PROCEEDINGS
OF THE TOMSK ORDER OF THE RED BANNER OF LABOR POLYTECHNIC
Vol. 65, issue 2          INSTITUTE named after S. M. KIROV          1950

MATERIALS ON THE STRATIGRAPHY AND TECTONICS

OF NORTHWESTERN ALTAI

Yu. A. KUZNETSOV

General plan of the structure of Northwestern Altai

The region of Northwestern Altai represents, in tectonic respect, a very interesting area where the structures of Gorny Altai and Rudny Altai join. The boundary between these structures may be drawn along the course of the Loktevka River and the headwaters of the Belaya River.

The northeastern part of the region described, which in its features may be assigned to the structure of Gorny Altai, is composed mainly of sandy-shaly strata of the Lower Ordovician, gathered into steep folds of variable strike and strongly schistose; moreover, the variability of strike is evidently due chiefly to the reconstruction of its main folds in connection with later movements. On the eroded surface of the Ordovician, in synclinal downwarps, limestone-shaly strata of the Gothlandian have in places been preserved; on the map they appear partly as irregular patchy spots (the Ini River basin) in the case of gentle structures, and partly as compressed synclines elongated in a northwestern direction. Somewhat apart stands the broad Kuryinsky–Maralikhinsky synclinal structure, composed of deposits of the Upper Ordovician, Gothlandian, and Devonian.

The southwestern part of the region is a component part and the northern continuation of the Rudny Altai graben [8; 2; 12; 13]. This sector is distinguished by the complete absence, in the stratigraphic section, of Gothlandian deposits and by the wide development of Devonian and Lower Carboniferous strata. Only here is there a massive development of porphyry intrusions of the Zmeinogorsk complex. In the southern part of this sector, south of the Savvushinsky granite massif, a broad anticlinal structure of northwestern strike is clearly outlined; its core is composed of metamorphic strata of the Lower Ordovician (the Kembrosilurian, according to Nekhoroshev) and is intruded by an enormous pluton of Alei plagioclase granites, while the limbs, complicated by a number of additional folds, are composed of Middle and Upper Devonian and Lower Carboniferous. The structure of the area north of the Savvushinsky pluton is unclear because of poor exposure and intense schistosity of all formations. Here a broad Devonian synclinal structure is indicated in the area of N. Firsova, with an axis plunging to the north, and an anticline of northwestern direction, composed of Lower Ordovician beds, passing approximately through the village of Ivanovka. Attention is drawn to the fact that the structure of Rudny Altai is considerably more saturated with intrusive bodies than the structure of Gorny Altai.

The structures of Gorny and Rudny Altai, as has long been known [2; 12; 13], are separated from one another by a powerful disjunctive, known in the literature under the name of the “Talovka–Ulba thrust” [2], accompanied by a broad “northeastern zone of crumpling” [12]. According to the data of Bublichenko and Nekhoroshev, the Talovka–Ulba thrust passes from the basins of the Ul-

ba and Uba via the upper reaches of the Belaya and Loktevka rivers to the Talovka River and the village of Ivanovka. The author’s investigations have shown that in the Ivanovka area there are indeed several zones of crumpling, trending northwest within the sandy-shaly sequence of the Lower Ordovician, but the principal dislocation, bringing formations of very different ages into direct contact, runs along the Loktevka River as far as the village of Kurya, where it bends arcuately to the northeast and goes to the Charysh River in the area of the village of Ozerki. It would therefore be more correct to call this disjunctive structure the Loktevka–Ulba thrust. It must be said, however, that its thrust nature is doubtful. As we shall see below, this is a typical “deep-seated fault” in the sense in which this type of structure is understood by Peive [16]. In the area of the village of Kurya, in the zone of the bend, the Loktevka–Ulba “thrust,” or, more correctly, “deep-seated fault,” branches into numerous individual faults, interconnected with one another, which accounts for the exceptionally complex scaly structure of this sector. The complex and not always clear character of movements along this zone has brought into direct contact the crystalline Precambrian limestones, Ordovician and Gotlandian sandstones and shales, Upper Devonian effusives, and even Lower Carboniferous limestones. The Loktevka–Ulba deep-seated fault, chiefly on the side of the Rudny Altai graben, is accompanied by a broad zone of crumpling, within which all sedimentary rocks are intensely foliated in a northwestern direction, while the igneous rocks have undergone the strongest cataclasis. At the latitude of the village of Kurya, the direction of slaty cleavage fanwise diverges and, in the zone adjoining the fault suture, smoothly changes its strike to northerly and then northeasterly.

