The Negev continental bridge: a chain in an intermodal transport system

This paper is a second follow-up discussion concerning the role, economic viability and operational characteristics of the Negev Continental Bridge in the fluid geo-political atmosphere of the Middle East. The two previous papers (Geoforum8, 29–32 and 311–318) discussed the viability of the Israeli Continental Bridge as an alternative to the Suez Canal. Now, two years after the Canal was re-opened for use by Israeli vessels, the annual amount of cargo movement across the Israeli land bridge is still growing, although it is less economical than the Suez Canal. It is thus suggested that there is a need to view the continental bridge as one part of a chain in an intermodal transport system.     

Seismic hazard of Egypt

Earthquake hazard parameters such as maximum expected magnitude,M _max, annual activity rate,, andb value of the Gutenberg-Richter relation have been evaluated for two regions of Egypt. The applied maximum likelihood method permits the combination of both historical and instrumental data. The catalogue used covers earthquakes with magnitude 3 from the time interval 320–1987. The uncertainties in magnitude estimates and threshold of completeness were taken into account. The hazard parameter determination is performed for two study areas. The first area, Gulf of Suez, has higher seismicity level than the second, all other active zones in Egypt.b-values of 1.2 ± 0.1 and 1.0 ± 0.1 are obtained for the two areas, respectively. The number of annually expected earthquakes with magnitude 3 is much larger in the Gulf of Suez, 39 ± 2 than in the other areas, 6.1 ± 0.5. The maximum expected magnitude is calculated to be 6.5 ± 0.4 for a time span of 209 years for the Gulf of Suez and 6.1 ± 0.3 for a time span of 1667 years for the remaining active areas in Egypt. Respective periods of 10 and 20 years were reported for earthquakes of magnitude 5.0 for the two subareas.     

Crustal assimilation in basalt and jotunite: Constraints from layered intrusions

To constrain the amount and rate of crustal contamination that is possible in basaltic and jotunitic magma, and to gain an insight into the physical and thermal processes of assimilation in crustal magma chambers, we have modelled published Sr and Nd isotopic data from three layered intrusions. Well-exposed sequences of cumulates with no evidence of magma recharge provide direct records of concurrent assimilation and fractional crystallization (AFC). The key to the modelling is that F, the mass fraction of magma remaining in the chamber, can be estimated from the thicknesses of the studied cumulate sequences. This allows AFC model curves to be fitted to the isotopic data by varying r, the ratio of the rate of mass assimilated to the rate of mass crystallized. The results of modelling show that r is nearly constant in 800 to 2000 m thick sequences of cumulates displaying up-section decreases in anorthite content of plagioclase, increases in whole-rock Sr₀ (initial ⁸⁷Sr/⁸⁶Sr) and decreases in whole-rock εNd₀ (initial εNd). The r-values of the layered sequences range from 0.12 in the Fongen–Hyllingen Intrusion, over 0.20 in the Bjerkreim–Sokndal Intrusion, to 0.27 in the Hasvik Intrusion. The total amount of assimilation, the bulk crust/magma ratio, reaches values of 0.08, 0.19 and 0.28 at the level of the most contaminated samples after 60% to 80% crystallisation, whereas the instantaneous crust/magma ratio of the most contaminated magmas were respectively 0.14, 0.46, and 0.70, for the three intrusions.Innumerable country rock xenoliths occur in the three layered intrusions and played a crucial role in the assimilation process. The xenoliths spalled off the roofs of the magma chambers during magma emplacement and their initial temperature and composition relate to r in the intrusions. In the Hasvik Intrusion (r = 0.27), the initial temperature of the country rocks was 450 °C and the xenoliths were fusible metasediments and therefore produced a high fraction of partial melt that could be assimilated. In the Bjerkreim–Sokndal Intrusion (r = 0.20), the country rocks were initially at temperatures of 640–880 °C but included both refractory massif-type anorthosite and fusible gneisses. In the Fongen–Hyllingen Intrusion (r = 0.12), the country rocks were cooler (300 °C) and the xenoliths include refractory metabasalt (dominant) and fusible metapelite. We argue that the refractory metabasalt and anorthosite xenoliths acted mainly as heat sinks, resulting in reduced r-values in Fongen–Hyllingen and Bjerkreim–Sokndal Intrusions.Heating of refractory and fusible xenoliths, and melting of fusible xenoliths absorbed sensible and latent heat of the magma. Energy-balanced modelling shows that up to 75% of the heat available was absorbed by xenoliths within the magma chambers, promoting higher rates of cooling and crystallisation than would have resulted from loss of heat to the envelope of country rocks alone. The high r-values reflect the amount of heat absorbed by heating and melting country rock within the magma chambers themselves, and their constancy reflects the ready availability of fusible xenoliths.     

