Geologicheskii Vestnik

The litho-facial features of carbonate and terrigenous-carbonate rocks of the Sandbian, Katian and Hirnantian stages of the Ordovician in the Nabiullino and Kurgashly sections are considered in the paper. The sedimentation environment ts into the model of sedimentation in the setting of a ramp-type terrigenous-carbonate shelf with the impact of storms and tidal currents. The Hirnantian event is lithologically recorded in the upper part of the section by a change of tempestite sedimentation with the tidal one; mainly shallow-water conodont biofacies are common. The subsequent change of carbonate sedimentation to clay sedimentation in the Late Ordovician – Early Silurian re ects the resumption of transgression and sinking of the platform edge due to expansion of the Paleo-Uralian Ocean. The formation of the Ordovician terrigenous-carbonate deposits was controlled by both geotectonic and global eustatic factors.

Ordovician, Sandbian, Katian, Hirnantian stages, conodonts, lithofacial analysis, tempestites, taidalites, sandy dolomites, Bashkir meganticlinorium

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