книги / Минерально-сырьевые ресурсы Пермского края

by the end of that period the sea was preserved only in the Western-Urals zone. After the continental break in the Zhivetsky age, Vorobievskaya, Ardatovskaya and Mullinskaya transgressions of the sea took place, which caused the alternation of sandy and sandy-aleurite collectors and clayey covers. After the continental break in the late-Vendian epoch the sedimentation started with the formation of allite rocks and oolites of ferruginous ores, and then of ter­ rigenous early-Franian sediments with the forma­ tion of the regional Timan clayey cover. From the late-Timan period the radical reformation of the structure plan of the sedimentary basin took place. The formation of the Ponomarev basin of the KamaViatka system of the uncompensated basins with the existence of Domanik (bitumen-bearing) sediments and edge reefs had started. In the middle-Franian period the transgression of the sea increased. Un­ compensated troughs of the Kama-Kinel and Ut- kinsk-Serebriansk systems of the uncompensated troughs of the late-Devonian — Turney paleo-shelf with reefogeneous masses along the edges and oil- and-gas mother bituminous ciliceous-clayey-car­ bonate shales (domanik type) inside these troughs started to form in the initial stage. The Kama-Viatka system of troughs was compensated.

Among those inter-formation troughs the reefo­ geneous paleo-plateaus were formed, isolated by the system of «branches» and narrow fluvial down-cut­ tings of paleo-rivers, along which the terrigenous material was transported from Syssolsk-Komi-Per- miatsky paleo-land in the direction of the Urals, becoming more fine-grained. As a result, the KamaViatka basin was soon planated, and in the Urals, in the Utkinsk-Serebriansk depression the thin-lami­ nated rocks with a composition analogous to stin­ king roofing shale of the European schtassfurt-car- bonate of zechstein were formed. At the Famen age, the sea shoaled and gradually stepped back to the southeast. The strengthening of the land denudation led to the beginning of the compensation of depres­ sions by the terrigenous-carbonate sediments, and younger Famen reefogeneous bodies were placed closer to the central parts of those structures.

The Carboniferous period of the territory deve­ lopment is subdivided into the early-, middleand late-Carboniferous epochs.

At the Turney age of the early-Carboniferous epoch, the development of the Famen-Turney and Turney reefs along the edges of intraformational de­ pressions and the gradual compensation of these de­ pressions by carbonate-terrigenous and terrigenous sediments was generally completed. At the end ofthat

age, the Kizcl regressive phase of sedimentation process started. At the Vizey age the uplifting of the whole territory occurred, along with the long phase of sti uggle between sea and land, lasting till the T ula lime . The polv-facies character of the Raday terrige­ nous sedimentation led to the later formation of coal deposits andoil-and-gas formation. In the late-Vizey period of the sedimentation conditions changed sharply, because of the transgression of the Tula sea in the north-western direction. The sea expansion alter the Tula time strengthened in the direction of Syssolsk-Komi-Permiatsk land. In the Serpukhov time, the sedimentation situation was preserved, but the sea shoaled and at the end of the period it re­ mained only in the Western-Urals in the Chussovaya river area.

The beginning of the Bashkir age of the middleCarboniferous epoch was characterized by the exi­ stence of eroded and karsted territory almost on the whole western platform part. But in the North-Kelt- men time, new sea transgression invaded from the south-east, which in the late-Bashkir period, even covered the area of the well 18 (Ust-Chernaya settlement) in the northern-western part of Perm Krai territory. At the end of the Bashkir age, at the Melekess time some uplift of the territory and the increase of tectonic activity took place. The Mos­ cow development period started with a short break in sedimentation, as in the basement of the Verey limestones along with pebbles and conglomeratebreccias, there were the interbeds of red-brown, yellow-grey, black and green clays with inclusions of anhydrite and silicon. The material was trans­ ported from Syssolsk land and Ksenofontovo area. The maximum transgression of the sea happened at the Kashir time. The late-Moscow time of develop­ ment is characterized by the inherited regime of sedi­ mentation of the limestone and dolomite silts in shallow water of the sea. The Upper-Kama basin acquired the submeridional trend with an axis from Gayny area (north) to Glazov area (south). The Sverdlovsk part of the Pre-Ural depression started to expand in continuously-discontinuously mode to the north and to the direction of the platform, with a formation of Myachkovsky algal reefs, which were substituted by carbonate-terrigenous and ter­ rigenous rocks to the east.

