The causes of the Great Ordovician Biodiversification Event (GOBE) remain a topic of debate. Recent studies indicate that global and regional oceanic oxygenation was a plausible trigger of the GOBE. The Ce anomaly of rare earth and yttrium (REY) elements in shallow marine carbonates is thought to be a powerful indicator of marine redox conditions of local waters. In this study, we analyzed REY, major and trace element compositions, and C and O isotopes of the Lower Ordovician microbial-dominant reefs on the Yangtze Platform, South China. We evaluate which carbonate components within the reefs most reliably record the seawater REY composition. The elemental correlations show that the REY elements of oncoids, stromatoporoids, sponges and carbonate infillings were affected by clastic influence, diagenetic processes, and the vital effects of carbonate secreting organisms; whereas the microbialites REY were partially modified by synsedimentary terrigenous and little diagenetic modification. Such introduction of synsedimentary terrigenous REY increased ΣREY and flattened the REY patterns of the microbialites, but the redox signals (Ce anomalies) of input source of the water column might still preserved in microbialites formed in situ. Although the magnitude of Ce anomalies is small, variation might still reflect authentic redox history of primary local seawater. In the middle Tremadocian, microbialites have positive Ce anomalies which were coeval to positive δ¹³C_carb shifts. The positive δ¹³C_carb shifts were documented from other sections of central Yangtze Platform, North American and Argentina, which might indicate global anoxic event. In the late Tremadocian to early Floian, microbialites have more visible negative Ce anomalies, which might indicate regional oceanic oxygenation event. The negative Ce anomalies provide direct local-geochemical evidence of oceanic oxygenation in the late Tremadocian-early Floian on the Yangtze Platform of South China, which might facilitate the first acme of biodiversification of local faunas predating the main pulse of the GOBE on the other palaeoplates.

奥陶纪生物多样性大事件 (GOBE) 的原因仍然是一个争论的话题。最近的研究表明，全球和区域海洋氧化作用可能是 GOBE 的触发因素。浅海碳酸盐岩中稀土和钇 (REY) 元素的 Ce 异常被认为是当地水域海洋氧化还原条件的有力指标。在这项研究中，我们分析了华南扬子地台下奥陶统微生物优势生物礁的 REY、主要和微量元素组成以及 C 和 O 同位素。我们评估了珊瑚礁中哪些碳酸盐成分最可靠地记录了海水 REY 成分。元素相关性表明，类瘤体、层孔体、海绵体和碳酸盐充填体的 REY 元素受碎屑影响、成岩过程、以及分泌碳酸盐的生物的重要作用；而微生物岩 REY 部分被同沉积陆源和很少的成岩修饰修饰。这种同沉积陆源REY的引入增加了ΣREY并使微生物岩的REY模式变平，但水柱输入源的氧化还原信号（Ce异常）可能仍保留在原位形成的微生物岩中。虽然 Ce 异常的幅度很小，但变化可能仍然反映了当地原生海水的真实氧化还原历史。在Tremadocian中期，微生物岩具有Ce正异常，与正δ同时期 这种同沉积陆源REY的引入增加了ΣREY并使微生物岩的REY模式变平，但水柱输入源的氧化还原信号（Ce异常）可能仍保留在原位形成的微生物岩中。虽然 Ce 异常的幅度很小，但变化可能仍然反映了当地原生海水的真实氧化还原历史。在Tremadocian中期，微生物岩具有Ce正异常，与正δ同时期 这种同沉积陆源REY的引入增加了ΣREY并使微生物岩的REY模式变平，但水柱输入源的氧化还原信号（Ce异常）可能仍保留在原位形成的微生物岩中。虽然 Ce 异常的幅度很小，但变化可能仍然反映了当地原生海水的真实氧化还原历史。在Tremadocian中期，微生物岩具有Ce正异常，与正δ同时期¹³ C_{碳水化合物}转变。从中央扬子地台、北美和阿根廷的其他部分记录了δ ¹³ C_{碳水化合物}的正变化，这可能表明全球缺氧事件。在 Tremadocian 晚期到 Floian 早期，微生物岩具有更明显的负 Ce 异常，这可能表明区域性海洋氧化事件。Ce负异常为华南扬子地台晚Tremadocian-Floian早期海洋氧化提供了直接的局部地球化学证据，这可能有助于在其他古板块上早于GOBE主脉动的地方动物群的生物多样性达到顶峰.