Types of conditions for karst formation in the USSR // Soviet Engineering Geology (Inzhenernaya Geologiya), 1988. – № 4. – P. 75-81. — Лаборатория геологии техногенных процессов

Summarized are data on the conditions of development of carbonate, sulfate, and salt karst in the USSR, which is characterized by diverse geological and climate conditions. Megatypes of conditions, which are reflected on a map, are identified on the basis of principles used in engineering geological typological zoning according to two indicators: geostructural and climate. Each megatype is characterized by definite principles of karst development, which must be considered in engineering geological evaluation of karst territories.

The economic development of territories where karsting rocks are distributed requires knowledge of the general principles of development of karst within individual regions. for this reason, it is advisable in studying the karst of vast territories to classify the conditions of karst formation determined by a combination of structural lithological and physicogeographic conditions.

Karst phenomena in carbonate (limestones, dolomites, transitional varieties, chalk, marbles), sulfate (gypsums, anhydrites), and haloid (rock salt), deposits from Archean to Neogene and Quaternary are widespread in the USSR, which has a complicated geological structure and covers four climate belts.

The spatial principles of development of karst in the USSR have been discussed by Maksimovich [10], Gvozdetskii [2], Rodionov. [11], et al. Existing schemes for the zoning of karst depending on scale are based mainly on consideration of the geotectonic or structural lithological conditions and do not reflect the entire diversity of modern natural conditions, of karst formation [7,8]. the principles of karst distribution are determined by the conditions and factors which have been created during the course of geological history, mainly the presence of karstlng rocks, their composition, fracturing, and bedding conditions [4]. Karsting rocks are confined to definite geostructural elements of the crust and are subject to geotectonic principles [14].

The development of modern karst is possible only within structures with an active tectonic regime, where as a result of positive movements the karsting rocks turn out to be in a zone of active water exchange. Tectogenesis of the recent stage of development of geostructures finds reflection in the features of the relief (depth of vertical dissection), thickness of the zone of active water exchange, and karsting. for example, the thickness of the zone of active karst formation in carbonate rocks on platforms usually does not exceed 150–200 m, and in mountain fold regions it reaches a thousand m or more, which is favorable for the formation of the deepest cavities (Snezhnyi-Mezhennyi in the Caucasus, Bzybskii ridge, has a depth of 1370 m). All this is reflected in the morphology, hydrogeological and engineering geological properties of karst massifs.

Karst develops in the supergene zone and is related to exogenic processes which depend on physicogeographic, particularly climate conditions (heat and moisture relationship). Karst is confirmed as an exogenic process on plains (platforms) by latitudinal zoning and in mountains by altitude zoning.

Thus, karst is caused not only by azonal structural geological (tectonic, controlling the distribution of karsting rocks of different age and composition), but also zonal climate conditions. in identifying the major conditions of karst formation we must consider these two groups of conditions, which may be done based on the principles applied in engineering, geological typological zoning [12, 13]. the authors of [5, 6] carry out engineering geological classification of territories with consideration of two groups of factors (geostructural and zonal geological), using a two-stage cross classification with two independent systems of taxonomic units.

Fоr conditions of karst formation in large first-order regions of the geostructural series, geostructures of different age with different types of tectogenesis of the recent stage of development are applied [9]: 1) continental platforms, i.e., relatively stable regions with predominance of weak long-term uplifts; 2) orogens with rapid differentiated recent movements of significant amplitudes. According to the age of the folded base the platforms are divided into ancient Archean-Early Proterozoic (I) and young epi-Paleozoic (II); orogens are divided into Baikal and Salair zones, formed mainly in the Vendian and Lower Paleozoic (III), Paleozoic or Caledonian and Hercynian (IV), Mesozoic-Early Cenozoic (V), and Late Cenozoic or Alpine (VI) folding.

Table 1 Megatypes of Conditions of Karst Formation in the USSR

Climate bells	Geostructures
	Platforms with weak N-Q uplifts		Orogens with active rapid N-Q uplifts
	I	II	III	IV	V	VI
Arctic A	—	—	—	TM	AO	—
Sub arctic B	SB	—	—	PN	KO	—
Temperate С	SB, RS	TU	TB	UR, KZ, AS, DU, NT	PR, SK	CC, CA, CR
Subtropical D	—	—	—	ST		TC, KD
Note. Dash indicates regions where karsting rосks are absent

Each of these geostructures is characterized by definite geological conditions of karst formation, which reflect the states of its development: age and composition of karsting rocks, their dislocation, forms of bedding and outcroppings, and relationship with nonkarsting rocks. for example, on ancient platforms karst is developed in carbonate, sulfate, and to a lesser degree salt rocks of the sedimentary nappe, bedded within gently sloping platform structures. Relatively weak recent uplifts were reflected in the shallow erosion dissection and comparatively thin zones of active karst formation. the change of the tectonic regime in the course of the long geological history was establishes in the presence of karst formations of different age, which may be related to different types of minerals. Modern karst appears in zones of active water exchange of large artesian basins.

In orogens (mountain folded regions of different age) with active recent movements karst is formed in highly dislocated, primarily carbonate rocks which are complicated by faults and are bedded within deeply dissected hydrogeological massifs with a thin zone of active water exchange and karst formation.

