Photometric study of distant open clusters in the second quadrant: NGC 7245, King 9, King 13 and IC 166

We present a UBV CCD photometric study of four open clusters, NGC 7245, King 9, IC 166 and King 13, located between   l = 90°  and 135°. All are embedded in a rich Galactic field. NGC 7245 and King 9 are close together in the sky and have similar reddenings. The distances and ages are: NGC 7245, 3.8 ± 0.35 kpc and 400 Myr; King 9 (the most distant cluster in this quadrant), 7.9 ± 1.1 kpc and 3.0 Gyr. King 13 is 3.1 ± 0.3 kpc distant and 300 Myr old. King 9 and IC 166 (4.8 ± 0.5 kpc distant and 1 Gyr old) may be metal-poor clusters  ( Z = 0.008)  , as estimated from isochrone fitting. The average value of the distance of young clusters from the Galactic plane in the above longitude range and beyond 2 kpc (−47 ± 16 pc, for 64 clusters) indicates that the young disc bends towards the southern latitudes.     

1896–2006 Sahelian annual rainfall variability and runoff increase of Sahelian Rivers

Updated rainfall data to 2006 confirm that the Sahelian rainfall has increased since the end of the 1990s, but the annual average rainfall is still as low as during the drought of the 1970s. The decrease of rainfall is higher in the Northwest and lower in the Southeast Sahel. The increase of temperature over West Africa during the end of the 20th century induced an increase of Potential Evaporation, which might reduce the runoff. However, the joint effect of climate change and of human activities on land cover over more than three decades is responsible for an increase of the runoff coefficients of the West African Sahelian Rivers since the 1970s, despite the rainfall shortage during the same period, as revealed by the analysis of runoff from Mauritania, Burkina-Faso and Niger. The runoff coefficients have increased in regions with less than 750 mm of annual rainfall, under Sahelian and subdesertic climates, leading to increased flood peaks, occurring earlier in the season. Even if it is difficult to separate which part of this runoff coefficient increase is due to climate change alone or to human impact on land cover, the highest values are observed in the most inhabited areas, where land cover is dominated by cultivated areas. This climatic/human impact on land cover is so huge that it has changed since decades the hydrological regimes of the Sahelian Rivers, from the small watershed to the largest one, such as the Niger River at Niamey.     

Preconcentration/Separation of Gold and Palladium by a Microcolumn Packed with Azadirachta Indica Leaf Powder and Their Determination in Geological Samples by ICP‐OES

A new method using a microcolumn (20 mm length × 2.0 mm i.d.) packed with Azadirachta Indica leaf powder (Neem leaf) as an adsorbent for the preconcentration/separation of Au and Pd prior to their determination by ICP‐OES in geological samples is presented. Various factors affecting the separation and preconcentration of the target analytes such as pH, sample flow rate and volume, eluent concentration and volume and interfering ions were studied and the optimal experimental conditions were established. The adsorption capacity of Azadirachta Indica leaf for Au and Pd was found to be 39.2 and 9.8 mg g⁻¹, respectively. The detection limits (3s) of this method for Au and Pd with an enrichment factor of 50 were 47 ng l⁻¹ and 59 ng l⁻¹ and the relative standard deviations were 4.8% and 5.7% (n = 7, adsorption capacity C = 5 ng ml⁻¹), respectively. In order to validate the proposed method, the certified reference material, GBW07293, was analysed, and a good agreement was obtained between the certified and determined values.     

Sedimentary architecture of an ancient linear megadune (Barremian,Neuquén Basin): Insights into the long‐term development and evolution of aeolian linear bedforms

Linear aeolian bedforms are the most abundant bedform type in Earth's dune fields, and are very common in the Solar System. Despite their abundance, the long‐term development of these bedforms and its impact upon the resulting sedimentary architecture in the geological record is still poorly understood. The aim of this paper is to study the exposed record of an ancient linear megadune in order to discuss its development and the factors that impact the sedimentary architecture of aeolian linear bedforms. The outcrops of the ancient Troncoso Sand Sea (Barremian, Neuquén Basin, Argentina) provide a unique opportunity to study a preserved megadune record with an external body geometry that confirms its linear morphology. Architectural analysis reveals significant differences in cross‐stratified set bodies and bounding surfaces’ features and allows for the identification of three architectural complexes within the bedform's record. Analysis of deterministic models, sedimentary body relative chronology and distribution suggest that these architectural complexes result from distinctive phases in bedform development. It also clearly shows that construction of the megadune was achieved by expansion from a core, and that its development was characterized by sustained growth and strong longitudinal dynamics, without net accumulation. This study indicates how sustained bedform growth, rather than accretion, can be a critical factor conditioning linear bedform architecture towards a more ‘classic’ (bimodal bounding surface and cross‐bedding dip directions) concentric sedimentary architecture style. Furthermore, this research reveals how this style of architecture could only be relatively common in the geological record when related to bedform topography preservation.     