From the southwest the structure of Rudny Altai is separated from the structure of the Kalba Range by the analogous “Irtysh thrust” [2],¹ accompanied by the “Irtysh crumpling zone” [13].

The Kurya–Maralikha syncline is truncated from the south by a clearly expressed broad disjunctive structure (the Semenov thrust of Bublichenko) [2], which, having been established earlier than the Loktevka–Ulba one, is clearly cut off by the latter. In addition to these principal dislocations, which determine the general structural plan of the entire region, a large number of small faults, as well as small zones of crumpling, are recorded.

Stratigraphy of Northwestern Altai

Precambrian

Until very recently, the question of the presence of the Precambrian within Northwestern Altai was not only called into doubt by the overwhelming majority of geologists who worked here, but was also resolved in the negative in the most categorical form [12]. However, more detailed investigations of recent years compel a change in these customary views. As a result of investigations in 1942–43, the author distinguished the Belorechenskaya Formation, consisting of gray shaly marbles and interbedded phyllites, which has been traced along the Loktevka River south of the village of Kurya in the form of a comparatively narrow tectonic wedge, pinched in the zone of the Loktevka–Ulba deep-seated fault. In degree of metamorphism, peculiarities of internal tectonics, and complete absence of fauna, the Belorechenskaya Formation differs sharply from the Upper Silurian deposits, generally speaking similar in lithological composition and forming similar wedges in the same tectonic zone. The ancient age

¹ Probably also a deep-seated fault, judging from the considerable difference in the Paleozoic stratigraphic columns of Kalba and Rudny Altai (Yu.K.).

the Belorechensk formation is proved by the presence of pebbles of gray schistose marbles, characteristic of this formation, in the conglomerates of the Lower Silurian; and since the Cambrian of the Altai is characterized by an entirely different lithological content, the assumption of a Precambrian age for the Belorechensk formation is quite natural, since it bears a striking resemblance to the carbonate-schist sequences of the Precambrian of the Eastern Altai and the Kuznetsk Alatau.

Silurian

Reliable Cambrian deposits are unknown in the northwestern part of the Altai, whereas Silurian deposits are widely developed; among them at least five independent formations are clearly distinguished, separated from one another by tectonic breaks and angular unconformities.

The oldest of the Silurian deposits, belonging to the lower part of the Ordovician, is a thick and widespread sequence that has been described under the name “Cambro-Silurian” and “Lower Silurian” (Nekhoroshev and other geologists of TsNIGRI), or as the zeleno-violet formation [1; 18]. Attempts have been made to subdivide this sequence. Thus, in Nekhoroshev’s works there is described and distinguished on maps: a) Cambro-Silurian (metamorphic suite), and b) faunistically characterized Lower Silurian; at the same time it turns out that the Lower Silurian deposits lie conformably on the Cambro-Silurian, while lithologically they are indistinguishable from one another. Vinkman and later Baklakov [1] subdivide this sequence into a) the zeleno-violet and b) the variegated formations, separated from one another by a tectonic break. The author’s investigations showed that there are no grounds for subdividing this thick and very homogeneous sequence. This sequence, by age belonging to the very lowest parts of the Lower Silurian, is characterized above all by its variegation and consists of thick horizons of sandstones alternating with aleuritic and pelitic shales; among the sandstones horizons of conglomerates are not uncommon, while limestones are exceptionally rare. The aleuritic-pelitic horizons are characterized by green and lilac colors, are always finely schistose and even phyllitized. The sandstones are more massive; the primary coloration is brown, lilac-brown, greenish gray. Poor rounding of the detrital material and its polymictic composition are characteristic. Sandstones with large fragments of platy argillites, which are typical mud-crack breccias [7], are common; Vinkman incorrectly interprets them as conglomerates with pebbles of phyllitized shales. The true conglomerates consist of pebbles chiefly of microquartzites, with admixed pebbles of sandstones, schistose marbles typical of the Belorechensk formation, quartz diorites, microgranites, and quartz albitophyres. Within this variegated sequence, Nikonov [15], in a section along the Bugryshikha, discovered a trilobite fauna, Megalaspis cf. planilambata Ang. and Ampyx, indicating an Arenigian age of the sequence. Another locality with a fauna of poorly preserved brachiopods, trilobites, and corals of Lower Silurian aspect was found on the Gornovka River, 1.5 km below the village of Mikhailovka. The thickness of the described sequence is very considerable and probably reaches several kilometers. It generally lies gently, but is gathered into small folds of the second order, in places open and in places strongly compressed. The strike of the bedding varies in different areas. This sequence has not undergone regional metamorphism and is affected only by slaty cleavage; moreover, only in zones of the most intense cleavage is some metamorphism manifested.

