Taphonomic phenomenon of ancient hair from Glacial Beringia: perspectives for palaeoecological reconstructions          下载免费PDF全文

Irina V. Kirillova  Johannes van der Plicht  Stanislav V. Gubin  Oksana G. Zanina  Olga F. Chernova  Elena G. Lapteva  Svetlana S. Trofimova  Eugeny V. Zinovyev  Anton A. Zharov  Elena O. Fadeeva  Thijs Van Kolfschoten  Fedor K. Shidlovskiy  Alexey A. Kotov 《Boreas: An International Journal of Quaternary Research》2016,45(3):455-469

An accumulation of mammoth hair, discovered in the Bol'shaya Chukochya River valley (northeast Yakutia, Russia), was found to contain remains of terrestrial and aquatic organisms, including plants, insects, crustaceans, birds and mammals. Radiocarbon dating indicated that this post‐mortem taphocoenosis represented multiple time periods. The mammoth hair was dated to older than 45 ka BP, the plants were dated to 12 750±50 a BP (which corresponds to a shift in the environmental conditions and landscapes during the formation of thermokarst in northeastern Russia) and the bird feathers were dated to 4115±40 a BP. A scenario of the formation of this fossil assemblage is proposed, covering the MIS 3‐1 time range. The hair also yielded various Arctic branchiopod crustaceans, which inhabit shallow temporary water bodies and therefore are important for reconstruction of palaeoenvironments. The cladoceran subgenus Daphnia (Ctenodaphnia), currently absent from the Asian part of Beringia, is reported from this region for the first time. The study demonstrates that the discovered permafrost‐preserved hair is a unique repository of Ice Age organisms.  相似文献   

The environment of early Mars and the missing carbonates     

David C. FERNÁNDEZ‐REMOLAR  Mónica SÁNCHEZ‐ROMÁN  Andrew C. HILL  David GÓMEZ‐ORTÍZ  Olga Prieto BALLESTEROS  Christopher S. ROMANEK  Ricardo AMILS 《Meteoritics & planetary science》2011,46(10):1447-1469

Abstract– A model is presented in which the aqueous conditions needed to generate phyllosilicate minerals in the absence of carbonates found in the ancient Noachian crust are maintained by an early CO₂‐rich atmosphere, that, together with iron (II) oxidation, would prevent carbonate formation at the surface. After cessation of the internal magnetic dynamo, a CO₂‐rich primordial atmosphere was stripped by interactions with the solar wind and surface conditions evolved from humid to arid, with ground waters partially dissolving subsurface carbonate and sulfide minerals to produce acid‐sulfate evaporitic deposits in areas with upwelling ground water. In a subsequent geochemical state (Late Noachian to Hesperian), surface and subsurface acidic solutions were neutralized in the subsurface through interaction with basaltic crust, allowing the precipitation of secondary carbonates. This model suggests that, in the early Noachian, the surface waters of Mars maintained acidity because of a drop in temperature. This would have favored increased dissolution of CO₂ and a reduction in atmospheric pressure. In this scenario, physicochemical conditions precluded the formation of surface carbonates, but induced the precipitation of carbonates in the subsurface.  相似文献   

Very low strengths of interplanetary meteoroids and small asteroids   总被引：1，自引：0，他引：1  

Olga POPOVA  Jiří BOROVIČKA  William K. HARTMANN  Pavel SPURNÝ  Edwin GNOS  Josep M. TRIGO‐RODRÍGUEZ 《Meteoritics & planetary science》2011,46(10):1525-1550

Abstract– We have assembled data on 13 cases of meteorite falls with accurate tracking data on atmospheric passage. In all cases, we estimate the bulk strength of the object corresponding to its earliest observed or inferred fragmentation in the high atmosphere, and can compare these values with measured strengths of meteorites in the taxonomic class for that fall. In all 13 cases, the strength corresponding to earliest observed or inferred fragmentation is much less than the compressive or tensile strength reported for that class of stony meteorites. Bulk strengths upon atmospheric entry of these bodies are shown to be very low, 0.1 to approximately 1 MPa on first breakup, and maximal strength on breakup as 1–10 MPa corresponding to weak and “crumbly” objects, whereas measured average tensile strength of the similar meteorite classes is about 30 MPa. We find a more random relation between bulk sample strength and sample mass than is suggested by a commonly used empirical power law. We estimate bulk strengths on entry being characteristically of the order of 10^?1–10^?2 times the tensile strengths of recovered samples. We conclude that pre‐entry, meter‐scale interplanetary meteoroids are typically highly fractured or in some cases rubbly in texture, presumably as a result of their parent bodies’ collisional history, and can break up under stresses of a few megapascals. The weakness of some carbonaceous objects may result from very porous primordial accretional structures, more than fractures. These conclusions have implications for future asteroid missions, sample extraction, and asteroid hazard mitigation.  相似文献   

