Äolische Sedimente und Monsunschwankungen im Gonghe Becken
During the last decades, the northeastern Tibetan Plateau (Fig. 1) became a key area for the reconstruction of the palaeoclimate evolution in Central Asia. At present the climate is controlled by the interplay of the two subsystems of the Asian summer monsoon, the East Asian summer monsoon and the Indian summer monsoon as well as by the westerlies and the Asian winter monsoon. Variations in these large atmospheric systems have a strong influence on the regional water budget. Palaeoclimate reconstructions are mainly based on proxy interpretation from lake sediments. However, comparison of the different lake records is hampered by varying reservoir effects in the lakes, which is strongly influencing the radiocarbon chronology. Aeolian sediments are widespread on the northeastern Tibetan Plateau and have been proven to be another valuable palaeoclimatic archive in the area. The time of the last aeolian transport can be directly dated by optical stimulated luminescence (OSL) dating.
The Gonghe Basin has a size of ~20.000 km² and is located at a mean altitude of 3.000 m asl (Fig. 2). It is the largest intramontane basin on the northeastern Tibetan Plateau. The formation of the basin started at ~14-6 Ma ago with the uplift of the Ela Shan in the southwest and Qinghai Nan Shan on the northern side. The uplift of the ranges is still continuing. The last major earthquake occurred in 1990 with a magnitude of 6.9. The basin is filled by several hundred meters of Tertiary and Quaternary sediments, basically consisting of fluvial gravels and lacustrine sediment. The Huang He has incised into these sediments up to 500 m.
According to our mapping of the aeolian surface sediments in the Gonghe Basin, loess is mainly preserved at the northern and southern side of the Basin (Fig. 5) whereas sands and active dunes are located in the center. Different wind speeds in different parts of the basin may be a possible explanation, fitting well to the observed sediment distribution. Higher winds transporting coarser grains prevail in the center while the wind speed at the sides of the basin is reduced resulting in absence of coarser grains. However, the occurrence of loess in the central part of the basin below the sands indicates phases of reduced wind speed and probably ceased sand transport. Changing environmental conditions are also documented in different grain-size variations in the loess on the northern and southern sides of the basin, probably combined with an asynchronous timing of the loess deposition. This is supported by the palaeosols on the northern side, which are rare on the southern side.
A new set of 43 OSL ages in combination with previous published samples enabled a detailed reconstruction of the monsoonal history. The Asian summer monsoon increased in strength already from around 15 to 14 ka onwards. However, maximum monsoonal conditions were only reached in the mid-Holocene from 7.5 to 2.5 ka. Since 2.5 ka drier conditions returned in the Gonghe Basin and the movement of the large dune systems increased.
Further information can be found in Stauch et al. (2017).
Impressionen Gonghe Becken
|Laufzeit||05/2013 - 04/2015|
|Förderung||DFG / RWTH Aachen University, Dr. G. Stauch|
|Projektpartner||Prof. Dr. Zhongping Lai – China University of Geosciences, Wuhan|
Das Projekt wurde im Rahmen des Zukunftkonzeptes II - Place to Be - RWTH Lecturer gefördert.
Der RWTH wird hiermit ganz herzlich für die Förderung gedankt.