The Kostin Formation, described by the author from the area of the settlement of Batun, belongs to the upper Ordovician. It has been traced as a comparatively narrow band, elongated in a latitudinal direction along the Semenov thrust, and is separated by disjunctive faults on one side from the sandy-shaly sequence of the Lower Ordovician, and on the other from the basic effusives of the upper Devonian. The Kostin Formation is composed mainly of greenish-gray calcareous sandstones and marls with a number of interbeds of sandy limestones and fine-pebble conglomerates. The limestones are sometimes crowded with a remarkably well-preserved fauna of brachiopods and trilobites, among which the following have been identified: Trinodus sp., Homalonotus sp., Telaphus sp., Glaphurus sp., Cybele sp., Phacopidae, Raphiophoridae, Asaphus sp., Cheirurus sp., Sphaerochocus sp., Trinucleus sp. The age of the fauna is limited to the lower Silurian, and more probably to its upper part (Llandeilo or Caradoc). The thickness of the formation (in an incomplete section) is not less than one kilometer. In the conglomerates of the Kostin Formation there are many pebbles of sandstones and shales of Lower Ordovician deposits with relict tectonic structures, which indicates a significant break and manifestation of folding between the time of accumulation of the Lower Ordovician beds and deposition of the Kostin Formation. Here, near the settlement of Batun, the Kostin Formation is transgressively overlain by the basal horizons of the middle Devonian, represented by reef “Murzin” limestone (see below).

Gotlandian deposits are widely distributed in the northeastern part of the area described, i.e., within Gorny Altai, but are entirely absent in the zone of Rudny Altai. Everywhere they rest transgressively on the lower Silurian, and within the Gotlandian three formations, separated from one another by unconformities, are distinguished quite clearly.

According to Nikonov’s observations [15], in the Tigirek-Chinetinsky region the Gotlandian deposits begin with a sequence of black shales with Monograptus priodon Bron., having a thickness of about one kilometer. The graptolite fauna determines quite precisely the Tarannon age of these shales. According to Nikonov, the black shales are overlain by calcareous sandstones and marls with interbeds of conglomerates and limestones with brachiopods and corals. Similar black shales with a somewhat older (Llandovery) graptolite fauna, Climacograptus, have been found in the basin of the Cheremshanka River. In other regions of Northwestern Altai the black shales are absent, and the upper Silurian begins directly with an extremely variegated sequence, in its composition, of marly shales, calcareous sandstones, and limestones with Halysites, Heliolites, etc.; at the base of this sequence there are conglomerates with quartz pebbles. These relationships permit one to speak of a significant erosion before the deposition of the marly-sandy-calcareous sequence, which destroyed the black graptolitic shales over most of Northwestern Altai, and make it possible to distinguish the latter as an independent formation (the Khankhar Formation of Usov [18]).

The above-mentioned variegated sequence of marls and sandstones with numerous, but thin, limestone horizons is much more widely developed; apparently it reaches a thickness of several kilometers. It may be distinguished under the name of the Anui Formation [18]. It is interesting that, with movement westward, the amount of limestone in its composition increases and, for example, in sections along the Belaya River (a tributary of the Loktevka), 7 limestone horizons with a total thickness of about 600 m were recorded, with the total thickness (incomplete) of the formation being 2 km.

The Gotlandian section in Northwestern Altai is crowned by massive limestones of the Chagyr Formation with Conchidium Knighti Sow., Favosites, Heliolites, Halysites, up to 400 m thick and of Wenlock age. The Chagyr limestones lie distinctly transgressively on older sequences, as was established by Bublichenko [2] and Vinkman, although very

often without conglomerates at the base. This latter circumstance at one time compelled Eliseev [4] to regard the gently dipping fields of the Chagyr limestones as overthrust sheets.

The Gotlandian deposits in Northwestern Altai are dislocated considerably less intensely than the Lower Ordovician deposits; moreover, brachyfolds are very characteristic of them, the limbs of which, however, are often complicated by additional folds, sometimes very compressed.

Devonian

The Devonian deposits of Northwestern Altai are divided into two types, sharply differing from one another in composition and in the character of the section. One of them is developed within Rudny Altai—this is the Zmeinogorsk Devonian field; the other—within the Gorny Altai block, in the northeastern part of the district—is the Kurya Devonian field. They are separated from one another by the deep-seated fault mentioned above, accompanied by the well-known northeastern zone of crumpling [12].

