Supporting Information

Fischer et al. 10.1073/pnas.1322577111 Geological Context Campbellrand, and Asbestos Hills, make up the Transvaal The Late Archean Transvaal Supergroup occurs across much of Supergroup. These record the initial transgression of the Kaapvaal the Kaapvaal Craton, broadly divided into Griqualand West and Craton and development of a marine sedimentary ramp flanking Transvaal structural subbasins (Fig. S1). The succession is re- the basement highs, the flooding of the entire craton and the markably well preserved and largely undeformed across much of progradation of a thick carbonate platform, and drowning of the the craton. Steeper dips occur in the Transvaal subbasin around carbonate platform followed by iron-formation deposition, re- the Bushveld Igneous Complex, and acute folding and faulting spectively. The Vryburg Formation was deposited during the first appears along the far western edge of the craton where Prote- post-Ventersdorp marine transgression of the Kaapvaal Craton rozoic red beds of the Olifantshoek Group are thrust over in Griqualand West. Based on correlation with units in the Transvaal rocks (1–4). Significant metamorphism is limited lo- Transvaal Basin, the Vryburg was deposited between 2,642 ± cally to rocks in the Transvaal basin near the Bushveld complex 3 Ma and 2,664 ± 1 Ma (16, 17). The lower Vryburg consists and the western fold-and-thrust belt; other regions remained primarily of ripple-laminated sandstones that deepen upward below greenschist-equivalent facies (3, 5). However, surficial into organic-rich and pyritic shales and turbidites. The upper oxidative weathering is extensive in South Africa. To obtain fresh contact is gradational, with increasing carbonate content up unweathered material for analysis, we sampled from deep di- section that eventually gives way to the shallow water stroma- amond drill core materials taken northeast of Prieska in the tolites and oolitic grainstones of the Boomplas Formation. An- Northern Cape Province, South Africa as a part of the Agouron other transgression separates the top of the Boomplas from the Institute South African Drilling Project (Fig. S1). Core GKF01 low-energy organic-rich and pyritic shales of the Lokammona captures a diverse range of siliciclastic and authigenic lithologies Formation. Again, carbonate content increases toward the gra- (carbonates, shales, and banded iron formation) within a well- dational upper contact with the overlying Monteville Formation, studied sequence stratigraphic framework (6–8) that provides a steepened carbonate ramp that developed during presumed useful insight into the vectors of time and environment (Figs. S2 and S3). This succession has been studied extensively for its highstand. Following Monteville deposition, the entire Kaapvaal – Craton was flooded and followed by widespread carbonate de- sedimentology, stratigraphy, paleontology, U Pb geochronology, ∼ – organic and carbonate C isotopes and contents (9), bulk rock position and development of the steep-margined 2,588 2,520 multiple S isotopes (10, 11), paleo- and rock magnetics (12), and Ma (17, 18) Campbellrand Platform, represented by the Lower bulk and trace element geochemistry (6, 13). Nauga/Reivilo and Upper Nauga formations. A major trans- The sedimentary geology of the Transvaal Supergroup in gression led to the eventual demise of the Campbellrand Plat- Griqualand West with special attention to relationships in GKF01 form and the deposition of the ∼2,460 Ma (19) Kuruman has been previously described (6–9, 14)—the observations im- Formation. Altogether the Transvaal Supergroup in Griqualand portant to this study are highlighted briefly here. The Transvaal West, during the development of Campbellrand platform and sits disconformably atop volcanics and intercalated sedimentary Kuruman Iron Formation, reflects the passive accumulation of rocks of the Ventersdorp Supergroup (felsic volcanics from the chemical precipitates and minor siliciclastics on thinned conti- upper Ventersdorp yielded a U–Pb ion microprobe age from nental crust adjacent to a major ocean basin in Late Archean zircon of 2.714 ± 8 Ma; ref. 15). Three subgroups, Schmidtsdrif, through earliest Paleoproterozoic time (Fig. S2).

