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(2020) Oxidation Pathway for Iron-Rich Stromatolites Deposited in the Lead up to the GOE

Heard A, Bekker A, Dauphas N, Tsikos H & Ireland T


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09c: Room 3, Thursday 25th June 08:24 - 08:27

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Submitted by Elizabeth Swanner on Wednesday 24th June 04:56
Since you did not show the stratigraphic trends for your geochemistry. I am wondering if there is any indication for a non-marine source for the iron in stromatolites. Is it possible the source of iron could be continental? Do your results exclude the possibility that Fe and Mn are forming rapidly upon discharge of anoxic groundwater (transporting Fe and Mn) to a shallow and oxic setting?
Thank you for the question, this is an interesting idea to consider. The geochemistry of these stromatolites does look like more continentally influenced than the underlying IF (higher detrital Al, Ti contents), so if anoxic groundwater contributed iron anywhere in this basin, the stromatolites would be the most likely place for this to happen. But the Fe/Mn and d56Fe values are roughly where I would expect them to be relative to the deeper water IF if there was a shared source of marine Fe2+ that was being progressively oxidized as it upwelled. The REE profiles (which were not in the presentation) also look like seawater. So the data we currently have do not rule out a complementary non-marine source for some iron, but it looks like much of the iron must come from seawater.

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