The Devonian of the Zmeinogorsk field begins with the Losikha horizon, consisting of conglomerates at the base and, above, of tuffs, greenish marls, sandstones, and limestones. The thickness of the horizon is about 80 m. In the sandstones there occur numerous shells of Spirifer frequens Bubl., Strophonella anaglipha Kays., and others; in the limestones—Spirifer daleidensis Stein., Sp. frequens Bubl., and others. Petz [17] assigned this fauna to the Koblenzian stage of the Lower Devonian, but later studies by Bublichenko [3] showed its somewhat younger age, namely—the base of the Middle Devonian. However, Bublichenko’s determinations are disputed by Khalfin [19], who considers Petz’s age determinations more correct. The presence of Pleurodictium in the calcareous-clayey shales of the area of the Cherepanovo mine also indicates the possibility of a Koblenzian age for the basal Devonian horizons. But in any case, the presence of a major hiatus, encompassing in time the end of the Gotlandian and the beginning of the Devonian, is undoubted for Northwestern Altai, since the basal Devonian horizons everywhere rest with angular unconformity on the sandy-shale Ordovician sequence, while the Upper Silurian is completely absent within Rudny Altai.

Above the Losikha horizon in the Zmeinogorsk district lies a thick effusive-tuffaceous sequence, consisting of tuffs, tuffaceous sandstones and shales, jasper and sheets of quartz and quartz-free keratophyres, spilites, and albitic diabases. Basic effusives alternate with acid ones, but are concentrated in the lower parts of the section. Sedimentary rocks occupy a wholly subordinate position in the section. The total thickness of the Middle Devonian exceeds 2 km.

Faunistically characterized Upper Devonian deposits are developed southwest of Zmeinogorsk, in the area of the settlements of Razdolnoye and Samarka. Here the Middle Devonian effusive-tuffaceous sequence is overlain by pink reef limestones 70–75 m thick, which are separated by a thin interbed of calcareous tuff from the overlying red massive limestones 50 m thick. The latter are overlain by black carbonaceous shales with a Buchiola fauna, and then by an effusive-tuffaceous sequence composed of lilac quartz porphyrites, amygdaloids, diabases, and their tuffs, with a visible thickness of 180 m. Both limestone horizons and the black carbonaceous shales contain an abundant Frasnian fauna; the Buchiola fauna is especially characteristic: Buchiola retrostriata Buch., B. cf. conversa Clarke, B. altaica n. sp., Posidonia mesacostalis Wisè, which enabled Khalfin to determine precisely the Lower Frasnian age of the horizon of black shales [20]. The total thickness of the Upper Devonian in Rudny Altai

reaches 4.5 km, but in the northern part described here its Upper Devonian is evidently blurred to a considerable degree, being represented mainly by basic effusives and their tuffs, which, unlike the Middle Devonian ones, are in a diagenetized state.

Within the Zmeinogorsk field the Devonian deposits form a large anticlinal fold of general northeastern strike, the limbs of which are complicated by additional, sometimes steep folds, while in the core rocks of the Lower Silurian crop out and the Aley plagiogranite massif is situated.

A quite different Devonian section is found in the area of the village of Kurya, i.e., within the structure of the Gorny Altai. According to the author’s data, here the Devonian deposits transgressively and with a sharp angular unconformity overlie rocks of the Lower Silurian, forming a gentle, broad synclinal fold, the southern limb of which is cut off by the Semenov thrust.

The basal horizon of the Devonian is represented by the Murzin limestones and limestone conglomerates, the thickness of which varies from 100–200 meters to a meter and less. This is a typical reef facies, in which massive limestones, filled with corals and stromatoporoids, along strike are replaced by conglomeratic limestones with partly rounded limestone pebbles and with a limestone cement containing the same fauna, and then by true conglomerates with well-rounded pebbles of limestone and foreign rocks. Parallel with such a change of the horizon, its thickness also decreases, and in places it wedges out completely. According to the determinations of Radugin, who processed Baklakov’s collections [1], the Murzin limestones (Akimovka locality) contain the fauna Cyathophyllum ex gr. C. caespitosum, Amphypora ramosa Phill., Amphypora compacta n. sp., Am. dimorphica n. sp., Actinostroma stellulatum Nic., Ac. aporosa n. sp., and others, and are of Middle Devonian age. The paleontological office of ZSGU, on the basis of the author’s collections and the presence in the Murzin limestones of Cyathophyllum cf. vogulicum B., C. aff. beloniense E. H., Atrypa kadzielniae Gür., and sponges of the family Titusvillitidae, gives a conclusion on the age of the horizon within the limits of \(D_2^2—D_3^3\). According to Yavorsky’s conclusion, the stromatoporoid fauna (identified as Clathrodiction incubonrer Javor., Stromatopora concentrica Goldf., Hermatostroma sp.) has the aspect of the Middle Devonian and even of its upper half.

