Vol 52, No 6 (2017)
- Year: 2017
- Articles: 9
- URL: https://journals.rcsi.science/0024-4902/issue/view/9867
Article
Sedimentary infill in the equatorial Mid-Oceanic Canyon, Atlantic Ocean
Abstract
Facts confirming the hypothesis of contourite sediment infill of the Equatorial Mid-Ocean Canyon (EMOC) are presented. We examined two cores recovered in Cruises 37 and 43 of the R/V Akademik Ioffe (2012, 2013). The cores recovered upper Quaternary miopelagic clays on the EMOC floor (AI-3149) and the adjacent abyssal plain (AI-2620). The study of these cores unraveled significant differences in their composition. In contrast to the lithologically homogeneous Core AI-2620, Core AI-3149 includes interlayers enriched in the biogenic CaCO3, terrigenous silt, and authigenic ferromanganese micronodules. These peculiarities are attributed to activity of the Antarctic Bottom Water (AABW) contour currents along the EMOC.
Distribution of n-alkanes in the ferromanganese nodule–sediment–pore water system (Clarion–Clipperton Fracture Zone)
Abstract
The paper presents the first results of a comparative study of the composition and distribution of organic matter (OM) (Corg, n-alkanes, Pr, Phy) in samples of the ferromanganese nodule–sediment–pore water system taken at a single site in the Clarion–Clipperton Fracture Zone, Pacific Ocean. Samples were taken during Cruise 120 of R/V James Cook in 2015. The results of the comparison of organogeochemical parameters in the lipid fraction of OM in ferromanganese nodules of different size and morphology with the underlying sediment (0–1 cm) and pore water revealed both principle genetic affinity of OM therein and significant discrepancies between the processes of diagenesis during the formation and growth of each individual ore sample.
Response of the bering sea to Heinrich Event 11
Abstract
The present paper addresses the issue of the existence of inferred hiatus on the Shirshov Ridge in the western Bering Sea, which is represented by a sand layer allegedly produced by intensification of the bottom current at the penultimate glacial/last interglacial boundary. Intensification of current velocity near the ocean floor likely provoked washout of the light fine fraction and enrichment of the sediment with heavy coarse particles. Comparison of our and published data on the western Bering Sea and North Atlantic revealed that the sand layer in sediments of the western Bering Sea at the penultimate glacial/last interglacial boundary is related to ice rafting and serves to some extent an analog of Heinrich Event 11 in the North Atlantic.
Sedimentary environments and geochemistry of Upper Eocene and Lower Oligocene rocks in the northeastern Caucasus
Abstract
Upper Eocene and Lower Oligocene rocks in the northeastern Caucasus were examined in the most representative Chirkei section (Sulak River basin). Sharp lithogeochemical distinctions between them were revealed. The results of the study of nannoplankton demonstrated that the Eocene/Oligocene interface occurs slightly below the boundary between the Belaya Glina and Khadum formations. The studied section revealed a series of nannoplankton bioevents facilitating its stratigraphic subdivision. It has been established that organic matter (OM) in rocks of the Khadum Formation is characterized by a relatively high degree of maturity. Probably, the material of mainly marine genesis contains a terrigenous OM admixture. Positive oxygen isotope anomaly in the upper part of the Belaya Glina Formation reflects global climate changes (cooling) near the Eocene/Oligocene interface. Limitation of the anomaly by the upper boundary of the Belaya Glina Formation is likely related to changes in water salinity variations in the Early Oligocene basin and intense early diagenetic processes in rocks therein. Lithological, geochemical, and paleoecological data suggest that the Khadum paleobasin was depleted in oxygen. Such environment was unstable with periodic intensification or attenuation. Paleoecology in the Belaya Glina basin was typical of normally aerated basins.
Variation of the chemical composition of sediments under middle- and low-temperature hydrothermal conditions in the southern trough of Guaymas Basin, Gulf of California: Communication 1. results of the study of bulk sediment samples
Abstract
The paper presents the results of the study of variations in the content of macro- and microelements (rare earth elements included) in the Upper Pleistocene sediments from DSDP Hole 477. The variations took place at the depth interval 110–191 m in the course of temperature drop to about 100°C in the upper part of the hydrothermal system. Variations in the content of most chemical elements in sediments from DSDP Hole 477 are manifested more weakly than in the underlying sediments of the interval 191–267 m of DSDP Hole 477A that were altered at a temperature of about 300°C. For many chemical elements, influence of the sedimentary cover on the compositional transformation of solutions during their interaction with sediments attenuates with the cooling of its upper part to the point of its complete termination.