Transfer functions under no-analog conditions: Experiments with Indian Ocean planktonic Foraminifera

This paper documents and investigates an important source of inaccuracy when paleoecological equations calibrated on modern biological data are applied downcore: fossil assemblages for which there are no modern analogs. Algebraic experiments with five calibration techniques are used to evaluate the sensitivity of the methods with respect to no-analog conditions. The five techniques are: species regression; principal-components regression [e.g., Imbrie, J., and Kipp, N. G. (1971). In “The Late Cenozoic Ages,” 71–181]; distance-index regression [Hecht, A. D. (1973). Micropaleontology19, 68–77]; diversity-index regression (Williams, D. F., and Johnson, W. C. (1975). Quaternary Research5, 237–250]; weighted-average method [Jones, J. I. (1964). Unpublished Ph. D. Thesis, Univ. of Wisconsin]. The experiments indicate that the four regression techniques extrapolate under no-analog conditions, yielding erroneous estimates. The weighted-average technique, however, does not extrapolate under no-analog conditions and consequently is more accurate than the other techniques. Methods for recognizing no-analog conditions downcore are discussed, and ways to minimize inaccuracy are suggested. Using several equations based on different calibration techniques is recommended. Divergent estimates suggest that no-analog conditions occur and that estimates are unreliable. The value determined by the weighted-average technique, however, may well be the most accurate.     

Geothermal potential of Egypt

One hundred and sixty samples of groundwater from nearly all parts of Egypt have been collected and chemically analyzed in order to assess the country's geothermal potential. The samples considered to be thermal include 20 wells (T > 35°C), 4 springs (T > 30°C) and 1 spring not included in the present inventory. The remaining samples, together with data from the literature, establish background chemistry. The hottest springs are located along the east shore of the Gulf of Suez: Uyun Musa (48°C) and 'Ain Hammam Faraoun (70°C). Additional warm springs are located along both shores of the Gulf of Suez and this region is the most promising for geothermal development. The Eastern Desert of Egypt, particularly the coastal area adjacent to the Red Sea has above normal heat flow ( ~ 72.0 < mWm⁻²) and therefore some geothermal potential although only one thermal well (Umm Kharga: 35.8°C) could be located, In the major oases of the Western Desert (Kharga, Dakhla, Farafra and Bahariya), the regional temperature gradient is low (< 20°C/km), but many of the wells tap deep artesian aquifers and produce large volumes of water in the 35–43°C range. Such wells constitute a low temperature geothermal resource. None of our samples in northern Egypt can be considered thermal including several reported “hot springs.” Application of the silica, NaKCa. and NaKCaMg geothermometers does not indicate the presence of a high temperature geothermal resource at any area we visited.     

Extraction of uranium ions from water: a rapid and convenient method using prepackaged ion exchange resins

Ion exchange resins are used successfully to extract and concentrate uranium ions from aqueous solutions although the procedures are time consuming. They utilize rather cumbersome resin columns, and consequently they have found little practical application in large geochemical surveys of isolated areas. An alternative approach using resin packages is proposed. The “package” is a teabag — convenient, cheap, disposable, and readily sealed. Laboratory and field tests indicate that the method combines simplicity, speed and economy with excellent precision and detection limits. Although the packaging procedure was designed specifically for the extraction of uranium from natural waters under field conditions, the method can be modified to extract elements other than uranium and presents a viable alternative to resin columns in a standard laboratory.     

