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31.
Quaternary climate change and Heinrich events in the southern Balkans: Lake Prespa diatom palaeolimnology from the last interglacial to present 总被引:1,自引:0,他引:1
32.
Krzysztof Kolon Aleksandra Samecka-Cymerman Alexander J. Kempers Lucyna Mróz 《Journal of Atmospheric Chemistry》2010,66(3):157-166
Concentrations of the elements Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, V and Zn were measured in the moss Pleurozium schreberi from the Tatra National Park, one of the most protected regions in Poland. The moss samples were collected at different elevations
between 860 and 2220 m a.s.l. P. schreberi was used as bioindicator for long range transported atmospheric pollution investigating the hypothesis that elevation influences
the concentrations of elements in this moss. Principal component and classification analysis (PCCA) distinguished between
mosses from the highest and the lowest elevations and mosses from West/East oriented valleys. P. schreberi from the highest elevations contained the highest concentrations of Cd, Cu, Cr, Fe, Mn, Pb, V and Zn. P. schreberi from the lowest elevation contained the highest concentration of K. P. schreberi from West/East oriented valleys contained the highest concentrations of Ni and Co. P. schreberi from the Tatra National Park, one of the most protected areas in Poland, receives metals originating from long distance aerial
transport. 相似文献
33.
Marek Biesiada Aleksandra Piórkowska 《Monthly notices of the Royal Astronomical Society》2009,396(2):946-950
It is generally expected that quantum gravity theory should yield the model of a space–time foam at short distances leading to Lorentz-invariance violation (LIV) manifested e.g. by energy-dependent modification of the standard relativistic dispersion relation. One direction of research, pursued intensively, is to measure the energy-dependent time-of-arrival delays in photons emitted by astrophysical sources located at cosmological distances. This is tempered, however, by our ignorance of intrinsic emission delays in different energy channels.
In this paper we discuss a test based on gravitational lensing. Monitoring time delays between images obtained in different energy channels, for example optical (low-energy) and TeV photons, may reveal extra delays due to the distorted dispersion relation typical in LIV theories, a test that is free from the systematics inherent in other settings. 相似文献
In this paper we discuss a test based on gravitational lensing. Monitoring time delays between images obtained in different energy channels, for example optical (low-energy) and TeV photons, may reveal extra delays due to the distorted dispersion relation typical in LIV theories, a test that is free from the systematics inherent in other settings. 相似文献
34.
Aleksandra Šajnović Ksenija Stojanović Branimir Jovančićević Anatoly Golovko 《Environmental Geology》2009,56(8):1629-1641
Sediments from the Valjevo-Mionica Basin of Neogene age were investigated in this study using different geochemical methods.
The results of the inorganic part analyses suggest that during genesis of the sediments, the contents of Na2O, B and As changed the most, which indicates that genesis of the investigated sediments was followed by climate changes and
volcanic activity. The quantity of other macro- and microelements did not vary significantly. Investigations of the organic
substance showed that it is native organic matter, which has been preserved to a significant extent, formed predominantly
of algal precursor organisms, which provided good quality, deposited under reducing conditions and that it is at a low maturity
level. As it has been established that genesis of the investigated sediments was mostly affected by an arid climate with more
intensive salinity, the aim of this study, was also to identify the processes which were the most affected by the change in
salinity, as well as biomarkers which are the most sensitive to this change. The results led to the conclusion that the salinity
increase in the depositional environment had a primary effect on the preservation of the organic substance and the formation
of the mineral searlesite. In addition, it was noticed that besides the Sq/nC26 ratio, the parameters nC17/nC27, CPI and Ph/nC18, are also significantly sensitive to salinity change in a depositional environment in case of immature organic substance
deposited under reducing conditions. 相似文献
35.