The Murzin limestone is everywhere conformably overlain by the Akimovka suite, which has a thickness of 800–900 m and consists of gray calcareous sandstones and marls containing abundant brachiopod fauna and plant remains; in one case a horizon of coral limestone (Talovka limestone) was recorded, lying conformably with the sandstones. In the author’s collections, Lomovitskaya established in the Akimovka suite the presence of a number of species from the genera and families Atrypa, Chonetes, Spiriferidae, Pentameridae, etc. All the identified forms are close to, but not identical with, those described in the literature, and the fauna has an endemic character. On the basis of the vertical distribution of forms, Lomovitskaya comes to the conclusion that the age of the Akimovka suite lies within \(D_2^1—D_3^1\). Along with brachiopods, the sandstones of the Akimovka suite contain plant remains: Rhombodendron sibiricum Chach., Archaeophyton sp., Calamophyton sp.

In the area of the village of Kurya the Akimovka suite is conformably overlain by the Kurya limestone, known in the literature, with a thickness of about 300 m; moreover, above it, stratigraphically, there is probably also a thick horizon of limestone, separated from the lower one by a bed of greenish-brown marls. The fauna of the Kurya limestones was described by Petz as early as [17], who identified from it Pachypora cervicornis Blainw., Cyathophyllum vermiculare Goldf., C. darwinii Frech., and others, and came to the conclusion as to its Middle Devonian...

age (Stringocephalus Stage). It should be noted that the limestones of Mount Surya, which Petz compared with the Kurya limestones, in fact represent the basal horizons of the Devonian (Murzin limestone). In the list of the fauna of the Kurya limestones given in one of Nekhoroshev’s works [11], new determinations of brachiopods are cited: Spirifer inflatus Schir., Rhynchonella gracilis Gür., Rh. parallelepipeda Bron., Productella subaculeata Murch., Cyrtina heteroclita Defr., Pentamerus acutilobatus Barr., Scendium aff. polonicum Gür., etc., confirming Petz’s conclusion as to the Stringocephalus age of the fauna.

The author combines this entire sequence, consisting of the Murzin limestone, the Akimovka suite, and the Kurya limestone, into the Murzin Formation, whose total thickness thus reaches on the average 1.5 km. The age of the Murzin Formation as a whole, apparently, falls within the Givetian Stage of the Middle Devonian.

The probable Upper Devonian in the Kurya area is represented by the Kukuy effusive formation, which clearly overlies the Kurya limestones with a concealed unconformity. The Kukuy Formation includes various tuffaceous rocks, hornblende and pyroxene porphyries of red, lilac, green, and black tones, i.e., occurring in a diagenetized state. At the base of the formation lie red tuffs and agglomerates, often with fragments of Kurya limestone, and in the upper horizons there is a thin interbed of dark-gray bituminous limestone with black cherts. The thickness of the Kukuy Formation reaches 1 km.

Thus, in the Kurya area the effusive albite-porphyry–spilite sequence with the Losikha horizon at its base is entirely absent, and in Zmeinogorsk the entire Murzin Formation is absent. It is difficult to assume that these sequences are synchronous. This is contradicted by their lithological composition and faunal characteristics. The Murzin Formation is probably younger than the Middle Devonian effusive sequence of the Zmeinogorsk area, and in this case a considerable hiatus must be assumed here between the accumulation of the latter and the formation of the Upper Devonian strata, corresponding to the accumulation and subsequent erosion of equivalents of the Murzin Formation. Thus, the history of development of two neighboring areas—Zmeinogorsk and Kurya—during Silurian and Devonian time was essentially different, and this can be explained only by the presence of a deep fault along the boundary between these areas and by differently directed oscillatory movements of the adjacent blocks of Gorny Altai and Rudny Altai, which conditioned the completely different character of the Silurian and Devonian sections in these structures.

Carboniferous

Carboniferous deposits have a limited distribution in Northwestern Altai. Apparently, the lowermost Carboniferous and the transitional Devonian–Carboniferous sequence (the Tarkhan suite) form a broad field in the upper reaches of the Aley River. Here a monotonous sequence of clayey shales interbedded with effusives, devoid of organic remains, has been mapped. Its Devonian–Carboniferous and Lower Carboniferous age is established precisely from paleontological data already on the territory of Kazakhstan, in the basin of the Uba River, where it extends continuously along strike.

A small tectonic wedge of greenish-black clayey shales with Fenestella and Polypora has been observed along the Glubochanka River, a tributary of the Malaya Belaya.

