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1.
In the middle of 2007, a severe flood affected the People’s Republic of Bangladesh. This is a natural disaster that takes
people’s lives, destroys livestock, infrastructures and communication systems and, damages crops and fish ponds. Despite many
adverse impacts, the flood situation is an accepted phenomenon to the citizens of Bangladesh, due to the immense increase
of soil fertility due to the flood, plus, the recharge of aquifer, ecosystem and fish. The flood of 2007 was the 5th major
flood of the last 20 years when more than thirty-five percent of the area of the country was inundated with flood water. As
in the past, the flood of 2007 had its own significance. The geography of the country contains a floodplain delta of three
major river basins: the Ganges, the Brahmaputra and the Meghna (GBM). The mean monthly rainfall plot from the TRMM satellite
data has shown that for both the Meghna and Brahmaputra basins, the rainfall was higher during July 2007 than any other months
of the last 2 years. This excess rainfall had accumulated in the Brahmaputra and Meghna rivers and carried downstream to Bangladesh.
This was the main cause of the flooding in 2007. The first crossing above the danger level of the river waters was observed
at Durgapur station of the Someswari and at Sunamganj station of the Surma on the nineteenth of July, 2007 inside Bangladesh.
In terms of magnitude of the peak and duration of the flood, the Brahmaputra was higher in 2007 than during 2004. However,
the Ganges river water level never crossed the danger level during flood of 2007. The Meghna was lower during the flood peak
for the duration of the flood in 2007. The year–to-year variability in both the magnitude and duration of the flood suggests
changes in rainfall and landuse pattern of the catchment. 相似文献
2.
Soloviev S. G. Kryazhev S. G. Semenova D. V. Kalinin Yu. A. Kryazhev V. S. Emkuzhev M. S. Bortnikov N. S. 《Geology of Ore Deposits》2021,63(5):409-430
Geology of Ore Deposits - The authors' determinations of the U–Pb isotopic age of zircon (LA–ICP–MS method) in the main types of igneous rocks emphasize the presence of both... 相似文献
3.
The reflectance of sediments (gray level) were measured on 11 sediment cores from the Norwegian–Greenland–Iceland Sea (Nordic
seas). The analyzed time interval covers the past five glacial–interglacial cycles. Although the results demonstrate that
the gray-level method has a potential for stratigraphic purposes, it is indicated that gray-level changes in the Nordic seas
are not necessarily driven by variations in the content of biogenic calcite. A detailed comparison of gray-level values with
contents of total CaCO3 (carbonate) and total organic carbon (TOC) reveals no overall causal link between these proxies. However, specific glacial
core sections with layers containing organic-rich sediment clasts as a consequence of iceberg-rafting seem to correlate well
with law gray-level values. Of those cores which show relatively high and comparable carbonate values in the last three main
interglacial intervals (stages 11, 5.5, and 1), stage 11 is always marked by the highest gray-level values. A close inspection
of the surface structure of the foraminiferal tests as well as the conduction of reflectance measurements on these tests leads
to the conclusion that enhanced carbonate corrosion occurred during stage 11. The test corrosion not only affected the reflectance
of the tests by making them appear whiter, it also seems responsible for the comparatively high gray-level values of the total
sediment in stage 11. In contrast, the relatively low gray-level values found in stages 5.5, and 1 are not associated with
enhanced test corrosion. This observation implies that variable degrees of carbonate corrosion can have a profound effect
on total sediment reflectance.
Received: 6 September 1998 / Accepted: 4 April 1999 相似文献
4.
