扬子地块埃迪卡拉纪浅层海洋氧化还原环境变化及其对生物演化的影响

Shallow-marine redox conditions during the Ediacaran in the Yangtze Plateform and its impact on bio-evolution

埃迪卡拉纪地球表生系统环境变化与生物演化历程息息相关,但是对两者之间相互作用关系的认识还存在争议。本文以华南三峡地区九龙湾剖面埃迪卡拉系陡山沱组沉积序列的碳酸盐岩为研究对象,利用稀醋酸分步淋洗提取碳酸盐相稀土元素信息,建立了埃迪卡拉纪陡山沱期Ce/Ce^(*)值演化曲线。九龙湾剖面Ce异常曲线记录了还原/锰化-强氧化-次氧化-强氧化-弱氧化/还原的演化过程,呈现两次完整的Ce负异常事件,说明埃迪卡拉纪陡山沱期浅层水体在长期氧化的历程中出现了两次显著的氧化事件。这两次氧化事件分别与发生在632 Ma和580 Ma的深部水体阶段性氧化相契合,而且同时期澳大利亚埃迪卡拉纪沉积序列也记录了Ce负异常,暗示埃迪卡拉纪陡山沱期海洋可能发生了两次全球性的广泛增氧事件。基于扬子地块陡山沱组生物化石群记录的主要化石群产出层位与陡山沱期海洋氧化的沉积序列呈现清晰的耦合关系,为海洋氧化促进埃迪卡拉纪陡山沱期多细胞后生动物的起源与演化提供了证据。

The environmental changes in the Ediacaran epigenetic system of the Earth are closely linked to the evolution of organisms.However,there is still ongoing debate surrounding their interaction.This study focuses on the carbonate sedimentary sequences of the Ediacaran Doushantuo Formation in the Jiulongwan section of the Three Gorges Region,South China.The rare earth elements information was extracted from the carbonate phase using dilute acetic acid distribution leaching.The obtained data was then utilized to construct the evolution curve of Ce anomalies,which underwent a process involving of reduction/manganization-strong oxidation-suboxidation-strong oxidation-weak oxidation/reduction.Two significant negative Ce anomalies were observed,indicating the occurrence of two significant oxygenation stages during the prolonged oxidation process of the Ediacaran Doushantuo shallow water.These two oxygenation events align with the periodic oxidation of deep water at 632 Ma and 580 Ma,respectively.Moreover,Ce negative anomalies were also found in contemporaneous sedimentary sequences in Australia,suggesting that global oxygenation events occurred in the Ediacaran Doushantuo ocean.The fossil record of the Doushantuo Formation in the Yangtze Plateform reveals that the duration of Doushantuo ocean oxidation corresponds to the production strata of major fossil groups.This finding supports the understanding that marine oxidation facilitated the origin and evolution of Ediacaran Doushantuo metazoans.