1. Stowe CW (1986) Synthesis and interpretation of structures along the northeastern 14. Fischer WW, Knoll AH (2009) An iron shuttle for deepwater silica in Late Archean and boundary of the Namaqua tectonic province, South Africa. Geol Soc S Afr Trans 89:185–198. Early Paleoproterozoic iron formation. Geol Soc Am Bull 121:222–235. 2. Beukes NJ (1987) Facies relations, depositional environments and diagenesis in a major 15. Armstrong RA, Compston W, Retief EA, Williams IS, Welke HJ (1991) Zircon ion early Proterozoic stromatolitic carbonate platform to basinal sequence, Campbellrand microprobe studies bearing on the age and evolution of the Witwatersrand triad. Subgroup, Transvaal Supergroup, Southern Africa. Sediment Geol 54:1–46. Precambrian Res 53:243–266. 3. Button A (1973) The stratigraphic history of the Malmani dolomite in the eastern and 16. Barton JM, Blignaut E, Salnikova EB, Kotov AB (1995) The stratigraphical position of the north-eastern Transvaal. Geol Soc S Afr Trans 76:229–247. Buffelsfontein Group based on field relationships and chemical and geochronological 4. Beukes NJ, Smit CA (1987) New evidence for thrust faulting in Griqualand West, South data. SAfrJGeol98:386–392. Africa; Implications for stratigraphy and the age of red beds. S Afr J Geol 90:378–394. 17. Walraven F, Martini J (1995) Zircon Pb-evaporation age determinations for the Oak 5. Miyano T, Beukes NJ (1984) Phase relations of stilpnomelane, ferri-annite, and Tree Formation, Chuniespoort Group, Transvaal Sequence; Implications for Transvaal- riebeckite in very low-grade metamorphosed iron-formations. SAfrJGeol87:111–124. Griqualand West basin correlations. S Afr J Geol 98:58–67. 6. Schröder S (2006) Stratigraphic and geochemical framework of the Agouron drill 18. Altermann W, Nelson DR (1998) Sedimentation rates, basin analysis and regional cores, Transvaal Supergroup (Neoarchean-Paleoproterozoic, South Africa). S Afr J correlations of three Neoarchaean and Palaeoproterozoic sub-basins of the Kaapvaal Geol 109:23–54. craton as inferred from precise U-Pb zircon ages from volcaniclastic sediments. Sediment 7. Knoll AH, Beukes NJ (2009) Introduction: Initial investigations of a Neoarchean shelf Geol 120:225–256. margin-basin transition (Transvaal Supergroup, South Africa). Precambrian Res 169:1–14. 19. Pickard A (2003) SHRIMP U–Pb zircon ages for the Palaeoproterozoic Kuruman Iron 8. Sumner DY, Beukes NJ (2006) Sequence stratigraphic development of the Neoarchean Formation, Northern Cape Province, South Africa: Evidence for simultaneous BIF Transvaal carbonate platform. Kaapvaal Craton, South Africa. 109:11–22. deposition on Kaapvaal and Pilbara Cratons. Precambrian Res 125:275–315. 9. Fischer WW, et al. (2009) Isotopic constraints on the Late Archean carbon cycle from 20. Gleason JD, Gutzmer J, Kesler SE, Zwingmann H (2011) 2.05-Ga isotopic ages for the Transvaal Supergroup along the western margin of the Kaapvaal Craton, South Transvaal Mississippi Valley-type deposits: Evidence for large-scale hydrothermal Africa. Precambrian Res 169:15–27. circulation around the Bushveld Igneous Complex. S Afr J Geol 119:69–80. 10. Ono S, Beukes NJ, Rumble D (2009) Origin of two distinct multiple-sulfur isotope 21. Sumner DY, Bowring SA (1996) U-Pb geochronologic constraints on deposition of the compositions of pyrite in the 2.5 Ga Klein Naute Formation, Griqualand West Basin, Campbellrand Subgroup, Transvaal Supergroup, South Africa. Precambrian Res 79:25–35. South Africa. Precambrian Res 169:48–57. 22. Klein C, Beukes NJ (1989) Geochemistry and sedimentology of a facies transition from 11. Ono S, Kaufman AJ, Farquhar J, Sumner DY, Beukes NJ (2009) Lithofacies control on limestone to iron-formation deposition in the early Proterozoic Transvaal Supergroup, multiple-sulfur isotope records and Neoarchean sulfur cycles. Precambrian Res 169:58–67. South Africa. Econ Geol 84:1733–1774. 12. De Kock MO, et al. (2009) Paleomagnetism of a Neoarchean-Paleoproterozoic carbonate 23. Beukes NJ, Klein C, Kaufman AJ, Hayes JM (1990) Carbonate petrography, kerogen ramp and carbonate platform succession (Transvaal Supergroup) from surface outcrop distribution, and carbon and oxygen isotope variations in an early Proterozoic and drill core, Griqualand West region, South Africa. Precambrian Res 169:80–99. transition from limestone to iron-formation deposition, Transvaal Supergroup, South 13. Kendall B, et al. (2010) Pervasive oxygenation along late Archaean ocean margins. Africa. Econ Geol 85(4):663–690. Nat Geosci 3:647–652. 24. Walker JCG (1984) Suboxic diagenesis in banded iron formations. Nature 309:340–342.