Sanja Mrki?Ksenija Stojanovi? Aleksandar Kosti?Hans Peter Nytoft Aleksandra Šajnovi? 《Organic Geochemistry》2011,42(6):655-677
The origin, depositional environment and maturity of petroleum source rocks were determined via conventional whole rock and biomarker analysis of samples from wells in the Banat Depression, where the most important Serbian oil and gas fields are located. The organic matter (OM) in organic-rich upper Tertiary siltstones and marls consists predominantly of Type II kerogen. Numerous biomarker parameters indicated mixed algal-terrestrial OM, related to a brackish or freshwater environment, whose salinity decreased from Middle to Upper Miocene. The OM was deposited under variable redox conditions, reducing to sub-oxic.The wells in the Banat Depression experienced variable high rates of rapid heating, providing an opportunity for examining the applicability of different thermal indicators in a hyperthermal basin. Rock-Eval and numerous biomarker parameters indicate that the main stage of oil generation begins at ca.130 °C and vitrinite reflectance (Rc) ca. 0.63% and reaches a maximum at ca.145-150 °C and Rc ca. 0.72-0.75%, while the late stage of oil generation starts at ca.155 °C and ca. Rc 0.78%, which corresponds, depending on geothermal gradient, to relative depths of 2100-2300 m, 2600-2900 m and 3050-3100 m, respectively. The naphthalene and phenanthrene maturity parameters proved to be less applicable than the biomarker ratios, particularly in the early to moderate maturation range. The newly proposed parameter C(14a)-homo-26-nor-17α(H)-hopane/C30hopane (C30HH/C30H) proved applicable to a wide range of maturity. 相似文献
36.
Karem Azmy Uwe Brand Paul Sylvester Sara A. Gleeson Alan Logan Maria Aleksandra Bitner 《Chemical Geology》2011,280(1-2):180-190
The ΣREE and shale-normalized (PAAS) REESN values of modern brachiopods (biogenic low-Mg calcite: bLMC) represented by several species from high- to low latitudes, from shallow- to deep waters and from warm- and cold-water environments, define three distinct average ‘seawater’ trends. The warm- and cold-water brachiopods define two indistinguishable (p < 0.050) groups that mimic open-ocean seawater REE chemistry, exhibiting the typical LREE enrichment with a slightly positive to negative Ce anomaly followed by an otherwise invariant series. Other recent brachiopods from an essentially siliciclastic seabed environment are distinct in both ΣREE and REESN trends from the previous two populations, showing a slight enrichment in the MREEs and an increasing trend in the HREEs. Other groups of modern brachiopods are characterized by elevated REESN trends relative to the ‘normal’ groups as well as by complexity of the series trends. The most characteristic feature is the decrease in the HREEs in these brachiopods from areas of unusual productivity (i.e., such as upwelling currents, fluvial input and aerosol dust deposition). Preserved brachiopods from the Eocene and Silurian exhibit REESN trends and Ce anomalies similar to that of the ‘open-ocean’ modern brachiopods, although, their enriched ΣREE concentrations suggest precipitation of bLMC influenced by extrinsic environmental conditions.Preservation of the bLMC was tested by comparing the ΣREE and REESN trends of preserved Eocene brachiopods to those of Oligocene brachiopods that were altered in an open diagenetic system in the presence of phreatic meteoric-water. The altered bLMC is enriched by approximately one order of magnitude in both ΣREE and REESN trends relative to that in bLMC of their preserved counterparts. Similarly, the ΣREE and REESN of preserved Silurian brachiopod bLMC were compared to those of their enclosing altered lime mudstone, which exhibits features of partly closed system, phreatic meteoric-water diagenesis. Despite these differences in the diagenetic alteration systems and processes, the ΣREEs and REESN trends of the bLMC of altered brachiopods and of originally mixed mineralogy lime mudstones (now diagenetic low-Mg calcite) are enriched by about one order of magnitude relative to those observed in the coeval and preserved bLMC.In contrast to the changes in ΣREE and REESN of carbonates exposed to phreatic meteoric-water diagenesis, are the REE compositions of late burial calcite cements precipitated in diagenetically open systems from burial fluids. The ΣREE and REESN trends of the burial cements mimic those of their host lime mudstone, with all showing slight LREE enrichment and slight HREE depletion, exhibiting a ‘chevron’ pattern of the REESN trends. The overall enrichment or depletion of the cement REESN trends relative to that of their respective host rock material reflects not only the openness of the diagenetic system, but also strong differences in the elemental and REE compositions of the burial fluids. Evaluation of the (Ce/Ce*)SN and La = (Pr/Pr*)SN anomalies suggests precipitation of the burial calcite cements essentially in equilibrium with their source fluids. 相似文献
37.
