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Two deep marine oxygenation events during the Permian-Triassic boundary interval in South China

Abstract. 

"Marine redox conditions through the Permian-Triassic (P-T) boundary interval have been intensively studied in South China with different redox proxies and from different sections. However, the resultant interpretations are inconsistent and sometimes even controversial, thereby impeding an overall understanding of global environmental changes and of causes for the P-T mass extinction events. This study summarizes and reevaluates these previous studies. [...]".

 

Source: Science Direct
Authors: Yuzhu Ge & David P.G. Bond
DOI: https://doi.org/10.1016/j.earscirev.2022.104220

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Chromium isotope evidence for oxygenation events in the Ediacaran ocean

Abstract. 

"Pulses of the Ediacaran ocean oxygenation were inferred from strong enrichments of redox-sensitive elements (RSEs; particularly Mo, V, U, Re) and negative pyritesulfur isotopes (δ34Spy) in black shales of the Doushantuo Formation in South China. These oceanic oxygenation events (OOEs) have been challenged by the lack of comparable RSE enrichments in correlative strata of northwestern Canada. Here we report four positive chromium isotope (δ53Cr) excursions with peak values (+0.79 ± 0.03‰ to +1.45 ± 0.06‰; 2SD) close to the average δ53Cr value of the modern ocean (+1.0 ± 0.3‰) at the intervals of OOEs, which are separated by low δ53Cr values close to that of the bulk silicate Earth (BSE, −0.124 ± 0.101‰). The positive δ53Cr excursions could be explained by episodic input of oxygenated water from the open ocean to the restricted Nanhua basin, or pulses of ocean oxygenation during the Ediacaran-early Cambrian. The two interpretations can explain the majority of the geochemical data available from the Wuhe section, but both have limitations. [...]". 

 

Source: Science Direct

Authors: Dongtao Xu et al.

DOI: https://doi.org/10.1016/j.gca.2022.02.019

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A transient oxygen increase in the Mesoproterozoic ocean at ∼1.44 Ga: Geochemical evidence from the Tieling Formation, North China Platform

Abstract.

"Oxygen availability is crucial for the evolution of eukaryotes in geological history, yet detailed Mesoproterozoic oceanic-atmospheric redox conditions remain enigmatic. In contrast to the generally accepted hypothesis of an anoxic mid-Proterozoic ocean and atmosphere, several transient oxygenation events may occur at the Earth’s surface during the Mesoproterozoic, especially for the period around 1.4 Ga. The North China Platform develops one of the most complete and continuous Mesoproterozoic stratigraphic successions globally, preserving key information on the redox state of the surface ocean–atmosphere system during the mid-Proterozoic. [...]".

 

Source: Science Direct

Authors: Yang Yu et al.

DOI: https://doi.org/10.1016/j.precamres.2021.106527

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Major Early-Middle Devonian oceanic oxygenation linked to early land plant evolution detected using high-resolution U isotopes of marine limestones

Abstract.

"The middle Paleozoic (∼420-350 Myr) records a major increase in ocean-atmosphere oxygen levels; however, the timing and pattern of oxygenation are poorly constrained. Two well-dated North American locations in Nevada and Illinois were used to generate a high-resolution U-isotopic profile (U) spanning ∼70 Myr of the middle Paleozoic. Stratigraphic and geochemical data support the interpretation that the Nevada profile represents a near-primary record of global-ocean redox variations. First-order U trends indicate strongly reducing oceans during the late Silurian and Early Devonian, terminated by a major oxygenation event near the Emsian-Eifelian boundary (∼395 Ma). More oxic seawater conditions persisted for the next 30+ Myr, but were punctuated by multiple Myr-scale anoxic events during the Middle-Late Devonian and Early Mississippian that correlate with known global biotic crises, positive C excursions, and widespread organic-rich facies deposition. [...]".

 

Source: Science Direct

Authors: Maya Elrick et al.

DOI: https://doi.org/10.1016/j.epsl.2022.117410

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Fe isotope composition of Archean sulfides do not record progressive oxygenation of the ocean

Abstract.

"In the history of this continuously evolving planet, the Great Oxygenation Event (GOE), which occurred at ca. 2.3 Ga (Bekker et al., 2004; Holland, 2006) was a critical environmental change. This event was first recognized by the disappearance of detrital uraninite, pyrite, and siderite, from the siliciclastic record, as well as by shales that do not contain appreciable amounts of redox-sensitive elements and paleosols that are not oxidized before ca. 2.3 Ga (Holland, 2006). [...]"

Source: Geology
Authors: Johanna Marin Carbonne
DOI: 10.1130/focus042020.1

Read the full article here.


Spatiotemporal redox heterogeneity and transient marine shelf oxygenation in the Mesoproterozoic ocean

Abstract.

"The Mesoproterozoic Era (1.6-1.0 Ga), long regarded as an interval of sluggish biotic evolution and persistently low atmospheric-oceanic oxygen levels, has become the subject of recent controversy regarding putative large-scale oxygenation events. In this study, we conducted a comprehensive investigation of redox, productivity, seawater sulfate concentrations, and hydrographic conditions for the ∼1.4-1.32-Ga Xiamaling Formation in the shallow Hougou and mid-depth Huangtugui sections in the Yanshan Basin (North China). [...]"

Source: Geochimica et Cosmochimica Acta
Authors: HaiyangWang et al.
DOI: 10.1016/j.gca.2019.11.028

Read the full article here.


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