Geochemical anomalies in South Caspian sediments

Study of the element composition of ten samples of modern terrigenous and carbonate sediments from the northern part of the Caspian Sea by the ICP-MS method showed that these sediments were enriched in sulfur, nonferrous metals, and some related minor elements including Se, Te, Re, and others in comparison with the average composition of sedimentary rocks. It is assumed that local hydrothermal seeps similar to those known on the Cheleken Peninsula and which may be formed in other areas of this tectonically active zone are the sources of these elements. In addition, such a composition of sediments may indicate the sporadic contamination of bottom water with hydrogen sulfide, which has been observed in areas of the South and Middle Caspian by many researchers.     

REE systematics in modern bottom sediments of the Caspian Sea and river deltas worldwide: Experience of comparison

The results of comparison of a number of main parameters of the chondrite-normalized REE distribution spectra in modern bottom, mainly pelitic, sediments of various sedimentary subsystems of the Caspian Sea and marginal filters of the Volga and Ural rivers with those characteristic of the pelitic fraction of modern bottom sediments of different river deltas worldwide are discussed. According to the features of the REE distribution spectra, as well as the ε_Nd(0) values, it has been established that most samples of the Caspian bottom sediments are similar to those of large rivers and rivers, draining watersheds composed of sedimentary formations.     

First results of investigation into the relation between magnetic properties of bottom sediments in the Northern Caspian and variations in the Caspian Sea level in the Late Neo-Pleistocene

The first data of investigation into the relation between changes in magnetic properties of the Northern Caspian sediments and variations in the Caspian Sea level in the Late Neo-Pleistocene are presented. It is shown that there is a certain correlation between magnetic characteristics of sediments and variations in the Caspian Sea level that cause changes in the lithological and faunistic composition of sediments.     

First find of kutnohorite in modern sediments of the South Caspian basin

High-manganese kutnohorite was found in the surface layer of bottom sediments of the South Caspian basin by the method of X-ray diffraction for the first time. Bottom sediments were collected by a multicorer during the 39th voyage of R/V Rift in 2012. Study of the samples by a complex of methods (X-ray diffraction, scanning electron microscopy, atomic absorption, and analysis of the carbon isotope composition) allowed us to attribute kutnohorite to autigenic minerals of the early stage of diagenesis.     

Holocene deposits in the Mangyshlak Peninsula,North Caspian Sea region

Comprehensive analysis of the data of high-precision seismoacoustic profiling, drilling and sampling of deposits using seabed corers, biostratigraphic studies, and radiocarbon age data was performed for the first time for Mangyshlak sediments in several bottom sites of the North Caspian. It was found that the Mangyshlak sediments comprise numerous linearly stretched depressions of 5–10 m in depth (morphologically similar to modern substeppe ilmen areas in the Volga River delta), which are covered by the Novocaspian sedimentary cover, and river incisions (among them the largest Volga River valley). In addition, the Mangyshlak sediments comprise the deltaic alluvial fans of different sizes along the shelf zone of the North Caspian. Analysis of mollusks and biogenic remains indicates that accumulation of the Mangyshlak sediments occurred in freshwater and slightly salty water environments under various hydrodynamic and hydrochemical conditions. According to radiocarbon dating of organic matter, the Mangyshlak sediments formed during sea regression in the range of 10-8 ka (isotopic age) or 11.5-8.5 ka (calendar age). Several types of sediments are distinguished: clayey-carbonate sediments, enriched with organic matter up to the formation of sapropel and peat, accumulated at the lowest sea level; weakly calcareous silty-clayey silts, formed during the subsequent intense filling of paleodepressions with terrigenous material. The features of the mineral composition of sediments are as follows: polymineral composition of clayey material with a high proportion of hydromica and disordered mixed-layered formations, a high content of minerals of the epidote group, amphiboles, and other accessory minerals. All of this indicates a genetic relationship between the Mangyshlak sediments and the Volga terrigenous material.     

