Relationship Between the Lithology of Active-Layer Materials and Mean Annual Ground Temperature in the Former Ussr

RELATIONSHIP BETWEEN THE LITHOLOGY OF ACTIVE-LAYER MATERIALS AND MEAN ANNUAL GROUND TEMPERATURE IN THE FORMER USSR

V.N. Konishchev

Department of Cryolithology and Glaciology, Faculty of Geography, Moscow State University, Moscow 119899, Vorobyovy Gory, Russia. e-mail: [email protected] Abstract

The accummulation of quartz particles within the 0.05-0.01 mm grain size fraction and of the feldspar particles within the 0.1-0.05 mm fraction due to freeze-thaw was confirmed by experimental data and laboratory investigations of cryogenic soils. A cryogenic weathering index (CWI) is proposed to estimate the role of cryogenic weathering in soil formation.

The general zonality of the CWI has already been defined. This permits one to express more precisely the relation between CWI values and mean annual ground temperature. This is obtained for different geocryologi- cal conditions.

Introduction the dimensions of the microfractures and defects that characterize the surface of mineral particles. Various types of stability coefficients, expressed as the Detailed study of cryogenic disintegration allows one ratio of stable to unstable minerals, are widely used as to differentiate globally the physical weathering palaeo-geographical indicators (e.g., Gaigalas et al., processes. The special index for cold regions which 1975). From the palaeo-geographical point of view, this characterizes the distribution of major rock-forming ratio reflects the general relation between the processes minerals over the granulometric spectrum is called the of physical and chemical weathering. cryogenic weathering index (CWI). Cryogenic weathering of polymictic source rocks and unconsolidated deposits is associated with strong QF11/ CWI = [1] physico-chemical disintegration of major rock-forming QF22/ minerals and the accumulation of the latter in definite granulometric fractions. where Q1 is quartz content (%) in the 0.05-0.01 mm The accumulation of a) quartz particles within the fraction; F1 - feldspar content (%) in the 0.05-0.01 mm 0.05-0.01 mm grain-size fraction, b) recent feldspar par- fraction; Q2 - quartz content (%) in the 0.1-0.05 mm ticles within the 0.1-0.05 mm fraction and c) biotite par- fraction; F2 - feldspar content (%) in the 0.1-0.05 mm ticles within the 0.25-0.1 mm fraction, due to freeze- fraction. thaw cycles has been confirmed earlier (e.g., Konishchev, 1982; Konishchev and Rogov, 1993). Laboratory results Correlation between the quartz and feldspar mineral distribution in specific grain-size fractions of unconsoli- Previous work (e.g., Konishchev, 1982) upon soils and dated fine-grained sediments in cold (cryogenic) sediments in areas of seasonal and perennial freezing regions was shown to be exactly opposite to the distrib- now allows a more rigorous substantiation of the rela- ution of these minerals in deposits formed under tem- tion between CWI and mean annual ground tempera- perate and warm-climate conditions. The reason for this ture (MAGT). Laboratory experiments reveal the is the protective role of a stable film of unfrozen water. dependence of the cryogenic disintegration rate of vari- This is highest with biotite and muscovite, less with ous minerals upon the temperature regime associated feldspar, and lowest with quartz (Konishchev, 1982). with freezing and thawing (Konishchev and Rogov, Cryogenic disintegration occurs when the thickness of 1983; Konishchev et al., 1983). the protective unfrozen water film becomes less than

V.N. Konishchev 591 Under natural conditions, cryogenic disintegration Relationship between CWI and temperature proceeds in accordance with different ground freezing IN MODERN soils and thawing regimes, and with temperature variation amplitudes. Two series of experiments were carried out The results of the experiments suggest that, under to study the influence of temperature conditions on the natural conditions, there is a consistent relationship cryogenic transformation of unconsolidated sediments between the CWI of sediments in the seasonally thawed of different mineral compositions. and perennially frozen layers, and the mean annual ground temperature. To quantify this relationship, CWI In the first experiments, granulometric mono-mineral values and corresponding mean annual ground tempe- fractions of standard sizes and of different minerals ratures were determined in different regions of seasonal were subject to cyclic freezing and thawing under four freezing and in the permafrost zone (Figure 1). regimes (t¡ = -5¡, +50¡C; t¡ = -10¡, +20¡C; t¡ = -20¡, +20¡C; t¡ = -40¡, +20¡C). The common factor for all CWI values and corresponding mean annual ground these regimes was the temperature transition through temperatures (at depth of 0.4-0.5 m) for 15 regions 0¡ C. within Northern Eurasia are calculated and plotted on Figure 2.

