Salt diapirs in the Dead Sea basin and their relationship to Quaternary extensional tectonics     

《Marine and Petroleum Geology》2001,18(7):779-797

Regional extension of a brittle overburden and underlying salt causes differential loading that is thought to initiate the rise of reactive diapirs below and through regions of thin overburden. We present a modern example of a large salt diapir in the Dead Sea pull-apart basin, the Lisan diapir, which we believe was formed during the Quaternary due to basin transtension and subsidence. Using newly released seismic data that are correlated to several deep wells, we determine the size of the diapir to be 13×10 km, its maximum depth 7.2 km, and its roof 125 m below the surface. From seismic stratigraphy, we infer that the diapir started rising during the early to middle Pleistocene as this section of the basin underwent rapid subsidence and significant extension of the overburden. During the middle to late Pleistocene, the diapir pierced through the extensionally thinned overburden, as indicated by rim synclines, which attest to rapid salt withdrawal from the surrounding regions. Slight positive topography above the diapir and shallow folded horizons indicate that it is still rising intermittently. The smaller Sedom diapir, exposed along the western bounding fault of the basin is presently rising and forms a 200 m-high ridge. Its initiation is explained by localized E–W extension due monoclinal draping over the edge of a rapidly subsiding basin during the early to middle Pleistocene, and its continued rise by lateral squeezing due to continued rotation of the Amazyahu diagonal fault.  相似文献   

Biologically mediated dissolution of calcium carbonate above the chemical lysocline?     

《Deep Sea Research Part I: Oceanographic Research Papers》1999,46(10):1653-1669

We find a diverse but increasing amount of evidence to suggest considerable dissolution of calcium carbonate, perhaps as much as 60–80%, in the upper 500–1000 m of the ocean, well above the chemical lysocline. The same biological processes that promote the rapid settling of carbonate particles (i.e. ingestion, digestion and egestion by zooplankton) as well as biologically mediated processes within flocculates and aggregates may be responsible – directly or indirectly – for much of this dissolution. The significance of shallow-water dissolution of carbonate particles necessitates further research into both its validity and, if true, specific causal mechanisms.  相似文献   

Fluvial incision and coarse gravel redistribution across the modern Dead Sea shelf as a result of base-level fall     

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   

Deformation within an exposed salt wall: Recumbent folding and extrusion of evaporites in the Dead Sea Basin     

《Journal of Structural Geology》2015

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Sr and Nd isotopes as tracers in pedogenic studies: Evidence for Saharan dust contribution to the soils of Muravera (Sardinia,Italy)     

《Chemie der Erde / Geochemistry》2015,75(3):301-315

Sr and Nd isotopes were applied to 5 soil profiles from the Muravera area, in south-eastern Sardinia.All the soils, which have developed during the Quaternary on the Lower Paleozoic metamorphic basement except for one on Eocene carbonates, are located far from major sources of pollution. Therefore, they are suitable for testing pedogenic processes and geochemical evolution to benefit for environmental studies.The Sr isotopic ratios range largely (δ⁸⁷Sr = 1.7–65.9‰), even in each soil profile. In particular, the observed increase of δ⁸⁷Sr with depth in the most of the metamorphic rock-based soils can be accounted for by the downward decrease of Sr contributions from organic matter and Saharan dust, both displaying lower isotopic ratios than the soil bedrocks. The carbonate rock-based soil exhibits δ⁸⁷Sr higher (1.7–18.1‰) than the bedrock, indicating a significant contribution of radiogenic Sr from the siliciclastic fraction of the soil, and probably from dust input. The Nd isotopic ratios are slightly variable through the profiles (ɛ_Nd from −7.8 to −14.5), confirming little mobility of Nd and Sm during the pedogenesis. Among the minerals present in the soils, phosphates, albite, and calcite are those important in providing low radiogenic Sr and Nd to organic matter of the soils.Lastly, this isotopic study has in particular allowed for evaluating the potential proportion of contribution of Saharan dust to south-eastern Sardinia, thus corroborating the findings of other studies related to soils from the central-western Mediterranean.  相似文献   

Investigation of small-scale droplet concentration inhomogeneities in a turbulent flow     

B. Grits  M. Pinsky  A. Khain 《Meteorology and Atmospheric Physics》2006,92(3-4):191-204

Summary This paper is focused on the numerical investigation of spatial characteristics of droplet concentration fluctuations, originating in a turbulent flow. The turbulent flow is simulated using a model of a statistically stationary, homogeneous and isotropic turbulent flow. We found that preferential droplet concentration with the maximum of spatial spectrum at about 1.5 cm is formed regardless of the droplet size (up to the droplet radius of 20 μm). The amplitude of fluctuations depends on the droplet radius and constitutes a significant part of mean concentration. Analogous simulations with non-inertial droplets (passive scalar) do not reveal such concentration fluctuations. Our main conclusion is, therefore, the following: preferential droplet concentration at the cm-scale forms in a turbulent flow due to droplets inertia.  相似文献   

Greigite detected as dominating remanence carrier in Late Pleistocene sediments, Lisan formation, from Lake Kinneret (Sea of Galilee), Israel     

H. Ron  N. R. Nowaczyk  U. Frank  M. J. Schwab  R. Naumann  B. Striewski  A. Agnon 《Geophysical Journal International》2007,170(1):117-131

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A field quantification of coastal dune perennial plants as indicators of surface stability, erosion or deposition     