Sr chemostratigrphy, δ13C, and δ18O of rocks in the Crimean carbonate platform (Late Jurassic, northern Peri-Tethys)
Abstract
The paper presents the results of study of the Sr, C, and O isotope compositions in Upper Jurassic carbonate rocks of the Baidar Valley and Demerdzhi Plateau in the Crimean Mountains represented by different facies of the carbonate platform at the northern active margin of the Tethys. The 87Sr/86Sr value in them varies from 0.70699 to 0.70728. Based on the Sr chemostratigraphic correlation, the age of massive and layered limestones in the western part of the Ai-Petri and Baidar yailas (pastures) is estimated as late Kimmeridgian–early Tithonian, whereas the age of flyschoids of the Baidar Valley are estimated as late Tithonian–early Berriasian. The nearly synchronous formation of carbonate breccias of the Baidar Valley and Demerdzhi Plateau in late Tithonian–early Berriasian is substantiated. A summary section of Upper Jurassic rocks is compiled based on the Sr chemostratigraphic data. It has been established that δ18O values in the studied carbonate sediments vary from–2.9 to 1.3‰ (V-PDB). At the same time, shallow-water sediments in the internal part and the edge of the Crimean carbonate platform are depleted in 18O (–2.9 to +0.1‰) relative to sediments on the slope and foothill (–0.5 to +1.3‰). It is demonstrated that δ13C values do not depend on the facies properties and decrease in younger carbonate sediments from 3–3.5‰ to 1–1.5‰ in line with the Late Jurassic general trend. The δ13C values obtained for the Crimean carbonate platform turned out to be 0.5–1‰ higher than the values typical of the deep-water marine setting at the western margin of the Tethys. These discrepancies are likely related to peculiarities of water circulation and high bioproductivity in marine waters of the northern Peri-Tethys.
Tectono-depositional history of the Central Russian aulacogen and Moscow syneclise
Abstract
The modern structure of the Central Russian region was formed by tight and long-term (hundreds of million years) interaction of tectonic and sedimentary processes in the upper crust and sedimentary cover. Petrophysical properties of the Paleoproterozoic crust predetermined the area for the development of regional strike-slip faults and aulacogen grabens in the Neoproterozoic. The transfer displacement of the aulacogen axis at the end of Riphean led to the partial erosion and redeposition of the preplate cover and caused the subsequent structural asymmetry of syneclise. The development of reversed structures in the plate cover (Sukhona mega swell) was caused by the slower subsidence of comparatively lighter fragments of the aulacogen crust relative to the surrounding frame.
Basic-to-acid and acid-to-basic zonation in the sulfur isotope composition of diagenetic sulfide nodules
Abstract
The typical for marine sediments decrease in the amount of sulfate ion in interstitial solutions with increasing depth owing to sulfate reduction and attenuation of the diffusion of near-bottom waters is manifested as the basic-to-acid zonation in the sulfur isotope composition of the diagenetic pyrite nodules (increase of δ34S values from the center to edge). In sandstones of the Early Carboniferous Emyaksin Formation, which is developed at middle reaches of the Vilyui River (Sakha-Yakutia), we detected a peculiar sulfide nodule. In contrast to common nodules, this nodule is marked by the δ34S value decreasing from 7.5…8.6‰ at the center to –30…–31.4‰ at the edge. Such acid-to-basic zonation is attributed to the origin of nodule in a freshened basin (delta) with a sulfate-depleted environment, which gave way to a sulfate-enriched environment owing to the expulsion brines from the underlying gypsiferous sequences.
Alteration mineralogy of eocene volcanic and volcaniclastic rocks from Sivas basin in Turkey
Abstract
The study area covers volcanic-volcanosedimentary units of Eocene age in the Sivas-Ulaş area from Turkey. The pyroclastic (tuffaceous claystone/siltsone/sandstone, crystal ash tuff) and volcanic (basalt, basaltic andesite, andesite) rocks of the Karacalar member from the Kaleköy Formation include volcanogenic (plagioclase, augite, hornblende, biotite), diagenetic (K-feldspar, mixed-layered chlorite-smectite/C-S, chlorite, analcime) and post-volcanic (calcite, dolomite, quartz) minerals. The volcanogenic (plagioclase), diagenetic (K-feldspar, C-S, chlorite), postvolcanic (quartz, calcite, dolomite) and detrital (illite) minerals were observed in the epiclastic (shale, siltstone, calcareous siltstone, sandstone, calcareous sandstone) and chemical (limestone, gypsum) rocks of the Yapali member from this formation. C-S + K-feldspar zoning is widely developed by due to the interaction between sea-water and volcanic glass in basic-intermediate composition, on the basis of optic and electron microscopes and also X-rays data. This zone corresponds to the deeper parts of the Sivas basin in the Eocene period and show vertically a transition into zeolite zone in approximately northern parts of the basin (Yavu area).