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1.
T.?A.?KhusidEmail author N.?S.?Os’kina N.?P.?Lukashina I.?F.?Gablina N.?V.?Libina A.?G.?Matul 《Stratigraphy and Geological Correlation》2018,26(1):109-120
Comparison of benthic foraminiferal assemblages from the core obtained within the Peterburgskoe ore field (Mid-Atlantic Ridge) and from the core taken five kilometers away from the ore field revealed evident differences in their composition, in the appearance of their shells, and also in the benthic–plankton species ratio. It was noted that the foraminiferal assemblage from the ore-bearing sediments of the Petersburg field was characterized by a higher relative content of benthic species and a large number of chemically altered and broken shells. The first occurrence of the species Osangularia umbonifera, which is able to exist in lowoxygen and CaCO3-undersaturated bottom waters at the boundary of biogenic sediments surrounding the ore field and in the ore-bearing sediments, was established. In the core section sampled beyond the ore field, the composition of foraminiferal assemblages differs insignificantly from typical oceanic ones. 相似文献
2.
A.N.C. Dias C.A.S. Tello F. Chemale M.C.T.F. de Godoy F. Guadagnin P.J. Iunes C.J. Soares A.M.A. Osório M.P. Bruckmann 《Journal of South American Earth Sciences》2011,31(2-3):298-305
Combined methods of fission track (FTM) and U–Pb in situ zircon dating were applied to sedimentary samples from the Vale do Rio do Peixe Formation, Bauru Basin, Brazil. Detrital zircons of nine samples were determined by the FTM, and the obtained ages varied from 239 Ma–825 Ma, which can be grouped into four main populations as the 230–300 Ma, 460–490 Ma, 500–650 Ma and 696–825 Ma groups. The U–Pb data show two clear source areas: the Early Paleozoic to Neoproterozoic zircons, ranging from 445 ± 14 to 708 ± 18 Ma, and the Paleoproterozoic zircons, ranging from 1879 ± 23 to 2085 ± 27 Ma. Subordinate occurrences of Early Neoproterozoic to Mesoproterozoic zircons (836 ± 15 and 1780 ± 38 Ma) were identified. The combined information allows us to characterize Early Brazilian, Brazilian and Rhyacian material as the main source for the zircons, which are areas situated to west of the Bauru Basin (e.g., Goiás Massif) that have been incorporated into the sedimentary cycles in the Phanerozoic (mainly in the Paraná Basin). FT zircon ages reflect the main denudation processes of the South American Plate from Neoproterozoic to Early Triassic as those related to orogenic cycles of Early Brazilian, Brazilian, Famatinian/Cuyanian and Gondwanide. 相似文献
3.
Carlos Osácar Jesús Palacián Manuel Palacios 《Celestial Mechanics and Dynamical Astronomy》1995,62(1):93-98
A numerical algorithm to evaluate the dilogarithmic function of a complex argument is proposed. The use of the dilogarithm in celestial mechanics appears in the exact Delaunay normalization of some functions involving the equation of the centre. 相似文献
4.
N. V. Narizhnaya M. Yu. Khovrichev A. A. Apetyan D. A. Bikulova A. P. Ershova I. A. Balyaev A. M. Kulikova K. I. Os’kina L. A. Maksimova 《Solar System Research》2018,52(4):312-319
We present the results of observations of the Galilean moons of Jupiter carried out at the Normal Astrograph of the Pulkovo Observatory in 2016?2017. We obtained 761 positions of the Galilean moons of Jupiter in the system of the Gaia DR1 catalog (ICRF, J2000.0) and 854 differential coordinates of the satellites relative to each other. The mean errors in the satellites’ normal places and the corresponding root-mean-square deviations are εα = 0.0020′′, εδ = 0.0027′′, σα = 0.0546′′, and σδ = 0.0757′′. The equatorial coordinates of the moons are compared to the motion theories of planets and satellites. On average, the (O–C) residuals in the both coordinates relative to the motion theories are less than 0.031′′. The best agreement with observations is achieved by a combination of the EPM2015 and V. Lainey-V.2.0|V1.1 motion theories, which yields the average (O–C) residuals of approximately 0.02″. Peculiarities in the behavior of the (O–C) residuals and error values in Ganymede have been noticed. 相似文献
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6.
I. F. Gablina L. L. Demina O. B. Dmitrenko N. S. Os’kina E. A. Popova T. A. Khusid V. V. Shilov 《Oceanology》2011,51(3):476-490
The first thorough analysis of microfossils from ore-bearing sediments of the Ashadze-1 hydrothermal field in the Mid-Atlantic
Ridge sampled during cruise 26 of the R/V Professor Logachev in 2005 revealed the substantial influence of hydrothermal processes on the preservation of planktonic calcareous organisms,
as well as on the preservation and composition of the benthic foraminifers. From the lateral and vertical distribution patterns
and the secondary alterations of the microfossils, it is inferred that the main phase of the hydrothermal mineralization occurred
in the Holocene. Heavy metals (Cu, Co, Cr, and Ag) were accumulated by foraminiferal tests and in their enveloping Fe-Mn crusts.
The distribution of authigenic minerals replacing foraminiferal tests demonstrates local zoning related to the hydrothermal
activity. There are three mineral-geochemical zones defined: the sulfide zone, the zone with an elevated Mg content, and zone
of Fe-Mn crusts. 相似文献
7.