Minerals are clearly divided into two groups with The CWI values characterize structurally differentiat- respect to these freezing-thawing regimes. The first ed taiga soils developed on surface loams in various group is composed of minerals with high surface ener- watersheds within the zone of seasonal freezing: gy (e.g., biotite and limonite). The cryogenic resistance Byelorussia (Minsk region, Poozyorye), Klin-Dmitrov of these minerals is minimal under the most rigorous site, Syktyvkar, Troitsko-Pechersk and Laryak (West regime (i.e., t¡ = -40¡, +20¡C). The second group com- Siberia) Ð Figure 1, Numbers 1, 2, 3, 4, 5, 6. prises minerals with relatively low surface energy (e.g., quartz, magnetite and apatite). The maximum destruc- The CWI values for soils in the permafrost zone were tion of grains of this group occurs under conditions of calculated for tundra-gley and taiga soils of the follow- complete moisture saturation and under probably the ing areas: (a) mainland tundra-(Vorkuta), Kular moun- most optimum regime of freezing and thawing tain ridge (Yana-Omoloy interfluve) (see Figure 1, (t¡ = -10¡ to -20¡ , +20¡C). The minerals that differ in Numbers 7, 8, 9); (b) areas of seasonal thaw-layer: their cryogenic resistance with respect to freeze-thaw Vorontsovsky; Chukochy Yars (see Figure 1, Numbers correspond to the mineral groups identified above. 10, 11); (c) eluvium of sandstone and siltstone- Sovinaya These changes are influenced by the degree of hill, Chukotka; lower reaches of Kolyma River (see humidity. Figure 1, Numbers 13, 14, 15); and (d) soil - eluvium developed in the Pamir highlands (see Figure 1, In the second experiments, a spectrum of granulome- Number 12). tric fractions of different minerals in a humid state was frozen and then subject to cyclic temperature variations CWI values were calculated as an average throughout (t¡ = -1¡, -20¡ C). These investigations aimed to establish the soil profile. The soil thickness does not exceed 50 whether cryogenic transformation took place or not, cm. In all cases, samples for CWI are located within the and what degree of phase translation occurred in active layer (i.e., the layer of seasonal freezing and unfrozen water which was associated with negative thawing). It is important to emphasize that all samples temperature variations. Such experiments help to were taken either from mature soils or from the cryo- reduce to a minimum the influence of the adjoining ice genic weathering crust of stable interfluve surfaces. on particle destruction. The experiments simulate conditions of cryogenic transformation of material during The soils analyzed represent mostly homogeneous the cold period of the year, after the freezing of the silty loams but sometimes include coarse materials active layer when the near-surface permafrost layer can (gravel, pebbles). The correlation between CWI and the also change sharply in temperature due to surface tem- mean annual ground temperatures (at depth of 0.5 m) is perature variations. strong (r = 0.94): the lower the temperature, the higher are CWI values (Figure 2). The most important and general result of this series of experiments is the inference that the cryogenic disinte- Conclusions gration of all minerals, with the exceptions of horn- blende and magnetite, is considerably lower with nega- The increasing severity of cryogenic conditions tive temperature variations than with temperature vari- changes the distribution pattern of the quartz-feldspar ations which involve a transition through 0¡ C. ratio within the sand-silt component of soils. This is the result of two processes: (1) cryogenic quartz disintegration and (2) chemical weathering of feldspars.