Glen M. MacDonald Andrei A. Velichko Constantine V. Kremenetski Olga K. Borisova Aleksandra A. Goleva Andrei A. Andreev Les C. Cwynar Richard T. Riding Steven L. Forman Tom W. D. Edwards Ramon Aravena Dan Hammarlund Julian M. Szeicz Valery N. Gattaulin 《Quaternary Research》2000,53(3):302
Radiocarbon-dated macrofossils are used to document Holocene treeline history across northern Russia (including Siberia). Boreal forest development in this region commenced by 10,000 yr B.P. Over most of Russia, forest advanced to or near the current arctic coastline between 9000 and 7000 yr B.P. and retreated to its present position by between 4000 and 3000 yr B.P. Forest establishment and retreat was roughly synchronous across most of northern Russia. Treeline advance on the Kola Peninsula, however, appears to have occurred later than in other regions. During the period of maximum forest extension, the mean July temperatures along the northern coastline of Russia may have been 2.5° to 7.0°C warmer than modern. The development of forest and expansion of treeline likely reflects a number of complimentary environmental conditions, including heightened summer insolation, the demise of Eurasian ice sheets, reduced sea-ice cover, greater continentality with eustatically lower sea level, and extreme Arctic penetration of warm North Atlantic waters. The late Holocene retreat of Eurasian treeline coincides with declining summer insolation, cooling arctic waters, and neoglaciation. 相似文献
38.
Mariusz Pełechaty Andrzej Pukacz Karina Apolinarska Aleksandra Pełechata Marcin Siepak 《Sedimentology》2013,60(4):1017-1035
A significant portion of calcium carbonate is deposited in lake sediments as a result of biological processes related to the photosynthetic activity of phytoplankton in the pelagic realm and, in addition, macrophytes in the littoral zone. Lake Wigry, one of the largest lakes in Poland (north‐east Poland), is characterized by: (i) carbonate sediments with a CaCO3 content exceeding 80% within the littoral zone; and (ii) large areas of submerged vegetation dominated by charophytes (macroscopic green algae, Characeae family). It is claimed that charophytes are highly effective in utilizing HCO3? and forming thick CaCO3 encrustations. Thus, this study was aimed at evaluating the CaCO3 production by dense Chara stands overgrowing the lake bottom reaching a depth of 4 m. In late July 2009, the fresh and dry mass of plants, the percentage contribution of calcium carbonate and the production of CaCO3 per 1 m2 were investigated along three transects at three depths (1 m, 2 m and 3 m, with each sample area equal to 0·0625 m2) per transect. The composition and structure of phytoplankton and the physico‐chemical properties of the water analysed in both the littoral and pelagic zones served as the environmental background and demonstrated moderately low fertility in the lake. The greatest dry plant mass exceeded 1000 g m?2 and CaCO3 encrustations constituted from 59% to over 76% of the charophyte dry weight. Thus, the maximum and average values of carbonates precipitated by charophytes were 685·5 and 438 g m?2, respectively, which exceeded previously reported results. A correlation of carbonate production with the depth of Chara stands was detected, and intermediate depths offered the most favourable conditions for carbonate precipitation (589 g m?2 on average). As precipitated carbonates are ultimately stored in bottom deposits, the results highlight the significance of charophytes in lacustrine CaCO3 sedimentation. 相似文献
39.
