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Osady eoliczne (wydmowe) w suchym i półsuchym regionie płaskowyżu Alashan (MongoliaWewnętrzna, Chiny)

Kenig K.

Przegląd Geologiczny

2012

Vol. 60, nr 5

267--272

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.

Comparative study on the Late Cenozoic red clay deposits from China and Central Europe (Hungary)

Kovács J., Varga G., Dezső J.

Geological Quarterly

2008

Vol. 52, No 4

369-369

In the eastern Loess Plateau region of Northern China, the Quaternary loess-palaeosol se quences of the last 2.6 Ma are underlain by the Hipparion Red-Earth Formation (namely the "Red Clay"). The red clay is also a significant deposit in Hungary, the origin of which is controversial. This paper is a comparative study of the Central European (Hungarian) red clay succession and the Xifeng Red Clay profile, the type section for this deposits in the eastern Loess Plateau region. Optical microscopic and SEM analysis were used for grain-size measurements, and both major- and trace-element geochemical properties were analysed to ad dress the question of the origin of Hungarian red clay as well as its environmental implication. We compare the Xifeng Upper Red-Earth (age: ~3.6 to 2.6 Ma BP) with the Hungarian, Tengelic Red Clay Formation (age: ~3.5 to 1.0 Ma BP); both are aeolian deposits ~ genetically related to the Quaternary loess -palaeosol sequence.