海洋地质与环境重点实验室知识库

现今在南半球西风带的驱动下，南极绕极流在南大洋绕南极洲顺时针环形流动，构成了全球温盐环流的重要一环，进而深刻影响着大气与海洋之间的热量、动量与碳交换。但在新生代之初，该流系并不存在，它的诞生离不开渐新世-中新世的板块构造运动，其中最为重要的便是德雷克海峡与塔斯马尼亚海水通道的扩张和加深，而上述构造活动不可避免地导致了印度洋北侧的印度尼西亚和特提斯这两个海水通道的收缩变浅以及西太平洋暖池的形成，并伴随着南极大陆的冰封和澳大利亚大陆的干涸，全球气候也从新生代之初的暖室向冰室过渡。

将古论今，重建上述关键气候转折期的构造、冰盖、海洋和大气耦合演化历史，有助于我们更好地认知未来气候变暖趋势下的全球变化，而中纬度东印度洋是开展这方面研究的理想靶区。2017年国际大洋发现计划（International Ocean Discovery Program, IODP） 369航次在澳大利亚西南岸外的曼达岬海盆钻取了晚白垩世以来的、总体连续的高质量长深海沉积物岩芯，更是为上述研究工作提供了良好的载体与契机。

本论文以渐新世-中新世U1516站位沉积物为研究对象，进行了沉积学、地球化学、古气候学和古海洋学综合研究。首先，本论文基于浮游有孔虫混合种的Sr同位素组成，并结合底栖有孔虫的氧、碳同位素组成对该站位现有年龄框架予以优化，进一步约束了旧年龄框架中的两期沉积间断（~12-22 Ma 和~23-27 Ma），优化后的年龄框架在中中新世、中新世初期和晚渐新世存在三处沉积间断，时间分别为12.8-16.7 Ma、22.4-23.1 Ma和24.8-26.9 Ma。

本研究对沉积物碎屑态组分进行了物质堆积速率，粒度，常、微量元素组成，粘土矿物组成与Sr-Nd同位素组成的综合性测试分析，重建了渐新世-中新世曼达岬海盆沉积物源-汇过程及物源区的气候演化历史。结果显示，所研究沉积物主要来自澳大利亚西南部，在17-34 Ma时气候干旱，物源区局限于利文地块；在5-13 Ma时降水增加，物源区向澳大利亚内陆扩张。本研究还发现U1516站位的风尘指标（Zr/Al和砂级组分通量）及大陆风化指标（CIA和高岭石/蒙脱石）的变化与南大洋表层海水温度的变化同步，表明南极冰盖通过改变南半球西风带的位置和强度，进而深刻影响了中纬度东印度洋的气候演化。

本研究基于浮游有孔虫混合种的钕同位素组成和有机地球化学的测试分析，重建了渐新世-中新世中纬度东印度洋的深水洋流演化和海洋环境演化历史。结果表明，在17-34 Ma时该地区的深水εNd值与南大西洋及印度洋中部的深水εNd的演化趋势一致；但在5-13 Ma时，南极冰盖的扩张和南极底层水输出的增加促进了印度洋环流与南极绕极流的流动，致使研究区与南大西洋及印度洋中部的深水εNd值的演化出现差异，到了中新世晚期，研究区的深水主要受到富氧的绕极流深水的影响，此外前人研究表明15 Ma之后南大洋的海洋极锋更加显著，海水活动性的增加促进了研究区的海洋生产力，改善了研究区深水的氧化还原条件，但也限制了有机碳的埋藏。

本研究首次重建了渐新世-中新世中纬度东印度洋的深部环流与气候演化历史，探究了地球从暖室向冰室过渡过程中，中纬度东印度洋地区的构造-冰盖-洋流-气候间的耦合过程，尤其是中中新世大陆冰盖在南极洲的稳定发育和向海延伸（海冰），深刻影响了研究区甚至是全球的海洋和大气循环，这为人类理解未来地球表层系统如何响应气候冷暖变化和南极冰盖的生长和消融提供了重要的历史范本。

