http://www.sciencedirect.com/science/article/pii/S167498711100079X

Lower Paleozoic rocks exposed in various regions of Egypt (south central Sinai, north Eastern Desert and southwest Western Desert), in addition to occurring in the subsurface such as north Western Desert and the Gulf of Suez. The Lower Paleozoic rocks in Egypt include surface and subsurface rock units of formational status. The surface rock units are the Taba, Araba and Naqus formations. The subsurface rock units include the Shifa, Kohla and Basur formations. The Infracambrian Taba Formation has been discovered recently in the outcrops of the south eastern Sinai in the Taba-Ras El-Naqab area. It is missing and/or not recognized in the subsurface. The Taba Formation consists mainly of reddish brown, unfossiliferous gravelly fine-to medium-grained sandstones cemented by kaolinite and have subordinate beds of paleosols. The Cambrian Araba Formation and its subsurface equivalent (the Shifa Formation) are essentially composed of reddish brown, fine-grained laminated sandstone and siltstone with abundant Skolithos and Cruziana sp. In contrast, the Ordovician-Silurian Naqus Formation and its subsurface equivalents (Kohla Formation and Basur Formation) are mainly composed of white, unfossiliferous, cross-bedded, medium- to coarse-grained sandstones with haphazardly distributed pebbles and cobbles. Sedimentological analysis indicates that the Araba Formation and its equivalents were deposited in a marginal-marine environment, whereas the Naqus Formation and its equivalents were laid down in a fluvio-glacial environment. Integrated stratigraphic and sedimentological studies of the Lower Paleozoic rocks permit reconstruction of the paleogeography of Egypt at that time. Egypt has been largely controlled since the Cambrian by the pre-existing structural framework of the pre-Phanerozoic basement rocks inherited from the Late Proterozoic Pan-African event. Additionally, sedimentation processes were controlled during Cambro-Ordovician times by tectonic movements, whereas glacio-eustatic control predominated during the Late Ordovician-Silurian Period. These studies suggest that most areas of Egypt were exposed lands with episodically transgression by epicontinental seas related to the paleo-Tethys. These lands formed a part of a stable subsiding shelf at the northern Gondwana margin.     

Authigenic carbonate precipitates from the NE Black Sea: a mineralogical,geochemical, and lipid biomarker study

Carbonate precipitates recovered from 2,000 m water depth at the Dolgovskoy Mound (Shatsky Ridge, north eastern Black Sea) were studied using mineralogical, geochemical and lipid biomarker analyses. The carbonates differ in shape from simple pavements to cavernous structures with thick microbial mats attached to their lower side and within cavities. Low δ¹³C values measured on carbonates (−41 to −32‰ V-PDB) and extracted lipid biomarkers indicate that anaerobic oxidation of methane (AOM) played a crucial role in precipitating these carbonates. The internal structure of the carbonates is dominated by finely laminated coccolith ooze and homogeneous clay layers, both cemented by micritic high-magnesium calcite (HMC), and pure, botryoidal, yellowish low-magnesium calcite (LMC) grown in direct contact to microbial mats. δ¹⁸O measurements suggest that the authigenic HMC precipitated in equilibrium with the Black Sea bottom water while the yellowish LMC rims have been growing in slightly ¹⁸O-depleted interstitial water. Although precipitated under significantly different environmental conditions, especially with respect to methane availability, all analysed carbonate samples show lipid patterns that are typical for ANME-1 dominated AOM consortia, in the case of the HMC samples with significant contributions of allochthonous components of marine and terrestrial origin, reflecting the hemipelagic nature of the primary sediment.     

Sr,Nd,Pb Isotope Geochemistry and Magma Evolution of the Potassic Volcanic Rocks,Wudalianchi,Northeast China

Wudalianchi volcanic rocks are the most typical Cenozoic potassic volcanic rocks in easten China.Compositional comparisons between whole rocks and glasses of various occurrences indicate that the magma tends to become rich in silica and alkalis as a result of crystal differentiation in the course of evolu-tion.They are unique in isotopic composition with more radiogenic Sr but less radiogenic Pb.^87Sr/^86Sr is higher and ^143Nd/^144Nd is lower than the undifferentiated global values.In comparison to continental pot-ash volcanic rocks,Pb isotopes are apparently lower.These various threads of evidence indicate that the rocks were derived from a primary enriched mantle which had not been subjected to reworking and shows no sign of incorporation of crustal material.The correlation between Pb and Sr suggests the regional heterogeneity in the upper mantle in terms of chemical composition.     