592 The 7th International Permafrost Conference Figure 1. Location of main sampling regions (1-15) 1 - podzol soil (Belorussia, Minsk) 2 - podzol soil (Belorussia, Poozyozye) 3 - podzol soil (Klin-Dmitrov site, southern taiga) 4 - podzol soil (Syktyvkar, middle taiga) 5 - podzol soil (West Siberia, Laryak, Northern taiga) 6 - gley- podzol soil (Troitsko-Pechersk, Northern taiga) 7 - peat-gley-soil (Vorgashor, southern tundra) 8 - peat-gley-soil (Vorkuta, southern tundra) 9 - loam eluvium (Kular mountain ridge) 10-tundra-gley-soil (Indigirka river, Vorontsovsky Jar) 11 -tundra-gley-soil (coast of East Siberian Sea, Chukochy Yar) 12-eluvium-solifluction deposits (Pamir mountain, 6200 m a.s.l. Furn Plato) 13-eluvium (East Siberian Sea, peninsula Svyatoy Mys) 14-eluvium (East Siberian Sea, peninsula Shyrokostan) 15-eluvium (Lower reaches of Kolyma River) A lowering of the mean annual ground temperature face. For quartz particles, this limit is 0.05-0.01 mm, for tends to increase the cryogenic weathering intensity. feldspars the limit is 0.1-0.05 mm. This is because the This leads to the accumulation of quartz particles in the thickness of the protective unfrozen water film on 0.05-0.01 mm grain-size fraction. The mechanism of feldspar particles is higher than on quartz particles. cryogenic disintegration is based on the wedging effect when ice forms in micro-cracks and induces volume An increase in mean annual ground temperate leads widening. This effect is very active in tiny fissures and to an increase in the duration of summer and the corres- channels and leads to the disintegration of particles on ponding intensity of chemical weathering processes in small blocks 10-100 mm in size. Other factors involved the active layer. The processes of chemical weathering in the cryogenic disintegration of particles are: a) cryo- do not affect the distribution of quartz particles in soils hydration weathering and the freezing of water in gas- because of the high chemical resistance of quartz. By liquid inclusions and b) the breakage of particles contrast, the feldspar particles are subject to chemical because of volume increase. These factors are controlled weathering (mostly hydrolysis) in the active layer. In by the layer of unfrozen water, which is smallest on the particular, chemically-weathered feldspars disintegrate surfaces of quartz particles compared with other miner- by cryogenic processes very actively and reach the als. Cryogenic disintegration reaches its maximum smallest grain-size dimensions (Konishchev, 1982). The when the thickness of the protective unfrozen water combination of these processes tends to increase the film becomes less than the dimensions of the fractures quantity of feldspar particles in the 0.1-0.05 mm and defects that characterize the mineral particle sur- fraction.

V.N. Konishchev 593 Figure 2. Relationship between cryogenic weathering index and mean annual ground temperature (tgm). The numbers are identical to those in Figure 1. Thus, the lower the temperature, the higher is the con- lose their mineral individuality. This relationship is also centration of quartz and feldspar grains in the 0.05-0.01 valid for non-saline soils and sediments. and 0.1-0.05 mm size fractions, respectively. Acknowledgements This basic relationship between CWI and mean annual ground temperature is true for all polymict sedi- The author gratefully acknowledges financial support ments characterized by a predominance (up to 80-90 %) from Russian Science Foundation (grant 97-05-64283) of quartz and feldspars within their mineral composi- and state support of Russian leading scientific schools tion. This conclusion is supported by observations in (grant 96-15-98457). The author also thanks Professor the northern part of the zone of seasonal freezing and in Hugh French (University of Ottawa) for substantial the permafrost zone, both areas where chemical wea- help in rewriting and editing this paper. thering of minerals is not strong and feldspars do not

References

Gaigalas, A.I., Karpukhin, S.S., Paramonova, N.N. and Konishchev, V.N. and Rogov, V.V. (1993). Investigation of Sudakova, N.G. (1975). Marine-lake deposits in the Cryogenic Weathering in Europe and Northern Asia. periglacial zone. Biuletyn Periglacjalny, 24, Lodz, 7-23. Permafrost and Periglacial Processes, 1, 49-64. Konishchev, V.N. (1982). Characteristics of Cryogenic weath- Konishchev, V.N., Rogov,V.V. and Kolesnikov, S.F. (1983). ering in the Permafrost zone of the European USSR. Arctic Investigation of main factors and mechanisms of cryogenic and Alpine Research, 3, 261-265. transformation of minerals. In Problems of Geocryology. Nauka Press, Moscow, pp. 56-65 (In Russian). Konishchev, V.N. and Rogov, V.V. (1983). The cryogenic evo- lution of mineral matter (an experimental model). In Proceedings of the Fourth International Conference on Permafrost. National Academy Press Washington, D.C. pp. 656-659.

594 The 7th International Permafrost Conference