基于多源数据的安徽庐枞盆地三维地质建模

基于安徽庐枞地区深部地质调查成果,探索了多源数据联合建模方法。以区域地质和成矿规律研究成果为基础,以深部探测最新认识为主线,综合地质、钻探、物探、遥感等多专业数据,联合构建庐枞盆地2 km以浅三维地质结构模型,实现了盆地结构、基底隆起、岩浆岩分布等三维地质结构的“透明化”表达。此外,构建了区内多个典型矿床模型,并对区域地质模型与典型矿床模型进行耦合验证,为庐枞地区三维成矿预测提供依据。     

鄂尔多斯盆地靖边油田东坑大阳湾区延9油藏主控因素分析

延9油层是靖边油田东坑大阳湾地区的主力产层.将沉积体系、低幅构造、古地貌等作为一个有机的整体,对靖边油田东坑大阳湾地区的油藏控制因素进行重点分析.结果表明,古地貌控制着东坑大阳湾地区延9沉积相的展布及低幅构造的形成,并通过与低幅构造、沉积砂体的良好配置,控制着油藏的分布.     

Landscape evolution and origin of Lake Fúquene (Colombia): Tectonics, erosion and sedimentation processes during the Pleistocene

The Basin of Ubaté–Chichinquirá (5°28′N, 73°45′ W, c. 2580 m altitude) includes the Fúquene Valley and is located in the central part of the Eastern Cordillera of Colombia. Rocks and sediments were folded and faulted during the Miocene, uplifted during the (late) Pliocene, and affected by glaciers during the Pleistocene. Successive glacial and interglacial periods left significant marks in the landscape which were used to reconstruct six stages in the development of the landscape along a relative chronology. During early Pleistocene episode 1 glaciers formed U-shape valleys. Evidence of the impact of ice sheets has been found as far downslope as ca. 2900 m elevation. During episode 2 moraines developed which were cut by the present San José River. During episode 3 abundant sediment was produced by glacial erosion. It accentuated the sculpturing of hard rock and deepening of the drainage basin. The ancestral Ubaté–Suarez River constituted a dynamic erosive system that gave rise to deep V-shaped valleys and progressively formed a set of intricate valleys with a high sediment production. Finally, intense glacial and fluvio-glacial erosion led to a geomorphological system with high energy levels and intensive sediment transport leading to wide valleys. During episode 4 the Ubaté–Suarez River eroded and deepened its valley until it captured the old El Hato–San José Valley. It caused intense erosion of the moraine and the fluvio-glacial gravels. Deep V-shaped valleys stabilized in the high areas of the main drainage system and these valleys form the present-day fluvial sub-basins. During episode 5 the deep valley in the northern part of the Basin of Ubaté–Chichinquirá developed. During middle Pleistocene episode 6 colluvial sediments formed the Saboya dam and a lake was formed in the river valley of which the present Lake Fúquene is only a small remnant. Lithological changes indicate fluctuating water levels and Lake Fúquene must have expanded periodically up to an area 5 to 10 times the present-day surface.     

Turbulent dynamo near tachocline and reconstruction of azimuthal magnetic field in the solar convection zone

