Molar tooth structures and origin of peloids in proterozoic carbonate platforms (Middle Riphean of the Turukhansk Uplift,Siberia)     

P. Yu. Petrov 《Lithology and Mineral Resources》2016,51(4):290-309

Structures and textures of the peloidal wackestones, as well as size, shape, and composition of peloidal grains, from the Mesoproterozoic (Middle Riphean) Sukhaya Tunguska carbonate platform in the Turukhansk Uplift (Siberia) are considered. It is shown that these grains formed in the course of diagenesis were closely associated with the microsparitic replacement and the formation of molar tooth (MT) structures. Diagenetic transformations of rocks were related to the activity of anaerobic microbial communities inside the buried carbonate silt layers. The microbial activity during diagenesis was governed by the carbonate sediment composition and conservation mechanism of the high-molecular organic matter of primary producers therein, since this organic matter was the nutritious substrate for the primary anaerobe communities.  相似文献   

Stratigraphy and correlation of Mesoproterozoic rocks associated with Mohar cauldron,Shivpuri district,Madhya Pradesh     

V. P. Gaur  Hemraj Survanshi  S. K. Shrivastava  K. V. Nambiar 《Journal of the Geological Society of India》2016,88(5):603-608

A circular structure, termed as cauldron of volcanic origin, was located near Mohar village in Shivpuri district (M.P.) in the year 2000. Subsequently, the same structure was called as Dhala structure of impact origin. There may be debate over the origin and evolution of this circular structure, but it is characterized by a unique lithological set-up within the Bundelkhand craton. The circular structure is defined by annular disposition of igneous and sedimentary rocks. This includes a set of felsic volcanic rocks and associated breccias named as Mohar Formation, exposed in the outer rim of the circular structure. The inner part of the circular structure has sedimentary sequence, termed as Dhala Formation.The field relations indicate that the Mohar and Dhala foarmations are younger than Bundelkhand granitoid complex but older than Kaimur Group. This period in Indian stratigraphy corresponds to Semri Group which consists of Porcellanite Formation, the rocks of which have formed due to deposition of volcanic ash.The geochronological data and field relations between different litho-units indicate that the Mohar volcanism which generated large volume of volcanic ash was a possible source for the formation of Porcellanite Formation. The deposition of sedimentary sequence in main Vindhyan basin was continued, whereas the volcanic activity in Mohar area continued till H ≈ 1.0 Ga. Since, acid volcanic activity has been reported in different parts of the world at H ≈ 1.0 Ga., it is possible that the Mohar acid volcanic activity is not an isolated event; instead it may be a part of global volcanic activities around H ≈ 1.0 Ga.  相似文献   

Dump slope stability analysis – A case study     

Prasanta Kumar Behera  Kripamoy Sarkar  Ashok Kumar Singh  A. K. Verma  T. N. Singh 《Journal of the Geological Society of India》2016,88(6):725-735

In opencast mining operation, the stability of waste materials stands at high priority from the safety and economic perspective. Poor management of overburden (OB) dump results the instability of slope in an opencast mine. The present paper deals with the stability analysis of dump material of an opencast coal mine at Talcher coal field, Angul district, Odisha, by means of different geotechnical parameters and mineralogical composition affecting the dump slope. The prolonged rainfall in the mining area causes dump failure and loss of valuable life and property. A recent dump failure that occurred in 2013 at Basundhara mines of Mahanadi Coalfields Limited (MCL), Odisha, took 14 lives, and created problems for the mining industry. Most of the dump failure that occurs in the study area are mainly due to increase in pore water pressure as a result of rainfall infiltration. The stability of the waste dump was investigated using the limit equilibrium analysis to suggest an economical, sustainable and safe disposal of the dump in the study area.  相似文献   

Nuclear fuel cycle and its impact on the environment     

B. F. Myasoedov  S. N. Kalmykov  Yu. M. Kulyako  S. E. Vinokurov 《Geochemistry International》2016,54(13):1156-1167

In this paper, we consider the present-day situation and outlooks of the development of nuclear power generation in Russia and other countries. It was noted that the implementation of the concept of a closed nuclear-fuel cycle accepted in Russia relies on the solution of the problem of the disposal of spent nuclear fuel (SNF) and radioactive waste (RAW). This paper presents the main results of investigations focused on the development of radiation-safe methods of manufacturing nuclear fuel elements, including mixed uranium–plutonium oxide fuel for fast-neutron reactors; creation of low waste-production technologies of SNF processing and RAW disposal; and the analysis of fundamental features of the behavior and speciation of radionuclides in environmental objects for the development of efficient methods of radioecological monitoring and remediation of radionuclide-contaminated areas.  相似文献   

