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31.
Michel Westphal Evgueni L. Gurevitch Boris V. Samsonov Hugues Feinberg & Jean Pierre Pozzi 《Geophysical Journal International》1998,134(1):254-266
The deep drill hole SG6 in western Siberia (66°N, 78.5°E) penetrated 1.1 km of lower Triassic basalts, which are possibly an extension of the central Siberian Permo– Triassic flood basalt province. About 300 samples of these basalts were progressively demagnetized and measured. Principal component analysis often shows multiple magnetizations carried by haematite and magnetite. The corrected mean inclinations are +77° and −77° for the haematite component. A magnetostratigraphic scale was derived and showed a N–R–N–R–N succession. This is quite different from the Noril'sk and Taimyr typical polarity scale, R–N.
The basalts found in the SG6 deep drill hole are slightly younger than those of central Siberia and Taimyr. They correspond to middle–upper Induan age, whereas the Noril'sk and Taimyr sections correspond to an uppermost Permian and lower Induan age. Altogether they indicate that, after a high output rate of volcanic material near the Permo–Triassic boundary, this activity slowed down drastically on the Siberian platform and Taimyr, but persisted for several million years in western Siberia. 相似文献
The basalts found in the SG6 deep drill hole are slightly younger than those of central Siberia and Taimyr. They correspond to middle–upper Induan age, whereas the Noril'sk and Taimyr sections correspond to an uppermost Permian and lower Induan age. Altogether they indicate that, after a high output rate of volcanic material near the Permo–Triassic boundary, this activity slowed down drastically on the Siberian platform and Taimyr, but persisted for several million years in western Siberia. 相似文献
32.
A. A. Filippov 《International Journal of Salt Lake Research》1996,5(4):315-327
The macrozoobenthos was investigated at eight sites in the Aral Sea inshore zone and in the lower reaches of the Syrdaria river. In the sea, the benthos comprised bivalve molluscsSyndosmya segmentum Recluz andCerastoderma isthmicum Issel, gastropods fromCaspiohydrobia Starob., the polychaeteNereis diversicolor O.F. Müller and the crabRhithropanopeus harrisii tridentatus (Maitland). In the Syrdaria, MysidaeParamysis lacustris (Czern.) and GammaridaeDikerogammarus aralensis (Uljanin) were found. These taxa have not been recorded from the Sea since the 1970s. The total zoobenthos biomass and density varied between the investigated Sea areas from 92 to 582 g/m2 and from 1,600 to 39,000 ind./m2, respectively. Spatial and temporal salinity changes within the range 20–41 g/L did not affect macrozoobenthos composition and structure. The conclusion is that the benthic ecosystem of the Aral Sea was in a state of comparative stability from the middle of the 1980s to the middle of the 1990s. Analysis of the zoobenthos in the inshore zone is proposed as a convenient and accessible method for monitoring the status of the zoobenthos of the entire Aral Sea. 相似文献
33.
34.
Boris P. Ilyashuk Andrei A. Andreev Anatoly A. Bobrov Vladimir E. Tumskoy Elena A. Ilyashuk 《Journal of Paleolimnology》2006,35(4):855-872
Chironomid, pollen, and rhizopod records from a permafrost sequence at Bol’shoy Lyakhovsky Island (New Siberian Archipelago)
document the development of a thermokarst palaeo-lake and environmental conditions in the region during the last Interglacial
(MIS 5e). Open Poaceae and Artemisia associations dominated vegetation at the beginning of the interglacial period. Rare shrub thickets (Salix, Betula nana, Alnus fruticosa) grew in more protected and wetter places as well. Saalian ice wedges started to melt during this time, resulting in the
formation of an initial thermokarst water body. The high percentage of semi-aquatic chironomids suggests that a peatland-pool
initially existed at the site. A distinct decrease in semi-aquatic chironomid taxa and an increase in lacustrine ones point
to a gradual pooling of water in the basin, which could in turn induce thermokarst and create a permanent pond during the
subsequent period. The highest relative abundance of Chironomus and Procladius reflects unfrozen water remaining under the ice throughout the ice-covered period during the later stage of palaeo-lake development.
