Permafrost

and +38°C in summer. Continuous permafrost distribution is evident in this region at least since
the middle Pleistocene. The study area is situated on the denudation plain to the west of the
Lena River. Quaternary deposits cover interfluve areas, slopes, and the bottoms of small river
valleys and runoff rills, and fill thermokarst depressions. Cryogenic eluvium, loess-like silts,
and peaty deposits are widespread. Jurassic sedimentary rocks underlie the Quaternary cover.
This presentation deals with cryolithological features of Quaternary deposits formed at the
headwaters of the Ulaakh River, a left tributary of the Lena. Intermittent streams in small dry
valleys drain this kettle or cirque-like depression, which is a typical morphological structure of
the denudation plain to the west of the Lena River. More than ten core profiles, as well as
related pits in the active layer, were investigated using a complex cryolithological approach
including study of cryostructure, ice content, grain size, and the mineralogical and chemical
composition of sediments. The results show that ice-saturated loess-like deposits with
polygonal ice wedges fill a dendritic system of runoff rills, which dissect slopes of the modern
Ulaakh valley. Orientation and morphological features of the rills give evidence that they are
ancient valleys of small rivers – the pre-Ulaakh‘s tributaries. The thickness of Quaternary cover
deposits depends on the size and maturity of the runoff rill and can reach 20-25 m. The
composition, fabric and cryostructure indicate that slope processes have played a significant
role in the accumulation of sediments. These deposits consist mainly of loess-like silts
interrupted by layers of sands and fragmental plant remains. Pebbles and stones are contained in
the basal layers. An average segregation ice content of 25-45% and the deep penetration of ice
wedges down to 15 m characterize these “Ice Complex” deposits. Granulometry and heavy
mineral composition of the investigated sediments suggest an aeolian origin of a great part of
silt-sized material, carried under varying wind strengths from the Lena valley. However, this silt
in most places was affected by slope processes and mixed with local weathering products.
Keywords: Central Yakutia, cryolithology, headwaters, loess-like deposits
Thermodynamic and Morphometric Permafrost Characteristics
Dynamics in Transbaikalia in Pleistocene and Holocene:
the Fundamental and Applied Results
D.M. Shesternev
(Institute Natural Resources, Ecology and Cryology, Siberian Branch, Russian Academy of Science.
P.O.Box 147, Butina, 90, 672090, Chita, Russia;E-mail: loc@mail.gin.ru)
Abstract: The problem of reconstructing the permafrost characteristics in connection with
cyclic character of climate changes was formulated by M.I.Sumgin in the beginning of XX
century. This problem stays topical now because the practical needs. It is connected with the
thermodynamic and morphometric permafrost characteristics change and also with the
activation of negative cryogenic processes that affect the engineering constructions and make a
danger for human life. For example, only in Transbaikalia within last 5 years, the permafrost
temperatures increasing, the reduction of the ground bearing capacity and the permafrost area
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