Large-Scale Smoke Haze over the European Part of Russia and Belorus in July 2016

Izvestiya, Atmospheric and Oceanic Physics - The smoke haze over the European part of Russia (EPR) and Belorus in July 2016 has been studied with the use of aerosol optical thickness (AOT) data...     

Volcanic arc of Kamchatka: a province with high-δO magma sources and large-scale O/O depletion of the upper crust

We present the results of a regional study of oxygen and Sr-Nd-Pb isotopes of Pleistocene to Recent arc volcanism in the Kamchatka Peninsula and the Kuriles, with emphasis on the largest caldera-forming centers. The δ¹⁸O values of phenocrysts, in combination with numerical crystallization modeling (MELTS) and experimental fractionation factors, are used to derive best estimates of primary values for δ¹⁸O(magma). Magmatic δ¹⁸O values span 3.5‰ and are correlated with whole-rock Sr-Nd-Pb isotopes and major elements. Our data show that Kamchatka is a region of isotopic diversity with high-δ¹⁸O basaltic magmas (sampling mantle to lower crustal high-δ¹⁸O sources), and low-δ¹⁸O silicic volcanism (sampling low-δ¹⁸O upper crust). Among one hundred Holocene and Late Pleistocene eruptive units from 23 volcanic centers, one half represents low-δ¹⁸O magmas (+4 to 5‰). Most low-δ¹⁸O magmas are voluminous silicic ignimbrites related to large >10 km³ caldera-forming eruptions and subsequent intracaldera lavas and domes: Holocene multi-caldera Ksudach volcano, Karymsky and Kurile Lake-Iliinsky calderas, and Late Pleistocene Maly Semyachik, Akademy Nauk, and Uzon calderas. Low-δ¹⁸O magmas are not found among the less voluminous products of stratovolcano eruptions and these volcanoes do not show drastic changes in δ¹⁸O during their evolution. Additionally, high-δ¹⁸O(magma) of +6.0 to 7.5‰ are found among basalts and basaltic andesites of Bezymianny, Shiveluch, Avachinsky, and Koryaksky volcanoes, and dacites and rhyolites of Opala and Khangar volcanoes (7.1-8.0‰). Phenocrysts in volcanic rocks from the adjacent Kurile Islands (ignimbrites and lavas) define normal-δ¹⁸O magmas. The widespread and volumetric abundance of low-δ¹⁸O magmas in the large landmass of Kamchatka is possibly related to a combination of near-surface volcanic processes, the effects of the last glaciation on high-latitude meteoric waters, and extensive geyser and hydrothermal systems that are matched only by Iceland. Sr and Pb isotopic compositions of normal and low-δ¹⁸O, predominantly silicic, volcanic rocks show negative correlation with δ¹⁸O, similar to the trend in Iceland. This indicates that low-δ¹⁸O volcanic rocks are largely produced by remelting of older, more radiogenic, hydrothermally altered crust that suffered δ¹⁸O-depletion during >2 My-long Pleistocene glaciation. The regionally-distributed high-δ¹⁸O values for basic volcanism (ca. + 6 to +7.5‰) in Kamchatka cannot be solely explained by high-δ¹⁸O slab fluid or melt (± sediment) addition in the mantle, or local subduction of hydrated OIB-type crust of the Hawaii-Emperor chain. Overall, Nd-Pb isotope systematics are MORB-like. Voluminous basic volcanism (in the Central Kamchatka Depression in particular) requires regional, though perhaps patchy, remobilization of thick (30-45 km) Mesozoic-Miocene arc roots, possibly resulting from interaction with hot (ca. 1300°C), wedge-derived normal-δ¹⁸O, low-⁸⁷Sr/⁸⁶Sr basalts and from dehydration melting of lower crustal metabasalts, variably high in δ¹⁸O and ⁸⁷Sr/⁸⁶Sr.     