Magnetic Susceptibility of Deep-Water Sediments of the South and Middle Caspian Sea

The dependence of magnetic susceptibility () of bottom sediments from the Caspian Sea on the composition of magnetoactive minerals contained in the heavy subfraction of fine-grained sand (0.125–0.100 mm) was established. Changes in the curve shape and value reflect a pulsating pattern of the input different (in magnetic properties) magmatic and metamorphic clastic minerals into sediments, as well as different intensities of the formation of authigenic magnetoactive iron sulfides under conditions of the multiple alternation of transgressive and regressive phases in marine basins. Values of and shapes of curves for the studied sedimentary sequences show that sediments in the South and Middle Caspian basins are characterized by different specific features.     

Genesis of organic and carbonate carbon in sediments of the North and Middle Caspian basins inferred from the isotope data

Isotopic compositions of organic (δ¹³C-C_org) and carbonate (δ¹³C-C_carb) carbon were analyzed in the particulate matter (hereafter, particulates) and sediments from the North and Middle Caspian basins. Isotopic composition of C_org was used for assessing proportions of the allochthonous and autochthonous organic matter in the particulates. Difference between the δ¹³C-C_org values in surface sediments and particulates is explained by the aerobic and anaerobic diagenetic transformations. Isotopic composition of C_org in sediments may be used as a tool for reconstructing the Quaternary transgressive-regressive history of the Caspian Sea.     

Oroclinal bending in the Alborz Mountains (Northern Iran): New constraints on the age of South Caspian subduction and extrusion tectonics

In this study, we report an extensive paleomagnetic study (76 sites) carried out in the Alborz Mts. (northern Iran), with the aim of reconstructing the rotation history and the origin of curvature of this orogenic chain. The analyzed deposits are the sedimentary successions of the Upper Red Formation (Miocene), Lower Red Formation (Oligocene) and Eocene clastic units. Paleomagnetic results indicate that the Alborz Mts. can be considered a secondary arc that originated as a linear mountain belt that progressively acquired its present day curvature through opposite vertical axis rotations along its strike. The curvature of the arc was entirely acquired after the middle-late Miocene, which is the age of the youngest investigated sediments (Upper Red Formation). Overall, our paleomagnetic data indicate that the Alborz Mts. can be considered an orocline.Our results define, for the first time, the rotational history of the entire Alborz curved mountain belt, and enable us to reconstruct the paleogeographic and tectonic evolution of northern Iran in the framework of Arabia-Eurasia continental deformation. The kinematics inferred by the pattern of paleomagnetic rotations is at odds with the present day kinematics of northern Iran, characterized by the westward extrusion of the South Caspian block, and by a left lateral shear between Central Iran and the central and western sectors of the Alborz Mts. By integrating paleomagnetic data with stratigraphic, thermochronological, structural and GPS information, we propose that the initiation of South Caspian subduction and the activation of westward extrusion of South Caspian block occurred diachronously and that the initiation of the present-day kinematics of northern Iran was quite recent (Lower Pleistocene, < 2 Ma).     

Geochemical features of the ecosystem of Lake Kolyvan (Altai territory) and related technogenic impact

Regularities of the formation of bottom sediments down to a depth of 1.2 m, as well as factors governing the composition of sediments, waters, and soils in the catchment area of the lake, are discussed. It has been established that the chemical composition of lacustrine sediments is closely associated with the composition of soils in the ambient watersheds, and the soils, in turn, are associated with the composition of the soil-forming rocks. The available data suggest an extremely irregular contamination of the lake system by technogenic radionuclides within the water area. Maximum radiocesium contamination of lacustrine bottom sediments is 350 mCi/km² (recalculated to year 2000). Concentrations of elements (Cu, Zn, Cr, Ni, Co, Mg, Be, Sb, Mn, and others) in bottom sediments, water, and soils in catchment areas of Lake Kolyvan do not exceed the background values (except for the Hg content in bottom sediments), suggesting that the area under consideration is not contaminated by inorganic technogenic components.     