The late-Carboniferous epoch of the geologic de­ velopment was characterized by further shoaling and salting of the sea. All over the territory of Perm Krai dolomites with inclusions of gypsum and anhydrite predominated among carbonates, in the north-west they were added by clays. In the south-east of the

Juruzan-Sylva basin reofa^rnous processes, inclu­ ding the formation of basements of the Duvan reefs and substitution of c a rb o n ate-reefogenous rocks by the formations of a « te r rig e n o u s wedge», advanced further north and west The end of the Moscow — late-Carboniferous period in the Middle Preduralie was marked with the beginning of the final stage of the Hercynian tectogenesis, connected with the ac­ tive formation of the Urals folded system and PreUral depression or by convention mistakenly called «foredeep».

The Permian — early-Triassic stage of the terri­ tory development was characterized by the most ac­ tive manifestations of the final stage of the Hercy­ nian tectogenesis. During the Assel age the dolomite silts were deposited in the shallow sea water to the west from the line Kueda — Ossa — Nytva —Gainy, to the east they were interbedded with calcic ones. In the eastern Prikamyie, the sea basin was more bathypelagic; so mostly carbonate sediments were formed in it. On the eastern edge of the carbonate enclosing rock the Duvan reefs were formed in the Sylva basin, further eastward — the rocks of the «terrigenous wedge» with Chigishansk reefogenous shoals. The terrigenous material was transpor­ ted from the Urals cordillera. During the Sakmar age the sea basin deepened. To the east, from the line Gainy — Krasnokamsk — Kueda up to the Tulumbassov (in the south) and Tunegov and Akchim (in the north) reefogenous structures (normally of biostromes’ type) of terrigenous silts accumulated. To the west of that line in the sea shallows lime-dolo­ mite silts accumulated, and further westward — dolo­ mite ones. To the east from the reefogenous-carbo- nate enclosing rock at first, as a rule, domanikoid bituminous shales of low thickness were formed, which were substituted by more and more thick coarse-fragmental flysch-molassa rocks of the «ter­ rigenous wedge» to the east. During the Artin age the facies situation of the sedimentation was com­ plicated. Further expansion of the Pre-Ural depres­ sion onto the platform took place, with an advance of the Sylva-Sargin reefs’ development zone to the west and a corresponding migration of the develop­ ment zones of domanikoid facies (the Divia suite) and the «terrigenous wedge». To the west, from reefogenous-carbonate enclosing rock, lime silts ac­ cumulated, and further westward dolomite and car­ bonate-sulphate ones accumulated due to the shal­ lowing of the sea. By the end of the Artinsky age the Pre-Ural depression has shaped into position clo­ se to the modern one. Due to the already started process of a subduction of the Russian and the

Western-Siberian plates of the earth’s crust and an underthrust of the first one onto the second, an obduced part of the Pre-Ural depression was crumpled into linear folds of the Urals type with the formation of thrusts and overthrusts, mainly developed in the area of lateral saddles that separated the depression into the Verkhne-Pechyora, Solikamsk, Sylva andJu- ruzan-Ay (in Bashkortostan) basins. This depres­ sion had the facies-sedimentary nature caused by a large thickness deficit of the upper-Carboniferous- Assel-Sakmarsko-Artinsk sediments in its central part, as compared to the carbonate-reefogenous en­ closing rock of the Russian plate and the area of the «terrigenous wedge» development. During the Kungur age, the basins of the Pre-Ural depression were composed by the deposits of evaporite formation.

