Correction notice Pervasive oxygenation along late Archaean ocean margins

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1 Correction notice Pervasive oxygenation along late Archaean ocean margins Brian Kendall, Christopher T. Reinhard, Timothy W. Lyons, Alan J. Kaufman, Simon W. Poulton and Ariel D. Anbar The accompanying Excel file was missing when this Supplementary Information file was originally posted online on 22 August The Excel file has now been posted online as of 26 August 2010.

2 SUPPLEMENTARY INFORMATION doi: /ngeo942 Supplementary Information For: Pervasive oxygenation along Late Archaean ocean margins by B. Kendall et al. nature geoscience 1

3 supplementary information doi: /ngeo942 Supplementary Figure S1. Summary of geochemical trends and interpretations for water column redox conditions on the slope of the Campbellrand Malmani carbonate platform (upper Nauga Formation shale beds) and in deeper waters after the carbonate platform drowned (Klein Naute Formation). Rocks in these cores are minimally deformed and have undergone sub-greenschist facies metamorphism. U-Pb zircon ages from volcanic ash beds in the Nauga Formation are summarized in ref. 14 and the age for the Kuruman Formation is from ref. 36. The intermittently euxinic interval in the lower Klein Naute Formation occurs below 305 m and 264 m depth in GKP01 and GKF01, respectively. Samples from stratigraphically higher intervals in the Klein Naute Formation record anoxic and ferruginous conditions in the water column. Geochemical 2 nature geoscience

4 doi: /ngeo942 supplementary information analyses from this ferruginous interval are derived largely from the more distal GKP01 core because black shale is scarce in the more proximal GKF01 core. Previous low-resolution geochemical analyses from the black shales in GKP01 largely focused on Mo abundances and isotopic compositions. That study used observations of mild Mo enrichments and heavy Mo isotope compositions from some samples to infer the presence of O 2 in the Late Archaean surface environment 52. Stratigraphic columns were modified from refs. 13, 14. nature geoscience 3

5 supplementary information doi: /ngeo942 Supplementary Figure S2. Relationship between δ 34 S and Δ 33 S of synsedimentary and early diagenetic sulphides in black shales of the Nauga and Klein Naute formations (including data from ref. 47). Both the shales from the intermittently euxinic interval in the lower Klein Naute Formation and the ferruginous shales and BIF from the lower Mount McRae Shale plot close to the Archaean reference array (Δ 33 S = 0.89 δ 34 S; represented by the dashed line) 8,10,47. Large positive Δ 33 S and positive covariation in Δ 33 S and δ 34 S has been hypothesized to reflect a mixing array of high-altitude (larger Δ 33 S) and ground-level (smaller Δ 33 S) atmospheric elemental sulphur aerosols. Thus, the dominant sulphur source for sedimentary pyrite formation during deposition of the lower Klein Naute Formation and lower Mount McRae Shale was commonly atmospheric in origin 8,10,47. This does not necessarily mean an absence of oxidative sulphide 4 nature geoscience

6 doi: /ngeo942 supplementary information weathering during this time, but rather that atmospheric reduced sulphur species often dominated the sedimentary sulphide mass balance. Generally smaller but non-zero Δ 33 S and relatively lighter δ 34 S characterize the black shales of the upper Klein Naute Formation and upper Mount McRae Shale. The S isotope shifts are hypothesized to reflect higher seawater sulphate concentrations from oxidative weathering of crustal sulphides and the mixing of oxidized, isotopically normal crustal sulphur with the mass-independent signature of photolytically produced sulphur 8,10. Sedimentary Fe speciation and S isotope data indicate that water column euxinia and increased sulphate concentrations occur contemporaneously in the Mount McRae Shale. Thus, an increased sulphate flux to the Hamersley Basin together with enhanced organic carbon export stimulated microbial H 2 S production, which overwhelmed the reactive Fe flux in the middle water column 10. However, water column euxinia precedes the shift to smaller Δ 33 S and lighter δ 34 S in the Klein Naute Formation. We hypothesize that water column euxinia in the lower Klein Naute Formation was facilitated by low reactive Fe availability (as opposed to an increase in sulphate availability). At the more proximal GKF01 locality, high TOC and heavy δ 34 S in the lower Klein Naute Formation suggests high organic carbon fluxes stimulated high rates of microbial sulphate reduction and depleted the inventory of dissolved seawater sulphate. The heavy δ 34 S arises from a small expression of mass-dependent S isotope fractionation during microbial sulphate reduction because of the small concentrations (possibly <200 µm) of seawater sulphate 53. Under these conditions, sedimentary sulphides have δ 34 S that is only slightly lighter than seawater sulphate. At the more distal GKP01 locality, lower rates of microbial sulphate reduction may have resulted in less depletion of the seawater sulphate inventory. Larger S isotope fractionations are then expressed during microbial sulphate reduction, leading to the nature geoscience 5

