本文選題：黃土高原 + 侵蝕環(huán)境　； 參考：《中國科學(xué)院研究生院(教育部水土保持與生態(tài)環(huán)境研究中心)》2016年博士論文

【摘要】：黃土高原土壤侵蝕是關(guān)系黃河中下游安全以及黃土高原區(qū)可持續(xù)發(fā)展的重要生態(tài)問題。過去學(xué)者們在黃土高原降雨侵蝕產(chǎn)沙過程、植被水土保持效應(yīng)、土壤侵蝕時空分布特征等方面的研究都取得了豐碩的成果,對現(xiàn)代黃土高原土壤侵蝕問題的防治起到了積極關(guān)鍵的作用。但學(xué)術(shù)界對黃土高原土壤侵蝕問題的由來、地質(zhì)歷史時期的發(fā)展規(guī)律以及土壤侵蝕的驅(qū)動機制和影響因素,還存在許多爭議,主要原因在于缺乏下游的地質(zhì)沉積記錄證據(jù)。本文通過科學(xué)鉆探對黃土高原南部關(guān)中盆地鹵陽湖區(qū)進(jìn)行了巖芯采樣分析,通過古地磁、光釋光等定年手段,對鹵陽湖1號鉆巖芯400 m以上的沉積速率,2號鉆50 m巖芯沉積速率,鹵陽湖東灘的天驕湖人工剖面2.8 m沉積速率進(jìn)行了計算,并通過碳酸鹽、粒度、磁化率等氣候環(huán)境代用指標(biāo)對2號鉆和天驕湖人工剖面進(jìn)行了詳細(xì)的氣候環(huán)境變化分析,主要得出以下幾項重要結(jié)果:(1)鹵陽湖1號鉆巖芯400 m(5.23 Ma)沉積速率計算結(jié)果表明,湖區(qū)沉積速率在2.58 Ma后有明顯上升,與黃土古土壤剖面底界年齡一致。鹵陽湖區(qū)5.23 Ma以來的沉積速率在4.18-3.58 Ma、2.5-1.7 Ma、1.07-0.78 Ma、0.78-0.12 Ma、0.12-0.09Ma、67-63 ka、13-9.8 ka,這7個時期有明顯加快,其中后6個時期與青藏高原自青藏運動(2.58 Ma開始)以來的抬升活動具有明顯的對應(yīng)關(guān)系,說明黃土高原土壤侵蝕周期在長時間尺度上受控于青藏高原的構(gòu)造隆升作用。第四紀(jì)以來鹵陽湖區(qū)沉積速率以0.12 Ma為界可劃分為前后兩個階段,2.58-0.12 Ma期間,鹵陽湖沉積速率變化微弱增加,變化范圍在3-10 cm/ka,0.12 Ma后,沉積速率明顯加大,0.12-0.09Ma間的平均沉積速率是前段時間的近10倍,說明0.12 Ma左右是黃土高原土壤侵蝕環(huán)境演變的重要轉(zhuǎn)折期。(2)鹵陽湖2號鉆50 m巖芯將近15萬年的沉積序列表明,12萬年前后構(gòu)造強烈抬升的同時,也恰好對應(yīng)黃土-古土壤S1階段,屬溫濕氣候期,該階段在鹵陽湖上游地區(qū)侵蝕面分布廣泛,在下游三門峽地區(qū)則發(fā)生了黃河徹底貫通的重大環(huán)境事件。這些證據(jù)說明鹵陽湖區(qū)在12萬年前后的高沉積速率是構(gòu)造強烈抬升、溫濕氣候環(huán)境以及三門峽的徹底貫通三種因素共同作用的結(jié)果。(3)鹵陽湖東灘2.8 m的人工剖面研究結(jié)果表明近三萬年來,鹵陽湖區(qū)湖泊水位經(jīng)歷了低-高-低的變化過程,與該區(qū)末次冰盛期以來的干-濕-干的氣候變化序列一致,表明鹵陽湖區(qū)水位變化主要受控于東亞夏季風(fēng)影響。全新世后期4.6 ka后的干旱氣候造成了鹵陽湖的大面積萎縮,為鹵陽湖的快速消亡創(chuàng)造了條件。在此基礎(chǔ)上,2 ka后圍湖造田,撈硝曬鹽等湖區(qū)周邊人為活動的快速增加,是導(dǎo)致鹵陽湖沉積速率快速上升,退化為鹽堿灘,并逐漸消亡的原因。
[Abstract]:Soil erosion in the Loess Plateau is an important ecological problem related to the safety of the middle and lower reaches of the Yellow River and the sustainable development of the Loess Plateau. In the past, scholars have achieved fruitful results in the process of rainfall erosion and sediment yield, the effect of vegetation soil and water conservation, and the space-time distribution characteristics of soil erosion on the Loess Plateau. It plays an active and key role in the prevention and control of soil erosion in the Loess Plateau. However, there are still many controversies about the origin of soil erosion in the Loess Plateau, the law of development in geological history, the driving mechanism and influencing factors of soil erosion, mainly due to the lack of evidence of geological deposition records in the lower reaches of the Loess Plateau. In this paper, the core sampling and analysis of Hanyang Lake region of Guanzhong Basin in the southern Loess Plateau are carried out through scientific drilling, and the dating methods such as paleomagnetism and photoluminescence are used. The sedimentation rates of the cores above 400 m in Hanyang Lake 1, 50 m in drill 2 and 2.8 m in the artificial section of Tianjiao Lake on the Dongtan of Hanyang Lake are calculated, and the carbonate, granularity, granularity are calculated. In this paper, the climatic and environmental changes of the artificial sections of No. 2 drill and Tianjiao Lake are analyzed by using the climatic and environmental proxy indexes such as magnetic susceptibility. The