The crystallization of plagioclase-bearing assemblages in mantle rocks is witness of mantle exhumation at shallow depth. Previous experimental works on peridotites have found systematic compositional variations in coexisting minerals at decreasing pressure within the plagioclase stability field. In this experimental study we present new constraints on the stability of plagioclase as a function of different Na2O/CaO bulk ratios, and we present a new geobarometer for mantle rocks. Experiments have been performed in a single-stage piston cylinder at 5–10 kbar, 1050–1150?°C at nominally anhydrous conditions using seeded gels of peridotite compositions (Na2O/CaO?=?0.08–0.13; X Cr = Cr/(Cr?+?Al)?=?0.07–0.10) as starting materials. As expected, the increase of the bulk Na2O/CaO ratio extends the plagioclase stability to higher pressure; in the studied high-Na fertile lherzolite (HNa-FLZ), the plagioclase-spinel transition occurs at 1100?°C between 9 and 10 kbar; in a fertile lherzolite (FLZ) with Na2O/CaO?=?0.08, it occurs between 8 and 9 kbar at 1100?°C. This study provides, together with previous experimental results, a consistent database, covering a wide range of P–T conditions (3–9 kbar, 1000–1150?°C) and variable bulk compositions to be used to define and calibrate a geobarometer for plagioclase-bearing mantle rocks. The pressure sensitive equilibrium: has been empirically calibrated by least squares regression analysis of experimental data combined with Monte Carlo simulation. The result of the fit gives the following equation: where P is expressed in kbar and T in kelvin. K is the equilibrium constant K?=?a CaTs × a en/a an × a fo, where a CaTs, a en, a an and a fo are the activities of Ca-Tschermak in clinopyroxene, enstatite in orthopyroxene, anorthite in plagioclase and forsterite in olivine. The proposed geobarometer for plagioclase peridotites, coupled to detailed microstructural and mineral chemistry investigations, represents a valuable tool to track the exhumation of the lithospheric mantle at extensional environments.
相似文献
$$\mathop {{\text{M}}{{\text{g}}_{\text{2}}}{\text{Si}}{{\text{O}}_{\text{4}}}^{{\text{Ol}}}}\limits_{{\text{Forsterite}}} +\mathop {{\text{CaA}}{{\text{l}}_{\text{2}}}{\text{S}}{{\text{i}}_{\text{2}}}{{\text{O}}_{\text{8}}}^{{\text{Pl}}}}\limits_{{\text{Anorthite}}~} =\mathop {{\text{CaA}}{{\text{l}}_{\text{2}}}{\text{Si}}{{\text{O}}_{\text{6}}}^{{\text{Cpx}}}}\limits_{{\text{Ca-Tschermak}}} +{\text{ }}\mathop {{\text{M}}{{\text{g}}_{\text{2}}}{\text{S}}{{\text{i}}_{\text{2}}}{{\text{O}}_{\text{6}}}^{{\text{Opx}}}}\limits_{{\text{Enstatite}}} ,$$
$$P=7.2( \pm 2.9)+0.0078( \pm 0.0021)T{\text{ }}+0.0022( \pm 0.0001)T{\text{ }}\ln K,$$
$${R^2}=0.93,$$
5.
V. P. Kovach A. B. Kotov D. P. Gladkochub E. V. Tolmacheva S. D. Velikoslavinsky B. M. Gorokhovsky V. N. Podkovyrov N. Yu. Zagornaya Yu. V. Plotkina 《Doklady Earth Sciences》2018,482(1):1138-1141
Results of U–Th–Pb LA–ICP–MS analysis of detrital zircons from metasandstones of the Chiney Subgroup (Udokan Group, Aldan Shield) have been obtained. It has been revealed that rocks of the Paleoproterozoic (about 1.90, 1.98, and 2.50 Ga) and Neoarchean (2.55 and 2.72 Ga) were their provenance sources. Deposition of the Chiney Subgroup occurred in the interval 1.87–1.90 Ga and was separated in time from the accumulation of the Kodar Subgroup siliciclastics (2.1–2.3 Ga). 相似文献
6.
Antonyuk R. M. Stepanets V. G. Degtyarev K. E. Tretyakov A. A. Bekenova B. K. Levin V. L. Li E. S. 《Doklady Earth Sciences》2021,500(2):826-832
Doklady Earth Sciences - Accessory zircon extracted from serpentinized dunite and harzburgite of the Tekturmas Zone of Central Kazakhstan, which is one of the largest ophiolite zones in the western... 相似文献
7.
