Fossil cyclic calcrete in the Kuwait Group clastic deposits (Mio-Pleistocene) of Kuwait,Arabian Gulf

An investigation of the upper Kuwait Group clastic sequence (Mio-Pleistocene) exposed along the Jal Az-Zor escarpment in north Kuwait revealed several horizons of fossil calcrete. Field occurrences and textural characteristics of the studied sequence indicated that the fossil calcrete was hosted in cyclic fluviatile muddy sandstones and developed through diagenesis during inter-fluvial periods. Depositional and diagenetic features of the calcretized fluviatile sandstone units suggested that each cycle started with the deposition of a fluviatile muddy host sandstone during a humid period. This was followed by a period of semi-aridity during which calcrete profiles developed. The upper part of the calcrete profiles was weathered and terra rosa type soil was formed during wet seasons. This was succeeded by a severe arid climate and the deposition of desert aeolian sand sheets. Fossil nodular calcrete was only developed within the fluviatile muddy sandstones. The calcretized sandstones were lithified in two stages of diagenesis-an early stage that was responsible for the authigenesis of microcrystalline calcite and the development of calcrete nodules, and a later stage during which macrocrystalline calcite cement was precipitated as an intergranular cement displacing and replacing the clay matrix of the host sediments and filling fractures and cavities in the calcrete nodules. The findings and conclusions of the present study will help in understanding the lithostratigraphic setting of the Kuwait Group clastic sequence in the northern Arabian Gulf region.

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Zusammenfassung Eine Untersuchung der klastischen Sequenz der oberen Kuwait-Gruppe, die entlang der Jal Az-Zor Zone in Nordkuwait aufgeschlossen ist, ergab mehrere Horizonte fossilen Kalksinters. Geländebeobachtungen und texturelle Charakteristik der Sequenz deuten an, daß der fossile Kalksinter in Zyklen eines feinkörnigen fluviatilen Sandsteines eingebettet ist und diagenetisch während interfluviatilen Stadien gebildet wurde. Merkmale der Ablagerungsverhältnisse und der Giagenese des verkalkten fluviatilen Sandsteines sprechen dafür, daß jeder Zyklus mit der Sedimentation des Sandsteines unter humiden Klimabedingungen begann. Auf dieses Stadium folgte eine Phase semiariden Klimas, während dessen sich die Kalksinterprofile entwickelten. Der obere Teil der Kalksinterabschnitte verwitterte in Regenzeiten, dabei bildeten sich »terra rosa«-Böden. Während des folgenden rauhen ariden Klimas wurden wüstenähnliche äclische Sande sedimentiert. Den fossilen knotigen Kalksinter findet man nur innerhalb des fluviatilen Sandsteines. Die Lithifizierung der Sandsteine erfolgte in zwei diagenetischen Phasen: In der frühen Phase wurde auhigener, mikrokristalliner Calcit und die Kalksinterknoten gebildet. Während der späteren Diagenesephase fiel makrokristalliner Calcit als intergranularer Zement aus, der die tonige Ausgangsmatrix substituierte und Klüfte sowie Hohlräume innerhalb der Kalksinterknoten ausfüllte. Beobachtungen und Interpretationen dieser Studie werden das Verständnis um den lithostratigraphischen Zusammenhang der klastischen Sequenz der Kuwait-Gruppe in der Region des nördlichen Arabischen Golfes erleichtern.

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Résumé La série élastique du groupe supérieur du Koweit (MioPleistocène), exposée le long de l'escarpement de Jal Az-Zor (nord du Koweit) montre plusieurs horizons de calcrètes fossiles. Les relations de terrain et les caractères structuraux de cette série montrent que ces calcrètes se sont formées dans des sables argileux fluviatiles cycliques, par un processus de diagenèse intervenu au cours de périodes interfluviales. Les caractères sédimentologiques et diagénétiques de ces roches suggèrent que chaque cycle a débuté par le dépôt, en période humide, des sables argileux fluviatiles et s'est poursuivi en période de semi-aridité par le développement des calcrètes. La partie supérieure des calcrètes a subi une altération atmosphérique avec formation d'un sol de type »terra rossa« au cours des saisons humides. Le cycle se termine par l'installation d'un climat strictement aride, avec dépôt de sables éoliens désertiques. Les calcrètes, nodulaires, se sont formées uniquement dans les sables argileux fluviatiles. Leur lapidification s'est opérée en deux stades: un premier stade responsable de l'apparition de calcite authigène microcristalline et du développement de nodules carbonates; un second stade marqué par la précipitation d'un ciment intergranulaire de calcite macrocristalline qui s'est substitué à la matrice argileuse du sédiment primaire et a rempli les fissures et cavités des nodules. Les résultats de cette étude permettent de mieux comprendre l'édification lithostratigraphique de la série clastique du Groupe du Koweit dans la région septentrionale du Golfe Arabique.

