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Supporting Information
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Redox heterogeneity of subsurface waters in the Mesoproterozoic ocean
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Keywords: Mesoproterozoic; redox; oxygen; Kaltasy Formation; microfossils;
Russia
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SUPPLEMENTARY METHODS
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Iron, carbon, sulfur, major- and minor-element geochemistry
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Samples were first crushed to flour in a tungsten-carbide shatterbox. Protocols for
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iron geochemical analyses are located in the main text, and expanded details of these
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procedures as implemented in this study (e.g. in-house sediment standard replicates run
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alongside samples in iron speciation studies) can be found in the Supplementary
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Materials of Sperling et al. (2013). Replicates of those in-house standards run alongside
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the Arlan samples were consistent with the measurements in Sperling et al. (2013) for the
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sequential extractions, and thus the precision estimates therein (<5% standard deviation
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and <2% standard error of the mean for samples with >0.3 weight percent iron) are
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applicable. A sample from the 203 Bedryazh core, B203-4450m, was run eight times
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through the chromium reduction extraction to estimate precision in pyrite iron
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measurements. Error in this measurement is estimated as a percent standard deviation of
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7.8%, and percent standard error of the mean of 2.8%. Long-term reproducibility of
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sulfur isotope measurements was 0.15‰, 0.16‰ and 0.2‰ on IAEA-S1, S2 and S3
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standards, respectively. Pyrite sulfur isotopes and weight percent TOC measurements on
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samples analyzed in duplicate showed very close correspondence between individual
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measurments (Table S2).
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Re-Os geochronology
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Samples were collected from two intervals of drill core 203 Bedryazh; i) 4197.97
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m to 4198.50 m and ii) from 4297.05 m to 4297.40 m. Rhenium-Osmium isotope analysis
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was carried out at Durham University’s TOTAL laboratory for source rock geochronology
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and geochemistry. Prior to crushing, all samples were polished to remove cutting and
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drilling marks to eliminate any metal contamination. The samples were dried at 60 °C for
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~12 hrs and were broken into chips with no metal contact before powdering in a
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zirconium ceramic mill to a fine powder ~30 µm. Each sample (~50 g) represent ~2 cm
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of stratigraphy. Between 1.4 g and 1.6 g of sample was digested and equilibrated in 10
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mL of CrVIO3-H2SO4 together with a mixed tracer (spike) solution of
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carius tubes at 220 °C for 48 h. Re and Os were extracted and purified using solvent
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extraction (NaOH and (CH3)2CO and CHCl3, respectively), micro-distillation and anion
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column chromatography methods and negative mass spectrometry as outlined by
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Cumming et al. (2013 and references therein). The CrVIO3-H2SO4 digestion method is
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employed as it has been shown to preferentially liberate hydrogenous Re and Os, thus
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yielding more accurate and precise age determinations (Selby and Creaser, 2003; Kendall
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et al., 2004; Rooney et al., 2011).
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Os and
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Re in
2
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Total procedural blanks during this study were 10.3 ± 0.09 pg and 0.08 ± 0.001 pg
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Os/188Os value of 0.432 ± 0.258 (1σ S.D.,
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for Re and Os respectively, with an average
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n = 3). Isotopic measurements were performed using a ThermoElectron TRITON mass
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spectrometer via static Faraday collection for Re and ion-counting using a secondary
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electron multiplier in peak-hopping mode for Os. In-house Re and Os solutions were
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continuously analyzed during the course of this study to ensure and monitor long-term
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mass spectrometry reproducibility. The Re solution is made from 99.999% zone-refined
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Re ribbon and yields an average 185Re/187Re value of 0.59818 ± 0.00152 (1 SD, n = 191)
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which is identical to that of (Rooney et al., 2010). The measured difference in 185Re/187Re
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values for the Re solution and the accepted
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1973) is used to correct the Re sample data. The Os isotope reference material is the
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Durham Romil Osmium Solution (DROsS), which yields a 187Os/188Os ratio of 0.10694 ±
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0.00051 (1 SD, n = 128) that is identical, within uncertainty, to those reported in (Rooney
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et al., 2010).
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Re/187Re value (0.5974) (Gramlich et al.,
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Uncertainties for 187Re/188Os and 187Os/188Os are determined by error propagation
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of uncertainties in Re and Os mass spectrometer measurements, blank abundances and
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isotopic compositions, spike calibrations and reproducibility of standard Re and Os
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isotopic values. The Re-Os isotopic data, 2σ calculated uncertainties for
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187
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Os date using Isoplot V. 4.15 with the λ 187Re constant of 1.666 x 10-11a-1 (Ludwig, 1980;
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Smoliar et al., 1996; Ludwig, 2011).