The late-Permian epoch was characterized by the accelerated transition to the continental mode of sedimentation. In the Ufa and the Kazan times, the continental lake-river conditions of sedimenta­ tion prevailed, while during the Tatar age a tecto­ nic mode inversion took place. The continental val­ ley was more depressing not in the eastern, but in the north-western areas at the place of Syssolsk- Komi-Permiatsky paleo-land, i.e. within the KomiPermiatsky buried arch. In the early-Triassic epoch, the Urals suffered further upliftimg. And in the arid climate, sedimentation take place only in the upper reaches of the Kama river in the Ind and the Oleneck ages.

At the end of the Hercynian cycle, the heteroge­ neous Upper-Kama basin, the Perm-Bashkirian arch, the Pre-Ural depression and the folded Urals ac­ quired their modern contours. The Meso-Cenozoic cycle was characterized by the strengthening of the tectonic movements in the Urals, especially in the late-Triassic and the early-Jurassic epochs. The plat­ form tectonics and Pre-Ural depression took the fi­ nal form. On the platform the transgression of the sea renewed in the Cellovey age of the middleJurassic epoch and developed in the north-west area of Perm Krai during the early-Cretaceous epoch, while the late-Cretaceous epoch was characterized by regression. In the Paleogene the development mode was inherited. Neotectonic movements star­ ted in between the Miocene and the Pliocene pe­ riods. Taking into consideration the depths ofthe flu­ vial down-cutting and mountains heights, their am­ plitudes reached several hundred meters and some­ times could exceed 1000 m (Narodnaya — 1894 m, Sablia — 1425 m). The relief formation of the terri­ tory’s northern part has been greatly influenced by terrigenous sediments, connected with repeated

Quaternary glaciation. The southern border of the maximum glaciation was located slightly to the north of the towns of Lysva and Krasnokainsk. The inheri

lance of the neotectonic movements has been ob­ served on the Kama, the Perm-Bashkirian arches and the Ufa plateau.

According to hydrogeological zoning, the wes­ tern territory of Perm Krai belongs to the EasternRussian and Pre-Ural composite basins of bed wa­ ters, while the eastern part of the region belongs to the Bolsheuralsk composite basin of crustal-block (bed-block) and bed waters.

The ground waters of the Eastern'Russian and Pre-Urals composite basins of bed waters belong to two hydrogeodynamic stages: the upper and the lo­ wer, and the border between them is the regional Iren aquiclude.

The upper hvdrogeodynamic stage is Quaternary alluvial local weak aquifer, which is 5—15 m deep, reaching 30—50 m and more only in the Kama river basin. The chemical composition of the ground wa­ ter is H C 03-Ca, Mg-Ca, and more rarely Na-Ca. The water is fresh, with the mineralization of 0.2— 0.5 g/dm3. In favourable conditions a construction of infiltrating water intakes with a capacity of 1 — 3 thou m3/day is possible.

The water-permeable Dneprovsky fluvioglacial local aquifer is spread in the northern section of Perm Krai. It is connected with fluvioglacial sands with the thickness from 1—2 to 10—40 m. The wa­ ter of the horizon is used for water supply of rural settlements. The water extraction is made by wells.

The water-bearing middle-upper-Jurassic terri­ genous complex is spread in the west and north-west of Perm Krai and is composed of sands, pebbles and sandy clays, with interbeds of aleurolites, up to 65 m thick. Waters of the complex are sub-head, rarely open-flow (without head). They are bedded 3.3—74 m deep, more often 20—30 m deep. The dis­ charge of the wells is 0.03—2.0 1/s. The waters are fresh with the mineralization up to 0.5 g/dm3; H C 03 and Cl-H C03with mixed cation composition. The complex is promising for water supply. ..