Mineralogy and chemical composition of the clay fraction of Neogene shales from the Surma Group in the Bengal basin,Bangladesh     

M. Julleh Jalalur Rahman  Rumana Yeasmin  Tom McCann 《Journal of the Geological Society of India》2016,88(6):705-710

Mineralogical and chemical investigations (<2μm clay separates) of shale samples from the Neogene-age Surma Group obtained from four wells (Habiganj-11, Shahbazpur-1, Titas-11, Titas-15) in the Bengal basin, Bangladesh, were carried out in order to reveal the clay mineral composition as reservoir exploration and exploitation requires a good understanding of the clay minerals. The samples were analyzed by X-ray diffraction (XRD), scanning electron microscope (SEM) and X-Ray fluorescence spectrometry (XRF). Mineralogically, the sub-surface Surma Group shales comprise predominantly quartz, plagioclase, illite, chlorite, kaolinite, with lesser amounts of K-feldspar, dolomite and smectite, and minor to trace amounts of calcite, siderite and pyrite. The chemical composition of the <2 μm clay separates also suggests an illite and chlorite-rich composition. With increasing burial depth, the Surma Group shales are enriched in illite. The gradual decreasing of the smectite clays with depth and ultimate disappearance at greater depths (≥ 3000 m) may have been responsible for the presence of the diagenetic illite. Based on the mineralogical composition it is most likely that the illite-chlorite associations together with quartz and feldspar were predominantly detrital in origin and thus reflect the presence of a rapidly-rising source terrain not subjected to intense weathering.  相似文献   

The evolution of slump-induced destruction of Kukuy Griva slope (Lake Baikal) revealed on the base of the data of seismic and acoustic surveys     

M. A. Solovyeva  A. V. Starovoytov  G. G. Akhmanov  O. M. Khlystov  A. V. Khabuev  M. Yu. Tokarev  D. A. Chensky 《Moscow University Geology Bulletin》2016,71(6):416-428

As a result of careful interpretation of the data of recent seismo-acoustic surveys, two major seismic complexes were identified in the structure of the upper sedimentary section of the north-western slope of Kukuy Griva (ridge). They are composed of several inner seismo-facies, which are very characteristic and separated with well-expressed regional reflector. Seismic and acoustic data revealed evidences of numerous landslide processes which were different in age and peculiarities of manifestation. For the first time, detailed schemes of seismo-facies distribution are compiled for major seismic complexes at the area. The boundary between seismic complexes is dated as 150 thousands years. It is shown that sliding was more intensive during Late Pleistocene and Holocene, reflecting activation of tectonic movements in this part of Baikal rift system.  相似文献   

The subsidence and thermal history of the Baikit anteclise sedimentary basin     

K. Yu. Vasilieva  E. A. Bakay  V. B. Ershova  R. R. Khusnitdinov  A. K. Khudoley  E. V. Kozlova  S. A. Soloveva 《Moscow University Geology Bulletin》2016,71(6):445-450

The Riphean rocks of the Baikit anteclise have been examined using pyrolysis Rock–Eval 6 to evaluate the subsidence history and erosion level. The studied Riphean rocks have the МK₃–МK₄ catagenesis grade. Based on the catagenesis of organic matter we propose a model of maximum burial before the beginning of the accumulation of Vendian deposits. Estimated calculations of subsidence and erosion have shown that the assessed catagenesis grade could be reached at a depth of 7 km, while the erosion level was approximately 5–7 km.  相似文献   

New insight into the composition and the structure of the deep layers of the terrestrial planets     

D. Yu. Pushcharovsky  Yu. M. Pushcharovsky 《Moscow University Geology Bulletin》2016,71(1):1-7

New approaches, which expand the ideas about the compositions and structures of the mantle of the Earth and terrestrial planets, are considered. New data indicate a more fractional structure of the deep layers of the Earth and the Moon. The experimental results at high pressures and temperatures allow modeling the change in the structure and properties of the most important components of the composition of the mantle and cores of the Earth and Moon, as well as the gas (Jupiter and Saturn) and ice (Uranus and Neptune) giants.  相似文献   