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Generalized geophysical model and dynamic properties of the continental crust

Detailed seismic investigations of the continental crust have produced evidence of definite regularities in the general layering of the consolidated crust despite its high degree of inhomogeneity. Three main layers may be resolved in the inner part of a continent: an upper layer with velocities of 5.8–6.4 km/s and a velocity gradient about 0.04–0.05 s⁻¹, an intermediate layer with velocities of 6.2–6.6 km/s and velocity gradient about zero, and a lower layer with velocities of 6.8–7.2 km/s and a high-velocity gradient of 0.05–0.1 s⁻¹. The intermediate layer is characteristically different not only because of its low average velocity gradient, but also because of its more pronounced horizontal layering, inversion zones, and its higher “transparency” and V_p/V_s ratio. The gravity and magnetic data have shown that basement inhomogeneities disappear at the top of the intermediate layer. Also there are few earthquakes in this layer. These pecularities may be interpreted as the result of partial melting (weakening) of rocks and their possible horizontal mobility inside this layer.Thus, dynamic models of tectonic processes must take into consideration the possible existence of a weak zone in the crust.     

First finds of Late Tithonian and middle-late Albian radiolarian assemblages in volcanogenic-siliceous rocks of the Amur River right lower reaches and their tectonic significance

The lithological-stratigraphic study of volcanogenic-siliceous rocks developed on the left side of the Machtovaya River, a right tributary of the Amur River, yielded the first radiolarian assemblages of the late Late Tithonian, the late Late Tithonian-early Valanginian, and the middle-late Albian age. It is established that the stratigraphic succession of volcanogenic-siliceous rocks in this area is composed of upper Tithonian-Valanginian dark red to red-brown cherts with basalts in the lower part of the section and Albian dark gray clayey cherts, olive-gray siliceous-tuffaceous argillites, and tufaceous siltstones in its upper part. The replacement of cherts by their clayey varieties likely occurred in the Aptian. The composition, structure, and age of these strata and the rocks constituting the Kiselevka-Manoma accretionary complex are different, which indicates their different tectonic origin.     

The possible influences of the increasing anthropogenic emissions in India on tropospheric ozone and OH

A 3-D chemical transport model (OSLO CTM2) is used to investigate the influences of the increasing anthropogenic emission in India. The model is capable of reproducing the observational results of the INDOEX experiment and the measurements in summer over India well. The model results show that when NOx and CO emissions in India are doubled, ozone concentration increases, and global average OH decreases a little. Under the effects of the Indian summer monsoon, NOx and CO in India are efficiently transported into the middle and upper troposphere by the upward current and the convective activities so that the NOx, CO, and ozone in the middle and upper troposphere significantly increase with the increasing NOx and CO emissions. These increases extensively influence a part of Asia, Africa, and Europe, and persist from June to September.     

Morphological peculiarities of Calanus finmarchicus and Calanus glacialis in the areas of the co-existence of their populations

Morphological studies of the females of Calanus finmarchicus, C. glacialis, and C. hyperboreus were performed for specimens sampled in different areas of the Greenland, Barents, Kara, and Laptev seas. Intraspecific variability was found for the ratio of the specimens characterized by different types of setae patterns on the endopodites of C. glacialis and C. finmarchicus. The variability of this parameter did not relate to the environmental peculiarities of the sampling sites and did not depend on the temperature regime. We assume that such differences may be the result of the hybridization of C. glacialis and C. finmarchicus due to the similarity of their reproduction systems and the overlapping of the body size ranges.     

