Vol 63 Iss. 2

The classic section of the Lower Famennian is considered to be the section of the central regions of the Russian Platform. In it, the Zadonsk and Yelets layers with numerous representatives of the Cyrtospirifer archiaci group lie on the Upper Frasnian sediments with Theodossia, and are covered by the Dankov-Lebedyansk layers with C. lebedianicus.

Upper Ordovician and Lower Silurian sediments are widespread in the Altai–Sayan folded region. They have been studied to varying degrees, are paleontologically characterized differently, and have different relationships with each other.

In the far southwest of Tuva, the Silurian sediments form small isolated downwarps. The largest of these is the Mugur syncline, and two other small folds are located in the area of the Ordovician Kargin syncline. ...

In the eastern part of the Malguzar Mountains (a northwestern spur of the Turkestan Range, in the upper Zaamin-su River basin), the transitional Silurian and Devonian strata cover a significant area. They form the flanks of a latitudinal synclinal structure and consist of terrigenous-carbonate rocks that are highly varied in composition. The most complete section of these deposits is found on the northern flank of the structure near the village of Myk in the upper reaches of the river. The village of Myk is located in the upper reaches of the Yetkichu River, a left tributary of the Zaaminsu River. The Zaaminsu River. Here, an alternation of organogenic and sedimentary limestones, limestone conglomerates, clay shales, and siltstones with lenses of sandstones, conglomerates, and gravelites is exposed. The sediments contain abundant organic remains: stromatopores, corals, brachiopods, bryozoans, gastropods, bivalves, nautiloids, and ostracods. The Upper Silurian and Devonian deposits in this area were studied by V. D. Chekhovich [1965], A. I. Kim, and N. M. Larin (1960–1962). The author examined these deposits in the summer of 1968. The data collected form the basis of this article.

Representatives of the family Megalodontidae are widely distributed on the South and North Islands of Novaya Zemlya, as evidenced by the collections of B. A. Alferov (1934), A. A. Petrenko (1936), and B. V. Miloradovich (1936), studied by us for this article.

The stage affiliation of the Kosva horizon is debatable. The existing points of view are based on different interpretations of geological and faunal data. Ostracods of the Kosva horizon were studied in two sections of the western slope of the Urals – Shirokovsky (Middle Urals, Kizelovsky district) and Usuili (Zilim River basin).

In the Kalba Range and the western part of Southern Altai, Carboniferous sediments strongly dominate over other sedimentary formations. They form part of the Kalba-Narym, West Kalba and Zharma structural-formational zones, differing in the character of their succession.

Within the Mezen Depression, the Carboniferous and Permian sediments have no natural outcrops on the surface; they are exposed by boreholes drilled in the last decade in the settlements of Verkhny Smolenets, Koinas, Selishche, Maibas and Fominskoye.

Deposits of the Artinskian Stage in the Middle Urals have been studied in the basins of the Yuryuzan, Ufa, Sylva, Kosva, and Usva rivers.

During the study of the Lower Permian sediments of the Southern Urals, massive reef algal limestones were encountered in the upper part of the Artinskian Stage, which are analogous to the reef algal limestones of the Sylva River basin in the Middle Urals in terms of their position in the section, reef-forming organisms, and faunal complex. They are best exposed in the Shafeevsky section.

Pamir is one of the areas where adrianitids are quite fully represented. From the Permian sediments of the southeastern Pamir, the family Adrianitidae includes: Emiliella incertum (Bose), Crimites pamiricus Toum., C. spathi Toum., C. murgabensis Pav., C. sp. A, Neocrimites nalivkini Toum., N. dutkevitchi sp. nov., N. pamiricus sp. nov., Pamiritella vinogradovi Toum., P. sp., Istycoceras bodylevskyi Pav., Pamirioceras markovskii Pav.

The distribution of brachiopods in the sediments of the Artinskian Stage of the Urals has been repeatedly considered in the literature by F. N. Chernyshev [1889, 1902], G. N. Fredericks [1918], B. V. Miloradovich [1949], and D. L. Stepanov [1939, 1951]. However, all researchers did not divide the Artinskian Stage into horizons based on brachiopods, although the abundance and diversity of Artinskian brachiopods have long suggested the possibility of using them to distinguish two substages and even local horizons of the Artinskian Stage [Stepanov, 1939, Miloradovich, 1949, 1951]. In addition, the so-called Sylva reefs occupy a controversial stratigraphic position, which M. V. Kulikov [1948], V. D. Nalivkin [1949], and D. L. Stepanov [1951] attributed to the uppermost part of the Artinskian Stage, adjacent to the Kungurian; B. V. Miloradovich [1949] determined their age as Kungurian.

Inoceramids (retroceramids) are widespread in the Middle Jurassic sediments of the eastern USSR. They are the dominant and often the only fossil remains in rocks of this age. Unfortunately, ammonite finds are extremely rare in layers with inoceramids, which makes it difficult to determine the age range of representatives of this most important group of Jurassic bivalves. Usually, their age is determined either conditionally or within very wide limits, whereas more precise dating from inoceramids will undoubtedly make it possible to develop a sufficiently detailed stratigraphy of Middle Jurassic deposits. Therefore, each joint find of retroceramids and ammonites is of great interest. Such finds were made by the author in western Priokhotie – on the coast of Tugur Bay of the Sea of Okhotsk. Here, rocks of the lower part of the Middle Jurassic – Aalenian and Bajocian stages, containing rich complexes of inoceramids, are exposed in coastal cliffs. The Aalenian deposits in this area are characterized by numerous ammonites, which make it possible to identify local zones and correlate them with the standard scale. The accompanying retroceramids are dated accordingly.

Marine sediments of the Albian Stage in southern and western Turkmenistan are represented by a succession of alternating clays, siltstones and sandstones with horizons of calcareous nodules and rare beds of shell limestones. They contain numerous fossils, among which ammonites are the most important for determining the age of the sediments in question, making it possible to establish a detailed stratigraphic scheme for the Albian sediments of Turkmenistan. In second place in importance for determining the age of the host sediments are bivalves and, above all, inoceramids. Different species of this family in the sections of the Albian of Turkmenistan usually occupy a certain stratigraphic interval ranging from one or two zones to two or three substages.

Almost throughout the Devonian, there were marine basins around the Pacific Ocean that belonged mainly to geosynclines. Caledonian folding, which occurred in the second half of the Silurian in the Paleozoic geosynclines, led to the formation of young mountain chains and island archipelagos that disconnected the continental seas.