Geological Society of America

T7 Iron Formations, Ferruginous Sediments, and Redox through Time and Space

Sunday, 22 September 2019
8:00 AM - 12:00 PM
Room 229A, North Building

THE FEASIBILITY OF POST-DEPOSITIONAL IRON FORMATION OXIDATION AND REDOX IMPLICATIONS FOR SEAWATER IN THE PALEOPROTEROZOIC

Paper number: T7-6
Program: Technical Sessions
Time: 9:15 AM – 9:35 AM

Authors

Leslie J. Robbins Presenting Author
Yale University, New Haven, CT
Leslie J. Robbins Presenting Author
University of Alberta, Edmonton, AB
Sean P. Funk
University of Alberta, Edmonton, AB
Daniel Alessi
University of Alberta, Edmonton, AB
Benjamin Rostron
University of Alberta, Edmonton, AB
Stefan V. Lalonde
European Institute for Marine Studies, Plouzane
Albertus J.B. Smith
University of Johannesburg, Johannesburg
Nicolas J. Beukes
University of Johannesburg, Johannesburg
Kurt Konhauser
University of Alberta, Edmonton, AB

Abstract

The oxide facies of Archean to Paleoproterozoic banded iron formations (BIF) have been interpreted to reflect either the direct or indirect oxidation of Fe(II) to Fe(III) through biological mechanisms. Recent models that ascribe the deposition of these BIF to reduced iron silicate precursors have challenged this view that planktonic cells control the redox structure of the ancient marine photic zone. A significant obstacle to accepting reduced phases as precursors to the oxidized minerals in BIF is the origin of mixed-valence to ferric phases, such as magnetite (Fe₃O₄) and hematite (Fe₂O₃) that characterize the oxide facies of these deposits. While post-depositional oxidation by groundwater has been suggested to account for their presence, their occurrence over large depositional basins, and the need to invoke unrealistic hydrogeological conditions in order to oxidize these reduced phases post-depositionally over reasonable time frames, strongly suggest that a ferric precursor, such as ferrihydrite (Fe(OH)₃), is more likely. Accordingly, the deposition of BIF is most consistent with biologically-driven iron oxidation within the water column, providing evidence for a dynamic redox structure within the photic zone of the Paleoproterozoic oceans. Furthermore, multiple lines of geochemical evidence, including iron isotopes and rare earth element patterns, support both an oxidized origin and indicate the preservation of primary marine signatures, respectively.

Geological Society of America Abstracts with Programs. Vol. 51, No. 5

doi: 10.1130/abs/2019AM-336110

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