Mineralogy and geochemistry of granitoids from Kinnaur region,Himachal Higher Himalaya,India: Implication on the nature of felsic magmatism in the collision tectonics     

Brajesh Singh  Santosh Kumar  Masao Ban  Kazuo Nakashima 《Journal of Earth System Science》2016,125(7):1329-1352

Felsic magmatism in the southern part of Himachal Higher Himalaya is constituted by Neoproterozoic granite gneiss (GGn), Early Palaeozoic granitoids (EPG) and Tertiary tourmaline-bearing leucogranite (TLg). Magnetic susceptibility values (<3 ×10^?3 SI), molar Al₂ O ₃/(CaO + Na₂ O + K ₂O) (≥1.1), mineral assemblage (bt–ms–pl–kf–qtz ± tur ± ap), and the presence of normative corundum relate these granitoids to peraluminous S-type, ilmenite series (reduced type) granites formed in a syncollisional tectonic setting. Plagioclase from GGn (An₁₀–An₃₁) and EPG (An₁₅–An₃₃) represents oligoclase to andesine and TLg (An₂–An₁₅) represents albite to oligoclase, whereas compositional ranges of K-feldspar are more-or-less similar (Or₈₈ to Or₉₅ in GGn, Or₈₆ to Or₉₇ in EPG and Or₈₇ to Or₉₄ in TLg). Biotites in GGn (Mg/Mg + Fe^t= 0.34–0.45), EPG (Mg/Mg + Fe^t= 0.27–0.47), and TLg (Mg/Mg + Fe^t= 0.25–0.30) are ferribiotites enriched in siderophyllite, which stabilised between FMQ and HM buffers and are characterised by dominant 3Fe\(\rightleftharpoons \)2Al, 3Mg\(\rightleftharpoons \)2Al substitutions typical of peraluminous (S-type), reducing felsic melts. Muscovite in GGn (Mg/Mg + Fe^t=0.58–0.66), EPG (Mg/Mg + Fe^t=0.31?0.59), and TLg (Mg/Mg + Fe^t=0.29–0.42) represent celadonite and paragonite solid solutions, and the tourmaline from EPG and TLg belongs to the schorl-elbaite series, which are characteristics of peraluminous, Li-poor, biotite-tourmaline granites. Geochemical features reveal that the GGn and EPG precursor melts were most likely derived from melting of biotite-rich metapelite and metagraywacke sources, whereas TLg melt appears to have formed from biotite-muscovite rich metapelite and metagraywacke sources. Major and trace elements modelling suggest that the GGn, EPG and TLg parental melts have experienced low degrees (～13, ～17 and ～13%, respectively) of kf–pl–bt fractionation, respectively, subsequent to partial melting. The GGn and EPG melts are the results of a pre-Himalayan, syn-collisional Pan-African felsic magmatic event, whereas the TLg is a magmatic product of Himalayan collision tectonics.  相似文献   

Characteristics of extreme dust events observed over two urban areas in Iran     

Abbas-Ali A Bidokhti  Maryam Gharaylou  Nafiseh Pegahfar  Samaneh Sabetghadam  Maryam Rezazadeh 《Journal of Earth System Science》2016,125(2):431-442

Determination of dust loading in the atmosphere is important not only from the public health point of view, but also for regional climate changes. The present study focuses on the characteristics of two major dust events for two urban areas in Iran, Kermanshah and Tehran, over the period of 4 years from 2006 to 2009. To detect extreme dust outbreaks, various datasets including synoptic data, dust concentration, reanalysis data and numerical results of WRF and HYSPLIT models were used. The weather maps demonstrate that for these events dusts are mainly generated when wind velocity is high and humidity is low in the lower troposphere and the region is under the influence of a thermal low. The event lasts until the atmospheric stability prevails and the surface wind speed weakens. The thermal low nature of the synoptic conditions of these major events is also responsible for deep boundary layer development with its thermals affecting the vertical dust flux over the region. Trajectory studies show that the dust events originated from deserts in Iraq and Syria and transported towards Iran. The main distinction between the two types of mobilizations seems to affect the dust concentrations in the Tehran urban area.  相似文献