The earthquake catalogue of the European area, 1901–1985, with unified magnitudes, has been used for the preparation of epicentre maps of the Mediterranean area. Epicentres have been plotted on three sheets for different magnitude ranges,M
B
(orm
B
) 5, 0,M
S
(orm
B
) = 4.4–4.9,M
S
(orm
B
) 4.3, according to the estimated levels of homogeneity. The first map (M 5) enables an objective comparison of seismicity over the whole Mediterranean area. The other two maps are complementary without the guarantee of completeness. Epicentres define the position of principal earthquake zones and levels of earthquake activity. The maps also serve as the starting point for further data processing. Graphs illustrating the time variation of earthquake activity in the whole area and the mean magnitude-frequency relationships are included. 相似文献
8.
9.
Thi Phuong Quynh Le Nhu Da Le Viet Nga Dao Emma Rochelle-Newall Thi Mai Huong Nguyen Cyril Marchand Thi Thuy Duong Thi Xuan Binh Phung 《Environmental Earth Sciences》2018,77(18):658
Global riverine carbon concentrations and fluxes have been impacted by climate and human-induced changes for many decades. This paper aims to reconstruct the longterm carbon concentrations and carbon fluxes of the Red River, a system under the coupled pressures of environmental change and human activity. Based on (1) the relationships between particulate and dissolved organic carbon (POC, DOC) or dissolved inorganic carbon (DIC), and suspended sediments (TSS) or river water discharge and on (2) the available detailed historical records of river discharge and TSS concentration, the variations of the Red River carbon concentration and flux were estimated for the period 1960–2015. The results show that total carbon flux of the Red River averaged 2555?±?639 kton C year?1. DIC fluxes dominated total carbon fluxes, representing 64% of total, reflecting a strong weathering process from carbonate rocks in the upstream basin. Total carbon fluxes significantly decreased from 2816 kton C year?1 during the 1960s to 1372 kton C year?1 during the 2010s and showed clear seasonal and spatial variations. Organic carbon flux decreased in both quantity and proportion of the total carbon flux from 40.9% in 1960s to 14.9% in 2010s, reflecting the important impact of dam impoundment. DIC flux was also reduced over this period potentially as a consequence of carbonate precipitation in the irrigated, agricultural land and the reduction of the Red River water discharge toward the sea. These decreases in TSS and carbon fluxes are probably partially responsible for different negatives impacts observed in the coastal zone. 相似文献
10.
《Russian Geology and Geophysics》2015,56(3):435-445
The spatial coexistence and synchronous formation of magmatogene porphyry Cu–Mo mineralization and epithermal gold mineralization are due to the genetic relationship between their formation processes. This relationship might be due to the generation of metal-bearing fluids of different geochemical compositions by the porphyry ore-magmatic system, which then participate in the formation of magmatogene porphyry Cu–Mo(Au) and associated epithermal gold deposits. Synthesis of fluid inclusions in quartz was performed for experimental study of the behavior of Cu, Mo, W, Sn, Au, As, Sb, Te, Ag, and Bi in heterophase fluids similar in composition and aggregate state to natural ore-forming fluids of porphyry Cu–Mo(Au) deposits. We have established that at 700 °C, a pressure decrease from 117 to 106 MPa leads to a significant enrichment of the gas phase of heterophase chloride fluid with Au, As, Sb, and Bi. The heterophase state of carbonate–chloride–sulfate fluids is observed at 600 °C and 100–90 MPa. It characterizes the highly concentrated liquid carbonate–sulfide phase–liquid chloride phase–low-density gas phase equilibrium. A decrease in the pressure of heterophase carbonate–chloride–sulfate fluid leads to a noticeable enrichment of its chloride phase with Cu, Mo, Fe, W, Ag, Sn, Sb, and Zn relative to the carbonate–sulfate phase. The processes of redistribution of ore elements between the phases of heterophase fluids can be considered a model of generation of metal-bearing chloride fluids, which occurs in nature during the formation of porphyry Cu–Mo(Au) deposits, as well as a model of generation of gas fluids supplying Au, Te, As, and other ore elements to the place of formation of epithermal Au–Cu and Au–Ag mineralization.© 2015, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved. 相似文献
11.