The aquiclude local weak water-bearing lowerTriassic terrigenous complex is developed in the west and north-west of Komi-Permiatsky Okrug, in the upper reaches of the Inva, Kossa, Vesliana rivers. Clayey rocks are predominant in the section. The thickness is 40—140 m. Ground waters are tapped with wells at the depths of 0.5—98 m. The waters are open flow and sub-head. Discharge of the wells varies from 0.008 to 0.5 1/s. The predominant chemical composition is H C 0 3-Ca, Mg-Ca, ra­

rely C1-HC03 waters with the mineralization up to 0.5 g/dm3. The waters of the complex may be used for Avater supply.

The weak water-bearing local water-bearing Ka- zan-Tatar aleurolite-sandstone complex is spread in the west of Perm Krai in the form of the meridional stripe. Sub-surface waters developed above the lo­ cal base level of erosion, are mainly H C 0 3 (rarely Cl-HC03and S 0 4-C1-HC03) with the mixed cation composition (Na-Mg-Ca, Mg-Ca-Na, rarely Mg-Ca and Ca-Mg). H C 03-Na waters with the mineraliza­ tion of 0.5—0.8 g/dm3 are also widely spread. Below the local base level of erosion along with waters of 1 g/dm3 mineralization, Cl and S 0 4-C1 sodium wa­ ters with the mineralization from 1.2 to 19 g/dm3 are widely spread. The depth of occurrence of fresh wa­ ters at water-sheds is 100—150 m and more, in the river valleys it is 20—40 m and less. The subsurface waters of the complex are used for domestic-drink­ ing water supply. Five ground-water basins were prospected.

The aquiclude local water-bearing Kazan-Tatar clayey complex is represented by clayey rocks. The thickness of the complex is 100—150 m. The waters are of both types open-flow and sub-head. The com­ plex is not rich in water and is unpromising for the water supply.

The weak water-bearing local aquiclude KazanTatar terrigenous complex unites generally terrige­ nous deposits bedded 100—150 m deep. The thick­ ness varies from 0 to 300—350 m. Sandstones, aleu­ rolites, conglomerates are the water-bearing sub­ stances, clay and argillites are the aquiclude ones. The filtering properties of rocks are low. Subsurface waters belong to the crack-bedded sub-head type. The com position is chloride-sodium rarely Cl-S04-Na occurs. Due to the high mineralization, the subsurface waters of the complex are unpromi­ sing for domestic-drinking water supply but can be used as mineral waters.

The low w ater-bearing local-w ater-bearing Sheshmin terrigenous complex is developed as a stripe of meridional trend from 10 to 60 km wide. It is represented by thick (80—340 m) heterogene­ ous thickness of red and multi-coloured gypsumed rocks. Sandstones are the main water-enclosing rocks. On the territories where the complex is cut by

C l-S 0 4 waters with différent cation composition zi:d the mineralization 1—3 g/ dm1term, which have Iven substituted by SCVC1 and Cl water with mineraliza­ tion over 5 g/dm 3at lower depths. Suite subsurface waters are used for the water supply of small settle­ ments and agricultural objects.

The water-bearing A ssel-A rtin lerrigenous complex is characterized by the facial-inconsislency of interbeds. Interbeds and lenses of conglomerates, sandstones, rarely of marls, limestones, water-proof clays, aleurolites and unfractured varieties ol sand­ stones are water-bearing, clays, aleurolites, unfrac­ tured varieties of sandstones are aquiclude. In the upper part of the section crack-subsurface waters are developed, and lower sub-head and open-flow crack-bed and crack-karst waters are developed. The chemical composition of the subsurface waters are НСОз-Са, Na-Ca, Mg-Cawith the minerali­ zation of 0.4 g/dm 3. More rare one can find S0 4-НСОз-Са mixed waters with mineralization up to 0.5 g/dm3. The complex waters are used for the water supply of agricultural objects and small settle­ ments.

