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News Article | February 15, 2017
Site: www.eurekalert.org

The annual summer monsoon that drops rain onto East Asia, an area with about a billion people, has shifted dramatically in the distant past, at times moving northward by as much as 400 kilometers and doubling rainfall in that northern reach. The monsoon's changes over the past 10,000 years likely altered the course of early human cultures in China, say the authors of a new study. Researchers from the Lamont-Doherty Earth Observatory and the Chinese Academy of Sciences in Xi'an studied ancient water levels for Lake Dali, a closed-basin lake in Inner Mongolia in the northeast of China. They found that the lake was six times larger and water levels were 60 meters higher than present during the early and middle Holocene--the period beginning about 11,700 years ago, and encompassing the development of human civilization. "I think it is important to emphasize that these spatial fluctuations in the monsoon drive large changes in northern China," said Yonaton Goldsmith, a graduate student at Lamont-Doherty Earth Observatory and lead author of the paper. "When the monsoon is strong, it shifts northward and northern China becomes green. When the monsoon is weak, the monsoon stays in the south and northern China dries out. Such large fluctuations must have altered the ecosystems in northern China dramatically." The study, appearing this week in the Proceedings of the National Academy of Sciences, also ties the shifting monsoon to changes in the earth's orbit and other periodic changes in the climate system. The study should help scientists understand how the monsoon is affected by those natural cycles, and how a changing climate today might influence the monsoon in the future. Goldsmith said it's still unclear how the monsoon will react to global warming. One view is that the monsoon should grow stronger, but the area studied has been drying out over recent decades, he said, "so there is still a lot that needs to be done in that region before we can get definitive answers." Dali Lake is located near the northwestern limit of the East Asian monsoon, and so would reflect the changes brought about when the monsoon shifted north. The researchers studied outcrops of sediments left behind when the lake was far larger, and used those and other markers to construct a timeline of lake levels, and the fluctuation of rainfall over millennia. They found that the lake reached peak levels around 123,000 years ago, again around 58,000 years ago, and once more between 11,000 and 5,500 years ago. They tie the periodic increases in rainfall to the range of the monsoon shifting north by as much as 400 kilometers. The lake record is "highly correlated" with measurements taken earlier from cave deposits in both northern and southern China. Between 5,500 and 5,000 years ago, the monsoon weakened and rainfall over northern China decreased by 50 percent, the researchers found. They speculate that this drying triggered a major cultural transition in the region. As they describe it, two early Neolithic societies, the Hongshan culture in North China and the Yangshao culture in central China, collapsed around 5,000 years ago. In central China, the following period saw the rise of more stratified and socially and politically complex societies, including the Longshan culture. Previously unoccupied areas on the eastern margin of the Tibetan plateau were populated. Meanwhile, northeast China experienced a sharp population decline, represented by the Xiaoheyan culture. "These findings show that climate change can have dramatic effects on human societies and highlight the necessity to understand the effect of global warming on rainfall patterns in China and all over the world," the authors write. Intense variations in rainfall may have played a role in the collapse of other civilizations. A study led by Lamont scientist Brendan Buckley, published several years ago, suggested that extended drought coupled with changes in the monsoon could have doomed Cambodia's ancient Khmer civilization at Angkor nearly 600 years ago. Drought is thought to have played a role in the decline of the Classic Maya civilization, too, though in that case, another Lamont study suggests that the Maya themselves contributed to the drought by clearing forests for cities and crops. The Lake Dali paper's other authors are Wallace S. Broecker, Pratigya J. Polissar and Peter B. deMenocal of Lamont-Doherty; Hai Xu, Jianghu Lan, Peng Cheng, Weijian Zhou and Zhisheng An of the State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences; and Naomi Porat of the Geological Survey of Israel. This work was supported by a Gary Comer Science and Education Foundation grant to Yonaton Goldsmith and Pratigya J. Polissar; Columbia's Center for Climate and Life; the National Basic Research Program of China Grant 2013CB955900; the External Cooperation Program of Bureau of International Cooperation, Chinese Academy of Sciences Grant 132B61KYSB20130003; and Lamont-Doherty Earth Observatory Contribution no. 8084.


