GEOGRAPHY

Studies have found that the modern Yellow River system began to form 1.25 million years ago


Landscape of the middle reaches of the Yellow River canyon with SMX19 core archive courtesy of Lanzhou University

The research team drilled in the Sanmenxia Basin to obtain core archives courtesy of Lanzhou University

Lanzhou University, together with the Institute of Geology of China Earthquake Administration, the First Monitoring Center of China Earthquake Administration, Shimane University of Japan, China University of Geosciences (Wuhan) and other units, carried out environmental drilling and cooperative research in the Sanmenxia Basin Center, and obtained the complete core archive of the history of the Yellow River through Sanmenxia, and through the comparison with the outcrop section at the edge of the basin, it was clear that the first appearance of river sediment at 108 meters of the core was the oldest imprint left by the Yellow River in the Sanmenxia area. Recently, the relevant research results were published in the “Science Bulletin”, which clarified the formation era of the modern Yellow River system, and provided a new perspective for studying the formation and evolution history of the world’s major rivers and the development mode of the water system.

The formation of the “several” character bays and the Sanmenxia flowing into the sea through the east are important symbols of the formation of the modern Yellow River system, but due to the lack of complete sedimentary records of river evolution in the middle reaches of the Yellow River, and the frequent diversion of rivers in the downstream areas, it is not easy to obtain first-hand information, and there are still differences in the current formation era of the modern Yellow River system 150,000 years ago, no later than 880,000 years, no later than 1.2 million years, 1.5-1.6 million years ago, 5 million years ago, and there are also different understandings of the reasons for its formation.

Sanmenxia is the last section of the gorge on the main stream of the Yellow River, which is the throat area connecting the middle and lower reaches of the Yellow River, and occupies a key position in the study of the formation and evolution of the Yellow River system. In the past, Chinese and foreign scientists mainly conducted research on outcrops in the Sanmenxia Basin and surrounding areas, but due to the discontinuity of late Cenozoic strata, the research profiles were often spliced by multiple short sections several kilometers apart, coupled with complex structures, high vegetation coverage, and serious stratigraphic weathering, there were great uncertainties in the sectional connection, sedimentary phase division, and dating, which was an important reason for the existing divergence of understanding.

Under the coordination and deployment of Chen Fahu, academician of the Chinese Academy of Sciences, Professors Wang Xin, Hu Zhenbo, Nie Junsheng, Pan Baotian and other joint cooperative units of the Key Laboratory of Geomorphological Evolution and Cenozoic Environment research team of the Ministry of Education in the Western Region of Lanzhou University jointly carried out research.

Through systematic sedimentology, paleomagnetic dating, source analysis (Sr-Nd isotope & heavy mineral combination), and paleoenvironmental substitution index record (particle size & soluble salts), the team showed that since 1.25 million years ago, river sediments in the Sanmenxia Basin have begun to develop on a large scale, clastic materials in the upstream Ordos land mass have begun to pour in, and the sedimentary environment has undergone a significant transformation from a closed saline-brackish lake environment to an open river environment. Based on the newly developed geomorphological analysis evidence, the series of yellow river terrace evidence published by Pan Baotian’s team, and the marginal sea sediments published in recent years, the research team put forward a new understanding that the modern Yellow River water system began to form 1.25 million years ago, and the accelerated decline of sea level during the global climate transition period in the Middle Pleistocene has an important impact on its formation. (Source: China Science Daily Wen Caifei Faisa)

Related paper information:https://doi.org/10.1016/j.scib.2022.06.003



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