Guillaume Paris
email: guillaumeparis@univ-lorraine.fr

Woodward W Fischer

Jena E Johnson

Samuel M Webb

Theodore M Present

Alex L Sessions

Jess F Adkins

Deposition of sulfate aerosols with positive Δ 33 S in the Neoarchean

Anomalous sulfur isotope compositions present in Archean rocks have been intensely scrutinized over the last 20 years because they record key aspects of Earth's atmospheric composition prior to the appearance of free molecular oxygen ca. 2.3 billion years ago. These isotopic compositions can be described as mass anomalous fractionations (MAF) and are produced in the atmosphere as UV light interacts with SO 2 molecules. Most interpretations suggest that atmospheric processes generate a reduced S-phase with a positive ( 33 S-enriched) MAF signature, as measured in pyrites, and an oxidized S-phase with a negative anomaly, as measured in bedded barite deposits.

However, recent data for carbonate-associated sulfate (CAS) -a direct proxy for the isotopic composition of sulfur from seawater sulfate -in Neoarchean rocks showed no such negative values, but rather the opposite. To understand if the positive MAF anomalies we measured in Neoarchean CAS reflect secondary processes (diagenetic, metamorphic, handling) instead of original signals of Archean seawater sulfate, we collected additional sample suites with various degrees of preservation and metamorphic alteration across the Campbellrand-Malmani platform in South Africa. Results illustrate that within this comprehensive suite, less-altered samples all contain positive MAF values while secondary processes tend to either remove CAS from the sample and/or decrease the 33 S-enrichment. This positive MAF signal in sulfate is therefore reasonably interpreted as a primary depositional origin, and implies that the assumption that sulfate always carries a negative MAF anomaly throughout the Archean rock record needs to be reconsidered. Our CAS observations suggest that future experiments and calculations should also consider atmospheric and/or sulfur cycling processes that can produce oxidized sulfur with a positive MAF signature.

Introduction

The evolution of Earth's atmosphere through geological time is a long-standing problem in the Earth Sciences. During Archean time (4.0 to 2.5 Ga), the Earth was characterized by a lack of oxygen in the atmosphere and oceans [START_REF] Holland | The chemical evolution of the atmosphere and oceans[END_REF][START_REF] Fischer | Evolution of Oxygenic Photosynthesis[END_REF]. Despite a lower intensity of solar irradiation, liquid water was sustained at Earth's surface, suggesting a significantly higher greenhouse gas content in the Archean atmosphere compared to today's [START_REF] Sagan | Earth and Mars: Evolution of Atmospheres and Surface Temperatures[END_REF][START_REF] Kasting | Long-term stability of the earth's climate[END_REF]. The major greenhouse gas is thought to have been carbon dioxide (CO 2 ) possibly together with much higher methane (CH 4 ) concentrations, with contributions from carbonyl sulfide (COS), ammonia (NH 3 ) or other greenhouse gases (e.g. [START_REF] Sagan | The Early Faint Sun Paradox: Organic Shielding of Ultraviolet-Labile Greenhouse Gases[END_REF][START_REF] Zahnle | The loss of mass-independent fractionation in sulfur due to a Palaeoproterozoic collapse of atmospheric methane[END_REF][START_REF] Domagal-Goldman | Organic haze, glaciations and multiple sulfur isotopes in the Mid-Archean Era[END_REF][START_REF] Thomazo | Methanotrophs regulated atmospheric sulfur isotope anomalies during the Mesoarchean (Tumbiana Formation, Western Australia)[END_REF][START_REF] Ueno | Geological sulfur isotopes indicate elevated OCS in the Archean atmosphere, solving faint young sun paradox[END_REF]. It is therefore of great interest to characterize not only the evolution of O 2 , but also the different gases that helped sustain liquid water on the early Earth. Because they are thought to have originated from reactions in the atmosphere, anomalous multiple sulfur isotope ratios [START_REF] Farquhar | Atmospheric Influence of Earth's Earliest Sulfur Cycle[END_REF] offer the opportunity of constraining multiple gas components at once (e.g. [START_REF] Endo | Sulfur isotope fractionation by broadband {UV} radiation to optically thin {SO2} under reducing atmosphere[END_REF].

Unusual sulfur isotope compositions have been observed in Archean sedimentary rocks until their disappearance from the rock record in early Proterozoic time associated with the Great Oxygenation Event [START_REF] Farquhar | Atmospheric Influence of Earth's Earliest Sulfur Cycle[END_REF][START_REF] Ono | New insights into Archean sulfur cycle from mass-independent sulfur isotope records from the Hamersley Basin, Australia[END_REF][START_REF] Guo | Reconstructing Earth's surface oxidation across the Archean-Proterozoic transition[END_REF][START_REF] Johnston | Multiple sulfur isotopes and the evolution of Earth's surface sulfur cycle[END_REF][START_REF] Luo | Rapid oxygenation of Earth's atmosphere 2.33 billion years ago[END_REF][START_REF] Philippot | Globally asynchronous sulphur isotope signals require re-definition of the Great Oxidation Event[END_REF]. Most processes on Earth separate sulfur isotopes in proportion to their relative mass difference, generating "mass-dependent fractionations" (MDF), so called because they follow a canonical equilibrium fractionation law [START_REF] Hulston | Variations in the S33, S34, and S36 Contents of Meteorites and Their Relation to Chemical and Nuclear Effects[END_REF]Eiler et al., 2014) where δ' 33 S=0.515×δ' 34 S (with δ' x S=ln[( x S/ 32 S) sample /( x S/ 32 S) reference ]; x=34 or x=33). The δ x S value is almost identical to δ' x S (δ x S=[( x S/ 32 S) sample /( x S/ 32 S) reference -1]). However, in the absence of molecular oxygen and ozone [START_REF] Farquhar | Observation of wavelength-sensitive massindependent sulfur isotope effects during SO2 photolysis: Implications for the early atmosphere[END_REF], UV-light interaction with SO 2 molecules generates anomalous sulfur isotopic compositions, (δ' 33 S≠0.515×δ' 34 S) usually described as "mass-independent fractionations" (MIF) or "mass-anomalous fractionation" (MAF), reported as Δ 33 S (Δ 33 S =δ' 33 S-0.515×δ' 34 S). We use here the broader expression "MAF" as such signatures could arise from a mass fractionation law different from the reference law rather than from truly mass-independent processes.

The unusual sulfur isotope abundances, or MAF, provide a strong line of evidence for an Archean atmosphere free of O 2 [START_REF] Pavlov | Mass-Independent Fractionation of Sulfur Isotopes in Archean Sediments: Strong Evidence for an Anoxic Archean Atmosphere[END_REF]. Beyond recognizing that Δ 33 S ≠ 0, knowing which species carry the positive and negative Δ 33 S anomalies can help determine which process (or processes) and UV wavelengths generated MAF in the distant past. In order to explain the exact structure of MAF data, gases other than SO 2 must be present in the Archean atmosphere. As a result, these data can help us to understand which gases contributed to sustain a sufficient greenhouse effect on the early Earth, such as CH 4 or NH 3 [START_REF] Zahnle | The loss of mass-independent fractionation in sulfur due to a Palaeoproterozoic collapse of atmospheric methane[END_REF][START_REF] Domagal-Goldman | Organic haze, glaciations and multiple sulfur isotopes in the Mid-Archean Era[END_REF][START_REF] Zerkle | A bistable organic-rich atmosphere on the Neoarchaean Earth[END_REF][START_REF] Izon | Biological regulation of atmospheric chemistry en route to planetary oxygenation[END_REF]. Understanding the exact processes that produced the Archean MAF and describing the underlying mass fractionation law(s) are therefore of significant value.

As soon as the MAF signatures were discovered [START_REF] Farquhar | Atmospheric Influence of Earth's Earliest Sulfur Cycle[END_REF], SO 2 photolysis lab experiments attempted to undercover the mechanisms that generated them [START_REF] Farquhar | Observation of wavelength-sensitive massindependent sulfur isotope effects during SO2 photolysis: Implications for the early atmosphere[END_REF].

Many mass fractionation mechanisms have been explored through photochemistry experiments under different UV wavelengths and atmospheric compositions [START_REF] Masterson | Sulfur mass-independent fractionation patterns in the broadband UV photolysis of sulfur dioxide: Pressure and third body effects[END_REF][START_REF] Whitehill | Excitation band dependence of sulfur isotope mass-independent fractionation during photochemistry of sulfur dioxide using broadband light sources[END_REF][START_REF] Ono | Contribution of isotopologue self-shielding to sulfur massindependent fractionation during sulfur dioxide photolysis[END_REF][START_REF] Whitehill | Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO2 and the implications to the early earth's atmosphere[END_REF][START_REF] Whitehill | SO2 photolysis as a source for sulfur massindependent isotope signatures in stratospehric aerosols[END_REF][START_REF] Endo | Sulfur isotope fractionation by broadband {UV} radiation to optically thin {SO2} under reducing atmosphere[END_REF]. These experimental approaches have been supplemented with 1-D column atmosphere models and isotopologue cross-section adsorption calculations [START_REF] Lyons | Mass-independent fractionation of sulfur isotopes by isotope-selective photodissociation of SO2[END_REF][START_REF] Danielache | High-precision spectroscopy of 32S, 33S, and 34S sulfur dioxide: Ultraviolet absorption cross sections and isotope effects[END_REF][START_REF] Lyons | Atmospherically-derived mass-independent sulfur isotope signatures, and incorporation into sediments[END_REF][START_REF] Ueno | Geological sulfur isotopes indicate elevated OCS in the Archean atmosphere, solving faint young sun paradox[END_REF][START_REF] Claire | Modeling the signature of sulfur mass-independent fractionation produced in the Archean atmosphere[END_REF][START_REF] Endo | Photoabsorption cross-section measurements of 32S, 33S, 34S, and 36S sulfur dioxide from 190 to 220 nm[END_REF][START_REF] Izon | Biological regulation of atmospheric chemistry en route to planetary oxygenation[END_REF][START_REF] Endo | Total Pressure Dependence of Sulfur Mass-Independent Fractionation by SO2 Photolysis[END_REF].

Overall, the photochemical processes generating S-MAF can in principle be differentiated based on the wavelengths reacting with SO 2 .

