早三叠世Smithian-Spathian之交海水温度变化与环境、生物事件-秦岭与华南地区对比研究

The end-Permian mass extinction is considered as the largest one in life’s history. It removed most marine organisms and led to the collapse of Permian ecosystem. Following the Permian-Triassic transition, the extreme hot temperature and Environmental deterioration delayed the recovery of Early Triassic ecosystem. Final recovery of marine ecosystems after the end-Permian mass extinction took 500 million years long..Occurring in the shadows of the end-Permian mass extinction, the Smithian-Spathian extinction in Early Triassic is recognized as a major Early Triassic extinction crisis with the characters of disappearance or near-disappearance of some ammonites, big drop of diversity of bivalves and conodonts, significant size reduction of conodonts and gastropods. Subsequently, it has been recognized some serious environmental events like high amplitude redox changes (anoxia, acidification), most significant and fastest Early Triassic carbon and sulfur isotope perturbations occurred around the Smithian –Spathian boundary. These biotic crises and environmental events also coincide with a peak of Early Triassic warmth that may be one of the hottest intervals of the Phanerozoic. Hence, the Smitian-Spathian event becomes as a hot topic in the world..Based on the well-preserved Smithian-Spathian sediments and faunas in Nanpanjiang Basin of South China and southern belt of Qinling area, this project plans to investigate climatic change, environmental and biotic crises around Smithian- Spathian transition and study their cause-and-effect relationship with multidisciplinary approaches. We will select Jinya section (Guangxi) and Bianyang section (Guizhou) in Nanpanjiang basin, Shangsi section (Sichuan) in upper Yangtze platform, Yiwagou section (Gansu) and Jinjiling section(Shaanxi) in southern Qinling as the target sections. The present project aims to establish the high-resolution biostratigraphic framework by big sample conodont studying ; to reconstruct the palaeotemperatures using oxygen isotopes of conodont apatite; to observe the biotic diversity and productivity variations by analyses of macro and micro faunal (ammonite, conodont, bivalve, gastropod, algae, foraminifers etc.) and carbon isotopes ; to reveal the environmental changes using paleoecological, sedimentary and geochemistry methods. Based above study, this project will analyses the relathionship of Smithian-Spathian extreme climate on environmental changes and biotic crisis. It will also compare the temperature difference and its impact on environmental and biotic events between South China and Qinling area. This project is significant for better understanding the extinction-recovery pattern and global carbon cycles in Early Triassic.

二叠纪-三叠纪之交发生的生物大灭绝事件是地质历史时期最大的一次灭绝事件。早三叠世气候和环境环境恶化造成全球海洋生态系统经历了长达500万年的复苏过程。早三叠世S-S界线附近生物危机以一些生物类别的消失、生物分异度下降、小型化等为特征，与极端高温、碳同位素及海洋氧化还原条件的大幅度变动密切相关，S-S界线附件极端气候和环境及其生物响应近年来已成为国际研究热点。本研究拟在华南和秦岭地区代表性剖面S-S界线上下，通过牙形石分析建立高精度生物地层格架，通过牙形石磷灰石氧同位素方法重建当时古海水温度的变化曲线，通过古生物学和微相研究的方法总结双壳类、菊石、牙形石等门类的生物多样性、生产力和个体大小变化，通过古生物学、沉积学、地球化学、同位素地球化学方法研究沉积环境的变化。进而分析该时期极端气候与环境变化与生物演化之间的因果关系，对比华南和秦岭地区同时期古海水温度的差异及异及其环境、生物效应。

继二叠纪-三叠纪之交生物大灭绝事件之后， 早三叠世Smithian-Spathian之交极热气候、环境及生物事件近年来已成为国际研究热点。过去有关S-S事件的研究主要集中在华南等赤道低纬度地区。本研究以对比研究不同纬度地区S-S界线处生物对环境、气候的变化响应为目标。本项目组在秦岭地区的甘肃、陕西和华南地区的湖北、四川、重庆等地系统测制了10条二叠系至下三叠统剖面，采集了2吨多牙形石样品及多门类大化石和各类岩石和地球化学样品，获得了1万多枚牙形石标本。在此基础上建立了各研究剖面上可靠的牙形石生物带，尤其是在秦岭地区的甘肃迭部益哇沟剖面建立了P/T之交至早三叠世Spathian期高精度的8个牙形石生物带，其中包括Smithian期的 3个带和Spathian期2个带。在益哇沟剖面发现了丰富的Smithian期具有平台型的舟形牙形石分子Scythogondolella mosheri 和Sc. Phryna，这是该属在古特提斯地区首次报道，一般认为Scythogondolella是耐热的广温性分子，这表明Smithian期秦岭与华南地区一样具有较高的古海水温度。研究表明，益哇沟剖面S-S界线处出现一些Smithian 期牙形石消失及多样性减少、牙形石出现小型化、沉积环境发生了明显的变化、碳同位素发生明显的漂移。从而证实S-S生物环境事件在纬度相对较高的秦岭地区同样存在。通过对秦岭镇安地区水峡口剖面二叠系的研究，建立了中二叠世Jinogondolella nankingensis and Jinogondolella aserrata 两个牙形石带，通过牙形石氧同位素再造了古海水温度的变化曲线，表明该地区中二叠世Roadian至Wordian转折期古海水温度变化曲线以及碳同位素漂移曲线与华南地区是一致的。此外，本项目组在贵州、云南、甘肃测制了7条晚三叠世海相地层剖面，在获得了2500多枚牙形石标本的基础上，建立了西南地区拉丁期-卡尼期的8牙形石带，通过牙形石氧同位素恢复古海水温度等多种分析方法，证实了晚三叠世卡尼洪水事件在华南地区的存在。