Inertinite-rich Tertiary coals from the Zeya–Bureya Basin, Far Eastern Russia

Selected Tertiary coals from the Zeya–Buryea Basin, Far Eastern Russia, were investigated for aspects of their coal type, rank, depositional environment and post-depositional history. The coals have been examined in outcrop (lithotype logging), microscopically (maceral, reflectance and fluorescence), and geochemically (proximate analysis).Two laterally extensive coal-bearing horizons occur: one of Palaeocene age and the other of early Miocene age. The Palaeocene coals were investigated in active open-cut mines at Raichikhinsk and Yerkovtsi and the early Miocene deposit in an abandoned open-cut mine at Cergeyevka.Palaeocene coals at Raichikhinsk and Yerkovtsi were indistinguishable from each other macroscopically, microscopically, and geochemically. The deposits were sufficiently coalified that brightness logging could be undertaken. Dull coals, with numerous fusainous wisps, were dominant. Four dulling-up sequences, which represent stacked peat deposits, were observed at Raichikhinsk. At Yerkovtsi, only a small section of the middle of the seam, which was mostly dull and muddy coal, was investigated. Petrographically, these coals were dominated by inertinite group macerals, which is unusual in non-Gondwanan coals and rare in the Tertiary. Rank classification was problematic with volatile matter (VM) content of vitrain (daf), macroscopic appearance, and microscopic textures suggesting subbituminous B rank, but carbon content, moisture content and specific energy indicating a lignite rank.Notwithstanding complications of rank, estimates of the maximum-range burial depths were calculated. Taking the VM (daf) content of vitrain as 48%, burial depth estimates range from 900 m for a high geothermal gradient and long heating time to a maximum of 3300 m for a low geothermal gradient and short heating time. These estimates are maxima as the coal rank may be lower than implied by the VM.The Cergeyevka deposit is a soft brown coal. Limited sampling of the upper-most portion indicated a high moisture content (75% daf) and an unusual, hydrogen-rich geochemistry. Lack of identifiable liptinites using either reflected light or fluorescence microscopy suggested a significant bituminite component. Otherwise, the coals appear to be typical for the Tertiary. An estimate of 125 m maximum burial depth was obtained using the bed-moisture content of the coal, which is around the present burial depth.Comparison of present-day thicknesses with inferred burial depths suggests that at least 500 m of section is missing between the Palaeocene coals and the early Miocene coals.Palaeoenvironmental considerations suggest that fire played a significant role in the accumulation of the peats at Raichikhinsk and Yerkovtsi. At Cergeyevka, peat accumulation ended by drowning of the mire.Two tuff beds were recognised within the seam at Raichikhinsk and one in the seam at Yerkovtsi. Correlation of the tuff beds is uncertain but they should prove useful in regional coal seam correlation and interpreting coal depositional environments. Geochemical analysis by XRF was complicated by high loss-on-ignition (LOI) values. Despite extensive alteration, an acid igneous source is implied from the presence of free quartz and TiO₂/Al₂O₃ ratios of 0.02 to 0.05.     

The Late Jurassic age and geochemistry of ultramafic-mafic massifs of the Selenga-Stanovoy superterrane (southern framing of the North Asian craton)

We present new data on the age and geochemistry of the Veselyi and Petropavlovsk ultramafic-mafic massifs of the Selenga-Stanovoy (West Stanovoy) superterrane on the southeastern framing of the North Asian craton. The massifs are composed of rocks of peridotitewebsterite-gabbro and peridotite-gabbro-monzodiorite associations, respectively. The latter combine normal, subalkalic, and alkaline rocks and thus are of diverse composition: from ultrabasites and pyroxenites through gabbroids to monzodiorites. The U-Pb zircon age of these massifs is 154 ± 1 and 159 ± 1 Ma, respectively, which permits them to be referred to as the youngest rocks of ultramafic-mafic complexes on the southern framing of the North Asian craton. The rocks of the studied massifs are enriched in LILE (K, Rb, Sr, Ba, LREE) and are depleted in HFSE (Zr, Nb, Hf, Ta). These rocks formed, most likely, in the rear of subduction zone or in the setting of the subducting-slab detachment.     

漠河前陆盆地砂岩岩石地球化学的构造背景和物源区分析

砂岩岩石地球化学对沉积盆地形成时期构造背景的稳定与否有着较高的敏感性, 已成为地质构造复杂地区研究的有效手段. 分析表明, 中生代漠河盆地砂岩在化学成分特征上显示出活动大陆边缘盆地的特点; 同时又充分地揭示出, 碎屑物质主要来自北侧的造山带并接受了盆地南侧的大陆区碎屑来源, 具有前陆盆地的二元物源特征. 根据岩石地球化学分析并结合构造等方面的研究结果, 认为中国黑龙江省漠河盆地的堆积物应属于磨拉石沉积, 所反映出的盆地构造类型应为前陆盆地, 而不是以往认为的裂谷盆地. 这一研究结果为漠河前陆盆地与相邻蒙古-鄂霍茨克造山带在中生代的构造成因关系提供了重要的岩石地球化学依据.     