Fischer et al. www.pnas.org/cgi/content/short/1322577111 1of6 South Africa

Johannesburg Transvaal

Pering Mine A' Griqualand West Transvaal Bushy Park Griqualand West Drill hole Pb-Zn Bushveld Complex Kalkdam Doornberg Kuruman Iron Formation Penge Iron Formation fault zone Katlani ADP-GKF01 Campbellrand Platform Malmani Platform Prieska A Schmidtsdrif Group Wolkberg Group 100 km

Fig. S1. Geologic map of Kaapvaal Craton showing the surface exposures of the Late Archean Transvaal Supergroup, broadly divided into two structural subbasins: Griqualand West and Transvaal proper (modified from ref. 8). The location of drill core GKF01 is marked. Stars denote widespread locationsofPb–Zn deposits in Transvaal Supergroup strata; names are shown for those being mined in the Griqualand West subbasin. This episode of sulfide mineralization was felt craton-wide, tied to the circulation of hydrothermal fluids related to the emplacement of the Bushveld Igenous Complex at 2.05 Ga (20).

SW NE 500 m 50 km

Kuruman Iron Formation

GKF01

Campbellrand Platform

Schmidtsdrif Subgroup banded iron formation Fe-rich carbonates and shales Ventersdorp Supergroup A Fe-poor carbonates A'

Fig. S2. Cross-section through the Cambellrand carbonate platform (oriented from A to A′ showing the distribution of iron-rich minerals as a function of facies (modified from ref. 14). Fine-grained siliciclastics were delivered across the platform to form lowstand wedges (8) that commonly accumulated sub- stantial concentrations of sedimentary organic matter (9) as well as reactive iron (13). These black shales constitute the lithologic host for substantial accu- mulations of pyrite and other sulfide-bearing minerals. The location and approximate stratigraphic position of drill core GKF01 is marked.

Fischer et al. www.pnas.org/cgi/content/short/1322577111 2of6 Karoo Supergroup (Dwyka) GKF01 Kuruman Formation 200 m Klein Naute Formation 300 m 2521 ± 3 Ma 1

400 m

500 m Upper Nauga Formation 600 m

700 m

800 m 2552 ± 11 Ma 2 Kamden 900 m Campbellrand Subgroup

1000 m

Transvaal Supergroup Lower Nauga / Reivilo Formation 1100 m

1200 m

1300 m Monteville Formation 2602 ± 14 Ma 3 1400 m Lokamona Formation

Boomplaas Formation 1500 m

Vryburg Formation Carbonate 2642 ± 3 Ma 4 Sand and siltstone Schmidtsdrif Sub. Shale Ventersdorp Supergroup Iron formation

Fig. S3. Lithostratigraphy and generalized sedimentology of drill core GKF01. Group and formation names, with geochronological constraints are shown alongside. Superscripts denote references: 1) ref. 21; 2) ref. 16; 3) ref. 18; and 4) ref. 17.