Mud volcanic natural phenomena in the South Caspian Basin: geology,fluid dynamics and environmental impact

The South Caspian sedimentary basin is a unique area with thick Mesozoic-Cenozoic sediments (up to 30–32 km) characterized by an extremely high fluid generation potential. The large amount of active mud volcanoes and the volumes of their gas emissions prove the vast scale of fluid generation. Onshore and offshore mud volcanoes annually erupt more than 10⁹ cubic meters of gases consisting of CH₄ (79–98%), and a small admixture of C₂H₆, C₃H₈, C₄H₁₀, C₅H₁₂, CO₂, N, H₂S, Ar, He. Mud volcanism is closely connected to the processes occurring in the South Caspian depression, its seismicity, fluctuations of the Caspian Sea level, solar activity and hydrocarbon generation.The large accumulations of gas hydrates are confined to the bottom sediments of the Caspian Sea, mud volcanoes crater fields (interval 0–0.4 m, sea depth 480 m) and to the volcanoes body at the depth of 480–800 from the sea bottom. Resources of HC gases in hydrates saturated sediments up to a depth of 100 m and are estimated at 0.2×10¹⁵–8×10¹⁵ m³. The amount of HC gases concentrated in them is 10¹¹–10¹² m³.The Caspian Sea, being an inland closed basin is very sensitive to climatic and tectonic events expressed in sea level fluctuations. During regressive stages as a result of sea level fall and the reducing of hydrostatic pressure the decomposition of gas hydrates and the releasing of a great volume of HC gases consisting mainly of methane are observed.From the data of deep drilling, seismoacoustics, and deep seismic mud volcanic activity in the South Caspian Basin started in the Lower Miocene. Activity reached its highest intensity at the boundary between the Miocene and Pliocene and was associated with dramatic Caspian Sea level fall in the Lower Pliocene of up to 600 m, which led to the isolation of the PaleoCaspian from the Eastern ParaTethys. Catastrophic reduction of PaleoCaspian size combined with the increasing scale of mud volcanic activity caused the oversaturation and intoxication of water by methane and led to the mass extinction of mollusks, fishes and other groups of sea inhabitants. In the Upper Pliocene and Quaternary mud volcanism occurred under the conditions of a semi-closed sea periodically connected with the Pontian and Mediterranean Basins. Those stages of Caspian Sea history are characterized by the revival of the Caspian organic world.Monitoring of mud volcanoes onshore of the South Caspian demonstrated that any eruption is predicted by seismic activation in the region (South-Eastern Caucasus) and intensive fluid dynamics on the volcanoes.     

First results on determination of chlorophill <Emphasis Type="Italic">A</Emphasis> and its derivatives in the system of trapped sedimentary material–fluffy layer–bottom sediment of the Caspian Sea

The first data were obtained on the vertical chlorin flux in the water column and its accumulation in the upper layer of sediments of the Caspian Sea. Seasonal variability of the chlorine concentration in sedimentary matter was evaluated. The tendency of decrease in the phytoplankton-synthesized (allochtonous) organic matter content was revealed over approximately the past 60 years.     

Factors controlling the mineralogy and geochemistry of the recent surface sediments of the Kalloni Gulf,Lesvos Island,Greece

