Precambrian fluvial deposits: Enigmatic palaeohydrological data from the c. 2–1.9 Ga Waterberg Group, South Africa     

Patrick G. Eriksson  Adam J. Bumby  Jacobus J. Brümer  Markus van der Neut 《Sedimentary Geology》2006,190(1-4):25-46

Precambrian fluvial systems, lacking the influence of rooted vegetation, probably were characterised by flashy surface runoff, low bank stability, broad channels with abundant bedload, and faster rates of channel migration; consequently, a braided fluvial style is generally accepted. Pre-vegetational braided river systems, active under highly variable palaeoclimatic conditions, may have been more widespread than are modern, ephemeral dry-land braided systems. Aeolian deflation of fine fluvial detritus does not appear to have been prevalent. With the onset of large cratons by the Neoarchaean–Palaeoproterozoic, very large, perennial braided river systems became typical. The c. 2.06–1.88 Ga Waterberg Group, preserved within a Main and a smaller Middelburg basin on the Kaapvaal craton, was deposited largely by alluvial/braided-fluvial and subordinate palaeo-desert environments, within fault-bounded, possibly pull-apart type depositories.

Palaeohydrological data obtained from earlier work in the Middelburg basin (Wilgerivier Formation) are compared to such data derived from the correlated Blouberg Formation, situated along the NE margin of the Main basin. Within the preserved Blouberg depository, palaeohydrological parameters estimated from clast size and cross-bed set thickness data, exhibit rational changes in their values, either in a down-palaeocurrent direction, or from inferred basin margin to palaeo-basin centre. In both the Wilgerivier and Blouberg Formations, calculated palaeoslope values (derived from two separate formulae) plot within the gap separating typical alluvial fan gradients from those which characterise rivers (cf. [Blair, T.C., McPherson, J.G., 1994. Alluvial fans and their natural distinction from rivers based on morphology, hydraulic processes, sedimentary processes, and facies assemblages. J. Sediment. Res. A64, 450–489.]). Although it may be argued that such data support possibly unique fluvial styles within the Precambrian, perhaps related to a combination of major global-scale tectono-thermal and atmospheric–palaeoclimatic events, a simpler explanation of these apparently enigmatic palaeoslope values may be pertinent. Of the two possible palaeohydrological formulae for calculating palaeoslope, one provides results close to typical fluvial gradients; the other formula relies on preserved channel-width data. We suggest that the latter will not be reliable due to problematic preservation of original channel-widths within an active braided fluvial system. We thus find no unequivocal support for a unique fluvial style for the Precambrian, beyond that generally accepted for that period and discussed briefly in the first paragraph.  相似文献   

A comparison of chironomid biostratigraphy from Lake Vuolep Njakajaure with vegetation, lake-level, and climate changes in Abisko National Park, Sweden     

Markus Heinrichs  Lena Barnekow  Sandra Rosenberg 《Journal of Paleolimnology》2006,36(2):119-131

Chironomid remains from the sediment of Lake Vuolep Njakajaure reflect limnological conditions resulting from changing climate and vegetation throughout the Holocene, but do not strictly follow accepted climate trends or the vegetation history based on regional pollen and macrofossil analyses. Chironomid community changes appear to be influenced by organic nutrient input from the surrounding catchment vegetation and lake hydrology, both of which are indirectly responding to some combination of climate change, hypolimnetic oxygen concentration, and changes in basin morphology. The chironomid-based quantitative mean July air-temperature reconstruction differs from other regional quantitative records; this discrepancy is likely related to limnological conditions particular to Lake Vuolep Njakajaure. Comparison of a northern Swedish temperature transfer function and one from western Canada reveals differences in the mean July air-temperature optima of several common taxa, suggesting that the existing conservative estimates of Holocene climate change in northern Sweden may be underestimated due to the limited temperature gradient captured by the Swedish training set.  相似文献   

Geometry and accuracy of reflecting points in bistatic satellite altimetry     

J. Kostelecký  J. Klokočník  C.A. Wagner 《Journal of Geodesy》2005,79(8):421-430

The analysis of the time and space distribution of specular (reflecting) points in bistatic altimetry between GPS and CHAMP satellites or SAC-C (taken as examples) is extended from Wagner and Klokočník (2003 J. Geod 77: 128–138). We demonstrate a significantly higher number and density of reflecting points in bistatic altimetry in comparison with traditional monostatic altimetry. After an outline of our older accuracy assessment for the vertical position of the reflecting point, we add a new independent derivation and compare both approaches. We account for orbit errors of both the transmitters (GPS) and receiver (CHAMP) satellites, and the measurement (delay) error. We found that the accuracy of the vertical position of the reflecting point decreases only slowly with increasing off-nadir angle and that the orbit errors must be accounted for if decimeter and better accuracy is required. In this paper, we do not study errors such as state of the ocean, technical parameters of the receiving system, and atmospheric corrections.  相似文献   

