Gvirtzman Z.,Geological Survey of Israel |
Steinberg J.,Ratio Oil Exploration
Tectonics | Year: 2012
 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.
Sandler A.,Geological Survey of Israel
Catena | Year: 2013
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.
Waldmann N.,University of Bergen |
Torfstein A.,Lamont Doherty Earth Observatory |
Stein M.,Geological Survey of Israel
Geology | Year: 2010
The rain regime of the Levant during the late Quaternary was controlled primarily by Mediterranean cyclonic systems associated with North Atlantic climate shifts. Lake levels in the Dead Sea basin have been robust recorders of the regional hydrology and generally indicate highstand (wet) conditions throughout glacial intervals and lowstands (dry) during interglacials. However, sporadic deposition of travertines and speleothems occurred in the Negev Desert and Arava Valley during past interglacials, suggesting intrusions of humidity from southern sources probably in association with enhanced activity of mid-latitude Red Sea synoptic troughs and/or low-latitude tropical plumes. The southerly incursions of wetness were superimposed on the long-term interglacial Levantine arid conditions, as reflected by the current prevailing hyperaridity, and could have had an important impact on human migration through the Red Sea-Dead Sea corridor. © 2010 Geological Society of America.
Almogi-Labin A.,Geological Survey of Israel
Journal of Human Evolution | Year: 2011
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.
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.