(1) At wavelengths between 190 and 220 nm, photolytic processes (SO 2 →SO+O), self-shielding of SO 2 (SO 2 absorbs the wavelengths with which it interacts) and/or pressure-broadening all occur [START_REF] Lyons | Atmospherically-derived mass-independent sulfur isotope signatures, and incorporation into sediments[END_REF][START_REF] Ono | Contribution of isotopologue self-shielding to sulfur massindependent fractionation during sulfur dioxide photolysis[END_REF][START_REF] Lyons | VUV pressurebroadening in sulfur dioxide[END_REF][START_REF] Endo | Total Pressure Dependence of Sulfur Mass-Independent Fractionation by SO2 Photolysis[END_REF]. Early SO 2 photolysis experiments at 193 nm generated negative-MAF sulfate ( ArF excimer laser; [START_REF] Farquhar | Observation of wavelength-sensitive massindependent sulfur isotope effects during SO2 photolysis: Implications for the early atmosphere[END_REF], focusing attention to this range of wavelengths. MAF-bearing sulfur species are produced because the photodissociation rates are a function of absorption cross-sections, slightly different for each SO 2 isotopologue. In addition, 32 SO 2 , the most abundant isotopologue, has a lower self-shielding reaction rate, with a dependence on SO 2 concentrations: the more SO 2 there is, the faster 32 SO 2 shields itself [START_REF] Lyons | Atmospherically-derived mass-independent sulfur isotope signatures, and incorporation into sediments[END_REF][START_REF] Ueno | Geological sulfur isotopes indicate elevated OCS in the Archean atmosphere, solving faint young sun paradox[END_REF][START_REF] Ono | Contribution of isotopologue self-shielding to sulfur massindependent fractionation during sulfur dioxide photolysis[END_REF][START_REF] Endo | Total Pressure Dependence of Sulfur Mass-Independent Fractionation by SO2 Photolysis[END_REF]. SO 2 is photolyzed to SO, which then carries a positive Δ 33 S isotopic anomaly and this signal is transferred to S 0 or possibly COS in the presence of CO. By mass-balance, the exiting SO 3 molecules should carry a negative anomaly. Subsequent oxidation of SO 3 generates sulfuric acid (H 2 SO 4 ) aerosols carrying the negative Δ 33 S anomaly that can then be transferred to the oceans. Paired with negative Δ 33 S Archean barite and positive Δ 33 S Archean pyrite, these experiments formed the basis for the original sulfur photochemical model on early Earth.

(2) At wavelengths between 250 and 350 nm, photoexcitation (SO 2 →*SO 2 ) occurs [START_REF] Ueno | Geological sulfur isotopes indicate elevated OCS in the Archean atmosphere, solving faint young sun paradox[END_REF][START_REF] Halevy | Production, preservation, and biological processing of mass-independent sulfur isotope fractionation in the Archean surface environment[END_REF][START_REF] Whitehill | Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO2 and the implications to the early earth's atmosphere[END_REF][START_REF] Endo | Total Pressure Dependence of Sulfur Mass-Independent Fractionation by SO2 Photolysis[END_REF]. MAF is produced during the transition of SO 2 from an excited singlet state 1 SO 2 (the spin of the excited electron is paired with that of the lowest, or ground, energy state) to an excited triplet state 3 SO 2 (where the excited electron spin is no longer paired with the ground state electron) and the anomaly can then be transferred to either the reduced or oxidized species after reaction with ground SO 2 [START_REF] Whitehill | Excitation band dependence of sulfur isotope mass-independent fractionation during photochemistry of sulfur dioxide using broadband light sources[END_REF]. Initial experiments with continuous wavelengths above 220 nm (Xe lamp) and KrF excimer laser generated positive-MAF sulfate [START_REF] Farquhar | Observation of wavelength-sensitive massindependent sulfur isotope effects during SO2 photolysis: Implications for the early atmosphere[END_REF]. In the context of Archean barite with negative-MAF sulfate, these longer wavelengths experiments seemed less relevant to Archean atmospheric chemistry. Furthermore, photoexcitation is considered a very minor pathway [START_REF] Endo | Sulfur isotope fractionation by broadband {UV} radiation to optically thin {SO2} under reducing atmosphere[END_REF].

(3) Across both ranges of wavelengths, recent lab experiments and numerical models have demonstrated the important role played by the absolute SO 2 concentration and the presence of other trace (COS, CO, etc.) and minor (CO 2 , CH 4 ) gases in setting the sign (+/-) of the MAF anomaly in pyrites [START_REF] Ueno | Geological sulfur isotopes indicate elevated OCS in the Archean atmosphere, solving faint young sun paradox[END_REF][START_REF] Claire | Modeling the signature of sulfur mass-independent fractionation produced in the Archean atmosphere[END_REF][START_REF] Izon | Biological regulation of atmospheric chemistry en route to planetary oxygenation[END_REF][START_REF] Endo | Total Pressure Dependence of Sulfur Mass-Independent Fractionation by SO2 Photolysis[END_REF]. In a CO-containing atmosphere, MAF processes could occur from a combination of collision-induced system crossing and self-shielding and therefore a combination of photoexcitation and photooxidation [START_REF] Whitehill | Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO2 and the implications to the early earth's atmosphere[END_REF][START_REF] Endo | Sulfur isotope fractionation by broadband {UV} radiation to optically thin {SO2} under reducing atmosphere[END_REF], which is hypothesized to match the measured Δ 36 S/ Δ 33 S ratio. During photoexcitation in the 250-350 nm region, the intersystem crossing from an excited singlet state 1 SO 2 to an excited triplet state SO 2 ( * SO 2 ) generates * SO 2 with a positive Δ 33 S through near-resonant spin coupling between both excited states (Whitehill et al., 2013). This anomaly is expected to be transferred to SO, and not to SO 3 , through the reaction *SO 2 +SO 2 →*SO+SO 3 , therefore delivering it ultimately to the reduced sulfur pool. But if the anomaly is captured as COS, it could be transferred to sulfate instead [START_REF] Savarino | UV induced mass-independent sulfur isotope fractionation in stratospheric volcanic sulfate[END_REF][START_REF] Whitehill | Excitation band dependence of sulfur isotope mass-independent fractionation during photochemistry of sulfur dioxide using broadband light sources[END_REF]. Experimental results are very sensitive to the initial conditions and to the overall composition of the artificial atmosphere. This is true in both older and more recent experiments. For example, CO is required to transfer the positive anomaly to COS [START_REF] Endo | Total Pressure Dependence of Sulfur Mass-Independent Fractionation by SO2 Photolysis[END_REF] and therefore the final result depends on the initial CO concentration in the reaction volume.

Based on the initial laboratory experiments of SO 2 irradiated by UV light, it was hypothesized that reduced sulfur species carried a positive Δ 33 S value and that higher-valent sulfur species (SO 3 , SO 4 2-) carried a commensurate negative counterpart (e.g. [START_REF] Farquhar | Observation of wavelength-sensitive massindependent sulfur isotope effects during SO2 photolysis: Implications for the early atmosphere[END_REF]. The cascade of reactions that subsequently occurred in the atmosphere would have transferred the positive Δ 33 S of reduced sulfur ultimately to pyrite, explaining the generally positive values measured in sedimentary pyrites [START_REF] Farquhar | Pathways for Neoarchean pyrite formation constrained by mass-independent sulfur isotopes[END_REF][START_REF] Halevy | Production, preservation, and biological processing of mass-independent sulfur isotope fractionation in the Archean surface environment[END_REF]. Pyrite is proposed to be formed through two different pathways. The first one is direct deposition of elemental sulfur chains S 8 (e.g. Ono et al., 2009a). Elemental sulfur can either produce pyrite following chemical reaction with ferrous sulfide [START_REF] Rickard | Kinetics and mechanism of pyrite formation at low temperatures[END_REF], or following further reduction through microbial disproportionation (e.g. [START_REF] Philippot | Early Archaean Microorganisms Preferred Elemental Sulfur, Not Sulfate[END_REF][START_REF] Farquhar | Pathways for Neoarchean pyrite formation constrained by mass-independent sulfur isotopes[END_REF]. In both cases, pyrites would carry the atmospheric reduced sulfur MAF (usually assumed to be positive). The second pathway is through microbial sulfate reduction (MSR) that reduces sulfate to sulfide, which would produce pyrite that carries the atmospheric oxidized sulfur MAF (usually assumed to be negative). MSR is assumed to have started possibly 3.5 Ga ago (e.g; [START_REF] Shen | Isotopic evidence for microbial sulphate reduction in the early Archaean era[END_REF][START_REF] Ueno | Quadruple sulfur isotope analysis of ca. 3.5 Ga Dresser Formation: New evidence for microbial sulfate reduction in the early Archean[END_REF][START_REF] Shen | Evaluating the role of microbial sulfate reduction in the early Archean using quadruple isotope systematics[END_REF]. However, it has been recently suggested that MSR would have evolved only 2.7 Ga ago and that organic sulfur played a major role in the pre-2.7 Ga sulfur cycle [START_REF] Fakhraee | Organic sulfur was integral to the Archean sulfur cycle[END_REF]. Even if it was relatively recently-evolved, MSR would have been active during the deposition of the Campbellrand-Malmani platform. In the end, such a model would result in sulfate carrying a negative Δ 33 S value and pyrites carrying either positive or negative Δ 33 S values.

Finally, geological support for a model where reduced sulfur carries the positive atmospheric MAF signature came from negative Δ 33 S values measured in Paleoarchean barites from South Africa, India and Australia [START_REF] Bao | The five stable isotope compositions of Fig Tree barites: Implications on sulfur cycle in ca. 3.2 Ga oceans[END_REF][START_REF] Philippot | Early Archaean Microorganisms Preferred Elemental Sulfur, Not Sulfate[END_REF][START_REF] Ueno | Quadruple sulfur isotope analysis of ca. 3.5 Ga Dresser Formation: New evidence for microbial sulfate reduction in the early Archean[END_REF][START_REF] Shen | Evaluating the role of microbial sulfate reduction in the early Archean using quadruple isotope systematics[END_REF][START_REF] Philippot | Variations in atmospheric sulphur chemistry on early Earth linked to volcanic activity[END_REF][START_REF] Roerdink | Multiple sulfur isotopes in Paleoarchean barites identify an important role for microbial sulfate reduction in the early marine environment[END_REF][START_REF] Muller | Multiple sulfur-isotope signatures in Archean sulfates and their implications for the chemistry and dynamics of the early atmosphere[END_REF] and slightly negative MAF measured in Archean volcanic massive sulfide deposits [START_REF] Jamieson | Neoarchaean seawater sulphate concentrations from sulphur isotopes in massive sulphide ore[END_REF]. Additional evidence interpreted within the frame of the canonical model came from the observation of diamond-hosted sulfides carrying a negative Δ 33 S and interpreted as the evidence of Archean biogenic pyrite recycled through the mantle [START_REF] Cabral | Anomalous sulphur isotopes in plume lavas reveal deep mantle storage of Archaean crust[END_REF]. Measurements within single grains of Archean pyrites revealed a roughly constant and negative Δ 33 S in pyrites with a broad range of δ 34 S values [START_REF] Farquhar | Pathways for Neoarchean pyrite formation constrained by mass-independent sulfur isotopes[END_REF][START_REF] Fischer | SQUID-SIMS is a useful approach to uncover primary signals in the Archean sulfur cycle[END_REF][START_REF] Zhelezinskaia | Large sulfur isotope fractionations associated with Neoarchean microbial sulfate reduction[END_REF]. To be consistent with the view that oxidized sulfur species carried a negative Δ 33 S value, the previous studies suggested that there was mass-dependent microbial reduction of negative Δ 33 S sulfate. However, scatter in δ 34 S values is also observed in pyrite grains with a positive Δ 33 S value [START_REF] Fischer | SQUID-SIMS is a useful approach to uncover primary signals in the Archean sulfur cycle[END_REF]. Questions remain about Archean MAF processes. Experiments highlight the many possible pathways involved in forming Archean-like MAF signals (e.g. [START_REF] Savarino | UV induced mass-independent sulfur isotope fractionation in stratospheric volcanic sulfate[END_REF][START_REF] Whitehill | Vibronic origin of sulfur mass-independent isotope effect in photoexcitation of SO2 and the implications to the early earth's atmosphere[END_REF][START_REF] Endo | Sulfur isotope fractionation by broadband {UV} radiation to optically thin {SO2} under reducing atmosphere[END_REF]. Recently, new theoretical considerations of atmospheric chemistry underlined that the role given to COS as a potential exit channel may have been excessive [START_REF] Babikov | Recombination reactions as a possible mechanism of mass-independent fractionation of sulfur isotopes in the Archean atmosphere of Earth[END_REF][START_REF] Babikov | One possible source of mass-independent fractionation of sulfur isotopes in the Archean atmosphere of Earth[END_REF][START_REF] Harman | Chain formation as a mechanism for massindependent fractionation of sulfur isotopes in the Archean atmosphere[END_REF]. They support instead that sulfur was exiting the atmosphere as elemental sulfur chains (S x ) of different sizes and not S 8 exclusively. This theory predicts an exit channel with elemental sulfur carrying negative Δ 33 S value and sulfate characterized by positive Δ 33 S values. Obtaining adequate oxidized sulfur from the rock record to measure its MAF value has proven to be challenging.

