Journal Article

Large Igneous Province Emplacement Triggered an Oxygenation Event at ∼1.4 Ga: Evidence From Mercury and Paleo‐Productivity Proxies

Zhou, Xiqiang, Shi, Xiaoying, Zheng, Wang, Huang, Kangjun, Xu, Lei, Lechte, Maxwell, Zhou, Limin, Tang, Dongjie

2024

Overview

The mid‐Proterozoic (∼1.8–0.8 Ga) ocean‐atmosphere system is hypothesized to have experienced fluctuations in redox conditions with transient oxygenation events. One of these happened at ∼1.4 Ga, and it is speculated that this event may link to the emplacement of large igneous province (LIP) at this time. However, direct evidence for this relationship remains to be proved. Here, we report Hg/TOC, P, and trace element concentrations across the ∼1.4 Ga oxygenation event in the Xiamaling Formation of North China. A prominent increase in Hg/TOC is slightly earlier than that of nutrient contents (especially P), pyrite and TOC abundances, suggesting that this distinct oxygenation event was likely the result of LIP activity at ∼1.4 Ga, which increased nutrient and sulfate supply from continental weathering to the ocean, sustaining elevated primary productivity, organic carbon and pyrite burial. This study indicates that LIP weathering could trigger transient oxygenation events during the mid‐Proterozoic. Plain Language Summary The mid‐Proterozoic (∼1.8–0.8 Ga) retains persistent low oxygen concentrations in atmosphere and shallow seawater but is occasionally punctuated by transient oxygenation events. Multiple lines of evidence from sedimentary geochemistry have argued a global oxygenation event at ∼1.4 Ga, and speculated that this event was closely related to large igneous province (LIP) activity at this time. Direct link between LIP activity and the oxygenation event, however, has rarely been addressed yet. As mercury in sedimentary rocks has been widely used to trace volcanism, we therefore report Hg/TOC, P, and trace element concentrations across the ∼1.4 Ga oxygenation event. The result shows that a prominent increase in Hg/TOC is clearly recognized in the shales that stratigraphically just underly the layers recording the oxygenation event, suggesting a close causal link between LIP emplacement and the oxygenation event. Accompanied with this Hg/TOC ratio peak, increased nutrient contents (especially P), pyrite and TOC abundances are also observed. Based on these observations, we proposed a model that the Xiamaling oxygenation event was the result of the LIP's emplacement at ∼1.4–1.35 Ga, which increased nutrient and sulfate supply from continental weathering to the ocean, sustaining elevated primary productivity, organic carbon and pyrite burial. Key Points High Hg/TOC ratios associated with large igneous province (LIP) emplacement were detected in the ∼1.4 Ga Xiamaling Formation shales of North China High P content accompanied with this interval indicates enhanced phosphorous input from LIP weathering to the ocean A causal link between the LIP weathering and oxygenation event at ∼1.4 Ga was suggested

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Abundance / Atmosphere / Gallium / Geochemistry / LIP weathering / Mercury / mid‐Proterozoic / Nutrients / Oceans / Organic carbon / Oxygen / Oxygenation / phosphorous / Precambrian / Primary production / primary productivity / Productivity / Pyrite / Seawater / Sedimentary rocks / Sulfates / Total organic carbon / Trace elements / Volcanic activity / Volcanism / Weathering / Xiamaling Formation