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Re/188Os and
Os/188Os and the associated error correlation function (rho) are regressed to yield a Re-
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Organic geochemistry
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To remove external contamination, these samples were first sonicated three times
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for 10 minutes each in a 7:3 dichloromethane: methanol (DCM Honeywell, GC299-4;
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MeOH Honeywell, GC230-4) solvent mixture to clean off external contamination. Next,
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5-7mm of the edge of the core was cut off using a tap water-cooled rock saw. The
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samples were then sonicated for an additional 10 minutes in a 9:1 DCM:MeOH solvent
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mixture and then for five minutes each in MeOH, DCM and hexane (Honeywell, GC215-
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4). To crush the cleaned rocks, a small steel/chrome puck mill (RockLabs) was used that
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had been pre-cleaned with three combusted sand blanks (~25g each, combusted 8 hours
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at 450 °C) and solvent-cleaned by sonicating twice each with MeOH, DCM and hexane
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for 20 minutes. This process was repeated between each sample. The crushed rock
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powder was then extracted using a CEM MARS Microwave Reaction System (Model:
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MARS 230/60; Model number: 907501). For this extraction step, the total rock powder
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was split into equal fractions between 20-35g, and was put into the Teflon MARS vessels
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with ~40ml of 9:1 DCM:MeOH. These were heated from room temperature to 100 °C
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(30 minute ramp) and held for 20 minutes. After cooling, the solvent was decanted and
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the remaining sediment was extracted two additional times, again with 9:1 DCM:MeOH.
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All three extracts were pooled, filtered and labeled as Bitumen #1 extract. Finally, these
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extracts were treated with activated copper (Cu pellets activated with 5-10ml 6N HCl,
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neutralized with Nano-Pure water, and washed with MeOH and DCM) to remove sulfur.
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The total lipid extracts were concentrated to <100 μl for analysis, and 50 ng each
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of D4 C29  (20R)-ethylcholestane (D4) and 3-methylicosane (ai-C22) were added as
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internal standards. Hydrocarbon biomarkers were analyzed using a HP 6890 GC, coupled
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to a Micromass AutoSpec Ultima mass spectrometer. The GC was fitted with a DB-1
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fused silica capillary column (60 m; 0.25 mm I.D.; 0.25 µm film thickness; J&W
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Scientific) and He was used as carrier gas. The GC temperature program was: 60 °C (2
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min) to 150 °C at 10 °C min-1, to 315 °C (held 24 min) at 3 °C min-1. The AutoSpec
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source was operated in multiple reaction monitoring (MRM) function where two groups
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of precursor-product transitions were monitored with a cycle time of ca. 1.5 seconds, the
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first for cheilanthanes and short-chain steranes and the second for C26-C30 steranes and
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C27-C35 triterpanes. The biomarkers were identified by comparison of their retention
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times with those of a synthetic reference oil (AGSO Standard Oil). For the n-alkanes, the
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total lipid extract was analyzed using a HP 6890N GC attached to an Agilent 5973 mass
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selective detector (MSD). The GC was fitted with a HP5-MS fused silica capillary
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column (30 m; 0.25 mm I.D.; 0.25 µm film thickness; Agilent Technologies) and He was
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used as carrier gas. The GC temperature program was: 65 °C (2 min) to 100 °C at 10 °C
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min-1, to 320 °C (held 20 min) at 4 °C min-1. Saturated hydrocarbons were analyzed in
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the full scan mode and identified by their mass spectra.
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SUPPLEMENTARY RESULTS
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Iron, carbon, sulfur, major- and minor-element geochemistry
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All major- and minor-element geochemical data for this core are contained in
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Supplemental Information Table S1. All iron, carbon, and sulfur measurements are
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contained in Supporting Information Table S2.
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In addition to the iron pools normally investigated in iron speciation analyses (e.g.
