The Serpukhovian Stage in the Verkhnyaya Kardailovka section,South Urals     

V. N. Pazukhin  E. I. Kulagina  S. V. Nikolaeva  N. N. Kochetova  V. A. Konovalova 《Stratigraphy and Geological Correlation》2010,18(3):269-289

The paper describes a Serpukhovian Stage section, exposed along the Ural River near the village of Verkhnyaya Kardailovka (Bashkortostan). The section is uniquely complete and is proposed as a GSSP candidate for the base of the Serpukhovian. The Upper Visean and Serpukhovian beds are represented by relatively deep facies, which contain ammonoids, conodonts, ostracods, foraminifers, and other fossils. The section is described bed-by-bed and subdivided into zones based on four faunal groups. The lower boundary of the Serpukhovian is placed at the base of the Lochriea ziegleri conodont zone. The stratigraphic units are correlated with synchronous beds of the East European Platform, the Donets Basin, Western Europe, Central Asia, and North America.  相似文献   

Insights into the structure of the Wyville Thomson Ridge overflow current from a fine-scale numerical model     

Nataliya Stashchuk  Vasiliy Vlasenko  Toby J. Sherwin 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(10):1192-1205

One of the major pathways in the northern part of the Meridional Overturning Circulation (MOC) is that of the deep water in the Nordic Seas that runs through the Faroe-Shetland Channel (FSC) and Faroe Bank Channel (FBC), as well as crossing the Wyville Thomson Ridge (WTR), on its way into the Atlantic Ocean. The WTR overflow cascades down the southern side of the ridge via the narrow Ellett Gully to the Cirolana Deep (CD) which, at 1700 m, is the deepest hole in the extreme north of the Rockall Trough. The overflow accounts for nearly 1/10th of the total Faroe-Shetland Channel Bottom Water (FSCBW) discharged through the Faroese channels and is an important intermediate water mass in the Rockall Trough. Over a period of only seven days in April 2003 bottom water temperatures cooled dramatically, from 4.46 to 3.03 °C in the CD and from 3.93 to 2.54 °C in the Ymir Trough (YT). A numerical general circulation model (MITgcm) has been applied in order to reproduce the details of this dense water overflow event. Model results were consistent with the observed cooling and total water transport. It was found that the descending gravity current forms a pair of mesoscale eddies with cyclonic and anticyclonic vorticity at the exit to the CD. Analysis of mixing processes were obtained when a passive tracer was included in the model. It was found that downstream flow is characterized by an explosive detrainment regime in the CD. The model sensitivity runs revealed that the final depth to which the overflow descends depends on the initial upstream velocity of the overflow, as well as the buoyancy difference. It is argued that models of overflows need to have realistic representations of the density structure of the overflow, and sufficiently fine vertical resolution, for the subsequent fate of the overflow to be accurately represented.  相似文献   

Black Sea seagrasses     

Milchakova NA  Phillips RC 《Marine pollution bulletin》2003,46(6):695-699

  相似文献   

Cation distribution and exsolution in the Luna-20 pyroxenes as the chronological indicator of their thermal history     

Nataliya Raphailovna Khisina  Evgeny Sergeevich Makarov 《Earth, Moon, and Planets》1977,17(2):149-165

