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Vol 52, No 1 (2017)
- Year: 2017
- Articles: 5
- URL: https://journals.rcsi.science/0024-4902/issue/view/9857
Article
Correlation of Neopleistocene tills in the northern Russian plain: Evidence from petrography of the coarse-clastic material
Abstract
The petrographic composition of boulder–pebble material from numerous till sections of the Timan–Pechora–Vychegda region was scrutinized to establish locations of glacial provenances and pathways of the terrigenous material transport during different Neopleistocene glaciations. Analysis of a great body of factual materials confirmed high feasibility of the application of petrographic data on the coarse-clastic material and the ratio of distal and proximal components in tills for their subdivision and correlation. The most reliable and regionally consistent criteria are represented by index boulders and orientation of elongated rock clasts, as well as isotope datings of rock clasts in till horizons.
69-79
Reflection of seismic paleoevents in Mesozoic–Cenozoic terrigenous sequences of the northern Caucasus
Abstract
Numerous traces of paleoseismic events (seismites) were established in Mesozoic–Cenozoic marine sedimentary sequences of the northern Caucasus. These traces are most prominent in the terrigenous Middle Miocene sandy–clayey sediments. Impact of seismic shocks upon the relatively weakly lithified sediments provoked distortion of the primary sedimentary structure, liquefaction of the sandy material, and injections of different morphologies (neptunic dikes and sills). The formation of jointing in sediments fostered their vertical permeability and promoted the migration of diagenetic solutions into the adjacent horizons, which stimulated the formation of subvertical carbonate bodies. The amount and intensity of seismic events varied at different stages of the accumulation of sequences and in different areas of the paleobasin. In the eastern sector of the northern Caucasus, seismic activity similar to the present-day general pattern was likely developed as early as the Middle Miocene: maximum activity in the Dagestan and its westward attenuation. Traces of seismic activity are also recorded in the Maikopian (Oligocene–Lower Miocene) and Lower–Middle Jurassic rocks.
1-19
Anyui Volcano in Chukotka: Age, structure, pecularities of rocks’ composition and eruptions
Abstract
The study of lavas and pyroclastics from Anyui Volcano made it possible to reconstruct succession of its eruption events. The age of the eruption is estimated by isotopic methods to be 0.248 ± 0.030 Ma. It is established that the last episode of volcanic activity in northeastern Russia occurred 0.2‒0.5 Ma ago (in its continental part, 0.2‒0.3 Ma ago). This episode is chronologically close to the last peak in activation of volcanism in the Arctic and Subarctic regions. The absence of features indicating glacial influence on lavas from Anyui Volcano provides grounds for an assumption that no significant glaciations took place in the continental areas of western Chukotka during the last 250 ka.
20-50
Isotope (δ13C and δ18O) and genetic features of manganese carbonates of the Mazul deposit (Krasnoyarsk region)
Abstract
New isotope and mineral data on manganese carbonates of the Mazul deposit (Krasnoyarsk region) in combination with morphology of ore bodies suggest that the ores were formed in several stages with the involvement of meteoric solutions through infiltration and, possibly, exfiltration mechanisms. Based on the geological–geochemical data, manganese carbonates of the Mazul deposit may be ascribed to a new genetic subtype of the catagenesis (epigenesis) zone.
51-60
Paleogeographic provinces of the periglacial loess association in the middle Volga basin
Abstract
Specific features of the formation and distribution of periglacial loess association in the Volga region are discussed. Based on generalization of the results of the systematic paleogeographic analysis, the paper presents a comprehensive characteristic of the polygenetic and polychronous loess rocks. The results show regional specifics in the structure and composition of loess rock horizons confined to different-aged paleogeographic zones of the Russian Plain. Provincial discrepancies in the distribution and thickness of loess rocks are demonstrated in the summary map. Comparison of the complex characteristics of the loess rocks provides insight into the general trend of spatiotemporal variability of their structure and composition. Latitudinal zonation is manifested in the thickening of loess rock sequences along the distal direction of the paleoglacial zone (on the average, from 1.3 m to 5–10 m or more) and is usually accompanied by increase in contents of the silty material and carbonates and degree of sagging. Moreover, the stratigraphic structure of sections becomes more complicated with increase of the age interval of loess–soil series. The spatiotemporal trends, which are revealed in the development and periodicity of loess formation, have a great significance for the reconstruction of paleogeographic events in the Neopleistocene.
61-68