The first terrace above the Ob’ floodplain near Kolpashevo: the age and formation conditions

The subaqueous sediments of the first terrace above the Ob’ River floodplain near the town of Kolpashevo are referred to as the Sartan cryochron. New data show that they formed mainly in the Early and Middle Holocene. The key section is on the right bank of the Novoil’inskaya Staritsa—a branch of the Ob’ River 10 km south of Kolpashevo. Radiocarbon dating of the peat at the terrace base yielded an age of 10,200 ± 55 years, which is close to the Pleistocene–Holocene boundary. The studied sample from the middle section has a 14C age of 5870 ± 55 years corresponding to the Atlantic Holocene optimum. The palynological data confirm the geologic structure of the section: The recognized spore-pollen spectra distinctly mark the first half of the Holocene and reflect the landscape changes. The results obtained help to refine stratigraphic charts and maps of Quaternary deposits and reconstruct the landscapes (including geochemical ones) and lithologo-facies and neotectonic conditions.