粒度和磁化率反映的中晚全新世以来玛曲高原的沙漠化演化
发布时间：2018-09-12 18:51
【摘要】：玛曲高原位于青藏高原东端,深受高原气候和东部季风气候的影响,广泛存在着风成沉积物,因此较完整地保存了黄土-古土壤-古风成砂的沉积序列,加之其处于黄土高原和青藏高原的过渡地带,气候环境变化更为敏感。玛曲高原现代沙漠化是在地质历史的基础上一个古砂翻新的过程,本文在玛曲高原东部选取了典型的黄土-古土壤-古风成砂沉积序列OL剖面和MO剖面作为研究对象,在高密度采样和14C定年的基础上,对两个剖面的沉积相、年代、磁化率、有机质、粒度及其参数等气候代用指标进行对比分析,借鉴前人对青藏高原全新世已取得的研究成果基础之上,与其它典型区域进行对比分析,以便填补玛曲高原地质时期沙漠化过程研究的空白,从而探讨气候变化和风沙活动的关系,此研究对丰富玛曲高原古环境及古气候变化、沙漠化形成演化等方面理论具有重要意义,可为现代沙漠化防治提供理论依据和实践指导。研究结果表明:(1)玛曲高原中晚全新世以来气候变化呈现冷干-温湿-凉干的变化趋势,风沙活动经历了强-弱-较强的演变。(2)古土壤发育时期气候温湿,古风成砂层气候相对冷干,黄土沉积时期气候由温湿向冷干过渡。(3)玛曲高原中晚全新世以来的风沙活动主要经历了以下四个阶段:1)4.6ka B.P.以前,气候以冷干为主,冬季风较强盛,风沙活动强,沙漠化程度加快;2)4.6~4.3 ka B.P.为气候凉润期,冬季风较弱,风沙活动较上一时期弱,沙漠化程度弱;3)4.3~0.3 ka B.P.为气候温湿期,夏季风较强,风沙活动弱,沙漠化程度很弱,这一时期可分为三个小阶段,即a阶段(4.3~3.6 ka B.P.)为气候由凉润向温湿过渡期,风沙活动由强变弱,发育了较弱的古土壤;b阶段(3.6~3.5 ka B.P.)为气候凉润期,风沙活动较a阶段强,沉积了黄土;c阶段(3.5~0.3 ka B.P.)为气候温湿期,夏季风较强,风沙活动弱,发育了较厚的古土壤;4)0.3ka B.P.为气候凉干期,冬季风较弱,风沙活动较弱,沙漠化程度较弱。(4)中晚全新世以来玛曲高原气候变化遵循“冷干强风-温湿弱风”的变化模式。通过对比分析发现玛曲高原中晚全新世以来的气候变化与青藏高原东北部乃至全球的气候变化都具有同步性。气候代用指标反映了玛曲高原中晚全新世以来分别在3.57 ka B.P.、3.47 ka B.P.、2.90 ka B.P.、2.50 ka B.P.、2.03 ka B.P.、1.84 ka B.P.、1.57 ka B.P.、1.30 ka B.P.、0.98 ka B.P.、0.80 ka B.P.、0.62 ka B.P.左右发生了11次较大的冷事件。其中3.57 ka B.P.与青海湖周边地区约3.5 ka B.P.以凉干气候为主、风沙活动增强相一致;3.47 ka B.P.、2.90 ka B.P.、2.50 ka B.P.的冷事件与3.37 ka B.P.、2.96 ka B.P.、2.49 ka B.P.发生在青海湖周边地区的强风沙活动相对应;2.96 ka B.P.的冷事件也与北大西洋在3.0 ka B.P.的寒冷事件具有很高的一致性;1.57 ka B.P.的气候变冷与甘青毗邻草原地区1.5 ka B.P.气候冷干对应良好;1.30 ka B.P.、0.80 ka B.P.和0.62 ka B.P.的冷事件与青藏高原东北部共和盆地在1.40 ka B.P.左右、0.8~0.5 ka B.P.处于寒冷阶段相一致。
[Abstract]:The Maqu Plateau is located in the eastern end of the Qinghai-Tibet Plateau. It is deeply influenced by the plateau climate and the eastern monsoon climate. There are widely aeolian sediments. Therefore, the depositional sequence of loess-palaeosol-aeolian sand has been preserved relatively intact. In addition, the Maqu Plateau is in the transition zone between the Loess Plateau and the Qinghai-Tibet Plateau. Desertification is a process of retrofitting ancient sand on the basis of geological history. In this paper, OL and MO sections of typical loess-paleosol-aeolian sand sedimentary sequences are selected as the research objects in the eastern part of Maqu plateau. On the basis of high-density sampling and 14C dating, sedimentary facies, age, magnetic susceptibility, organic matter, grain size and their distribution in the two sections are studied. In order to fill in the blank of the study on the desertification process in the geological period of the Maqu plateau and to explore the relationship between climate change and aeolian sand activity, this study enriches the Maqu plateau by comparing and analyzing the climate substitution indexes such