The transition to a sulphidic ocean ~ 1.84 billion years ago

Details The transition to a sulphidic ocean ~ 1.84 billion years ago The transition to a sulphidic ocean ~ 1.84 billion years ago

Sep 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004natur.431..173p&link_type=abstract

Nature, Volume 431, Issue 7005, pp. 173-177 (2004).

Computer Science

31

Scientific paper

The Proterozoic aeon (2.5 to 0.54 billion years (Gyr) ago) marks the time between the largely anoxic world of the Archean (> 2.5Gyr ago) and the dominantly oxic world of the Phanerozoic (< 0.54Gyr ago). The course of ocean chemistry through the Proterozoic has traditionally been explained by progressive oxygenation of the deep ocean in response to an increase in atmospheric oxygen around 2.3Gyr ago. This postulated rise in the oxygen content of the ocean is in turn thought to have led to the oxidation of dissolved iron, Fe(II), thus ending the deposition of banded iron formations (BIF) around 1.8Gyr ago. An alternative interpretation suggests that the increasing atmospheric oxygen levels enhanced sulphide weathering on land and the flux of sulphate to the oceans. This increased rates of sulphate reduction, resulting in Fe(II) removal in the form of pyrite as the oceans became sulphidic. Here we investigate sediments from the ~1.8-Gyr-old Animikie group, Canada, which were deposited during the final stages of the main global period of BIF deposition. This allows us to evaluate the two competing hypotheses for the termination of BIF deposition. We use iron-sulphur-carbon (Fe-S-C) systematics to demonstrate continued ocean anoxia after the final global deposition of BIF and show that a transition to sulphidic bottom waters was ultimately responsible for the termination of BIF deposition. Sulphidic conditions may have persisted until a second major rise in oxygen between 0.8 to 0.58Gyr ago, possibly reducing global rates of primary production and arresting the pace of algal evolution.

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