In the vicinity of the village of Kurya, in the zone of the bend of the Loktevka–Ulba deep fault, the author mapped three isolated tectonic scales composed of Lower Carboniferous limestones. The visible thickness of the limestones—

about 200 m. They contain an abundant fauna of corals and brachiopods of Lower Carboniferous type, while the Tournaisian age (Bukhtarma Formation) is confidently established by Nekhoroshev [10; 12].

History of the Development of Northwestern Altai

The composition of the formations, their internal structure, and the relations between them make it possible to outline a long and complex history of the development of Northwestern Altai and, in particular, a number of phases of folding manifested here.

Very few documents have been preserved that testify to the Precambrian history of the region, and one can speak only of the fact that in the Upper Precambrian in Northwestern Altai there took place the accumulation of thick and homogeneous sequences of limestones and argillaceous shales, so typical of the Proterozoic of Eastern Altai and the Kuznetsk Alatau. In the interval of time encompassing the Upper Proterozoic and the entire Cambrian, a number of foldings probably occurred, accompanied also by intrusive activity. In any case, in the conglomerates of the thick sandy-shale sequence of the lower Ordovician (Cambro-Silurian) there is already gravel of schistose marbles with relict tectonostructures typical of the Belorechensk Formation of probable Proterozoic age, as well as gravel of intrusive rocks.

Beginning with the Lower Ordovician, the history of the development of Northwestern Altai becomes clearer. At this time, possibly including the Upper Cambrian, in a shallow-water basin of geosynclinal type there accumulated a thick, many-kilometer sequence of sandstones, siltstones, and conglomerates with very rare interbeds of limestone, probably of clastic origin. The polymictic composition of the sandstones, typical of geosynclinal sequences in general, is characteristic; moreover, the abundance of fragments of feldspars and fragments of effusive rocks in the composition of the sandstones indicates only the erosion of some more ancient effusive sequences, probably Cambrian, and this material was brought from afar, since gravel of the corresponding effusives is absent from the conglomerates. Therefore the idea, common among many geologists who worked in Rudny Altai, of the tuffaceous character of the sandy-shale sequences of the Cambro-Silurian and Lower Silurian is incorrect. There were no manifestations of volcanic activity during the deposition of the Cambro-Silurian or Lower Silurian sequences in Northwestern Altai. This entire sandy-shale sequence was gathered into compressed folds of predominantly northwestern, but generally variable, strike, during a phase of folding that took place somewhere in the middle of the Ordovician and is known to Siberian geologists under the name of the West Altai phase. In Northwestern Altai there are no signs of the manifestation of intrusive activity in connection with this phase, and its slight metamorphism is dislocational in character or else is associated with the contact effect of considerably younger intrusions.

In the upper part of the Ordovician in Northwestern Altai a marine regime is again established; moreover, in contrast to the Lower Ordovician sequences, the Kostin Formation, having an age within the Llandeilo–Caradoc, was formed already under conditions of an open sea, with well-sorted clastic material coming from the continent. The manifestation of the West Altai phase of folding is proved by the presence, in the conglomerates of the Kostin Formation, of gravel of sandstones and shales belonging to the Lower Ordovician sequence, with the gravel characterized by the presence of relict tectonostructures. The true thickness of the Kostin Formation is unknown, but it is unlikely to have been large, since this formation almost ...

completely destroyed by denudation, and was preserved only in one sector—in the Kuryinsko-Maralikhinskaya synclinal structure. The manifestation of a phase of folding at the boundary between the Ordovician and the Gotlandian (the Taconic phase) can only be inferred from the presence of a considerable erosion confined to this time and from the consequent deposition of Upper Silurian sediments directly upon the eroded surface of the sandy-shaly strata of the Lower Ordovician.

The Taconic phase was probably weak and, perhaps, manifested itself only in oscillatory movements, since in the character of its folds the Kostin Formation does not differ from the Gotlandian formations.

Throughout the entire Gotlandian, the same conditions of an open sea persisted in Northwestern Altai. During this time a thick sequence accumulated, reaching 3.5 km in thickness, consisting of the Khankhar Formation of graptolite shales, the Anui sandy-marly formation, and the Chagyr limestones. These three formations are separated from one another by breaks, possibly corresponding to the Uksunai and Chagyr phases of folding in Usov’s scheme [18]. The first was expressed weakly, since it is recorded only by the presence of an erosion surface; the second was more intense, because the Chagyr limestones lie transgressively and sometimes with angular discordance upon the more ancient strata. But no decisive restructuring of the structures in connection with these phases of folding nevertheless took place, since the entire complex of Gotlandian sediments participates in the same folded structures. Likewise, no manifestations of magmatic activity connected with them are known.