G. S. Ripp I. A. Izbrodin E. I. Lastochkin A. G. Doroshkevich M. O. Rampilov V. F. Posokhov 《Geochemistry International》2016,54(9):748-764
Isotope-geochemical study of the Ermakovskoe fluorine–beryllium deposit was carried out to estimate the ore sources and role of host carbonate rocks in its formation. We analyzed oxygen and carbon isotope compositions in marbles, skarn carbonates, ore and post-ore parageneses; oxygen isotope compositions in oxides, silicates, apatite; and sulfur isotope composition in sulfides and sulfates. Sources of fluids participating in the rock and ore formation were determined using hydrogen and oxygen isotope compositions in hydroxyl-bearing minerals: phlogopite from marbles, vesuvian from skarns, eudidymite and bertrandite from ore parageneses, and bavenite of the post-ore stage. Isotopic studies suggest crustal source of sulfur, oxygen, and carbon dioxide, while oxygen and hydrogen isotope compositions in the hydroxyl-bearing minerals points to the contribution of meteoric waters in the formation of the fluorine-beryllium ores. 相似文献
12.
E. I. Yartsev I. V. Vikentyev V. Yu. Prokofiev 《Moscow University Geology Bulletin》2017,72(2):132-138
The Dzhusinskoe pyrite–polymetallic deposit is characterized by an abundant concentration of dykes of basic and intermediate rocks. Thermal metamorphism of ore-host rocks and the recrystallization of ore minerals are associated with the intrusion of post-ore dykes. A regular increase in the homogenization temperature from 156° at a distance from a dyke to 287–305°C in the contact zone was established. Highly saline (6.4–15.7 wt % NaCl eq.) CO2–H2O–NaCl fluids under high pressure (up to 1500 bar) can be associated with the processes of contact and regional metamorphism. 相似文献
13.
Doklady Earth Sciences - The distribution patterns of rare earth metals (REM) in the rocks of the Kugda massif (Polar Siberia) are assessed. The REM content decreases from early olivinite rocks,... 相似文献
14.
Ryazantsev A. V. Skoblenko A. V. Golionko B. G. Artyomova O. A. 《Doklady Earth Sciences》2021,501(2):1009-1014
Doklady Earth Sciences - Metagabbroid garnet amphibolite formed after high-pressure granulite with an estimated P–T peak of 12–16 kbar at 700–790°C occurs at the sole of the... 相似文献
15.
《Russian Geology and Geophysics》2014,55(11):1264-1277
On the northeastern slope of the Kuznetsk Alatau, small differentiated alkaline basic intrusive massifs form an isometric area ~ 100 km across. They are composed of subalkalic and alkali gabbroids, basic and ultrabasic foidolites, nepheline and alkali syenites, and carbonatites. Results of complex (U–Pb, Sm–Nd, and Rb–Sr) isotope dating suggest that alkaline basic magmatism developed at two stages, in the Middle Cambrian–Early Ordovician (~ 510–480 Ma) and in the Early–Middle Devonian (~ 410–385 Ma). Finding of accessory zircons (age 1.3–2.0 Ga) in alkaline rocks suggests that the ascent of mantle plume was accompanied by the melting of fragments of Proterozoic mature continental crust composing the basement of the Caledonian orogen of the Kuznetsk Alatau. Probably, parental Cambrian–Ordovician alkaline mafic melts initiated metasomatism and lithosphere erosion. During the next melting of lithosphere substrate in ~ 100 Myr, this caused the generation of magmas of similar composition with inherited isotope parameters (εNd(T) ≈ + 4.8 to + 5.7, TNd(DM) ≈ 0.8–0.9 Ga) pointing to the similar nature of their matter sources in the moderately depleted mantle. 相似文献
16.
