兰州大学机构库 >资源环境学院
晚新生代天水盆地孢粉记录的气候变化与青藏高原隆升
Alternative TitleLate Cenozoic climate change and uplift of the Tibetan Plateau—Palynological evidence from the Tianshui Basin
刘佳
Thesis Advisor李吉均
2016-12-08
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name博士
Keyword晚新生代 天水盆地 孢粉 生物和环境演化 高原隆升
Abstract

新生代以来青藏高原隆升改变了亚洲的大气环流模式,引起或加强亚洲季风环流和内陆干旱环境,并可能对全球降温过程以及北半球冰盖的形成产生深刻影响。长期以来,青藏高原隆升的时间和幅度,以及与之相关的亚洲季风及内陆干旱化起源和发展等重大科学问题一直受到研究者的关注。对关键时期高原及周边地区气候事件的研究将有助于我们深入理解亚洲季风、内陆干旱化的形成和演化过程及其驱动机制,甚至能够反演青藏高原的隆升过程和幅度。此外,青藏高原及其邻区是世界上生物多样性热点地区之一,生活大量特有种,其物种形成与该区域重大构造活动和气候变化有关,生物进化方面的研究也能够为我们提供独特的视角来理解高原隆升及其环境效应。

高原东北缘的陇中盆地,地处青藏高原和黄土高原的转换部位,同时处在中国三大自然区的交汇地带,在构造上位于青藏高原东北向伸展的最前缘,对气候和构造响应敏感。天水盆地是陇中盆地的一个次级盆地,晚新生代以来的地层分布广泛、连续,并且富含动植物化石,记录了晚新生代以来的青藏高原隆升过程及其气候效应。孢粉因为外壁质密坚硬,耐腐蚀,产量大,散布广泛,易保存,气候意义明确等优点,是研究古气候的重要代用指标。

本文选择天水盆地有精细磁性地层年代控制的尧店剖面和喇嘛山剖面以及平行的灰泥沟剖面,通过详细的孢粉学研究,重建晚中新世以来盆地植被和气候演化序列,并探讨其驱动机制。同时,综合青藏高原及周边新生代古高程重建结果、具高程意义植物化石资料以及生物演化方面的研究,初步分析青藏高原隆升过程和幅度。获得以下主要结论和认识:

1. 基于天水盆地晚中新世以来的孢粉记录恢复的植被和气候变化过程与邻近地区具有可比性。11.4–7.4Ma期间研究区为温暖湿润的阔叶林景观,后期森林变得开阔;7.4–6.4Ma期间森林-草原发育,气候变干;3.6–3.2Ma期间盆地内部发育干草原;3.2–2.6Ma期间气候温凉湿润,植被垂直分带明显,湖泊周边生长以松、榆、栎和铁杉为主的针阔叶混交林,随海拔增高出现以云杉和冷杉为主的亚高山针叶林,后期(2.74Ma)温度进一步下降,植被带整体下移。

2. 对比亚洲其它地区记录表明内陆干旱化始于~8Ma。孢粉记录的研究区持续变干过程与晚中新世以来全球持续变冷一致,而植被演替序列记录的两次变干过程也与青藏高原在此期间的隆升事件大体吻合。因此,我们认为晚中新世全球变冷和青藏高原隆升共同导致研究区环境变干。晚上新世天水地区降水丰沛,可能原因是高原东北缘地区强烈隆升,在山前地区产生强烈的地形效应,形成地形雨,分布喜湿的亚高山针叶林。同时也可能与晚上新世东亚夏季风的增强有关。

3. 喇嘛山组页岩形成时的环境温暖湿润,湖边发育栎林,随海拔增长依次发育松、铁杉林和云杉、冷杉林。使用共存分析法重建古气候:年平均温度17.1(12.1–22.1)°C,最热月温度24.5(21.0–28.0)°C,最冷月温度4.4(1.8–7.0)°C,气温年较差19(13–25)°C,年平均降水量930(655–1204)mm,最热月降水量220(191–248)mm,最冷月降水量13(7–19)mm。与现代中国西南地区四川省资阳和遂宁的亚热带季风气候类似,冬季比较温暖。同时,从孢粉和粒度研究推测喇嘛山组页岩为年纹层,暗色层形成于冬春季,浅色层形成于夏秋季,进一步说明晚上新世天水地区受季风气候影响。

4. 对高原及周边地区云杉属、冷杉属分布资料的研究表明,高原及周边山地在晚上新世海拔增高,亚高山针叶林普遍分布,进入第四纪温度降低,亚高山针叶林向低海拔地区扩张,高原也进一步隆升,内部发育草甸或荒漠,亚高山针叶林仅存在于高原周边山地。生物分子系统发生学与亲缘地理学研究表明高原及周边地区特有种形成或与其近亲分化时间集中在晚中新世晚期和上新世,并在第四纪期间种内分化加速,这些不同类群生物在分化时间上的巧合可能暗示高原物种进化受到晚中新世-上新世高原隆升的影响。

Other Abstract

The uplift of Tibetan Plateau not only has induced or strengthened the Asian monsoon circulation and aridification of the Asian interior, but also possibly has exerted deep impact both on the process of global cooling and the formation of the northern hemisphere ice sheet for it changed the Asian atmospheric circulation pattern since the Cenozoic. These important scientific problems, such as the time and amplitude of uplift of the Tibetan Plateau, the origin and development of the Asian monsoon and aridification of the Asian interior, has been receiveing attention by researchers. In addition, the Tibetan plateau and its adjacent regions, where live a large number of endemic species and its time of speciation and speciational evolution are related with the regional tectonic activity and climate change, is one of the hotspots of biodiversity in the world. Furthermore, researching on the biological evolution can also provide a unique perspective to understand the uplift of Tibetan Plateau and its environmental effects.