In the last few years it has frequently been suggested that Ba is a useful indicator of paleoproductivity. The formation of some sapropels in the Eastern Mediterranean is considered to be related to, or to coincide with, periods of enhanced productivity. A high-resolution sampling study has been undertaken in order to investigate whether the Ba distribution in sapropels reflects a primary input signal or whether it has been altered by diagenetic processes.
On the basis of our results we suggest that three diagenetic stages determine the distribution of Ba. During deposition of the sapropel (stage 1) Ba is mobilized as anoxic conditions prograde. After deposition of the sapropel (stage 2), a progressive oxidation front develops. This front induces the formation of Mn and Fe enrichments and barite precipitation at the oxic/anoxic boundary. Barite precipitation is believed to be caused mainly by a rise in the porewater sulphate concentration after sulphides have been oxidized by the front.
Upon burial (stage 3), suboxic conditions develop as the oxygen becomes exhausted again. In contrast to Fe- and Mn-oxyhydroxides which dissolve and reprecipitate at higher levels, barite is preserved because dissolved sulphate is not depleted.
The interpretation of the Ba distribution in organic-rich sediment is not straightforward. Diagenetic reallocation of a primary Ba signal will possibly disturb the relationship between Ba and organic production. Consequently, one must be very cautious when invoking Ba as a paleoproductivity indicator. 相似文献
8.
Until now, the age of deep-water scleractinians was determined based only on rare finds of these corals in terrestrial sequences,
which constitute <10% of their known diversity. Inasmuch as most of the non-zooxanthellate coral species dwell in the ocean
beyond the shelf zone (up to the abyssal depths) and their fossil remains are missing from terrestrial sections, we propose
a new approach to the assessment of their age based on paleoecological features: the seawater temperatures in the geological
past and the habitat temperature ranges established for 53 coral species. The study confirmed our previous assumption concerning
the very young age of the deep-water fauna. 相似文献
9.
T. Sriwana M. J. van Bergen J. C. Varekamp S. Sumarti B. Takano B. J. H. van Os M. J. Leng 《Journal of Volcanology and Geothermal Research》2000,97(1-4)
Kawah Putih is a summit crater of Patuha volcano, West Java, Indonesia, which contains a shallow, 300 m-wide lake with strongly mineralized acid–sulfate–chloride water. The lake water has a temperature of 26–34°C, pH=<0.5–1.3, Stot=2500–4600 ppm and Cl=5300–12 600 ppm, and floating sulfur globules with sulfide inclusions are common. Sulfur oxyanion concentrations are unusually high, with S4O62−+S5O62−+S6O62−=2400 – 4200 ppm. Subaerial fumaroles (<93°C) on the lake shore have low molar SO2/H2S ratios (<2), which is a favorable condition to produce the observed distribution of sulfur oxyanion species. Sulfur isotope data of dissolved sulfate and native sulfur show a significant 34S fractionation (ΔSO4–Se of 20‰), probably the result of SO2 disproportionation in or below the lake. The lake waters show strong enrichments in 18O and D relative to local meteoric waters, a result of the combined effects of mixing between isotopically heavy fluids of deep origin and meteoric water, and evaporation-induced fractionation at the lake surface. The stable-isotope systematics combined with energy-balance considerations support very rapid fluid cycling through the lake system. Lake levels and element concentrations show strong seasonal fluctuations, indicative of a short water residence time in the lake as well.Thermodynamic modeling of the lake fluids indicates that the lake water is saturated with silica phases, barite, pyrite and various Pb, Sb, Cu, As, Bi-bearing sulfides when sulfur saturation is assumed. Precipitating phases predicted by the model calculations are consistent with the bulk chemistry of the sulfur-rich bottom sediments and their identified mineral phases. Much of the lake water chemistry can be explained by congruent rock dissolution in combination with preferential enrichments from entering fumarolic gases or brines and element removal by precipitating mineral phases, as indicated by a comparison of the fluids, volcanic rocks and lake bed sediment.Flank springs on the mountain at different elevations vary in composition, and are consistent with local rock dissolution as a dominant factor and pH-dependent element mobility. Discharges of warm sulfate- and chloride-rich water at the highest elevation and a near-neutral spring at lower level may contain a small contribution of crater-lake water. The acid fluid-induced processes at Patuha have led to the accumulation of elements that are commonly associated with volcano-hosted epithermal ore deposits. The dispersal of heavy metals and other potentially toxic elements from the volcano via the local drainage system is a matter of serious environmental concern. 相似文献
10.
D. J. Huisman G. T. Klaver A. Veldkamp B. J. H. van Os 《International Journal of Earth Sciences》2000,89(1):154-169
2 O contents, which can be attributed to the Alpine source supplying fresh, sodic plagioclase-rich material instead of the local,
strongly weathered sediments. Increasing K2O/Al2O3 can be attributed to a similar decrease in degree of weathering. However, this trend is disturbed by the loss of K from clay
minerals during weathering in organic-rich layers. Local high TiO2 anomalies, caused by preferential sorting and concentration, are found in most Pliocene sections, but they are absent in
the Upper Pliocene and Lower Pleistocene Alpine-derived deposits. This change is probably due to a change in the energy of
the fluvial system. Finally, (pyrite-) S contents drop (siderite-) Fe contents rise. Micromorphological observations indicate
that the Pliocene pyrite was formed when freshwater deposits were flooded with seawater during short-term events. The decrease
in S, and the increase in siderite-Fe, can be attributed to decreasing marine influence, as a result of the marine regression
at the Pliocene–Pleistocene transition.
Received: 28 August 1999 / Accepted: 2 November 1999 相似文献