The chironomid record points to three successive stages during the history of the lake: (1) a peatland pool; (2) a pond (i.e.,
shallower than the maximum ice-cover thickness); and (3) a shallow lake (i.e., deeper than the maximum ice-cover thickness).
The trend of palaeo-lake development indicates that intensive thermokarst processes occurred in the region during the last
Interglacial. Shrub tundra communities with Alnus fruticosa and Betula nana dominated the vegetation during the interglacial optimum. The climate was moister and warmer than present. The results of
this study suggest that quantitative chironomid-based temperature reconstructions from Arctic thermokarst ponds/lakes may
be problematic due to other key environmental factors, such as prolonged periods of winter anoxia and local hydrological/geomorphological
processes, controlling the chironomid assemblages. 相似文献
35.
Alicia Correa Boris F Ochoa-Tocachi Christian Birkel Ana Ochoa-Sánchez Charles Zogheib Carolina Tovar Wouter Buytaert 《水文研究》2020,34(24):4609-4627
Páramos, a neotropical alpine grassland-peatland biome of the northern Andes and Central America, play an essential role in regional and global cycles of water, carbon, and nutrients. They act as water towers, delivering water and ecosystem services from the high mountains down to the Pacific, Caribbean, and Amazon regions. Páramos are also widely recognized as a biodiversity and climate change hot spots, yet they are threatened by anthropogenic activities and environmental changes. Despite their importance for water security and carbon storage, and their vulnerability to human activities, only three decades ago, páramos were severely understudied. Increasing awareness of the need for hydrological evidence to guide sustainable management of páramos prompted action for generating data and for filling long-standing knowledge gaps. This has led to a remarkably successful increase in scientific knowledge, induced by a strong interaction between the scientific, policy, and (local) management communities. A combination of well-established and innovative approaches has been applied to data collection, processing, and analysis. In this review, we provide a short overview of the historical development of research and state of knowledge of the hydrometeorology, flux dynamics, anthropogenic impacts, and the influence of extreme events in páramos. We then present emerging technologies for hydrology and water resources research and management applied to páramos. We discuss how converging science and policy efforts have leveraged traditional and new observational techniques to generate an evidence base that can support the sustainable management of páramos. We conclude that this co-evolution of science and policy was able to successfully cover different spatial and temporal scales. Lastly, we outline future research directions to showcase how sustainable long-term data collection can foster the responsible conservation of páramos water towers. 相似文献
36.
Atkin E. V. Bulatov V.L. Vasiliev O. A. Voronin A. G. Gorbunov N. V. Grebenyuk V. M. Dorokhov V. A. Karmanov D. E. Kovalev I.M. Kudryashov I. A. Kurganov A.A. Merkin M. M. Panov A.D. Podorozhny D. M. Polkov D. A. Porokhovoi S. Yu. Sveshnikova L. G. Tkachev L.G. Tkachenko A. V. Turundaevskiy A. N. Filippov S. B. Shumikhin V. V. 《Astronomy Reports》2019,63(1):66-78
Astronomy Reports - Some results of studies of cosmic rays obtained during the NUCLEON space experiment in 2015–2017 are presented. This experiment was intended for direct measurements of the... 相似文献
37.
One of the best-studied volcanoes of the world, Mt. Etna in Sicily, repeatedly exhibits eruptive scenarios that depart from the behavior commonly considered typical for this volcano. Episodes of intense explosive activity, pyroclastic flows, dome growth and cone collapse pose a variety of previously underestimated threats to human lives in the summit area of the volcano. However, retrospective analysis of these events shows that they were likely caused by the same very sets of premises and starting conditions as “normal” eruptions, yet combined in an unexpected, probably unique, way. To cope with such unexpected consequences, we involve an approach of artificial intelligence developed specially for needs of the geosciences, the event bush. Scenarios inferred from the event bush fit the observed ones and allow to foresee other low-probability events that may occur at the volcano. Application of the event bush provides a more impartial vision of volcanic phenomena and may serve as an intermediary between expert knowledge and numerical assessment, e.g., by means of Bayesian Belief Networks. 相似文献
38.