The Longzhong Basin lies at the northeastern Tibetan Plateau, which is geomorphologically located at transition part of the Tibetan Plateau and the Chinese Loess Plateau, tectonically at the Tibetan plateau northeastward extends to the most front place, geographically at the junction of the Tibetan Plateau, the monsoon region and the northweast arid area. Therefore, this place is sensitive to climate change and tectonic response. The Tianshui basin, which is a sub-basin of the Longzhong basin, contains a widely distributed, continuous record of plants and mammalian fossil-rich sedimtens, recording the process of the uplift of Tibetan Plateau and its climate effects. Having lots of advantages such as hard and compact extine, anti-corrosion, large production, widespread and easy to save into fossils, sporopollen became one of the most important proxies to study paleoclimate and geomorphic evolution.

Here we present the detailed palynological records of three sections (Yaodian, Lamashan and Huinigou) from the Tianshui Basin, reconstructing the vegetation sucession and climate change since the late Miocene, and explore its influence mechanism. Integrating with the achievements of Cenozoic paleoaltimetry reconstruction, the flora which have elevational significance and the species evolution researchs in the Tibetan plateau and its adjacent regions, we provide preliminary results on the process and amplitude of the uplift of Tibetan Plateau. The main results and conlusions are listed as follows:

1. The evolution of vegetation and climate change since late Miocene in the Tianshui basin are in well comparison with those from adjacent regions. A temperate forest with a rather humid climate existed in the basin between 11.4 and 10.1 Ma, followed by a temperate open forest environment with a less humid climate between 10.1 and 7.4 Ma, then gave way to an open temperate forest–steppe environment with a relatively arid climate between 7.4 and 6.4 Ma, and arid steppe esisted in the interior basin between 3.6 and 3.2 Ma. After that, a subalpine coniferous forest developed in the basin between 3.2 and 2.6Ma with temperate cool and moist climate.

2. The vegetation succession demonstrates that the aridification of the Asian interior occurred after ~7–8 Ma, which is confirmed by other evidence from Asia. Furthermore, the aridification trend on the northeastern Tibetan Plateau paralleled the global cooling of the late Miocene; the stepwise vegetation succession is consistent with the major uplift of the northeastern Tibetan Plateau during this time. These integrated environmental proxies indicate that the long-term global cooling and the Tibetan Plateau uplift caused the late Miocene aridification of the Asian interior. The late Pliocene humid climate attributed to this phenomenon may be that the strong uplift of NE Tibetan Plateau in the late Pliocene induced intense topography effects in the piedmont zone in Tianshui area, where generated orographic precipitation and hygrophilous subalpine coniferous forest was distributed, as well as the strengthen of the east Asian summer monsoon.

3. The fine laminated sediments in the Lamashan formation formed in warm and humid climatic conditions. Using the method of Coexistence Analysis to reconstruct paleoclimate, seven climate indexes are calculated: the mean annual temperature 17.1(12.1–22.1)°C, the mean temperature of the warmest month 24.5(21.0–28.0)°C, the mean temperature of the coldest month 4.4(1.8–7.0)°C, the difference of temperature between the coldest and warmest months 19(13–25)°C, the mean annual precipitation 930(655–1204)mm, the maximum monthly precipitation 220(191–248)mm and the minimum monthly precipitation 13(7–19)mm. It suggests a warmer and wetter climate than today, similar to that of present-day Ziyang and Suining County, Sichuan Province, southwest China, with subtropical monsoon climate. Meanwhile, from the palynological and grain size evidences, we can speculate that the fine laminated sediment in Lamashan formation is varve (dark laminae forming in winter and spring, pale laminae forming in summer and fall), which can further confirm that a monsoon climate dominate the Tianshui Basin during the late Pliocene.

4. Intergrated the Picea and Abies pollen distribution, we found that subalpine coniferous forest did not widely distributed in the plateau and its adjacent regions untill the late Pliocene, indicating the uplift of the Tibetan Plateau during that time. During the Quaternary, accompany with the further uplift of the Tibetan Plateau and the global cooling, subalpine coniferous forest existed in surrounding mountains of the Tibetan Plateau, and expanded downward area, meadow or desert appeared in internal region of the Tibetan Plateau. The studies from molecular phylogenetics and phylogeography indicated that the formation of endemic species and the differentiation time of its ancestry species in Tibetan plateau and its adjacent regions concentrated on the late Miocene and Pliocene, and intraspecific differentiations were accelerating during the Quaternary. The coincidence about the same differentiation time in diverse species may be implied that the evolution of plateau species was affected by the uplift of Tibetan Plateau during late Miocene-Pliocene.

URL查看原文
Language中文
Document Type学位论文
Identifierhttp://ir.lzu.edu.cn/handle/262010/240050
Collection资源环境学院
Recommended Citation
GB/T 7714
刘佳. 晚新生代天水盆地孢粉记录的气候变化与青藏高原隆升[D]. 兰州. 兰州大学,2016.
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