7 supplementary information doi: /ngeo942 preservation of a larger isotopic offset between sedimentary sulphides (i.e., lighter δ 34 S) and seawater sulphate. Middle water column euxinia could have occurred during deposition of the upper Klein Naute Formation in the Griqualand West Basin, but not at the deep water depths represented by the GKP01 and GKF01 localities at this time. The upsection shift to smaller Δ 33 S and relatively lighter δ 34 S in the Klein Naute Formation and Mount McRae Shale may be a time-correlative geochemical signature that marks the onset of a more vigorous oxidative sulphur cycle 8. We note, however, that it is difficult to rule out a scenario in which this isotopic shift is driven by a change in the relative input of deep ocean sulphate (slightly negative Δ 33 S) and atmospheric reduced sulphur (positive Δ 33 S) to sedimentary pyrite. For example, the average Δ 33 S of black shale beds in the more proximal GKF01 core is typically more positive compared to the stratigraphically equivalent interval in the more distal GKP01 core (see table below). This relationship between Δ 33 S and water depth likely reflects a relatively larger role of atmospheric sulphur inputs to shallower water environments. Nevertheless, the correlative shift to smaller Δ 33 S and relatively lighter δ 34 S in the black shales of the upper Klein Naute Formation and upper Mount McRae Shale, deposited from water columns of different redox character (ferruginous and euxinic, respectively), does imply a temporal trend rather than a local paleoenvironmental control. In further support of this statement, we note that the younger Kuruman BIF and its stratigraphic correlative the Brockman BIF (Hamersley Basin) also have small Δ 33 S (typically 0 ± 2 ; refs. 8, 10). In contrast, S isotope data from Gyr-old black shales (Jeerinah Formation) and BIF (Marra Mamba Formation) stratigraphically underlying the Mt. McRae Shale cluster near the Archaean reference array and often have large Δ 33 S (up to 10 ; see ref. 10). Collectively, the observations from 6 nature geoscience

8 doi: /ngeo942 supplementary information deep-water shales and BIFs point to a temporal increase in atmospheric po 2 at the Archaean- Proterozoic transition, which predated the Great Oxidation Event. The timing of this change may be closely approximated by a Re-Os depositional age of 2501 ± 8 Myr from black shales in the upper Mt. McRae Shale 7. The shallower-water Nauga Formation has variable but generally large Δ 33 S, and contains examples of both lighter and heavier δ 34 S relative to the Archaean reference array, which may indicate mixing of sulphide from open- and closed-system microbial sulphate reduction, respectively, with atmospherically derived sulphur 47. For further explanation of the Nauga Formation S isotope systematics, the reader is referred to ref. 47. Average and standard deviation of S isotope data for each black shale interval. GKF01 δ 34 S ( ) GKP01 δ 34 S ( ) GKF01 Δ 33 S ( ) GKP01 Δ 33 S ( ) Bottom water Redox state Nauga N1 8.4 ± ± ± ± 1.6 Oxic (> 1 cm) Nauga N2 0.5 ± ± ± ± 1.7 Oxic (< 1 cm) Nauga N3 3.3 ± 1.3 n/a 3.7 ± 0.7 n/a Oxic (< 1 cm) Klein Naute 5.4 ± ± ± ± 2.8 Euxinic Klein Naute 5.3 ± ± ± ± 1.3 Ferruginous Nauga N1 = m in GKP01, m in GKF01; Nauga N2 = m in GKP01, m in GKF01; Nauga N3 = m in GKF01; Klein Naute (intermittently euxinic) = m in GKP01, m in GKF01; Klein Naute (ferruginous) = m in GKP01, m in GKF01. If bottom water redox state is oxic, the depth of O 2 penetration below the sediment-water interface is given. Averages include data from ref. 47. Additional References 52. Wille, M. et al. Evidence for a gradual rise of oxygen between 2.6 and 2.5 Ga from Mo isotopes and Re-PGE signatures in shales. Geochim. Cosmochim. Acta 71, (2007). 53. Habicht, K. S. et al. Calibration of sulfate levels in the Archean ocean. Science 298, (2002). nature geoscience 7