Tectonic Setting of the Middle–Upper Cambrian Sediments of Bolshevik Island and Troynoy Island (Russian Arctic): a Case of Clastic Rocks from Metaterrigenous Complexes

The new data on the tectonic setting and conditions for the Middle‒Late Cambrian deposits formation in the southern part of the North Kara terrane, presented in our research, the data induced from the studies of clastic rocks in the metaterrigenous basement complexes of Troynoy Island (Izvestia CEC archipelago) and the northern part of Bolshevik Island (Severnaya Zemlya archipelago). The sandstones of both regions are similar in the lithic wacke composition and contain the same groups of rocks fragments. Detrital zircons and Cr-spinels from sandstones of both regions have the same Zr/Hf and TiO2/Al2O3 ratios, respectively. The similarity of even-aged sediments from both regions can be explained by their accumulation due to the demolition of detrital material from a single source eroded area, which is a segment of the accretionary uplift of the Timan‒Severnaya Zemlya orogenic belt, with the newly formed continental Neoproterozoic‒Cambrian crust. Low- and medium-grade metamorphosed terrigeneous complexes dominated in the structure of the source area. Presence of volcanic and intrusive complexes in the source area is marked by clastic Cr-spinels with geochemical signatures of volcanic arc and suprasubductional ophiolites origin. By the beginning of the Ordovician, the Middle‒Late Cambrian sediments were also crushed, metamorphosed and included in the structure of the Timan‒Severnaya Zemlya orogenic belt. Peculiarities of petrographic and grain-size composition and sorting of the sandstones from the north of Bolshevik Island are more typical for the sediments of gravity turbidite flows, in deep or relatively deep water conditions. The deposits of Troynoy Island could be formed at the shallow and coastal-marine environments.