Mineral magnetic signatures in a long core from Lake Qarun, Middle Egypt

The analysis and interpretation of changes in mineral magnetic signatures from a long (ca. 8.2 m) sedimentary sequence recovered from Lake Qarun, Middle Egypt in 2003 spanning a timescale of approximately the last 2,000 years is reported. A suite of mass specific susceptibility and magnetic remanence measurements were made at irregular intervals downcore on 39 samples. These samples were selected on the basis of trends and abrupt changes in whole-core magnetic susceptibility measured using a Bartington^® MS2E sensor and were analysed for low and high temperature loss on ignition and their particle size distribution. Trends in all mineral magnetic concentration parameters are remarkably similar and were initially used to divide the core into three magnetically distinct zones. The upper and lower sections of the core (0–119 cm and 445–822 cm depth) are characterised by low values for all magnetic concentration parameters. Between 153 and 380 cm depth, concentration parameters are considerably higher, although somewhat variable. The S ratio and percentage loss of remanence after 24 h (IRM_loss) follow a different trend and are inversely related to each other. A low S ratio (<0.7) is associated with a loss of remanence of >4%. On the basis of these parameters, the core can be divided into four zones, and differences in magnetic mineralogy between these four zones were confirmed by measurement of IRM acquisition curves. The major difference between concentration parameters and ratios or percentage loss of IRM lies in the identification of an additional zone below 619 cm depth where the S ratio is high and IRM_loss is low. There is little evidence to suggest that the magnetic signatures are controlled by particle size or by trends in organic matter and/or carbonate content. The signatures appear to be predominantly detrital and show little evidence of post-depositional alteration through dissolution or authigenic addition of bacterial magnetite or greigite. Analysis of Saharan dust deposition rates in Northern Egypt suggests that atmospheric fallout is likely to make only a very minor contribution (<1%) to sedimentation rates in Lake Qarun. The downcore trends therefore appear to reflect major changes in fluvial sediment sources over the ca. 2,000 year time period spanned by this ～8 m core. Preliminary mineral magnetic characterisations of potential local sources suggest that these cannot account for the range of signatures recorded in the Qarun sediments and it is hypothesised that these sediments are derived from Nile river floods.     

Structure-specific selection of earthquake ground motions for the reliable design and assessment of structures

A decision support process is presented to accommodate selecting and scaling of earthquake motions as required for the time domain analysis of structures. Code-compatible suites of seismic motions are provided being, at the same time, prequalified through a multi-criterion approach to induce response parameters with reduced variability. The latter is imperative to increase the reliability of the average response values, normally required for the code-prescribed design verification of structures. Structural attributes like the dynamic characteristics as well as criteria related to variability of seismic motions and their compliance with a target spectrum are quantified through a newly introduced index, δ _sv–sc , which aims to prioritize motions suites for response history analysis. To demonstrate the applicability of the procedure presented, the structural model of a multi-story building was subjected to numerous suites of motions that were highly ranked according to both the proposed approach (δ _sv–sc ) and the conventional one (δ _conv ), that is commonly used for earthquake records selection and scaling. The findings from numerous linear response history analyses reveal the superiority of the proposed multi-criterion approach, as it extensively reduces the intra-suite structural response variability and consequently, increases the reliability of the design values. The relation between the target reliability in assessing structural response and the size of the suite of motions selected was also investigated, further demonstrating the efficiency of the proposed selection procedure to achieve higher response reliability levels with smaller samples of ground motion.     

Long-term variability of UV radiation in the spectral range of 300–380 nm in Moscow

The seasonal and interannual variability of global ultraviolet (UV) radiation in the spectral range of 300-380 nm (0380) in Moscow in 1968-2014 is analyzed. The effect of cloudiness on the magnitude of 0380 is assessed. The smallest (-22...-26%) losses due to cloudiness are registered in May-August, and the highest ones (to -45%) are observed in October-November. According to the UV radiation reconstruction model and measurement data, the long-term deviations of 0380 from the average (for 1968-1997) due to clouds can reach + (11-12)%. The statistically significant positive linear trend in total annual 0380 is revealed from the data of both the reconstruction model and observations (about 1.5% per decade for 1968-2014 and 3% per decade for 1979-2014).     

Cooling rates of seven hexahedrites

Cooling rates for seven hexahedrites, (Uwet, Coahuila, Walker County, Lombard, Quillagua, Hex River Mountains and Tocopilla) have been determined using a ternary diffusion controlled phase growth analysis developed by the authors. The model is applied to the exsolution and growth of plate phosphides in the kamacite phase of hexahedrites during cooling of the meteorite in its parent body. The effects of cooling rate, bulk composition, nucleation temperature and diffusion field length are considered. A unique cooling rate was determined by comparing the Ni content and width of several phosphides in a given hexahedrite to computer-generated curves of Ni content vs phosphide width. Six hexahedrites have cooling rates of approximately 2°C/10⁶yr. One hexahedrite, Coahuila, has a somewhat higher cooling rate of 10°C/10⁶ yr. These cooling rates fall within the range calculated by an independent method for octahedrites. The cooling rate analysis indicates that the hexahedrites, except for one possible exception, were formed in or close to the core of a parent body ~ 150 km in radius.