Spatial and Temporal Redox Heterogeneity Controlled by a Fe(II), Anoxic Upwelling System in the Early Mesoproterozoic Ocean

• Published in: Geophysical research letters Vol. 50; no. 10
• Main Authors: Ye, Mingze, Zhang, Shuichang, Ye, Yuntao, Wu, Minghao, Wang, Xiaomei
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28-05-2023; Wiley
• Subjects: Ammonium; Ammonium compounds; Anoxia; Anoxic sediments; Availability; Carbonates; Deep water; Denitrification; early Mesoproterozoic; Eukaryota; Eukaryotes; Evolution; Heterogeneity; Iron; Manganese; Nitrate reduction; Nitrates; Nutrient availability; Nutrients; Ocean circulation; Oceans; Oxygen; Productivity; redox heterogenity; Sediment; Sediments; Surface water; Trace metals; Upwelling; Yanliao Basin
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2023GL103598

The availability of oxygen and nutrients during the Mesoproterozoic (1.6–1.0 Ga) is thought to influence the rate of eukaryote evolution. The cause of the transition from low productivity in the upper Wumishan Formation to organic‐rich sediments in the Hongshuizhuang Formation remains unknown. We report FeHR/FeT, Fepy/FeHR, MoEF, UEF, VEF, and [Ce/Ce*]SN in one core of the Yanliao Basin to study the redox evolution and compare it with other sections in different depths of the Yanliao Basin to get clues of the spatial and temporal redox heterogeneity. Mo‐U covariation, low Co × Mn and CoEF × MnEF, and distribution patterns of trace metals indicate the upwelling events. An upwelling system could fuel nutrients to promote productivity levels in surface water and contribute to anoxic deep waters. The uniformly positive δ15N values are interpreted as sufficient NO3− reduction via denitrification and dissimilatory nitrate reduction to ammonium in a ferruginous upwelling condition.
Plain Language Summary
During the Mesoproterozoic Era (1.6–1.0 Ga), ocean anoxia and nutrient limitation have been suggested to explain why complex multicellular eukaryotes did not expand until later in the Neoproterozoic Era. Among several kilometers thick marine carbonates that dominated the Early Mesoproterozoic Era (∼1.6–1.4 Ga) in North China, a suite of black shales discovered in the Hongshuizhuang Formation (∼1.46–1.45 Ga) exhibits high nutrient contents. The origin of nutrient availability needs to be correctly understood. To reveal the potential cause behind these highly productive sediments, we use multiple proxies to study the changes in nutrient and oxygen levels during the Hongshuizhuang Formation deposition. Our results demonstrate that upwelling events provide nutrient availability, which further constrains inconsistent redox evolution in different areas. The loss of sufficient nutrient nitrogen to N2 in the oxic surface water could be largely traced from persistent deep‐ocean Fe(II) consumption brought by upwelling.
Key Points
The Yanliao Basin has good connectivity with the Proto‐Asian Ocean, with upwelling events at ∼1.46–1.45 Ga
Spatial and temporal redox heterogeneity is observed in the Hongshuizhuang Formation, North China, at ∼1.46–1.45 Ga
Increasing surface productivity in the Hongshuizhuang Formation was fueled mainly by open‐marine upwelling