The water-bearing local weak water-bearing low­ er-Permian carbonate series comes to the surface in the dome of the Perm-Bashkirian arch. It is com­ posed of limestone and dolomites and to the west is submerged under the Iren sediments. The Phillipov and Atrin carbonate sediments are more irrigated. Water-abundance and the filtering characteristics of rocks are accounted by their being fractured and karsted. Close to the surface subsurface waters have the mineralization of 0.3—0.5 g/dm 3, rarely it reaches 1.0 g/dm3. The chemical composition of the waters is H C 03-Mg, Ca, Ca-Mg. When the water­ bearing rocks plunge under the Iren gypsums, the water mineralization rises to 3.0 g/dm3 and more, and the water composition changes to SO4 and CI-SO4, hydrogen sulphide appears. The subsurface waters of the series are used for domestic-drinking water-supply.

Lower hydrodynamic level. Six oil-gas- and wa­ ter-bearing complexes (OGWC) can be distinguished in the zone of rather hard water exchange in the Paleozoic section: the upper-coal lower-Permian water-bearing complex of mainly carbonate rocks; the Moscow carbonate-terrigenous upper-Vizey- Bashkirian carbonate; the lower-middle-Vizey ter­ rigenous; the upper-Devonian-Turney carbonate; middle-upper-Devonian terrigenous (see «Oil and gas» section). The most common hydrodynamic properties of the OGWC are the hydrostatic chan­ ges of bed pressures, which depend on the depth, and

lb ai is the evidence of the hydraulic unity of the whole water-saturated section. An analysis of pie- zomciric maps demonstrates the lack of regional '.--'■■insit rio\v directed from the classic regional areas ■ v b-cc ’o i lie relief areas. The local trend of internal

cy 01 fhc npgoing brines’ movement has been pre­ dominated by head gradients along a vertical line from 1.9'ÎO'3to 7.9-10-1. The main hydrochemical regularities of the OGWC are identified by the mine­ ral-geochemical composition of the medium (rocks and sedimentation waters) and conditions of hydrodynamic interaction with the water-bearing horizons (water) levels. The practical significance studying the OGWC is connected with the existence of oiland gas-bearing, industrial water, as well as favourable conditions for distributing the polygons of under­ ground burial of industrial wastewaters and the in­ dustrial gas storehouse/depository (IGS / 1SD). The upper-Vizey-Bashkirian and upper-Devonian-Tur­ ney sediments which have the biggest potential ca­ pacity (paleo-karst geofiltration/geofiltering me­ diums) are considered to be the most likely opera­ tional construction objects for burial polygons. Pos­ sible objects for the organization of the IGS/ISD can be made in the lower-middle-Vizey OGWC.

The Big Urals complex basin of crust-block (bedblock and bed waters,) covers the eastern part of Perm Krai. Tectonically, it relates to the Western - Urals fold zone and the Central-Urals uplift of the Urals. Ranging from the Proterozoic to the lowerPermian, the subsurface waters are connected with the water-bearing complexes of the fold zones of se­ dimentary, metamorphic and magmatic rocks. With­ in the limits of Perm Krai, on the territory of the fold zone of the Urals there are nine water-bearing complexes.

The Assel-Artin terrigenous water-bearing com­ plex is situated on the western slope of the Urals, along the eastern edge of the Pre-Ural trough. It is constructed of conglomerates, sandstone, aleurolite, and clays with a rare interlayer of limestone and marls. Spring discharges can be up to 0.5 1/s, while in the fold zones it may reach 100 1/s and over. Characteristic spring discharges are 0.1 — 1.71/s, and in the deformed zones it can reach 8.51/s. The che­ mical composition of water is H C 0 3-Ca with mi­ neralization of 0.1—0.4 g/dm3. The organized water supply the expected discharge is 1 —2 1/s with single wells, and up to several liters per second with the water intake series in the fold zones.

