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Millimeter-scale variations of stable isotope abundances in carbonates from banded iron-formations in the Hamersley Group of Western AustraliaSeveral diamond drill cores from formations within the Hamersley Group of Western Australia have been studied for evidence of short-range variations in the isotopic compositions of the carbonates. For a set of 32 adjacent microbands analyzed in a specimen from the Marra Mamba Iron Formation, carbon isotope compositions of individual microbands ranged from -2.8 to -19.8 per mil compared to PDB and oxygen isotope compositions ranged from 10.2 to 20.8 per mil compared to SMOW. A pattern of alternating abundances was present, with the average isotopic contrasts between adjacent microbands being 3.0 per mil for carbon and 3.1 per mil for oxygen. Similar results were obtained for a suite of 34 microbands (in four groups) from the Bruno's Band unit of the Mount Sylvia Formation. Difficulties were experienced in preparing samples of single microbands from the Dales Gorge Member of the Brockman Iron Formation, but overall isotopic compositions were in good agreement with values reported by previous authors. Chemical analyses showed that isotopically light carbon and oxygen were correlated with increased concentrations of iron. The preservation of these millimeter-scale variations in isotopic abundances is interpreted as inconsistent with a metamorphic origin for the isotopically light carbon in the BIF carbonates. A biological origin is favored for the correlated variations in 13C and Fe, and it is suggested that the 13C-depleted carbonates may derive either from fermentative metabolism or from anaerobic respiration. A model is presented in which these processes occur near the sediment-water interface and are coupled with an initial oxidative precipitation of the iron.
Document ID
20040089872
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Baur, M. E.
(University of California Los Angeles 90024, United States)
Hayes, J. M.
Studley, S. A.
Walter, M. R.
Date Acquired
August 21, 2013
Publication Date
January 1, 1985
Publication Information
Publication: Economic geology and the bulletin of the Society of Economic Geologists
Volume: 80
ISSN: 0361-0128
Subject Category
Exobiology
Funding Number(s)
CONTRACT_GRANT: NGR15003-118
Distribution Limits
Public
Copyright
Other
Keywords
NASA Program Exobiology
Non-NASA Center
NASA Discipline Number 50-20
NASA Discipline Exobiology

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