Geochemical behaviour of some heavy metals of the Grot flotation tailing, Southeast Serbia 总被引:1,自引:1,他引:0
Bo?idar V. Djoki? Vidojko Jovi? Milun Jovanovi? Aleksandra ?iri? Dragan Jovanovi? 《Environmental Earth Sciences》2012,66(3):933-939
Grot tailing dump has the highest altitude of all tailing dumps in the Republic of Serbia. About 5.5 million tons of hydrocycloned
sand was deposited in the tailing dump. This material was formed by flotation processing of ore from the Blagodat ore field.
Vegetation was not developed in any part of the tailing. Minerals determined by X-ray diffraction analyses of representative
samples form the tailing are quartz, clay minerals, calcite, feldspars, hematite, siderite, pyrite, sphalerite, galena and
chalcopyrite. No regularities were noticed in their quantitative distribution. Statistical analysis of chemical fluctuations
of lead, zinc, copper, arsenic and manganese concentrations showed that those with the highest concentrations are usually
found on the central plateau. Lead displays the largest concentration range in the whole tailing. Maximal concentrations are
found on the central and minimal in the south-western plateau. Zinc concentrations are up to 5,000 mg/kg, except in the central
plateau where they reach extreme several times higher values. Copper concentrations are increased in the central plateau.
In other parts of the tailing, concentrations are uniform and several times lower. Arsenic concentrations are mostly uniform,
with the exception of extreme values in the north-western parts of the central plateau. Manganese shows uniform concentrations,
somewhat increased on the south-eastern plateau. Chemical heterogeneity of the tailing material was influenced by the chronological
discontinuity of the deposition and resedimentation. Resedimentation was the main cause of the fluctuation in the concentrations
of the most mentioned heavy metals. 相似文献
40.
Ingrid Anell Valentin Zuchuat Anna Daniela Rhnert Aleksandra Smyrak‐Sikora Simon Buckley Gareth Lord Harmon Maher Ivar Midtkandal Kei Ogata Snorre Olaussen Per T. Osmundsen Alvar Braathen 《Basin Research》2021,33(1):478-512
The study describes the depositional development and sediment partitioning in a prograding paralic Triassic succession. The deposits are associated with the advance of large prism‐scale clinoforms across a shallower platform area. Approaching the platform, the limited accommodation and associated relative higher rates of deposition generated straighter clinoforms with lower foreset angles. The vertical restriction across the platform is interpreted to have amplified the tidal signature. Sediment was redistributed from the coast into increasingly sandy delta‐front deposits, compared to offshore equivalents. The deposits comprise extensive compound dune fields of amalgamated and increasingly clean sandbodies up‐section. Rapid deposition of significant amounts of sand led to differential subsidence and growth‐faulting in the delta front, with downthrown fault blocks further amplifying the tidal energy through funnelling. A mixed‐energy environment created along‐strike variability along the delta front with sedimentation governing process‐regime. Areas of lower sedimentation were reworked by wave and storm‐action, whereas high sedimentation rates preserved fluvially dominated mouth bars. A major transgression, however, favoured tidally dominated deposits also in these areas, attributed to increasing rugosity of the coastline. Formation of an extensive subaqueous platform between the coast and delta front dampened incoming wave energy, and tidally dominated deposits dominate the near‐shore successions. Meanwhile formation of wave‐built sand‐bars atop the platform attest to continued wave influence. The strong tidal regime led to the development of a heterolithic near‐shore tidally dominated channel system, and sandier fluvial channels up‐river. The highly meandering tidal channels incising the subaqueous platform form kilometre wide successions of inclined heterolithic stratification. The fluvially dominated channels which govern deposition on the delta plain are narrower and slightly less deep, straighter, generally symmetric and filled with cleaner sands. This study provides important insight into tidal amplification and sand redistribution during shallowing on a wide shelf, along with along‐strike process‐regime variability resulting from variations in sediment influx. 相似文献