Middle to late Pleistocene record of explosive volcanic eruptions in marine sediments offshore Kamchatka (Meiji Rise,NW Pacific)

This paper presents the first detailed study of a late Pleistocene marine tephra sequence from the NW Pacific, downwind from the Kamchatka volcanic arc. Sediment core SO201-2-40, located on the Meiji Rise ~400 km offshore the peninsula, includes 25 tephras deposited within the last 215 ka. Volcanic glass from the tephras was characterized using single-shard electron microprobe analysis and laser ablation inductively coupled mass spectrometry. The age of tephras was derived from a new age model based on paleomagnetic and paleoclimate studies. Geochemical correlation of distal tephras to Kamchatkan pyroclastic deposits allowed the identification of tephras from the Karymsky, Gorely, Opala and Shiveluch eruptive centers. Three of these tephras were also correlated to other marine and terrestrial sites and hence are identified as the best markers for the north-west Pacific region. These are an early Holocene tephra from the Karymsky caldera (~8.7 ka) and two tephras falling into the Marine Isotope Stage (MIS) 6 glacial time: an MIS 6.4 tephra from Shiveluch (~141 ka) and the MIS 6.5 Rauchua tephra (~175 ka) from Karymsky. The data presented in this study can be used in paleovolcanological and paleoceanographic reconstructions.     

Early Holocene M~6 explosive eruption from Plosky volcanic massif (Kamchatka) and its tephra as a link between terrestrial and marine paleoenvironmental records

We report tephrochronological and geochemical data on early Holocene activity from Plosky volcanic massif in the Kliuchevskoi volcanic group, Kamchatka Peninsula. Explosive activity of this volcano lasted for ~1.5 kyr, produced a series of widely dispersed tephra layers, and was followed by profuse low-viscosity lava flows. This eruptive episode started a major reorganization of the volcanic structures in the western part of the Kliuchevskoi volcanic group. An explosive eruption from Plosky (M~6), previously unstudied, produced tephra (coded PL2) of a volume of 10–12 km³ (11–13 Gt), being one of the largest Holocene explosive eruptions in Kamchatka. Characteristic diagnostic features of the PL2 tephra are predominantly vitric sponge-shaped fragments with rare phenocrysts and microlites of plagioclase, olivine and pyroxenes, medium- to high-K basaltic andesitic bulk composition, high-K, high-Al and high-P trachyandesitic glass composition with SiO₂ = 57.5–59.5 wt%, K₂O = 2.3–2.7 wt%, Al₂O₃ = 15.8–16.5 wt%, and P₂O₅ = 0.5–0.7 wt%. Other diagnostic features include a typical subduction-related pattern of incompatible elements, high concentrations of all REE (>10× mantle values), moderate enrichment in LREE (La/Yb ~ 5.3), and non-fractionated mantle-like pattern of LILE. Geochemical fingerprinting of the PL2 tephra with the help of EMP and LA-ICP-MS analyses allowed us to map its occurrence in terrestrial sections across Kamchatka and to identify this layer in Bering Sea sediment cores at a distance of >600 km from the source. New high-precision ¹⁴C dates suggest that the PL2 eruption occurred ~10,200 cal BP, which makes it a valuable isochrone for early Holocene climate fluctuations and permits direct links between terrestrial and marine paleoenvironmental records. The terrestrial and marine ¹⁴C dates related to the PL2 tephra have allowed us to estimate an early Holocene reservoir age for the western Bering Sea at 1,410 ± 64 ¹⁴C years. Another important tephra from the early Holocene eruptive episode of Plosky volcano, coded PL1, was dated at 11,650 cal BP. This marker is the oldest geochemically characterized and dated tephra marker layer in Kamchatka to date and is an important local marker for the Younger Dryas—early Holocene transition. One more tephra from Plosky, coded PL3, can be used as a marker northeast of the source at a distance of ~110 km.     