The Vizey-Artin carbonate water-bearing comp­

lex is composed of fold ? od к л rsted carbonate rocks. The water level of the rocks :s irregular. The water’s chemical composition is mainly H C 03-Ca, minera­ lization is about 0.2--0.5 g / dm3. The subsurface wa­ ter is used for economic-drinking water-supply of towns, such as Chussovoy, Kizel and various other settlements.

The Western-Urals sporadically watery regional water-proof is spread on the limbs of anticlinal and synclinal structures. The water-bearing structures are the interlayer of sandstone in the bed/formation of argillites, aleurolites and coal shales. The water level of the rocks is low. The complex is not promising for use as an economic-drinking water supply.

The Frank-Turney carbonate water-bearing complex is made up of limestone with subordinate low/power interbeds of fragment rocks. The abun­ dance of water in the complex is irregular. Spring discharges vary from 0.1 to 2001/s. The specific dis­ charges of wells in the zones of rupture deforma­ tion can reach 15 1/s. The complex water is mainly H C 03-Mg-Ca with mineralization up to 1.0 g/dm3. The subsurface water is used for economic-drink­ ing water supply.

The Devonian terrigenous water-bearing com­ plex is composed of sandstone, argillite, aleurolites,

conglomerates, and the clayey and ciliceous shale of the middleand lower-Devonian. It is about 200— 250 m thick, and the water abundance is low. The complex has practically no significance for eco­ nomic-drinking water-supply.

The Ordovician-Silurian carbonate water-bear­ ing complex is composed of limestone. In the water abundant zones the spring discharges are about 200—2501/s. The chemical composition of water is НСОз-Са and Mg, and the mineralization can reach up to 0.2—0.3 g/dm3.The complex is used for watersupply by means of capped springs.

The Ordovician-Silurian terrigenous water-bear­ ing complex is made of sandstone, argillite, aleuro­ lites, conglomerates, clayey and ciliceous shale. There is low water abundance in the rocks. The complex has no practical significance.

The Proterozoic —lower-Paleozoic terrigenouscarbonate water-bearing complex is composed of sandstone, argillite, aleurolites, conglomerates, clay­ ey shale, effusive. The water of the complex has not been used.

The water-bearing complex of magmatic rocks is mainly connected with the lower-Paleozoic intru­ sions of different composition. The complex is not promising for water-supply organization due to the low water abundance and spread.

On the territory of Perm Krai, the geological processes causing karst phenomena have been cont­ rolled by the lithologic complexes and their tec­ tonic situation (the eastern margin/outskirts of the Eastern-European platform, Pre-Ural foredeep, fold Urals). A combination of lithologic complexes and characteristics of tectonic structure defines meri­ dional zones of karst process situations. On the Krai territory, natural karst and its anthropogenous modifications correspond with the territories that spread carbonate, sulphate and salt rocks. In the region, the intensively karsted rocks (limestone, dolomite, gypsum, anhydrite, salt rock) of the ages from the Proterozoic to the upper-Permian come up onto the surface or occur shallowly on the areas over 30 thou km2.

Within the limits of the eastern outskirts of the Eastern-European platform and, adjoining to it, part of the Pre-Ural trough, the gypsum, anhydrite, lime­ stone, and dolomite of the Kungur and Artin levels of the lower section of the Permian system have been mostly karsted. The most intensive karst process is manifested in the limits of arches and limbs of val­ leys, banks and domes. Within the limits of the

Verkhne-Pechyora and Solikamsk depressions in the Pre-Ural foredeep, the thick salt-bearing sedi­ ments of the Kungur level were developed. In the Sylva depression, mainly gypsum has been karsted, to a lesser extent salts, occurring among non-karsted sediments. Within the limits of the Western-Urals fold zone, limestone of the Devonian coal, the Per­ mian system and to a certain extent older rocks have been karsted. Karst manifestations coincide with the rupture deformation zones and with the litholic con­ tacts of limestone and dolomite with non-karsted rocks. In the zone of the Central-Urals uplift, in the development areas of the rupture deformation, the Proterozoic and lower-Paleozoic limestone, dolo­ mite and marble have been karsted.