During the process of continuous post-crystallization cooling, the degree of phase transformation in pyroxenes (ordering and decomposition of solid solutions) is determined by the total cooling time and by cooling rates at individual stages; this degree can also be applied to the estimation of the sub-solidus cooling time of pyroxenes and of rocks, genetically associated with them (geochronometer). The degree of Fe²⁺-Mg order in distribution between theM ₁ andM ₂ sites observed in orthopyroxenes can be used as the criterion for the sub-solidus cooling rates of orthopyroxenes. A technique for approximate estimation of cooling time (rates) of orthopyroxenes in the 1000–500°C interval is suggested on the basis of an ion exchange reaction kinetic model, with the adoption of a few assumptions. X-ray structural analysis study revealed the character of the Fe²⁺-Mg intersite distribution in the M-511 and M-533 orthopyroxenes from the Luna-20 regolith; the obtainedK _D values make 0.072(T _e ^o ~ 460°C) and 0.06 (T _e ^o ~ 480°C), respectively. The corresponding evaluation of the linear cooling rate in the 1000-500°C range, as inferred by the obtained data, gave the value of 0.2–0.25° h^–1. Two features of the exosolution relate to the sub-solidus cooling rate of clinopyroxenes: the degree of phase separation by composition W_o and the exsolution scale . The monocrystal X-ray diffraction study, the transmission electron microscopy and the X-ray microprobe analysis produced the exsolution parameters for clinopyroxenes 2001-3, 2001-6 and 559 from the Luna-20 regolith: W_o 26%, 28% and 45% respectively; 300 Å, 1000 Å and 60 , respectively. The solvus temperatures (T _e) of the clinopyroxenes 2001-3 and 2001-6 make, respectively, 1100 ± 25°C and 1095 ± 45°C; the spinodal temperatures (T _s) areT _s =T _e – 50°C and represent quenching temperatures of the given pyroxenes in relation to the exsolution process. The cooling time fromT _cryst. toT _s was estimated and the value of the formal linear cooling rate was found to be ~ 90° h^–1 (2001-3) and ~ 8° h^–1 (2001-6). The average value of the pyroxene 559 sub-soldius cooling rate in the 1150–1000°C range was four orders less. The obtained data were discussed in view of the possible genesis of the studied Luna-20 pyroxenes.  相似文献   

Mineralogical and geochemical indicators of anoxic sedimentation conditions in local depressions within the Sea of Okhotsk in the late Pleistocene-Holocene     

A. N. Derkachev  N. A. Nikolaeva  A. V. Mozherovsky  T. N. Grigor’eva  E. D. Ivanova  S. P. Pletnev  N. N. Barinov  V. M. Chubarov 《Russian Journal of Pacific Geology》2007,1(3):203-229

This paper reports specific mineralogical and geochemical characteristics of deposits from the local depressions of the Derugin Basin. They were formed in an environment with periodic changes from oxic to anoxic conditions and show evidence for the presence of hydrogen sulfide in bottom waters. The deposits of this type can be considered as a modern model for ancient ore-bearing black shale associations. Compared with typical metalliferous black shale sequences, which are characterized by high contents of organic matter, the sediments described here are depleted in the elements of the organophilic association (Mo, Ni, Cu, Zn, V, and U) but have higher Mn contents.  相似文献   

The 1996 subaqueous eruption at Academii Nauk volcano (Kamchatka) and its effects on Karymsky lake     

S. M. Fazlullin  S. V. Ushakov  R. A. Shuvalov  M. Aoki  A. G. Nikolaeva  E. G. Lupikina 《Journal of Volcanology and Geothermal Research》2000,97(1-4)

A subaqueous eruption in Karymsky lake in the Academii Nauk caldera dramatically changed its water column structure, water chemistry and biological system in less than 24 h, sending major floodwaves down the discharging river and eruption plumes with ash and gases high into the atmosphere. Prior to the eruption, the lake had a pH of about 7, was dominated by bicarbonate, and well stocked with fish, but turned in early 1996 into a stratified, initially steaming waterbody, dominated by sulfate with high Na and K levels, and devoid of fish. Blockage of the outlet led to rising waterlevels, followed by dam breakage and catastrophic water discharge. The total energy input during the eruption is estimated at about 10¹⁶ J. The stable isotope composition of the lake water remained dominated by the meteoric meltwaters after the eruption.  相似文献   

The Main Factors of Uranium Accumulation in the Ishim Plain Saline Lakes (Western Siberia)     

Vladimirov  A. G.  Krivonogov  S. K.  Karpov  A. V.  Nikolaeva  I. V.  Razvorotneva  L. I.  Kolpakova  M. N.  Moroz  E. N. 《Doklady Earth Sciences》2018,479(2):511-517

Hydrochemical analysis of the high-salinity lakes in the Ishim Plain (>250–300 g/L) located at the border with the Northern Kazakhstan uranium ore province is performed. The studies have shown that the main factor of concentration and redistribution of uranium in the lake basins of the Ishim Plain are the processes of intense salt deflation causing sanding of lakes and uranium depletion in the near-surface layer of the bottom deposits. The correlation between the hydroxide forms of uranium binding in the bottom lacustrine deposits of the Ishim Plain and the coffinite composition of the Semizbai deposit makes it possible to consider this province to be promising for the discovery of hydromineral uranium deposits.

