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991.
Yeşim İslamoğlu Mathias Harzhauser Martin Gross Gonzalo Jiménez-Moreno Stjepan Coric Andreas Kroh Fred Rögl Jan van der Made 《International Journal of Earth Sciences》2010,99(1):183-200
The Oligocene depositional history of the Thrace Basin documents a unique paleogeographic position at a junction between the
Western Tethys and the Eastern Paratethys. As part of the Tethys, shallow marine carbonate platforms prevailed during the
Eocene. Subsequently, a three-staged process of isolation started with the Oligocene. During the Early Rupelian, the Thrace
Basin was still part of the Western Tethys, indicated by typical Western Tethyan marine assemblages. The isolation from the
Tethys during the Early Oligocene is reflected by oolite formation and endemic Eastern Paratethyan faunas of the Solenovian
stage. The third phase reflects an increasing continentalisation of the Thrace Basin with widespread coastal swamps during
the Late Solenovian. The mollusc assemblages are predominated by mangrove dwelling taxa and the mangrove plant Avicennia is recorded in the pollen spectra. The final continentalisation is indicated by the replacement of the coastal swamps by
pure freshwater swamps and fluvial plains during the Late Oligocene (mammal zone MP 26). This paleogeographic affiliation
of the Thrace Basin with the Eastern Paratethys after ~32 Ma contrasts all currently used reconstructions which treat the
basin as embayment of the Eastern Mediterranean basin. 相似文献
992.
Crustal thinning beneath the Rwenzori region, Albertine rift, Uganda, from receiver-function analysis 总被引:1,自引:1,他引:0
Ingo Wölbern G. Rümpker A. Schumann A. Muwanga 《International Journal of Earth Sciences》2010,99(7):1545-1557
The Rwenzori mountains in western Uganda, with a maximum elevation of more than 5,000 m, are located within the Albertine
rift valley. We have deployed a temporary seismic network on the Ugandan side of the mountain range to study the seismic velocity
structure of the crust and upper mantle beneath this section of the rift. We present results from a receiver-function study
revealing a simple crustal structure along the eastern rift flank with a more or less uniform crustal thickness of about 30 km.
The complexity of inner-crustal structures increases drastically within the Rwenzori block. We apply different inversion techniques
to obtain reliable results for the thickness of the crust. The observations expose a significantly thinner crust beneath the
Rwenzori range with thickness values ranging from about 20–28 km beneath northern and central parts of the mountains. Our
study therefore indicates the absence of a crustal root beneath the Rwenzori block. Beneath the Lake Edward and Lake George
basins we detect the top of a layer of significantly reduced S-wave velocity at 15 km depth. This low-velocity layer may be
attributed to the presence of partial melt beneath a region of recent volcanic activity. 相似文献
993.
Nuray Tokgöz 《Environmental Earth Sciences》2010,59(7):1559-1567
The concept of sustainable development has gained wide acceptance in the fields of mining and environmental studies. Mining
is a temporary activity, but its impact on the environment persists long after mine closure. The aim of this research is to
investigate the effect of land-use change on the stability of the Agacli landslide, northern coastal part of the Istanbul
(Turkey), spanning periods of mining, reclamation, and afforestation. Geological and geophysical surveys were performed to
determine the effects of erosion on the landslide. To assess the possibility of water responsible for triggering a landslide–gully
complex, the dynamic elastic parameters of the field are calculated. Field observations indicate that surface erosion and
gully development have ceased in the afforested area; however, gullies in non-forested areas continue to increase in size
and depth. Uncontrolled surface water and water from stock watering ponds have trigger erosion and rapid sedimentation of
the landslide–gully complex, resulting in over-steepening and enhanced landslide activity on the flanks of the main slide. 相似文献
994.
995.
Soil-precipitation feedbacks during the South American Monsoon as simulated by a regional climate model 总被引:1,自引:0,他引:1
Anna A. Sörensson Claudio G. Menéndez Patrick Samuelsson Ulrika Willén Ulf Hansson 《Climatic change》2010,98(3-4):429-447
We summarize the recent progress in regional climate modeling in South America with the Rossby Centre regional atmospheric climate model (RCA3-E), with emphasis on soil moisture processes. A series of climatological integrations using a continental scale domain nested in reanalysis data were carried out for the initial and mature stages of the South American Monsoon System (SAMS) of 1993–92 and were analyzed on seasonal and monthly timescales. The role of including a spatially varying soil depth, which extends to 8 m in tropical forest, was evaluated against the standard constant soil depth of the model of about 2 m, through two five member ensemble simulations. The influence of the soil depth was relatively weak, with both beneficial and detrimental effects on the simulation of the seasonal mean rainfall. Secondly, two ensembles that differ in their initial state of soil moisture were prepared to study the influence of anomalously dry and wet soil moisture initial conditions on the intraseasonal development of the SAMS. In these simulations the austral winter soil moisture initial condition has a strong influence on wet season rainfall over feed back upon the monsoon, not only over the Amazon region but in subtropical South America as well. Finally, we calculated the soil moisture–precipitation coupling strength through comparing a ten member ensemble forced by the same space–time series of soil moisture fields with an ensemble with interactive soil moisture. Coupling strength is defined as the degree to which the prescribed boundary conditions affect some atmospheric quantity in a climate model, in this context a quantification of the fraction of atmospheric variability that can be ascribed to soil moisture anomalies. La Plata Basin appears as a region where the precipitation is partly controlled by soil moisture, especially in November and January. The continental convective monsoon regions and subtropical South America appears as a region with relatively high coupling strength during the mature phase of monsoon development. 相似文献
996.