L. G. Bragina 《Stratigraphy and Geological Correlation》2016,24(2):141-166
A scheme of radiolarian zonal subdivision is proposed for the upper Albian–Santonian of the Tethyan regions of Eurasia. The upper Albian contains one zone: Crolanium triangulare; the Cenomanian contains three zones: Patellula spica (lower Cenomanian), Pseudoaulophacus lenticulatus (middle Cenomanian), and Triactoma parva (upper Cenomanian); the Turonian contains four zones: Acanthocircus tympanum (lower Turonian (with no upper part)), Patellula selbukhraensis (upper part of the lower Turonian), Phaseliforma turovi (middle Turonian (with no upper part)), and Actinomma (?) belbekense (upper part of the middle Turonian–upper Turonian); the Coniacian contains two zones: Alievium praegallowayi (lower part of the Coniacian) and Cyprodictyomitra longa (upper part of the Coniacian); the Santonian contains three zones: Theocampe urna (lower Santonian), Crucella robusta (middle Santonian–lower part of the upper(?) Santonian), and Afens perapediensis (upper part of the upper Santonian). The biostratigraphic subdivisions are correlated with biostrata in the schemes proposed previously for the Tethys and Pacific. A new species Patellula selbukhraensis Bragina sp. nov. is described. 相似文献
17.
The collection of fossil plants sampled by geologists from VNIGRI at the end of the 20th century from Triassic continental sections drilled by many wells and cropping out in several natural localities and stored at the Museum of Petroleum Geology and Paleontology of the same institute was critically revised. The use of the epidermal method for the study of plant remains with consideration of recent publications dedicated to continental sections of Central Europe made it possible to substantially broaden the taxonomic composition of the Triassic flora and first specify the composition of its pteridosperm representatives. Unlike the Triassic floras of Western Europe, the pteridosperms the Pechora region appeared to be relatively diverse. They number 37 species of 11 genera, which are confined to the upper part of the Triassic sequence: Anguran and Naryan-Mar formations and their analogs. The Middle Triassic, mainly, Ladinian, age of these formations is reliably substantiated both by paleontological (vertebrate and palynological) data and by results of the comparative analysis of the Anguran–Naryan-Mar taphofloras and coeval European type floras dated back to the Anisian–Ladinian by marine faunal remains. The stratigraphic significance of pteridospermous plant remains becomes undoubted for continental sections of the Timan–Pechora basin, while the genera Scytophyllum, Kalantarium, and Kirjamkenia may be considered with respect to their diversity and abundance as representing orthostratigraphic taxa. 相似文献
18.
《Tectonophysics》2001,330(1-2):93-102
The fractality of the earthquake sequence (1983–1997) of Irpinia–Basilicata (Southern Italy), one of the most seismically active regions of the Mediterranean area, has been analysed by temporal and spatial fractal tools. The fractal exponent α, estimated by the Allan Factor method, characterises the time-clustering behaviour of the set of earthquakes, while the correlation dimension DC, calculated by means of the correlation integral method, gives information on the space-clustering behaviour of the sequence of seismic events. Analysing the variations of both the parameters, we recognised the presence of a strong space–time clusterisation associated with the major events that occurred in the investigated area. 相似文献
19.
Ivanova A. A. Salnikova E. B. Kotov A. B. Syritso L. F. Plotkina Yu. V. 《Doklady Earth Sciences》2021,498(1):384-387
Doklady Earth Sciences - The principal possibility of using high-uranium metamict zircon with a high self-irradiation α-dose for U–Pb geochronological studies (ID-TIMS) is demonstrated.... 相似文献
20.
Comparative analysis of the composition and formation conditions of the dunite–pyroxenite association of the Guli Pluton and ultramafic vulcanite (meimechite) showed the similarity of their initial melts and the same type of crystallization, demonstrating the cumulative origin of dunite. 相似文献