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61.
Jan Mangerud Valery I. Astakhov Andrew Murray John Inge Svendsen 《Global and Planetary Change》2001,31(1-4)
Beach and shoreface sediments deposited in the more than 800-km long ice-dammed Lake Komi in northern European Russia have been investigated and dated. The lake flooded the lowland areas between the Barents–Kara Ice Sheet in the north and the continental drainage divide in the south. Shoreline facies have been dated by 18 optical stimulated luminescence (OSL) dates, most of which are closely grouped in the range 80–100 ka, with a mean of 88±3 ka. This implies that that the Barents–Kara Ice Sheet had its Late Pleistocene maximum extension during the Early Weichselian, probably in the cold interval (Rederstall) between the Brørup and Odderade interstadials of western Europe, correlated with marine isotope stage 5b. This is in strong contrast to the Scandinavian and North American ice sheets, which had their maxima in isotope stage 2, about 20 ka. Field and air photo interpretations suggest that Lake Komi was dammed by the ice advance, which formed the Harbei–Harmon–Sopkay Moraines. These has earlier been correlated with the Markhida moraine across the Pechora River Valley and its western extension. However, OSL dates on fluvial sediments below the Markhida moraine have yielded ages as young as 60 ka. This suggests that the Russian mainland was inundated by two major ice sheet advances from the Barents–Kara seas after the last interglacial: one during the Early Weichselian (about 90 ka) that dammed Lake Komi and one during the Middle Weichselian (about 60 ka). Normal fluvial drainage prevailed during the Late Weichselian, when the ice front was located offshore. 相似文献
62.
We simulate the rise through the upper convection zone and emergence through the solar surface of initially uniform, untwisted,
horizontal magnetic flux, with the same entropy as the nonmagnetic plasma, that is advected into a domain 48 Mm wide by 20 Mm
deep. The magnetic field is advected upward by the diverging upflows and pulled down in the downdrafts, which produces a hierarchy
of loop-like structures of increasingly smaller scale as the surface is approached. There are significant differences between
the behavior of fields of 10 kG and 20 or 40 kG strength at 20 Mm depth. The 10 kG fields have little effect on the convective
flows and show small magnetic-buoyancy effects, reaching the surface in the typical fluid rise time from 20 Mm depth of 32
hours. 20 and 40 kG fields significantly modify the convective flows, leading to long, thin cells of ascending fluid aligned
with the magnetic field and their magnetic buoyancy makes them rise to the surface faster than the fluid rise time. The 20 kG
field produces a large-scale magnetic loop that as it emerges through the surface leads to the formation of a bipolar, pore-like
structure. 相似文献
63.
Seth Stein Joseph F. Engeln Douglas A. Wiens Robert C. Speed Kazuya Fujita 《Tectonophysics》1983,99(2-4)
The Lesser Antilles subduction zone is an extreme case of the subduction of old (~ 90 m.y.) lithosphere at a slow (~ 2 cm/y) convergence rate. Focal mechanisms of the largest earthquakes in the area have been obtained using body and surface wave data. During the time period (1950–1978) studied the subduction seismicity appears to represent primarily intraplate rather than interplate deformation. All three large (magnitude seven) earthquakes were from intraplate normal faults; no large thrust faulting earthquakes and few small ones occurred. These observations suggest that the plate boundary is largely decoupled, that subduction is at least partially aseismic, and that the downgoing slab is in a state of extension. 相似文献
64.
Kurt Johansson Rune B. Larsen Markku J. Lehtinen Lars Persson Mika Raeisaenen Stig A. Schack Pedersen Paer Weihed Nils-Gunnar Wik 《《幕》》2008,31(1):133-139
The Nordic countries, including Greenland, have a long tradition in mining. The industrial minerals sector is expanding in most Nordic countries and extensive development has taken place during the last few years. The main commodities mined are carbonate rocks, quartz, feldspar, apatite, olivine and talc.
A number of diferent types of dimension stones are quarried in all countries. Rock aggregates are increasingly important, replacing sand and gravel aggregate as construction materials in some countries due to the need to protect ground water supplies. 相似文献
A number of diferent types of dimension stones are quarried in all countries. Rock aggregates are increasingly important, replacing sand and gravel aggregate as construction materials in some countries due to the need to protect ground water supplies. 相似文献
65.
Herbjørn Presthus Heggen John Inge Svendsen Jan Mangerud Øystein S. Lohne 《Boreas: An International Journal of Quaternary Research》2012,41(4):527-545
Recently, the sediment stratigraphy and geochronology of the well‐known Palaeolithic site Byzovaya in northern Russia were investigated. New technological analyses of the artefacts suggest a Middle Palaeolithic Mousterian culture, and occupation by Neanderthals, not Modern humans as previously thought. We present here a new and detailed documentation of the stratigraphy, including the geological context of the artefacts and faunal remains. From sedimentological criteria we confidently interpret the find‐bearing strata as debris‐flow deposits, covered by aeolian sediments. The chronology is based on radiocarbon and luminescence (OSL) dates from the find‐bearing and overlying strata. The results are utilized to reconstruct the geological history at the excavation area. The stratigraphy varies considerably across the excavation area. The most intact and undisturbed part of the sequence was found inside the most recent Excavation II. In this part the artefacts and bones appear to have been permanently sealed and protected by aeolian sand. The older Excavation I shows a more complicated stratigraphy, as the finds may have been temporarily exposed during the early Holocene owing to ravine incision and slumping activity. The individual radiocarbon dates that were collected from different parts of the site and from various stratigraphic positions are re‐investigated in this study. By using Bayesian statistics the conclusion is that the site was occupied during a restricted period around 30.6–34.7 ka. A series of partly unpublished OSL dates of coversand from different sites demonstrates a regional aeolian signal during the Lateglacial in northern Russia, 15–14 ka. 相似文献
66.
