The Lomagundi Carbon Event (LE), the large, long-lived Paleoproterozoic positive carbon isotope excursion, is traditionally associated with a significant increase in atmospheric oxygen. However, the magnitude and extent of atmosphere–ocean oxygenation during this critical period of Earth’s history remain poorly constrained. Here, we present molybdenum isotope data and Ce anomaly values of Paleoproterozoic Jingshan Group marble samples deposited coincident with the peak of LE. Analyzed samples are characterized by near-modern seawater δ98Mocarb values (maximum = 2.13 ‰ ± 0.05), crustal Ce anomalies (average = 1.03), and δ98Mocarb values (average = 0.41 ‰). The great variation of Mo isotope values displayed by samples recovered from a thin stratigraphic interval likely reflect the existence of a small Mo reservoir during LE. We suggest that Mo removal from poorly oxygenated oceans under ferruginous conditions was responsible for the contraction of the Mo oceanic reservoir. Mo concentrations and isotope values of deposits coincident with this time interval appear to have been controlled by iron and manganese oxides shuttle. Placed in the context of Earth’s oxygenation history, our findings suggest that O2levels of the atmosphere–ocean system remained much less (1 % PAL) than the present level with occasional episodes of increased or pulsed atmospheric oxygen during the peak of LE.

中文翻译：

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华北克拉通景山组大理岩在 Lomagundi 事件期间记录的 Mo 同位素和 Ce 异常的脉冲大气氧合


Lomagundi 碳事件 （LE） 是大型、长寿命的古元古代正碳同位素偏移，传统上与大气中氧气的显着增加有关。然而，在地球历史的这一关键时期，大气-海洋氧化的幅度和范围仍然受到很好的限制。在这里，我们展示了与 LE 峰值重合沉积的古元古代景山组大理石样品的钼同位素数据和 Ce 异常值。分析样品的特征是近现代海水 δ98Mocarb 值（最大值 = 2.13 ‰ ± 0.05）、地壳 Ce 异常（平均值 = 1.03）和 δ98Mocarb 值（平均值 = 0.41 ‰）。从薄地层层段中回收的样品显示的 Mo 同位素值的巨大变化可能反映了 LE 期间存在一个小的 Mo 储层。我们认为，在铁质条件下，从含氧不良的海洋中去除 Mo 是导致 Mo 海洋储层收缩的原因。与该时间间隔相吻合的矿床的 Mo 浓度和同位素值似乎受到铁和锰氧化物穿梭的控制。在地球氧合历史的背景下，我们的研究结果表明，大气-海洋系统的 O2 水平仍然远低于目前的水平 （1 % PAL），在 LE 高峰期偶尔会出现大气氧气增加或脉冲事件。