as parameters and other climate substitution indexes, drawing lessons from the research achievements of predecessors on the Holocene of the Qinghai-Tibet Plateau and other typical regions. The results show that: (1) Since the middle and late Holocene, the climate change in the Maqu Plateau has shown a trend of cold-dry, warm-humid, cool-dry, and the aeolian sand activity has experienced a strong-weak-strong trend. (3) Sandstorm activities in the Maqu Plateau since the Middle and Late Holocene have mainly undergone the following four stages: (1) before 4.6 Ka B.P., the climate was mainly cold and dry, with strong winter wind, strong aeolian sand activity and desertification. 2) 4.6-4.3 Ka B.P. is a cool and humid period with weak winter monsoon, weak aeolian sand activity and weak desertification degree; 3) 4.3-0.3 Ka B.P. is a warm and humid period with strong summer monsoon, weak aeolian sand activity and weak desertification degree. The period can be divided into three small stages, i.e. stage a (4.3-3.6 Ka B.P.) is a transition from cool to warm and humid climate. During the transitional period, the aeolian sand activity changed from strong to weak and developed weak paleosols; stage B (3.6-3.5 Ka B.P.) was a cool and humid period, and aeolian sand activity was stronger than stage a, thus depositing loess; stage C (3.5-0.3 Ka B.P.) was a warm and humid period with strong summer monsoon and weak aeolian sand activity, and developed thick paleosols; and stage 4) 0.3 Ka B.P. was a cool and dry period with weak winter wind and weak wind. The climate change of the Maqu Plateau follows the pattern of "cold-dry strong wind-warm-humid weak wind" since the Middle-Late Holocene. The climate change of the Maqu Plateau since the Middle-Late Holocene is synchronous with the climate change in the northeast of the Qinghai-Tibet Plateau and the whole world. It reflects 11 major cold events since the middle and late Holocene in the Maqu Plateau, including 3.57 Ka B.P., 3.47 Ka B.P., 2.90 Ka B.P., 2.50 Ka B.P., 2.03 Ka B.P., 1.84 Ka B.P., 1.57 Ka B.P., 1.30 Ka B.P., 0.98 Ka B.P., 0.80 Ka B.P., 0.62 Ka B.P., 3.57 Ka B.P. and 3.5 Ka B.P. around the Qinghai Lake. The cold events of 3.47 Ka B.P., 2.90 Ka B.P., 2.50 Ka B.P. correspond to the strong wind and sand activities of 3.37 Ka B.P., 2.96 Ka B.P., 2.49 Ka B.P. in the area around Qinghai Lake; the cold events of 2.96 Ka B.P. correspond to the cold events of 3.0 Ka B.P. in the North Atlantic Ocean. The cold events of 1.30 Ka B.P., 0.80 Ka B.P. and 0.62 Ka B.P. coincided with the cold events of 1.40 Ka B.P., 0.8 Ka B.P. and 0.5 Ka B.P. in the Gonghe Basin in the northeastern Qinghai-Tibet Plateau.
