塔吉克盆地晚始新统-中新统风成沉积序列的年代学和古环境记录研究

The Asian aridification and its forcing mechanism are one of the most predominate scientific topics in Earth Sciences, however, there remains lack of in-situ Cenozoic paleoenvironmental records from arid central Asia. Our preliminary study indicates that the main body of the late Eocene to Miocene sedimentary sequences in the Tajik Basin is aeolian in origin. Further confirm their origin, constrain the timing when the aeolian matirial accumulated, and establish high-resolution multi-proxy indices records of climate changes could potentially provide crucial geological evidence for understanging important scientific issues, such as the early Cenozoic aridification history in Arid central Asia, their regional differences, and the major forcing factors. In this work, we attempt to: 1) carry out province analysis and depositional modal study, to strengthen our preliminary aeolin origin interpretations of the sedimentary rocks; 2) develop systemic chronological investigations on the representative sections, to establish a reliable magnetostratigraphic frame for the aeolian sequences; 3) conduct relative high-resolution measurements of proxy indices, such as grain size, redness, TOC, to probe into the timing and amplitude of major paleoenvironmental events in the Tajik Basin during the early Cenozoic; 4) carry out comparable work with the early Cenozoic peleoenvironmental records in Tarim Basin, to understand the relative contributions of the retreat of the Paratethys and the uplift of the Pamir on the paleoclimatic changes in the Asia interior at different time.

新生代亚洲内陆干旱化过程及其驱动机制是国际古环境研究的热点和重点，然而迄今缺少直接来自于中亚干旱区的新生代古环境记录。申请人和国际合作者对塔吉克盆地早新生界沉积序列初步的沉积学研究表明，盆地内部厚愈800 m的晚始新统-中新统地层主体为风成沉积。深入验证这套地层的成因，明确大规模风成物质开始出现的年代，建立较高分辨率的古气候代用指标序列，能为认识早新生代中亚干旱区的干旱化历史及其主控因素提供关键证据。本研究拟在前期工作基础上，及时开展“风积地层”的物源分析和发育模式研究，完善对其成因的论证；开展代表性剖面的年代学研究，建立可信的古地磁年代框架，明确大规模风成物质开始堆积的年代；开展较高分辨的粒度、TOC等常规古气候代用指标记录研究，建立西风区早新生代古气候演化序列；对比分析塔吉克盆地和塔里木盆地早新生代古环境记录，理解副特提斯海退缩和帕米尔高原抬升在不同时段对亚洲内陆区域气候的具体影响。

新生代亚洲内陆干旱化过程及其驱动机制是国际古环境研究的热点和重点，然而迄今缺少直接来自于中亚干旱区的新生代环境变化记录。塔吉克盆地属亚洲中部的典型西风环流影响区，新生代以来受副特提斯海退缩和帕米尔高原隆升的影响极为显著，是开展内陆干旱化历史及驱动机制研究的重要地区。. 本项目围绕申请人前期工作中发现的早新生界副特提斯海-风成沉积序列，对塔吉克盆地代表性剖面开展系统的年代学、沉积学、物源分析、古气候代用指标记录研究，取得以下主要研究进展：1）通过古地磁、火山灰 U-Pb、古生物、碎屑锆石 U-Pb、碎屑独居石 U-Pb、磷灰石裂变径迹等建立了塔吉克盆地早新生界沉积序列的年代标尺，论证了副特提斯海在在~37.4 Ma从塔吉克盆地最终退出、帕米尔高原在晚渐新世（~25 Ma）发生了显著的加速隆升；2）综合沉积相、稳定同位素、粒度、色度、元素地球化学、粘土矿物等证据，建立了中亚干旱区特征时段多指标体系的气候环境变化序列，揭示了中亚中部干旱环境自晚始新世 (~37.4 Ma) 开始孕育、在早渐新世进入新的发展阶段、在晚渐新世(~25 Ma) 趋于湿润的演化框架；3）结合地质记录和数值模拟证据，论证了副特提斯海的退缩诱发了晚始新世亚洲内陆干旱化，提出帕米尔-天山的构造隆升及其与西风环流的相互作用导致晚渐新世亚洲内陆环境东西向分异的新认识。. 本研究，为认识新生代亚洲内陆干旱化历史和空间演化过程提供了境外干旱区新记录，理解内陆干旱环境时空演化的驱动机制提供了新视角。研究成果在Geology、Geophysical Research Letters (封面文章)、Quaternary Science Reviews (邀请文章) 等国内外重要学术刊物发表，取得了较大的学术影响力。依托项目毕业硕士1人、博士一人，顺利完成了人才培养目标。