On sedimentary waves at the western slope of the Middle Caspian Sea

Based on data of high-resolution acoustic profiling performed in the upper part of the sedimentary succession at the western continental slope of the Middle Caspian Sea (at a depth range from 100 to 400 m), we revealed specific accumulative forms of a running wave type. Examination of their morphology and inner structure allowed us to suggest two mechanisms of their formations: (a) by means of flank growth due to migration of channels of sedimentary flow associated with the Samur and other rivers and (b) due to flows of sedimentary material forming sedimentary waves.     

Late Mesozoic volcanism of the eastern part of the Argun superterrane (Far East): Geochemistry and 40Ar/39Ar geochronology

This study presents geochronological data (⁴⁰Ar/³⁹Ar) obtained for Mesozoic volcanic rocks superimposed upon different-aged rocks from the eastern portion of the Argun superterrane. The new data on their age corresponds to the two episodes of magmatic activity distinctly manifested within the East Asia during the Mesozoic and proves the asynchronous development of the volcanic complexes, which make up the eastern and western flanks of the Umlekan-Ogodzha volcanoplutonic belt. It is assumed that the Umlekan-Ogodzha belt is a near EW section of a series of different-aged near NS-trending volcanoplutonic belts subparallel to the Pacific margin.     

Petrochemistry, geochemistry, and genesis of the Chek-Chikan gabbronorite Massif, southeastern framing of the North Asian craton

The Chek-Chikan Massif is a typical representative of basic magmatism, which is widely spread within the Dzhugdzhur-Stanovoi superterrane. The massif consists of gabbronorites, amphibole gabbros, gabbroanorthosites, and anorthosites. The geochemical similarity of the gabbronorites, amphibole gabbros, and anorthosites suggests their genetic link and allows us to consider them as products of intrachamber differentiation. The main geochemical peculiarity of this rock association is the high degree of the melt fractionation. The rocks of the considered massif are enriched in large ion lithophile elements such as Sr (424–1018 ppm) and Ba (50–754 ppm) and have moderate to low contents of such high-field strength elements as Nb (1–17 ppm), Hf (0.4–1.0 ppm), and Th (0.05–1.14 ppm). According to the model calculations, the initial melt had a basaltic composition and crystallized at a temperature of ∼1180 °C and pressure up to 4 kbar. The U-Pb zircon age of the massif is 203 ± 1 Ma. The geochemical peculiarities of the massif and its confinement to the northern framing of the eastern segment of the Mongol-Okhotsk fold belt make it possible to presume that its formation was related to either the activity of the Siberian plume, to one of the stages of closure of the Mongol-Okhotsk paleoocean in the rear part of subduction zone, or to the slab break off.     

Infrasonic Signals from Earthquakes of December 5, 2014, in the Water Area of Lake Hovsgol,Northern Mongolia

Doklady Earth Sciences - A comprehensive analysis of waveforms of seismic and infrasonic vibrations from the earthquake that occurred on December 5, 2014, in the water area of Lake Hovsgol was...     

Water regime and variations in hydrochemical characteristics of the soda Salt Lake Khilganta (Southeastern Transbaikalia)

Hydrochemical and biogeochemical processes in Lake Khilganta were studied during more than ten years. The lake was shown to pass through periods of wetting and drying. This is accompanied by considerable changes in water chemistry and microbiological processes. During the passage from a wet to a dry period, lake water mineralization increases from 40 to 260 g/l and pH decreases from 9.9 to 7.1. At the same time, the isotope composition of organic matter carbon in bottom deposits becomes lighter (from −15.6 to −30.6‰), as well as that of carbon in carbonates (from +4.1 to −8.6‰), due to the lower rate of photosynthetic processes in lake bacterial mats. The order of salt precipitation during the passage from a wet to a dry period and the mechanism of maintaining water pH are considered. A possible similarity between the modern processes in Lake Khilganta and the processes in analogous Pre-Cambrian water bodies is discussed, and the hypothesis regarding the possibility of wider development of soda water bodies at early stages of Earth’s history is considered.     

Anomalous propagation of VHF radiowaves behind the horizon in the seismic region

A theory of electromagnetic radiation generation by random electric discharges in the troposphere and VHF radiowave scattering by these discharges has been developed. The discharge model, which makes it possible to calculate the spatiotemporal distribution of the discharge channel conductivity depending on the electric current value in this discharge, has been obtained. The electromagnetic radiation spectrum in the troposphere occupied by random discharges has been calculated. VHF electromagnetic wave scattering by random electric discharges in the troposphere has been considered. Equations have been derived, and the method for calculating the average value of the electromagnetic wave field scattered by random discharges has been developed. The calculations indicated that the scattered wave field amplitude is much larger than the diffraction wave field amplitude behind the horizon. The theoretical results agree with the observations of the electromagnetic radiation and VHF transmitter signals behind the horizon relative to the earthquake epicenter during the earthquake preparation.