Large perturbations of the carbon and sulfur cycle associated with the Late Ordovician mass extinction in South China
Tonggang Zhang et al., CRC in Biogeochemistry, University of Quebec at Montreal, Montreal H3C 3P8, Canada. Pages 299-302.
The Late Ordovician mass extinction took place in the Hirnantian Stage (445.6-443.7 million years ago) and is the second largest of all great extinction events over the past 543 million years. During this biological crisis, it has been estimated that 26% of all families, or 49% of all genera, became extinct. The Late Ordovician extinction appears to coincide with the Late Ordovician glaciation that developed in high-latitude Gondwanaland. This has led many to propose that the glaciation and extinction were causally linked. In this study, Zhang et al. performed high-resolution carbon and sulfur isotopic studies on Late Ordovician sedimentary rocks from South China. Their geochemical data reveal large perturbations of the sulfur and carbon cycle accompanying the mass extinction, and their isotopic data suggest deep-water anoxia in South China, in contrast to the conventional view that the global oceans were oxygenated. Zhang et al. argue that anoxia may have contributed to the episodic and stepwise extinction in the Hirnantian Stage, in conjunction with harsh climate and temperature changes related to glaciation.
Circum-Pacific arc flare-ups and global cooling near the Eocene-Oligocene boundary
Brian R. Jicha et al., Dept. of Geolo
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Geological Society of America