GEOCHEMISTRY: Lost Superocean

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Science  21 Sep 2001:
Vol. 293, Issue 5538, pp. 2173c
DOI: 10.1126/science.293.5538.2173c

The largest mass extinction occurred about 250 million years ago at the boundary between the Permian and the Triassic. At that time, almost all of the continents were part of one supercontinent called Pangea, which was surrounded by a superocean called Panthalassa. Carbon isotopic records from marine deposits near the continental shelf of Pangea show an extreme excursion, signifying that a major climatic change, quite possibly related to the mass extinction, occurred at about the same time.

Musashi et al. have analyzed the carbon isotopic record of Permo-Triassic marine deposits from two ancient volcanic seamounts in southwest Japan. These seamounts were located in the Panthalassa superocean, far away from the continental shelf of Pangea, and their carbon isotopic record represents a sampling of the lost superocean's environment. The seamount carbonate minerals and organic materials show a sharp increase in the light isotope, carbon-12, consistent with major changes seen in organic and inorganic carbon from other records. Thus, this signature of the lost superocean provides further evidence for a dramatic and global alteration of the carbon cycle (affecting organisms and sedimentary rocks). Additional modeling of the carbon record may help to determine whether the global climate change and mass extinctions may both have been related to a large impact event. — LR

Earth Planet. Sci. Lett. 191, 9 (2001).

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