晚始新世-渐新世东南印度洋沉积物源-汇过程及其古气候指示意义

Sediment source-to-sink processes of the southeastern Indian Ocean during the Late Eocene-Oligocene and their potential significance for paleoclimate

晚始新世-渐新世期间南大洋及其周边地区的古气候响应研究有助于我们更好地认识地质历史上的重大气候转型机制和预测未来地球系统对于气候突变的响应,然而迄今为止,仍缺乏对该区域周边陆地的古气候响应研究。基于国际大洋发现计划(IODP)369航次U1516站位深海沉积物的年龄框架以及常量、微量和稀土元素组成,确定了该沉积物主要来源于澳大利亚西南部大陆,进而重建了构造时间尺度上物源区的化学风化历史。在此基础上,探讨了晚始新世-渐新世气候转折期南大洋周边大陆的古气候演化过程及其对于全球气候变化和区域古地理改变的响应。在始新世-渐新世转折期[34.1,33.6)Ma和[31.3,29.8)Ma期间,物源区的古气候主要受控于邻近区域古地理格局重大变化的影响,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期间,物源区的古气候则主要响应全球气候的变化,在前一阶段由干冷向湿热转变,而陆表化学风化强度相应增高;在后一阶段,气候保持在相对稳定的干冷状态,陆表化学风化强度也较弱。

Understanding the paleoclimate responses in Southern Ocean and its surrounding land can help us to better explore the major climate transition mechanisms in geological history and predict the response ofthe earth system to abrupt climate changes in the future,while,there is still a lack of research on the paleoclimatere sponse of the surrounding land in Southern Ocean.Based on the age framework,major,traceand rare earth element compositions of the deep-sea sediments at Site U1516 of the International Ocean Discovery Program(IODP)369,we determined that the sediments were mainly from the southwest continent of Australia,and then reconstructed the chemical weathering history of the source area on the tectonic time scale.In addition,we combined with the previous research results to discuss the paleoclimate evolution of continents surrounding Southern Ocean during the Late Eocene-Oligocene climate transition period and its response toglobal climate changes and regional paleogeographic changes.During the Eocene-Oligocene transition(e.g.,34.1 to 33.6 Ma and 31.3 to 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 bedry and cold and the decrease of chemical weathering intensity on the land surface.During the period of 33.6 to 31.3 Ma and 29.8 to 25.2 Ma,the palaeoclimate of the source area mainly responded to global climate changes.In theformer stage,the paleoclimate changed from dry and cold to wet and hot,the intensity of chemical weathering on the land surface increased correspondingly;In the latter stage,the climate maintained in a relatively stable dry and cold state,the intensity of chemical weathering on the land surface is also weak.