There is a significantly larger amount of MAF data from Archean pyrites compared to Archean sulfate minerals. Sulfate concentrations in Archean oceans were much lower than today [START_REF] Grotzinger | New constraints on Precambrian ocean composition[END_REF][START_REF] Crowe | Sulfate was a trace constituent of Archean seawater[END_REF][START_REF] Fakhraee | Sedimentary sulfur isotopes and Neoarchean ocean oxygenation[END_REF], leaving only specialized deposits of sulfate minerals (e.g. [START_REF] Bao | The five stable isotope compositions of Fig Tree barites: Implications on sulfur cycle in ca. 3.2 Ga oceans[END_REF][START_REF] Philippot | Variations in atmospheric sulphur chemistry on early Earth linked to volcanic activity[END_REF][START_REF] Roerdink | Multiple sulfur isotopes in Paleoarchean barites identify an important role for microbial sulfate reduction in the early marine environment[END_REF][START_REF] Ueno | Quadruple sulfur isotope analysis of ca. 3.5 Ga Dresser Formation: New evidence for microbial sulfate reduction in the early Archean[END_REF]. The Paleoarchean barites used to constrain the negative MAF signal derive from volcanoclastic deposits with a petrogenesis that might not lead them to preserve marine sulfate isotopic compositions [START_REF] Roerdink | High-resolution quadruple sulfur isotope analyses of 3.2 Ga pyrite from the Barberton Greenstone Belt in South Africa reveal distinct environmental controls on sulfide isotopic arrays[END_REF][START_REF] Muller | Multiple sulfur-isotope signatures in Archean sulfates and their implications for the chemistry and dynamics of the early atmosphere[END_REF][START_REF] Lowe | Crustal fracturing, unconformities, and barite deposition[END_REF]. In contrast to these older barites, we have observed positive Δ 33 S values in younger Neorchean carbonate-associated sulfate (CAS; [START_REF] Paris | Neoarchean carbonateassociated sulfate records positive Δ33S anomalies[END_REF]. CAS is known to derive initially from seawater sulfate in younger successions (e.g. [START_REF] Rennie | Cenozoic record of δ34S in foraminiferal calcite implies an early Eocene shift to deep-ocean sulfide burial[END_REF][START_REF] Toyama | Sulfur isotope ratios in co-occurring barite and carbonate from Eocene sediments: A comparison study[END_REF]. These observations and models contradict the established paradigm that sulfate carried MAF negative signatures throughout Archean time. Similar observations of positive Δ 33 S in CAS had been previously made, but considered as deriving from secondary processes [START_REF] Domagal-Goldman | Organic haze, glaciations and multiple sulfur isotopes in the Mid-Archean Era[END_REF]. There could be a possibility that the Neoarchean CAS that we previously measured is affected by post-depositional processes, as CAS can be potentially altered during diagenesis, metasomatism or sulfate extraction [START_REF] Gill | Behavior of carbonate-associated sulfate during meteoric diagenesis and implications for the sulfur isotope paleoproxy[END_REF][START_REF] Wotte | Carbonate-associated sulfate: Experimental comparisons of common extraction methods and recommendations toward a standard analytical protocol[END_REF][START_REF] Rennie | Foraminiferal calcite provides new insight into the coupled carbon & sulfur isotope evolution of the ocean in the Palaeogene[END_REF][START_REF] Present | Large Carbonate Associated Sulfate isotopic variability between brachiopods, micrite, and other sedimentary components in Late Ordovician strata[END_REF][START_REF] Fichtner | Diagenesis of carbonate associated sulfate[END_REF][START_REF] Present | Diagenetic controls on the isotopic composition of carbonate-associated sulphate in the Permian Capitan Reef Complex, West Texas[END_REF].

In this study, we examined the composition and preservation of multiple sulfur isotopes within the sedimentary succession of the Campbellrand-Malmani platform to pinpoint depositional compositions and assess if post-depositional processes have impacted the isotopic composition measured on CAS from samples collected across the platform [START_REF] Paris | Neoarchean carbonateassociated sulfate records positive Δ33S anomalies[END_REF]. To this end, we sampled different formations that capture different ages, depositional environments, and metamorphic histories across the platform. We utilized the preservation contrast between the better-preserved western part of the craton (Griqualand West structural sub-basin) and the eastern part of the craton (Transvaal basin), where tectonics and the massive plutonic Bushveld Intrusive Complex may have altered the sulfur isotope signals contained in carbonate rocks more strongly than what is observed in Griqualand West [START_REF] Gleason | 2.05-Ga Isotopic Ages for Transvaal Mississippi Valley-Type Deposits: Evidence for Large-Scale Hydrothermal Circulation around the Bushveld Igneous Complex, South Africa[END_REF][START_REF] Fischer | SQUID-SIMS is a useful approach to uncover primary signals in the Archean sulfur cycle[END_REF][START_REF] Johnson | Effects of metamorphism and metasomatism on manganese mineralogy: Examples from the Transvaal Supergroup[END_REF]. To assess how exhumation and weathering could also have played a role, we compare the signal measured in rocks coming from outcrops to rocks derived from deep diamond drill cores.

Finally, to augment our previous study in which only pure carbonates were analyzed, we purposely measured sulfate from various recrystallized and metasomatized samples, including partially silicified samples as well as samples rich in pyrite, to compare how clear post-depositional alteration processes and potential contaminants impacted the CAS sulfur isotopic compositions.

Geological context

The Transvaal Supergroup in South Africa is preserved in two distinct structural basins (Griqualand West and Transvaal) and covers over 0.2×10 6 km 2 [START_REF] Beukes | Facies relations, depositional environments and diagenesis in a major early Proterozoic stromatolitic carbonate platform to basinal sequence, Campbellrand Subgroup, Transvaal Supergroup, Southern Africa[END_REF]. Within the Transvaal Supergroup, the Neoarchean Campbellrand-Malmani platform contains attractive targets for micro-CAS analyses with a unique abundance of in-situ, benthic carbonate precipitation and the occurrence of extremely diverse stromatolitic and microbialite fabrics [START_REF] Beukes | Facies relations, depositional environments and diagenesis in a major early Proterozoic stromatolitic carbonate platform to basinal sequence, Campbellrand Subgroup, Transvaal Supergroup, Southern Africa[END_REF][START_REF] Sumner | U-Pb geochronologic constraints on deposition of the Campbellrand Subgroup, Transvaal Supergroup, South Africa[END_REF]Sumner, 1997b;[START_REF] Sumner | Implications for Neoarchaean ocean chemistry from primary carbonate mineralogy of the Campbellrand-Malmani Platform, South Africa[END_REF][START_REF] Knoll | Introduction: Initial investigations of a Neoarchean shelf margin-basin transition (Transvaal Supergroup, South Africa)[END_REF]. The platform initiated as a carbonate ramp, now preserved as the Schmidtsdrif Subgroup, and developed into a mature rimmed carbonate shelf that spread across the entire Kaapvaal Craton [START_REF] Sumner | Sequence Stratigraphic Development of the Neoarchean Transvaal carbonate platform, Kaapvaal Craton, South Africa[END_REF] accumulating over 1 km in thickness of marine carbonate. In the Prieska area, deeper basin sediments are preserved and the thickness is ~500 m [START_REF] Beukes | Facies relations, depositional environments and diagenesis in a major early Proterozoic stromatolitic carbonate platform to basinal sequence, Campbellrand Subgroup, Transvaal Supergroup, Southern Africa[END_REF]Sumner, 1997b). Eventually the carbonate platform drowned during a major transgression that translated into the deposition of iron formations of the Asbestos Hills Subgroup (Kuruman Iron Formation in Griqualand West and the Penge Iron Formation in the Transvaal).

Compared to other Neoarchean strata, the Campbellrand platform is markedly well preserved, particularly in Griqualand West where the strata are flat-lying, and the regional metamorphism is generally low-grade, not exceeding the greenschist facies (200-400°C Miyano and Beukes, 1984;Miyano and Beukes, 1997). The western edge of the craton is marked by thin-skinned folding and faulting, resulting in Campbellrand rocks overthrusting the Proterozoic red beds of the Olifantshoek Group [START_REF] Beukes | Facies relations, depositional environments and diagenesis in a major early Proterozoic stromatolitic carbonate platform to basinal sequence, Campbellrand Subgroup, Transvaal Supergroup, Southern Africa[END_REF]. Petrographic textures in carbonate lithologies from the west reflect this excellent preservation potential as they commonly contain fabric-retentive, early diagenetic dolomite, as well as primary calcite in many areas [START_REF] Sumner | Implications for Neoarchaean ocean chemistry from primary carbonate mineralogy of the Campbellrand-Malmani Platform, South Africa[END_REF][START_REF] Fischer | Isotopic constraints on the Late Archean carbon cycle from the Transvaal Supergroup along the western margin of the Kaapvaal Craton, South Africa[END_REF]. To the east, the Transvaal area is marked by steep structural dips, and he Bushveld Igneous Complex intruded the Neoarchean strata ca. 2.05 Ga ago [START_REF] Walraven | A chronostratigraphic framework for the northcentral Kaapvaal craton, the Bushveld Complex and the Vredefort structure[END_REF][START_REF] Buick | Precise U-Pb titanite age constraints on the emplacement of the Bushveld Complex, South Africa[END_REF], resulting in steeper structure dips, higher metamorphic temperatures, and greater metasomatism than the Griqualand West region [START_REF] Kaneko | Contact metamorphism of the Bushveld Complex in the northeastern Transvaal, South Africa[END_REF]Miyano and Beukes, 1997).

The platform is broadly divided into two large sequences that can be correlated from Griqualand West to the Transvaal (Fig. 1). The first sequence is the Lower Nauga/Reivilo formation while the second one is the Upper Nauga Formation, which is overlain by the Naute/Gamohaan/Frisco formation (Sumner, 1997a;[START_REF] Sumner | Sequence Stratigraphic Development of the Neoarchean Transvaal carbonate platform, Kaapvaal Craton, South Africa[END_REF]. Each of them represent aggradational packages separated by a thin transgressive unit at the top of the Lower Nauga/Reivilo formation in the Griqualand West area, the Kamden Iron Formation. Carbonate deposition was reestablished by the time of deposition of the Upper Nauga Formation. The Campbellrand-Malmani platform slope was then at its steepest, with a lagoon that developed episodically behind the reef margin.