The formation of the Upper Silurian geosynclinal basin ended with intense folding confined to the end of the Gotlandian and, perhaps, to the beginning of the Devonian. In connection with this phase (or phases) of tectogenesis (the Ardenian or Erian according to Usov’s scheme [18]—the Zmeinogorsk according to Bublichenko [2]), the folded structures of the Gotlandian, and perhaps together with them also those of the Kostin Formation of the Ordovician, were formed in their present or nearly present aspect. It is very probable that this phase of folding was accompanied by intrusive activity (“Caledonian” intrusions of Rudny Altai). The corresponding intrusives have not yet been separated from the mass of younger ones, but pebbles of acid intrusive rocks are common in the basal conglomerates of the Devonian. In connection with these movements, a considerable reconstruction of the relief took place. Probably all of Northwestern Altai at this time represented land; moreover, the southwestern part (the “Rudny graben”) of the region, along the line of the Loktevka-Ulba deep fault, proved to be considerably more uplifted in comparison with the northeastern part, owing to which throughout the territory of Rudny Altai, by the time of the onset of the Devonian sea, the Upper Silurian deposits had been completely destroyed by denudation.

It was indicated above that the Devonian sections of the northeastern (Kuryinsko-Maralikhinskaya synclinal structure) and southwestern parts of the region differ greatly from one another, which apparently is explained by the presence of the same deep fault and by the manifestation of oscillatory movements and erosions that interrupted, at different times in neighboring blocks of Rudny and Gorny Altai, the accumulation of the Devonian strata.

In the Eifelian age, and perhaps even earlier, the sea again advanced upon Altai, and soon thereafter vigorous submarine eruptions of keratophyre and spilite lavas began; together with tuffs, these are the chief components of the Middle Devonian section of Rudny Altai. But this effusive-tuffaceous sequence is entirely absent in the northwest—in the Kuryinsky district, where the Devonian section begins with younger, probably Givetian, marine deposits of the Murzinka Formation; moreover, there were no outpourings of keratophyre and spilite lavas here at all, since

since in the conglomerates of the Murzinka formation there are no pebbles of the corresponding effusive rocks. The Murzinka formation, on the contrary, is absent in Rudny Altai, where it was completely washed away before the accumulation of the Upper Devonian sedimentary-effusive strata (owing to the uplift of the Rudny Altai block).

In the Upper Devonian, over most of Northwestern Altai, the same marine environment is preserved and vigorous volcanic activity continues, but the character of the lavas changes. These are andesite-dacite lavas, now occurring in a diagenetized state. In the north—in the Kuryinsky district—these lavas produced subaerial outpourings; in Rudny Altai they were essentially submarine. In the upper parts of the Upper Devonian, effusive activity weakens and, including the Lower Carboniferous as well, deposition of marine sediments proceeds, only occasionally interrupted by outbursts of volcanic activity.

According to Nekhoroshev [12; 14], folding took place in the Lower Carboniferous within Western Altai, accompanied by the intrusion of granodiorites and diorites. Kassin [6] moves the time of intense folding for Eastern Kazakhstan—which crumpled the Devonian and Lower Carboniferous deposits and determined their present structure—to the Middle Carboniferous, which is more probable. The intrusions of the granodiorite complex are associated with this first phase of the Variscan cycle of tectogenesis; with the subsequent phases are associated the intrusions of the Zmeinogorsk complex and the polymetallic deposits connected with them. Upper Paleozoic sedimentary strata are absent in Northwestern Altai; therefore only by analogy with Kazakhstan can it be supposed that here too, beginning with the Middle Carboniferous, a continental regime predominated. The last phase of the Variscan cycle of tectogenesis, possibly corresponding to the Middle Permian, was accompanied by the emplacement of mica granites.

The scheme presented for the sequence of intrusive complexes developed in Northwestern Altai approximately corresponds to Eliseev’s [5] views and is in contradiction with those of Nekhoroshev [12; 14], who is not inclined to separate in time the intrusions of the Zmeinogorsk complex and of the mica-granite complex, and assigns both to the Middle Permian. The presence of a considerable time gap between these two intrusions is proved above all by their different relation to the zones of crumpling.