Source and flux of POC in two subtropical karstic tributaries with contrasting land use practice in the Yangtze River Basin

Elemental (C/N ratio) and C isotope composition (δ¹³C) of particulate organic C (POC) and organic C content (OC) of total suspended solids (TSS) were determined for two subtropical karstic tributaries of the Yangtze River, the Wujiang (the eighth largest tributary) and Yuanjiang (the third largest tributary). For the latter, two headwaters, the karstic Wuyanghe and non-karstic Qingshuijiang were studied. The Wujiang catchment is subject to intensive land use, has low forest coverage and high soil erosion rate. The δ¹³C of POC covered a range from −30.6‰ to −24.9‰, from −27.6‰ to −24.7‰, and from −26.2‰ to −23.3‰ at the low-water stage, while at the high-water stage varied in a span between −28.6‰ and −24.4‰, between −27.7‰ and −24.5‰, and between −27.6‰ and −24.2‰ for the Wujiang, Wuyanghe, and Qingshuijiang, respectively. The combined application of C isotopes, C/N ratio, OC, and TSS analyses indicated that catchment soil was the predominant source of POC for the Wujiang while for the Wuyanghe and Qingshuijiang, in-stream processes supplied the main part of POC in winter and summer. A significant increase in δ¹³C value (1.4‰) of POC was found in the Wujiang during summer, and was attributed to the enhanced soil erosion of the dry arable uplands close to the riverbanks of the main channel. Based on a conservative estimate, POC fluxes were 3.123 × 10¹⁰, 0.084 × 10¹⁰, and 0.372 × 10¹⁰ g a⁻¹ while export rates of POC were 466, 129, and 218 mg m⁻² a⁻¹ for the Wujiang, Wuyanghe, and Qingshuijiang, respectively. The POC export rate for the karstic Wujiang, with intensive land use, was 2–3 higher than that of the karstic Wuyanghe or of the non-karstic Qingshuijiang where soil erosion was minor. Such high values imply rapid degradation of related karstic ecosystems impacted by intensive land use activities, and pose a potential threat to the health of the Three Gorges Reservoir.     

Ordovician conodonts of the Tarim Region, Xinjiang, China: Occurrence and use as paleoenvironment indicators

A review of the distribution of different Ordovician conodont faunas in eight areas of the Tarim Region shows that these conodont faunas can be classified into the North China and South China types. The North China type is characterized by Aurilobodus leptosomatus, A. aurilobodus, A. simplex, Tangshanodus tanshanensis, Loxodus dissectus, Parasseratognathus paltodiformis, Microcoelodus symmetricus, Belodina compressa, B. confluens, Pseudobelodina dispansa, Yaoxianognathus yaoxianensis, and Taoqupognathus blandus. These were adapted to shallow, warm-water environments. The South China type is represented by the genera Amorphognathus, Baltoniodus, Cahabagnathus, Eoplacognathus, Lenodus, Microzarkodina, Oepikodus, Paroistodus, Paracordylodus, Periodon, Polonodus, and Pygodus, which were adapted to outer shelf, deeper, and colder water environments. Using the general pattern of conodont distribution, it is possible to interpret the various depositional environments and to reconstruct broad changes in palaeogeography of the Tarim Region during Ordovician time. In general, during Tremadocian to early Middle Ordovician time, most of the Tarim Region was a shallow semi-restricted platform that became deeper towards the north and east, with an open platform in Kalping and in the northern part of Taklimakan Desert. A slope and deep basin existed in the current Tianshan Mountains region. The Tarim sea was shallow during the Early Ordovician and became deeper during “Caradocian” (Sandbian and Early Katian) time, to become shallow again during “Ashgillian” (Late Katian) time, with the exception of part of central Taklimakan, which was a land area during “Caradocian” (Sandbian and Early Katian) time.     

