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| Titel |
Aeolian transport pathways along the transition from Tibetan highlands towards northwestern Chinese deserts |
| VerfasserIn |
Veit Nottebaum, Frank Lehmkuhl, Georg Stauch |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250091272
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| Publikation (Nr.) |
 EGU/EGU2014-5555.pdf |
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| Zusammenfassung |
| The identification and semi-quantification of aeolian transport pathways enhances the
understanding of aeolian sediment archive formation and thus supports reliability and
explanatory power concerning palaeoenvironmental reconstructions.
Grain size analysis of 279 surface sediment samples from the transition of Tibetan
highlands (Qilian Shan) towards northwestern Chinese deserts allows the differentiation of
contributing pathways among three types of aeolian sediments: silty loess, sandy loess,
and aeolian sands. The study area exhibits a high diversity of geomorphological
surfaces due to varieties in relief, elevation and climatic conditions. Therefore, it
provides the opportunity to investigate the characteristics of sediments in different
geomorphological settings. Using the peaks of grain size frequency’s standard deviation
of primary loess allows identification of the most sensitive fractions to varying
accumulation conditions. mU/fS-ratio (7–13 μm/58–84 μm) of primary
silty loess relates the far-travelled dust proportion to the locally transported fine
sand component. In vicinity to fluvial channels in the foreland mU/fS-values are
significantly decreased, whereas mU/fS-values increase with altitude (r2 = 0.74). This
indicates higher contribution of long distance transport compared to lower regions. A
prominent increase of mU/fS-values above 3000masl likely indicates an increasing
contribution of fine and medium silt particles transported by Westerlies in higher
altitudes. In contrast, lower areas seem to be more strongly influenced by low altitude
monsoon currents (NW-Winter-/SE-summer monsoon). The difference in grain size
properties is additionally enhanced by the contrasting geomorphologic settings along the
mountain declivity: Plain foreland alluvial fans support fine sand supply and availability
whereas steep high mountain topography provides only limited potential for fine
sand deflation. Similarly, the relatively low relief in intramontane basins leads to
fluvial sediment aggradation and allows comparably high fine sand deflation. This
supports the formation of sandy loess in these regions and on foreland alluvial fans,
whereas in contrast, sandy loess is absent in the high mountain geomorphologic
setting.
Aeolian sand distribution in the study area indicates a high dependence on sand supply. In
eastern forelands perennial Hei River and northerly bordering Badain Jaran desert are
important sand sources and hence support dune field formation in the northern Qilian Shan
foreland (Hexi Corridor). In contrast, western forelands, dominated by gravel gobi surfaces,
exhibit very few aeolian sand accumulations on the surface. The latter area shows only
ephemeral discharge and is lacking large sand source areas. Therefore, although
sufficient wind speeds occur, aeolian sand transport is limited due to restricted sand
supply.
Concluding, the medium scale geomorphological setting (103 m) exerts a rather
underestimated influence when reconstructing aeolian transport processes. However,
considering the spatial distribution of aeolian sediments in combination with their
grain size distribution allows the reconstruction of dominant transport pathways. |
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