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31.
Landslide susceptibility assessment using the bivariate statistical analysis and the index of entropy in the Sibiciu Basin (Romania) 总被引：13，自引：6，他引：7
Mihaela Constantin Martin Bednarik Marta C. Jurchescu Marius Vlaicu 《Environmental Earth Sciences》2011,63(2):397-406
The Sibiciu Basin is located in Romania between the Buzău Mountains and the Buzau Subcarpathians (Curvature Carpathians and
Subcarpathians). The geology of the basin consists of Paleogene flysch deposits represented by an alternation of sandstones,
marls, clays and schists and Neogene deposits represented by marls, clays and sands. The area is affected by different types
of landslides (shallow, medium-deep and deep-seated failures). In Romania, in the last decades, direct and indirect methods
have been applied for landslide susceptibility assessment. The most utilized before 2000 were based on qualitative approaches.
This study evaluates the landslide susceptibility in the Sibiciu Basin using a bivariate statistical analysis and an index
of entropy. A landslide inventory map was prepared, and a susceptibility estimate was assessed based on the following parameters
which influence the landslide occurrence: slope angle, slope aspect, curvature, lithology and land use. The landslide susceptibility
map was divided into five classes showing very low to very high landslide susceptibility areas. 相似文献
32.
A full understanding of the Mio-Pliocene palaeogeographical and palaeoenvironmental changes in the circum-Mediterranean region during the Messinian Salinity Crisis (MSC) is at present hampered by the lack of reliable chronostratigraphic correlations between the Mediterranean and Paratethys regions. Here, we present magnetostratigraphic ages for the Upper Miocene to Pliocene deposits of the southern Carpathian foredeep in Romania. These ages are in good agreement with those recently obtained from the eastern Carpathian foredeep and define a new chronology for the eastern Paratethys. The Meotian/Pontian boundary is not biostratigraphically constrained in our sections, but according to the geological map of the region arrives at ∼5.8 Ma. The Pontian/Dacian boundary is dated at c. 4.8 Ma and the Dacian/Romanian boundary at c. 4.1 Ma. The main part of the MSC (5.96–5.33 Ma) is thus represented by the Pontian Stage, but the observed palaeoenvironmental and biostratigraphic changes in our sections of the eastern Paratethys do not indicate any relation with the dramatic desiccation and reflooding events of the Mediterranean. 相似文献
33.
Gerald Herrling Marius Becker Alice Lefebvre Anna Zorndt Knut Krämer Christian Winter 《地球表面变化过程与地形》2021,46(11):2211-2228
The bed of estuaries is often characterized by ripples and dunes of varying size. Whereas smaller bedforms adapt their morphological shape to the oscillating tidal currents, large compound dunes (here: asymmetric tidal dunes) remain stable for periods longer than a tidal cycle. Bedforms constitute a form roughness, that is, hydraulic flow resistance, which has a large-scale effect on tidal asymmetry and, hence, on hydrodynamics, sediment transport, and morphodynamics of estuaries and coastal seas. Flow separation behind the dune crest and recirculation on the steep downstream side result in turbulence and energy loss. Since the energy dissipation can be related to the dune lee slope angle, asymmetric dune shapes induce variable flow resistance during ebb and flood phases. Here, a noncalibrated numerical model has been applied to analyze the large-scale effect of symmetric and asymmetric dune shapes on estuarine tidal asymmetry evaluated by residual bed load sediment transport at the Weser estuary, Germany. Scenario simulations were performed with parameterized bed roughness of symmetric and asymmetric dune shapes and without dune roughness. The spatiotemporal interaction of distinct dune shapes with the main drivers of estuarine sediment and morphodynamics, that is, river discharge and tidal energy, is shown to be complex but substantial. The contrasting effects of flood- and ebb-oriented asymmetric dunes on residual bed load transport rates and directions are estimated to be of a similar importance as the controls of seasonal changes of discharge on these net sediment fluxes at the Lower Weser estuary. This corroborates the need to consider dune-induced directional bed roughness in numerical models of estuarine and tidal environments. 相似文献
