Low-level River Terraces And Loess Deposits Of Typical Profile From Heiyukou To Zhangjiawan In The Middle Reach Of The Yellow River

River terraces as one of the basic form of fluvial geomorphology, research them not only can recover the evolutionary history of fluvial geomorphology but also extract the tectonic movement and climate change-related information. In the last century, by studying river terraces, researchers were in agreement with the genesis and evolution of Yellow River. But the most studies are mainly concentrated on the oldest terrace while few studies on low-level terraces. Therefore we necessary to conduct in-depth study the low-level terraces of the Yellow River.The thick loess deposits on river terraces of the regional can be used as a carrier of ancient climate change to study, and It’s good for us to a whole understanding of the scientific issues of Tibetan Plateau tectonic uplift and environmental effects from a broader, genetically related areas. The section of Zhangjiawan records climate change since230ka BP, has a great significance to reveal the climate change of the area. Also provide a new field evidence and new avenues of understanding for some controversy or lack of evidence in the region geoscience problems.We selected Heiyukou-Zhangjiawan region as the study area in our work, and proposed the history of Yellow river and genesis of the terraces in study area. Based on palaeomagnetic data and loess-paleosol sequence, the ages of five terraces(T5-T1) along Yellow River around Heiyukou-Zhangjiawan region have been confirmed. The five river terraces were formed about1.24Ma BP、0.609Ma BP、0.245Ma BP。0.128Ma BP and0.01Ma BP, corresponds to the paleosol S14, S5, S2, S1and SO. The paleosol overlying all terraces around Heiyukou-Zhangjiawan region along Yellow River indicate that climate change played an important role in terrace formation. By the linear analysis of the terrace above river and age we find that tectonic uplift and climate change may each have played variable roles in the low-level terraces around Heiyukou-Zhangjiawan zone, tectonic uplift provide a vertical space of cut for the terrace formation, river incision should occur in the glacial to interglacial transition period.We studied the thick loess-paleosol layer deposits on the Zhangjiawan T3terrace. Based on sedimentological analysis of Zhangjiawan section, data processing and integrated analysis of sediments in magnetic susceptibility, grain-size and anisotropy of magnetic susceptibility (AMS), We extracted climate and environment change information in the region since230ka. According to the comparative analysis among particle size climate Multi-proxy and susceptibility age model, combining with the sedimentological characteristics of section, time sequence since the last230ka of Zhangjiawan was established and divided into five stages:the penultimate interglacial (229-194ka BP), the penultimate glaciation (194-130ka BP), the last interglacial (130-73ka BP), Last Glaciation (73-11ka BP) and post-glacial age (11-0ka BP).There are two layers of sand in Zhangjiawan section, reveal that the Maowusu Desert had at least two marked expanded period in the past23million years, indicate two unusually dry period in Shanshan Canyon at the same time, The records in the section of ZhangJiaWan can be compared with the deep sea oxygen isotope record on the time scale of10ka and has recorded the evolution of East Asian Monsoon since230ka BP. The longest axis deflection angle direction (Dec-Kmax) of Anisotropy of magnetic susceptibility (AMS) indicate the paleowind direction near ground mainly to NE-SW in Shanshan gorge and the average wind direction of206。.