Currently, the Antarctic Circumpolar Current driven by the westerlies of Southern Hemisphere flows clockwise around Antarctica in the Southern Ocean. It is an important part of the global thermohaline circulation, profoundly influencing the exchange of heat, momentum, and carbon between the atmosphere and the ocean. However, at the beginning of the Cenozoic, this current system did not exist. Its emergence is closely related to plate tectonic movements during the Oligocene-Miocene, especially the deepening of the Drake Passage and the Tasmanian Seaway. These tectonic activities above inevitably led to the contraction and shallowing of the Indonesian and Tethys seaways on the north side of the Indian Ocean, as well as the formation of the western Pacific warm pool, accompanied by the glaciation of Antarctica and the aridification of the Australian continent, and change the global climate from a greenhouse to an icehouse state.
Examining the past to understand the present, and reconstructing the coupled evolutionary history of tectonics, oceans, atmosphere, and ice sheets during these crucial climate transitions, helps us better understand global changes under the trend of future climate warming. The mid-latitude eastern Indian Ocean serves as an ideal target area for such research. The International Ocean Discovery Program Expedition 369 in 2017 drilled high-quality, overall continuous deep-sea sediment cores from the Mentelle Basin offshore southwest Australia, providing an excellent opportunity for researching the topics above.
This study conducts comprehensive studies of sedimentology, geochemistry, paleoclimatology, and paleoceanography on the Oligocene-Miocene sediments from Site U1516. First, based on the Sr isotopic composition of mixed-species planktonic foraminifera, and combined with the oxygen and carbon isotopic composition of benthic foraminifera, the existing age model of the site was optimized. This further constrained two periods of sedimentation hiatuses (approximately 12-22 Ma and 23-27 Ma) in the old age model. According to the optimized age model there are three sedimentation hiatuses in the mid-Miocene, early Miocene, and late Oligocene, occurring at 12.8-16.7 Ma, 22.4-23.1 Ma, and 24.8-26.9 Ma, respectively.
The study conducts comprehensive tests and analyses of mass accumulation rate, grain size, major and trace element compositions, clay mineral compositions and strontium-neodymium (Sr-Nd) isotope compositions on clastic component of sediment, reconstructing the sediment source-to-sink processes and climate evolution history of study area during Oligocene and Miocene. Results indicate that the primary sediment provenance was southwestern Australia, with a limited extent during 17-34 Ma due to arid climatic conditions, expanding inland during 5-13 Ma with increased precipitation. Additionally, the study reveals synchrony between the dust proxy indicators (Zr/Al and sand flux) and continental weathering indicators (CIA and kaolinite/smectite ratio) at the U1516 site and changes in sea surface temperatures in the Southern Ocean, demonstrating the profound impact of the Antarctic ice sheets on the climate evolution of the study area by altering the location and strength of Southern Hemisphere westerly winds.
This study reconstructed the evolution history of deep-water ocean currents and marine environmental changes in the mid-latitude East Indian Ocean from the Oligocene to the Miocene, based on the testing and analysis of neodymium isotopic composition of mixed species of planktonic foraminifera and organic geochemistry. The results indicate that during 17-34 Ma, the deep-water εNd values in this region evolved similarly to those in the South Atlantic and central Indian Ocean. However, from 5 to 13 Ma, the expansion of the Antarctic ice sheet and increased outflow of Antarctic Bottom Water promoted the circulation of the Indian Ocean and the Antarctic Circumpolar Current, leading to differences in the evolution of deep-water εNd values between the study area and the South Atlantic and central Indian Ocean. By the late Miocene, deep-water circulation in the study area was primarily influenced by oxygen-rich Circumpolar Deep Water. Additionally, previous studies suggest that after 15 Ma, the oceanic polar front in the Southern Ocean became more prominent, increasing oceanic productivity in the study area and improving the redox conditions of deep water. However, it also limited organic carbon burial.
This study reconstructs for the first time the evolution of deep-water circulation and climate in the mid-latitude eastern Indian Ocean during Oligocene and Miocene, exploring the coupled processes of tectonics, ice sheets, ocean currents, and climate in this region during the transition from a greenhouse to an icehouse Earth. The expansion of the continental ice sheets in Antarctica and the development of sea ice from the late Middle Miocene profoundly influenced oceanic and atmospheric circulation not only in the study area but also globally, providing an important historical template for understanding how the Earth's surface system responds to climate variations and the growth and retreat of the Antarctic ice sheets in the future.

第1章 绪论 1

1.1 选题背景与研究意义 1

1.2 渐新世-中新世全球气候与构造演化 3

1.2.1 渐新世 3

1.2.2 中新世 5

1.3 中纬度东印度洋深部环流与古气候研究 8

1.4 研究目标与技术路线 9

第2章 区域概况 13

2.1 地质概况 13

2.1.1 曼达岬海盆 13

2.1.2 西南澳大利亚 14

2.2 构造演化 15

2.3 洋流分布与水团特征 19

2.3.1 表层与次表层洋流系统 19

2.3.2 南极底层水 20

2.3.3 32°S印度洋洋流剖面上的水团分布 22

2.4 西南澳大利亚的古地貌演化 24

2.4.1 陆地排水系统 24

2.4.2 风化壳 25

2.5 西南澳大利亚的气候演化 25

第3章 研究材料与方法 29

3.1 研究材料 29

3.2 研究方法 31

3.2.1 物质堆积速率 31

3.2.2 粒度 31

3.2.3 粘土矿物分析 32

3.2.4 常、微量元素组成分析 33

3.2.5 底栖有孔虫的氧、碳同位素组成分析 34

3.2.6 浮游有孔虫的锶、钕同位素组成分析 35

3.2.7 沉积物的锶、钕同位素组成分析 37

3.2.8 有机地球化学分析 37

第4章 年龄框架 39

4.1 航次报告中的年龄框架介绍 39

4.2 利用海水锶同位素进行地层对比 40

4.3 与航次报告中的年龄框架的对比 49

4.4 区域-全球氧、碳、锶同位素对比 51

4.5 小结 51

第5章 曼达岬海盆沉积演化 53

5.1 矿物学和沉积学记录 53

5.1.1 物质堆积速率 53

5.1.2 粒度分布 54

5.1.3 粘土矿物组成 54

5.2 沉积地球化学记录 55

5.2.1 常量元素组成 55

5.2.2 微量元素组成 56

5.2.3 沉积物Sr-Nd同位素组成 61

5.3 物源识别 61

5.3.1 潜在物源分析 61

5.3.2 火山物质识别 64

5.3.3 沉积物Sr-Nd同位素组成 65

5.3.4 稀土元素组成 68

5.3.5 粘土矿物组成 73

5.4 源-汇过程与古气候意义 75

5.4.1 渐新世-早中新世 75

5.4.2 中中新世-晚中新世 78

5.5 小结 79

第6章 海洋环境演化 81

6.1 浮游有孔虫的钕同位素组成 81

6.2 有机地球化学记录 81

6.3 深部环流演化 82

6.3.1 渐新世-早中新世 85

6.3.2 中中新世-晚中新世 87

6.4 海洋环境演化 88

6.5 研究区气候-海洋-冰盖的耦合变化 93

6.6 小结 95

第7章 总结与展望 97

7.1 总结与创新点 97

7.2 展望 98

参考文献 99

致谢 117

作者简历及攻读学位期间发表的学术论文与其他相关学术成果 119