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881.
Consequences of climate change for the soil climate in Central Europe and the central plains of the United States 总被引:2,自引:0,他引:2
Miroslav Trnka Kurt Christian Kersebaum Josef Eitzinger Michael Hayes Petr Hlavinka Mark Svoboda Martin Dubrovský Daniela Semerádová Brian Wardlow Eduard Pokorný Martin Možný Don Wilhite Zdeněk Žalud 《Climatic change》2013,120(1-2):405-418
This study aims to evaluate soil climate quantitatively under present and projected climatic conditions across Central Europe (12.1°–18.9° E and 46.8°–51.1° N) and the U.S. Central Plains (90°–104° W and 37°–49° N), with a special focus on soil temperature, hydric regime, drought risk and potential productivity (assessed as a period suitable for crop growth). The analysis was completed for the baselines (1961–1990 for Europe and 1985–2005 for the U.S.) and time horizons of 2025, 2050 and 2100 based on the outputs of three global circulation models using two levels of climate sensitivity. The results indicate that the soil climate (soil temperature and hydric soil regimes) will change dramatically in both regions, with significant consequences for soil genesis. However, the predicted changes of the pathways are very uncertain because of the range of future climate systems predicted by climate models. Nevertheless, our findings suggest that the risk of unfavourable dry years will increase, resulting in greater risk of soil erosion and lower productivity. The projected increase in the variability of dry and wet events combined with the uncertainty (particularly in the U.S.) poses a challenge for selecting the most appropriate adaptation strategies and for setting adequate policies. The results also suggest that the soil resources are likely be under increased pressure from changes in climate. 相似文献
882.
Cathodoluminescence as a tool to discriminate impact melt,shocked and unshocked volcanics: A case study of samples from the El'gygytgyn impact structure 下载免费PDF全文
Lidia Pittarello Julia Roszjar Dieter Mader Vinciane Debaille Philippe Claeys Christian Koeberl 《Meteoritics & planetary science》2015,50(11):1954-1969
El'gygytgyn (Chukotka, Arctic Russia) is a well‐preserved impact structure, mostly excavated in siliceous volcanic rocks. For this reason, the El'gygytgyn structure has been investigated in recent years and drilled in 2009 in the framework of an ICDP (International Continental Scientific Drilling Program) project. The target rocks mostly consist of rhyodacitic ignimbrites and tuffs, which make it difficult to distinguish impact melt clasts from fragments of unshocked target rock within the impact breccia. Several chemical and petrologic attempts, other than dating individual clasts, have been considered to distinguish impact melt from unshocked volcanic rock of the targets, but none has proven reliable. Here, we propose to use cathodoluminescence (imaging and spectrometry), whose intensity is inversely correlated with the degree of shock metamorphism experienced by the investigated lithology, to aid in such a distinction. Specifically, impact melt rocks display low cathodoluminescence intensity, whereas unshocked volcanic rocks from the area typically show high luminescence. This high luminescence decreases with the degree of shock experienced by the individual clasts in the impact breccia, down to almost undetectable when the groundmass is completely molten. This might apply only to El'gygytgyn, because the luminescence in volcanic rocks might be due to devitrification and recrystallization processes of the relatively old (Cretaceous) target rock with respect to the young impactites (3.58 Ma). The alteration that affects most samples from the drill core does not have a significant effect on the cathodoluminescence response. In conclusion, cathodoluminescence imaging and spectra, supported by Raman spectroscopy, potentially provide a useful tool for in situ characterization of siliceous impactites formed in volcanic target. 相似文献
883.
884.
Geochemical studies of impact breccias and country rocks from the El'gygytgyn impact structure,Russia 下载免费PDF全文
Ulli Raschke Ralf Thomas Schmitt Iain McDonald Wolf Uwe Reimold Dieter Mader Christian Koeberl 《Meteoritics & planetary science》2015,50(6):1071-1088
The complex impact structure El'gygytgyn (age 3.6 Ma, diameter 18 km) in northeastern Russia was formed in ~88 Ma old volcanic target rocks of the Ochotsk‐Chukotsky Volcanic Belt (OCVB). In 2009, El'gygytgyn was the target of a drilling project of the International Continental Scientific Drilling Program (ICDP), and in summer 2011 it was investigated further by a Russian–German expedition. Drill core material and surface samples, including volcanic target rocks and impactites, have been investigated by various geochemical techniques in order to improve the record of trace element characteristics for these lithologies and to attempt to detect and constrain a possible meteoritic component. The bedrock units of the ICDP drill core reflect the felsic volcanics that are predominant in the crater vicinity. The overlying suevites comprise a mixture of all currently known target lithologies, dominated by felsic rocks but lacking a discernable meteoritic component based on platinum group element abundances. The reworked suevite, directly overlain by lake sediments, is not only comparatively enriched in shocked minerals and impact glass spherules, but also contains the highest concentrations of Os, Ir, Ru, and Rh compared to other El'gygytgyn impactites. This is—to a lesser extent—the result of admixture of a mafic component, but more likely the signature of a chondritic meteoritic component. However, the highly siderophile element contribution from target material akin to the mafic blocks of the ICDP drill core to the impactites remains poorly constrained. 相似文献
885.
