The aeolian sedimentation record of the Thar desert |
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| Authors: | A K Singhvi Amal Kar |
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| Institution: | (1) Physical Research Laboratory, 380 009 Navrangpura, Ahmedabad, India;(2) Central Arid Zone Research Institute, 342 003 Jodhpur, India |
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| Abstract: | A review of the aeolian sedimentary record of the Thar desert is presented. This includes a regional survey of the major dune
forms, their genesis and their relationship to climate and other regional landforms. A key aspect of this work is the chronometry
of the dunes using luminescence methods. Luminescence dating of sand has enabled quantification of the duration of the phases
of sand aggradation and quiescence, time scales of dune migration and the dating of pedogenic carbonates. We demonstrate that
the conventional wisdom of synchronicity of dune aggradation with glacial epoch is not true in the context of Thar sands and
here only a short durationwindow of opportunity existed for dune aggradation. Luminescence ages further suggest that this window occurred during a transitional climatic
regime from glacial to interglacial about 4–10 ka after the glacial epoch. Other inferences included are that:
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• the aeolian activity in the Thar began over > 150 ka, resolving that Thar is not of anthropogenic origin as suggested previously;
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• the present spatial extent of the aeolian activity in the Thar is in a contracted stage compared to that in the geological
past, which refutes the arguments on its rapid north-eastward expansion;
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• the current dune migration rates in areas of significant human-induced disturbances are much higher than during the geological
past;
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• the monsoon activity in the Thar varied significantly, from being minimal during the isotopic marine stages 4 and 2 to being
close to the present during stage 3;
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• on shorter time scales the dune activities correlated with the lacustrine records of the region with a phase difference
of a few centuries and a periodicity of ∼ 1500 years;
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• the sand aggradation climate in the southern margin in Gujarat gradually shrank northwards such that in general dunes older
than 10 ka are seen in the extreme southern margin and dunes younger than 2ka ages occur mostly in the western part of Rajasthan.
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| Keywords: | Sand dune aeolian process sediment deep profile luminescence dating chronology Thar Rajasthan Gujarat |
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