Quaternary sediment characteristics and paleoclimate implications of deposits in the Three Gorges and Yichang areas of the Yangtze River

摘要

The Three Gorges and Yichang areas of the Yangtze River are close to the eastern edge of the Qinghai-Tibet Plateau. Sediment proxies of paleoclimate trends in these areas are of great significance for the interpretation of the regional climatic impact of the episodic uplift of the Qinghai-Tibet Plateau. We examined the macro-sedimentary characteristics, clay mineralogy and geochemistry of sediments from the fan delta and lake deposits and the two river terraces of early and middle Quaternary age in the Yichang area and from the planation surfaces and the five main river terraces of early to late Quaternary age in the Three Gorges areas. The early and middle Quaternary had a generally warm-wet paleoclimate from 1260 to 300 ka. The regional climate changed to generally drycold conditions during late Quaternary (110-10 ka), that can be correlated to glacial cycles in the Tibetan Plateau. During the late Quaternary, especially after its Gonghe Movement (150 ka) uplift, the Qinghai-Tibet Plateau had a significant impact on regional climate. Comparing the formation age and source direction of the Wushan loess in the Three Gorge with loess in the western Sichuan (the Ganzi loess), in the Loess Plateau and distributing in the middle and lower reaches of the Yangtze River (the Xiashu loess), it can be found that coupling of the Kun-Huang Movement of the Qinghai-Tibet Plateau occurred at 1100-600 ka and Mid-Pleistocene Transition and global cooling resulted in the sharp increase of East Asian winter monsoon and plateau monsoon, forming the western Sichuan loess and Xiashu loess. The Gonghe movement (150 ka) of the Plateau once again enhanced the plateau monsoon and blocked the Indian summer monsoon moving north-eastward. As a result, the cold-dry climate appeared in the Sichuan Basin and the Three Gorges area, resulting in the deposition of loess from the Zoige Basin to Wushan area. (C) 2019 Elsevier B.V. All rights reserved.