Recent years have been marked by progress in studying the structure of natural X-ray amorphous substances, anthraxolites included, by scanning electron and atomic power microscopy. Integration of the available data on molecular and supramolecular structure of higher anthraxolites from Karelia, Novaya Zemlya, and the Urals allowed elaboration of new classification criteria for solid bitumen, namely, degree of structure perfection and micromineral composition. This approach will help to eliminate disadvantages of traditional investigation of solid bitumen. 相似文献
39.
Boris Kostic M. Peter Süss Thomas Aigner 《International Journal of Earth Sciences》2007,96(4):743-767
Quaternary sands and gravels form important, yet often highly heterogeneous economic deposits. Detailed 3-D analysis of the
sedimentary structure and stratigraphy of these deposits allows for an accurate estimation of exploitable material. This paper
presents a case study in SW Germany reconstructing the 3-D distribution of glacial sediments based on a high-resolution, process-orientated
sedimentary facies classification and lithostratigraphy integrated within the geo-modelling package gOcad. Situated along
the maximal ice-extent of the Rhine glacier during the last glaciation, the study area is characterised by a morphologically
prominent terminal moraine and its associated sandur, which form the stratigraphically youngest sediments of a glacial basin,
partially exposed in two gravel pits. These outcrops helped to reconstruct the complex sedimentary architecture of the northern
part of the glacial basin. The regional analysis is based on core data, as well as geoelectric and geomagnetic surveys. All
data were integrated into km-scale, high-resolution geological 3-D models, depicting the large-scale dynamics of multiple
glacier advances and retreats during the Early to Late Pleistocene. These models allow quantifying the thickness and volume
distribution of exploitable sandy gravel and help to evaluate the occurrence of non-exploitable interbedded diamicton horizons.
The high quality and quantity of gravels particularly north of the terminal moraine classifies the investigated area as very
prospective for raw materials exploitation in the future. 相似文献
40.
Matthias Zillmer Boris Kashtan & Dirk Gajewski 《Geophysical Journal International》1998,132(3):643-653
Wave propagation in weakly anisotropic inhomogeneous media is studied by the quasi-isotropic approximation of ray theory. The approach is based on the ray-tracing and dynamic ray-tracing differential equations for an isotropic background medium. In addition, it requires the integration of a system of two complex coupled differential equations along the isotropic ray.
The interference of the qS waves is described by traveltime and polarization corrections of interacting isotropic S waves. For qP waves the approach leads to a correction of the traveltime of the P wave in the isotropic background medium.
Seismograms and particle-motion diagrams obtained from numerical computations are presented for models with different strengths of anisotropy.
The equivalence of the quasi-isotropic approximation and the quasi-shear-wave coupling theory is demonstrated. The quasi-isotropic approximation allows for a consideration of the limit from weak anisotropy to isotropy, especially in the case of qS waves, where the usual ray theory for anisotropic media fails. 相似文献
The interference of the qS waves is described by traveltime and polarization corrections of interacting isotropic S waves. For qP waves the approach leads to a correction of the traveltime of the P wave in the isotropic background medium.
Seismograms and particle-motion diagrams obtained from numerical computations are presented for models with different strengths of anisotropy.
The equivalence of the quasi-isotropic approximation and the quasi-shear-wave coupling theory is demonstrated. The quasi-isotropic approximation allows for a consideration of the limit from weak anisotropy to isotropy, especially in the case of qS waves, where the usual ray theory for anisotropic media fails. 相似文献