main results are as follows: 1) the calculation results of the sedimentation rate of the core of Hanyang Lake 1 are as follows: the core of Huiyang Lake 1 is 400 m / m ~ (5.23) Ma), and the results are as follows: The sedimentary rate of the lake area increased obviously after 2.58 Ma, which is consistent with the age of the bottom boundary of the loess paleosol profile. The sedimentation rate since 5.23 Ma in Hanyang Lake area is 4.18-3.58 Ma ~ 2.5-1.7 Ma ~ 1.07-0.78 Ma ~ (0.7) -0.12 Ma ~ 0.12 Ma ~ 0.12-0.09 Ma ~ (67) ~ (63) ka ~ (- 9.8) ka, and the latter six periods are obviously related to the uplift activity of Qinghai-Xizang Plateau since the Qinghai-Xizang Plateau started at 2.58 Ma, and there is a significant correlation between the latter six periods and the uplift activity of Qinghai-Tibet Plateau since the Qinghai-Tibet Plateau started at 2.58 Ma. The results show that the soil erosion period in the Loess Plateau is controlled by the tectonic uplift of the Qinghai-Xizang Plateau on a long time scale. Since the Quaternary period, the sedimentary rate of the Hanyang Lake area has been divided into two stages (0.12 Ma, 2.58-0.12 Ma), and the variation of the deposition rate of the lake has increased slightly, ranging from 3-10 cm / kg to 0.12 Ma. The average deposition rate of 0.12-0.09 Ma is 10 times higher than that of the previous period. It shows that 0.12 Ma is an important turning point of soil erosion environment evolution on the Loess Plateau. It also corresponds to the loess paleosol S1 stage, which belongs to the climate period of temperature and humidity. It is widely distributed in the upper reaches of Hanyang Lake, and a major environmental event of the Yellow River is completely connected in the lower Sanmenxia area. These evidences indicate that the high deposition rate of the lake area around 120,000 years is a strong tectonic uplift. The result of the combined action of three factors, namely, temperature and wet climate environment and the thorough penetration of Sanmenxia, shows that the lake water level in Hanyang Lake area has undergone a process of low to high to low variation in the past 30, 000 years, according to the artificial section of 2. 8 m on the east beach of Hanyang Lake. It is consistent with the dry-wet-dry climate change sequence since the last ice peak in this area, which indicates that the water level change in the Hanyang Lake region is mainly controlled by the East Asian Summer Monsoon (East Asian Summer Monsoon). The arid climate after 4.6 ka in the late Holocene resulted in a large area shrinkage of Hanyang Lake, which created conditions for the rapid extinction of Hanyang Lake. On this basis, the rapid increase of anthropogenic activities around the lake area after 2 ka, such as reclaiming the lake and recovering salt, is the reason why the deposition rate of Hanyang Lake increases rapidly, which degenerates into saline-alkali beach and gradually dies away.
【學(xué)位授予單位】：中國科學(xué)院研究生院(教育部水土保持與生態(tài)環(huán)境研究中心)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：S157.1

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