Fischer et al. www.pnas.org/cgi/content/short/1322577111 3of6 iron oxide-rich IF

siderite-rich IF

carbonates

pyritic black shales

10-3 10-2 10-1 110 TOC (wt. %)

Fig. S4. Boxplots showing quartile ranges of organic carbon concentrations (in weight percent) in the dominant lithofacies from slope and basinal paleo- environments on the Campbellrand carbonate platform. Data from refs. 9, 22, and 23. The amount of residual organic matter correlates with relative sedi- mentation rate, the overall valence state of iron, and the amount of sulfur (23) in these diagenetically stabilized lithologies (e.g., ref. 24). Early diagenetic pyrite nodules are common in the black shales and, to a lesser degree, carbonates, are essentially absent from either oxide or siderite facies iron formation.

Fischer et al. www.pnas.org/cgi/content/short/1322577111 4of6 Fig. S5. Photographic plate of pyrite textures from carbonate and shale lithologies in Griqualand West. Core slabs shown are NQ (47.6 mm) diameter and oriented for stratigraphic up. Note the conspicuous dipping laminations, which along with a ballmark system and geophysical wireline data, allow core samples to be georeferenced. (A) Multiple types of early diagenetic pyrite nodules show differential compaction and plastic deformation; (B) pyrite intraclast breccia surrounded by black shale; (C) early diagenetic chert nodules and lenses surrounded by rims of later pyrite; (D) pyritized subtidal fenestral microbialite (with void-filling sparry calcite cement) overlain by finely laminated detrital carbonate into siderite facies banded iron formation. (E) Early diagenetic pyrite nodules preferentially grew along beds of detrital carbonate surrounded by black shale. (F) Early diagenetic pyrite nodules and lenses in black shale. (G) Late diagenetic pyrite nodule composed of coarse euhedral pyrite grains concentrated along laminations; note the lack of differential compaction. (H) Early diagenetic chert nodules in black shale with pyrite rims; note the late euhedral pyrites developed at the contact between the black shale and siderite-facies iron formation in the center of the sample. (I) Black shale with abundant pyrite nodules grading into fenestral microbialite with pyritized microbial roll-up structures.

Fig. S6. Reflected light photomicrographs of analytical grids showing the location of analysis spots across nodules and cement shown in Fig. 1 D and E on the Left and Right, respectively. Annotated images are shown alongside to mark interpretations. Closed circles denote nodules and open circles denote cement; spots that mix textures are shown as half circles. For scale, the size of the spots is 25 μm.

Fischer et al. www.pnas.org/cgi/content/short/1322577111 5of6 Fig. S7. Magnetic sulfur-bearing phases have a unique isotopic signature. (A) Kernel-smoothing probability density estimates of δ34S vs. Δ33S for the isotope ratio grids shown in Fig. 1E. The data are divided into spatial categories based on petrographic texture (shown in Fig. S6) and field strength > 30 nT (shown in Fig. 1). (B) Pairwise Kolmolgorov–Smirnov tests on Δ33S reject the null hypothesis (P << 0.05) that the data in these distinct petrographic textures derive from the same underlying distributions.

a. b. c. 6 late 6 6 early 4 4 4

2 2 2

0 0 0 S (‰ VCDT) S (‰ VCDT) S (‰ VCDT) −2 −2 −2 33 33 33

−4 −4 −4

−20 −10 0 10 20 −20 −10 0 10 20 −20 −10 0 10 20 34S (‰ VCDT) 34S (‰ VCDT) 34S (‰ VCDT)

Fig. S8. Cross-plots of multiple sulfur-isotope ratio data (δ34S vs. Δ33S) for 264.05 m (A), 1,419.40 m (B), and 290.28 m (C). Data from late sulfide-bearing phases (determined by either petrography, magnetics, or both) are distinguished from early phases by different symbols, pluses versus empty circles, respectively. VCDT, Vienna Canyon Diablo Troilite.

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Dataset S1 (TXT)

Fischer et al. www.pnas.org/cgi/content/short/1322577111 6of6