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1.
An Early Pleistocene fluvio-lacustrine sequence from the extremely arid southern Negev desert, Israel, indicates that climatic conditions during that period were humid enough to support the formation of a lake (Lake Zihor) there. The lacustrine sediments were deposited in a tectonic valley that developed along the Zihor tectonic line after the deposition of the Pliocene Arava Formation. They intercalate with fluvial sediments that contain several horizons of reddish calcic paleosols. The lacustrine sequence comprises three sedimentary cycles. Each starts with a dark clay layer overlain by a white limestone unit, both of which contain abundant freshwater fauna, and terminates with a green detrital limestone that contains only one type of brackish-water ostracod. The top of each green limestone unit is characterized by pedogenic features and microrelief, indicating desiccation of the lake and soil development. Isotope data support the hypothesis that the white limestone was deposited in an open, freshwater lake. The incision of the present channel of Nahal (wadi) Zihor in the lacustrine sediments is manifested by a series of rock-cut and fluvial terraces (Q1–Q4) capped by gypsic-salic soils, which reflect the onset of the present, extremely arid climate. Over 100 find-spots and larger occurrences of prehistoric artifacts assigned to the Lower Paleolithic were discovered near Lake Zihor. On the basis of techno-typological and stratigraphic considerations, these assemblages are divided into two groups, the first of which may be contemporaneous with the lake, while the second is found mainly on the younger Q1 and Q2 terraces. It is estimated that the lake existed for more than 100,000 years. The climate during this period was probably semiarid, but water budget calculations suggest that, in addition to surface runoff, seepage of groundwater along the Zihor Line contributed a considerable amount of water to the lake. 相似文献
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Natural Hazards - How do people and communities respond to catastrophes? A natural disaster is a type of external, quasi-random and unexpected catastrophic shock that generates psychological,... 相似文献
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Laure Dosso Barry B. Hanan Henri Bougault Jean-Guy Schilling Jean-Louis Joron 《Earth and Planetary Science Letters》1991,106(1-4)
Basalts dredged along the Mid-Atlantic Ridge axis between 10°N and 17°N have been studied for their trace element characteristics [1]. To give complementary information on mantle source history and magma genesis, these samples have been analysed for their SrNdPb isotopic compositions. There is a good correlation between the structure of the ridge axis which shows a topographic anomaly centered around 14°N and hygromagmaphile element ratios such as Rb/Sr, (Nb/Zr)N or Sm/Nd as well as isotopic ratios plotted as a function of latitude. The samples coming from the 14°N topographic high show new MORB SrNd isotopic characteristics which pictured in a classical mantle array diagram, put their representative points close to HIMU sources of ocean islands such as St. Helena, Tubuaïand Mangaia. The 14°N mantle source presents geochemical characteristics which indicate mantle differentiation processes and a mantle history that are more distinct than so far envisaged from typical MORB data. Pb data indicates that the 14°N mantle source cannot be the result of binary mixing between a depleted mantle and a HIMU-type source. Rather, the enriched endmember could itself be a mixture of Walvis-like and HIMU-like materials. The geochimical observations presented favour the model of an incipient ridge-centered plume, in agreement with [1]. 相似文献
4.
Shales and phyllites from the turbidite sequences of the 2.9 Ga Mosquito Creek Formation of the East Pilbara, Western Australia contain varying amounts of paragonite and mixed Na–K micas (MNKMs), the 0 0 l X-ray diffraction reflections of which are unresolved from the 10-Å reflections, and only partly resolved from the 5-Å reflections of white K-mica (WKM). The Kübler index (‘crystallinity’), the full width at half maximum (FWHM) of the WKM, obtained from these composite reflections by applying a three-peak deconvolution procedure, reveals a metamorphic zoning of the Mosquito Creek Formation. The highest, “epimetamorphic”, grade occurs in the — largely Na-mica free — southern part, with lower, medium- to high-anchimetamorphic, grades in the central part, notably in a WSW-ENE anticlinal zone extending from Nullagine to the Blue Spec Mine. The Na-mica free metasediments of the Glen Herring Shale of the Fortescue Group, overlying the Mosquito Creek Formation to the W, show only a slightly lower metamorphic grade. The low b0 lattice parameter of the WKMs indicates a very low metamorphic P/T gradient. The Na-mica bearing metasediments of the Mosquito Creek Formation correspond to a kaolinite-bearing protolith, strongly Al-enriched and K-depleted with respect to the presumably granitic-tonalitic source rock. 相似文献
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Ouchene Hanan Chahouri Abir Hafidi Najat Elouizgani Hassan Hermas Jamila 《Ocean Science Journal》2021,56(4):344-354
Ocean Science Journal - Seasonal variations of the gonad index (GI), the biochemical composition, and the concentration of heavy metals in the gonads of the sea urchin, Paracentrotus lividus... 相似文献
7.