Karst forms are the result of the karst process manifested in various geologic-hydrogeologic and physical-geographic conditions. They are divided into three main types: surface, subsurface and tran­ sition from surface to subsurface. The most typical representatives of the surface type karst are karr, crater, basins, ditches, broad gullies and valleys. To the transition forms belong ponors, wells. Repre­ sentatives of the underground forms are cavities,

cracks widened with solution and caves ot' dilïerent configurations and sizes. All form types exisl to a certain extent on the karsted territories of Term Krai. Among the underground forms of karst, the cavities and caves have been the most widely spread types. Today over 700 karst caves with a total stretch of 72 km are known in the Krai. Perm Krai is not only a significant region in which the classic litho­ logic karst types’ develop (carbonate, sulphate and chloride). It is also the territory in which carbonate cement leaching in terrigenous rocks manifests, where specific karstogenous deposits like karst

breccias, karst-collapsed have been widely spread. Quite often they are considered to be an indepen­ dent karsting bed. In the territory o f Perm Krai, the biggest spread, in terms of area, has breccias formed in the conditions of oscillation zones of the sub­ surface waters and zones of horizontal circulation. These breccias have been called «olkhovskye»

Lower Sylva, Iren and Kishert districts. These are­ as of sulphate and carbonate-sulphate types of karst cover 3910 km: of the territory.

Peculiarities of karst development in the carbo­ nate-sulphate shaleose beds of the eastern outskirts of the Eastern-European platform and the adjoining parts of the Pre-Ural foredeep are connected with a relatively intensive solution of gypsum and anhyd­ rite layers in the zone of their contacts with carbo­ nate interbeds. While in the carbonate interlayer one can observe only the development of caverns and secondary porosity.

The distinctions of the physic-mechanical at­ tributes of sulphate and carbonate layers, i.e. their different crack shattering, has defined the develop­ ment of morphologically specific forms of solution in carbonate-sulphate bed. Among them, the unique forms are «organ tubes», vertical canals of a cylind­ rical form with a diameter up to 1—2 m. They are often connected with collapsed craters on the thick rock surface. The width of «organ tubes» is defined by thickness, the strength and fracture level of car­ bonate and sulphate interbeds, and the hydrogeolo­ gical conditions of vertical downcast circulation of fracture-karst waters.

Neither along the section nor at the trend has the carbonate-sulphate bed been karsted regularly. That is connected with the properties of the discharge of subsurface water, which has a confined type. The result of the discharge distribution properties is the

existence of dry pillar, whose central part has not been practically affected by the forms of subsurface solution. The carbonate layers, whose mechanical properties are more rigid, overlapping easily solu­ ble sulphates, have formed relatively strong arches over the cavities. That creates the possibility that these cavities will develop into large sizes, often with a diameter over 5 m. As soon as cavities have achieved critical sizes the stability of carbonate arch is decreases. So it falls down and forms karst gap on the surface.

In the areas where sulphate stratums have been directly overlapped by fragment, clayey-fragment or the sand-gravel sediments of the Cenozoic, the for­ ming of cavities has coincided, in the contact zone, with coverings, but inside the stratum the karst forms have been weakly developed. The intensity of karst formation and the morphological properties of the karst forms depend on the covering lithology, their penetrability and their thickness.

In a specific geological situation, a place con­ tains fracture karsted rocks which occur under the bed of water-permeable dispersed accumulations mainly of alluvial genesis. Such areas are the pla­ ces of classic manifestation of the sub-alluvial («kamsky» according to G. A. Maximovich) karst type.

Tectonically, the territory of karst manifestation corresponds with the arch ofthe Ufa billow. Geomorphologically the area takes the area of the Ufa bil­ low with the absolute relief marks at 250—300 m,

and has undergone uplift from the late-Paleogene. Deep river valleys and ravines have divided the pla­ teau surface.

The active water-change zone is represented by