In order to extend the abilities of the αΩ dynamo model to explain the observed regularities and anomalies of the solar magnetic activity, the negative buoyancy phenomenon and the magnetic quenching of the α effect were included in the model, as well as newest helioseismically determined inner rotation of the Sun were used. Magnetic buoyancy constrains the magnitude of toroidal field produced by the Ω effect near the bottom of the solar convection zone (SCZ). Therefore, we examined two “antibuoyancy” effects: i) macroscopic turbulent diamagnetism and ii) magnetic advection caused by vertical inhomogeneity of fluid density in the SCZ, which we call the ∇ρ effect. The Sun's rotation substantially modifies the ∇ρ effect. The reconstruction of the toroidal field was examined assuming the balance between mean‐field magnetic buoyancy, turbulent diamagnetism and the rotationally modified ∇ρ effect. It is shown that at high latitudes antibuoyancy effects block the magnetic fields in the deep layers of the SCZ, and so the most likely these deep‐rooted fields could not become apparent at the surface as sunspots. In the near‐equatorial region, however, the upward ∇ρ effect can facilitate magnetic fields of about 3000 – 4000 G to emerge through the surface at the sunspot belt. Allowance for the radial inhomogeneity of turbulent velocity in derivations of the helicity parameter resulted in a change of sign of the α effect from positive to negative in the northern hemisphere near the bottom of the SCZ. The change of sign is very important for direction of the Parker's dynamo‐waves propagation and for parity of excited magnetic fields. The period of the dynamo‐wave calculated with allowance for the magnetic quenching is about seven years, that agrees by order of magnitude with the observed mean duration of the sunspot cycles. Using the modern helioseismology data to define dynamo‐parameters, we conclude that north‐south asymmetry should exist in the meridional field. At low latitudes in deep layers of the SCZ, the αΩ dynamo excites most efficiency the dipolar mode of the meridional field. Meanwhile, in high‐latitude regions a quadrupolar mode dominates in the meridional field. The obtained configuration of the net meridional field is likely to explain the magnetic anomaly of polar fields (the apparent magnetic “monopole”) observed near the maxima of solar cycles. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

全反射SH地震波的Goos-Hänchen效应动校正时差

利用SH地震波（偏振化方向垂直入射面的横波）在地层界面反射系数的附加相角导出了SH波Goos-Hänchen效应所引起的横向偏移和横向偏移渡越时间,给出了Goos-Hänchen效应正常时差公式,讨论了Goos-Hänchen效应对反射SH波正常时差的影响,绘出了横向偏移、横向偏移渡越时间、Goos-Hänchen效应正常时差及Goos-Hänchen效应正常时差校正量曲线.数值算例表明：对掠入射波或入射角在临界角附近的入射波,SH反射波的横向偏移、横向偏移渡越时间非常大,Goos-Hänchen效应对正常时差会产生较大的测量误差,在其他角度的入射波,横向偏移（横向偏移渡越时间）与波长（周期）为同一个数量级.横向偏移效应对SH反射波的传播走时影响是不可忽略的,因此在实际的地震资料处理中应进行横向偏移效应误差校正.     

The Carlés copper–gold–molybdenum skarn (Asturias, Spain): geometry, mineral associations and metasomatic evolution

This paper presents the petrographical, mineralogical and geochemical characteristics of the Carlés Cu–Mo–Au ore deposit, located in the Rio Narcea Gold Belt (Cantabrian zone of the Iberian Massif). It is related to a small postkinematic calc-alkaline monzogranite, which intrudes as a cedar-tree laccolith into the upper siliciclastic Furada Formation (late Silurian age) and the Nieva carbonates (early Devonian age). The Carlés deposit consists mainly of a well-developed exoskarn. The exoskarn is mostly calcic skarn made up of early garnet and pyroxene, and later amphibole, magnetite and sulfides. The presence of magnesian skarn has been recorded on the north side of the intrusion (roof of granitoid). Magnesian skarn consists of olivine, which is partially replaced by diopside and phlogopite and spinel. Close to the igneous rock, skarns are overprinted by strong potassic alteration. The ore is related to the skarn retrogradation and post-skarn veining and faulting. The skarn-related ore consists of earlier, uneconomic magnetite and Fe–As sulfide assemblages and economic Cu–Au–Ag (Bi–Te) assemblages on the eastern and western sides of the contact aureole, and uneconomic Mo and subeconomic Fe–As–Cu–Au–Ag on the northern side of the contact. Later subeconomic Fe–As–Sb–(Zn–Sn–Cu–Au–Ag) assemblages crosscut the granitoid, skarn, marbles and mineral associations developed previously, and are related to younger episodes of fracturing and faulting. Fluid inclusions in the first hydrothermal stage consist of an aqueous solution with significant contents of CO₂, which reach unmixing conditions as a result of a decrease in P–T conditions. This led to two types of solutions, aqueous solutions of moderate to high salinity and hydrocarbon solutions of low salinity. This unmixing phenomenon controlled the first stage of gold precipitation. During the late hydrothermal activity, primary low-salinity-aqueous-carbonic inclusions with contrasting densities are found. They homogenize into vapor, critical or liquid phase. Homogenization temperatures are practically the same in all inclusions, indicating a boiling phenomenon that could control a new precipitation of gold.