Earth and Planetary Science Letters 303 (2011) 121–132 Contents lists available at ScienceDirect Earth and Planetary Science Letters journal homepage: www.elsevier.com/locate/epsl Iron and carbon isotope evidence for microbial iron respiration throughout the Archean Paul R. Craddock ⁎, Nicolas Dauphas Origins Laboratory, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637, United States article info abstract Article history: Banded Iron-Formations (BIFs) are voluminous chemical sediments that are rich in iron-oxide, carbonate and Received 17 August 2010 silica and whose occurrence is unique to the Precambrian. Their preservation in the geological record offers Received in revised form 20 December 2010 insights to the surface chemical and biological cycling of iron and carbon on early Earth. However, many details Accepted 22 December 2010 regarding the role of microbial activity in BIF deposition and diagenesis are unresolved. Laboratory studies have Available online 22 January 2011 + shown that reaction between carbon and iron through microbial iron respiration [2Fe2O3∙nH2O+CH2O+7H → 2+ − Editor: R.W. Carlson 4Fe +HCO3 +(2n+4)H2O+chemical energy] can impart fractionation to the isotopic compositions of these elements. Here, we report iron (δ56Fe, vs. IRMM-014) and carbon isotopic (δ13C, vs. V-PDB) compositions of Keywords: magnetite and of iron-rich and iron-poor carbonates in BIFs from the late Archean (~2.5 Ga) Hamersley Basin, iron-formation Australia and the early Archean (~3.8 Ga) Isua Supracrustal Belt (ISB), Greenland. The range of δ56Fe values Hamersley measured in the Hamersley Basin, including light values in magnetite and heavy values in iron-rich carbonates Isua (up to +1.2‰), are incompatible with their precipitation in equilibrium with seawater. Rather, the data together iron carbonates with previously reported light δ13C values in iron-rich carbonates record evidence for diagenetic reduction of iron respiration ferric oxide precursors to magnetite and carbonate through microbial iron respiration (i.e., dissimilatory iron reduction, DIR). Iron and carbon isotope data of iron-rich metacarbonates from the ISB are similar to those of late Archean BIFs. The isotopic signatures of these metacarbonates are supportive of an early diagenetic origin despite metasomatic overprint, and preserve evidence of microbial iron respiration within the oldest recognized sedimentary rocks on Earth. © 2010 Elsevier B.V. All rights reserved. 1. Introduction et al., 2000; Farquhar et al., 2000; Kasting, 1987; Ono et al., 2003; Pavlov and Kasting, 2002), is uncertain. Photochemical oxidation of Fe(II) Banded Iron-Formations (BIFs) are conspicuously laminated marine in surface ocean waters owing to interaction with incident UV radiation chemical sediments that are characterized by high concentrations of iron- has been proposed as an entirely abiological means of accounting for bearing minerals (20–40 wt.