Devonian Carbonate Facies of the Chizhapka Bank of the Nyurol Paleobasin,Southeastern Part of Western Siberia

Comprehensive lithogenetic analysis of the Nyurol paleobasin revealed a large shoal area surrounded by basins. The shoal area is composed of organogenic buildups covered by sediments of isolated and inner lagoons. The organogenic buildups are divided into two types: Stromatopora bioherms and mud-mounds. Regularities of the distribution of organogenic buildups are considered.     

Clay minerals in the middle-upper Miocene sediments of the Taman trough: Composition and paleogeographic significance

The pioneer compositional analysis carried out for clayey sediments from most regional Miocene stages of the Taman trough made it possible to define the main types of clays and trace their variability through the section. It is established that the composition of these clays is largely controlled by the sedimentary rather than postsedimentary lithogenetic factors. The maximal hydromica (hereafter, illite) concentrations (up to 73%) are recorded in sediments deposited during orogenesis activation and major regressions (terminal Tarkhanian, Sarmatian, and early Pontian). The dominant role and elevated concentration of the smectite component are characteristic of sediments corresponding to transgressive phases of the basin development. The shallow-water sediments, which show a notable facies heterogeneity, differ from their deepwater counterparts by a higher diversity in the clay composition. These regularities in the distribution of clay minerals may be used for the lithostratigraphic subdivision of the sequences with a lower content of the fossil mollusc assemblages.     

Carbon and oxygen stable isotopes in the middle-upper miocene and lower pliocene carbonates of the Eastern Paratethys (Kerch-Taman Region): Palaeoenvironments and post-sedimentation changes

C and O isotope composition of Middle-Upper Miocene and Lower Pliocene carbonates from Kerch-Taman Region (Eastern Paratethys) have been studied in order to reconstruct palaeoenvironmental variability and post-sedimentation changes. The δ¹³C and δ¹⁸О values of the Upper Sarmatian to Lower Pliocene organogenic carbonates reflect the desalinization of paleobasins, global Late Miocene Cooling, and increase in seasonal temperature fluctuations. Isotopic composition of the Middle Sarmatian organogenic carbonates was strongly influenced by evaporation processes, high bioproductivity, and local submarine methane emissions. Warm climate and low bioproductivity together with unstable hydrological regime during the Late Chokrakian and the Karaganian times influenced the isotope composition of primary carbonates. Calcite shell of Spiratella sp. (δ¹³C =–0.4‰ and δ¹⁸О =–0.4‰) from Tarkhanian sediments was formed in warm marine environment. Dolomitization prevails over other secondary mineralization in the studied carbonate rocks. Two groups of secondary dolomites that are characterized by negative and positive δ¹³C values have been recognized. Lowe δ¹³C values (up to–31.4‰) in dolomites indicate the influence of both dissolved inorganic carbon (DIC) from oxidized organic matter (С_org) and methane. Dolomites with positive δ¹³C values (7.0 and 7.8‰) associat with migration of CO₂- and CH₄-containing saline groundwater.     

Depositional Environments in the Eastern Paratethys during the Final Middle Miocene Transgression (Kura Basin,Eastern Georgia)

Lithology and Mineral Resources - The mineral composition and depositional environments of the Konkian in eastern Georgia (Kura trough, eastern Paratethys) corresponding to the Kosovian...     

