古海洋氧化还原条件的遗迹化石定量表征特征:以华南二叠纪末生物大灭绝事件为例*

地质历史时期的重大生物—环境事件往往伴随着古海洋海水氧化还原条件的改变,而遗迹化石作为原位保存的生物成因沉积构造,对于解读古海洋氧化还原条件具有显著的优势。通过对前人常用的遗迹学参数进行分析总结,发现遗迹化石多样性、生物扰动强度、潜穴直径、特征遗迹化石组合这4项定量参数可以表征古海洋氧化还原条件的变化。文中以华南二叠系乐平统遗迹化石及生物扰动构造作为研究对象,系统分析了二叠纪末生物大灭绝事件前后遗迹化石参数表征的古海洋氧化还原条件变化特征:自吴家坪期晚期华南古海洋开始出现缺氧,然而该缺氧状态在长兴期不具有持续性,而是呈现出周期性缺氧/贫氧→富氧/有氧的波动特征;在二叠纪末生物大灭绝之前,煤山剖面高精度的定量遗迹学参数指示长兴组24e层顶部存在缺氧事件,并与大灭绝事件有着良好的对应关系。这一实例具体展示了遗迹学参数在古海洋水体氧化还原条件重建中应用前景广阔。

Quantitative characterization of ichnological parameters for indicating palaeo-ocean redox conditions: a case study of the end-Permian mass extinction in South China

Major biotic and environmental events in Earth history are often accompanied by palaeo-ocean redox condition changes,as biogenetic sedimentary structures in situ,trace fossils play a significant role in reconstructing palaeo-ocean redox conditions. This study analyzes and summarizes the previous ichnological parameters,and suggests the ichnodiversity,bioturbation degree,burrow size,and key ichnotaxa can be quantitatively used to indicate the palaeo-ocean redox conditions. Additionally,Lopingian trace fossils and bioturbation structures in South China are systematically analysed in order to reconstruct the redox conditions during the end-Permian mass extinction. The quantitative ichnological parameters reveal that the ocean anoxic event occurs in late Wuchiapingian,and the ocean anoxia is not permanent in Changhsingian,instead,obvious periodic fluctuations between anoxic/dysoxic and oxic can be observed. The high-resolution quantitative ichnological proxies at Meishan section suggest that ocean anoxia occurs in the top of Bed 24e in the Changhsing Formation,appears to correlate with the biotic mass extinction. The above examples show that the application of ichnological parameters in the reconstruction of palaeo-ocean redox conditions has broad prospects.