V. Yu. Rusakov

Mineralogical and geochemical zoning of sediments at the Semenov cluster of hydrothermal fields, 13°31′-13°30′ N, Mid-Atlantic Ridge

New material from eight columns recovered during Cruise 32 of the R/V Professor Logachev in 2009 was used to explore the lithological facies, biostratigraphy, mineralogy, and geochemistry of sediments from the northwestern (active) and eastern (inactive) hydrothermal vent fields of the Semenov cluster. Mineral types of sediments were distinguished, and a general scheme was proposed for the vertical structure of the hydrothermal-sedimentary sequence overlying massive sulfide ores. It was found that the ore-bearing sediments exhibit a vertical zoning in the distribution of mineral assemblages, which are controlled by oxygen activity. The mechanisms of the formation of atacamite, CuCl2 · 3Cu(OH)2, which is a widespread mineral in red iron-oxide bodies replacing sulfides (gossans), were evaluated.

Chemical composition of late Pleistocene-Holocene pelagic sediments in Gakkel Ridge, Arctic Ocean

The paper presents data on the chemical composition of Late Pleistocene-Holocene sediments in the Gakkel Ridge according to data on sediment core PS 70/306-3, offers a hypothetical litho-stratigraphic model, and provides data on chemo-stratigraphic horizons distinguished based on the distribution of carbonates, organic carbon, metals (Fe, Mn, Cu, Zn, Co, Ni, V, Pb), As, and P in the core. Chemical transformations of sediments at the redox barrier are discussed, along with relations between the composition of the sediments and the facies sedimentation conditions.

Geochemical characteristics of hydrothermal plumes above the TAG and Broken Spur fields of the Mid-Atlantic Ridge

The paper reports data on the distribution of solute (Mn, Zn, Cu, Pb, and Cd) and particulate (Fe, Mn, Zn, Cu, Pb, Ni, and Co) species of metals in hydrothermal plumes above the active TAG and Broken Spur hydrothermal fields (26° N and 29° N in the MAR rift valley, respectively). Sediment-trap data on fluxes of hydrothermal-sedimentary material in the areas indicate that (i) the predominant Zn source for the metalliferous sediments at the TAG field is material precipitating from a plume of neutral buoyancy, and (ii) the predominant source of Fe and Co is redeposited ore material coming from the area of extensive settling of sulfides.

Comparative analysis of the mineral and chemical compositions of black smoker smoke at the TAG and Broken Spur hydrothermal fields, mid-Atlantic ridge

The paper presents newly obtained data on the fluxes of hydrothermal-sedimentary material collected with sedimentation traps within 3 m from the bottoms of black smokers at the TAG and Broken Spur hydrothermal fields and reports the results of comparative analysis of the mineralogical and chemical compositions of this material. The sedimentary material deposited near the vent was determined to account to approximately 3% of the overall mass of the orebody. The results demonstrate that, in both cases, the trap material is characterized by high contents of ore components and ore-forming chemical elements (Fe, Cu, Zn, and Co), and Se, As, Sb, Ba, and P compared to tholeiitic basalts from which these elements are leached. However, the material of a more “mature” (having an age of 40–50 ka) hydrothermal spring at the TAG field contains 40% Fe hydroxides, in contrast to the material of a spring at the Broken Spur field (age <1000 yr) whose material is dominated by sulfides (72%) and contains much pyrrhotite. These springs also show principal differences between the enrichment coefficients for Se (by a factor of 4.8), As (3), Ca (4.1), and Si (5.2). These differences are thought to reflect various evolutionary stages of the circulating hydrothermal systems.

The use of statistical methods for studying the chemical composition of oceanic sediments: Evidence from deep-water Upper Pleistocene-Holocene sediments in the Gakkel ridge, part II

This paper is a continuation of the work that was published in Geochemistry International in 2010 [1]. Based on lithological and trace-element study of sediments, a hypothetical lithostratigraphic model was proposed and lithostratigraphic horizons were identified. In this paper, we carried out statistical treatment of chemical data (on 28 elements) on the Upper Pleistocene-Holocene sediments of the Gakkel Ridge (core PS 70/306-3). Cluster analysis coupled with lithostratigraphic data was used to distinguish individual groups (clusters) of the core beds, while factor analysis allowed deciphering the main stages in the sedimentation history.

Late Quaternary Migrations of the Subarctic Front in the North Atlantic (Based on Lithology and Nannofossils)

A complex of lithological and micropaleontological methods were used for the study of sediments from the central North Atlantic (50–60°N). The data on the lithology, carbonate content, and occurrence of ash interbeds and ice-rafted material, combined with the nannofossil zonal biostratigraphy, allowed detailed subdivision of five core sections obtained during Cruise 48 of R/V Akademik Mstislav Keldysh. MIS 1–MIS 9 are established in the sections. In some of them, climatic changes related to migrations of the Subarctic Front are established based on the lithology and the characteristic coccolithophorid species: for example, a higher latitudinal position of the front is revealed for the Eemian interglacial (Substage 5e) as compared with that in the Holocene.