The paleoceanography in the Nordic seas was characterized by apparently repeated switching on and off of Atlantic water advection. In contrast, a continous influx of Atlantic waters probably occurred along the northern Barents Sea margin during the last 150?ka. Temporary ice-free conditions enhanced by subsurface Atlantic water advection and coastal polynyas accelerated the final ice sheet build-up during glacial times. The virtually complete dissolution of biogenic calcite during interglacial intervals was controlled mainly by CO2-rich bottom waters and oxidation of higher levels of marine organic carbon and indicates intensive Atlantic water inflow and a stable ice margin. 相似文献
67.
Félix Darve Stein Sture René de Borst Andrew J. Whittle Ian M. Smith 《国际地质力学数值与分析法杂志》2009,33(3):n\a-n\a
68.
Roberto Bugiolacchi Urs Mall Susan McKenna-Lawlor Kjell Brønstad Finn Søraas Rolf B. Pedersen 《Icarus》2011,213(1):43-63
Newly acquired, sequentially spaced, high-resolution near-infrared spectra across the central section of crater Copernicus’ interior have been analyzed using a range of complementary techniques and indexes.We have developed a new interpretative method based on a multiple stage normalization process that appears to both confirm and expand on previous mineralogical estimations and mapping. In broad terms, the interpreted distribution of the principle mafic species suggests an overall composition of surface materials dominated by calcium-poor pyroxenes and minor olivine but with notable exceptions: the southern rim displays strong ca-rich pyroxene absorption features and five other locations, the uppermost northern crater wall, opposite rim sections facing the crater floor, and the central peak Pk1 and at the foot of Pk3, show instead strong olivine signatures.We also propose impact glass an alternative interpretation to the source of the weak but widespread olivine-like spectral signature found in low-reflectance samples, since it probably represents a major regolith constituent and component in large craters such as Copernicus.The high quality and performance of the SIR-2 data allows for the detection of diagnostic key mineral species even when investigating spectral samples with very subdued absorption features, confirming the intrinsic high-quality value of the returned data. 相似文献
69.
Manfred Frechen Dietrich Ellwanger Matthias Hinderer Jörg Lämmermann-Barthel Inge Neeb Astrid Techmer 《International Journal of Earth Sciences》2010,99(8):1955-1974
During the Pleistocene, the Rhine glacier system acted as a major south–north erosion and transport medium from the Swiss
Alps into the Upper Rhine Graben, which has been the main sediment sink forming low angle debris fans. Only some aggradation
resulted in the formation of terraces. Optically stimulated luminescence (OSL) and radiocarbon dating have been applied to
set up a more reliable chronological frame of Late Pleistocene and Holocene fluvial activity in the western Hochrhein Valley
and in the southern part of the Upper Rhine Graben. The stratigraphically oldest deposits exposed, a braided-river facies,
yielded OSL age estimates ranging from 59.6 ± 6.2 to 33.1 ± 3.0 ka. The data set does not enable to distinguish between a
linear age increase triggered by a continuous autocyclical aggradation or two (or more) age clusters, for example around 35 ka
and around 55 ka, triggered by climate change, including stadial and interstadial periods (sensu Dansgaard–Oeschger cycles).
The braided river facies is discontinuously (hiatus) covered by coarse-grained gravel-rich sediments deposited most likely
during a single event or short-time period of major melt water discharge postdating the Last Glacial Maximum. OSL age estimates
of fluvial and aeolian sediments from the above coarse-grained sediment layer are between 16.4 ± 0.8 and 10.6 ± 0.5 ka, and
make a correlation with the Late Glacial period very likely. The youngest fluvial aggradation period correlates to the beginning
of the Little Ice Age, as confirmed by OSL and radiocarbon ages. 相似文献
70.
Interest in integrating human connections and natural areas into resource management decision making has steadily increased. While efforts to validate place meaning dimensions have identified meanings beyond established place dependence and identity concepts, further research to identify tangible and intangible meanings of nature-based recreation areas is needed. This study sought to examine place meanings as a second-order construct consisting of ecological integrity, economic dependency, place dependence, family identity, community identity, and place identity and to determine the influence of place meanings on participatory planning intentions (PPI). Data were collected from Florida Fish and Wildlife Conservation area visitors. Confirmatory factor analysis revealed that six factors were reliable and valid, representing place meanings as an overarching concept. Structural equation modeling showed a significant association between place meanings and PPI. These findings demonstrated the importance of understanding place meanings that influence behavioral intentions, which is relevant to understanding participation in planning processes. 相似文献