Vol 37 Iss. 2

Geosynclinal and platform sedimentary complexes (formations)Geosynclinal sediments are intensely folded, metamorphosed and ruptured by synorogenic intrusions. They usually have a greater thickness - thousands of meters for a system and even for divisions of the system. Only in geosynclinal sediments are found flysch and molasse complexes, graywacke and aspid shale strata, and thick reef limestones.

Faunistically characterized Ordovician sediments are known in northeastern Tuva (Sistigkhem Formation) and along the northern margin of the Tuva Basin, in the Uyuk River basin (Malinov Formation). In recent years, our work proved the wide development of Ordovician sediments (Shemushdag Formation) in Western Tuva. Previously, these strata were attributed to the Silurian and were considered to be Landoverian.

Since 1935, the author has received abundant paleontological material from Jurassic and Cretaceous sediments of the Soviet Arctic. The author has been studying this material, which was constantly replenished with new collections, until very recently. In the present article, the results of the study of ammonites from the Kellovenian deposits of the Soviet Arctic are collected. The publication of these results is necessary especially because, despite the wide development of paleontological work in this area, there is no detailed description of its Kellovian fauna in the literature so far (except for the very brief description of several species in the works of D. N. Sokolov and A. P. Pavlov).

Recently, the question of the upper boundary of the Eifelian Stage in the Urals has become more acute. Two All-Union meetings (in Sverdlovsk in 1957 on the unification of stratigraphic schemes of the Urals and in Leningrad in 1958 on facies maps of the Devonian period) made two different decisions on this question. In Sverdlovsk, it was decided to assign the Calceolian and Biysky layers on the western slope and their analogs on the eastern slope to the Eifelian Stage. In Leningrad, the decision of the 1951 All-Union meeting on the development of a unified scheme of Devonian stratigraphy was left in force.

The material on quadrangular corals was given to the author by E. A. Modzalevekna (area of Imachi station, Urusha River, and Gazimurovsky Plant); additional material on the Ildikan Formation of the Gazimurovsky Plant area was received from T. M. Malich, corals from Blagodatnoye settlement (Nerchinsk area) - from A. Lokerman. Difficult geological conditions did not favor good preservation of fossil remains of quadrangular corals. In spite of this, it was possible to characterize the age of all the formations from which the corals were brought.

The study of Devonian quadrangular corals was undertaken to substantiate the Devonian stratigraphy for the state geological survey of the Altai Mountains. During 1956-1958, coral collections from the following areas were processed: 1) the upper reaches of the Char River - Kalbinsky Ridge (collection of G. I. Sokratov, VSEGEI, 1953-1955); 2) the right bank of the Bukhtarma River [collection of V. P. Pnev, Irtyshskaya R. Pnev, Irtysh group of parties, East Kazakhstan Geological Administration (EKGU), 1956-1957]; 3) Pnevskoye field (collection of V. P. Pnev, 1953); 3) Pnev. Pnev, 1953); 4) Northern slope of the Sarym-Sakty ridge (collection of V. P. Pnev and V. Popov, 1956); 5) Southern Primarkakulia (collection of D. P. Avrov, N. P. Ivanov, VSEGEI; V. P. Pnev and others, VKSU, 1953-1957); 6) Uimenskaya Depression - Mountain Altai (collection of Y. S. Maimin, VSEGEI, 1957); 7) Kyzyl-Shin River basin - Mountain Altai (collection of E. N. Yanov, VSEGEI, 1957); 8) Zay-San area - Saursky Ridge (collection of V. V. Lebedev, VSEGEI, 1953; G. P. Kleiman and S. Kell, VKSU, 1953); 8) Zay-San area - Saursky Ridge (collection of V. V. Lebedev, VSEGEI, 1953; G. P. Kleiman and S. Kell, VKSU, 1957). Kell, VKSU, 1957).

Southern Altai is a promising polymetallic region of Altai. Seven deposits and a large number (about 100) of points of lead-zinc and copper mineralization have been discovered within its limits. The polymetallic mineralization is spatially closely related to deposits of the Kultabar Formation of the Koblenz-Eifel age. Younger and older sediments are generally of little interest with respect to polymetallic mineralization. Thus, the Kultabar Formation is the main ore-bearing sequence of polymetallic mineralization in the Southern Altai.

The Narymo-Bukhtarminskaya depression separates the system of South Altai ridges from the Mountain and Ore Altai. It is a large depression of a clear-cut shape, extending in latitudinal direction for almost 150 km with a width from 1-2 to 10-12 km.

The folded formations developed in the northwestern part of the Turgai Trough appear on the day surface only in the valleys of the Tobol River and its largest tributaries, where they were studied by Meglitsky and Antipov, A. A. Krasnopolsky, A. N. Geisler (1929), D. S. Steinberg (1929), A. P. Zotov (1935) ( A. G. Behr, G. A. Sokolov (1934), E. A. Ushakova (1932), K. I. Dvortsova (1937-1940), F. N. Ruvikova (1937-1940), and F. N. Ruvikova (1937-1940). G. Ber, G. A. Sokolov (1934), E. A. Ushakova (1932), K. I. Dvortsova (1937-1940), F. N. Rukavishnikov (1938), A. P. Krotov (1943), E. I. Klevtsov (1946-1947), N. N. Pikhtovnikova (1946), E. A. Mazina and other researchers. Huge areas of watersheds remained practically unexplored.

During geological mapping of folded areas, the geologist-surveyor constantly has to face the question of dissection and correlation of sedimentary deposits containing remains of fossil organisms of poor preservation or not characterized by them at all. In small-scale geological surveys, well-known features are used for this purpose: similarity and difference in lithology; degree of metamorphism; nature of folding; relationship with intrusions of a certain complex; any characteristic features of the selected sediment complex, if these features are syngenetic with these sediments and therefore relate only to them (oblique layering, presence of nodules of various kinds, etc.).

There are several points of view on the conditions of slab formation. One group of researchers sees the main cause of layer formation in geotectonic fluctuations of the Earth's crust, which control the process of sediment accumulation. Other researchers consider the main cause of layer formation to be a change in the conditions of sediment formation as a result of changes in the physical-geographical regime; at the same time, they do not attribute significant importance to the geotectonic factor.