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Poulton and Canfield, 2005), the iron in Acid Volatile Sulfides (FeAVS) and Poorly-
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Reactive Silicates (FePRS) was investigated. Acid Volatile Sulfur is generally a minor
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component of ancient rocks (Canfield et al., 1986; Rice et al., 1993), but as this sulfur is
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also extracted along with pyrite sulfur in the Chromium Reducible Sulfur (CRS)
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extraction, significant Acid Volatile Sulfur will lead to erroneous interpretations of
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FePyrite. This is in part because many AVS phases are secondary. More importantly,
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FePyrite is calculated by taking the sulfur extracted during CRS and making a
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stoichiometric conversion to pyrite (FeS2). The stoichiometry of FeAVS phases (e.g. iron
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monosulfides such as pyrrohtite) will differ from the assumed pyrite stoichiometry and
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lead to an erroneous FePyrite value. The presence of FeAVS was investigated here using the
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hot 6N HCl + 0.3M SnCl2 extraction of Rice et al. (1993). In contrast to a boiling acid
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treatment that results in non-complete extraction of AVS in ancient rocks, this extraction
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removes 100% of AVS, but also extracts a small amount (<5%) of well-crystalized
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pyrite, depending on grain size and crystallinity. The Arlan samples investigated had very
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small yields when analyzed with the hot acid + tin chloride extraction, corresponding to
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an average FeAVS of 0.006 ± 0.004 weight percent (Table S2). When corrected for small
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amounts of pyrite extraction as noted by Rice et al. (1993), most samples had zero FeAVS,
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and no sample had more than 0.01 weight percent FeAVS. Thus, Acid Volatile Sulfur can
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be considered a negligible component of these rocks.
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The other iron pool that may affect interpretation of iron speciation data is the
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presence of significant enrichments of iron in Poorly-Reactive Silicates (FePRS). It has
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recently been recognized in iron speciation studies that under anoxic and ferruginous
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water columns, authigenic iron-rich clays may precipitate (e.g. Cumming et al., 2013).
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The exact conditions causing such precipitation are still unknown, but as the iron in these
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authigenic clays are not extracted by the sequential extraction protocol employed here
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(Poulton and Canfield, 2005), such enrichments will be missed, and an anoxic water-
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column might appear ‘oxic.’ FePRS was calculated by measuring the iron obtained in a
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boiling 1-min HCl extraction, and then subtracting the sum of the three sequentially-
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extracted phases, following Cumming et al. (2013). Cumming et al. (2013) compared
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these values (and the ratio of FePRS/FeT) to the values for ‘normal’ Phanerozoic rocks as
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reported by Poulton and Raiswell (2002). We follow this practice, but note that the
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measurements made by Poulton and Raiswell (2002) used an older methodology where
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non-pyrite highly-reactive iron was measured solely with a dithionite extraction rather
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than the full sequential extraction of Poulton and Canfield (2005). Consequently, the
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FePRS values as calculated by Cumming et al. (2013) and also in this study, where FePRS =
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Fe1 Min boiling HCl – Feacetate – Fedithionite – Feoxalate will not directly correspond to the
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corresponding measurements in Poulton and Raiswell (2002), where FePRS = Fe1 Min boiling
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HCl
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S2) and the average FePRS/FeT ratio of 0.20 ± 0.06 is not enriched compared to Modern
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or Phanerozoic normal shales (Poulton and Raiswell, 2002; Cumming et al., 2013). No
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Arlan samples has the extremely high FePRS enrichments of samples suggested to be
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affected by the authigenic enrichment of iron-rich clays, such as the Nonesuch Shale,
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where FePRS/FeT ratios are often near 0.8 (Cumming et al., 2013). Combined with the
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lack of enrichment of total iron with respect to aluminum (see main text), we conclude
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that these shales do not have significant FePRS enrichment.
– Fedithionite. Iron in poorly-reactive silicates (FePRS) averaged 0.66 ± 0.25 wt% (Table
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Re-Os geochronology
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Elemental Re and Os abundances for horizon 4198 meters range from 0.1 to 0.6
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Re/188Os and
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Os/188Os ratios between
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ppb, and 11.3 to 34.6 ppt, respectively, with
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42 and 109, and 1.204 and 2.795, respectively (Table S3). The samples from the B203-
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4297 m interval have Re abundances from 0.1 to 0.7 ppb and Os abundances from 10.3 to
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32.8 ppt, with
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3.652, respectively; Table S3).
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Re/188Os and
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Os/188Os values between 60 and 138, and 1.558 and
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Regression of the isotopic composition data for the 4198 m interval yields a
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Model 1 age of 1414 ± 40 Ma (n = 6, Mean Square of Weighted Deviates [MSWD] =
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0.35, initial
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B203-4298 m interval yields a Model 1 age of 1427 ± 43 Ma (n = 6, Mean Square of
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Weighted Deviates [MSWD] = 0.23, initial 187Os/188Os [Osi] = 0.12 ± 0.09; Figure 2).
