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Biosignatures link microorganisms to iron mineralization in a paleoaquifer

Karrie A. Weber, Trisha L. Spanbauer, David Wacey, Matthew R. Kilburn, David B. Loope and Richard M. Kettler
Biosignatures link microorganisms to iron mineralization in a paleoaquifer
Geology (Boulder) (June 2012) 40 (8): 747-750


Concretions, preferentially cemented masses within sediments and sedimentary rocks, are records of sediment diagenesis and tracers of pore water chemistry. For over a century, rinded spheroidal structures that exhibit an Fe(III) oxide-rich exterior and Fe-poor core have been described as oxidation products of Fe(II) carbonate concretions. However, mechanisms governing Fe(III) oxide precipitation within these structures remain an enigma. Here we present chemical and morphological evidence of microbial biosignatures in association with Fe(III) oxides in the Fe(III) oxide-rich rind of spheroidal concretions collected from the Jurassic Navajo Sandstone (southwest United States), implicating a microbial role in Fe biomineralization. The amount of total organic carbon in the exterior Fe(III) oxides exceeded measured values in the friable interior. The mean delta (super 13) C value of organic carbon from the Fe(III) oxide-cemented exterior, delta (super 13) C of -20.55 per mil, is consistent with a biogenic signature from autotrophic bacteria. Scanning electron micrographs reveal microstructures consistent with bacterial size and morphology, including a twisted-stalk morphotype that resembled an Fe(II)-oxidizing microorganism, Gallionella sp. Nanoscale associations of Fe, O, C, and N with bacterial morphotypes demonstrate microorganisms associated with Fe(III) oxides. Together these results indicate that autotrophic microorganisms were present during Fe(III) oxide precipitation and present microbial catalysis as a mechanism of Fe(III) oxide concretion formation. Microbial biosignatures in rinded Fe(III) oxide-rich concretions within an exhumed, Quaternary aquifer has broad implications for detection of life within the geological record on Earth as well as other Fe-rich rocky planets such as Mars, where both Fe(II) carbonate and Fe(III) oxide-rich concretions have been identified.

ISSN: 0091-7613
EISSN: 1943-2682
Serial Title: Geology (Boulder)
Serial Volume: 40
Serial Issue: 8
Title: Biosignatures link microorganisms to iron mineralization in a paleoaquifer
Affiliation: University of Nebraska, School of Biological Sciences, Lincoln, NE, United States
Pages: 747-750
Published: 20120615
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 31
Accession Number: 2012-065564
Categories: Sedimentary petrologyGeochemistry of rocks, soils, and sediments
Document Type: Serial
Bibliographic Level: Analytic
Annotation: With GSA Data Repository Item 2012205; accessed on July 5, 2012
Illustration Description: illus.
Source Medium: WWW
N37°40'00" - N37°45'00", W111°25'00" - W111°19'60"
Secondary Affiliation: University of Western Australia, AUS, Australia
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 201234
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