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Accueil du site → Doctorat → Allemagne → 2016 → Paleoclimatic implications from late Quaternary terrestrial archives in the Gobi Desert : examples from the Ejina Basin and Orog Nuur Basin

RWTH Aachen University (2016)

Paleoclimatic implications from late Quaternary terrestrial archives in the Gobi Desert : examples from the Ejina Basin and Orog Nuur Basin

Yu, Kaifeng

Titre : Paleoclimatic implications from late Quaternary terrestrial archives in the Gobi Desert : examples from the Ejina Basin and Orog Nuur Basin

Paläoklimatische Implikationen von spätquartären terrestrischen Archiven in der Wüste Gobi : Beispiele aus dem Ejina Becken und dem Orog Nuur Becken

Auteur : Yu, Kaifeng

Université de soutenance : RWTH Aachen University

Grade : Doktors der Naturwissenschaften 2016

Résumé partiel
Considerable efforts have been devoted to disentangle the late Quaternary moisture and thermal evolution of arid central Asia. However, an array of paramount aspects has inhibited our complete understanding of the broad pattern of Quaternary moisture and thermal history of arid central Asia and underlying mechanisms.The Ejina Basin, with its suite of different sediment archives, is known as one of the main sources for the loess accumulation on the Chinese Loess Plateau. In order to understand mechanisms along this supra-regional sediment cascade (aeolian, fluvial and alluvial sediments), it is crucial to decipher the archive characteristics and formation processes. Five sediment archives from three lithologic units exhibit geochemical characteristics as follows : (i) aeolian sands have high contents of Zirconium and Hafnium, whereas only Hafnium can be regarded as a valuable indicator to discriminate the coarse sand proportion ; (ii) sandy loess has high Calcium and Strontium contents which both exhibit broad correlations with the medium to coarse silt proportions ; (iii) lacustrine clays have high contents of felsic, ferromagnesian and mica source elements e.g., Potassium, Iron, Titanium, Vanadium, and Nickel ; (iv) fluvial sands have high contents of Magnesium, Chlorine and Sodium which may be enriched in evaporite minerals ; (v) alluvial gravels have high contents of Chromium which may originate from nearby Cr-rich bedrock. Temporal variations can be illustrated by four robust factors : weathering intensity, silicate-bearing mineral abundance, saline / alkaline magnitude and quasi-constant aeolian input. In summary, the bulk-composition of the late Quaternary sediments in this arid context is governed by the nature of the source terrain, weak chemical weathering, authigenic minerals, aeolian sand input, whereas pedogenesis and diagenesis exert only limited influences. Hence, here demonstrates a practical geochemical strategy to discriminate sediment archives and thereafter enhance our ability to offer more intriguing information about the sedimentary processes in the arid central Asia.On the other hand, two parallel cores (ONW I, 6.00 m ; ONW II, 13.35 m) were retrieved from lake Orog Nuur, in the Gobi Desert of Mongolia. Ample evidences reveal a marked moisture pulse during the Marine Isotope Stage 3 ( 36- 24 ka) which might have induced the maximum last glacial expansion in the high elevated Khangai Mountains. A sharp transition of Termination I ( 11 ka) is illuminated by geochemical, palynological, and ostracod data. Lower area of the Orog Nuur catchment was dominated by Artemisia steppe community in the late Pleistocene and altered gradually to Chenopodiaceae desert steppe in the Holocene. The early Holocene is also characterized by relatively humid environment, albeit discordant downcore variability of moisture and thermal signals can be derived between palynological and bulk-geochemical signals. Water body in the Holocene appears to be a distinct alkaline environment which was subjected to frequent allogenic input and disturbance of the late Pleistocene anoxic states.

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