Gvirtzman Z.,Geological Survey of Israel | Steinberg J.,Ratio Oil Exploration
Tectonics | Year: 2012

[1] While the breakup of Arabia and Africa began in the early Oligocene, the northwestern boundary of the Arabian Plate along the Dead Sea Transform (DST) formed 10-15 Myr later (early-middle Miocene). During the early stage of breakup the Red Sea Rift continued propagating northwestward, forming the Suez Rift. The present ∼45° northward twist of the plate boundary from the Red Sea toward the Gulf of Eilat (Aqaba) still did not exist. What happened at the northern tip of the Suez Rift at that time? How was strain distributed to its surroundings, and where did the plate boundary continue from there? Here we describe an abandoned segment of the Arabian northwestern plate boundary that extended from the northern tip of the Suez Rift northeastward, along the Levant margin. Seismic data collected offshore Israel support a subsurface, deep-rooted fault zone running along the base of the continental slope. These faults indicate Oligocene transpressional lateral shearing. We propose that during the early stage of continental breakup a left-lateral strike-slip motion of ∼10 km took place along this embryonic plate boundary. Such deep-rooted tectonism implies that unlike the passive situation of the Israel-Sinai continental margin witnessed presently and before the Oligocene, during the early stage of the Africa-Arabia breakup this part of the continental margin was reactivated. We further suggest that the inland jump of the plate boundary toward the DST was not immediate and that during the transitional period the Israel-Sinai triangular block was an independent subplate with deformation all around it. © 2012. American Geophysical Union. All Rights Reserved.


Siman-Tov S.,Hebrew University of Jerusalem | Aharonov E.,Hebrew University of Jerusalem | Sagy A.,Geological Survey of Israel | Emmanuel S.,Hebrew University of Jerusalem
Geology | Year: 2013

Many faults are characterized by naturally polished, reflective, glossy surfaces, termed fault mirrors (FMs), that form during slip. Recent experiments also find that FMs form during rapid sliding between rock surfaces, and that FM formation coincides with pronounced friction reduction. The structure of FMs and the mechanism of their formation are thus important for understanding the mechanics of frictional sliding, particularly during earthquakes. Here we characterize the small-scale structure of natural carbonate FMs from three different faults along a tectonically active region of the Dead Sea transform. Atomic force microscopy measurements indicate that the FMs have extremely smooth surface topography, accounting for their mirror-like appearance. Electron microscope characterization revealed a thin (<1 μm) layer of tightly packed nanoscale grains coating a rougher layer comprising micron-size calcite crystals. The crystals contain closely spaced, plastically formed twins that define new subgrain boundaries. The narrow subgrains are observed to break into submicron pieces near the sheared surface. This observation suggests a new brittle-ductile mechanism for nanograin formation. The role of ductility during frictional sliding, both in forming the nanograin layer, and in the deformation process of the powder, may be critical for understanding shear on geological faults. © 2013 Geological Society of America.


Segev A.,Geological Survey of Israel | Rybakov M.,Geological Survey of Israel
Journal of the Geological Society | Year: 2010

This study synthesizes geological and geophysical evidence concerning the structure and character of the central and southern Jurassic Levant continental margin during Cretaceous-Tertiary time. From the beginning of the Cretaceous and until Cenomanian time, the Levant margin was strongly affected by extensional tectonics, cyclical igneous activity and rifting coupled with thermal and vertical fluctuations. It is suggested here that during the Senonian-Maastrichtian convergence of Afro-Arabia and the Mesotethys, and the Tauride part of Eurasia, the Herodotus basin oceanic crust subducted along the Eratosthenes Arc, below the short-lived abandoned Levant back-arc basin. Such a plate configuration assumes regional shear zones, as follows: (1) between the Eratosthenes Arc from the south and the Kyrenia Arc from the north: the NW-SE Carmel-Azraq-Sirhan fault system; (2) between the Sinai and the African plates: the Suez fault system; (3) between the Mesotethys and the African plates: the northern Egypt-Sinai-Negev west-east transversal fault system. Distinct tectonomagmatic quiescence between Late Maastrichtian and Late Eocene time allowed thermal relaxation and subsidence of the Levant margin until the apparent achievement of local isostatic compensation and the consequent development of the longest transgression over the Afro-Arabian ramp. © 2010 Geological Society of London.


Steinitz G.,Geological Survey of Israel | Piatibratova O.,Geological Survey of Israel
Geophysical Journal International | Year: 2010

High time resolution monitoring of radon, using alpha detectors is carried out in a massive and jointed syenite located in arid southern Israel. Monitoring, at a resolution of 15-min, is conducted in two boreholes at depths of 1.2 and 85-90 m, resulting in more then 10-yr long time-series. Systematic temporal variation patterns, manifesting large relative signals are composed primarily of annual (AR), multiday (MD), daily (DR) and subdaily (SDR) radon signals. Prominent periodic diurnal variation underlies the DR and probably also the SDR signals. Diurnal (S1; 24-hr) and semidiurnal (S2; 12-hr) constituents characterize the DR signal at 1.2 m, while diurnal constituents typical for gravity related periodicities (M2, O1) are absent. The amplitudes of the S1 and S2 constituents, calculated for consecutive 512-hr-long time intervals, exhibit a similar covarying annual pattern. The periodic DR signal is absent at 85 m depth. The peak time of SDR signals, occurring at this depth in some days, exhibits a 24- and 12-hr periodicity. Time offsets of hours are observed between time-series of the measured signal from the two levels. The lag, investigated for the decomposed MD signal, using consecutive 20-d-long time intervals, shows that the signal at depth systematically lags by around 9 hr the signal at the shallow level. Discrepancy of the patterns of the temporal variation in the time domain, and also in the frequency and time-frequency domains of the diurnal periodic components, indicates that atmospheric influence on the radon signal is insignificant even at a depth of 1.2 m. Combining this conclusion with the compound interrelations occurring among the different radon signals suggests that other geophysical processes are driving the radon variation in the subsurface geogas. It is suggested that the significant S1 and S2 signatures, and their modulations, are imposed on the radon system by means of a direct link with solar radiation tide. © 2009 Geological Survey of Israel Journal compilation © 2009 RAS.