Cruziana semiplicata from the Furongian (Late Cambrian) of Severnaya Zemlya Archipelago,Arctic Russia,with a review of the spatial and temporal distribution of this ichnospecies     

Sren Jensen  Olga K. Bogolepova  Alexander P. Gubanov 《Geological Journal》2011,46(1):26-33

The Furongian (Late Cambrian) Kurchavinskaya Formation of October Revolution Island, Severnaya Zemlya Archipelago, Arctic Russia , contains two distinctive morphotypes of the trace fossil Cruziana, both of which we assign to Cruziana semiplicata. A wider form shows characteristics typical of this ichnospecies with inner and outer lobes and marginal ridges. A narrow form has only an inner lobe with siculate, often interfering scratch‐marks, and rare, narrow marginal ridges. This narrow form, which shows characters in common with Cruziana tortworthi, probably represents burrowing in a strongly head‐down orientation. The record from October Revolution Island provides additional evidence that the palaeogeographical distribution of Cruziana semiplicata is not restricted to Gondwana, but also extend to parts of Baltica and North Kara. Cruziana semiplicata is known from the Furongian and Tremadocian of Gondwana, whereas on Baltica it is known only from the Furongian. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Parameterizing a hydrological model using a short-term observational dataset to study runoff generation processes and reproduce recent trends in streamflow at a remote mountainous permafrost basin     

Nataliia Nesterova  Olga Makarieva  David Andrew Post 《水文研究》2021,35(7):e14278

Recent decades have seen a change in the runoff characteristics of the Suntar River basin in the mountainous, permafrost, hard-to-reach region of Eastern Siberia. This study aims to investigate and simulate runoff formation processes, including the factors driving recent changes in hydrological response of the Suntar River, based on short-term historical observations of a range of hydrological, climatological and landscape measurements conducted in 1957–1959. The hydrograph model is applied as it has the advantage of using observed physical properties of landscapes as its parameters. The developed parametrization of the goltsy landscape (rocky-talus) is verified by comparison of the results of simulations of variable states of snow and frozen ground with observations carried out in 1957–1959. Continuous simulations of streamflow on a daily time step are conducted for the period 1957–2012 in the Suntar River (area 7680 km², altitude 828–2794 m) with mean and median values of Nash–Sutcliff criteria reaching 0.58 and 0.67, respectively. The results of simulations have shown that the largest component of runoff (about 70%) is produced in the high-altitude area which comprises only 44% of the Suntar River basin area. The simulated streamflow reproduces the patterns of recently observed changes, including the increase in low flows, suggesting that the increase in the proportion of liquid precipitation in autumn due to air temperature rise is an important factor in driving streamflow changes in the region. The data presented are unique for the vast mountainous parts of North-Eastern Eurasia which play an important role in the global climate system. The results indicate that parameterizing a hydrological model based on observations allows the model to be used in studying the response of river basins to climate change with greater confidence.  相似文献   

Mapping groundwater‐dependent ecosystems using remote sensing measures of vegetation and moisture dynamics          下载免费PDF全文

Olga V. Barron  Irina Emelyanova  Thomas G. Van Niel  Daniel Pollock  Geoff Hodgson 《水文研究》2014,28(2):372-385

Protection of groundwater‐dependent ecosystems (GDEs) is an important criterion in sustainable groundwater management, particularly when human water consumption is in competition with environmental water demands; however, the delineation of GDEs is commonly a challenging task. The Groundwater‐dependent Ecosystem Mapping (GEM) method proposed here is based on interpretation of the land surface response to the drying process derived from combined changes in two multispectral indices, the Normalised Difference Vegetation Index and the Normalised Difference Wetness Index, both derived from Landsat imagery. The GEM method predicts three land cover classes used for delineation of potential GDEs: vegetation with permanent access to groundwater; vegetation with diminishing access to groundwater; and water bodies that can persist through a prolonged dry period. The method was applied to a study site in the Ellen Brook region of Western Australia, where a number of GDEs associated with localised groundwater, diffuse discharge zones, and riparian vegetation were known. The estimated accuracy of the method indicated a good agreement between the predicted and known GDEs; Producer's accuracy was calculated as up to 91% for some areas. The method is most applicable for mapping GDEs in regions with a distinct drying period. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Projected risks to groundwater‐dependent terrestrial vegetation caused by changing climate and groundwater abstraction in the Central Perth Basin,Western Australia          下载免费PDF全文