The Bazhenov Horizon of West Siberia: structure,correlation, and thickness

The type sections of the Bazhenov Horizon and formations recognized within this horizon have been identified based on a comprehensive analysis of paleontological, lithological, geophysical (well-log and CDP seismic data), and geochemical data on the West Siberian Basin. The Bazhenov Horizon was traced throughout the entire West Siberian sedimentary basin. The criteria for the recognition of the top and base of this horizon within the stratigraphic equivalents of the Bazhenov Formation were suggested. The proposed facies-stratigraphic zonation of the Bazhenov Horizon reflects the spatial location of all formations identified within this horizon. As seen on the newly proposed thickness map, the Bazhenov Horizon reaches a thickness of 15-25 m within the Bazhenov and Tutleim Formations, 30-35 m within the Mulym’ya Formation, 30-45 m within the Danilov Formation, 40-65 m within the Mar’yanovka Formation, up to 100 m within the Golchikha Formation, > 350 m within the Yanovstan Formation, up to 35 m within the Bagan Formation, and 35-40 m within the Maksimkin Yar Formation. A marginal filter (according to A.P. Lisitzin) has been identified along the East Siberian land.     

Distribution of organic matter in rocks of the Bazhenov horizon (West Siberia)

We studied the distribution of organic carbon in rocks of the Bazhenov horizon, a unique object of predominantly biogenic sedimentation in the West Siberian sedimentary basin. The contents of organic carbon in the rocks were determined using the data from 4094 core analyses and core-log relationships derived from 48,500 radioactive- and electrical-log measurements. For the Bazhenov and Tutleima Formations, both approaches gave the same results. The average content of organic carbon in the rocks is 7.7%. These data were used to compile a detailed map of the distribution of organic carbon contents in sedimentary rocks of the basin. It was shown that the average organic carbon content in the rocks increases from 2-4% on the periphery of the basin to 10-12% in its central, deepest part. The distribution of C_org values in the basin is highly asymmetric. The highest C_org values are observed in the southwestern part of the basin interior, where beds with > 10% C_org range in thickness from 5 to 12-15 m. In sections, the highest C_org values are observed in their middle and upper parts, composed predominantly of silicites and mixtites enriched in biogenic silica.     

Methane Distribution in Antarctic Sound (Southern Ocean)

Oceanology - The paper presents the first data on the methane distribution in the water column of Antarctic Sound (Atlantic sector of the Southern Ocean) acquired during an integrated expedition of...     

Distribution Patterns of Methane,Hydrogen, and Helium in the Water Column of the Kara Sea

Oceanology - Estimates of the content of dissolved methane, hydrogen, and helium in seawater of the Kara Sea were obtained. It was found that the methane concentration in the studied areas varied...     

Water in the structure of minerals from mantle peridotites as controlled bythermal and redox conditions in the upper mantle

Hydrous species and the amount of water (OH^? ions and crystal hydrate H₂O) in structures of nominally anhydrous rock-forming minerals (olivine, ortho- and clinopyroxenes) were studied with Fourier spectroscopy in peridotite nodules (19 samples) from Cenozoic alkali basalts of the Baikal-Mongolia region (Dariganga Plateau, Taryat Depression, and Vitim Plateau). Single-crystal samples oriented relative to the crystallographic axes of minerals were examined with an FTIR spectrometer equipped with an IR microscope at the points of platelets free from fluid inclusions. FTIR spectra were measured in regions of stretching vibrations of OH^? and H₂O (3800–3000 cm^?1) and deformation vibrations of H₂O (1850–1450 cm^?1). The water content in mineral structures was determined from integral intensities. To estimate the conditions of entrapment and loss of structural water in minerals, their chemical composition, including Fe²⁺ and Fe³⁺ contents, was determined with an electron microprobe analysis and Mössbauer spectroscopy. The bulk chemical composition of some nodules was determined with XRF and ICP MS. The total water content (OH^? + H₂O) varies from 150 to 1140 ppm in olivines, from 45 to 870 ppm in clinopyroxenes, and from 40 to 1100 ppm in orthopyroxenes. Both water species in the mineral structures are retained down to a depth of 150–160 km in wide temperature and pressure ranges (1100–1500 °C, 32–47 kbar) at the oxygen fugacity of ?1.4 to ?0.1 log units relative to that of the quartz-fayalite-magnetite buffer.