Immediately after deposition of these facies, a major transgression led to the final demise of the platform, recorded within the Naute/Gamohaan/Frisco formation. In Griqualand West, this flooding is recorded in a sequence characterized by deep subtidal fenestral microbialites with increasing chert content, ultimately grading into the Kuruman Iron Formation. In the Transvaal, the Frisco Formation evolves from ripple marks, cross laminations, and ooids to sequential carbonate/chert layers and finally into the Penge Iron Formation. The Penge and Kuruman Iron formations cap the platform across the entire Kaapvaal Craton.

Sampling was targeted to investigate the sulfur isotope differences between the Griqualand West and Transvaal areas and between formations in the same area of the platform, as well as comparing the CAS preservation in core versus outcrop samples. As a result, our sulfur isotope data come from samples collected from five different stratigraphic sections through the platform, mostly from cores and outcrops from the Lower Nauga/Reivilo formation and the Naute/Gamohaan/Frisco formation. A few additional samples come from a core through the Monteville Formation. In Griqualand West, the Boetsap section (27° 57.88' S 024° 27.24' E; [START_REF] Truswell | Stromatolitic associations and their palaeo-environmental significance: A re-appraisal of a lower Proterozoic locality from the northern Cape Province, SouthAfrica[END_REF][START_REF] Sumner | Neoarchean carbonates -clues to early life and early ocean chemistry[END_REF][START_REF] Sumner | Implications for Neoarchaean ocean chemistry from primary carbonate mineralogy of the Campbellrand-Malmani Platform, South Africa[END_REF] captures shallow subtidal paleoenvironments of the Reivilo Formation deposited during the early development of the Campbellrand platform and consists of two parts, Lower (samples WJG1) and Upper Falls (samples W1; [START_REF] Paris | Neoarchean carbonateassociated sulfate records positive Δ33S anomalies[END_REF].

Textures consist of minor grainstones and abundant precipitated stromatolites including seafloor aragonite fans [START_REF] Sumner | Implications for Neoarchaean ocean chemistry from primary carbonate mineralogy of the Campbellrand-Malmani Platform, South Africa[END_REF]. Most of the carbonates in this part of the platform have been altered with a fabric-retentive dolomitization, though in this section some horizons are still present as limestone (e.g. [START_REF] Paris | Neoarchean carbonateassociated sulfate records positive Δ33S anomalies[END_REF]. GKP 01 (samples GKP) is a drill core collected with the Agouron Institute South African Drilling Project that penetrates through the proximal slope facies of the Campbellrand platform [START_REF] Knoll | Introduction: Initial investigations of a Neoarchean shelf margin-basin transition (Transvaal Supergroup, South Africa)[END_REF]. We targeted cements associated with deep subtidal fenestral microbialites deposited deeper in the basin in the Lower Nauga Formation. SAC samples were collected from the BH1-Sacha core [START_REF] Altermann | Sedimentology and facies development of an Archaean shelf: carbonate platform transition in the Kaapvaal Craton, as deduced from a deep borehole at Kathu, South Africa[END_REF] that captures shallow parts of the platform paleoenvironments. Samples WJG3 and W2 come from the Kuruman Kop section [START_REF] Sumner | Neoarchean carbonates -clues to early life and early ocean chemistry[END_REF][START_REF] Sumner | Implications for Neoarchaean ocean chemistry from primary carbonate mineralogy of the Campbellrand-Malmani Platform, South Africa[END_REF]27° 22.82' S 024° 20.82' E) and capture the terminal drowning of the carbonate platform from a shallow lagoonal evaporitic environment (WJG3) to a subtidal microbialite facies that includes abundant early marine cements (W2). The lagoonal facies sediments comprise interbedded fenestrate microbial laminations and isopachously domed limestone [START_REF] Sumner | Sequence Stratigraphic Development of the Neoarchean Transvaal carbonate platform, Kaapvaal Craton, South Africa[END_REF]. The deep subtidal, fenestral microbialite facies of the 2.521 Ga Gamohaan Formation contains abundant herringbone calcite, interpreted as an early seafloor precipitating cement [START_REF] Sumner | Sequence Stratigraphic Development of the Neoarchean Transvaal carbonate platform, Kaapvaal Craton, South Africa[END_REF][START_REF] Sumner | U-Pb geochronologic constraints on deposition of the Campbellrand Subgroup, Transvaal Supergroup, South Africa[END_REF][START_REF] Sumner | Herringbone calcite; petrography and environmental significance[END_REF]. In the Campbellrand platform, herringbone calcite occurs as encrusting beds and is an important phase of void-filling cementation associated with the deep subtidal fenestral microbialites [START_REF] Sumner | Herringbone calcite; petrography and environmental significance[END_REF]. Core WB-98 captures the same transition as WJG3 and W2 samples from Kuruman Kop. However, while the facies are similar between WB-98, WJG3 and W2, and all represent the Lower Nauga Formation, most samples in WB-98 contained mm to cm pyrite nodules. We note that such nodules are similar to those investigated in a similar core [START_REF] Kamber | Micro-scale sulphur isotope evidence for sulphur cycling in the late Archean shallow ocean[END_REF]. Their presence makes core WB-98 a poor prospect for accurate CAS measurements due to the enhanced possibility of for oxidized pyrite contamination, but an interesting target for the current investigation. Some samples from this core appeared surficially oxidized at the time of collection, possibly due to the storage conditions (Fig. S4). Thus, WB-98 provides us with an opportunity to test how poor preservation and secondary oxidation of abundant pyrite affects the CAS sulfur isotope signal.

In the Transvaal area, we sampled the Rotterdam Farm section (samples WJG9; 24° 33.643' S ; 027°21.251' E). The Rotterdam Farm section captures the Frisco Formation, a package laterally equivalent to and comprised of similar facies to the Gamohaan Formation. This formation was deposited in a more updip, proximal setting, and like the Gamohaan and Naute formations, the strata record the drowning of the platform, though the Frisco Formation contains more siliciclasticrich beds than the Gamohaan/Naute formation. The Rotterdam Farm outcrop evolved from a shallow sedimentation environment, as indicated by cross-stratified ooid grainstones, now silicified, to a deeper more quiescent environment and eventually the deposition of the Penge Iron Formation. Rocks in this part of the platform witnessed more deformation and higher temperatures, and the samples we selected contained evidence of both early and late silicification that may have occurred during ca. 2.05 Ga Bushveld-related metamorphism and associated hydrothermal fluids circulation [START_REF] Schiffries | The Bushveld hydrothermal system; field and petrologic evidence[END_REF]. Through these Transvaal area rocks, we were able to explore the effects of metasomatism and metamorphism on the CAS record.

Methods

Sample preparation and petrographic observations

We selected a subset of samples across the various environments and lithologies encountered in the platform. Samples were sectioned using a rock saw, orthogonal to bedding, and polished for petrographic inspection. The slabs were cleaned with MilliQ water, then micromilled using a Sherline 5410 mill equipped with a RoundTool diamond-coated carbide end mill (GR4SI 1/16 D1; 1.5mm diameter) to collect 40 to 150 mg of powders from different petrographic textures.

Representative thin sections were made and observed microscopically using polarized and transmitted light (Fig. S1-S3).

CAS isolation

All plastics (centrifuge tubes, autosampler vials and Biorad columns) were leached in 10% reagent grade HCl and rinsed 5 times in MilliQ water. Teflon vials were cleaned in 5% Seastar HNO 3 , rinsed 5 times in MilliQ water, refluxed overnight with concentrated Seastar HNO 3 at 160ᵒC and rinsed 3 times in MilliQ water. For each sample, up to 40 mg of powder were weighed and sonicated for 60 min in 1 M NaCl. All samples were then centrifuged and rinsed 4 times in MilliQ water. After drying, the samples were weighed again, dissolved in 10% HCl, centrifuged, and the supernatant was collected in a Savillex Teflon vial. The supernatant was dried at 120ᵒC on a hot plate under HEPA filtered laminar flow air and the insoluble residue was dried in an oven at 90ᵒC. The residues were weighed, and the dried supernatant was dissolved in HCl. Biorad disposable columns were loaded with 2 ml of clean AG1X8 anion-exchange resin 100-200 mesh [START_REF] Das | Application of an improved ion exchange technique for the measurement of d34S values from microgram quantities of sulfur by MC-ICPMS[END_REF][START_REF] Paris | Neoarchean carbonateassociated sulfate records positive Δ33S anomalies[END_REF]. The resin was then cleaned with 20 ml of 10% HNO 3 , 20 ml of 10% HCl and 10 ml of 0.5% HCl. Samples were loaded onto the resin, cations were removed by rinsing the column with 5 times 5 ml of MilliQ water, and sulfate was eluted with 3×4 ml of 0.5 M HNO 3 [START_REF] Paris | Neoarchean carbonateassociated sulfate records positive Δ33S anomalies[END_REF]. Seawater and corals internal standards were processed through the columns following the same procedures as checks on the consistency of our procedure over time.

Sulfur isotopes, sulfate concentration, and stable isotope measurements

Sulfur isotopes were measured as 32 S + , 33 S + and 34 S + ions at Caltech on a Neptune Plus multicollector inductively-coupled plasma mass spectrometer (MC-ICPMS, Thermo Fisher Scientific) in high resolution mode. We used a desolvating membrane (Aridus, Cetac) as an introduction system to decrease interferences and make measurements of sulfur possible, following a method described previously [START_REF] Paris | MC-ICP-MS measurement of δ34S and ∆33S in small amounts of dissolved sulfate[END_REF][START_REF] Paris | Neoarchean carbonateassociated sulfate records positive Δ33S anomalies[END_REF]. Samples were measured by samplestandard bracketing to correct instrumental fractionation. The bracketing standard was a Na 2 SO 4 solution concentrated at 20 µmol/l. Na + was added to the samples after purification as NaOH to match the sodium concentration of the bracketing standard [START_REF] Paris | MC-ICP-MS measurement of δ34S and ∆33S in small amounts of dissolved sulfate[END_REF]. Sulfur isotope ratios of the Na 2 SO 4 bracketing solution were determined by comparing it directly to a solution of international standard IAEA-S1 (δ 34 S VCDT = -0.3‰, δ 33 S VCDT = -0.055‰, [START_REF] Ding | Calibrated sulfur isotope abundance ratios of three IAEA sulfur isotope reference materials and V-CDT with a reassessment of the atomic weight of sulfur[END_REF][START_REF] Ono | Mass-dependent fractionation of quadruple stable sulfur isotope system as a new tracer of sulfur biogeochemical cycles[END_REF]. The δ 34 S VCDT value of our bracketing Na 2 SO 4 solution is -1.55‰±0.16 (2sd) and the δ 33 S VCDT value is -0.77±0.17‰ (Δ 33 S = 0.02±0.17‰) and was determined previously [START_REF] Paris | MC-ICP-MS measurement of δ34S and ∆33S in small amounts of dissolved sulfate[END_REF]. All values were corrected assuming linear drift and corrected for instrumental background. ratios through the consistency or our standards that cover most of the range of δ 33 S and δ 34 S values measured in our CAS. Consistency standards (seawater and a deep-sea coral aragonite) were purified and measured alongside the Archean carbonates. We measured average δ 34 S and Δ 33 S values of 20.95 ± 0.19 ‰ and 0.10 ± 0.24‰ for seawater (2sd, n=4) and 22.35± 0.22 ‰ and 0.02 ± 0.22‰ (2sd, n=4) for our coral consistency standards, in agreement with our previous investigations. Individual TPB were measured in each batch of column. We performed the blank corrections using the average of all measured ratios to improve accuracy but using the average concentrations of each batch. In addition to our consistency standards, we added two Paleoproterozoic samples from an economic drill-core (T92/7 and T92/22, Mooidraai Formation, provided by Prof. Beukes, see Fig. 1). Despite their low sulfur content (20 to 180 ppm) similar to the other samples analyzed in this article, they display no MAF values (average Δ 33 S=0.21±0.30‰, n=3), in agreement with the timing of MAF disappearance evaluated in South Africa [START_REF] Guo | Reconstructing Earth's surface oxidation across the Archean-Proterozoic transition[END_REF][START_REF] Luo | Rapid oxygenation of Earth's atmosphere 2.33 billion years ago[END_REF]. Values are presented in the appendix.