The current study evaluates clay distribution in modern surface sediments, mainly soils, to which desert dust is a major contributor. The mineralogical composition of the clay fraction of seventy seven samples was analyzed by X-ray diffraction. Twenty nine soil and dust samples were also analyzed for their bulk chemical composition. The samples are settled dust, soils developed on various sedimentary rocks, stream and lake sediments. They were collected along a climate gradient from hyper-arid to Mediterranean regimes in Israel. The purpose of the study is to decipher the main factors that control variable clay distribution along this gradient including annual precipitation, substrate type and topography. The common clay composition for most samples, of all sources, is illite-smectite (IS). >. kaolinite. >. illite. Trace amounts of chlorite, palygorskite, goethite and quartz might be present. Pedogenic processes are recognized even under arid climate where loessial soils display kaolinite depletion and more illitic IS phases than dust. Two main processes shape clay composition under a Mediterranean climate regime, regardless of the parent material. A smectitization process occurs in leached, low-permeable clayey soils, and reaches optimum evolution with ~. 90% smectite, or smectitic IS. This evolutionary trend is also recognized in poorly-drained soils of catenary chains that are related to other soil types like terra rossa, hamra and pale rendzina. Kaolinitization and apparently illite pedogenic formation occur in well-drained red Mediterranean soils of the terra rossa and hamra types to the detriment of smectitic IS phases of parent materials. In the most evolved terra rossa and hamra soils kaolinite becomes the principal mineral and illite is significantly enriched. Pedogenic evolution of the clay fraction mineralogical composition affects bulk chemical composition of most soil types. Clay inheritance from the bedrock is rather limited in leached soils. It is widely recognized in pale rendzina soils by the presence of smectite, or smectite and palygorskite, derived from late Cretaceous or Eocene chalks, respectively. Streams' clay composition, like that of dust, is fairly uniform, as streams average various sources across their drainage basins. However, composition variations can be attributed to local contribution from certain sources. © 2013.


Baer G.,Geological Survey of Israel | Hamiel Y.,Geological Survey of Israel
Geophysical Journal International | Year: 2010

A magma-driven rifting episode occurred at the Harrat Lunayyir (Harrat Al-shaqa) volcanic field, western Arabia, between 2009 April and July. It was accompanied by a swarm of more than 4000 M > 2 earthquakes, the largest ever documented in that region, with a peak Mw 5.7 shock on May 19. We combine Interferometric Synthetic Aperture Radar (InSAR) measurements and elastic modelling with seismic moment calculations to resolve the evolution of surface deformation associated with this event. Phase discontinuities and low-coherence lineaments are used to infer the location of the main active structures during the various deformation stages and descending-track interferograms that span the entire period are inverted to resolve the slip and opening distributions along two graben-bounding normal faults and a dyke, respectively. Assuming negligible rift-parallel displacements, we combine ascending- and descending-track interferograms to derive the vertical and rift-perpendicular deformation, which add up to a maximum surface extension of 1.5 m across the rift and subsidence of 0.8 m. The far-field deformation is dominated by the dyke opening, whereas the near-field displacements are mostly associated with movements along the faults. The cumulative seismic moment released during the entire swarm period accounts for about 14 per cent of the total geodetic moment, compared to about 55 per cent at the 2007 Gelai (Tanzania) and about 8 per cent at the 2005 Manda Hararo-Dabbahu (Afar) events. We propose that the differences in moment partitioning ratios are due to the different crustal and seismogenic layer thicknesses in the three regions and represent different stages in the evolution of a volcanic rift. The Gelai event represents the most juvenile stage of rifting, the Dabbahu event represents the most evolved and the Harrat Lunayyir event represents a rift that is intermediate between the two in its degree of maturity. © 2010 The Authors Journal compilation © 2010 RAS.