【学位授予单位】：西北师范大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P534.632;P931.3
本文编号：2239919
[Abstract]:The Maqu Plateau is located in the eastern end of the Qinghai-Tibet Plateau. It is deeply influenced by the plateau climate and the eastern monsoon climate. There are widely aeolian sediments. Therefore, the depositional sequence of loess-palaeosol-aeolian sand has been preserved relatively intact. In addition, the Maqu Plateau is in the transition zone between the Loess Plateau and the Qinghai-Tibet Plateau. Desertification is a process of retrofitting ancient sand on the basis of geological history. In this paper, OL and MO sections of typical loess-paleosol-aeolian sand sedimentary sequences are selected as the research objects in the eastern part of Maqu plateau. On the basis of high-density sampling and 14C dating, sedimentary facies, age, magnetic susceptibility, organic matter, grain size and their distribution in the two sections are studied. In order to fill in the blank of the study on the desertification process in the geological period of the Maqu plateau and to explore the relationship between climate change and aeolian sand activity, this study enriches the Maqu plateau by comparing and analyzing the climate substitution indexes such as parameters and other climate substitution indexes, drawing lessons from the research achievements of predecessors on the Holocene of the Qinghai-Tibet Plateau and other typical regions. The results show that: (1) Since the middle and late Holocene, the climate change in the Maqu Plateau has shown a trend of cold-dry, warm-humid, cool-dry, and the aeolian sand activity has experienced a strong-weak-strong trend. (3) Sandstorm activities in the Maqu Plateau since the Middle and Late Holocene have mainly undergone the following four stages: (1) before 4.6 Ka B.P., the climate was mainly cold and dry, with strong winter wind, strong aeolian sand activity and desertification. 2) 4.6-4.3 Ka B.P. is a cool and humid period with weak winter monsoon, weak aeolian sand activity and weak desertification degree; 3) 4.3-0.3 Ka B.P. is a warm and humid period with strong summer monsoon, weak aeolian sand activity and weak desertification degree. The period can be divided into three small stages, i.e. stage a (4.3-3.6 Ka B.P.) is a transition from cool to warm and humid climate. During the transitional period, the aeolian sand activity changed from strong to weak and developed weak paleosols; stage B (3.6-3.5 Ka B.P.) was a cool and humid period, and aeolian sand activity was stronger than stage a, thus depositing loess; stage C (3.5-0.3 Ka B.P.) was a warm and humid period with strong summer monsoon and weak aeolian sand activity, and developed thick paleosols; and stage 4) 0.3 Ka B.P. was a cool and dry period with weak winter wind and weak wind. The climate change of the Maqu Plateau follows the pattern of "cold-dry strong wind-warm-humid weak wind" since the Middle-Late Holocene. The climate change of the Maqu Plateau since the Middle-Late Holocene is synchronous with the climate change in the northeast of the Qinghai-Tibet Plateau and the whole world. It reflects 11 major cold events since the middle and late Holocene in the Maqu Plateau, including 3.57 Ka B.P., 3.47 Ka B.P., 2.90 Ka B.P., 2.50 Ka B.P., 2.03 Ka B.P., 1.84 Ka B.P., 1.57 Ka B.P., 1.30 Ka B.P., 0.98 Ka B.P., 0.80 Ka B.P., 0.62 Ka B.P., 3.57 Ka B.P. and 3.5 Ka B.P. around the Qinghai Lake. The cold events of 3.47 Ka B.P., 2.90 Ka B.P., 2.50 Ka B.P. correspond to the strong wind and sand activities of 3.37 Ka B.P., 2.96 Ka B.P., 2.49 Ka B.P. in the area around Qinghai Lake; the cold events of 2.96 Ka B.P. correspond to the cold events of 3.0 Ka B.P. in the North Atlantic Ocean. The cold events of 1.30 Ka B.P., 0.80 Ka B.P. and 0.62 Ka B.P. coincided with the cold events of 1.40 Ka B.P., 0.8 Ka B.P. and 0.5 Ka B.P. in the Gonghe Basin in the northeastern Qinghai-Tibet Plateau.
【学位授予单位】：西北师范大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P534.632;P931.3
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相关期刊论文 前1条
1 吕厚远,韩家懋,吴乃琴,郭正堂;中国现代土壤磁化率分析及其古气候意义[J];中国科学(B辑 化学 生命科学 地学);1994年12期
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