In parallel, an aliquot of the purified sample is used to measure sulfate content by ion chromatography at the ESE (Caltech) using a Dionex ICS-3000 system (Thermo Fisher Scientific) using in-house concentration standards to assess accuracy and precision. The CAS concentrations were calculated from the measured sulfate amount, and from the dry weights of the cleaned powder and the insoluble residue. The insoluble residue was evaluated by weighing the centrifuge tube before and after dissolution of the carbonate. The soluble fraction was calculated by difference and evaluated between 22% and 107 % of the initial weight, possibly due to difference of statics from one weighing session to the next. In the absence of a clear way to evaluate uncertainty in these calculations, it was therefore assumed to be 10 % RSD. In a few cases, the soluble fraction could not be evaluated and was assumed to be 95% in order to calculate the CAS concentration of the sample. Because the concentrations were measured after purification, we also applied a blank correction. Total procedural blanks (TPB) were measured as they were run on the Neptune for isotopic ratios. The signal was compared to the bracketing standard to calculate the amount of sulfur. In some cases, more powder than necessary was drilled and duplicates were run from the same dissolved powders.

Uncertainties for sulfur isotopic compositions are given as blank-corrected 2 standard deviations.

There are two steps in the blank correction. First, the machine blank from the MC-ICPMS is subtracted using the signal measured in the blank solution (5% HNO 3 +40 µmol/L NaOH to match the Na-addition to the samples). Second, we correct for the total procedural blank (TPB) that includes reagents and sample handling. To measure the TPB we processed empty vials through the whole procedure. Typically there is not enough sulfur to run both the IC and the ICPMS for TPB samples. We evaluated the amount of TPB sulfur on the MC-ICPMS instead. To do so, we diluted the TPB in a known volume of HNO 3 +NaOH solution and assumed a linear response of intensity to sulfur concentration, and report the results in the appendix. We used these numbers in the following TBP correction equations as ratios ( 34 R blk ) and not delta values to correct the isotopic ratio ( 34 R meas) to the true CAS isotopic ratio ( 34 R carb : An analogous set of equations can be written for evaluating 33 R carb . Uncertainty in the TPB corrected ratio was calculated by propagating the standard deviation obtained for random populations of 1000 values with a normal distribution that has the same evaluated standard deviation as each member of equation ( 3) and (4). The blank correction increases the typical δ 34 S reproducibility from 0.2 to 0.35‰ and the Δ 33 S one from 0.40 to 0.70‰ (2sd). Carbon and oxygen isotopes were measured at Caltech using a Delta V Plus isotope ratio mass spectrometer (Thermo Fisher Scientific) equipped with the GasBench II. About 100 μg of powder was weighed and then digested for at least 2 h at 72°C with 85% phosphoric acid in 12 mL vials pre-flushed with helium.

× = × + × ( 1
Accuracy was assessed by running two in-house calcite standards at the beginning and end of each analytical session. Reproducibility was monitored by running a Carrera marble standard between every five samples and 0.22‰ for δ 13 C and 0.85‰ for δ 18 O as 2SD.

Synchrotron data

We used sulfur K-edge X-ray absorption spectroscopy (XAS) to study the electronic structure and the redox state of the sulfur present in some of the carbonate samples that we analyzed in this study. A few mg of powder were placed onto sulfur-free (< 1 ppm) mylar tape (St. Gobain) in a milled aluminum sample holder. X-ray absorption near edge structure (XANES) spectra for bulk S valence state were collected at beamline 14-3 at Stanford Synchrotron Radiation Lightsource photooxidation by the X-ray beam). We fit the data using the SIXPACK software [START_REF] Webb | SIXPack a Graphical User Interface for XAS Analysis Using IFEFFIT[END_REF] and the following standards: CAS-sulfate, pyrite, S 8 , sulfoxide, sulfonate, methionine, sulfate ester and kerogen type 1 and 2 (Table 1). S 8 was measured from a Sigma-Aldrich alpha-S 8 powder.

Pnon yrite, kerogen type 1 and 2, CAS, gypsum and barite were measured from geological samples at SLAC. SO4-ester (dextran sulfate), sulfoxides (methionine sulfoxide), thioether (methionine), sulfonic acids/sulfonate (taurine) were measured as solutions (to minimize the self-absorption artifacts and spectral differences due to crystal packing made up to 30-100 mM in PBS at pH 7.4

(except for dextran sulfate which was analyzed at pH 8.2). Standards are shown in Fig. S5. The relative proportions of each sulfur species are given in Table 1.

Results

Petrographic observations

Samples with a lower degree of post-depositional alteration hail from outcrops and cores located in the better-preserved Griqualand West region (Fig. S1). As previously described [START_REF] Paris | Neoarchean carbonateassociated sulfate records positive Δ33S anomalies[END_REF], samples from the Boetsap outcrop of the Reivilo Formation (W1, [START_REF] Paris | Neoarchean carbonateassociated sulfate records positive Δ33S anomalies[END_REF]WJG1, this study) are relatively well-preserved precipitated stromatolites, including aragonite fans, and minor grainstones (Fig. S1a). These rocks have largely been dolomitized but some horizons are The WB-98 drill core also provides a record of the Gamohaan Formation but these strata contain abundant mm to cm pyrite nodules. This sample showed signs of external oxidation that most likely occurred after core extraction and are removed by polishing (Fig. S4), but we cannot exclude that the pyrite minerals were partially oxidized before we handled them. Thus, we characterize the WB-98 samples as less pristine reservoirs for CAS as they contain potentially contaminating sulfides and sulfide-derived sulfate produced during oxidative weathering.

Unlike the Griqualand West area, the Campbellrand-Malmani strata in the Transvaal region were subject to metamorphism and metasomatic fluids introduced by the Bushveld intrusion [START_REF] Kaneko | Contact metamorphism of the Bushveld Complex in the northeastern Transvaal, South Africa[END_REF][START_REF] Walraven | A chronostratigraphic framework for the northcentral Kaapvaal craton, the Bushveld Complex and the Vredefort structure[END_REF][START_REF] Buick | Precise U-Pb titanite age constraints on the emplacement of the Bushveld Complex, South Africa[END_REF]. Samples collected from outcrops at Rotterdam Farm from the Frisco Formation, equivalent to the Naute/Gamohaan formations, show extensive silicification, including completely quartz-replaced ooids and cherty marble with common euhedral sulfides and silicified veins (Figure S4).

Geochemical data

The carbonate content of our samples varies from ~10 to ~100 weight percent, reflecting the wide variety of materials analyzed. Carbon and oxygen isotope data are consistent with previous studies of carbonates from the Campbellrand-Malmani platform [START_REF] Fischer | Isotopic constraints on the Late Archean carbon cycle from the Transvaal Supergroup along the western margin of the Kaapvaal Craton, South Africa[END_REF]. The δ 13 C values range from -4 to 0.5‰ with most points clustering around -1‰ while δ 18 O data range from -18 to -6‰ with most points between -9‰ and -6‰ (Fig. 2).

Our data reveal that almost all CAS samples analyzed are characterized by positive ∆ 33 S in carbonates with very low sulfate content (Fig. 3,4,5). For all samples, the ∆ 33 S values range from -0.5 ‰ to +8.0 ‰, the δ 34 S values range from -7‰ to +25‰ and the sulfate contents range from 1 to >1000 ppm. Almost all the data indicate a CAS content lower than 150 ppm with the exception of two samples from WB-98. A few negative ∆ 33 S values were encountered but they usually corresponded to the samples with the lowest amount of recovered sulfate (3 nmol or less, for concentrations usually lower than 3 ppm). As a result, the errors make the determined values not significantly different from zero. With the exception of one point from the Boetsap outcrop (Δ 33 S ≈ +2‰, δ 34 S≈ +25‰), all data follow a positive correlation between the major isotope composition and the 33 S anomaly. The δ 34 S, Δ 33 S and CAS measurements agree with our previously published data [START_REF] Paris | Neoarchean carbonateassociated sulfate records positive Δ33S anomalies[END_REF], but some differences are observed. The highest sulfate contents (>150 ppm) are found in samples from core WB-98, while samples from the Transvaal area display the lowest concentrations (Fig. 4). In addition, the samples from the Boomplaas Formation (core GKP 01) are characterized by less positive Δ 33 S values and very negative δ 18 O. Those samples consist of a very different lithology, dominated by 'giant' ooids.

Overall, our sulfur isotopic data appears to contain three clear endmembers (Fig. 4). Endmember

1

XANES data

XANES analyses of microdrilled untreated powders reveal sulfur speciation in our samples [START_REF] Paris | Neoarchean carbonateassociated sulfate records positive Δ33S anomalies[END_REF]. Typical spectral data are shown in Fig. 6 and indicate that sulfur was present in our samples as a mixture between various species of reduced sulfur and sulfate, as expected. For most of the samples, we obtained a visually satisfactory fit, except for sample WJG3 51. The fit produced a non-existent reduced sulfur peak and failed to fit the shape of the sulfate peak (Fig. S6). The XANES data revealed that most samples contained at least some CAS, in agreement with our previous study [START_REF] Paris | Neoarchean carbonateassociated sulfate records positive Δ33S anomalies[END_REF]. Most samples also contained sulfate present as SO4ester, but also traces of gypsum and barite. Kerogen-sulfur was the most abundant reduced sulfur species in our samples and we usually did not detect a lot of pyrite or S 8 . In addition, we found presence of sulfonate in two samples and thioether in one sample.

