Hypostratotype section of the Vendian Ust’-Sylvytsa Formation in the Kvarkush-Kamennogorsk Anticlinorium (Central Urals)

Research subject. The sedimentary sequences of the Ust’-Sylvitsa Formation of the Upper Vendian Sylvitsa Group were studied in Kvarkush-Kamennogorsk Anticlinorium in the sections on Lake Shyrokovsky coastline and Chusovoi City area in the Perm Krai region of Russia.

Results. A three-membered structure of the formation was established, which includes the Lower, Middle, and Upper members. The Lower Member is characterised by sandstones that are thick, brownish, greyish to green-greyish, coarse-grained, and have multi directional herringbone cross-stratification that is often marked by clusters of chocolate-brown flat clay pebbles. The total thickness of the Lower Member is 540 m. The Middle Member (up to 30-m-thick) is represented mainly by massive sandstones without visible stratification and clay pebbles. It reveals marking levels (horizons): a layer of whitish apoclays, from which the U-Pb age of zircon 563 ± 3.5 Ma was previously obtained; and a layer of sandstone with relatively large clasts of feldspar. The section is completed by the Upper Member (up to 80-m-thick), which is characterised by mottled alternation of mudstones, siltstones and sandstones. It also revealed arumberiamorph microbially induced sedimentary structures (Arumberia), as well as levels with ash beds with anomalous whitish to cherry-brown colouring, which may serve as an additional feature in lithostratigraphic correlation of the sequences.

Conclusions. The Ust’-Sylvitsa Formation section in the Lake Shyrokovsky and Chusovoi City area is represented most completely in comparison with the stratotype section on the Chusovaya River near the mouth of the Sylvitsa River, and we propose it as a composite hypostratotype section.

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