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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

Read the full article here.


Marine redox fluctuation as a potential trigger for the Cambrian explosion

Abstract.

The diversification of metazoans during the latest Neoproterozoic and early Cambrian has been attributed to, among other factors, a progressive rise in surface oxygen levels. However, recent results have also questioned the idea of a prominent rise in atmospheric oxygen levels or a major or unidirectional shift in the marine redox landscape across this interval. Here, we present new carbonate-associated uranium isotope data from upper Ediacaran to lower Cambrian marine carbonate successions. [...]"

Source: Geology
Authors: Guang-Yi Wei et al.
DOI: 10.1130/G40150.1

Read the full article here.


Heterogenous oceanic redox conditions through the Ediacaran-Cambrian boundary limited the metazoan zonation

Abstract.

"Recent studies have enhanced our understanding of the linkage of oxygenation and metazoan evolution in Early Cambrian time. However, little of this work has addressed the apparent lag of animal diversification and atmospheric oxygenation during this critical period of Earth history. This study utilizes the geochemical proxy and N isotope record of the Ediacaran–Cambrian boundary preserved in intra-shelf basin, slope, and slope basin deposits of the Yangtze Sea to assess the ocean redox state during the Early Cambrian metazoan radiation. [...]"

Source: Scientific Reports
Authors: Junpeng Zhang, Tailiang Fan, Yuandong Zhang, Gary G. Lash, Yifan Li & Yue Wu
DOI: 10.1038/s41598-017-07904-3

Read the full article here.


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