Provenance of the Palaeocene-Eocene clastic rocks of the Komandorsky Islands

The Palaeocene–Eocene sequence on the Komandorsky Islands is represented by sediments and minor volcanics with a total thickness of more than 3000 m. Sandstone, siltstone, mudstone, siliceous rocks and conglomerate, which have accumulated in the upper and middle parts of a deep-water fan, prevail. All the debris was delivered from the north-east, from the side of the contemporary Komandorsky basin in the Bering Sea. Products of volcanic denudation and fresh tephra dominate its composition. However, at some levels the sandstone contains fragments of jasper, quartzite, slate, schist, gabbro and granite as well as non-volcanic quartz along with a volcanic component. The heavy minerals fraction of the sandstone contains considerable quantities of apatite, zircon, garnet and chromite, as well as pyroxenes, amphiboles and magnetite. The chemical composition of the garnet is specific to metamorphic rocks. A significant admixture of chromite is indicative of denudation from an ophiolite complex. The folded and partly metamorphosed pre-Palaeogenic rocks were a source of these fragments. Their most likely source terrane was the Shirshov-Bowers chain (Cretaceous palaeoarc). The Komandorsky block originally was the forearc part of the Aleutian arc where the latter was superimposed on the Shirshov-Bauers chain. A subsequent north-west displacement of forearc structures, in response to the transform fault at the boundary between the Pacific and North American plates, could have resulted in the separation of the Komandorsky block from its Early Palaeogene debris source area.     

Provenance areas of the Kerch-Taman trough in the pliocene and pleistocene

According to their structural and mineralogical features, Akchagilian sandy deposits of the Kerch-Taman trough are similar to deposits from the Don River, while Karangatian sandy deposits are similar to alluvial deposits from the Kuban River. Two associations of heavy minerals, which indicate the predominant provenance of debris from southern areas of the Russian Platform and Greater Caucasus, were identified. It is proposed that the Kerch-Taman trough was filled mainly by terrigenous material from the Russian Platform in the Late Neogene. In the Late Pleistocene, the Caucasus region became dominant as a provenance area.     

Cyclostratigraphy of Pontian deposits of the Eastern Paratethys (Zheleznyi Rog section,Taman Region)

The first data on the cyclostratigraphy of Pontian deposits of the Eastern Paratethys were obtained by studying the magnetic susceptibility of Upper Miocene rocks of the Zheleznyi Rog section in the Taman Region. Based on statistical methods, using the Lomb-Scargle and REDFIT periodograms, cycles related to long-period insolation oscillations (precession of the Earth’s orbit and variations in Earth’s axial tilt) were revealed. It is proposed that a hiatus occurred (about 150000–200000 years) at the Novorossian/Portaferian boundary (Lower Pontian/Upper Pontian) due to the onset of the maximum Messinian Salinity Crisis.     

Astronomically-tuned cyclicity in Upper Maeotian deposits of the eastern paratethys (Zheleznyi Rog section,Taman)

Astronomically-tuned cyclicity in Upper Maeotian deposits of the Zheleznyi Rog section (Taman, Eastern Paratethys) was revealed first time using the methods of cyclostratigraphy. According to the spectral analysis of the data on the magnetic susceptibility of rocks and basing on the peaks of Lomb-Scargle and REDFIT periodograms, cyclicity with a length of 7.1–8.9 m was established in studied deposits. These cycles are comparable with the period of oscillations of the Earth’s axis angle to the plane of its orbit, which corresponds to 41000 years. The data we obtained confirm the idea of the correlation of Upper Maeotian deposits to the greater part of the Chron C3An and duration of the late Maeotian no longer than 700000–750000 years.     

The Chenka sandstone Sequence (Lower Jurassic) of the Crimean Mountains: Stratigraphy and depositional environments

The position of the Chenka Sequence in the section, original data on its clay minerals, facies and structural parageneses with consideration of volcanic and climatic events, as well as the available published information provide grounds for accepting it as Pliensbachian-Toarcian in age. It is shown that the Chenka sandstones are a facies or group of facies deposited in deltaic-plain or delta-front environments and that it cannot be ranked as an autonomous formation or other stratigraphic unit.     

Upper Meotian facies of the Taman Trough

The facies structure and depositional environments of upper Meotian (Maeotin in European literature) sediments in the Taman Trough are considered. Eight facies of a shallow basin are defined and described in detail in the examined sections. It is established that depositional environments in the basin in the initial late Meotian were determined to a significant extent by the dominant influx of fresh (river) waters from the northeast. Diatomaceous sediments, which became later widespread, reflect cyclic ingressions of saline waters. Their enhanced inflow in the terminal late Meotian is evident from the taxonomic composition of diatom and molluscan assemblages.