早三叠世海、陆相地层对比及生物―环境演变过程

The difficulty for the correlation between the marine and non-marine stratigraphic sequences has strongly restricted the full understanding of the nature of the end-Permian mass extinction events and the biotic-environmental interaction and co-evolution during the recovery time at the beginning of the Mesozoic. A range of innovative scientific advances achieved in the recent studies of marine facies badly need to be approved and improved in a global scale. This project proposes that the environmental stratigraphic method is applied for the construction of the marine and nonmarine Lower Triassic stratigraphic framework based upon the correlation of some typical events or events-group, e.g. at the P/T and S/S boundaries, which are analyzed for the temporal and spatial attributes and recognized in the various facies. Whereafter, a compositive stratigraphic sequence is constituted in each facies and subdivided through multidisciplinary methods in order to enhance the resolution of the stratigraphic correlation between the marine and terrestrial facies. Furthermore, the significant biotic and environmental events are selected from the various facies to be correlated and integrated into a single Early Triassic biotic-environmental-chronostratigraphic sequence, and then the time-series of the events is understandable and the causal relationship can be analyzed. Consequently, the interaction and co-evolution of the biotic and environmental events through the great transitional time can be studied, and the impact of global change on the biotic revolution and origination might be evaluated from the angle of the marine-terrestrial or atmosphere-ocean interaction. Meanwhile, this project will provide a new idea for the establishment of the Auxiliary Stratotype Section and Point (ASSP) for the global terrestrial chronostratigraphic boundaries.

海、陆相地层对比已成为制约全面认识古生代末大灭绝事件性质和中生代初复苏期生物与环境相互作用和协同演化的瓶颈，当前海相地层研究中所取得的重大科学进展，迫切需要从全球尺度加以考证和完善。本项目提出采用环境地层学方法，借助于对P/T和S/S界线处典型事件或事件群时空属性的解析和在各沉积区的辨识，进行跨相区地层对比，搭建早三叠世海、陆相地层对比的大格架；再通过各区域地层序列的精细研究再分，来提升跨区域地层对比的分辨率。然后，分析和提取各沉积区重要的生物和环境事件，将它们对比整合到早三叠世统一的生物―环境―年代综合地层序列上，以观察各类生物―环境事件的时序和分析其因果关系，进而探索该重大突变期生物与环境的相互作用和协同演化关系，并从海―陆（水―气）互动的角度分析全球变化对生物重大变革和新生发展的影响。同时，本项目也将为全球陆相年代地层界线辅助层型的建立提供新的思路。

二叠纪―三叠纪之交地质突变期发生了显生宙最大规模的生物灭绝及其后历时最长的生物复苏，是国际地学界长期研究的热点和焦点。海、陆相地层对比已成为制约全面认识该大灭绝事件性质和随后的复苏期生物与环境相互作用和协同演化的瓶颈，亟需大量而深入的工作来揭示海、陆相地层中的环境与生物信息，从而对该重大地质事件中地球系统的演变过程有更完整而清晰的认识。.本项目采用生物—环境—年代地层学的综合研究方法，搭建了不同沉积区的海、陆相地层对比格架，对重要的生物和环境事件开展了高分辨率的精细对比研究。地层对比方面，建立和完善了华南海相沉积区、黔西滇东和陕西渭北海陆过渡相沉积区、华北和新疆内陆相沉积区晚二叠世-早三叠世综合地层划分和对比方案。陆相沉积记录方面，利用植物化石分异度、植物有机碳同位素、化学风化指数和木炭丰度等多手段识别出了陆地生物和环境事件。首次提出并论证了华南陆地生态系在海相灭绝事件之前经历了强烈的扰动。化学风化指数揭示了P-T之交陆地风化增强和升温。高分辨率的C3植物有机碳同位素计算重建了大气CO2浓度在灭绝事件中升高了六倍，且与当时的升温时间密切相关。海相沉积记录方面，从生物大小、元素循环和沉积标志等多角度深入剖析了海洋生物与环境事件。海相牙形石大小演变的长尺度和精细研究表明早三叠世牙形石动物经历了多阶段的大小变化，可能指示了当时海洋环境的强烈波动。综合碳、氮、硫同位素，铁组分和草莓状黄铁矿数据，论证了海洋缺氧的频繁发生是导致早三叠世生物迟缓复苏的原因之一。在生态系统演化方面，高分辨率的无脊椎动物大数据揭示了海洋由灭绝前的固着型动物占据主导地位的生态系转变为灭绝后以游泳型动物占据主导地位的生态系。遗迹学指标指示了早三叠世晚期陆相生态系复苏已经达到较高水平。本项目初步构建了三叠纪复苏期生物―环境―年代综合地层序列，对分析古、中生代之交重大地质突变期及其后生物与环境之间的互动演变过程具有重要意义。项目实施以来，围绕设计主题共发表标注论文42篇，其中SCI期刊论文38篇，包括1篇Sciences Advances，3篇Nature Communications和3篇Geology。项目执行期间共培养青年教师4名，毕业博士和硕士研究生11名。