Rengin Gök Hanan Mahdi Haydar Al-Shukri Arthur J. Rodgers 《Geophysical Journal International》2008,172(3):1179-1187
We report the crustal structure for two locations in Iraq estimated by joint inversion of P -wave receiver functions (RFs) and surface (Rayleigh) wave group velocity dispersion. RFs were computed from teleseismic recordings at two temporary broad-band seismic stations located in Mosul (MSL) in the Zagros Fold Belt and Baghdad (BHD) in the Mesopotamian Foredeep. Group velocity dispersion curves at the sites were derived from continental-scale tomography. The inversion results show that the crustal thicknesses are 39 km at MSL and 43 km at BHD. We observe a strong Ps Moho at BHD consistent with a sharp Moho discontinuity. However, at MSL we observe a weak Ps Moho suggesting a transitional Moho where crustal thickening is likely to be occurring in the deep crust. Both sites reveal low velocity surface layers consistent with sedimentary thickness of about 3 km at station MSL and 7 km at BHD and agreeing well with the previous reports. Ignoring the sediments, the crystalline crustal velocities and thicknesses are remarkably similar at both stations. The similarity of crustal structure suggests that the crust of the northeastern proto-Arabian Platform was uniform before subsidence and deposition of the sediments in the Cenozoic. If crystalline crustal structure is uniform across the northern Arabian Platform then crustal thickness variations in the Zagros Fold Belt and Thrust Zone should reveal the history of deformation and crustal shortening in the Arabian–Eurasian collision zone and not reflect pre-existing crustal thickness variations in the Arabian Plate. 相似文献
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Jörg Geldmacher Kaj Hoernle Barry B. Hanan Janne Blichert-Toft F. Hauff James B. Gill Hans-Ulrich Schmincke 《Contributions to Mineralogy and Petrology》2011,162(1):21-36
The broad belt of intraplate volcanism in the East Atlantic between 25° and 37° N is proposed to have formed by two adjacent
hotspot tracks (the Madeira and Canary tracks) that possess systematically different isotopic signatures reflecting different
mantle source compositions. To test this model, Hf isotope ratios from volcanic rocks from all individual islands and all
major seamounts are presented in this study. In comparison with published Nd isotope variations (6 εNd units), 176Hf/177Hf ratios span a much larger range (14 εHf units). Samples from the proposed Madeira hotspot track have the most radiogenic
Hf isotopic compositions (176Hf/177Hfm up to 0.283335), extending across the entire field for central Atlantic MORB. They form a relatively narrow, elongated trend
on the Nd vs. Hf isotope diagram (stretching over > 10 εHf units) between a depleted N-MORB-like endmember and a moderately
enriched composition located on, or slightly below, the Nd–Hf mantle array, which overlaps the proposed “C” mantle component
of Hanan and Graham (1996). In contrast, all samples from the Canary hotspot track plot below the mantle array (176Hf/177Hfm = 0.282943–0.283067) and form a much denser cluster with less compositional variation (~4 εHf units). The cluster falls between
(1) a low Hf isotope HIMU-like endmember, (2) a more depleted composition, and (3) the moderately enriched end of the Madeira
trend. The new Hf isotope data confirm the general geochemical distinction of the Canary and Madeira domains in the East Atlantic.
Both domains, however, seem to share a common, moderately enriched endmember that has “C”-like isotope compositions and is
believed to represent subducted, <1-Ga-old oceanic lithosphere (oceanic crust and possibly minor sediment addition). The lower
176Hf/177Hf ratio of the enriched, HIMU-like Canary domain endmember indicates the contribution of oceanic lithosphere with somewhat
older recycling ages of ≥1 Ga. 相似文献
10.
The Cairo earthquake (12 October 1992; m b = 5.8) is still and after 25 years one of the most painful events and is dug into the Egyptians memory. This is not due to the strength of the earthquake but due to the accompanied losses and damages (561 dead; 10,000 injured and 3000 families lost their homes). Nowadays, the most frequent and important question that should rise is “what if this earthquake is repeated today.” In this study, we simulate the same size earthquake (12 October 1992) ground motion shaking and the consequent social-economic impacts in terms of losses and damages. Seismic hazard, earthquake catalogs, soil types, demographics, and building inventories were integrated into HAZUS-MH to produce a sound earthquake risk assessment for Cairo including economic and social losses. Generally, the earthquake risk assessment clearly indicates that “the losses and damages may be increased twice or three times” in Cairo compared to the 1992 earthquake. The earthquake risk profile reveals that five districts (Al-Sahel, El Basateen, Dar El-Salam, Gharb, and Madinat Nasr sharq) lie in high seismic risks, and three districts (Manshiyat Naser, El-Waily, and Wassat (center)) are in low seismic risk level. Moreover, the building damage estimations reflect that Gharb is the highest vulnerable district. The analysis shows that the Cairo urban area faces high risk. Deteriorating buildings and infrastructure make the city particularly vulnerable to earthquake risks. For instance, more than 90 % of the estimated buildings damages are concentrated within the most densely populated (El Basateen, Dar El-Salam, Gharb, and Madinat Nasr Gharb) districts. Moreover, about 75 % of casualties are in the same districts. Actually, an earthquake risk assessment for Cairo represents a crucial application of the HAZUS earthquake loss estimation model for risk management. Finally, for mitigation, risk reduction, and to improve the seismic performance of structures and assure life safety and collapse prevention in future earthquakes, a five-step road map has been purposed. 相似文献