The above work mainly focuses on the investigation of physical geography and human geography, and the research on Quaternary geology and ecological environment is still relatively shallow, but it laid the foundation for the subsequent Quaternary geological work. The study of Quaternary geology and ecological environment in this area mainly began in 1980s. Wang Tianzhen (1989) divided the Quaternary strata in the source area of the Yellow River into lower Pleistocene, middle Pleistocene, upper Pleistocene and Holocene according to the data of dating, sporopollen and geomorphology. Bian Chunyu et al. (1990) summarized the types of frozen soil landforms in the source region of the Yellow River and discussed their forming conditions. Wang Shaoling et al. (1990, 1992) reported that buried ice formed in the last glacial period was found in the Quaternary sediments on the north bank of Ering Lake, and the lower Pleistocene series was divided into upper and lower parts. During the geological and mineral survey and highway exploration in the source area of the Yellow River1:200,000, Qinghai Geological Survey Team and Hydrogeological Team studied the Quaternary geology, geomorphology and ancient glacier activities in the source area of the Yellow River (Qinghai Regional Geological Survey Comprehensive Brigade, 1986, 1992,1993; The second regional geological survey brigade of Qinghai Province, 1994), such as the division and comparison of sedimentary genetic types and ages, the study of its distribution scope and law, and the study of Quaternary glacial activity. Due to the limited conditions at that time, although their work needs to be deepened, it is a good start for the later Quaternary research.
Since 1989, some teachers and students in the Department of Geography of Lanzhou University have made many investigations and studies on the ancient glaciers and glacial landforms in the source area of the Yellow River, and put forward that there are ice sheets in the source area of the Yellow River (Zhou Shangzhe et al., 199 1, 1994). It is considered that Bayan Kara had four times in the Pleistocene (the Yellow River Glaciation and the Yellow River Glaciation from the beginning). According to a large number of moraines and boulders preserved in Qingshui River in the south of Bayan Kara and Yematan in the north, it is inferred that the penultimate ice age is a big ice cap or a small ice cap, and the last ice age is the largest, with an area of 80000km2 (Zhou Shangzhe, 1995).
Zheng Benxing et al. (1996) studied the moraine and glacier landforms in the source area of the Yellow River, and considered that there were at least three glacial periods in the Quaternary. According to the geomorphology of ancient ice bucket, final moraine ridge and moraine lake, the bottom of ancient ice bucket was about 4800m higher than that of modern snow line in the last glacial period. In the penultimate ice age, the top planation plane-Chalaping high moraine platform 150 ~ 200m was cut under the wide glacier valley in the north of Bayan Kara. The snow line of this ice age is about 4600 meters above sea level, which is 200 meters lower than that of the last ice age. Glacial boulders in the penultimate ice age are widely distributed in the planation plane and foothills of central Bayan Kara. Most boulders are strongly weathered granite and granodiorite. It is considered that during the penultimate ice age, a large ice sheet centered on Buqingshan, Anima and bayan har was formed, with a distance of about 105km from north to south. Zhou Shangzhe and Zheng Benxing agree on the point that glacier activity reached the maximum range in the penultimate ice age, but the difference is the division of ice stages in the last ice age.
In the upper reaches of the Yellow River, the meandering shape of the river is extremely unusual, which has attracted the attention of geologists and geographers. They think that there may be a river attack. Wang Yunfei et al. (1995) studied the continuous sediments near the RH Konggu Lake in Zoige. The results show that the source erosion of the Yellow River at 38 ~ 35 kBP captured Zoige Lake and enabled the Yellow River to grow. Yang Dayuan et al. (1996) studied the terraces of Guide Basin and Gonghe Basin in the upper reaches of the Yellow River, and found that the terraces in the upstream direction were decreasing. According to the dating, it is considered that Longyang Gorge was cut at 60ka BP, while Tangnai Gorge in the upstream was penetrated at 20ka BP. The cutting time of the rock gorge in the source area of the Yellow River may be later. Li Changan et al. (1998, 1999) studied the landforms and sedimentary basins in the East Kunlun area, and thought that there was a great water system adjustment in the upper reaches of the Yellow River in the Late Quaternary. At about150kBP, Jia Luhe, Nuomuhong River and Golmud River in Qaidam Basin were strongly eroded from the source, and cut in from Buda Mountain in Borhan to capture the east-west direction. Since Holocene, with the uplift of East Kunlun Mountain, the strong headwater erosion in the upper reaches of Jia Luhe pushed Buqingshan River basin southward by 6 ~ 10 km.
