Facies and genetic dissection of modern alluvium in the lower reaches of the Kuya river in the northwest of the Bolshezemelskaya tundra

Facies genetic dissection of modern floodplain sediments in the K 12 section in the Kuya river valley (lower reaches) in the northwest of the Bolshezemelskaya tundra was carried out. According to the largescale maps and satellite images of the “Earth Planet” program, a geomorphological diagram of the research site was compiled and the development of the floodplain segment was traced. Based on lithological features and granulometric analysis data three packs of sediments were identified in the structure of the K 12 outcrop thick ness. At the base of the section (pack 1, layer 1) gray finegrained clay sand with inclusions of pebble and gravel is deposited (layer thickness is 1.15 m). The sediments are the riverbed shoal subfacies of the channel alluvium. The accumulation of the riverbed shoal subfacies occurred under conditions of the lateral displacement of the channel towards the undercut shore and the formation of a sandy channel bank. During periods of high water, when the sandbank was occupied by water and became part of the channel, sand and gravel material were deposited. Above (pack 2, layer 2 3) are gray bluey clayey silt and clayey peat (layer thickness is 1.15 m), composing the secondary reservoirs subfacies of the floodplain. Formation of secondary reservoirs subfacies began when the bottom part of the floodplain turned into a depression, in which a reservoir was formed. Poorly drained floodplain surface contributed to the preservation of water in it throughout the entire warm season. Overmoistening of the floodplain caused swamping processes and from that moment the lake marsh reservoir began to develop. Its sediments in the section are represented by peat. Radiocarbon Dating of organic material from the section bottom indicates that waterlogging of the reservoir occurred in the Late Subatlantic Holocene period (750 ± 8014C BP). The sediments are overlapped by the riverine floodplain subfacies (pack 3, layer 4, 5), represented by brown sandy loam with plant residues (layer thickness is 1.7 m).Based on the results of palynological studies of the oxbow lake deposits of two sections, the vegetation and climate features of the four stages of the Late Holocene (SA 1, SA 2, SA 3 and SA R) were reconstructed. The composition of the spectra reflects the development of mossy shrub tundra and thecoldest climatic conditions in the early Subatlantic. A sharp increase in the pollen content of trees in the spectra indicates the spread of forest tundra vegetation and warming in the middle of the Subatlantic (SA 2). The diagrams show the landscape climatic changes that occurred during the Small Ice Age at the end of the Subatlantic