Factors controlling the development of prism faces in granite zircons: a microprobe study

Based on microprobe work, we present arguments that the size relations of the two common prisms {100} and {110} of accessory granite zircons are strongly influenced by chemical factors. Magmatic growth zoning patterns, which we have studied by means of backscattered electron imaging in special zircon sections orientated perpendicular to the c-axis, do not support previous models which assumed temperature or the degree of ZrSiO₄ supersaturation to be the primary prism-form-directing factors. The element U, which usually occupies the Zr-sites of granite zircoms to some degree, is strongly suspected of producing an (adsorptive) growth-blocking effect for {110}-type faces thus creating crystals with {110}-dominated prism morphology. A second independent mechanism that is likely to form zircons with large {110} prisms is the common substitution Zr⁴⁺+Si⁴⁺ versus Y(REE) and P contents (relative to Zr) are, according to our model, predestinated to produce zircons with large {100} prisms and vice versa.Dedicated to Prof. Günther Frasl on the occasion of his seventieth birthday     

Graphite in Kupferschiefer (Poland) and its genetic meaning

Graphite forms crystals up to 0.08 mm in size in carbonates or argillaceous carbonates directly under- and overlying black shale. Increased contents of Si, Al, Ca, and K in graphite are related to intercalations of graphite-montmorillonite and less to intercalations of graphite-illite. Quartz and gibbsite are also detected. The formation of graphite was probably a two-stage process:

1. Catalytic oxidation of organic matter. As a result of oxidation original organic matter has been enriched as aromatic hydrocarbons (benzene ring compounds) being most resistant to oxidation.
2. Ordering of conjugated benzene rings on the 001 montmorillonite plane as a matrix. As a result, the c₀ of dry montmorillonite increased to 1.678±0.020 or 2.450±0.050 nm. Primary layers of graphite became themselves matrices for the next layers of conjugated rings producing microscopically visible graphite.

To a less extent the process of dehydrogenesis and conjugation of aromatic rings took place in a reaction with Al, Si, and OH of phyllosilicates producing Al(OH)₃ (gibbsite), former H₄SiO₄ (now quartz), and H₂O.     

STRESS-METAMORPHISM AND ISOTOPIC AGE OF SHEAR ZONE GRANITOID TECTONITES OF IRTYSH SHEAR ZONE (ALTAI REGION)

The Irtysh shear zone (ISZ) of Altai region is the lineament structure of the collision-suture type, where granites of Kalba complex and granodiorites of Zmeinogorsk complex are exposed to regional gneiss-formation and stress-metamorphic alterations. This study is based on detailed structural observations at special grounds using optical and electron microscopy, and on the behavior analysis of isotopic systems from altered granitoids.Within the ISZ area we have established the continuous rows of granitoid stress-metamorphism from initial recrystallization of protolite, its cataclasis and mechanical flaring up to complete recrystallization with alteration of mineral composition and formation of the streaky complexes of granite tectonites of blastomylonite and blastocataclasite types. The directed alteration of rocks has several impulse and is expressed by a change in morphology of mineral grains and their relations, magnification of deformation component in the rock structure, and formation of new mineral phases on the basis of initial ones without surface fluidization. At transformation of isotopic systems from granitoid, their feldspars,biotite and hornblende, we can observe “rejuvenation“ of the rock substrate from 270- 290 Ma for Kalba granitoids to 220-235 Ma for their tectonites, and for Rudny Altai granodiorites, their ages changes from 285-317 Ma to 232-257 Ma for their tectonites.     

Pressure covariability over the Atlantic,Europe and N. Africa. application: Centers of action for temperature,winter precipitation and summer winds in Athens,Greece

Summary This paper deals with the surface pressure covariability over the Altantic/European sector of the Northern Hemisphere, using monthly grid point data for the 100 year period 1890–1989. Factor analysis is applied to 90 grid point time series for January, February, July, and August. The initial 90 pressure variables can be reduced to 7–8 factors in winter and 10 in summer. A winter teleconnection was identified, known as the seesaw phenomenon, between the Icelandic low and the Azores subtropical anticyclone. In order to define the centers of action for temperature, winter precipitation and summer northerly wind frequency (etesian days) in Athens and in the Aegean sea, the variability of the factor scores and of these weather elements is compared. It is shown that the center of action for temperature in Athens is found to be in north and northwest Europe (centered over southern Scandinavia). For winter precipitation, the center of action is located in the west and southwest Mediterranean and northwest Africa. Finally, for the etesian winds frequency variability, this center of action is found over the northern Adriatic and northern former Yugoslavia, while there is no evidence of influence by the southwest Asia thermal low.With 12 Figures     

Vertical circulation in the tropical atmosphere during extreme El Niño-Southern Oscillation events

Scenarios for the development of large-scale vertical circulation anomalies during warm and cold phases of El Niño-Southern Oscillation are generalized based on the NCEP/NCAR reanalysis data for 1958-1998. Composite models of the cells of vertical circulation in the monsoon and trade-wind regions of the tropical Pacific are obtained for the first time for El Niño and La Niña separately. An unprecedented shift of the ascending branch of the zonal Walker circulation from the “maritime continent” of Indonesia to the east, to the central and eastern Pacific, was observed during the warm phase over the tropical Pacific; this shift was accompanied by an abrupt increase in the tropical cyclogenesis activity in the southern Pacific zone of convergence. On the contrary, during the cold phase, the ascending motions in the region of the summer Australian monsoon are subject to abrupt intensification. The reconstruction of the vertical meridional circulation during the warm phase manifested itself in the almost complete disappearance of the Hadley classic circulation over the central Pacific, characteristic of the trade-wind intertropical convergence zone (ITCZ), and in its replacement by the latitudinal monsoon circulation typical of the ITCZ over the Indian Ocean. During a cold phase, the Hadley circulation is both restored and intensified.