Discussion

To understand the sulfur photochemistry and associated sulfur fractionation laws generated by Archean atmospheric processes, most models rely on data from sedimentary pyrites and assume that sulfate exited the atmosphere already carrying a negative Δ 33 S value. Existing direct oxidized sulfur data derive primarily from Paleoarchean barites [START_REF] Bao | The five stable isotope compositions of Fig Tree barites: Implications on sulfur cycle in ca. 3.2 Ga oceans[END_REF][START_REF] Ueno | Quadruple sulfur isotope analysis of ca. 3.5 Ga Dresser Formation: New evidence for microbial sulfate reduction in the early Archean[END_REF][START_REF] Shen | Evaluating the role of microbial sulfate reduction in the early Archean using quadruple isotope systematics[END_REF][START_REF] Philippot | Variations in atmospheric sulphur chemistry on early Earth linked to volcanic activity[END_REF][START_REF] Roerdink | Multiple sulfur isotopes in Paleoarchean barites identify an important role for microbial sulfate reduction in the early marine environment[END_REF][START_REF] Muller | Multiple sulfur-isotope signatures in Archean sulfates and their implications for the chemistry and dynamics of the early atmosphere[END_REF]. These barites were all deposited between 3.5 and 3.1 Ga ago and therefore cover only a small fraction of the Archean Eon. Furthermore, their existence is a something of a paradox for an ocean with low sulfate concentrations where sulfate evaporites are not observed in the rock record [START_REF] Grotzinger | New constraints on Precambrian ocean composition[END_REF]. Thus, the barite may not represent Archean open-ocean sulfate as they are associated with volcaniclastic deposits [START_REF] Philippot | Variations in atmospheric sulphur chemistry on early Earth linked to volcanic activity[END_REF] or reflect hydrothermal systems [START_REF] Van Kranendonk | Volcanic degassing, hydrothermal circulation and the flourishing of early life on Earth: A review of the evidence from c. 3490-3240 Ma rocks of the Pilbara Supergroup, Pilbara Craton, Western Australia[END_REF]. In contrast to the barite record, the data presented here shows an unambiguously positive Δ 33 S signal in carbonate-associated sulfate throughout our diverse sample set, consistent with previous results [START_REF] Paris | Neoarchean carbonateassociated sulfate records positive Δ33S anomalies[END_REF]. Our diverse dataset, ranging from cores to outcrops and from pure carbonate samples to samples with complex mineralogy or preservational history, further reveal seawater sulfate deposition and preservation across the marine carbonate platform captured by the ~2.5 Ga Campbellrand-Malmani sequence. In the following discussion, we first assess if this positive Δ 33 S signal is primary or post-depositional.

We then compare the CAS data and the pyrite data in the Campbellrand platform and finally discuss the possible atmospheric origin of the positive Δ 33 S in CAS.

Does post-depositional history affect the sulfur isotopic signal?

A positive Δ 33 S anomaly in oxidized sulfur species is at odds with most interpretations of the Archean sulfur cycle. We combined the current dataset and our previous data to test whether the omnipresent positive Δ 33 S signal that we measured could actually derive from preservational biases or metamorphic history. The data in Fig. 3 indicate that positive Δ 33 S values are also correlated with δ 34 S values. Fig. 4 shows that, across the entire platform, the sulfate content and Δ 33 S values define a domain delimited by three likely endmembers. These are not necessarily mixing relationships, but rather types of samples with characteristic relationships between their sulfur isotope value and sulfate content. The different cores and sections do not appear randomly distributed between these three endmembers and we hypothesize that each of them corresponds to a different phase of the geological history of the platform.

We first ensure that we measured sulfur from CAS. CAS is present in almost all our samples. We also found abundant sulfur both as kerogen and SO 4 -ester. We do not expect sulfur from kerogen to contribute to our measured CAS because sulfur extraction from organic matter, especially kerogens, require stronger chemical reagents than those we used for CAS extraction (e.g. [START_REF] Raven | Sulfur isotopic composition of individual organic compounds from Cariaco Basin sediments[END_REF]. Similarly, pyrite was present only in small amounts in our samples and it is not significantly dissolved in our protocol [START_REF] Present | Large Carbonate Associated Sulfate isotopic variability between brachiopods, micrite, and other sedimentary components in Late Ordovician strata[END_REF]. S 8 was present in only two of the tested powders. Barite could not have been dissolved during our process, which is also designed to not collect gypsum [START_REF] Present | Diagenetic controls on the isotopic composition of carbonate-associated sulphate in the Permian Capitan Reef Complex, West Texas[END_REF]. However, we cannot exclude that we could have leached sulfate from SO4-ester groups and that our sulfur isotopic composition resulted from a CAS-SO 4 ester mix. Such groups are found for example in brachiopod shell carbonates where they play a role in biomineralization; however, they are not a known diagenetic product (Richardson et al., 2019a;Richardson et al., 2019b). In any case, the sulfate in those groups likely would have initially been derived from seawater sulfate, just like the CAS.

We propose that Endmember 1 (high Δ 33 S, intermediate [CAS]) records the most pristine original sulfate isotopic composition. This endmember consists primarily of samples from two outcrops located at the base and the top of the platform in the Griqualand West area: Boetsap and Kuruman Kop. Some of the data points were previously published [START_REF] Paris | Neoarchean carbonateassociated sulfate records positive Δ33S anomalies[END_REF] and others come from additional sampling from those two locations and new data presented here. Carbonates are preserved as fabric-retentive dolomite or limestone that initially precipitated as seafloor carbonate cements, occasionally associated with microbial mats [START_REF] Sumner | Sequence Stratigraphic Development of the Neoarchean Transvaal carbonate platform, Kaapvaal Craton, South Africa[END_REF][START_REF] Sumner | U-Pb geochronologic constraints on deposition of the Campbellrand Subgroup, Transvaal Supergroup, South Africa[END_REF][START_REF] Sumner | Herringbone calcite; petrography and environmental significance[END_REF]. Carbon and oxygen isotope data agree with previous investigations [START_REF] Fischer | Isotopic constraints on the Late Archean carbon cycle from the Transvaal Supergroup along the western margin of the Kaapvaal Craton, South Africa[END_REF]. We initially chose these samples as the best candidates for retaining Archean CAS because they show no sign of post-exhumation oxidation, they contain only traces of disseminated pyrite, and they display no petrographic evidence of deformation or metamorphic alteration [START_REF] Paris | Neoarchean carbonateassociated sulfate records positive Δ33S anomalies[END_REF], only reaching low-grade greenschist facies [START_REF] Miyano | Phase relations of stilpnomelane, ferri-annite, and riebeckite in very low-grade metamorphosed iron-formations[END_REF]. Overall, the sulfate content of those rocks (roughly 10 to 50 ppm) is consistent with precipitation of inorganic aragonite in seawater with sulfate concentrations around 100 µmol/L or precipitation calcite at concentrations lower than 30 µmol/L [START_REF] Barkan | Sulfur isotope fractionation between aqueous and carbonate-associated sulfate in abiotic calcite and aragonite[END_REF], a range that agrees with existing seawater sulfate concentration estimates for the Neoarchean [START_REF] Crowe | Sulfate was a trace constituent of Archean seawater[END_REF][START_REF] Fakhraee | Sedimentary sulfur isotopes and Neoarchean ocean oxygenation[END_REF]. However, no constraints exists on dolomite, or during the aragonite-calcite diagenetic inversion (except during meteoric diagenesis, [START_REF] Gill | Behavior of carbonate-associated sulfate during meteoric diagenesis and implications for the sulfur isotope paleoproxy[END_REF].

Unlike Endmember 1, we suggest that Endmember 2 (low Δ 33 S, low [CAS]) documents sulfur isotopes affected by late diagenesis and/or metamorphism and metasomatic fluids. Endmember 2 contains samples from the Rotterdam farm outcrop, both located in the Transvaal area, as well as some samples from the Griqualand West area such as late void-filling spar. The Transvaal area was chosen to assess the influence of post-depositional history as depositional depth and metamorphic history were different between the two parts of the platform, including the Bushveld intrusion ca. 2.05 Ga ago [START_REF] Walraven | A chronostratigraphic framework for the northcentral Kaapvaal craton, the Bushveld Complex and the Vredefort structure[END_REF]. Selected locations reached temperatures up to 500°C and contain substantial petrographic evidence of metamorphism (Miyano and Beukes, 1997). Samples from the Rotterdam Farm location were sometimes silicified, preventing us at times from drilling out sample material. Petrographically, they show silicified fractures and extensive replacement of carbonate ooids by chert. Other samples were characterized by low weight percent (<10%) carbonate and CAS content. The samples that were affected by the Bushveld metamorphism have the lowest sulfate content, sometimes close to our total procedural blank.

Some of those points can therefore not be represented in Figs 3 and 4 but would likely extend Endmember 2 farther to the right in Fig. 4. We also note that samples WJG9 143 from the Rotterdam farm outcrop is characterized by homogeneous δ 13 C values and heterogeneous sulfur isotopic compositions (both δ 34 S and Δ 33 S). Such a pattern is not necessarily surprising if the rocks were initially deposited in a sulfate-poor environment. These results suggest that no massive sulfate overprinting occurred in these rocks. In addition, some samples from Griqualand West also belong to this endmember. For example, two samples (spar) of GKP 01 from the Lower Nauga/Reivilo Formation are characterized by Δ 33 S values close to zero and very low CAS content (less than 5 ppm, [START_REF] Paris | Neoarchean carbonateassociated sulfate records positive Δ33S anomalies[END_REF]. This core did not strongly experience the Bushveld contact metamorphism, however these rocks contain void-filling sparry cements that reflect residual porosity readily accessed by Bushveld hydrothermal fluids [START_REF] Gleason | 2.05-Ga Isotopic Ages for Transvaal Mississippi Valley-Type Deposits: Evidence for Large-Scale Hydrothermal Circulation around the Bushveld Igneous Complex, South Africa[END_REF][START_REF] Paris | Neoarchean carbonateassociated sulfate records positive Δ33S anomalies[END_REF].

Overall, Endmember 2 shows diagenetic or metamorphic alteration of the rocks that tends to erase the Δ 33 S-δ 34 S trend, not create it. The carbonates might all be secondary and reprecipitated in a fluid that was poor in sulfate. We conclude that these secondary processes do not explain the positive Δ 33 S values in Endmember 1.

Endmember 3 (low Δ 33 S, high [CAS]) is the richest in sulfate and corresponds mainly to samples from the pyrite-rich and secondarily-oxidized core WB-98, and thus we contend that this endmember reflects the effects of incipient oxidative weathering. WB-98 samples have abundant pyrite nodules and showed clear visual signs of surficial oxidation. As a result, they do not represent the ideal target to explore the sulfur isotopic composition of seawater CAS, but could represent a source of sulfate with a positive Δ 33 S if we assume that pyrite oxidation is the origin for the CAS measured in our samples. However, WB-98 is characterized by lower Δ 33 S and δ 34 S values and richer sulfate contents than samples from other locations, likely connected to the presence of (re)oxidized pyrite. We purposefully drilled a pyrite nodule texture as a way to test the influence of the presence of pyrite and to investigate whether the positive Δ 33 S could be derived from pyrite oxidation, either in the lab or during the depositional history of the rock. This sample (WB98 998d, Fig. S4, sample marked "Py" in Fig. 3, 4, and 7A) is an outlier. It has by far the highest sulfate content and the most negative δ 34 S and Δ 33 S values from the entire dataset. The pyrite sample initially contained ~25% of pyrite (10 mg) and we recovered 2.4 µmol SO 4 2-(most likely including sulfate from CAS and from oxidized pyrite). If we assume that all the sulfate came from pyrite oxidation, 2.4 µmol SO 4 2-would correspond to the oxidation of ~150 µg of pyrite (~1.5% of the pyrite included in our drill sample). We cannot determine however whether such oxidation occurred in the core prior to sampling or in the lab after sampling. The former is likelier than the latter as our protocol is not able to oxidize pyrite to such an extent [START_REF] Present | Large Carbonate Associated Sulfate isotopic variability between brachiopods, micrite, and other sedimentary components in Late Ordovician strata[END_REF].