Eduardo Zorita Anders Moberg Lotta Leijonhufvud Rob Wilson Rudolf Brázdil Petr Dobrovolný Jürg Luterbacher Reinhard Böhm Christian Pfister Dirk Riemann Rüdiger Glaser Johan Söderberg Fidel González-Rouco 《Climatic change》2010,101(1-2):143-168
Two European temperature reconstructions for the past half-millennium, January-to-April air temperature for Stockholm (Sweden) and seasonal temperature for a Central European region, both derived from the analysis of documentary sources and long instrumental records, are compared with the output of climate simulations with the model ECHO-G. The analysis is complemented by comparisons with the long (early)-instrumental record of Central England Temperature (CET). Both approaches to study past climates (simulations and reconstructions) are burdened with uncertainties. The main objective of this comparative analysis is to identify robust features and weaknesses in each method which may help to improve models and reconstruction methods. The results indicate a general agreement between simulations obtained with temporally changing external forcings and the reconstructed Stockholm and CET records for the multi-centennial temperature trend over the recent centuries, which is not reproduced in a control simulation. This trend is likely due to the long-term change in external forcing. Additionally, the Stockholm reconstruction and the CET record also show a clear multi-decadal warm episode peaking around AD 1730, which is absent in the simulations. Neither the reconstruction uncertainties nor the model internal climate variability can easily explain this difference. Regarding the interannual variability, the Stockholm series displays, in some periods, higher amplitudes than the simulations but these differences are within the statistical uncertainty and further decrease if output from a regional model driven by the global model is used. The long-term trend of the CET series agrees less well with the simulations. The reconstructed temperature displays, for all seasons, a smaller difference between the present climate and past centuries than is seen in the simulations. Possible reasons for these differences may be related to a limitation of the traditional ‘indexing’ technique for converting documentary evidence to temperature values to capture long-term climate changes, because the documents often reflect temperatures relative to the contemporary authors’ own perception of what constituted ‘normal’ conditions. By contrast, the amplitude of the simulated and reconstructed inter-annual variability agrees rather well. 相似文献
997.
998.
999.
In the present study, the stable isotopes δ18O and δ2H were used for assessment of the water balance in a heterogeneously structured catchment area in the Lusatian Lignite Mining District, in particular, for estimation of the annual groundwater inflow and outflow (IGW and OGW) of Mining Lake Plessa 117. The application of stable isotopes was possible since the water exchange in the catchment area had reached steady‐state conditions after the abandonment of mining activities in 1968 and the filling of the voids and aquifers by re‐rising groundwater in the years thereafter. Diverging slopes of the Evaporation Line and the Global Meteoric Water Line manifested as evaporation from the lake catchment area. The calculated isotope water balance was compared with the commonly used surface water balance, which is unable to differentiate between IGW and OGW, and with a local groundwater model. The groundwater model calculated an IGW of about 811 000 m3 yr?1 and an OGW close to zero, whereas the isotope water balance showed fluxes of about 914 000 and 140 000 m3 yr?1, respectively. Considering the contribution of the groundwater inflow to the total annual input into the lake (ΔIT) and the mean residence time (τ), where the groundwater model and the isotope water balance calculated 42 and 47% for ΔIT and 4·3 and 3·9 years for τ, respectively, it was shown that both water balance calculation methods led to comparable results despite the differences in IGW and OGW. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
1000.
A chronostratigraphy based on luminescence data was established at a key loess profile (Duttendorf) in the northern alpine foreland of Austria. The data help to constrain the timing and duration of the Last Glacial Maximum (LGM) in the area of one of the largest east Alpine piedmont glaciers, the Salzach palaeoglacier. Climate deterioration and maximum advance of this glacier were coeval with the beginning of the main loess accumulation phase in the glacier forefield at ~29–30 ka. A late LGM‐outwash gravel layer deposited on top of the loess profile marks the end of the LGM glacier activity at ~20 ka. The geomorphological setting around the loess profile provides evidence of a major glacier oscillation during the course of the LGM, a phenomenon qualitatively known from other alpine palaeoglaciers but never interpreted in terms of palaeoclimate. A LGM glacier oscillation similar to that of the Salzach palaeoglacier was reported recently from the south Alpine Tagliamento palaeoglacier, suggesting a common forcing. The onset of loess deposition at Duttendorf and the tentatively contemporal advance of the Salzach palaeoglacier reflect, as do other data, the drastic cooling in Europe as a result of Heinrich event 3. The first glacier maximum is not well constrained in the study area but a correlation with the better dated Tagliamento amphitheatre suggests a possible response to Heinrich 2. The second re‐advance occurred synchronously (within dating uncertainties) in both palaeoglaciers forefields (at ~21 ka) but the forcing mechanism remains unknown. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献