Knowledge Resource Center for Ecological Environment in Arid Area
| 天山北麓金沟河剖面的孢粉记录与中亚干旱化 | |
| 唐自华 | |
| 出版年 | 2010 |
| 学位类型 | 博士 |
| 导师 | 丁仲礼 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 中亚地区作为典型中纬度非地带性内陆干旱区不仅是岩石圈、水圈、大气圈相互作用的结果，而且通过粉尘影响地表的能量平衡和生物地球化学循环，成为地球气候系统的重要动力因素。但是，由于长尺度的、连续的、定年可靠的内陆环境序列的缺乏，迄今为止研究者对亚洲中部干旱环境的起源、发展与动力依然知之甚少。本项研究对天山北麓已有准确生物地层学和磁性地层学年代控制的金沟河剖面进行了系统的孢粉分析，恢复了晚渐新世以来亚洲中部植被演化历史，建立了亚洲中部晚渐新世以来的环境演化序列，并讨论了全球气候、区域构造、海陆分布等因素对亚洲中部干旱环境的贡献。\n孢粉记录表明，~28-23.8Ma，天山北麓主要以森林草原为主；大约在23.8-23.3Ma之间，旱生草本植被逐渐取代森林草原，一直持续到17.3 Ma前后；17.3-16.2 Ma，植被多样性显著增加，孢粉通量显示区域植被仍以草原为主，水分条件较好的地区木本植被恢复；16.2 Ma开始，木本植被减少，至13.5Ma前后，与今类似的荒漠植被形成。\n金沟河的孢粉记录揭示了中亚干旱化持续发展的过程。两次主要的干旱化事件发在23.3Ma和16.2Ma前后。渐新世末的干旱事件是现代亚洲中部干旱状况的最早记录之一，与外围的风尘记录高度一致。中新世气候适宜期中亚干旱状况有所缓解。随后，16.2 Ma开始天山北麓再度逐渐变干，干旱区面积也逐渐向周边扩张，与目前类似的亚洲干旱区格局在中新世末形成。\n比较干旱化进程与全球记录气候记录显示，二者在长期趋势上关系密切，暗示晚新生代降温对中亚干旱化的长期趋势有重要影响；金沟河剖面的颜色、沉积相、沉积速率和岩石磁学的变化与干旱化进程高度相关，表明区域构造，包括天山和青藏高原的抬升，对亚洲中部干旱化事件明显的控制作用，——主要通过阻挡水汽输送、影响大气环流以及通过改变海陆分布增加水汽输送距离来影响亚洲中部的干湿状况。北半球西风带加强对晚新生代亚洲中部的干湿变化影响微弱。 |
| 英文摘要 | Central Asia, as a typical non-zonal arid region, results from interactions of lithosphere, hydrosphere, and atmosphere, and in turn influences energy budget balance and biogeochemical cycle via dust emission, playing as a vital dynamic component of the climate system. To date onset, evolution and mechanism of the mid-latitude arid condition is poorly constrained mainly because continuous, long-term, well-dated records are sparse. We here present a palynological record of the Jingou River section from the northern Tian Shan, which has been well-dated by biomagnetostratigraphy, with aims of development of paleofloral time series and then reconstruction of palaeoenvironment in central Asia. At last impacts of global climate, regional tectonics, and land-sea distribution and other factors on central Asian aridification are discussed.\n The palynological record shows that during ~28-23.8 Ma forest-steppe dominated the northern Tian Shan; during 23.8-23.3 Ma xerophilous herbs with Chenopodiaceae-Artemisia pollen dominance gradually replaced the forest-steppe and continuously developed until ~17.3 Ma. During the globally optimum period 17.3-16.2 Ma pollen diversity increased. Pollen flux shows that steppe vegetation is regionally dominated and tree distributed in humid belt. Later forest taxa decrease and proportion of xerophilous herbs enhanced. Around 13.5 Ma modern-like desert vegetation established in the North Tian Shan and thereinafter dominated.\n The palynological record reveals a gradually increased aridity in central Asia since late Oligocene. Two main drying events occurred at around 23.3 and 16.2 Ma. The latest Oligocene drying is one of the earliest drying records from mid-latitude Asian inland, providing a convincing explanation for the early Miocene eolian deposits in downwind regions, such as the North Pacific and the Chinese Loess Plateau. During the Mid-Miocene climate optimum the arid condition of central Asia were ameliorated. This is followed by a drying trend with a pervasive expansion of arid condition to the surrounding area since 16.2 Ma, and modern pattern of arid Asia is developed at around late period of Late Miocene. \n \n The long-term trend of the floral and vegetation change presented here was well correlated with the global climate evolution, implying the long-term arid trend of central Asia is directed by global cooling during the late Cenozoic. Changes in sediment color (a*), sedimentary facies, sedimentation rate and AMS parameters show a close relationship with the drying events, maybe indicating that regional tectonics including uplift of Tian Shan and growth of Tibet control the drying events in central Asia. We suggested that tectonic processes induced by the Indo-Eurasian collision lead to the drying via alteration of air motion through the tectonic uplift and change in land-sea distribution. Enhanced Northern Hemisphere westerlies during the late Cenozoic have little influence on the drying trend of central Asia on tectonic time scale for its inceasing strenghth with the late Cenozoic cooling contradicts the observerd drying trends. |
| 中文关键词 | 中亚 ; 干旱化 ; 晚新生代 ; 孢粉 ; 金沟河剖面 |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 第四纪地质学 |
| 来源机构 | 中国科学院地质与地球物理研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/286835 |
| 推荐引用方式 GB/T 7714 | 唐自华. 天山北麓金沟河剖面的孢粉记录与中亚干旱化[D]. 中国科学院大学,2010. |
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