Detailed chemical and mineralogical data are presented for 37 samples of surface sediments collected from the Kalloni gulf, (eastern half), Lesvos island, northern Greece. The sediments are largely carbonate-rich muds, though near the eastern and northern coast of the gulf higher proportions of biogenic and lithogenic sands and gravels occur. The main minerals are quartz, feldspar (andesine), clay minerals (montmorillonite, illite, Kaolinite) and the carbonate minerals (calcite, Mg-calcite, aragonite). The mathematical method of factor analysis was applied in order to explain the mineralogical and geochemical variations. These variations can be interpreted in terms of variations in provenance and depositional environment. Six factors were produced accounting for 83.6 % of the total data variance: (a) a Si-Al-Na-K-Ti-Rb-Ba-Y-Zr factor controlled by clays and detrital minerals such as feldspars and zircon opposed by a CaCO₂-Cu-Sc-Sr-La association (carbonate, minerals), (b) an organic carbon factor (C-Fe-Ce-Zn-Rb-Ni-Y-Nb), (c) a Fe-Mg-Cr-Ni factor representing control by peridotite, (d) a Ce-Nd-Fe-Ni-Zn-La factor controlled by silicate minerals, (e) a Al-Fe-Ti-P-V factor controlled by chlorite amphiboles or pyroxenes of volcanic or basaltic intrusions, (f) a Mn-Fe-Zn-factor controlled by iron-manganese oxides. Similarities in trace element composition among Kalloni gulf bottom sediments, and source lithologies indicate that the trace elements are derived from the adjacent landmasses. The AI/Ti ratio of the sediments is consistent with the terrigenous nature of sendimentation in the Kalloni gulf.     

Petroleum systems and the history of their formation in the northern Caspian Sea basin

This study presents the consideration of the geological history and petroleum systems in the northern Caspian Sea basin (on the basis of basin modeling using the TemisSuite2008 software package). The key patterns of the distribution of oil and gas fields and their phase composition are described. Kulaginskii Ridge and the adjacent areas are considered. The preceding data are generalized and new data are used.     

Evidence for the zircon origin of cadmium anomalies in bottom sediments from the littoral zone of the northern part of Lake Ladoga

The minor-element composition of bottom sediments from the littoral zone of the northern part of Lake Ladoga was studied. Close relationships between the anomalous Cd concentrations in lake sediments and Quaternary glacial formations on the territory of Karelia were shown. A negative correlation of Cd with other heavy metals and a positive correlation with Zr were observed. Most likely, Cd is an impurity in zircons from sandy and sandy loam sedimentary formations on the northern coastal area of Lake Ladoga.     

Gas seeps in the North Caspian water area

Seismoacoustic profiling and sonar survey of the North Caspian water area revealed in some areas signs of intense release of methane from the sedimentary sequence. This fact was also supported by submarine videorecording data. Such sites are characterized by hummocky and ridgy morphologies, which accommodate local cone-shaped bodies (up to 1.3–1.5 m high) overgrown with algae, Balanus, and shelly material. Based on dredging data, these rises are composed of hard sandstones and shells. They can cover the seafloor or make up separate interlayers in the bottom sediments down to a depth of 2.7 m. Mineralogical studies demonstrated that the coarse-grained sediments are cemented with Mg-calcite, with δ¹³C reaching ?32.6‰. They also include microcrystalline barite and globular iron sulfides. The results of investigation suggest that the local activation of authigenic mineral formation is related to gas discharge sources.     

Distribution of hydrocarbons in water and bottom sediments of the Northern and Middle Caspian Sea

A study of two classes of hydrocarbons (HCs)—aliphatic and polycyclic aromatic—in suspended matter of the surface waters and bottom sediments of the Northern and Middle Caspian Sea (R/V Nikifor Shurekov, October 2015) is described. It has been determined that oil pollution transported by river runoff and fluid streams flowing from sedimentary formations in the northeastern part are the main sources of hydrocarbons in the river–sea boundaries of the Volga, Terek, and Sulak rivers.     

Thermodynamic model of formation of carbonates and uranium mineral phases in lakes Namshi-Nur and Tsagan-Tyrm (Cisbaikalia)

The Tazheran lakes are located compactly in the small Tazheran steppe area. Their bottom sediments are predominantly various calcite-dolomite carbonates, and their waters are rich in uranium. The studies have shown that the main process in these lakes is chemogenic carbonate precipitation with the participation of carbon dioxide formed through the bacterial destruction of organic matter. For thermodynamic modeling of the composition of bottom sediments, we chose two lakes with different basic parameters. Calculations were made for the 15-component heterogeneous system H₂O-Na-Ca-Mg-K-Sr-Ba-Si-Al-Cl-C-S-Fe-U-Mn including particles in the solution, minerals, and gases at 25 °C and 1 bar. As starting information, we used the obtained analytical data on the natural composition of waters and bottom sediments. The results show that calcite-dolomite carbonates are predominant in the bottom sediments and the destruction of organic matter results in reducing conditions. This confirms the hypothesis of the formation of mineral phases of U(IV) during diagenetic processes in the bottom sediments of the studied lakes.     