Particle size dependent response of aerosol counters     

A. Ankilov  A. Baklanov  M. Colhoun  K. -H. Enderle  J. Gras  Yu. Julanov  D. Kaller  A. Lindner  A. A. Lushnikov  R. Mavliev  F. McGovern  T. C. O'Connor  J. Podzimek  O. Preining  G. P. Reischl  R. Rudolf  G. J. Sem  W. W. Szymanski  A. E. Vrtala  P. E. Wagner  W. Winklmayr  V. Zagaynov 《Atmospheric Research》2002,62(3-4)

During an international workshop at the Institute for Experimental Physics of the University of Vienna, Austria, which was coordinated within the Committee on Nucleation and Atmospheric Aerosols (IAMAS-IUGG), 10 instruments for aerosol number concentration measurement were studied, covering a wide range of methods based on various different measuring principles. In order to investigate the detection limits of the instruments considered with respect to particle size, simultaneous number concentration measurements were performed for monodispersed aerosols with particle sizes ranging from 1.5 to 50 nm diameter and various compositions.The instruments considered show quite different response characteristics, apparently related to the different vapors used in the various counters to enlarge the particles to an optically detectable size. A strong dependence of the 50% cutoff diameter on the particle composition in correlation with the type of vapor used in the specific instrument was found. An enhanced detection efficiency for ultrafine hygroscopic sodium chloride aerosols was observed with water operated systems, an analogous trend was found for n-butanol operated systems with nonhygroscopic silver and tungsten oxide particles.  相似文献   

Water solubility in orthopyroxene   总被引：7，自引：0，他引：7  

Markus Rauch  Hans Keppler 《Contributions to Mineralogy and Petrology》2002,143(5):525-536

The solubility of water in pure enstatite was measured on samples synthesized at 1,100 °C and pressures to 100 kbar. Enstatite crystals were grown under water-saturated conditions from a stoichiometric mixture of high-purity SiO₂ and Mg(OH)₂. Water contents were calculated from polarized FTIR spectra measured on oriented single crystals. The water solubility in orthoenstatite increases with pressure to 867ᆷ ppm H₂O by weight at 75 kbar. At 100 kbar, in the stability field of high-clinoenstatite, a water solubility of 714ᆷ ppm was observed. The water solubility in enstatite at 1,100 °C can be described by the equation c_H2O=Af_H2O exp(-P(V/RT), where f_H2O is water fugacity, A=0.0204 ppm/bar and (V=12.3 cm³/mol. The infrared spectra of the hydrous enstatite crystals show a sharp, intense band at 3,363 cm^-1 and a broad, weaker band at 3,064 cm^-1. Both bands are strongly polarized parallel c. Most likely, pairs of protons attached to non-bridging oxygen atoms substitute for Mg²⁺. In order to investigate the effect of chemical impurities on water solubility in enstatite, an additional series of experiments was carried out with gels doped with Al, B, or Li as starting material. Whereas, the presence of Li and B had no detectable effect on water solubility, the addition of about 1 wt% Al₂O₃ increased water solubility in enstatite from 199 to 1,100 ppm at 1,100°C and 15 kbar. In the infrared spectra of these aluminous samples, additional bands occur in the range from 3,450 to 3,650 cm^-1. Similar bands are also observed in natural, aluminous orthopyroxenes and are most likely caused by protons coupled with Al according to the substitution of Al³⁺+H⁺ for Si⁴⁺. A series of hydrous annealing experiments on a natural, gem-quality aluminous enstatite from Tanzania yielded water solubilities generally consistent with the results from the synthetic model systems. The results presented here imply that pure enstatite has a similar storage capacity for water as olivine; however, aluminous orthopyroxenes in the mantle may dissolve much larger amounts of water comparable with the entire mass of the present hydrosphere. Moreover, the mechanism of aluminum substitution in orthopyroxenes, i.e., the distribution of Al between tetrahedral and octahedral sites, may be a potential probe of water fugacity.  相似文献   

Crisis, coincidences and strategic market behaviour: the internationalization of Indonesian clothing brand-owners     

