Structure, composition and conditions of formation of quaternary sediments in the Keltmin burial canyon (southeast of the Komi Republic)

Our lithological study of the Quaternary strata in the section of the well 17843 resulted in identification of three sediments sequences of various thickness and composition. In the lower part of the well, at depths of 43.2-27 m ( layers 5, 4d and 4c ), the sediments were formed probably in fluvioglacial conditions. The sediments are characterized by high content of ilmenite - 7-14 %, and group of titanium minerals - 7-12 %, where concentrations of leucoxene and titanite are increased. The content of chromespinellides increases downwards from 2 to 4.4 %. In the depth interval 25.9-23.6 m ( lay 4b ), a dense, poorly-sorted silty clay without clastic material is exposed; its genesis is unclear. Clay is characterized by the highest amount of heavy fraction in the section - 1.91 %, and contains an abnormally high amount of magnetite - on average 31 %. The upper 22 m of the sequence ( layers 4a and 3-1 ) are represented by alluvium - well-sorted medium-fine-grained sand with amphibole-ilmenite-garnet-epidote association of heavy minerals and increased amounts of metamorphic minerals - 7-10 %, chromespinellides - 4-6 %, and magnetite - 4-8 %. Such complex of heavy minerals in the sediments, forming the canyon, testifies to the participation of the Ural magmatic and metamorphic complexes in their formation; the supply of minerals from the Kama seems to be very problematic. Palynological analysis data obtained from layers 5, 4d , and 4b reflect a regular vegetation change of the final stages during the interglacial. Spruce-pine forests with fir, cedar, treelike and dwarf birches, alder and willow were gradually replaced by tundra plant communities, where, along with bog-tundra formations, there were xerophytic communities with wormwood Artemisia sp., Chenopodiaceae, and rare Ephedra sp.