Regardless, sulfate from pyrite oxidation clearly overprinted the sulfur signals of WB-98 if it started with a composition near Endmember 1. If correct, pyrite contamination lowers the measured isotopic composition and does not generate the positive signal we see in Endmember 1, especially in this part of the platform where nodular pyrites are documented as having negative Δ 33 S [START_REF] Fischer | SQUID-SIMS is a useful approach to uncover primary signals in the Archean sulfur cycle[END_REF].

The rest of the samples falls between the three endmembers. This includes part of the samples from Kuruman Kop, Boetasp, core BH1-Sacha, GKP-01. In particular, samples from the Boomplaas Formation (core GKP 01) are characterized by less positive Δ 33 S values than endmember 1 and very negative δ 18 O. Because they are the only samples from this formation, we cannot draw any specific conclusion; however we note that those samples are lithologically unique within our sample set, consisting of coarse sand to gravel-sized ooid, pisoid, and 'giant' ooid packstone (Fig. S1). However, it is difficult to interpret the extent to which samples between the endmembers represent, or not, a combination of the processes mentioned previously.

As an alternative hypothesis to Endmember 1 being a pristine record of marine sulfate, we considered if Endmember 1 could reflect the oxidation of disseminated positive-MAF pyrites in the absence of negative MAF nodules. Most disseminated pyrites exhibit positive MAF values (Ono et al., 2009a;Ono et al., 2009b) and their oxidation would tend to increase Δ 33 S values of sulfate. However, XANES results indicate that our Endmember 1 samples do contain CAS (Fig. 6), and only have rare to extremely rare disseminated pyrites, as confirmed by direct observations of the thin sections matching the drilled areas performed for some of the samples (Fig. S1, S2, S3).

Therefore, in Endmember 1 samples, the sulfate we measure could either be purely CAS, or a mixture of CAS and oxidized disseminated pyrite. For example, XANES data reveal that sample W1-5 contains ~10% sulfur in sulfate and the rest as pyrite (~75%) or organic (~15 %) sulfur, yielding Δ 33 S values as high as +10.4 ‰ [START_REF] Paris | Neoarchean carbonateassociated sulfate records positive Δ33S anomalies[END_REF]). If we assume that the Δ 33 S value of sulfate should be close to Eoarchean barites (i.e. lower than -0.5‰), this means our measured Δ 33 S would require the contribution of oxidized pyrites with values of Δ 33 S higher than +11.6‰. Such high Δ 33 S values have not been documented in contemporaneous pyrites (Fig. 7). The highest published value of disseminated pyrite in the Reivilo Formation is Δ 33 S = +10.34‰ [START_REF] Izon | Multiple oscillations in Neoarchaean atmospheric chemistry[END_REF], with the exception of pyrites from the Fig Tree Group (Δ 33 S values up to 14‰), but they would be an unlikely candidate as a source of sulfur to the basin because they are characterized by negative δ 34 S values, lower than -20‰ [START_REF] Philippot | Variations in atmospheric sulphur chemistry on early Earth linked to volcanic activity[END_REF]. Thus the published pyrite data do not support such a mixing, even assuming all pyrite is oxidized during sample preparation. The fact that pyrite and CAS isotopic compositions do not overlap in the Gamohaan formation (from the better-preserved Kuruman Kop section) further supports that CAS sulfur isotope data from Endmember 1 do not reflect procedural pyrite oxidation, as further discussed in section 5.2. As a result, we feel confident that Endmember 1 likely contains the most pristine CAS in the platform.

We therefore assume that this positive Δ 33 S signal reflects sulfate incorporated in the rocks during their precipitation from seawater as early cements across the Neoarchean platform, in agreement with our previous interpretation [START_REF] Paris | Neoarchean carbonateassociated sulfate records positive Δ33S anomalies[END_REF].

How could Δ 33 S-positive sulfate form?

There (1) In order to create sulfate with positive MAF signature, we could consider oxidative weathering of positive Δ 33 S pyrites during the Archean. First, this idea is in conflict with the observation of unoxidized detrital pyrites in underlying and overlying strata [START_REF] Johnson | O2 constraints from Paleoproterozoic detrital pyrite and uraninite[END_REF]. Even in a fully oxygenated atmosphere, modern weathering of Archean crust with anomalous Δ 33 S pyrite produces sulfur with no MAF [START_REF] Torres | Riverine evidence for isotopic mass balance in the Earth's early sulfur cycle[END_REF]. For Archean weathering to generate sulfate with a positive Δ 33 S value, oxidation of the S-species carrying only the positive Δ 33 S signal is required. In addition, highly positive Δ 33 S pyrites such as the values found in our CAS measurements are only found in the latest Neoarchean pyrites, suggesting that this weathering would need to involve contemporaneous pyrites from the Campbellrand platform, which is difficult to envision. It has been suggested that biologically-mediated weathering of sulfur minerals could have started about 2.7 Ga ago [START_REF] Stüeken | Contributions to late Archaean sulphur cycling by life on land[END_REF], which could possibly be reconciled with detrital pyrite observations assuming differential pyrite weathering using a biological oxidant other than O 2 . In sum, we suggest that Archean oxidation of pyrites is inconsistent with both modern and ancient observations of pyrite weathering.

(2) An alternative explanation for the positive Δ 33 S values measured in sulfate to be produced as a result of oxidation of more reduced sulfur species would be microbially-mediated sulfide oxidation to sulfate at the time of rock formation, or sulfur-disproportionation (e.g. [START_REF] Philippot | Early Archaean Microorganisms Preferred Elemental Sulfur, Not Sulfate[END_REF][START_REF] Shen | Evaluating the role of microbial sulfate reduction in the early Archean using quadruple isotope systematics[END_REF][START_REF] Farquhar | Pathways for Neoarchean pyrite formation constrained by mass-independent sulfur isotopes[END_REF]. Microbial activity is expected in Noeoarchean basins (e.g. [START_REF] Farquhar | Pathways for Neoarchean pyrite formation constrained by mass-independent sulfur isotopes[END_REF], especially in the case of samples from cores GKP 01 and WB-98 or from the Kuruman Kop outcrop, where microbial fenestrae and rolled microbial mats are observed (e.g. Fig. S4). If we follow the canonical model and assume that atmospheric sulfate carries a negative Δ 33 S, the positive Δ 33 S isotopic compositions we measure in Neoarchean CAS would imply that sulfate derived from sulfide oxidation or elemental sulfur disproportionation completely erased the isotopic signature of the atmospheric input in the Campbellrand-Malmani basin. We do not ever measure negative CAS Δ 33 S in pristine samples. Our observation implies that seawater sulfate in this basin did not carry a negative Δ 33 S value, regardless of the atmospheric processes involved.

(3) Instead, we argue that the positive MAF values in CAS result from atmospheric processes that generate an oxidized sulfur species carrying the positive Δ 33 S anomaly, with reduced sulfur in early diagenetic disseminated pyrites deriving from microbial reduction of this sulfate. Outcrop samples reveal Δ 33 S values that are more positive than those measured from core samples.

However, cores and outcrops do not cover the same formations and we cannot interpret this difference in detail. However, because we have the most data for samples from Boetsap and Kuruman Kop, both outcrops from different locations of the Griqualand West part of the platform (bottom and top of the Campbellrand-Malmani platform, respectively), we investigate the relationship between δ 34 S and Δ 33 S for these two suites of samples, including previous data [START_REF] Paris | Neoarchean carbonateassociated sulfate records positive Δ33S anomalies[END_REF]. Fig. 7 shows that in a δ 34 S vs. Δ 33 S crossplot, most of the data from the Gamohaan (top of the platform, Kuruman Kop outcrop, Fig. 7A) and the Reivilo Formation (base of the platform, Boetsap outcrop, Fig. 7B) plot along straight lines. The slope of this line is identical, within error, to the Archean array, initially defined by bulk rock measurements (δ 34 S=0.89×Δ 33 S; Ono et al., 2009a) and attributed to MAF formation by interaction of UV-light with SO 2 molecules.

We also note that the Gamohaan Formation, as recorded by the better-preserved Kuruman Kop, contains CAS and pyrite data that do not overlap with each other, reinforcing our interpretation that we did not simply measure reduced sulfur that would have been reoxidized during rock handling. The isotopic relationships between these two phases may reflect different aspects of environmental processes. In the Reivilo formation, almost all of the CAS data strictly follow the Archean array, outside of one point with a very high δ 34 S, while pyrite data from previous publications are more varied (Fig 7B). If the original oxidized sulfur species in seawater had a positive Δ 33 S, then sulfur dioxide gas emitted from the mantle with Δ 33 S ≈ 0‰ experienced atmospheric photochemical reactions that led to positive Δ 33 S sulfate. Presumably the negative Δ 33 S would be carried in the resulting reduced sulfur species. Part of the positive Δ 33 S sulfate could have then been reduced through a mass-dependent reduction process, such as microbial sulfate reduction (double-headed arrow in Fig. 7), to be preserved as sedimentary pyrites carrying positive Δ 33 S values -forming the Archean pyrite array. Disseminated pyrite crystals could also be formed secondarily or altered by later processes, such as disseminated pyrite from shales adjacent to the Campbellrand platform that were characterized magnetically as secondary (Fischer et 2014). These MDF processes such as microbial and thermochemical sulfate reduction do not affect the Δ 33 S value and could explain why the δ 34 S data of reduced sulfur covers a wider range than the CAS data.

Our hypothesis that positive-MAF was carried by oxidized sulfur species and negative MAF was hosted by reduced sulfur species would explain why positive Δ 33 S can be found in both disseminated pyrite and CAS, as well as why negative values are found only in pyrites across the Campbellrand platform and not in CAS. Within this framework, we interpret the CAS sulfur isotopes in the Gamohaan Formation as reflecting the non-quantitative formation of pyrite. As a result, sulfate would keep its initial Δ 33 S positive trend, but the δ 34 S values of the sulfate would be offset from pyrite towards positive values. We indeed observed a positive offset of ~5‰ from sulfate to pyrite in the Gamohaan Formation (Fig. 7A), which is small yet consistent with microbial sulfate reduction [START_REF] Crowe | Sulfate was a trace constituent of Archean seawater[END_REF]. The observation of such an offset in the Gamohaan formation rich in microbial mats, unlike its observation in the Reivilo formation where no such mats are observed, would be consistent with microbial processes occurring. The overall relationship between sulfate and pyrite in all measurements of the Campbellrand platform is consistent with the hypothesis that disseminated pyrites formed from sulfate carrying a positive Δ 33 S value.

