Lithochemical composition of sandstones of the Vendian Asha Group, South Urals

Аннотация

The mineralogical–petrographic and chemical study of sandstones of the Vendian Asha Group in the Bashkir anticlinorium, the western slope of the South Urals, showed that this large stratigraphic unit consists of sedimentary associations formed in different conditions: (1) Pre-Uryuk sediments (Tolparovo, Suirovo, and Bakeevo formations) accumulated during marine regression possibly in the course of significant glacioeustatic sea level fluctuations and formation of the foredeep of Timanides. (2) Sediments of the Uryuk Formation, including alluvial and several related sediments. Analysis of the Qm–F–Lt, Qt–F–L, and ln(Q/L + CE)–ln(Q/F) diagrams showed that they were derived from magmatic/plutonic rocks in the inner parts of the East European Craton. Based on the distribution of data points of psammites in the Qt/(F + R)–Qp/(F + R) diagram, they were accumulated in the semihumid/semiarid conditions. (3) Coastal, shallowmarine, and fluvial/proluvial (?) sediments of the Basa, Kukkarauk, and Zigan formations. They were formed by the erosion of provenances located supposedly east of the present-day Bashkir anticlinorium. The psammites of the Asha Group were analyzed using the sandstone formation model proposed models proposed in (Dickinson et al., 1985; Garzanti et al., 2007). The distribution of data points of psammites from three uppermost formations of the Asha Group in the Qm–F–Lt and Qt–F–L diagrams suggests that they were accumulated by the redeposition of erosion products of the so-called clastic wedges of recycled orogens (clasticwedge provenance) made up of the fluvial and turbidite complexes of the foreland, fore-arc, or residual oceanic basins.