Markus Hassler 《Area》2003,35(3):241-250

Despite the fact that most Indonesian brand-owners continue to emphasize their marketing activities in the domestic market, several brand-owners have started to export clothing under their own label. This has been particularly the result of the economic crisis in the late 1990s, which affected companies serving the domestic market. Companies were trying to compensate for the loss of sales on the domestic market by redirecting their marketing activities to foreign countries. This export strategy has been driven largely by the sole aim to survive. However, in addition to these export activities, some companies have rather sophisticated, long-standing business relations to their distributors in overseas markets. This paper explores these export activities in the context of the global commodity chain framework.  相似文献   

The Cretaceous and younger thermal history of the KTB site (Germany): apatite fission-track data from the Vorbohrung     

D. A. Coyle  G. A. Wagner  E. Hejl  R. Brown  P. Van den Haute 《International Journal of Earth Sciences》1997,86(1):203-209

A detailed fission-track analysis was carried out on 41 apatite samples from the 4001-m-deep pilot hole of the German Continental Deep Drilling Program (KTB). The investigations include dating by the population method and length measurements of horizontal confined tracks. Age and length information indicate that all samples above the present-day partial annealing zone cooled from temperatures above 120?°C in the Cretaceous. The top two kilometres of the profile show less variation of age with depth than was expected. Modelling of the profile indicates that the distribution of fission track ages with depth requires that the profile was disturbed during or after cooling through the partial annealing zone. Modelling of individual samples reveals that at least the upper 2?km experienced reverse faulting, effectively thickening the upper part of the rock column by up to 1000?m in the Tertiary. A present-day partial annealing zone for apatite was observed between 2000 and 4000?m (～60–110?°C). This confirms earlier in situ observations of the position of the partial annealing zone.  相似文献   

Petrologic studies of terrestrial organic matter in Carpathian flysch sediments, southern Poland     

Marian Wagner 《International Journal of Coal Geology》1996,29(4):259-272

In the Carpathian Flysch, coal is present either as exotics of Carboniferous coal deposits or as autochthonous, thin layers of lustrous coal. This paper present the results of the studies of coal-bearing rocks that are coeval with the enclosing flysch sediments. These coals form lenses up to 0.15 m thick. Their morphology precludes an exotic origin. The main petrographic component is collinite with admixtures of poorly fluorescing telinite. Minor components are: exudatinite, sporinite, fusinite, micrinite and sclerotinite. Mineral matter consists of framboidal pyrite clay minerals and quartz.The random reflectance of telocollinite varies from 0.38% to 0.72%, which corresponds to subbituminous and bituminous ranks. Correlation between chemical analysis, coking properties and relfectance measurements, leads to the conclusion that boundary between subbituminous and bituminous coals should be defined by the following values: C=80wt%, VOLATILES=43wt%; calorific VALUE=32.3 MJ/kg; and R^o=0.56–0.57%.Atypical properties, such as: upper C value (75–80wt%); high volatile matter contents (over 43wt%) and low random reflectance (^o about 0.38–0.57%) in subbituminous coals; low C value (about 80–82wt%); low reflectance (0.56–0.72%); and good coking properties, of the bituminous coals are attributed to quick coalification during increasing temperature as a result of tectonic stress.  相似文献   

GRASS as Open Source Free Software GIS: Accomplishments and Perspectives     

Helena Mitasova  Markus Neteler 《Transactions in GIS》2004,8(2):145-154

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Geomorphological and pedological investigations on the glacial history of the Kali Gandaki (Nepal Himalaya)     

Markus Wagner 《GeoJournal》2005,63(1-4):91-113

In semi-arid orographic left tributaries of the Kali Gandaki at the northern and western flank of the Nilgiri Himal, glacio-geomorphological and pedological investigations were carried out on prehistoric moraines. Geomorphological relief analysis was derived from other literature and the own fieldwork of the author. The resulting glacial chronology was used as benchmark to explore the limits of different pedological dating methods regarding the degree of soil development. These methods are based on iron fractionation, total element contents and particle size distribution. In general the different glacial stages are mirrored correctly in the relative graduation of soil development. The ratio of well crystallised pedogenic iron-oxides to the total iron content and the ratio fine clay to total clay are most suitable, because they are almost independent from existing changes in the lithological composition. The total element based weathering indices are less suitable, because they react highly sensitive to the geology dependent shift to higher carbonate content. Most of the grain size based weathering indices are inapplicable because of the typically high textural variability within till deposits.  相似文献