NOAM LEVIN  GIORA J. KIDRON†  EYAL BEN-DOR 《Sedimentology》2008,55(4):751-772

Dune plants both modify the wind field around them and are impacted by various stress factors, among them sand erosion and sand deposition. As coastal dunes are being either stabilized or remobilized, in response to the changes in the rates of sand and dune movement, the vegetation cover and composition are expected to vary reflecting the differences in the sedimentary conditions. In this field study 315 quadrats of 100 m², in which the perennial plant species were sampled, were analysed with respect to annual rates of sand erosion and deposition that were measured using erosion pins. A visual exploratory data analysis was introduced, based on selective filtering of samples according to their vegetation cover. This method, combined with established statistical tools, enabled the authors to uncover the inclination and indicative power of nine perennial dune plants to either a stabilized or a mobile environment, and to establish whether they are more prevalent in places undergoing sand erosion or sand burial. Two species were found to be clear indicators of a stabilized environment, Stipagrostis lanata , and Retama raetam . Of the species indicating a mobile environment, only one may be stated as a clear indicator of sand erosion: Silene succulenta , with Cyperus macrorrhizus coming close to being an indicator of a less mobile erosive environment. The best indicator species for sand burial was found to be, as expected, Ammophila arenaria , with Artemisia monosperma also indicating high rates of sand mobility especially when its relative cover is higher than 80%. Such information can be used to monitor natural processes of dune stabilization or reactivation, or to assess the success of a management plan that aims at stabilizing a dune, or at remobilizing it by removing vegetation.  相似文献   

Holocene and Pleistocene pluvial periods in Yemen,southern Arabia     

Dominik Fleitmann  Stephen J. Burns  Marek Pekala  Augusto Mangini  Abdulkarim Al-Subbary  Mohammad Al-Aowah  Jan Kramers  Albert Matter 《Quaternary Science Reviews》2011,30(7-8):783-787

Arabia is an important potential pathway for the dispersal of Homo sapiens (“out of Africa”). Yet, because of its arid to hyper-arid climate humans could only migrate across southern Arabia during pluvial periods when environmental conditions were favorable. However, knowledge on the timing of Arabian pluvial periods prior to the Holocene is mainly based on a single and possibly incomplete speleothem record from Hoti Cave in Northern Oman. Additional terrestrial records from the Arabian Peninsula are needed to confirm the Hoti Cave record. Here we present a new speleothem record from Mukalla Cave in southern Yemen. The Mukalla Cave and Hoti Cave records clearly reveal that speleothems growth occurred solely during peak interglacial periods, corresponding to Marine Isotope Stages (MIS) 1 (early to mid-Holocene), 5.1, 5.3, 5.5 (Eemian), 7.1, 7.5 and 9. Of these humid periods, highest precipitation occurred during MIS 5.5 and lowest during early to middle Holocene.  相似文献   

High-resolution isotope records of early Holocene rapid climate change from two coeval stalagmites of Katerloch Cave,Austria     

Ronny Boch  Christoph Spötl  Jan Kramers 《Quaternary Science Reviews》2009,28(23-24):2527-2538

Two coeval stalagmites from Katerloch Cave show pronounced intervals of low δ¹⁸O values around 8.2, 9.1, and 10.0 kyr (all ages are reported before the year 2000 AD) and represent an inorganic U–Th dated climate archive from the southeast of the European Alps, a region where only very few well-dated climate records exist. The O isotope curves, providing near-annual resolution, allow a direct comparison to the Greenland ice core records, as temperature was the primary factor controlling the O isotopic composition of Katerloch speleothems.The 8.2 kyr climate anomaly lasted about one century, from 8196 to 8100 yr, with a maximum amplitude of 1.1‰ at 8175 yr. The event is characterized by a rapid onset and a more gradual demise and U–Th data as well as annual lamina counting support a rapid climate change towards cooler conditions within 10–20 yr. There is no strong evidence that the 8.2 kyr anomaly was superimposed on a pronounced longer-term cooling episode, nor do the new data support two separate cooling events within the 8.2 kyr event as reported by other studies. Our record also shows a distinct climate anomaly around 9.1 kyr, which lasted 70–110 yr and showed a maximum amplitude of 1.0‰, i.e. it had a similar duration and amplitude as the (central) 8.2 kyr event. Compared to the 8.2 kyr event, the 9.1 kyr anomaly shows a more symmetrical structure, but onset and demise still occurred within a few decades only. The different progression of the 8.2 (asymmetrical) and 9.1 kyr anomaly (symmetrical) suggests a fundamental difference in the trigger and/or the response of the climate system. Moreover, both stalagmites show evidence of a climate anomaly around 10.0 kyr, which was of comparable magnitude to the two subsequent events.Using a well constrained modern calibration between air temperature and δ¹⁸O of precipitation for the study area and cave monitoring data (confirming speleothem deposition in Katerloch reflecting cave air temperature), a maximum cooling by ca 3 °C can be inferred at 8.2 and 9.1 kyr, which is similar to other estimates, e.g., from Lake Ammersee north of the Alps. The O isotopic composition of meteoric precipitation, however, is a complex tracer of the hydrological cycle and these temperature estimates do not take into account additional effects such as changes in the source area or synoptic shifts. Apart from that, the relative thickness of the seasonally controlled lamina types in the Katerloch stalagmites remains rather constant across the intervals comprising the isotopic anomalies, i.e. the stalagmite petrography argues against major shifts in seasonality during the early Holocene climate excursions.  相似文献