Olga Barron  Ray Froend  Geoff Hodgson  Riasat Ali  Warrick Dawes  Phil Davies  Don McFarlane 《水文研究》2014,28(22):5513-5529

The effect of potential climate change on groundwater‐dependent vegetation largely depends on the nature of the climate change (drying or wetting) and the level of current ecosystem dependence on groundwater resources. In south‐western Australia, climate projections suggest a high likelihood of a warmer and drier climate. The paper examines the potential environmental impacts by 2030 at the regional scale on groundwater‐dependent terrestrial vegetation (GDTV) adapted to various watertable depths, on the basis of the combined consideration of groundwater modelling results and the framework for GDTV risk assessment. The methodology was tested for the historical period from 1984 to 2007, allowing validation of the groundwater model results' applicability to such an assessment. Climate change effects on GDTV were evaluated using nine global climate models under three greenhouse gas emission scenarios by applying the climate projections to groundwater models. It was estimated that under dry climate scenarios, GDTV is likely to be under high and severe risk over more than 20% of its current habitat area. The risk is also likely to be higher under an increase in groundwater abstraction above current volumes. The significance of climate change risk varied across the region, depending on both the intensity of the change in water regime and the sensitivity of the GDTV to such change. Greater effects were projected for terrestrial vegetation dependent on deeper groundwater (6–10 m). Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Sedimentation of harmful dust by means of ultrasonic waves and additional disperse phase     

Sergey Titov  Maria Stepkina  Alexandra Antonnikova  Natalya Korovina  Boris Vorozhtsov  Eugeny Muravlev  Olga Kudryashova 《Arabian Journal of Geosciences》2015,8(12):11321-11328

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Phase relations in Fe–Ni–C system at high pressures and temperatures     

O.?NaryginaEmail author  L.?S.?Dubrovinsky  N.?Miyajima  C.?A.?McCammon  I.?Yu.?Kantor  M.?Mezouar  V.?B.?Prakapenka  N.?A.?Dubrovinskaia  V.?Dmitriev 《Physics and Chemistry of Minerals》2011,38(3):203-214

We performed comparative study of phase relations in Fe_1−x Ni _x (0.10 ≤ x ≤ 0.22 atomic fraction) and Fe_0.90Ni_0.10−x C _x (0.1 ≤ x ≤ 0.5 atomic fraction) systems at pressures to 45 GPa and temperatures to 2,600 K using laser-heated diamond anvil cell and large-volume press (LVP) techniques. We show that laser heating of Fe,Ni alloys in DAC even to relatively low temperatures can lead to the contamination of the sample with the carbon coming from diamond anvils, which results in the decomposition of the alloy into iron- and nickel-rich phases. Based on the results of LVP experiments with Fe–Ni–C system (at pressures up to 20 GPa and temperatures to 2,300 K) we demonstrate decrease of carbon solubility in Fe,Ni alloy with pressure.  相似文献   

Geochemical and isotopic (Sr, U) variations of lake waters in the Ol’khon Region, Siberia, Russia: Origin and paleoenvironmental implications     

François Chabaux  Mathieu Granet  Philippe Larqué  Jean Riotte  Eugeni V. Skliarov  Olga Skliarova  Ludmilla Alexeieva  François Risacher 《Comptes Rendus Geoscience》2011,343(7):462-470

The geochemical study of springs and lake waters from the Ol’khon Region, Siberia, confirms the strong chemical variability of these water samples, more particularly regarding their salinity. Such variability does not result from a simple mixing process between surface freshwaters and deeper saline waters. The variability, observed at the scale of a few square kilometers, would preferentially result from a secondary concentration processes (evaporation and/or cryogenesis) of lake waters of variable intensity from one lake to another. The U-disequilibria data suggest that the duration of the secondary process is certainly an important parameter to be considered to account for the variable salinity of these lakes. The data indicate that the lakes, however modest in size, could be as old as several ky, confirming therefore that the lake sedimentary deposits could represent relevant paleoenvironmental recorders for the last thousands years.  相似文献