The Origin and Distribution of Salts on Alluvial Fans in The Atacama Desert,Northern Chile     

I. A. Berger  R. U. Cooke 《地球表面变化过程与地形》1997,22(6):581-600

The Atacama Desert has been predominantly hyperarid since the middle Miocene. Combined ionic and X-ray diffraction analysis shows that calcium sulphate is prevalent on three similar alluvial fans in salar basins across a transect of different environments in Antofagasta Province, northern Chile. Differences between the fans were largely due to the effect of local factors on salt input, secondary redistribution and deposit preservation. Thus carbonate was notable in the High Andes (fan C) and Pre-Cordillera (fan B), whereas in the Central Valley (fan A) greater qualities of the more soluble salts (chlorides and nitrates) probably reflect the higher level of aridity and an oceanic source (the camanchaca). Calcium sulphate distribution on the alluvial fans and on adjacent hilltops indicates an aeolian origin. Evidence from the Pre-Cordillera (fan B), however, suggests that salt input may have been episodic, related to changes in conditions within the general aridity and possibly to stone pavement and soil development. Calcium sulphate sources range from an input in Andean precipitation and the camanchaca to abundant regional evaporite deposits. It is probable, however, that products of Andean volcanism constitute the dominant primary source of calcium sulphate, and that the salt has subsequently been distributed widely within the endoreic basins of the region by a combination of groundwater, surface flow and the wind. © 1997 John Wiley & Sons, Ltd.  相似文献   

Groundwater recharge estimation from ephemeral streams. Case study: Wadi Tabalah,Saudi Arabia     

Ali U. Sorman  Mohamed J. Abdulrazzak  H. J. Morel-Seytoux 《水文研究》1997,11(12):1607-1619

Estimation of groundwater recharge to an unconfined aquifer is studied using analytical and numerical techniques and results are compared with field observations. There is an acute need for such estimation in water balance studies in arid climates, and the case study in this paper is for such a region. The wetting front movement in the unsaturated zone depends on antecedent soil moisture, the ponded water depth and its duration, and on the position of the water table and the hydraulic properties of the unsaturated zone. A hydraulic connection between the recharge basin and the aquifer is not immediately established because the wetting front is unsaturated. A numerical model is applied to estimate recharge in an arid-zone wadi, and its validity is tested by comparing it with an analytical solution of the equations. The calculated recharge values matched the piezometric levels observed at a well site at the edge of the wadi channel. The total recharge depths found by integration in the time domain provided a good estimate of the transmitted volume of water per unit length of wadi channel. The findings were confirmed by runoff volume measurements at gauging stations located in the basin. © 1997 John Wiley & Sons, Ltd.  相似文献   

Colluvial deposits in northwest Deccan,India: their significance in the interpretation of Late Quaternary history     

Veena U. Joshi  Vishwas S. Kale 《第四纪科学杂志》1997,12(5):391-403

The Deccan Trap region exhibits an erosional landscape over a relatively ancient and stable Deccan shield. The Quaternary history of the area has been reconstructed on the basis of evidence from alluvial deposits occurring along the major rivers. However, recent investigations have revealed that evidence for geo-environmental change during the Quaternary Period is also contained in the colluvial deposits that occur in the foothill zones. The colluvial deposits, ranging in thickness from 1 to 10 m, invariably occupy gently inclined pediment slopes. The sediments are presently deeply dissected by gullies, and the process of colluviation has almost ceased. These deposits are best preserved in the semi-arid parts of the region. Detailed textural, geochemical and stratigraphical studies at four different sites reveal similar input processes, the slight variations being attributed to local environmental factors. Scanning electron microscopy studies of some grains indicate marginal contribution of aeolian processes at the time of deposition. Mesolithic artefacts and a few U/Th dates indicate that the colluviation took place during the Late Quaternary. The properties of the deposits suggest relatively high energy conditions as well as a remarkable variability in the intensity of hillslope processes. These properties are indicative of semi-arid conditions during which the regolith was stripped from devegetated hillslopes and was deposited on the pediments. A variety of evidence indicates that the period of colluviation coincided with arid conditions during the Last Glacial Maximum. The geomorphological and archaeological evidence also indicates that incision by gully systems was initiated during the early Holocene humid phase. The environmental conditions deduced for the study area are similar to those reported for other parts of the intertropical zone. © 1997 John Wiley & Sons, Ltd.  相似文献   

A long-term photometric study of the pre-main-sequence star V 350 Cep     

E.H. Semkov  A.S. Mutafov  U. Munari  M. Rejkuba 《Astronomische Nachrichten》1999,320(2):57-61