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Os/188Os [Osi] = 0.20 ± 0.06; Figure 2). The Re-Os isotopic data for the
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Sample
Re
(ng/g)
±
Os
(pg/g)
±
4198.5
4198.33
4198.18
4197.97
4198.28
4198.4
0.10
0.09
0.24
0.58
0.14
0.21
0.0004
0.0003
0.0008
0.0019
0.0005
0.0007
11.5
11.3
17.0
34.6
12.4
14.2
0.2
0.2
0.4
0.3
0.3
0.3
50.0
42.4
86.7
108.9
65.9
90.6
2.0
1.7
2.2
1.1
2.1
2.6
4297.05
4297.08
4297.18
4297.2
4297.30
4297.4
0.23
0.68
0.21
0.24
0.16
0.14
0.0008
0.0022
0.0007
0.0008
0.0005
0.0005
12.9
32.8
10.3
14.7
15.6
12.2
0.3
0.8
0.3
0.3
0.3
0.3
119.3
146.5
138.3
103.7
59.9
67.9
2.4
4.0
2.2
3.3
2.4
2.6
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Re/188Os
±
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Os/188Os
±
rhoa
Osib*,§
1.387
1.204
2.258
2.795
1.793
2.384
0.079
0.069
0.069
0.037
0.072
0.094
0.706
0.705
0.706
0.699
0.706
0.706
0.20
0.20
0.20
0.22
0.23
0.24
3.009
3.652
3.438
2.613
1.558
1.752
0.027
0.090
0.030
0.040
0.088
0.100
0.706
0.706
0.707
0.706
0.706
0.706
0.15
0.15
0.13
0.13
0.12
0.13
All uncertainties are given at the 2 sigma level
a
Rho is the associated error correlation
b
Osi = initial 187Os/188Os isotope ratio calculated at the Re-Os isochron age of 1414* and 1440§ Ma.
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Table S3- Re and Os abundance and isotopic compositions for 203 Bedryazh core-4297
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and 4198 m intervals.
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REFERENCES CITED
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186
187
188
189
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191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
Canfield DE, Raiswell R, Westrich JT, Reaves CM, Berner RA (1986) The use of
chromium reduction in the analysis of reduced inorganic sulfur in sediments and shales.
Chemical Geology 54, 149-155.
Cumming VM, Poulton SW, Rooney AD, Selby D (2013) Anoxia in the terrestrial
environment during the late Mesoproterozoic. Geology 41, 583-586.
Gramlich JW, Murphy TJ, Garner EL, Shields WR (1973) Absolute isotopic abundance
ratio and atomic weight of a reference sample of rhenium: Journal of Research of the
National Bureau of Standards. Section A: Physics and Chemistry 77A, 691-698.
Kendall BS, Creaser RA, Ross GM, Selby D (2004) Constraints on the timing of
Marinoan “Snowball Earth” glaciation by 187Re-188Os dating of a Neoproterozoic postglacial black shale in Western Canada. Earth and Planetary Science Letters 222, 729740.
Ludwig KR (1980) Calculation of uncertainties of U-Pb isotope data. Earth and
Planetary Science Letters 46, 212-220.
Ludwig KR Isoplot/Ex, Version 4.15: A geochronological toolkit for Microsoft Excel.
Geochronology Center Berkeley http://www.bgc.org/isoplot_etc/isoplot.html accessed
2011.
Poulton SW, Raiswell R (2002) The low-temperature geochemical cycle of iron: from
continental fluxes to marine sediment deposition. American Journal of Science 302, 772805.
Poulton SW, Canfield DE (2005) Development of a sequential extraction procedure for
iron: implications for iron partitioning in continentally derived particulates. Chemical
Geology 214, 209-221.
Rice CA, Tuttle ML, Reynolds RL (1993) The analysis of forms of sulfur in ancient
sediments and sedimentary rocks: comments and cautions. Chemical Geology 107, 83-95.
Rooney AD, Chew DM, Selby D (2011) Re-Os geochronology of the NeoproterozoicCambrian Dalradian Supergroup of Scotland and Ireland: implications for
9
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
Neoproterozoic stratigraphy, glaciation and Re-Os systematics. Precambrian Research
185, 202-214.
Rooney AD, Selby D, Houzay J-P, Renne PR (2010) Re-Os geochronology of a
Mesoproterozoic sedimentary succession, Taoudeni basin, Mauritania: Implications for
basin-wide correlations and Re-Os organic-rich sediments systematics. Earth and
Planetary Science Letters 289, 486-496.
Selby D, Creaser RA (2003) Re-Os geochronology of organic rich sediments: an
evaluation of organic matter analysis methods. Chemical Geology 200, 225-240.
Smoliar MI, Walker RJ, Morgan JW (1996) Re-Os ages of Group IIA, IIIA, IVA and
IVB iron meteorites. Science 271, 1099-1102.
Sperling EA, Halverson GP, Knoll AH, Macdonald FA, Johnston DT (2013) A basin
redox transect at the dawn of animal life. Earth and Planetary Science Letters 371-372,
143-155.
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