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Badan Jaran Desert And Tengger Desert Sediment Characteristics Contrast Study

Posted on:2012-05-01Degree:DoctorType:Dissertation
Country:ChinaCandidate:E J LiFull Text:PDF
GTID:1110330335472014Subject:Physical geography
Abstract/Summary:PDF Full Text Request
Badain Jaran Desert and Tengger Desert are located in the arid area of northwest China. They are bounded by the Yabulai mountain and belong to Alashan League, Inner Mongolia. As their unique geomorphology, it is recognized as the ideal region to study the aeolian geomorphology, hence draw a great attention of the scholars at home and abroad. The studies of Badain Jaran Desert mainly focused on geomorphology, genesis, source of the groundwater and geochronology, et al. The studies of Tengger Desert were mainly done in the southeast area of the desert, focused on genesis and evolution of the desert, aeolian deposits, aeolian physics, sedimentary structure, et al. However, the systematic studies on the material composition are still very little, not to say the contrastive study of the aeolian deposits in the both deserts. The studies on the characteristics of aeolian deposits make great sense in the determining of aeolian sedimentary environment, exploring the source of the aeolian deposits and the evolution of the aeolian geomorphology. In order to do the research, the author collected the samples in the typical surface, different sedimentary layers, typical dune and cross-section of the Badain Jaran Desert and Tengger Desert. And made a comparative study of the representative samples from the characteristic of grain size, mineral composition, and geochemical element and so on, and analysed the similarities and differences of the deposits in the two deserts. These provide an important basis to investigate the source and formation of the sand in the two deserts. The main conclusions are following:1.The grain size analysis results of the deposits in the Badain Jaran-Tengger Deserts(1) The grain size composition analysis shows that the sediments of the two deserts are mainly comprised of medium and fine sand, and the surface sediments of Badain Jaran Desert are slightly coarser than that of Tengger Desert. The grain size composition of different type of dunes and different landform positions of the two deserts are different:mobile dunes and shrub canopy dunes of Badain Jaran Desert are mainly composed of fine and medium sand, but flat sandy land and inter-dunes are mainly composed of coarse and medium sand; while all the dunes,ridges,and inter-dunes of Tengger Desert are primarily composed of fine and medium sand.It is similar to the grain size composition in different sedimentary layers namely the vertical section of the two deserts, which are primarily composed by fine and medium sand.The frequency curve is mainly unimodal for dune sands of both deserts, but there are some differences of the peaks'range of grain size, that is the peaks'range of Badain Jaran Desert is broad, while the Tengger Desert is relatively concentrate.(2) grain size parameters shows that the Badain Jaran Desert's mean grain size of the surface deposits and the longitudinal profile of typical dunes is coarser than that of Tengger Desert, while the surface grain size of typical dunes is finer than that of Tengger Desert. The sorting parameters show that the sediments from the two deserts are better sorted to well sorted with a distribution of near symmetric skewness and mesokurtic.The sediments from the surface and longitudinal profile of Badain Jaran Desert is slightly worse sorted than that of Tengger Desert, while it is slightly better sorted of the sediments from the surface of typical dunes than that of Tengger Desert.(3) From a regional perspective, The grain size parameters of the sediments from the both deserts have no distinct regional change, but the Tengger Desert is slightly better than the Badain Jaran Desert.2.The mineral assemblages of sands in the Badain Jaran-Tengger Desert(1) The main light minerals in Badain Jaran Desert and Tengger Desert are mainly comprised of quartz and feldspar, but the content proportion of the light minerals of surface sediments in Badain Jaran Desert is slightly lower than that of Tengger Desert, and the Light mineral composition maturity in Tengger Desert is also slightly lower than that of Badain Jaran Desert.(2) From a regional perspective, the light mineral composition maturity shows no regularity and anti-regularity in Badain Jaran Desert. But in Tengger Desert, the light mineral composition maturity shows distinct regional change. That is in the NW-SE cross sections which are parallel to the dominant wind direction, the light mineral composition maturity becoming better.(3) The types of heavy minerals in both Badan Jaran Desert and Tengger Desert are consistent, but the heavy mineral proportion of sediments in Badan Jaran Desert is slightly higher than that in Tengger Desert. And the weathering degree of the sediments in Badan Jaran Desert is slightly weaker than that in Tengger Desert. The weathering degree of the sediments in windward slope is better than that in leeward slope in both Badain Jaran Desert and Tengger Desert.(4) The weathering degree of apatite in Badan Jaran Desert is weaker than that in Tengger Desert. The source area of the both deserts is very close. The source of sand is basisc acid rocks, which is rich of garnet. The mineral maturity in the both deserts is not high3. The geochemical element analysis results(1) Badain Jaran-Tengger Desert contains the same types of the main major elements, both have a high average content of SiO2 and Al2O3, except the CaO enriches in the Badan Jaran Desert compares to the Tengger Desert, the other major elements contents are similar to the Tengger Desert. Compare to the average chemical composition of the upper continental crust (UCC), except the SiO2, the other major elements of both deserts are suffered a relatively loss. The content distribution curves of major elements of different regional cross sections in the both deserts is more consistent, but the spatial distribution regularity of major elements is more remarkable in Tengger Desert than that of Badan Jaran Desert. (2) Both Badain Jaran Desert and Tengger Desert are most abundant in Ba, the average content of trace elements, such as Sr,Go,Cr,Zr,Rb and so on are relatively higher, the content of the other trace elements are relatively less. Except the content of Cu are slightly different in both deserts, the average content of the other trace elements have little difference. Compare to the average chemical composition of the upper continental crust(UCC), both deserts are relatively enrich of Co and Cr. The content of Ba and Ni are equivalent to UCC, the other trace elements show migration and lesching out. The content distribution curves of different regional cross sections in the both deserts are similar, and the regional regularity is not remarkable.(3) There are some difference in the chemical composition of the aeolian deposits in the both deserts, but the difference is tiny. The aeolian deposits of the both deserts are of good homogeneity, which is at the initial stage of continental weathering. The chemical weathering degree in Tengger Desert is slightly stronger than that in the Badain Jaran Desert.4. Through the contrast studies of desert sedimentary characteristic on regional scale between Badain Jaran Desert and Tenger Desert, this paper draw a conclusion that the regional variation law of desert sedimentary in Tengger Desert is slightly superior to that of desert sedimentary in Badain Jaran Desert. It is inferred that the regional precipitation regularity of desert sedimentary become better and better toward the southeast in arid region in northwest China, that is to say, the precipitation regularity in deposit area is superior to that in erosion area.Based on the comparative study of the grain size, mineral and geochemical elements of sediments from Badain Jaran Desert and Tengger Desert, this paper obtained the similarities and differences of aeolian sediments'characteristics in the both deserts. This study can provide reliable basis on the discussion of sand source, the inversion of material forming processes, as well as the restoration and reconstruction of aeolian environment of the two deserts.
Keywords/Search Tags:Badain Jaran-Tengger Desert, sediment characteristics, material source
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