RECONSTRUCTION OF THE FORMATION HISTORY OF THE PEAT PLATEAU IN THE LOWER REACHES OF THE NADYM RIVER
O.S. Sizov1, A.A. Yurtaev2, A.V. Soromotin2, E.M. Koptseva3, A.O. Volvakh4, E.V. Abakumov3, N.M. Berdnikov5, N.V. Prikhodko2, D.S. Guryev6
1Institute of Oil and Gas Problems RAS, Gubkina str. 3, Moscow, 119333, Russia
2Tyumen State University, Volodarsky str. 6, Tyumen, 625003, Russia
3St. Petersburg State University, 16th line V.O. 29, St. Petersburg, 199178, Russia
4Sobolev Institute of Geology and Mineralogy, SB RAS, Akademika Koptyuga ave. 3, Novosibirsk, 630090, Russia
5Earth Cryosphere Institute, Tyumen Scientific Centre SB RAS, Malygina str. 86, Tyumen, 625026, Russia
6LLC Severavtodor, Komsomolskaya str. 10B, Nadym, Yamal-Nenets Autonomous District, 629730, Russia
Keywords: Frost mound, frozen ground, permafrost zone, Upper Quaternary deposits, Nadym region
Abstract
The study presents new data on the cryolithological structure of a ridge-shaped peat plateau typical for the north of Western Siberia, located in the lower reaches of the Nadym River. Two wells were drilled at the top of the ridge and in the inter-ridge depression, with subsequent core analysis. Grain size distribution, shape and surface structure of sand quartz grains, botanical composition and radiocarbon age of organogenic deposits were determined. The study revealed the presence of a three-layer peat-sand-loam ridge structure. The lower loam layer with a ~60 % volumetric ice content was affected by frost heaving. Layers of pure ice are identified below this loam layer. The ridge was formed as a result of water migration with the complementary influence of ice injection; it is of the peat-mineral type. In the ridge formation history, we identified the stages of loam and sand deposits accumulation at the end of the Late Pleistocene; bogging occurred at the beginning of the Holocene (10.6-9.8 ka BP), while active frost heaving was during the Subboreal stage (5.5-5.0 ka BP). Currently, there is a decrease in the upper organic horizon thickness and some erosion. It is proposed to consider peat-mineral and mineral frost heave landforms (mounds and ridges) as separate type of cryogenic landforms.
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