Knowledge Resource Center for Ecological Environment in Arid Area
| 晚新生代以来中国西北植被演化及反映的干旱化过程 | |
| 其他题名 | Aridification in northwestern China since the late Cenozoic evidenced by the vegetation change |
| 祝淑雅 | |
| 出版年 | 2016 |
| 学位类型 | 硕士 |
| 导师 | 吴海斌 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 亚洲内陆干旱化是与我国西部人类生存环境和社会可持续发展联系紧密的重大科学问题，其起始时间、演变过程及驱动机制是新生代北半球环境演化的研究热点之一，涉及全球变冷和青藏高原隆起等一系列重大科学问题。过去几十年，尽管已有研究取得了亚洲内陆干旱化起源和演化历史的框架性认识，但是由于不同区域、不同沉积记录所反应的干旱化过程可能存在差异，对亚洲内陆干旱化起源、演化及机制还存在很多争议。本文系统整理了晚新生代以来具详细定年的30条孢粉序列，利用生物群区化方法，定量化重建了晚新生代以来每百万时段我国植被的时空演化；并利用现代类比法，定量化重建了晚新生代以来我国内陆（准噶尔盆地和青藏高原北缘）的降水变化序列；通过内陆地区的降水变化、森林覆盖度（Landscape Openness）和草本百分含量变化，揭示了晚新生代以来我国内陆干旱环境的演化过程，并探讨其可能的驱动机制。主要得到以下几点认识：（1）在植被演化方面，~36-28Ma，我国主要为森林植被类型，其中在青藏高原和西北地区也主要以森林植被为主；~28-24Ma，出现荒漠、草原植被，且分布于青藏高原及西北地区，24-18Ma，森林植被减少，荒漠、草原增多，并扩张至黄土高原，18-8Ma，荒漠、草原分布未明显扩张，8Ma以来森林植被减少，荒漠、草原增多，特别是3Ma以来，青藏高原、黄土高原和西北地区大部分森林植被都转变为荒漠、草原植被。（2）在古气候定量化方面，新生代以来，西北干旱区年均降水和有效湿度呈逐渐减少的趋势，其中青藏高原北缘在~52-18Ma，年均降水量约为800-1000mm，~14Ma开始降水量逐步减少至200mm左右，与现今水平相当；准噶尔盆地在~36-33Ma，降水约为600-1000mm，~30-24Ma减少至400-600mm，比现今增多了100-400mm，~24Ma进一步减少至200-400mm，与现今基本相当，甚至低于现今降水量。（3）在干旱化及机制方面，~52-24Ma气候相对湿润；~24Ma 西北地区出现干旱环境，~24-14Ma，干旱化缓慢增强，其中在~18-14Ma干旱程度稍有减弱；~14-8Ma，干旱化进一步发展，~8Ma以来，干旱程度显著增强。我们认为我国内陆~24Ma出现的干旱环境可能与青藏高原隆升及副特提斯海的退缩有关，之后干旱化过程受全球变冷影响逐步加强，~8Ma以来我国内陆的急剧干旱化可能与北半球高纬变冷的关系更为密切。 |
| 英文摘要 | The aridification in the Asian interior is one of the key climate events in the Cenozoic. Over the past score years, although numerous studies from separated locations within the continental interior obtain the fundamental framework for the aridification, discrepancy exists among various records from different areas, and the history of the aridification is still open to debate.Here we systematically collected 30 palynological sequences with detailed age controls in china, and used the biomization method to reconstruct the vegetation changes in northwestern China during the late Cenozoic. Meanwhile, we reconstructed the mean annual precipitation change within northwestern China by the method of Modern Analog Analysis. And based on the changes of the vegetation and the annual precipitation, the evolutionary history of aridification in northwestern China during the late Cenozoic was obtained. The main conclusions are as following:(1) The vegetation: China was occupied mainly by forest from ~36-28Ma, as well as in Tibetan Plateau and northwestern China. However, steppe started to expand during ~28 and 24Ma, subsequently, the forest cover declined and the percent of steppe and deserts type increased during the interval from ~24-18Ma. Moreover, most of northwestern China was stabilized with steppe or deserts during ~18-8Ma, whereas, the steppe or deserts was significantly increased since ~8Ma, even most forests was replaced by steppe and deserts especially from ~3Ma.(2) The evolution of mean annual precipitation: The precipitation has gradually reduced in northwestern China during the late Cenozoic. In the north rim of Tibetan Plateau, the mean annual precipitation was about 800-1000mm from ~52-18Ma and declined to about 200mm since ~14Ma, which was similar to modern value. In addition, the mean annual precipitation was about 600-1000mm during ~36-33Ma in Junggar Basin, and declined to about 400-600mm within ~30-24Ma, which still increased about 100-400mm compare to modern value. Whereas, the mean annual precipitation further reduced to 200-400mm since ~24Ma, which is similar or even below to today.(3) The evolutionary history of aridification: China witnessed a relatively humid climatic during ~52-24Ma. However, aridification was appeared in northwestern China since ~24Ma, and aridity was slowly increased between ~24-14Ma, and gradually enhanced during ~14-8Ma, finally, significantly increased since ~8Ma. We attribute the early stepwise aridification to the retreat of the Paratethys Sea and to the uplift of Tibetan Plateau, and the subsequent gradual aridification trends to the ongoing late Cenozoic global cooling. The significant aridification since ~8Ma may be linked with the enhanced cooling in the northern high latitudes. |
| 中文关键词 | 植被演化 ; 降水定量化 ; 干旱化 ; 晚新生代 ; 西北地区 |
| 英文关键词 | vegetation evolution mean annual precipitation aridification Late Cenozoic northwestern China |
| 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/2XILL650/287669 |
| 推荐引用方式 GB/T 7714 | 祝淑雅. 晚新生代以来中国西北植被演化及反映的干旱化过程[D]. 中国科学院大学,2016. |
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