The zones of crumpling evidently began to form almost simultaneously with the intrusion of the plagioclase granites of the Zmeinogorsk complex, which in the marginal parts often bear traces of protoclase and were subsequently in places strongly cataclasized. The last phase intrusions of this complex—quartz albitophyres—were emplaced into an already schistose Devonian sequence; moreover, the orientation of the plutons is determined precisely by the schistosity, and not by plicative structures. But the formation of the zones of crumpling continued even after the formation of the porphyry intrusions, which not infrequently prove to be strongly flattened and schistosed, with the formation of porphyroids and various cataclasites and cataclastic orthogneisses. As for the mica granites, they cut and metamorphose already cataclasized porphyries (the eastern contact of the Savvushinsky pluton, observations of the author) and, although themselves affected by zones of crumpling, are so to a considerably lesser degree and with a different manifestation. In them a coarse cataclasis appears, without development of true cataclastic gneisses so typical of the zones of crumpling passing through the rocks of the Zmeinogorsk complex. Thus, the zones of crumpling formed over a considerable span of time, probably throughout the entire Variscan cycle of tectogenesis.

As for the deep-seated rupture, which, as we have already established, is in essence the Loktevka-Ulba “thrust,” and along which the northeastern zone of crumpling is oriented, it was initiated considerably ...

considerably earlier, in any case already in the Lower Silurian, and continued to develop throughout the Paleozoic. The result of oscillatory movements of large amplitude and with a sign changing over time was a significant difference in the stratigraphic columns of the Silurian and Devonian for the neighboring regions of Rudny Altai and Gorny Altai. The formation of folding zones and the exceptional saturation of the Rudny Altai graben with acidic intrusions are probably also connected with the life of deep-seated faults.

The latest movements of a fault character, which caused the stepped uplift of Altai and rejuvenated its relief, are quite precisely recorded in the time interval between the deposition of the mantle deluvial-proluvial loams and the deposition of the second terrace of the modern hydrographic network. These movements are reflected in the principal features of the modern geomorphology of Northwestern Altai.

References

1. Baklakov M. S.—Elements of the stratigraphy and metallogeny of the northwestern part of Altai, Problems of Soviet Geology, No. 4, 1937.

2. Bublichenko N. A.—The principal tectonic lines of Rudny Altai, in: Bolshoi Altai, Publishing House of the Academy of Sciences of the USSR, vol. 2, 1936.

3. Bublichenko N. L.—On certain Middle Devonian brachiopods of Altai, Izv. Geol. kom., XXXVI VI, 10, 1927.

4. Eliseev N. A.—On thrusts in Rudny Altai, Transactions of GGRU, issue 28, 1931.

5. He.—Petrography of Rudny Altai and Kalba, Petrography of the USSR, ser. 1. Regional Petrography, issue 6, Academy of Sciences of the USSR, 1938.

6. Kassin N. G.—General characterization of volcanic and metamorphic phenomena in Eastern Kazakhstan, Geology of the USSR, vol. XX, part 1, 1941.

7. Nalivkin D. V.—The doctrine of facies, 1933.

8. Nekhoroshev V. P.—Geological sketch of Rudny Altai, Izv. Glav. geol.-razv. upravleniya, vol. 49, No. 5, 1930.

9. The same.—Tectonics and metallogeny of Southwestern Altai, Izv. Vsesoyuzn. geol. razv. obedineniya, vol. 51, issue 15, 1932.

10. The same.—New data on the geology of Bolshoi Altai, in: Bolshoi Altai, vol. 2, 1936.

11. The same.—Explanatory note to the geological map of the basin of the upper reaches of the Irtysh (Bolshoi Altai) at a scale of 1:500000, ONTI, 1936.

12. The same.—The northeastern folding zone in Rudny Altai, in: Materials on the Geology of Rudny Altai, Council of the Academy of Sciences of the USSR, 1940.

13. The same.—Folding zones of Rudny Altai, ibid.

14. The same.—The Saur tectonic and intrusive phase in Southwestern Altai, Soviet Geology, No. 2, 1944.

15. Nikonov.—Sketch of the geology and stratigraphy of the Tigirek-Chineti district in Rudny Altai, Transactions of GGRU, issue 28, 1931.

16. Peive A. V.—Deep-seated faults in geosynclinal regions, Izv. AN SSSR, geological series, No. 5, 1945.

17. Petts G. G.—Geological description of sheet 13 of row X of the 10-verst map of Tomsk Province, Transactions of the Geological Section of the Cabinet, vol. 6, issue 1, 1904.

18. Usov M. A.—Phases and cycles of tectogenesis of the West Siberian Territory, Tomsk, 1936.

19. Khalfin L. L.—The Devonian of Altai, Izv. Tomsk Polytechnic Institute, vol. 65, issue 1, 1948.

20. Khalfin L. L.—On the Buchiol shales of Rudny Altai, Izv. West Siberian Branch of the Academy of Sciences, geological series, issue 1, 1947.