Remarkable bedding features occur in Middle Cambrian platy limestone of the Western Hills close to Beijing in NE-China, which are intercalated in a sequence of shallow water carbonates (mudstones, storm deposits, oolitic grainstones). The platy limestone beds (up to 5 cm thickness) have undergone complex diagenetic compaction and pressure solution. Varying facies types are characterized by wavy, stylolitic boundaries with different thickness of clay accumulation and common lateral pinch out. Cross-cutting relationships of stylolites commonly destroy primary bed-surfaces. This indicates an intimate interfingering resulting in an indenting fabric of primary separated facies types. Nevertheless, primary sedimentary boundaries can be recognized. There occur varying types of compaction features documented by different stylolite types with varying amplitudes and thickness of clay-enrichments (parallel clay seams, stylolamination, stylo-nodular and stylo-brecciated structures with multi-grained seams). Bedded limestone of the type documented, generally belong to the limestone family of Plattenkalk, Lithographic Limestone or platy limestone, which can form in different environments. Consequently, using these names without detailed data on some specific parameters (e.g. thickness, surface morphology, composition of allochems, particle and crystal size) results in more confusion and hinders the comparison of Plattenkalk, Lithographic Limestone and platy limestone from different locations throughout the earth history. Therefore, a classification is proposed here which is based on macroscopic, microscopic, and sub-microscopic parameters. Plattenkalk and platy limestone are considered to form the two main groups. Plattenkalk beds are laterally consistent and have parallel, horizontal surfaces. Platy limestone can pinch out laterally and reveals irregular and inclined bed surfaces. Single beds in both can have different thickness, internal structure (e.g. micritic, microsparitic) and fabric (e.g. homogeneous, nodular), particle content and other variations (e.g. chemical, mineralogical). These parameters should be added to the basic name and used in a system similar to Folk’s limestone classification. Lithographic Limestone is defined as a subgroup of Plattenkalk with well-defined parameters. A consequent use of this classification will also help to understand fossil preservation and/or non-preservation in different types of Plattenkalk, Lithographic Limestone, and platy limestone. 相似文献
886.
Naki Akçar Susan Ivy-Ochs Peter W. Kubik Christian Schlüchter 《Swiss Journal of Geoscience》2011,104(3):445-453
Understanding and interpretation of ‘numbers’ produced about the depositional age of an erratic boulder by cosmogenic nuclide surface-exposure dating is important in the construction of glacial chronology. We have sampled three ‘Findlinge’ (glacially transported boulders) located on the right-lateral margin of the Aare glacier at Möschberg, Grosshöchstetten, southeast of Bern, with the aim of shedding light on this topic. The boulders have the same depositional, but different post-depositional histories: simple exposure; exhumation; and human impact. This sampling is specially selected for this study, since the boulders showing exhumation and human impact would not have been sampled in a regular surface-exposure dating application. We measured cosmogenic 10Be concentrations and calculated apparent exposure ages that are 13.6 ± 0.5, 18.1 ± 0.8, and 7.5 ± 0.4 ka, respectively. The exposure age of the first boulder reflects exhumation. The apparent exposure age of 18.1 ± 0.8 ka (erosion-corrected exposure age 19.0 ± 0.9 ka) from the second boulder correlates well with the end of the Alpine and global last glacial maximum. The third boulder shows evidence of quarrying as it is surrounded by a rim of excavation material, which is also reflected by the 7.5 ± 0.4 ka apparent exposure age. We modeled the variation of 10Be concentrations with depth down into the sediment in which the first (exhumed) boulder was once buried in, and down into the third (quarried) boulder. According to our modeling, we determined that the exhumed ‘Findling’ was buried in sediment at a depth of around 0.5 m, and around 2 m of rock was quarried from the third ‘Findling’. Our results reveal the importance of sampling for surface-exposure dating within a well defined field context, as post-depositional impacts can easily hinder exposure-dating of surfaces. 相似文献
887.
The settlement and development of Québec’s maritime coastline has generally taken place without consideration for coastal dynamics and coastal hazards. Consequently, fighting coastal erosion has become a necessity. Until now, the construction of rigid walls and encroachments has been the preferred approach to the problem. In the Chaleur Bay region, coastal communities are particularly vulnerable to erosion and flooding because a number of residential, commercial and transportation infrastructures have been installed on beach terraces and sand spits. Recent storms, such as the storm of December 2, 2005, have made possible a better understanding of how these rigid defence structures amplify the effects of storm surges and waves. These structures drive the sand away from the coast, lowering beach levels and even causing beaches to vanish entirely from the areas situated in front of the defence structures. The end result is a weakening of the natural capacity of these coastal systems to absorb the energy of waves and a greater risk of coastal flooding. An integrated approach using local knowledge on the one hand, along with LIDAR surveys and a DGPS system on the other hand, have made possible to map the levels reached by flooding at the time of the storm. The results indicate that such levels vary greatly in spatial terms and that the difference between the levels actually reached and the water level measured by tide gauge can be as much as 2 m; a difference that is due to anthropogenic perturbations. This raises questions concerning the safety and the reference levels used for mapping coastal flooding risk. Taking into account knowledge of local communities, analysis of water levels, geomorphological indicators and aggravating anthropogenic factors, an approach and basic criteria are put forward with a view of establishing a reference level for the mapping of flood risk that can be used by community land-use planners. 相似文献
888.
