兰州大学机构库 >资源环境学院
Alternative TitleThe paleoenvironmental evolution during the Pliocene-Pleistocene transition recorded by the Gaolanshan Red clay-Loess core in the Lanzhou Basin
Thesis Advisor李吉均 ; 彭廷江
Degree Grantor兰州大学
Place of Conferral兰州
Degree Name硕士
Degree Discipline自然地理学
Keyword上新世-更新世转型 红粘土-黄土 高原隆升 生物标志化合物 碳同位素 温度重建
Abstract上新世-更新世转型是上新世温暖气候向第四纪冰期-间冰期旋回过渡的关键时期,同时也是冰盖开始大规模扩张的重要演化期。与此同时,青藏高原的强烈隆升不仅改变了亚洲季风环流格局,加剧了亚洲内陆干旱化进程,深刻改变了青藏高原及周边地区的地貌格局和生态环境状况。尤其亚洲地区由于青藏高原强烈隆升的影响,在青藏高原周边地区堆积巨厚砾岩,而黄土高原地区则开始堆积上新世红粘土-第四纪风成黄土序列。因此,开展上新世-更新世转型期的生态环境演变历史研究不仅可以加深对青藏高原隆升环境效应的理解,而且能对探讨构造和全球变冷等相互耦合关系提供重要借鉴。兰州盆地位于我国三大自然地理区划的交接部位,同时也位于青藏高原东北边缘,对气候变化和构造活动响应均比较敏感,是探讨构造-气候相互作用的理想区域。本文以兰州盆地皋兰山钻孔底部红粘土-黄土岩芯(265~230 m)为研究对象,在已有黄土地层学和高精度磁性年代学研究基础上,详细开展了生物标志化合物(正构烷烃和微生物膜类脂物)和同位素地球化学(总有机碳和单体碳同位素)多指标测试分析,据此分别重建了兰州盆地上新世-更新世转型期(3~2.2 Ma)的古温度、古水文和古生态演化历史。通过进一步综合对比全球其他海陆记录和区域构造活动历史,尝试探讨了兰州地区上新世-更新世气候转型的可能驱动因素。主要结论如下:1.皋兰山上新世-更新世转型期风成沉积中正构烷烃多以C31为主峰的单峰模式,奇偶优势明显,可能指示草原植被为主的生态特征。在L32和L33典型黄土层正构烷烃呈双鼓包分布,遭受了明显的微生物降解,结合有机碳同位素、粒度和磁化率等推测其均受外源输入影响。2.通过综合对比有机碳同位素和单体碳同位素,发现总有机碳同位素可能受外源输入混合的影响,在重建兰州地区上新世-更新世转型期古生态时需谨慎。基于正构烷烃常规指标和单体碳同位素综合研究表明,皋兰山上新世-更新世转型期古生态整体以C3植被为主,且冰期-间冰期旋回尺度上波动不明显,仅在3 Ma左右发生C4植被快速减少事件。3.通过微生物膜类脂物重建了皋兰山上新世-更新世转型期的古温度、古水文演化。结合古生态历史,推测兰州皋兰山共发生两次重大转变:第一次转变发生在2.8 Ma,沉积相从红粘土转变为黄土,受温度下降影响,C4植被减少,但未发生干旱化;第二次转变发生在2.7~2.6 Ma,温度和降水协同大幅下降,干旱化明显加剧,但生态类型仍以C3植被为主,推测主要受青藏高原快速隆升和北极冰盖扩张的综合影响。
Other AbstractThe Pliocene-Pleistocene transition represents the critical stage from the Pliocene warm climate to the Quaternary glacial-interglacial cycle. The Northern Hemisphere has experienced the onset of ice sheet expansion during this period. Meanwhile, the intensive tectonic uplift of the Tibetan Plateau has not only changed the pattern of the Asian monsoon circulation and resulted in the interior Asian aridification, but also profoundly shaped the geomorphologic pattern and ecological environment of the Tibetan Plateau and its surrounding areas. For example, thick conglomerates have been accumulated around the Tibetan Plateau due to the dramatic uplift of the Qingzang Movement, while the Chinese Loess Plateau began to deposit the continuous Pliocene red clay-Quaternary loess-paleosol sequence. Therefore, the study on the environment evolution during this transition can not only further understand the environmental effects of Tibet uplift, but also provide an important reference for discussing the coupling relationships between tectonic activity and global cooling. The Lanzhou basin, located at the junction of three natural geographical divisions in China and in the northeastern margin of the Tibetan Plateau, is the ideal region to illustrate the interactions between the tectonic activity and climate change.In this study, the continuous red clay-loess sequence (265~230 m) of the Gaolanshan core in the Lanzhou basin were well constrained based on the previous loess stratigraphy and high-resolution paleomagnetic chronology, and detailed analyzed via the integrated biomarker compound (n-alkanes and microbial membrane lipids) and isotope geochemistry (total organic carbon and compound-specific carbon isotopes) methods. So the paleotemperature, paleohydrology and paleoecological evolution during the Pliocene-Pleistocene transition (3~2.2 Ma) in Lanzhou basin were firstly reconstructed. Furthermore, the possible driving mechanism was discussed by comparing the global marine and continental records with regional tectonic activity history. The main conclusions are as follows:1. The n-alkanes in the eolian sequence from Gaolanshan during the Pliocene-Pleistocene transitional period showed a unimodal pattern with C31 as the main peak, which indicated the dominance of grassland vegetation. In the typical loess layers of L32 and L33, n-alkanes were characterized by double bulge, indicating the influence of microbial activities. Combined with the changes in organic carbon isotope, grain size and magnetic susceptibility, we suggested that n-alkanes were affected by exogenous input.2. By the comprehensive comparison of organic carbon isotope and compound specific carbon isotope, we found that organic carbon isotope could be affected by exogenous input. Thus, we point out that caution should be taken in the application of total organic carbon isotopes in reconstructing the paleoecology during the Pliocene-Pleistocene in Lanzhou Basin. Based on the conventional indexes and compound specific carbon isotope of n-alkanes, the paleoecology during the Pliocene to Pleistocene transition in Gaolanshan was dominated by C3 vegetation, which did not show obvious fluctuations on glacial-interglacial scale. It should be noticed that there was a sharp decrease of C4 vegetation during 3 Ma.3. The paleotemperature and paleohydrological evolution during the late Pliocene-Pleistocene transitional period in Gaolanshan were reconstructed by microbial membrane lipid. Integrated paleoecology, paleotemperature, paleohydrological changes, two major events in Gaolanshan were proposed. The first event happened in 2.8 Ma when the sedimentary facies changed from red clay to loess, the C4 vegetation declined due to the decrease of temperature. Meanwhile, the precipitation hardly changed. The second transition occurred from 2.7 to 2.6 Ma, during which the temperature and precipitation decreased synchronously. The vegetation was dominated by C3, which closely linked with the rapid uplift of the Tibet plateau and the expansion of ice volume in the Northern Hemisphere.
Document Type学位论文
First Author AffilicationCollege of Earth Environmental Sciences
Recommended Citation
GB/T 7714
李孟. 兰州皋兰山红粘土-黄土记录的上新世-更新世转型期环境演变[D]. 兰州. 兰州大学,2019.
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