Sequence development of Late Cenomanian–Turonian carbonate ramps, platforms and basins in Israel

The Cenomanian–Turonian carbonate-dominated lithofacies of Israel reflect a complex interplay between tectonics, sea-level change, and palaeoecology. Improved correlation based on revision of the bio- and chronostratigraphic framework has enabled the establishment of a sequence-stratigraphic model comprising five sequences delineated by four sequence boundaries, in the Late Cenomanian–Early Coniacian interval. The Late Cenomanian–Turonian succession begins with prograding, highstand, carbonate-platform deposits of the first sequence. Interruption of progradation and drowning of this platform took place within the Late Cenomanian guerangeri Zone (=the vibrayeanus Zone in Israel), resulting in a drowning unconformity which is regarded as a Type 3 sequence boundary (labelled CeUp). The drowning is attributed in part to extinctions in the rudist-dominated biofacies (e.g., Caprinidae), which led to reduced carbonate production and enhanced the impact of the sea-level rise. Similar drowning of Tethyan platforms around the C/T boundary has been linked to the establishment of coastal upwelling and consequent eutrophication. Outer ramp hemipelagic facies (Derorim and the Lower Ora formations) replaced the platform carbonates, thickening substantially southwards in the Eshet-Zenifim Basin of southern Israel. Along the ancient continental slope (Mediterranean coastal plain) evidence of this drowning is obscured by submarine erosion, while in central and northern Israel the drowned section is represented by condensation or a hiatus, reflecting an elevated, sediment-starved sea-floor. A carbonate platform dominated by rudistid shoals (‘Meleke’ Member; Shivta Formation) was re-established in the Judean hills and northern Negev during the middle part of the Turonian coloradoense Zone (local zone T4). Later, during kallesi Zone times (T7), the platform facies prograded southwards towards the Eshet-Zenifim intra-shelf basin. The drowning succession and overlying resurrected carbonate platform are topped in central and southern Israel by a pronounced Type 1 sequence boundary (Tu1) between the kallesi (T7) and ornatissimum (T8) zones (Middle Turonian). In central Israel and northern Negev the sequence boundary is overlain by lowstand deposits of the ‘Clastic Unit’ and by the transgressive and highstand inner to mid-ramp deposits of the Nezer and Upper Bina formations. In the southern Negev the sequence boundary is overlain by lowstand and transgressive systems tracts of mixed carbonates, siliciclastics, and localized evaporites (Upper Ora Formation), and then by mid to inner ramp carbonates of the Gerofit Formation. The latter represents a very high rate of accumulation, indicating rapid, continued subsidence balanced by platform growth. The Tu2 sequence boundary of the Late Turonian is expressed in the southern Negev by a shift from inner ramp carbonates of the Gerofit Formation to outer ramp chalky limestones of the Zihor Formation, indicating localized drowning. The succeeding Co1 sequence boundary again indicates localized drowning of the prograding highstand deposits of the Zihor Formation (‘Transition Zone’) overlain by Lower Coniacian transgressive deposits of the upper part of the Zihor Formation. All of these third-order sequences are expressed in southern Israel, where the rate of subsidence was in balance with sea-level fluctuations. In contrast, the Judean Hills and eastern Galilee areas have a more incomplete succession, characterized by hiatuses and condensation, because of reduced subsidence. More distal areas of continuous deep-water deposition in western Galilee and the coastal plain failed to record the Middle Turonian lowstand, while a longer term, second-order sequence spanning the entire Late Cenomanian–Early Coniacian interval, is present in the Carmel and Yirka Basin areas.     