Geochemistry of trace element in carbonaceous sediments from recent seas and oceans

Published and original data on the contents of 50 elements in carbonaceous sediments from seas (Black, Baltic, and Caspian) and fertile oceanic shelves (shelves of Namibia, Peru, Chile, and California) are generalized. The comparison of these results with the average composition of ancient carbonaceous shales reveals both similarities and differences in the distribution of indicator trace elements (Re, Hg, Se, Ag, Cd, Tl, U, Mo, As, Ni, and Zn). Correlation coefficients were analyzed to determine the characteristic element associations. It is established that oceanic carbonaceous sediments are closer in composition to carbonaceous shales than their marine analogues, which is related to the differences in sedimentation conditions, including hydrological, hydrochemical, and biogeochemical factors. The role of anoxic environment in the accumulation of chalcophile elements in sediments is estimated. The comparison of the contents of some mobile trace elements in oceanic water and carbonaceous sediments of modern oceans demonstrates that the water composition affects the composition of carbonaceous sediments and can be used for deciphering the composition of ancient ocean water.     

Organic matter in the bottom sediments of the Ob Bay: Distribution,nature, and sources

The lateral variability of main geochemical parameters of dispersed organic matter (DOM) in the bottoms sediments of the Ob Bay was studied using materials of areal geological survey. It was found that they correspond to background compositions of estuarine-delta facies of the Western Arctic shelf, being mainly determined by the influx of river run-off and coastal abrasion. The distribution of DOM and its components is controlled by the hydrodynamic regime of the water area and grain-size composition of sediments. The molecular composition of hydrocarbon markers (n-alkanes, cyclanes, and arenes) confirms the dominant role of terrigenous humic material in the formation of DOM of the bottom sediments, while temporal stability of quantitative and qualitative geochemical characteristics indicates the stability of the Ob Bay ecosystem.     

Composition and origin of organic matter in surface sediments of Lake Sarbsko: A highly eutrophic and shallow coastal lake (northern Poland)

We present an organic geochemical study of surface sediments of Lake Sarbsko, a shallow coastal lake on the middle Polish Baltic coast. The aim was to provide evidence concerning the origin of the organic matter (OM) and its compositional diversity in surface deposits of this very productive, highly dynamic water body. The content and composition of the OM in the bottom sediments were investigated at 11 sampling stations throughout the lake basin. OM sources were assigned on the basis of bulk indicators [total organic carbon (TOC), total nitrogen (TN), δ¹³C_TOC and δ¹⁵N and extractable OM yield], biomarker composition of extractable OM and compound-specific C isotope signatures. The source characterization of autochthonous compounds was verified via phytoplankton analysis. The distribution of gaseous hydrocarbons in the sediments, as well as temporal changes in lake water pH, the concentration of DIC (dissolved inorganic carbon) and δ¹³C_DIC were used to trace OM decomposition.The sedimentary OM is composed mainly of well preserved phytoplankton compounds and shows minor spatial variability in composition. However, the presence of CH₄ and CO₂ in the bottom deposits provides evidence for microbial degradation of sedimentary OM. The transformation of organic compounds in surface, bottom and pore waters via oxidative processes influences carbonate equilibrium in the lake and seasonally favours precipitation or dissolution of CaCO₃.The data enhance our understanding of the relationships between the composition of sedimentary OM and environmental conditions within coastal ecosystems and shed light on the reliability of OM proxies for environmental reconstruction of coastal lakes.