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An essay on regional geology and stratigraphy of the Upper Cretaceous deposits of southern Urals territories

Edward O. AMON, Joyce R. BLUEFORD, Patrick DE WEVER & Victor I. ZHELEZKO

en Geodiversitas 19 (2) - Pages 293-317

Published on 24 June 1997

The Turgay region is considered the north-eastern border of the Peri-Tethyan basins during the Cretaceous. This area contained elements of each areas faunas; the relatively warm Peri-Tethys faunas with the cooler West Siberia faunas. Cretaceous deposits are found throughout the southern Urals, especially in the western and southern Primugodzharie, Aktyubinskian Priuralie, and Pri-Irgizsky areas. Cretaceous deposits are covered by Cenozoic rocks, shown from well cores from the south-eastern border of Mugodzhar mountains, Turgay and northern PriAralie. The Lower Cretaceous in the southern Urals was predominately continental. In the western Primugodzharie and Aktyubinskian Priuralie region, marine sediments of Neocomian, Aptian and Albian age were deposited. Red continental sedimentary rocks were deposited during the Neocomian. Coal and bauxite were deposited during Aptian and Albian. The Lower Cretaceous boundary was marked by a marine regression, while the Aptian and Late Albian-Early Cenomanian are characterized by extensive continental rocks on the entire territory, with the exception of the Turgay region. A widespread marine transgression is evident during the Cenomanian. This transgression influenced the sedimentation in the southern Urals, East European, Scythian, Turan and West Siberian platforms. Upper Cretaceous was dominated by shallow marine facies, coastal and shore deposits. Marine transgression continued until Late Maastrichtian. The end of the Late Maastrichtian was characterized by the appearance of very shallow water and lagoonal regressive facies. The Cretaceous/Paleogene boundary was marked by a pause of sedimentation with erosional unconformities in the boundary between the Maastrichtian and Danian. Foraminifera, radiolaria, belemnites, selachians, mollusca, pollen, and spore reveal the timing of events and suggest the paleoenvironment of this region during the Upper Cretaceous.

Keywords :

stratigraphy, correlation, Cretaceous, South Ural, paleontology