海洋地质与环境重点实验室知识库

本论文通过对东南印度洋国际大洋发现计划369航次U1513和U1516站位沉积物碎屑态组分的物质堆积速率、粒度和元素地球化学以及全样沉积物的有机地球化学组成方面综合性分析，示踪了白垩纪和古近纪时期构造时间尺度上这些站位所沉积碎屑态组分的物质来源，并重建了此时澳大利亚西南部大陆的化学风化和古气候演化历史及其主要控制因素；特别是系统揭示了白垩纪大洋缺氧事件OAE 1d期间南半球高纬度印度洋的陆源碎屑物质输入、有机质来源及其深海埋藏、海表生物生产力水平和海底氧化-还原状态等古环境关键因素之间的耦合关系，进而对于该事件的具体成因机制有了新的认识。

物源分析结果表明：白垩纪阿尔布期-塞诺曼期（102.8-99.4 Ma）和晚始新世-渐新世（34.1-25.2 Ma）时期东南印度洋曼达岬盆地沉积物碎屑态组分的来源很稳定，均主要来自于澳大利亚西南部大陆（包括伊尔干克拉通、阿尔巴尼亚-弗雷泽造山带和利文杂岩体）。

晚始新世-渐新世时期，澳大利亚西南部大陆的化学风化和古气候演变主要受全球气候和区域古地理格局变迁的影响。在始新世-渐新世转折期和31.3-29.8 Ma，物源区的上述变化主要受控于邻近区域的古地理格局变迁，具体表现为气候条件趋于干冷和陆表化学风化强度降低的特征。在33.6-31.3 Ma和29.8-25.2 Ma，物源区的上述变化则主要响应了全球气候：在前一阶段气候由干冷向湿热转变，陆表化学风化强度也相应增高；在后一阶段气候则为相对稳定的干冷状态，陆表化学风化强度也弱。上述低时间分辨率研究结果及其与前人相关研究成果间的良好吻合性，为我们首次完整地重建南半球高纬度地区白垩纪OAE 1d事件的演化过程及其成因机制奠定了坚实的实验方法基础。

OAE 1d期间地处高纬度东南印度洋的曼达岬盆地古海洋环境发生了重大变化，主要表现为：澳大利亚西南部大陆陆源物质（包括碎屑物质、有机质和淡水）输入量的增多；海底有机质埋藏通量显著增加，同时有机质的来源由海陆混合转变为以陆源为主；海表生物生产力水平明显下降；深海底层水向缺氧状态转变。通过与前人相关典型记录间的系统对比，我们进一步探讨了该事件的具体成因机制：这很可能是一次全球性的大洋缺氧事件。此时中部凯尔盖朗大火成岩省的活跃释放出了大量的CO₂，促成了全球性的暖室气候条件，致使陆地的水文循环加快并将大量的陆源物质输送到海洋中。一方面，增加的陆源有机质输入和降解会消耗海底的氧气，使其向缺氧状态转变；另一方面，大量陆源淡水的输入还可能会引起上部海水的层化现象，这也会加剧深海的缺氧状态。

Based on a multiple-proxy approach including siliciclastic mass accumulation rate, grain size, elemental geochemistry and organic geochemistry, sediments from International Ocean Discovery Program Site U1513 and U1516 in Southeastern Indian Ocean were used to trace siliciclastic sediment sources during Cretaceous and Paleogene, reconstruct the history of chemical weathering intensity and paleoclimate evolution in Southweatern Australia during Late Eocene-Oligocene and analysis its forcing mechanisms, investigate the interplay between terrigenous detrital input, organic material (OM) source and burial, marine productivity, deep-sea redox conditions during OAE 1d as well as the process and mechanism of OAE 1d.

Provenance analysis indicates that the siliciclastic sediments of Mentelle Basin were mainly derived from the Southwestern Australia Continent including Yilgarn Craton, Albany-Fraser Orogen and Leeuwin Complex during Albian-Cenomanian (102.8-99.4 Ma) and Late Eocene-Oligocene (34.1-25.2 Ma).

The chemical weathering and paleoclimatic evolution of Southwestern Australia were mainly affected by the changes of global climate and regional paleogeographic patterns during the Late Eocene-Oligocene. During Eocene-Oligocene transition and 31.3-29.8 Ma, the paleoclimate in the source area was mainly controlled by the significant changes in the paleogeographic pattern of the adjacent area, which was characterized by the climate conditions tending to be dry and cold and the decrease of continental chemical weathering intensity. At 33.6-31.3 Ma and 29.8-25.2 Ma, the paleoclimate of the source area mainly responded to global climate changes. In the former stage, the paleoclimate changed from dry and cold to wet and hot, the continental chemical weathering intensity increased correspondingly; In the latter stage, the climate maintained in a relatively stable dry and cold state, the continental chemical weathering intensity is also weak. Our above-mentioned low-resolution results and their good agreement with previous research provide the reliable experimental and analytical methods for the first reconstruction of the process and mechanism of Cretaceous OAE 1d at southern high latitudes.

The paleoocean environment changed greatly in Mentelle Basin located at southern high latitudes during OAE 1d including significantly enhanced terrigenous fresh-water, siliciclastic fraction and organic material inputs, increased organic material burial, accompanied by decreased surface productivity and bottom-water oxygenation. In addition, the relatively high consistency between our sedimentary records with the typical sedimentary records of OAE 1d at mid- and low-latitudes and other paleoenvironmenal proxies further demonstrate OAE 1d was a globally distributed event. During OAE 1d when the climate was relatively warm and humid induced by the release of pCO₂ associated with the Central Kerguelen Large Igneous Province, massive amounts of freshwater and terrigenous organic materials input flowed into the study area, subsequently exacerbated the stratification of the water column and consumed oxygen in the bottom water, resulting in the widespread anoxic bottom water condition.

    5.3 物源分析....................................................................................................40

    5.4 白垩纪OAE 1d期间研究区陆源物质输入演化历史……………….......42

    5.5 白垩纪OAE 1d期间研究区古环境演化历史及其成因机制…………........ 45

第6章 结论..............................................................................................................50

参考文献....................................................................................................................53

致谢....................................................................................................................63

作者简历及攻读学位期间发表的学术论文与研究成果.........................................65