  相似文献   

Geochemistry of rare-earth elements in thermal waters of Uzon-Geyzernaya hydrothermal system (Kamchatka)     

G.A. Karpov  P.A. Schroeder  A.G. Nikolaeva 《Russian Geology and Geophysics》2018,59(8):925-934

Precisional analyses of the abundances of La, Ce, and major elements in thermal waters and rocks of the Uzon-Geyzernaya volcanotectonic depression, supplemented by published data on a number of modern high-temperature hydrothermal systems of Kamchatka and two other areas of the world, allowed defining genetically important patterns of rare-earth elements (REE) distribution. The La and Ce abundances positively correlate with silica contents both in fresh igneous rocks of the study areas and in the products formed by hydrothermal processes.All studied hydrothermal clays are enriched in La and Ce. The general enrichment trend is similar to the pattern of positive correlation between the La and Ce abundances. Geothermal waters display a strong relationship between REE enrichment and pH. Enhanced REE enrichment trend is observed in thermal waters with abundant SO₄^2 ? and K. The REE versus Cl and B diagrams show two individual fields reflecting the level of acidity-alkalinity of thermal waters. These data demonstrate that La and Ce concentrations in the products of modern hydrothermal systems (in fluids and secondary mineral phases) are governed by wallrock composition, anionic water composition, and pH/Eh-dependent adsorption processes.  相似文献   

Integrated Onshore‐Offshore Investigation of a Mediterranean Layered Coastal Aquifer     

Johanna Lofi  Philippe Pezard  Frédéric Bouchette  Olivier Raynal  Pierre Sabatier  Nataliya Denchik  Arnaud Levannier  Laurent Dezileau  Raphaël Certain 《Ground water》2013,51(4):550-561

Most of the Mediterranean coastal porous aquifers are intensively exploited. Because of climatic and anthropogenic effects, understanding the physical and geological controls on groundwater distribution and flow dynamics in such aquifers is crucial. This study presents the results of a structural investigation of a system located along the coastline of the Gulf of Lions (NW Mediterranean). A key aspect of this study relies on an onshore‐offshore integrated approach combining outcrops, seismic profiles, and borehole data analysis. This multidisciplinary approach provides constraints on pore‐fluid salinity distribution and stratigraphic organization, which are crucial in assessing the modes of groundwater/seawater exchanges. Onshore, Lower Pliocene deposits dip gently seaward. They are unconformably overlain by Holocene clays in the lagoons. Offshore the Pliocene deposits either outcrop at the seabed or are buried below nonconsolidated sands infilling paleo‐valleys. Beneath the lido, the groundwater salinity distribution consists of salty pore water, overlying fresher pore water. Active circulation of groundwater masses is inferred from the geophysical results. In particular, offshore outcrops and paleo‐valleys may play an important role in salt water intrusion.  相似文献   

Geochemistry of native gold from deposits of various types   总被引：1，自引：0，他引：1  

L. A. Nikolaeva  A. N. Nekrasova  S. A. Milyaev  S. V. Yablokova  A. M. Gavrilov 《Geology of Ore Deposits》2013,55(3):176-184

The ICP-MS-analyzed 490 samples of lode and placer gold allowed us to detect a wide spectrum of trace elements in native gold from the most abundant gold-polysulfide-quartz, low-sulfide gold-quartz, and gold-silver deposits from various gold provinces and districts of the Russian Federation. The typical set of elements in gold of each deposit type has been determined. The distribution of REE, rare alkali and alkaline earth metals in native gold is estimated for the first time, and a geochemical index has been proposed to typify gold occurrences. Compositional differences of native gold are also caused by regional metallogenic features of gold provinces. The results obtained make it possible to determine a type of lode and placer gold occurrences at early stages of geological exploration.  相似文献