Estimation of the scale of spatiotemporal variability in the lithological and geochemical characteristics of suspended particulate matter and bottom sediments at the mouth of the Volga River and the adjacent zone of the northern Caspian

Based on the data of synchronous observations of hydrophysical and biogeochemical parameters in the near-mouth and shallow-water areas of the northern Caspian in 2000–2001, the scale of spatiotemporal variability in the following characteristics of the water-bottom system was estimated (1) flow velocity and direction within vortex structures formed by the combined effect of wind, discharge current, and the presence of higher aquatic plants; (2) dependence of the spatial distribution of the content and composition of suspended particulate matter on the hydrodynamic regime of waters and development of phytoplankton; (3) variations in the grain-size, petrographic, mineralogical, and chemical compositions of the upper layer of bottom sediments at several sites in the northern Caspian related to the particular local combination of dominant natural processes; and (4) limits of variability in the group composition of humus compounds in bottom sediments. The acquired data are helpful in estimating the geochemical consequences of a sea level rise and during the planning of preventive environmental protection measures in view of future oil and gas recovery in this region.

Supply and precipitation of hydrothermal iron in the rift valley of the Mid-Atlantic Ridge at 26° and 29° N

This publication considers the probing data on aquatic anomalies (hydrothermal plumes) in the areas of 26° and 29° N of the Mid-Atlantic Ridge (MAR). The mass of the hydrothermal iron supply and the intensity of the iron sedimentation onto the bottom were estimated by means of sediment traps. It was found that the plume of the TAG hydrothermal vent 6 km3 in volume contained about 67 t of suspended Fe; the plume of the Broken Spur field (up to 8.24 km3 in volume) contained 23.5 t or less because of the lower concentration. The data on the sedimentary matter fluxes showed that 0.3–0.5% of the hydrothermal iron was precipitated immediately from a plume of neutral buoyancy onto the bottom; the bulk of the iron was dissipated into the environment. From the dimensions of the plumes, the flow dynamics, the iron concentrations in the plumes, and the amounts of iron supplied by hydrothermal vents, it was found that the resident time of the plumes considered was from 5 to 10 days.

Lithological and geochemical typification of surface bottom sediments in the Kara Sea

The Kara Sea is part of the Western Arctic shelf of Eurasia. The deposition of sediments in this shallow sea is largely determined by solid runoff from two great Siberian rivers (the Yenisei and Ob) and the glacial periods when the sea area repeatedly (during the Quaternary) dried up and was covered by continental glaciers. The rise of the World Ocean due to Holocene warming resulted in a significant expansion of the sea area to the south and complete degradation of the ice sheet. In this article, new data on the geochemical composition of the surface (0- to 2-cm) layer of sea-bottom sediments are considered, which reflects the spatial distribution of marine sediments during the maximum sea level. Cluster analysis of the variance for 24 chemical elements reveals sediment chemotypes, and critical analysis of their relationship with lithotypes is performed. The presented data have been collected on cruises of the R/V Akademik Boris Petrov in 2000, 2001, and 2003 and the R/V Akademik Mstislav Keldysh in 2015.

Heavy metal distribution in the surface layer of bottom sediments of the Kara Sea

This paper addresses the distribution of heavy metals (Co, Ni, Cu, Zn, Cd, Sn, Sb, Pb, and Bi) as well as Si, Al, Fe, and Mn in the surface (0–2 cm) layer of bottom sediments of the Kara Sea. The contents of these elements are determined in each of the previously distinguished facies-genetic types of terrigenous sediments: fluvial, glacial, estuarine, shallow water–marine, “background” marine, and relict sediments. It is shown that these types reflect the modern conditions of accumulation of river discharge material, which forms fans of two greatest Siberian rivers, Ob and Yenisei. The main stages are distinguished in heavy metal accumulation. The first stage is related to the avalanche sedimentation of terrigenous sediments in the estuary and characterized by the elevated contents of Co, Ni, Cu, Zn, Cd, Sb, and Bi. The second stage reflects the mechanical differentiation of sedimentary material by waves and bottom currents in a shallow-water sea part adjacent to the estuarine zone, with accumulation of Pb- and Sn-bearing “heavy” ore minerals. The deepwater background terrigenous–marine sediments accumulate mainly Ni, Zn, and Cd, as well as Mn. The relict sediments differ in the high contents of Si, Mn, and Sn.