华南晚二叠世至中三叠世牙形石原位锶同位素分析及其在评价古海洋化学条件和陆地风化作用的应用

The proposed study aims to conduct for the first time the high-resolution, in situ analysis of strontium isotopes of conodont bioapatites collected from the Late Permian to Middle Triassic successions of South China. These conodonts are measured using laser ablation multiple collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) techniques. Additional to the previously obtained conodont specimens, the proposed project will also sample systematically several relatively better studied and conodont-rich Upper Permian to Middle Triassic sections, which represent various depositional environments varying from shallow platform to basin shelf settings. Accordingly, strontium isotopic results can indicate the relationships among weathering intensity on land, oceanic biogeochemical conditions and biotic crises during this critical period in various depositional settings. In particular, episodes and magnitudes of terrestrial weathering intensity from the Late Permian to Middle Triassic can be reconstructed and tested by means of in suit conodont strontium isotope excursions. Ultimately，the proposed study provides some new ideas in searching the causes triggering the end-Permian mass extinction and subsequent, much delayed recovery. The present study also fills the gap in the studies on in situ strontium isotopic analysis of global Late Permian to Middle Triassic conodonts, and provides insights into some innovative approaches and techniques for traditional palaeontology. The conodont strontium isotopic excursions also provide independent geochemical information for reconstructing sea-level changes during the Palaeozoic-Mesozoic transition, and the processes of biotic recovery and radiation in Triassic oceans in South China.

本项目拟对华南不同相区几条研究程度较高并富含牙形石化石的二叠、三叠系剖面进行系统地采集牙形石样品，同时也充分利用早前已获得的牙形石标本,首次利用LA-MC-ICP-MS技术对牙形石微区原位锶同位素组成进行分析、测量，并恢复它们在晚二叠世至中三叠世的变化趋势。配合其它已发表的碳、硫同位素结果，探讨该时期华南不相区中牙形石原位锶同位素组成与陆地风化作用强度、古海洋化学条件的变化以及主要生物事件之间的耦合关系。同时，恢复华南地区该时期陆地风化作用强度变化的趋势、时限和幅度。最终，为查明引起二叠纪末生物大灭绝的元凶以及之后极其缓慢复苏的原因提供新的研究思路。该项研究填补全球有关晚二叠世至中三叠世高分辨率牙形石原位锶同位素组成及演化特征研究的空白，为传统古生物与地层学的创新探索出新的技术方法。该项目的成功实施还将为恢复华南地区古、中生代之交海平面变化和三叠纪生物复苏-辐射过程提供独立的地球化学信息。

项目研究了扬子地区（如安徽平顶山西剖面、 湖北峡口、甘溪和建始剖面、江西沿沟剖面）、南盘江盆地地区（如广西作登和太平剖面）、日本西南部（Kamura剖面）和印度克什米尔地区（Guryul Ravine 剖面）一系列代表性剖面的牙形石生物地层，系统的利用牙形石化石，依托LA-MC-ICP-MS微区原位锶同位素分析技术和实验方法对获得的二叠纪/三叠纪界线附近和早-中三叠世的牙形石进行分析测试和结果分析。首先系统探究了锶同位素信号在牙形石和围岩中保存的差异，以及牙形石不同部位（如牙尖、牙冠和牙基）的锶同位素变化。然后恢复了全球海洋从晚二叠世至中三叠世的锶同位素演变曲线，讨论了这一时期地球陆地风化作用强度变化的趋势、时限和幅度。最后探讨了该时期华南不相区中牙形石原位锶同位素组成与陆地风化作用强度、古海洋化学条件的变化以及主要生物事件之间的耦合关系。这一研究为深入研究全球古生代末生物大灭绝及其后生物复苏过程中环境气候变化之间的联系提供了重要依据，为古-中生代之交大灭绝的研究提供了重要参考资料。