% bulk Fe) commonly interbedded with ferric iron in BIFs (Braterman et al., 1983; Cairns–Smith, 1978). Oxidation layers of silica, and whose occurrence is unique to the Precambrian of Fe(II) by O2 produced via photosynthesis has also been suggested (James, 1954, 1983). The mineralogy of the best-preserved BIFs consists of (Cloud, 1965, 1973), implying an indirect biological influence on BIF combinations of four dominant facies: oxide (magnetite, hematite), formation and hinting at the presence of free O2 oases in the Archean carbonate (siderite, ankerite, Fe–dolomite and, less commonly, calcite), surface ocean. Alternatively, direct biological activity has been implicated, chert and silicate (stilpnomelane, riebeckite, greenalite, minnesotaite), via anoxygenic photosynthesis that coupled oxidation of Fe(II) to and locally sulfide (pyrite) and phosphate (apatite). Most known BIFs reduction of inorganic carbon to yield organic compounds (Garrels have ages in the range ~3.8 to 1.8 Ga, but these formations also occur to a et al., 1973; Kappler et al., 2005; Konhauser et al., 2007; Widdel et al., lesser extent in the Neoproterozoic at ~700 Ma (Klein, 2005). The study of 1993). It is also uncertain the extent to which the mineral assemblages these formations preserved in the rock record offers critical insights to preserved in BIFs reflect either primary precipitates from seawater, surface geochemical cycles and chemical evolution of the ocean and possibly in near-chemical equilibrium with the ocean and atmosphere, or atmosphere in the Precambrian, and in particular the Archean (≥2.5 Ga). are authigenic minerals formed during early sedimentary diagenesis and Despite significant scientific interest and research, however, there is burial metamorphism. For example, the mineralogical, chemical (e.g., rare no consensus on the origin of BIFs. The primary mechanism for oxidation earth element) and isotopic (e.g., δ13C, δ18O) characteristics of iron-rich of Fe(II)aq in an Archean ocean that was purportedly anoxic (Canfield carbonates such as siderite [FeCO3]andankerite[Ca0.5(Fe,Mg)0.5CO3]in BIFs have been used to argue either for primary precipitation from an anoxic and stratified water column (Beukes et al., 1990; Kaufman et al., ⁎ Corresponding author. Tel.: +1 773 834 3997. 1990; Klein and Beukes, 1989) or for an authigenic origin (Becker and E-mail address: [email protected] (P.R. Craddock). Clayton, 1972; Heimann et al., 2010; Walker, 1984). 0012-821X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.epsl.2010.12.045 122 P.R. Craddock, N. Dauphas / Earth and Planetary Science Letters 303 (2011) 121 Table 1 Iron and carbon isotopic compositions of oxides and carbonate from drill core samples of the Brockman Iron Formation, Hamersley Basin. Samplea Hole a Macroband Mesoband Type Depthb δ13C δ56Fe δ57Fe (m) (‰)c (‰) d (‰)d Ankerite Siderite Ankerite/Siderite Magnetite Hematite Ankerite/Siderite Magnetite Hematite Dales Gorge Member, Brockman Iron Formation Drill core from Wittenoom Gorge Area (118° 28′ E; 22° 25′ S) 13324 M1 27 BIF 12 Magnetite 85.2 0.424±0.031 0.630±0.043 13327 WC2 27 BIF 11 Chert 98.4 −11.41 −11.08 −0.289±0.031 0.205±0.031 −0.442±0.049 0.316±0.049 13327 WC1 27 BIF 11 Chert 98.4 −15.05 0.013±0.031 0.465±0.031 0.008±0.046 0.699±0.043 13321 HC 27 BIF 10 Chert+hematite 99.5 −6.98 −7.45 −0.705±0.031 0.908±0.038 −1.023±0.083 1.369±0.044 13318 M3 27 BIF 7 Magnetite 122.2 −9.24±0.03 0.006±0.036 0.005±0.057 13318 Pl 27 BIF 7 Chert 122.2 −9.83±0.04 −0.584±0.029 −0.865±0.051 13318 FM1 27 BIF 7 Chert 122.2 −9.72±0.06 0.118±0.031 −0.210±0.034 