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Evolution and degradation of flat‐top mesas in the hyper‐arid Negev,Israel revealed from 10Be cosmogenic nuclides 
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下载免费PDF全文 Ronen Boroda Ari Matmon Rivka Amit Itai Haviv Maurice Arnold Georges Aumaître Didier L. Bourlès Karim Keddadouche Yehuda Eyal Yehouda Enzel 《地球表面变化过程与地形》2014,39(12):1611-1621
Mesas are ubiquitous landforms in arid and semiarid regions and are often characterized by horizontal stratified erodible rocks capped by more resistant strata. The accepted conceptual model for mesa evolution and degradation considers reduction in the width of the mesa flat‐top plateau due to cliff retreat but ignores possible denudation of the mesa flat‐top and the rates and mechanism of erosion. In this study we examine mesas in the northeastern hyperarid Negev Desert where they appear in various sizes and morphologies and represent different stages of mesa evolution. The variety of mesas within a single climatic zone allows examination of the process of mesa evolution through time. Two of the four sites examined are characterized by a relatively wide (200–230 m) flat‐top and a thick caprock whereas the other two are characterized by a much narrower remnant flat‐top (several meters) and thinner caprock. We use the concentration of the cosmogenic nuclide 10Be for: (a) determining the chronology of the various geomorphic features associated with the mesa; and (b) understanding geomorphic processes forming the mesa. The 10Be data, combined with field observations, suggest a correlation between the width of flat‐top mesa and the denudation and cliff retreat rates. Our results demonstrate that: (a) cliff retreat rates decrease with decreasing width of the flat‐top mesa; (b) vertical denudation rates increase with decreasing width of the flat‐top mesa below a critical value (~60 m, for the Negev Desert); (c) the reduction in the width of the flat‐top mesa is driven mainly by cliff retreat accompanied by extremely slow vertical denudation rate which can persist for a very long time (>106 Ma); and (d) when the width of the mesa decreases below a certain threshold, its rate of denudation increases dramatically and mesa degradation is completed in a short time. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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On free oscillations of the earth 总被引：2，自引：0，他引：2
This survey concerns mostly the theory of free oscillations, with a section on experimental work included at the end. Developments over the last 15 years are examined. The general theory of free oscillations is reviewed, and the effect on free oscillations of such factors as heterogeneity, the Earth's rotation and non-sphericity, and the source of the oscillations are discussed. Earth models, which have been obtained from oscillation data, are reviewed, and their use in forming theoretical seismograms is described.See note at p. 426.Note 相似文献
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A theoretical model for reverse water-level fluctuations induced by transient permeability in thrust fault zones 总被引：1，自引：0，他引：1
A numerical model was applied to simulate the poroelastic response to changes in fault permeability as a result of earthquakes. The ‘fault valve’ model describes faults as impermeable barriers for fluids except immediately after earthquakes, when fault zones are damaged and transient pathways for fluids are created. In this case the fault is viewed as a discharging well, draining fluids from the surrounding rock. The reverse water-level effect is characterized by the increase of water level in adjacent aquifers and aquitards, resulting from withdrawing fluids through a well. Theoretical calculations suggest that the reverse water-level effect exists also in earthquake cycling and is in the same order of magnitude as the co-seismic hydraulic head change. A significant rise of the hydraulic head (>1 m) occurs within the country rock from both sides of the fault. The rise of the water level takes months to years to occur, and perhaps that is why it cannot be easily distinguished from seasonal hydrologic changes observed in the field. The reverse water-level effect also propagates away from the fault at a rate of hundreds of meters per year, depending on the permeability of the country rock. In deep formations where the permeability is low, the propagation takes years. The magnitude of the reverse water-level effect is greater when the fault efficiently drains fluids, when it is highly permeable and slow to reseal. 相似文献
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Eyal Iaroslavitz 《Icarus》2007,187(2):600-610
We examine the deposition of heavy elements in the envelope of a protoplanet growing according to the core accretion scenario of Pollack et al. [Pollack, J.B., Hubickyj, O., Bodenheimer, P., Lissauer, J.J., Podolak, M., Greenzweig, Y., 1996. Icarus 124, 62-85]. We use their atmospheric models and the deposition rates that they computed, and we calculate the amount of heavy elements that can be dissolved in the envelope. For planetesimals composed of a mixture of water, CHON, and rock, we find that almost all of the water is dissolved in the atmosphere. A substantial amount of CHON is also dissolved but it remains sequestered at high temperatures near the core. Some fraction of the rock is also dissolved in the very high temperature region near the core envelope boundary. If this dissolved material can be mixed upward later in the planet's evolution, the resulting structure would be much closer to that determined by matching the moments of Jupiter's gravitational field. 相似文献
