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    Wyświetlanie 1-3 z 3
    Tytuł:
    Zróżnicowanie teksturalne osadów wybranych środowisk sedymentacyjnych Fuerteventury Wyspy Kanaryjskie
    Textural diversity of selected sedimentary environments of Fuerteventura (Canary Islands)
    Autorzy:
    Kalinska, E.
    Powiązania:
    https://bibliotekanauki.pl/articles/2084350.pdf
    Data publikacji:
    2012
    Wydawca:
    Uniwersytet Warszawski. Wydział Geografii i Studiów Regionalnych
    Tematy:
    osady plazowe
    Wyspy Kanaryjskie
    osady eoliczne
    cechy teksturalne
    wyspa Fuerteventura
    Opis:
    The detalied analysis of textural features like the grain size distribution with Folk and Ward indicators, rounding and frosting of quartz grains and mineral composition of the beach and aeolian sediments of Fuerteventura Island were undergone. Not only variety, but also commonly features allow to conclude about environmental conditions while depositing. The mineral composition of both beach and aeolian deposits is strongly controlled by the geological structure of the island. Beach deposits are characterized by enrichment in partially rounded frosted quartz grains (EM/RM) instead of typical beach-like grains (EL and EM/EL). It might be caused by strong influence of Saharan Air Layer (Calima). Aeolian deposits are slightly transformed by wind in comparision with the beach deposits. They build, however significant forms.
    Źródło:
    Prace i Studia Geograficzne; 2012, 49; 91-102
    0208-4589
    Pojawia się w:
    Prace i Studia Geograficzne
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Osady eoliczne (wydmowe) w suchym i półsuchym regionie płaskowyżu Alashan (MongoliaWewnętrzna, Chiny)
    Aeolian (dune) deposits in arid to semi-arid region of the Alashan Plateau (Inner Mongolia, China)
    Autorzy:
    Kenig, K.
    Powiązania:
    https://bibliotekanauki.pl/articles/2074941.pdf
    Data publikacji:
    2012
    Wydawca:
    Państwowy Instytut Geologiczny – Państwowy Instytut Badawczy
    Tematy:
    osady eoliczne
    megadunes
    obszary pustynne
    regiony źródłowe
    kierunek wiatru
    Pustynia Alashan
    Hunshandake
    Chiny
    aeolian deposits
    megadiunes
    sandy lands
    source regions
    wind directions
    Alashan Desert
    China
    Opis:
    In northern China, sandy and rocky deserts are located in arid regions west of the Helan Mountains (Helan Shan), while the areas of fixed sand dunes stretch in semi-arid regions east of the Helan Mountains. Helan Mountains, trending nearly NS in the northern part of China's Inner Mongolia Autonomous Region, are a natural border between the dry climate to the west and the semi-dry climate to the east. In the Badain Jaran Desert (part of the Alashan Desert), there are the largest dunes in China, and possibly the largest in the world. They attain a height of up to 460 m in the southeastern part of the desert. Due to their size, they are called megadunes by the Chinese researchers. They are accompanied by numerous smaller dunes, developed in various forms, which cover their slopes. As a result, megadune complexes form, reaching 10 km in length. The general direction of the dunes is NE-SW. In their lower parts, they are covered with sparse xerophytic vegetation, mainly Artemisia and Ephedra. In interdunal depressions of the Badain Jaran Desert, there are numerous (140) permanent, relatively shallow and drying-up lakes, overgrowing with vegetation. Their average depths are 2 m, rarely reaching 16 m mainly in the northern part. The water in the lakes is highly alkaline, with pH values of up to 10.5. Sometimes, the accumulation of salt is so substantial that allows it to be extracted. The groundwater in the immediate surroundings of dunes shows a much lower alkalinity and the average pH is 7.8. To the east of the Helan Mountains, there are several deserts of generally smaller areas and specific environmental nature. This is a sandy land of Hunshandake. Dunes and dune fields are lower and less well developed morphologically, reaching an average of 5-10 m in height. They are mostly stabilized completely or partially by vegetation. The main trend of dunes here is WNW-ESE. Locally, shallow lakes occur in interdunal areas. Studies of mineral and chemical composition of silt material are important for the considerations of the source and direction of silt transport in Asia. One of the diagnostic components of detrital minerals is dolomite. The newest studies of silts recently deposited in Beijing provide information about the wind-transportation direction. It appears that there is a fundamental difference in the mineral composition of silts originating from the dust storm (in 2006) and silts from the entire spring period. Such conclusions are also confirmed by the content of rare earths elements in the 2006 dust storm sediments from Beijing and, comparatively, from other deserts as potential source areas of silts (Yang et al., 2007b). Isotopic investigations of Nd and Sr in aeolian sediments of northern China confirm such a possibility. An important problem for the areas located in northern China is the process of desertification. Noticeable differences have occurred already during the last three decades. They consist in changes in the distribution of movable dunes, which is relative to the humidity and temperature. It is believed that the climate may be the main factor causing desertification in Hunsheandake. In other regions of China, there is another significant factor: human activity, especially shepherding that causes the process of desertification and environmental degradation.