Tephras in lacustrine sediments of the Sarliève marsh (French Massif Central): age and preservation

The Sarliève marsh sediments (Massif Central, France) contain two tephras. The first tephra [, ca. 12 000 BP], regionally well known, enables to date the beginning of lacustrine infill to the Lateglacial. The second tephra, the ‘tephra de Sarliève’, the emitting volcano of which is unknown, would be dated to around the Early Subboreal from pollen data. This occurrence, after the discovery of the ‘tephra de Beaunit’, emphasizes that volcanic eruption(s) occurred in the ‘Chaîne des Puys’ or in the volcanic Cézallier more than 1000 years after the last known eruption (Pavin) in the ‘Chaîne des Puys’ at around 6.6/6.7 ka (5800/5900 BP). In the Sarliève piles, these tephras, well preserved in thick and more silicated deposits of deltas, were not observed in carbonated basin sediments where they were altered. The abundance of authigenic zeolites formed during the Lateglacial in restricted depocentre lacustrine waters allows us to detect initial CF1 tephra occurrence. To cite this article: A. Fourmont et al., C. R. Geoscience 338 (2006).     

The use of assumed displacement fields in finite-element analysis to calculate the gravity effect of crustal deformation

An expression is derived which relates a displacement field u defined on a continuum to the change in gravity (Δg_D) brought about by deformation:

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where GG is the gravitational constant; ρ_R is the pre-deformation density function; V_R is the volume occupied by the continuum before deformation; T_D is a transformation which represents the one-to-one mapping of V_R onto the volume V_A occupied by the continuum after deformation: A₁ = R₁ + U₁(R₁, R₂, R₃)T_D: A₂ = R₂ + U₂ (R₁, R₂, R₃)A₃ = R₃ + U₃ ( R₁, R₂, R₃) where A₁, a₂, A₃, are the Cartesian coordinates of a point in V_A; R₁, R₂, R₃ are the Cartesian coordinates of a point in V_R; U₁, U₂, U₃, are the components of u; and α is the distance from the field point (x, y, z) to a general point in V_A or V_R. The derivation is based on the principle of conservation of mass as stated in continuum mechanics. The formulation of the finite-element procedure for problems in linear elasticity typically involves the selection of an assumed function for u within each element. Unknown constants which characterize the function are determined in terms of nodal displacements. The integral in the first equation above may therefore be evaluated for each element, and the results summed to obtain Δg_D. Convergence to the exact solution for Δg_D depends on the convergence of the finite-element solution for u. The procedure is demonstrated for axisymmetric, torsion-free deformation of a solid of revolution in which the elements are tori of triangular cross-section. These results may be useful in the analysis of gravity change associated with tectonic deformation of the earth's crust.     

A Late Hauterivian short-lived anoxic event in the Mediterranean Tethys: the ‘Faraoni Event’

A Late Hauterivian interval (127.5 Ma), called the ‘Faraoni Event’, which is characterised by the deposition of deep-marine black shales in the Mediterranean Tethys, is demonstrably of sufficient geological brevity to be qualified as an anoxic event. This event lies within the Pseudothurmannia catulloi ammonite subzone, coincides with the extinction of the calcareous nannofossil species Lithraphidites bollii, and records an increase in a globular planktonic foraminifer. High quantities of marine organic matter were preserved in pelagic successions from northern and central Italy, Switzerland, southeastern France, southern Spain and probably elsewhere in the Mediterranean Tethys and Atlantic Ocean. Carbon-isotope stratigraphy from Tethyan and Atlantic sections shows a minor positive excursion in the uppermost part of the Hauterivian and Lowermost Barremian, suggesting accelerated extraction of organic carbon from the ocean reservoir just after the ‘Faraoni Event’. The duration of this short event is less than 100 ka according to cyclostratigraphy and coincides with a third-order sea-level rise. It is likely that similar forcing mechanisms responsible for global OAEs operated during this short time interval. To cite this article: F. Baudin, C. R. Geoscience 337 (2005).     