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Haggai Eyal Elad Dente Itai Haviv Yehouda Enzel Thomas Dunne Nadav G. Lensky 《地球表面变化过程与地形》2019,44(11):2170-2185
Global eustatic lowstands can expose vast areas of continental shelves, and occasionally the shelf edge and the continental slope. The degree of fluvial connectivity to receding shores influences the redistribution of sediments across these emerging landscapes. Shelf and slope emergence in the Dead Sea since the middle of the 20th century, offers a rare opportunity to examine evolution of stream connectivity in response to continuous base-level decline. We characterize the connectivity evolution of two streams, using high-resolution time series of aerial imagery and elevation models, field mapping, and grain-size analyses. Our rich spatiotemporal dataset of evolving channel geomorphology, sediment transport conditions, and sediment redistribution, allows calculating potential coarse sediment mobility in response to base level decline. Following shelf emergence, alluvial fans first prograded onto the low-gradient shelf under unfavourable conditions for transporting coarse sediment to the regressing shoreline. Then, with shelf and slope emergence, the two adjacent streams evolved differently. The smaller, more arid watershed still maintains its highstand delta progradation on the shelf and is practically disconnected from the receding lake. The larger catchment, heading in wetter environments and having a narrower shelf, has incised the shelf and renewed and gradually intensified the sediment transport from the highstand to the lowstand delta. Sediment mobilization to lowstand shorelines is controlled by the evolution of the channel profile and by the average speed of gravel transport (10s-100s m yr-1). These findings from the Dead Sea are relevant to fluvial processes operating on continental shelves during glacial maxima. Streams would have commonly stored high proportions of their coarse sediment on the continental shelves rather than efficiently connecting with the lowstand level. Additionally, differences in sediment routing patterns should exist among nearby streams, primarily due to continental margin geometry and watershed hydrology. © 2019 John Wiley & Sons, Ltd. 相似文献
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The feasibility of combining two sensors for monitoring gas concentrations over a large area, is demonstrated via controlled simulation experiments. The network considered was a lidar combined with a point detector—the MIRAN spectrophotometer equipped with a flow-through gas cell. The first has a spatial scanning capacity and a very good time resolution, whereas the second has an inherent temporal memory effect. Algorithms for operating the two sensors coincidentally, taking their physical characteristics into account, were constructed. A good fit was found between measured concentrations in the MIRAN and reconstructed concentrations, using the lidar data for the same environment. Thus complementary operation can be achieved. The MIRAN temporal memory effect can be overcome by correlating the concentration calculated over different time intervals. 相似文献
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Y. Katzir B.A. Litvinovsky B.M. Jahn M. Eyal A.N. Zanvilevich J.W. Valley Ye. Vapnik Y. Beeri M.J. Spicuzza 《Lithos》2007,97(3-4):336-364
Late Neoproterozoic bimodal dyke suites are abundant in the Arabian–Nubian Shield. In southern Israel this suite includes dominant alkaline quartz porphyry dykes, rare mafic dykes, and numerous composite dykes with felsic interiors and mafic margins. The quartz porphyry chemically corresponds to A-type granite. Composite dykes with either abrupt or gradational contacts between the felsic and mafic rocks bear field, petrographic and chemical evidence for coexistence and mixing of basaltic and rhyolitic magmas. Mixing and formation of hybrid intermediate magmas commenced at depth and continued during emplacement of the dykes. Oxygen isotope ratios of alkali feldspar in quartz porphyry (13 to 15‰) and of plagioclase in trachydolerite (10–11‰) are much higher than their initial magmatic ratios predicted by equilibrium with unaltered quartz (8 to 9‰) and clinopyroxene (5.8‰). The elevation of δ18O in alkali feldspar and plagioclase, and extensive turbidization and sericitization call for post-magmatic low-temperature (≤ 100 °C) water–rock interaction. Hydrous alteration of alkali feldspar, the major carrier of Rb and Sr in the quartz–porphyry, also accounts for the highly variable and unusually high I(Sr) of 0.71253 to 0.73648.
The initial 143Nd/144Nd ratios, expressed by εNd(T) values, are probably unaltered and show small variation in mafic and felsic rocks within a narrow range from + 1.4 to + 3.3. The Nd isotope signature suggests either a common mantle source for the mafic and silicic magmas or a juvenile crustal source for the felsic rocks (metamorphic rocks from the Elat area). However, oxygen isotope ratios of zircon in quartz porphyry [δ18O(Zrn) = 6.5 to 7.2‰] reveal significant crustal contribution to the rhyolite magma, suggesting that mafic and A-type silicic magmas are not co-genetic, although coeval. Comparison of 18O/16O ratios in zircon allows to distinguish two groups of A-type granites in the region: those with mantle-derived source, δ18O(Zrn) ranging from 5.5 to 5.8‰ (Timna and Katharina granitoids) and those with major contribution of the modified juvenile crustal component, δ18O(Zrn) varying from 6.5 to 7.2‰ (Elat quartz porphyry dykes and the Yehoshafat alkaline granite). This suggests that A-type silicic magmas in the northern ANS originated by alternative processes almost coevally. 相似文献