From the end of 1990s to the beginning of 20th century, we have done some research on landform evolution and also done some work on Quaternary environmental changes. Zhang Yufang et al. (1995, 1999) studied the Holocene vegetation and climate characteristics in the source region of the Yellow River. Yu Qingwen et al. (1999) restored the late Quaternary vegetation types and paleoclimate characteristics in Tuosuo Lake area based on the sporopollen data. Cheng Jie et al. (200 1a, b, c, 2002b, 2003) studied the frozen soil landform, Quaternary strata and paleoclimate in the source area of the Yellow River, especially a shallow well profile near maduo county. Based on the data of sporopollen, clay minerals and organic carbon, the Holocene vegetation characteristics and paleoclimate characteristics of the source region of the Yellow River were restored, and it was pointed out that the temperature in the source region of the Yellow River was higher than today during the great warm period. Cheng Jie et al., 2006), which has not been mentioned before.
The change of ecological environment in the source area of the Yellow River did not attract people's attention until the end of 1990s. China Academy of Sciences, Qinghai Provincial Department of Land and Resources, Lanzhou University, China Geo University (Beijing) and other units have conducted some research on this (Kang Weixin,1998; Li Laixing et al.,1998; Wei Zhenduo,1998; Ye Chunmei,1998; Li Wanshou et al., 2000; Shen et al., 2000; Zheng Xinmin, 2000; Wang Genxu et al, 2000,2001; Cheng Jie et al, 200 1b, 20065438+0c; ; Sha Zhanjiang et al, 2001; Zhuang Yongcheng et al., 200 1), and think that the ecological environment, land desertification and soil erosion in this area are aggravated, such as the increase of land desertification area, the degradation of grassland, the decline of water conservation ability and the decline of groundwater level. The research history of Quaternary geology, geomorphology and ecological environment in the source area of the Yellow River is summarized in Table 1-3.
Table 1-3 Quaternary geological and environmental research history of the source area of the Yellow River 1-3 Quaternary geological and environmental research history of the source area of the Yellow River.
sequential
In fact, although many people have worked in the source area of the Yellow River, compared with other areas, the study of Quaternary geology and paleoenvironment in the source area of the Yellow River is still very weak, and many problems need further study and a lot of work needs to be done. The main problems in the study of Quaternary geology and paleoenvironment in this area are as follows.
1) The sequence of Quaternary strata is not completely clear and lacks dating data, so a relatively accurate Quaternary stratigraphic system has not been established. This undoubtedly affects the in-depth study of Quaternary geology in this area, and also brings some difficulties to the study of Quaternary ecological environment.
2) There are still different opinions on the division of Quaternary glacial periods in this area, and the opinions on the determination of the penultimate glacial period and the third glacial period are relatively consistent. The main difference is the division of the late Pleistocene ice age, whether it is divided into one stage or two stages. In Europe, some people think that the last ice age started from 1 15kBP or 120kBP (that is, the last ice age was from MIS5 d to MIS2), including the second half of the Yumu Ice Age and the Rhys-Yumu Interglacial Age. The last glacial period can be divided into early Yumu Glacier (1 17 ~ 62ka BP) or early Wichita Glacier and late Yumu Glacier (42 ~ 13ka BP) or late Wichita Glacier (Zubakov et al., 1990), while the last interglacial.