Effets d'amplification du changement d'usage des terres sur le taux de CO2 atmosphériqueAmplification effect of changes in land use and concentration of atmospheric CO2

A model is presented here, which attempts to determine interactions between change in land use and concentration of atmospheric CO₂ over the 1700–2100 period. The main impact of the conversion of forests to agricultural areas is the increase of atmospheric CO₂ because of the losses of biomass and soil carbon in favour of the atmosphere. This raise will probably increase in the next years, correlated with the proportion of cultivated areas. We show here that this first-order effect is amplified by the correlative decrease of terrestrial sinks of CO₂; in fact, as forests are replaced by cultivated parcels, carbon residence time in biosphere decreases, as well as sequestration ability of these ecosystems. This amplification effect leads to an additional increase in atmospheric CO₂, which could reach 100 ppm in 2100. The uncertainties on the range of such an increase are important since they cumulate both uncertainties on the behaviour (sink or source) of terrestrial ecosystems in the future and inherent uncertainties of the modeling of carbon fluxes linked to changing land uses… Such an additional increase in CO₂ is partially limited by the ocean reservoir and by the existing CO₂ sinks in primary non-anthropologically disturbed ecosystems. The results imply that conservation of primary forests, for which primary productivity and carbon time of residence are high, is an efficient strategy for greenhouse-effect mitigation. To cite this article: V. Gitz, P. Ciais, C. R. Geoscience 335 (2003).     

Reversed magnetozone in the late Pleistocene sediments from the Pacific coast of Odaka, northeast Japan

Paleomagnetic measurements have been carried out on 103 specimens taken at about 15 cm intervals in a sea cliff exposing the marine terrace formation. Secondary components were removed by partial demagnetization in a peak field of 200 Oe. Two short reversed magnetozones are recognized. Geological and biostratigraphical evidence indicates that they are equivalent to the Blake event, which was first reported by Smith and Foster (1969) (Science 163, 565–567) from the North Atlantic deep-sea cores. The present result suggests a split nature for the Blake Event.     

Electronic absorption spectroscopy of natural (Fe2+, Fe3+)-bearing spinels of spinel s.s.-hercynite and gahnite-hercynite solid solutions at different temperatures and high-pressures

Natural Fe²⁺, Fe³⁺-bearing spinel solid solutions from the spinel s.s.-hercynite and gahnite-hercynite series were analyzed and studied by electronic absorption spectroscopy in the spectral range 30000–3500 cm^–1 in the temperature and pressure ranges 77 T_K 600 and 10^–4 P_GPa 11.0. Two crystals were light-violet in color (type I) and six green or bluish-green (type II). The spectra of both types of spinels are dominated by an UV-absorption edge near 28000 to 24000 cm^–1, depending on the iron contents, and a very intense band system in the NIR centered around 5000 cm^–1, which is caused by spin-allowed dd-transition of tetrahedral Fe²⁺, derived from ⁵ E⁵ T₂. The strong band is in all spinels studied, split into four sub-bands, which can only be observed in very thin platelets. Between the UV-edge and the high-energy wing of the NIR-band there occur a number of very weak bands in type I spinels while the green type II spinels show some of these with significantly enhanced intensity. The intensity of the very weak bands is nearly independent from temperature. Such bands are attributed to spin-forbidden electronic transitions of ^IVFe²⁺. Temperature and pressure dependence of the intensity enhanced bands of spinels type II indicate that they are caused by ^IVFe²⁺ and ^VIFe³⁺. They are attributed to spin-forbidden transitions ⁶A_1g⁴A_1g, ⁴E_g, ⁴T_2g and ⁴T_1g of ^VIFe³⁺, the two latter being strongly intensified by exchange-coupling interaction with adjacent ^IVFe²⁺. The pressure dependence of ^IVFe²⁺ dd-band system in the NIR caused by spin-allowed ⁵ E⁵ T₂ transition noticeably differs from that of octahedral Fe²⁺, an effect which is attributed to a dynamic Jahn-Teller effect of ^IVFe²⁺ in the spinel structure.