The Upper Jurassic basalts (150–160 Ma) described as the Ichetui Formation over the territory of the Tugnui, Margintui, and Maly Khamar-Daban volcanic structures have been studied paleomagnetically. It is shown that natural remanent magnetization still contains a component which may reflect the geomagnetic field direction at the beginning of the Late Jurassic. This is supported by reversal and conglomerate tests. Calculation of mean paleopole gives: Plat = 63.6°, Plong = 166.8°, α95 = 8.5°. These values well coincide with the data for the Badin Formation from Mogzon depression, which lies east of the study area and approximately dates from the Kimmeridgian-Oxfordian interval of the Late Jurassic. At the same time, those poles statistically differ from the European and Southeast Asian poles of the same age. The available paleomagnetic data suggest that at the beginning of the Late Jurassic the Mongol-Okhotsk Ocean was probably still open. Since the early Late Jurassic the continental blocks of Southeastern Asia and Siberian part of the Eurasian plate had been approaching, with the Siberian domain rotating clockwise. Analysis of the total of data shows that sinistral strike-slip deformations were present not only in southern Siberia but also between the Siberian and European Platforms. Thus, the deformations of the Central Asian crust in the early Late Jurassic reflect the intraplate strike-slip motions coeval with the closure of the Mongol-Okhotsk Ocean and are governed by the clockwise rotation of the Siberian part of the Eurasian plate relative to its European part.

New structural, petrological, chemical, isotope, and paleomagnetic data have provided clues to the Late Riphean–Paleozoic history of the Uda–Vitim island arc system (UVIAS) in the Transbaikalian sector of the Paleoasian ocean, as part of the Transbaikalian zone of Paleozoids. The island arc system consists of three units corresponding to main evolution stages: (i) Upper Riphean (Late Baikalian), (ii) Vendian–Lower Paleozoic (Caledonian), and (iii) Middle–Upper Paleozoic (Hercynian). The earliest stage produced the base of the system composed of Late Riphean ophiolite (971–892 Ma, U-Pb) and volcanic (837–789 Ma, U-Pb) and sedimentary rocks (hemipelagic siliceous sediments and dolerite sills) which represent the Barguzin–Vitim oceanic basin and the Kelyana island arc. The main event of the second stage was the formation of the large UVIAS structure (over 150,000 km2) which comprised the Transbaikalian oceanic basin, the forearc and backarc basins, and the volcanic arc itself, and consisted of many volcanic-tectonic units exceeding 100 km2 in area (Eravna, Oldynda, Abaga, etc.). Lithology, stratigraphy, major–element compositions, and isotope ages of Vendian–Cambrian volcanic rocks and associated sediments indicate strong differentiation of calc-alkaline series and the origin of the island arc system upon oceanic crust, in a setting similar to that of the today’s Kuriles–Kamchatka island arc system. The Middle–Upper Paleozoic stage completed the long UVIAS history and left its imprint in sedimentary and volcanic rocks in superposed trough basins. The rocks were studied in terms of their biostratigraphic and isotope age constraints, as well as major- and trace-element compositions, and were interpreted as products of weathering and tectonic-magmatic rework of the UVIAS units.

We propose a model of the geodynamic evolution of the Dzhida island-arc system of the Paleoasian Ocean margin which records transformation of an oceanic basin into an accretion-collision orogenic belt. The system includes several Vendian-Paleozoic complexes that represent a mature oceanic island arc with an accretionary prism, oceanic islands, marginal and remnant seas, and Early Ordovician collisional granitoids. We have revealed a number of subunits (sedimentary sequences and igneous complexes) in the complexes and reconstructed their geodynamic settings. The tectonic evolution of the Dzhida island-arc system comprises five stages: (1) ocean opening (Late Riphean); (2) subduction and initiation of an island arc (Vendian-Early Cambrian); (3) subduction and development of a mature island arc (Middle-Late Cambrian); (4) accretion and formation of local collision zones and remnant basins (Early Ordovician-Devonian); and (5) postcollisional strike-slip faulting (Carboniferous-Permian).

Different exogenetic processes proceeded actively in the Azov-Kuban depression, which represented a denudation plain in the geological past at the bound aries of the lithosphere, hydrosphere, and atmosphere. In the Azov Region, these processes were followed by formation of unique polygenetic sedimentary com plexes with clear washout traces, specific lithological and mechanical rock compositions, and frequent change of layering types and layer thickness.Such complexes include the section of loose sedi ments with different genesis and thickness from the lower Pleistocene (?) to the Holocene exposed on the southern coast of Taganrog Bay near the Semibalki locality. In terms of paleontology, some sediments are barren, while others contain a few remains of mam mals. Most paleontological material was delivered from the towpath. The stratigraphic sequence of the paleogeographic events that had an effect on these sediments is still unclear due to the insignificant num ber of paleontological findings and change of geologi cal bodies in space.Recent investigations have succeeded in finding a geological body characterized by small thickness (25 cm at most) above the water level of Taganrog Bay west of the Deep Draw (Fig. 1) where remains of large mammals and one Tetracorallia (Rugosa) were depos ited in situ. Moreover, the source delivering some paleontological material to the towpath has been revealed. The layer is exposed near a basement of loose sediments, which has been described by some authors, between greenish gray clay with remains of Archidisk odon meridionalis, Equus robustus, Trogontherum cuvier, Cervidae and clay fine grained sand [2] or between gray lake clay and unlayered yellow clay sand [3].The layer is separated from under and overlying layers by washout boundaries proving the difference in time of their accumulation and pauses in sedimenta tion. As for the lithological and mechanical composi tions, this layer is composed of fine and medium grained highly carbonated gray sand with rolled rock fragments of different sizes and clay balls. Bone remains, rock fragments, and other inclusions are cemented by sand. The bone remains are similar in fossilization color and degree to remains from the underlying lake clay, but are different from remains from the overlapping over Tamanian Scythian clays. The lithological features of this layer indicate that acti vation of channel and basin erosion led to accumula tion of breccias from fine grained sand, rock frag ments, clay balls, and mammal remains. Its small thickness is likely related to the following: erosion manifested itself as washout zones separating the layer from overlying sediments.This layer is also a water bearing level that is con firmed by both drainage of underground waters near the basement of polygenetic sediments and cane (Phragmites australis [= Ph. communis]) growing at the boundary of the sand sequence and clay, which is a watertight stratum. Discharge of underground waters initiates landslide processes, most actively to the west of the section ne...