­marine sandstones are characterized by a low degree of chemical maturity. Their composition was formed as a result of mechanical mixing of magmatic (acid and basic) and metasediment basement rocks fragments at a high rate of sediment accumulation.
Keywords: sandstone, chemical composition, sedimentary conditions, volcanites.