Geostructure with favorable geological conditions for karst formation are situated in different climate belts, which determine the relationship of heat and moisture: from severe arctic in Taimyr and Islands of the Arctic Ocean to desert subtropical in the southern part of Central Asia [1]. in the arctic, subarctic, and partly moderate (taiga regions of East Siberia) belts karst appears under conditions of development of permafrost rocks. Most of the territory of the USSR occupies the temperature belt with, sufficient moisture, represented by diverse landscape zones. Dry subtropical climate (100–200 mm) precipitation a year is favorable for the development of karst. the amount of atmospheric precipitation and their distribution in time, which determine the conditions of Supply and regime of karst water of the zone of active water exchange have influence on the intensity of karst and its change with respect to seasons.

Thus, as zonal units climate belts can be adopted: arctic (A), subarctic (B), temperate © and subtropical (D). as a result of the combination of Indicators of geo-structural and climate series we identify megatypes of conditions of karst formation (Table 1) by analogy with engineering geological megatypes of territories [5, 6].

The megatype is defined as the geostructural region with a certain regime of Neogene-Quaternary movements, which are reflected in the relief, within which the ancient and modern karst controlled by climate conditions are reflected in the karsting rocks. Based on a geological map on a scale of 1.10.000.000 [3] we compiled a schematic map of the distribution of carbonate, sulfate, and salt karst in the USSR, which shows the megatypes of conditions of karst formation (Fig. 1). it is a fundamental map, which reflects the main conditions for the development of karst and may be used to identify mesotypes and types of karst territories in more detailed, investigations. the selection of classification units and the establishment of boundaries between them at all levels involve great difficulties due to the insolubility of many problems in geotectonics and physical geography.

Fig. 1. Megatypes of conditions of karst formation. Lithologlcal varieties of karst: 1) limestone and dolomite, 2) Cretaceous, 3) gypsum-anhydrite, 4) salt, 5) boundaries of structures, 6) boundaries of climate belts, 7) mega-types (see text for names).

Represented in the territory of the USSR are the following megatypes of conditions of karst formation (Table 1): Ib and Ic) Siberian Platform (SB): Ic) Russian Platform (RS); IIc) Turanian Plate (TV); IIIc) Transbaikal (TB); IVa) Taimyr (TM); IVb) Paikhoi-Movaya Zemlya (PN); IVc) Ural (RU); Kazakhstan (KZ); Altai-Sayan (AS); Daurskli CDU); Northern Tien Shan (NT); IVd) Southern Tien Shan (ST); Va) Islands of Arctic Ocean (AO); Vb) Kolyma-Omolon (KO); Vc) Primorskii (PR); Sakhalin (SK); VIc) Caucasus (CC), Crimea (CR); Carpathian (CA); VId) Transcaucasus (TC); Kopet-Dag (KD).

The typological approach to the study of karst opens broad possibilities for generalizations, since it presumes obligatory consideration of both regional geostructural and zonal physicogeographic conditions. Each megatype reflects the conditions of karst formation and is characterized by definite, principles of development, of karst, whose knowledge lets us predict the karst process and consider its influence on other components of the geologilcal environment and human economic activity.

REFERENCES:

Atlas of the USSR [in Russian], Giavnoe Upravlenie Geodezii i Kartografii pri Sovete Ministrov SSSR, Moscow, 1984.
N. A. Gvozdetskii, Karst [in Russian], Mysl, Moscow, 1981.
Geological Map of the USSR. Scale 1.10.000.000 [in Russian], VSEGHI, Moscow, 1975.
K. A. Gorbunova, Gypsum Karst of the USSR [in Russian], Perm, 1977.
S. B. Ershova, Typological engineering geological zoning of the Earth, in: Tectonic Foundations of Engineering Geology. Geological Foundations, Edited by E. M. Sergeev [in Russian], Nedra, Moscow, pp. 312–321, 1985.
S. B. Ershova and E. M. Sergeev, Features of engineering geological typological zoning of the Earth, in: Problems of Engineering Geology and Soil Science [in Russian], Izd-vo MGU, Moscow, no. 5, pp. 289–303, 1983.
Engineering Geology of the USSR. Russian Platform [in Russian], Izd-vo MGU, Moscow, vol. 1, 1978.
Karst of the Par East [in Russian], Izd-vo DNTs an SSSR, Vladivostok, 1980.
N. I. Nikolaev, Editor, Map of Recent Tectonics of the USSR and Adjacent Regions. Scale 1.5.000.000 [in Russian], VSEGEI, Moscow, 1979.
G. A. Maksimovich, Tectonic principles of karst distribution in the USSR, in: General Problems of Karst Studies [in Russian], izd-vo an SSSR, Moscow, pp. 40–54, 1962.
N. V.Rodionov, Karst of the European USSR, Urals, and Caucasus [in Russian], Gosgeoltekhizdat, Moscow, 1963.
V. T. Trofimov, Zoning in engineering geology, in: Theoretical foundations of Engineering Geology. Geological Foundations [in Russian], Edited by E. M. Sergeev, Nedra, Moscow, pp. 294–299, 1935.
V. T. Trofimov,. «Principles and. indicators of engineering geological zoning», in: Theoretical Foundations of Engineering Geology. Geological Foundations [in Russian], Edited by E. M. Sergeev, Nedra, Moscow, pp. 299–312, 1985.
K. A. Gorbunova and N. G. Maximovich, Typological zonation of karst in the USSR, Communication Nine, Congreso Internacional de Espeleologie, Barcelona, vol. 1, pp. 191–193, 1966.