二叠-三叠纪之交特提斯浅海古海洋氧化—还原状态的时空波动：来自微生物岩的沉积记录

The redox conditions and anoxic events during the Permian-Triassic transition is a highlight of earth science research, which is critical to the understanding of the end-Permian mass extinction and Triassic delayed recovery. However, the starting time of the anoxic events remains highly controversial. To improve the understanding on this issue, we aim to determine the starting time, distribution and water depth of the anoxic events in this project, based on a case study of the 8 microbialite sections on the Tethyan shelf. Based on the results, the temporal and spatial redox fluctuations of ancient oceans can be revealed. Then, the mechanism of the fluctuations can be addressed. Specifically, the stratigraphic framework will be established firstly, based on lithologic and carbon isotope stratigraphic studies combined with previous results. Then, using Ce negative anomaly and other geological and geochemical indexes, we will reveal the redox evolution history of the studied sections in the stratigraphic framework. Afterwards, we will address microfacies of each section and compare their ancient water depth, using the microfacies analysis integrated with principal component analysis. Finally, we will perform a comprehensive analysis and discussion to figure out regularities and mechanism of the temporal and spatial redox fluctuations during Permian-Triassic transition on the Tethyan shelf. Results can also provide references for the regional basic hydrocarbon geological study and exploration.

二叠-三叠纪之交全球古海洋氧化-还原状态（缺氧事件）是当前地球科学的研究热点，对于认识二叠纪末生物灭绝事件及其后早三叠世的生物缓慢复苏具有重要意义，但缺氧事件的发生时间存在极大不确定性。本项申请，拟选择特提斯浅海地区的8条微生物岩剖面开展实例研究，通过精细的对比分析缺氧事件的时空分布和影响水深，查明古海洋氧化-还原状态的时空波动，并讨论成因。首先，根据岩石和碳同位素地层学研究，结合已有地层学研究基础，建立区域地层对比格架；在此基础上，在地层对比格架中，以铈异常为检测指标，辅以其他地质地球化学参数，查明各剖面氧化-还原状态的时空波动与演化；再次，应用结合主成分分析法的微相分析技术，开展沉积环境分析和古水深排序；最后，在地层格架中综合分析讨论缺氧事件的时空演变规律及成因机制。研究认识还可供区域二叠系-三叠系油气地质研究和勘探参考。

通过对四川鱼洞子、广西太平、匈牙利Bükk Mountains和土耳其Çürük Dag剖面开展精细地质描述和多地质地球化学指标氧化-还原研究，得到以下主要认识：1）通过巨、宏、中、微尺度微生物岩精细描述，结合已有研究基础，指出特提斯海域东西两侧的PTBMs在组构组成和结构构造上均存在明显差异。东特提斯PTBMs以凝块石为主，组成凝块的囊状钙质微生物保存较好；西特提斯PTBMs大量发育叠层石，凝块石极少保存钙质微生物。2）综合利用LA-ICP-MS稀土元素分析、总有机碳和总硫分析、化石含量和大小统计等手段，建立了各研究剖面水体氧化-还原状态的垂向演化序列，其PTBMs均发育于氧化海水之中。3）在碳同位素-生物地层对比框架的约束下，重建了特提斯浅海区域水体的氧化-还原状态时空演化，分析讨论了缺氧事件的过程、成因和影响。晚二叠世末期的斜坡及盆地环境，海水主要以滞留、缺氧及硫化为特征。缺氧事件在二叠纪末达到高潮，可能波及了碳酸盐岩台地的边缘和内部等浅水地带，但因为后期海退而缺失了缺氧记录。海侵之后，特提斯浅海地区海水全面氧化，至少在早三叠世最初期未受到缺氧事件波及。