Results from photographic and CCD photometric observations of the pre-main sequence star V 350 Cep are presented. A continued gradual rise of brightness resembling the light curves of the FUOR type stars is observed. A search in the WFPDB was made to find old photographic observations of V 350 Cep.  相似文献   

Compactification and cosmic string phenomenology     

U. Bleyer  O. Heinrich  V. M. Nikolaenko 《Astronomische Nachrichten》1990,311(3):177-181

A U(1) model of gravitational, Higgs and, gauge fields is analysed. Two phases of the system are considered. In the case with broken symmetry we have the Nielsen-Olesen configuration. In the symmetric phase we find a space-time metric S² × E₁². This appears in full analogy to the Freund-Rubin compactification due to an antisymmeric tensor field. The connection of these structures with cosmic string phenomenology is analysed.  相似文献   

The action of the satellite 1981 S13, and the optical depth profile of the Encke-gap ringlet in the Saturn A ring     

F. Spahn  A. Saar  St. Schmidt  U. Schwarz 《Astronomische Nachrichten》1992,313(2):101-105

The radial optical depth profile of the Encke ringlet obtained by the occultation experiment of the Voyager photopolarimeter (PPS data) is explained to be caused by the gravitational action of the recently discovered stallite 1981 S13 and a second smaller moonlet orbiting near one of its either libration points — L₄ or L₅. To this aim the results of previous and new numerical particle simulations as well as an extension of the scattering theory concerning a single moonlet to a pair of satellites have been used leading to a triple-peaked ringlet near the orbits of the moonlets. The width and the shape of that ringlet and its separate peaks depend on the mass ratio of both moonlets and on their orbital eccentricites. The best resemblance between the PPS data and the theoretical profile is obtained if the mass ratio of the either moonlets takes M₂/M_1981S13 ≈ (0.8 … 3.0) × 10⁻² and the eccentricities hold: e_1981S13 < h_1981S13; e₂ ≈ h₂ (the values h are the Hill scales of either moonlets defined by h_1981S13/2 ≈ (M_1981S13/2/3M_h)^1/3, M_h = Saturn mass). Furthermore, our results yield a size of 1981 S13 of < 15 km in diameter.  相似文献   

西藏阿里札达盆地下更新统香孜组地层厘定与层序地层划分     

朱大岗  孟宪刚  邵兆刚  杨朝斌  韩建恩  余佳  孟庆伟  吕荣平 《地质力学学报》2006,12(4):406-415

根据札达盆地香孜组河湖相地层剖面的接触关系、沉积旋回、沉积体系和岩相岩性特征,可将札达盆地下更新统香孜组河湖相地层划分为2个沉积相、3个岩段。香孜组一、二岩段为一套砾岩夹砂岩的粗碎屑岩,属典型的冲（洪）积扇沉积物;第三岩段为砾岩与砂岩互层,属冰水冰缘相沉积。ESR法和古地磁法测年结果表明,札达盆地香孜组河湖相地层的形成时代为早更新世早期（2．68—1．36Ma）。札达盆地为一同生断陷盆地,在后期重新复活的过程中,盆地只经历了冲积体系域和水进体系域。冲积体系域形成于札达盆地早更新世早期重新复活层序发育的早、中期,水进体系域形成于札达盆地早更新世早期重新复活层序发育的晚期。  相似文献   

New mass formula for spherically symmetric stellar configurations     

U. Bleyer  L. Sh. Grigorian  R. M. Avakian  E. V. Chubarian 《Astronomische Nachrichten》1995,316(1):1-7

A new formula is derived for the mass of spherically symmetric stellar configurations. An expression will be given where the mass square is connected to an integral over the pressure of gravitating matter. This formula turns out to hold for Newtonian gravity, for Einstein's GRT, for projective and bimetric scalar-tensor and further theories of gravitation.  相似文献   

A refined model for the influence of ocean tides on UT1 and polar motion     

U. Seiler  J. Wünsch 《Astronomische Nachrichten》1995,316(6):419-423

Periodic changes in Universal Time and polar motion have been derived from a numerical ocean model for a number of small partial tides. Combined with the results reported earlier our model now includes the 34 most important constituents of degree 2 (measured by the amplitude of the tidal potential). The results show that the terms neglected in all existing models amount to 80 μs in UT1 and to 0.3 mas in polar motion.  相似文献   

Seasonal budgets of the nutrient elements N and P at the surface of the German Bight during winter 1996, spring 1995, and summer 1994     

U. Brockmann  T. Raabe  K. Hesse  K. Viehweger  S. Rick  A. Starke  B. Fabiszisky  D. TopÇu  R. Heller 《Ocean Dynamics》1999,51(2-3):267-291

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