This paper presents two novel nonlinear models of u-shaped anti-roll tanks for ships, and their linearizations. In addition, a third simplified nonlinear model is presented. The models are derived using Lagrangian mechanics. This formulation not only simplifies the modeling process, but also allows one to obtain models that satisfy energy-related physical properties. The proposed nonlinear models and their linearizations are validated using model-scale experimental data. Unlike other models in the literature, the nonlinear models in this paper are valid for large roll amplitudes. Even at moderate roll angles, the nonlinear models have three orders of magnitude lower mean square error relative to experimental data than the linear models. 相似文献
889.
This paper focuses on Messinian Salinity Crisis (MSC) evaporites in the Cyprus Arc (eastern Mediterranean) using high‐resolution reflection seismic and multi‐beam data. The results shed new light on the Miocene to Present tectonic evolution of this area and contribute to our general knowledge of the MSC in a deep basin setting. The evaporites and overlying formations show a complex deformation pattern due to a combination of thick‐skinned plate‐tectonic convergence and thin‐skinned disharmonic deformation related to the mobile evaporite‐bearing unit. Several MSC markers are identified and precisely mapped: the base of the MSC unit is a ‘decollement’ level, whereas the top is clearly identified as a toplap surface. Intra‐MSC markers and two MSC subunits are identified and mapped over the entire study area. The geometry of MSC markers shows that the lower MSC subunit was deposited in a relatively quiet tectonic setting. The nature of the anisopachous upper unit indicates a syn‐depositional phase of large‐scale plate‐tectonic activity. A thin‐skinned phase of compressional deformation during the Late Miocene affected the entire MSC unit, overlain by undeformed Pliocene–Quaternary layers. A second thin‐skinned phase, well expressed in the bathymetry, occurred from the Pliocene to Recent, resulting in extensional gravity‐gliding within the evaporites and the Pliocene–Quaternary sequence. We show that the MSC had a dramatic impact on the regional structure. For instance, the erosive nature of the top of the MSC unit is linked to the desiccation episode rather than to the cessation of tectonic activity. This particularly strong and short‐lived erosion may have been enhanced by the regional effects of the MSC, owing to differential uplift/subsidence caused by the drawdown. The evaporites are essential markers for constraining the tectonic framework, provided that active deformation can be distinguished from passive gliding associated with extensional/contractional deformation. 相似文献
890.
In this paper, we will present the stratigraphic evolution, internal facies architecture and geomorphology of the Middle Pleistocene Emme delta, controlled by rapid high‐amplitude lake‐level change. The Emme delta was deposited on the northern margin of glacial Lake Weser, located in north‐west Germany. Rates of lake‐level rise were probably >50 mm year?1 and rates of lake‐level fall 30–50 m within a few days or weeks, due to the opening of lake outlets. We use digital elevation models, sedimentology and shear wave seismics to improve earlier reconstructions and investigate the influence of rapid base‐level change on delta development. Shear wave seismic data resolve architectural elements in the range of metres and bridge the common gap between outcrop and conventional compression wave seismic data. The radial delta complex is about 2 km long, 1.8 km wide and up to 70 m thick, overlying a concave, up to 13° steep dipping ramp surface. It consists of vertically and laterally stacked delta lobes, caused by lobe switching during base‐level change. During the lake‐level rise, vertically stacked (Gilbert‐type) delta systems formed. The decrease in thickness and lateral extent indicates a rapid upslope shift of depocentres. A high rate and magnitude of lake‐level fall (50 m) promoted the development of a single incised valley and the deposition of forced regressive coarse‐grained delta lobes in front of the valley. The incised valley was filled during decreasing rates of lake‐level fall and low base‐level, because the alluvial gradient was larger than the emergent lake profile. Attached sand‐rich forced regressive aprons formed during lower magnitudes of lake‐level falls in the range of 30–35 m. Valley incision occurred, but was limited to the uppermost portion of the delta, controlled by the steep slope. The incised valley related to the final lake drainage is associated with long‐wavelength (60–90 m) bedforms at the downslope end, attributed to the formation of standing waves as a result of a hydraulic jump. Estimated palaeoflow depth during standing wave formation was ~9–14 m and flow velocity was 10–12 m s?1. Because subsidence, waves or tides did not play a major role, the Emme delta can be used as an analogue‐based predictive stratigraphical and sedimentological model for steep glacigenic deltas controlled by rapid base‐level change and can help to understand better the facies distribution and three‐dimensional geometry of these depositional systems. 相似文献