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Nancy J. Brown-Peterson C. Steve Manning Nancy D. Denslow Marius Brouwer 《Aquatic Sciences - Research Across Boundaries》2011,73(1):127-141
Identification of organisms able to act as biological indicators of hypoxia exposure is important given the increasing frequency
of hypoxic events worldwide. Grass shrimp, Palaemonetes pugio, are ubiquitous estuarine residents in the southeastern US, where they commonly experience cyclic hypoxia. We hypothesized
that reproductive and gene expression patterns of grass shrimp in cyclic hypoxic field sites relative to normoxic sites would
be similar to previous results from cyclic hypoxia laboratory experiments showing differential up- and down-regulation of
hypoxia-responsive genes. There were few differences in gene expression of indigenous shrimp collected during summer from
two Gulf of Mexico estuarine systems [East Bay, FL (EB) and Weeks Bay, AL (WB)], although down-regulation of the gene coding
for vitellogenin-1 corresponded with a decreased relative fecundity and fewer ovigerous females at cyclic hypoxic field sites,
suggesting an overall impact on reproduction. The gene expression profiles of grass shrimp caged for 7 days in field sites
differed by estuary, but few hypoxia-responsive genes identified in laboratory studies were differentially expressed in field
shrimp. Overall, genes coding for protein synthesis, protein degradation, carbohydrate and lipid metabolism and electron transport
were mostly up-regulated in EB caged shrimp but generally down-regulated in WB caged shrimp and laboratory shrimp. Thus, caged
grass shrimp from different bay systems exhibited profoundly different gene expression profiles. Such profiles may serve as
sensitive bioindicators of differences in water quality, habitat quality or food resources among estuaries but are not effective
as indicators of hypoxia exposure. 相似文献
36.
Volcaniclastic aeolian deposits at Sunset Crater,Arizona: terrestrial analogs for Martian dune forms
Sunset Crater in north‐central Arizona (USA) is a 900‐year‐old scoria‐cone volcano. Wind action has redistributed its widespread tephra deposit into a variety of aeolian dune forms that serve as a terrestrial analog for similar landforms and aeolian processes on Mars. Fieldwork was conducted to collect essential geomorphological and sedimentological data, and to establish a baseline for the type and morphometry of dunes, physical properties, interactions with topography, and saltation pathways. Our analyses focused primarily on coppice dunes, falling dunes, wind ripples, and sand streaks. For all collected volcaniclastic aeolian sediment samples, the sand‐size fraction dominated, ranging from almost 100% sand to 74.6% sand. No sample contained more than 1.6% silt. The composition is overwhelmingly basaltic with non‐basaltic particles composing 2 to 6% of the total. Coppice (nebkha) dunes form where clumps of vegetation trap saltating particles and create small mounds or hummocks. Mean grain size for coppice dune samples is coarse sand. Measured dune height for 15 coppice dunes ranged from 0.3 to 3.3 m with a mean of 1 m. Mean length was 6.7 m and mean width was 4.8 m. Falling dunes identified in this study are poorly developed and thin, lacking a prominent ramp‐like structure. Mean wavelength for three sets of measured ripples ranged from 22 to 36 cm. Sand streaks extend downwind for more than a kilometer and are up to 200 m in width. They commonly occur on the lee side of mesas and similar landforms and are typically the downwind continuation of falling dunes. Falling dunes, wind ripples, and sand streaks have been identified on Mars, while coppice dunes are similar to Martian shadow or lee dunes in which sand accumulates in the lee of obstacles. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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38.
Marius Visarion Serban Veliciu Mihai StefĂnescu Reviewer V. Čermák 《Studia Geophysica et Geodaetica》1978,22(2):196-200
Summary Using heat flow and heat generation measurements together with deep seismic sounding and gravity data, a reasonable geothermal model has been constructed for the Romanian Carpathian Bend. At the level of the MOHO discontinuity the calculated temperatures exhibit conspicuous differences between inner and outer border of the Carpathian Bend and a horizontal gradient of 200–300 °C/100 km in the region is not to be excluded.Paper presented at the KAPG Symposium on Geothermics in Liblice, November 1976. 相似文献
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