0.373 ±0.029 0.198±0.046 −0.298±0.054 0.561±0.051 13318 M1 27 BIF 7 Magnetite 122.3 0.159±0.029 0.230±0.051 13318 M2 27 BIF 7 Magnetite 122.3 0.112±0.031 0.179±0.046 13316 M1 27 BIF 6 Magnetite 128.1 0.650±0.038 0.949±0.058 13316 CA1 27 BIF 6 Fine−band combination 128.2 −9.31 0.641±0.031 0.636±0.033 0.933±0.083 0.914±0.060 13316 CB1 27 BIF 6 Coarse-band combination 128.2 −9.01 −9.41 0.178±0.033 0.196±0.031 0.283±0.060 0.244±0.049 13309 FM1 27 BIF 1 Chert 162.2 −9.87 0.057±0.031 0.588±0.031 0.070±0.046 0.852±0.043 13309 PC1 27 BIF 1 Chert 162.3 −10.06 −0.161±0.031 0.490±0.030 −0.236±0.043 0.710±0.046 13309 QIO1 27 BIF 1 Chert-matrix 162.4 0.675±0.031 0.790 ±0.034 0.990±0.046 1.144±0.054 13309 M2 27 BIF 1 Magnetite 162.4 0.488±0.030 0.694±0.044 13326 M1 28 BIF 12 Magnetite 110.9 0.418±0.031 0.610±0.046 – 13328 WC2 28 BIF 11 Chert 114.9 −11.07 −12.48 −0.555±0.031 −0.757±0.049 132 13328 WC1 28 BIF 11 Chert 115.0 −12.86 0.426±0.038 0.630±0.044 13322 WC1 28 BIF 10 Chert 125.2 −9.73 0.453±0.035 0.662±0.047 13322 WCIA 28 BIF 10 Chert 125.2 −9.61 0.294±0.027 0.419±0.040 13322 M1 28 BIF 10 Magnetite 125.2 0.730±0.033 1.107±0.060 13322 HC 28 BIF 10 Chert+hematite 125.2 −6.76 −8.26 −0.792±0.038 0.398±0.030 −1.142±0.044 0.584±0.057 13322 WHC 28 BIF 10 Chert+hematite 125.2 −6.50±0.03 −7.80 −1.081±0.033 −1.601±0.060 13322 FM1 28 BIF 10 Chert 125.3 −8.96 −9.79 0.787±0.033 1.194±0.033 1.158±0.044 1.778±0.044 13322 QIO1 28 BIF 10 Chert-matrix 125.3 0.566±0.038 0.998±0.038 0.847±0.058 1.477±0.058 13319 FM3 28 BIF 7 Chert 146.5 −9.74±0.03 −0.318±0.029 −0.287±0.030 −0.470±0.043 −0.422±0.044 13319 FM2 28 BIF 7 Chert 146.6 −10.18±0.01 0.086±0.030 0.064±0.030 0.156±0.044 0.077±0.044 13319 M1 28 BIF 7 Magnetite 146.6 −0.022±0.030 0.014±0.044 13319 FM1 28 BIF 7 Chert 146.6 −9.90 0.075±0.030 −0.149±0.029 0.093±0.044 −0.212±0.043 13313 M1 28 BIF 2 Magnetite 174.5 1.085±0.029 1.582±0.043 13310 PC1 28 BIF 1 Chert 186.7 −0.181±0.028 0.159±0.035 −0.303±0.047 0.241±0.047 M 2 40 BIF 2 Magnetite 196.8 0.551±0.035 0.810±0.047 P 2 40 BIF 2 Chert 196.8 −9.70±0.02 P 2A 40 BIF 2 Chert 196.8 −9.80±0.06 Table 1 (continued) Samplea Hole a Macroband Mesoband Type Depthb δ13C δ56Fe δ57Fe (m) (‰)c (‰) d (‰)d Ankerite Siderite Ankerite/Siderite Magnetite Hematite Ankerite/Siderite Magnetite Hematite Dales Gorge Member, Brockman Iron Formation Drill core from Wittenoom Gorge Area (118° 28′ E; 22° 25′ S) FM 2 40 BIF 2 Chert 196.8 −10.28±0.02 M 3 51 BIF 12 Magnetite 104.5 0.314±0.028 0.478±0.047 QIO 51 51 BIF 5 Chert-matrix 155.4 −0.189±0.028 −0.282±0.047 M 1 51 BIF 5 Magnetite 155.6 −0.092±0.035 −0.111±0.047 P l 51 BIF 5 Chert 155.6 −8.65 Drill core from Yampire Gorge Area (118° 37′ E; 22° 27′ S) 13325 WC2 Y3 BIF 12 Chert 66.2 −10.95±0.02 −0.305±0.041 0.202±0.029 −0.448±0.072 0.298±0.041 13325 M2 Y3 BIF 12 Magnetite 66.2 0.351±0.029 0.515±0.041 13325 M1 Y3 BIF 12 Magnetite 66.3 0.344±0.051 0.519±0.133 13325 FM1 Y3 BIF 12 Chert 66.3 −10.96 0.301±0.033 0.297±0.029 0.410±0.083 0.433±0.041 13325 WC1 Y3 BIF 12 Chert 66.4 −10.84±0.01 −0.404±0.029 0.194±0.029 −0.588±0.043 0.282±0.133 13329 M1 Y3 BIF 11 Magnetite 70.7 −12.59±0.50 −0.005±0.031 −0.017±0.083 13329 FM1 Y3 BIF 11 Chert 70.8 −11.11 0.244±0.033 0.408±0.033 0.674 ±0.051 0.395±0.083 0.632±0.083 1.057 ±0.133 P.R.