Climate change is frequently considered an important driver of hominin evolution and dispersal patterns. The role of climate change in the last phase (900-700 ka) of the Middle Pleistocene Transition (MPT) in the Levant and northeast Africa was examined, using marine and non-marine records. During the MPT the global climate system shifted from a linear 41 k.yr. into a highly non-linear 100 k.yr. system, considerably changing its global modulation. Northeast Africa aridity further intensified around 950. ka, as indicated by a sharp increase in dust flux, and a jump to overall higher levels thereafter, coinciding with a lack of sapropels in the deep eastern Mediterranean (930-690. ka). The increased dust flux centering at ∼800. ka corresponds to the minima in 400 k.yr. eccentricity, a minima in 65 °N solar forcing and in the weakest African monsoon precession periodicity. This resulted in expansion of hyper-arid conditions across North Africa, the lowest lake levels in eastern Africa and the lowest rainfall in the Nile River headwaters. In the eastern Mediterranean an increasing continental signature is seen in glacial stages 22 (∼880. ka) and 20 (∼800. ka). Lower arboreal pollen values also indicate arid conditions during these glacial stages. The southern and eastern parts of the Negev Desert, unlike its northern part, were hyper-arid during the MPT, making them highly unsustainable. The fluctuations in the stands of Lake Amora follow global climate variability but were more moderate than those of its last glacial Lake Lisan successor. In the northern Jordan-Valley Hula Lake, frequent fluctuations in lake level coincide with both global climate changes and minor changes in water salinity varying from fresh to oligohaline. It appears therefore that the most pronounced and widespread deterioration in climate occurred in northeast Africa from 900 to 700. ka, whereas in the Levant the corresponding climatic changes were more moderate. © 2010 Elsevier Ltd.


Bar-Matthews M.,Geological Survey of Israel | Ayalon A.,Geological Survey of Israel
Holocene | Year: 2011

Mid-Holocene (7000a-4000 yr BP) paleoclimate conditions were reconstructed for the eastern Mediterranean region through a high-resolution (3a-20 yr) oxygen and carbon isotopic record in a speleothem from Soreq Cave, Israel. Mid-Holocene climate change is characterized by sinusoidal cycles lasting ~1500 years, that represent changes of ~400 mm (between ~700 and ~300 mm) in annual rainfall, coincident with major cultural changes. Two major cultural changes occurred during wet events at 6550a-6450 yr BP and 4800a-4700 yr BP, associated with the transitions from mid-Chalcolithic to late-Chalcolithic period and from the early Bronze II to early Bronze III, respectively. The transition from late Chalcolithic to early Bronze I occurred during a dry period at 5700a-5600 yr BP. Superimposed on these cycles, several short-lived decadal- to centennial-scale climatic events were identified. Dry events occurred at 6650a-6600 yr BP, 6250a-6180 yr BP, 5700a-5600 yr BP, 5250a-5170 yr BP and 4200a-4050 yr BP. The last two events coincide with the cultural collapse of the Uruk society in Mesopotamia and the Akkadian Empire. Short climatic wet events occurred at 6700a-6680 yr BP, 6170a-6100 yr BP, 5760a-5740 yr BP and 5500a-5450 yr BP. © The Author(s) 2011.


Shalev E.,Geological Survey of Israel | Lyakhovsky V.,Geological Survey of Israel
Geophysical Journal International | Year: 2013

Induced seismicity by wellbore fluid injection is an important tool for enhancing permeability in hydrocarbon and geothermal reservoirs. We model nucleation and propagation of damage zones and seismicity patterns for two-dimensional plane strain configuration at a depth of 5 km using novel numerical software developed in the course of this study. Simulations include the coupling of poro-elastic deformation and groundwater flow with damage evolution (weakening and healing) and its effect on the elastic and hydrologic parameters. Results show that the process occurring during fluid injection can be divided into four stages. The duration of each stage depends on the hydrological and mechanical parameters. Initially, fluid flows into the rock with no seismic events (5 to 20 hr). At this stage, damage increases from 0 to 1 creating two sets of conjugate zones (four narrow damage zones). Thereafter, the occurrence of seismic events and faulting begins and accelerates for the next 20 to 70 hr. At the initial part of this stage, two of the damage zones create stress shadows on the other two damage zones that stop progressing. The velocity of the advancing damage is limited only by the rock parameters controlling damage evolution. At the third stage, which lasts for the following 20-30 hr, damage acceleration decreases because fluid transport becomes a limiting factor as the damage zones are too long to efficiently transfer the pressure from the well to the tip of the damage zones. Finally, the damage decelerates and even stops in some cases. The propagation of damage is controlled and limited by fluid transport from the injection well to the tip of the damage zones because fluid transport does not keep up with the dilatancy of the damage zones. The time and distance of propagation depend on the damage-permeability coupling and the remote shear stress. Higher remote shear stress causes shorter initial periods of no seismicity; strong damage-permeability coupling causes longer acceleration stage. © The Authors 2013. Published by Oxford University Press on behalf of The Royal Astronomical Society.

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