3) Whether the source area of the Yellow River was covered by the "big ice sheet" on the Qinghai-Tibet Plateau in Quaternary: firstly, whether there was a big ice sheet on the Qinghai-Tibet Plateau; Second, if there is a big ice sheet, when did it form? Third, there was a local ice sheet in the source area of the Yellow River, but there was no unified large ice sheet in the Qinghai-Tibet Plateau. Wang (1965), M. Kule (1987, 1988, 199 1), (19 1), Gu However, Shi Yafeng (1994, 1996, 1997), Zheng Benxing (1996) and Zhou Shangzhe (200 1) disagreed with this view, and thought that in the late Pleistocene, the Qinghai-Tibet Plateau If there is a large area of ice sheet on the Qinghai-Tibet Plateau, it is only possible in the early Middle Pleistocene (Shi Yafeng et al., 2000). Liu Dongsheng et al. (1999) used a computer model to simulate the Qinghai-Tibet Plateau ice sheet, and thought that there might be an ice sheet on the Qinghai-Tibet Plateau. It seems that this problem is more complicated, involving the identification of ancient glaciers and its indicative significance.
4) The study of Quaternary eco-environmental changes in the source region of the Yellow River is very weak, except for a few Holocene studies (Zhang Yufang et al.,1999; Yu Qingwen et al.,1999; Cheng Jie et al., 2002), the study of Pleistocene is almost blank. To study the climate and ecological environment changes in Pleistocene, we must first have a good stratigraphic profile. Because the source area of the Yellow River is flat, the relative height difference is small, and the Quaternary outcrop is not good, which is also a reason for the weak research in this field. Therefore, it is necessary to drill holes to obtain an ideal Quaternary stratigraphic profile and study the Pleistocene paleoclimate and environment.
5) The predecessors of Quaternary climate in the source area of the Yellow River have done some work (Wang Shaoling et al.,1992; Zhou Shangzhe et al., 1994,1995; Fang et al.,1998; Cheng Jie et al., 2002b, 2003), but due to the lack of continuous and complete Quaternary stratigraphic section, these studies only involve individual periods and are discontinuous in time, so it is difficult to form a complete system that can reflect the Quaternary climate in the source area of the Yellow River.
6) The formation time and Great Lakes period of two lakes (Yeling Lake and Zhaling Lake) in the source region of the Yellow River. Ering Lake and Zhaling Lake are the two largest lakes in the source area of the Yellow River. When did they form? What is the relationship with the early lakes in the source area of the Yellow River? How are they formed? These problems need to be solved. The Qinghai-Tibet Plateau had a lake expansion period in the late Late Pleistocene (Li, 2000; Zhu Dagang et al., 2004), Is it the same in the source area of the Yellow River? If so, how many times has the lake expanded? Was there a Great Lakes Period in Holocene? Wait a minute. These are issues that many scientists are concerned about.
7) Recently, the research on the ecological environment in the source area of the Yellow River is still very weak, and only a few articles are involved (Wang Genxu et al., 2000; Cheng Jie et al, 200 1b, 20065438+0c; ; Sha Zhanjiang et al, 2001; Zhuang Yongcheng et al, 200 1), but the depth is far from enough. The cause, speed and trend of ecological environment deterioration in this area need more detailed work. Only by understanding these problems can we predict the future trend of ecological environment change, put forward scientific prevention measures and ways, and solve the contradiction between local ecological environment protection and social development.
The solution of the above problems will undoubtedly make a big step forward in the study of Quaternary geological environment in the source area of the Yellow River, which is of great significance to the study of the uplift of the Qinghai-Tibet Plateau and its environmental effects, the evolution of China monsoon, the evolution of landforms between the first and second steps, the development history of glaciers in the Qinghai-Tibet Plateau, and the protection of ecological environment in the source area of the Yellow River. However, some of these problems have been involved by predecessors, and some have been studied, but they have not yet been solved, and some problems have little to do with many doubts and need more detailed work. This book is a study of some of the above problems, providing some new information and gaining some new understanding.