    Źródło:
    Przegląd Geologiczny; 2012, 60, 5; 267--272
    0033-2151
    Pojawia się w:
    Przegląd Geologiczny
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Stopień przekształcenia eolicznego wybranych cech teksturalnych osadów wydmowych południowej Szwecji
    Degree of aeolian modification of some textural features of the dune deposits in south Sweden
    Autorzy:
    Mycielska-Dowgiallo, E.
    Powiązania:
    https://bibliotekanauki.pl/articles/2085674.pdf
    Data publikacji:
    1988
    Wydawca:
    Uniwersytet Warszawski. Wydział Geografii i Studiów Regionalnych
    Tematy:
    Szwecja Południowa
    osady wydmowe
    cechy teksturalne
    przeksztalcenia eoliczne
    Opis:
    Investigations comprised deposits forming two dunes at Dammsjön and at Lennheden (district of Dalarna, north of Uppsala) and - for comparison – deposits of aquatic origin underlaying the dune at Lennheden as well as the fluvioglacial deposits from the outcrops of Brovallen and Norr Amsberg, which form the esker of Badelunda. The principal object of investigations was to determine the degree at which source deposits were transformed into aeolian sands. Fraction 0.8-1 mm was used in the analysis of quartz grain rounding by Krumbein's (1941) and Krygowski's (1964) methods; the share of quartz in the deposit was determined (Tab. 1). The composition of heavy minerals was determined with the use of fraction 0.1-0.2 mm while the type of surface relief of quartz grains was examined under the electron microscope in fraction 0.5-0.8 mm. The results of all the analyses have shown that the aeolian process which has formed the dunes under investigation in South Sweden has only slightly modified the source deposits or affected the textural features of aeolian deposits. All the deposits investigated, irrespective of their origin, are characterized by an identical and very poor rounding of quartz grains. It has not been noticed that aeolian deposits should contain more well rounded grains than the basement. In Polish dunes, occurring beyond the area of the last glaciation, the share of the γ group (best rounded grains, rolling down the plate of Krygowski’s graniformameter at 8° of gradient inclusive) is not only very high but they contain much more grains of this group than the basement deposits. This increase reaches 1.9% in the dunes of the Vistula valley near Płock (Krajewska, 1983) not far from the maximum reach of the last glaciation, and up to 14.6% near Warsaw (Pruszyńska, 1980). Neither has an increase of quartz been observed in the Swedish dunes as compared with the source deposits. In Polish dunes, analysed by Urbaniak-Biernacka (1976) in eleven areas, the percentage of quartz, as compared with basement deposits, is higher by 0.3-4.1 % in volume. The analysis of the composition of heavy minerals has shown that both in aeolian sands and in the sands of the immediate basement as well as in fluvioglacial sands those minerals prevail which are least resistant to chemical weathering and mechanical abrasion (Fig. 1). The total share of heavy minerals is somewhat higher in fluvioglacial sands and in the basement than in aeolian sand (Tab. 2). It may be then supposed that this was a process of selective segregation and blowing away of more favorably shaped grains and not one of selective destruction of grains less resistant to destructive factors. In Polish dunes, formed beyond the area of the last glaciation, there is a visible increase of the content of garnet - a mineral most resistant to mechanical abrasion, it is higher by 0.6-22.8% of volume as compared with the basement (Urbaniak-Biernacka, 1976). In the dunes of the Vistula valley near Płock not only a higher share of garnet but also of zirconium and disthene has been observed in the dune deposits (Krajewska, 1983). Of all the investigations only a detailed analysis of the quartz grain surface under the electron microscope has shown some differences in the relief character between grains from fluvioglacial deposits and those from the dunes. Those differences can be noticed in magnification no less than 400 X and only on convex fragments, particularly on edges. These surfaces are always fresh on grains from fluvioglacial deposits, while a certain amount of grains from aeolian environment have chipping on convex fragments of the grain surface, which resemble those produced in a simulated aeolian process (Lindé, Mycielska-Dowgiałło, 1980). Similar chipping has been observed on mat round grains of aeolian origin found in Pleistocene deposits in the Piaski mine, near Bełchatów (Goździk, Mycielska-Dowgiałło, 1982). On the grains of these two different types (aeolian and fluvioglacial sands) various weathering forms were found usually occupying concave fragments of the surface. They are probably relicts of processes which occurred much earlier, some of them certainly before the Pleistocene. All the data presented above seem to evidence a very short aeolian process that has formed the Swedish dunes under investigation. There was no time for an increase, through a process of selection, of the content, in the deposit, of quartz - the most resistant mineral to mechanical abrasion - or for the enrichment of heavy minerals in minerals more resistant to mechanical abrasion (e.g. garnet), neither for the removal of undurable minerals (e.g. amphiboles and pyroxenes). The process must have been so short that it did not change the general abrasion of the quartz grains but only slightly affected the relief character of the convex fragments of the surface of some quartz grains which is not visible until magnified over 400 X in the electron microscope. It should be noted at the same time that the process, however short, has built distinct dune forms. Morphometric surveys of the dune forms are not sufficient to determine the duration and intensity of the aeolian process but investigations should always be based on the textural features of aeolian deposits and their comparison with the same features in source deposits. The degree of transformation of the deposits is the right indicator of the duration of this process.
    Źródło:
    Prace i Studia Geograficzne; 1988, 09; 115-139
    0208-4589
    Pojawia się w:
    Prace i Studia Geograficzne
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-3 z 3

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