This observed sulfate-sulfide relationship emphasizes the fact that the only samples revealing clearly negative Δ 33 S are nodular or layered pyrites while the disseminated pyrites tend to display positive values in existing data for the Campbellrand-Malmani platform [START_REF] Kamber | Micro-scale sulphur isotope evidence for sulphur cycling in the late Archean shallow ocean[END_REF][START_REF] Farquhar | Pathways for Neoarchean pyrite formation constrained by mass-independent sulfur isotopes[END_REF][START_REF] Fischer | SQUID-SIMS is a useful approach to uncover primary signals in the Archean sulfur cycle[END_REF] Until recently, in light of only one sulfate archive (barites), previous studies that resulted in modeled or experimental positive Δ 33 S sulfate were disregarded. The first models based on crosssection adsorptions yielded positive anomalies in sulfate [START_REF] Ueno | Geological sulfur isotopes indicate elevated OCS in the Archean atmosphere, solving faint young sun paradox[END_REF]. This result was considered unfit to explain the Archean MAF signature. [START_REF] Ueno | Geological sulfur isotopes indicate elevated OCS in the Archean atmosphere, solving faint young sun paradox[END_REF] thus developed the idea that the presence of COS in the atmosphere shielded part of the photolysis spectrum in order to generate a negative anomaly, because COS preferentially absorbs wavelengths between 200 and 210 nm. During photooxidation in the 180-220 nm region, the predicted photolytic processes yield Δ 33 S values whose sign depends strongly on the cross-section adsorption profiles. The initial sign of the MAF signal in sulfate was calculated as positive [START_REF] Claire | Modeling the signature of sulfur mass-independent fractionation produced in the Archean atmosphere[END_REF] but then changed to negative using revised spectra [START_REF] Endo | Photoabsorption cross-section measurements of 32S, 33S, 34S, and 36S sulfur dioxide from 190 to 220 nm[END_REF][START_REF] Izon | Biological regulation of atmospheric chemistry en route to planetary oxygenation[END_REF]. By contrast, because the latest cross-sections produce fractionation that appear in agreement with negative sulfate [START_REF] Endo | Photoabsorption cross-section measurements of 32S, 33S, 34S, and 36S sulfur dioxide from 190 to 220 nm[END_REF][START_REF] Izon | Biological regulation of atmospheric chemistry en route to planetary oxygenation[END_REF], no additional calculations have been produced to understand if the presence of other gases could affect the UV spectrum and lead to positive sulfate formation.

However, two other known processes can create a positive Δ 33 S in sulfate. Photooxidation without self-shielding can create sulfate with a (small) positive Δ 33 S [START_REF] Endo | Sulfur isotope fractionation by broadband {UV} radiation to optically thin {SO2} under reducing atmosphere[END_REF]. Fractionation during S x sulfur chain formation [START_REF] Babikov | Recombination reactions as a possible mechanism of mass-independent fractionation of sulfur isotopes in the Archean atmosphere of Earth[END_REF][START_REF] Babikov | One possible source of mass-independent fractionation of sulfur isotopes in the Archean atmosphere of Earth[END_REF]) also creates positive Δ 33 S values in sulfate. This result stems from the unlikelihood of combining 2 minor isotopes in one chain and that S 4 and S 8 should therefore carry a negative Δ 33 S value [START_REF] Harman | Chain formation as a mechanism for massindependent fractionation of sulfur isotopes in the Archean atmosphere[END_REF].

If Archean atmospheric processes did produce sulfate with positive Δ 33 S, then the negative Δ 33 S values in rare Paleoarchean barite might be better understood as an exception rather than the norm.

These barites might have precipitated following increased sulfate deposition during intensive volcanic events, as suggested by microanalytical Secondary Ion Mass Spectrometry measurements of sulfur isotopes [START_REF] Philippot | Variations in atmospheric sulphur chemistry on early Earth linked to volcanic activity[END_REF][START_REF] Muller | Multiple sulfur-isotope signatures in Archean sulfates and their implications for the chemistry and dynamics of the early atmosphere[END_REF], though the interpretation of a volcanic array remains equivocal [START_REF] Roerdink | High-resolution quadruple sulfur isotope analyses of 3.2 Ga pyrite from the Barberton Greenstone Belt in South Africa reveal distinct environmental controls on sulfide isotopic arrays[END_REF]. During these events, the SO 2 emitted by volcanoes could be affected by photooxidation processes in the SO 2 -and COS-rich plume. As explored rigorously, photooxidation processes at high COS concentration are expected to generate sulfate aerosols carrying a negative Δ 33 S [START_REF] Ueno | Geological sulfur isotopes indicate elevated OCS in the Archean atmosphere, solving faint young sun paradox[END_REF][START_REF] Muller | Multiple sulfur-isotope signatures in Archean sulfates and their implications for the chemistry and dynamics of the early atmosphere[END_REF], possibly with a contribution of self-shielding, though excessive partial pressure of SO 2 could lead to MAF suppression [START_REF] Endo | Total Pressure Dependence of Sulfur Mass-Independent Fractionation by SO2 Photolysis[END_REF]. Therefore, there is a likely possibility that sulfate deposited during such intense volcanic events carried an isotopic composition different than the 'normal'

background sulfate aerosol deposition. During volcanic events, the presence of potential oxidants may change or there may be self-shielding and/or shielding by OCS as SO 2 concentrations locally increase. In addition, barites are not characterized by homogeneously negative Δ 33 S values as some of them carry a less negative to slightly positive MAF [START_REF] Muller | Multiple sulfur-isotope signatures in Archean sulfates and their implications for the chemistry and dynamics of the early atmosphere[END_REF]. Observations of such heterogeneities raise the possibility that sulfate deposition is not characterized by a constant negative anomaly, which has also been suggested by other studies [START_REF] Ueno | Geological sulfur isotopes indicate elevated OCS in the Archean atmosphere, solving faint young sun paradox[END_REF][START_REF] Claire | Modeling the signature of sulfur mass-independent fractionation produced in the Archean atmosphere[END_REF][START_REF] Paris | Neoarchean carbonateassociated sulfate records positive Δ33S anomalies[END_REF][START_REF] Harman | Chain formation as a mechanism for massindependent fractionation of sulfur isotopes in the Archean atmosphere[END_REF]. If correct, CAS would record the 'normal' MAF law under an optically thin atmosphere in contrast to the barite deposits recording processes such as self-shielding that occurred during volcanic events. Alternatively, different processes could occur during different period of the Archean, similar to previous suggestions of atmospheric composition oscillations or secular changes (e.g. [START_REF] Domagal-Goldman | Organic haze, glaciations and multiple sulfur isotopes in the Mid-Archean Era[END_REF][START_REF] Izon | Multiple oscillations in Neoarchaean atmospheric chemistry[END_REF][START_REF] Ueno | Geological sulfur isotopes indicate elevated OCS in the Archean atmosphere, solving faint young sun paradox[END_REF], and sulfate aerosols could be positive at times and negative at others.

Conclusion

The Campbellrand-Malmani carbonate platform provides useful constraints on the isotopic compositions of seawater sulfate and offers unique insights into Neoarchean sulfur cycling. The platform offers contrasting degrees of preservation of both pyrite and sulfate-bearing lithologies.

We used this diverse record to explore the quality of the Archean CAS archive, and hone interpretations of the Neoarchean sulfur cycle. The data show that sulfate incorporated into and preserved in carbonates (CAS) records a positive Δ 33 S value that cannot be explained through secondary processes or contamination from pyrite. We found no sulfate carrying a negative Δ 33 S deposited across this 150-million-year interval of time. This apparent contradiction with negative from [START_REF] Sumner | Sequence Stratigraphic Development of the Neoarchean Transvaal carbonate platform, Kaapvaal Craton, South Africa[END_REF][START_REF] Johnson | Manganeseoxidizing photosynthesis before the rise of cyanobacteria[END_REF][START_REF] Johnson | O2 constraints from Paleoproterozoic detrital pyrite and uraninite[END_REF]. For each location we indicated in parentheses the code used for the sample names, when different from the core/location names. All samples were collected for the current study except W1 and W2, which are samples previously analyzed [START_REF] Paris | Neoarchean carbonateassociated sulfate records positive Δ33S anomalies[END_REF]. Thin gray lines indicate the Archean array [START_REF] Ono | New insights into Archean sulfur cycle from mass-independent sulfur isotope records from the Hamersley Basin, Australia[END_REF]Ono et al., 2009b). In panel A, pyrite data are a compilation of the Gamohaan-Koegelbeen formations, bulk [START_REF] Kaufman | Late Archean Biospheric Oxygenation and Atmospheric Evolution[END_REF][START_REF] Izon | Multiple oscillations in Neoarchaean atmospheric chemistry[END_REF] and "in-situ" [START_REF] Kamber | Micro-scale sulphur isotope evidence for sulphur cycling in the late Archean shallow ocean[END_REF] and the Klein Naute -upper part of the Upper Nauga formations, bulk (Ono et al., 2009a;Ono et al., 2009b) and "in-situ" (Ono et al., 2009a;[START_REF] Fischer | SQUID-SIMS is a useful approach to uncover primary signals in the Archean sulfur cycle[END_REF]. The arrow at lower left indicates the point drilled through a pyrite nodule. The thick line indicates the linear regression calculated from the data. In panel B, pyrite data are a compilation of data for the Reivilo formation, bulk [START_REF] Farquhar | Pathways for Neoarchean pyrite formation constrained by mass-independent sulfur isotopes[END_REF][START_REF] Izon | Multiple oscillations in Neoarchaean atmospheric chemistry[END_REF]Ono et al., 2009b;[START_REF] Zerkle | A bistable organic-rich atmosphere on the Neoarchaean Earth[END_REF] and "in-situ" [START_REF] Farquhar | Pathways for Neoarchean pyrite formation constrained by mass-independent sulfur isotopes[END_REF]. The thick lines indicate the linear regression calculated from the data, excluding the data point at δ 34 S=25 ‰. The ellipse indicates the pyrite data with negative Δ 33 S values.

  ] carb = (n carb × 96.04) / m carb (4), with m carb the carbonate weight of the sample.

(

  SSRL) in Menlo Park, California. Samples were measured in fluorescence mode, using a 4element Vortex detector (Hitachi) equipped with Xspress3 pulse processing electronics (Quantum Detectors). A sodium thiosulfate (NaS 2 O 3 ) standard was used for energy calibration, with the first pre-edge peak (fluorescence maxima) set at 2472.02 eV. Duplicate to quadruplate spectra through the sulfur K-edge were collected for all samples by measuring fluorescence while scanning from 2460 to 2540 eV, and averaged to obtain better spectral resolution and help reduce noise. Repeat analyses of identical spots showed no evidence of redox changes during analysis (e.g.

  still limestone, and they mark the base of the Campbellrand-Malmani platform capturing shallow subtidal paleoenvironments. A new pisolite sample from the Monteville Formation (sample GKP 1175, Fig.S1c-d) supplements our previous data[START_REF] Paris | Neoarchean carbonateassociated sulfate records positive Δ33S anomalies[END_REF]) from core GKP 01. We note that those samples consist of a very different lithology, dominated by micritized ooids, pisoids, and 'giant' ooids packstone/rudstone. The Kuruman Kop outcrop, with deep subtidal, fenestral microbialite facies, records the terminal carbonate deposition of the drowning platform in the Gamohaan Formation. Samples from this outcrop show micritized oncoids interspersed between drusy to blocky cement, including the early herringbone calcite cement, with rare m-scale pyrite crystals (Fig.S1b, S2, S3).

  are at least three potential ways to explain how seawater sulfate in the Campbellrand basin can exhibit positive Δ 33 S values. (1) The marine sulfate in the waters overlying the Campbellrand-Malmani platform could be dominated by sulfate coming from oxidative weathering of positive Δ 33 S pyrite, (2) microbial metabolisms (sulfur disproportionation or sulfur oxidation) led to forming sulfate with positive Δ 33 S values or (3) Neoarchean atmospheric processes could have generated original sulfate with a positive Δ 33 S.

Δ

  33 S recorded in Paleoarchean barites and many current assumptions about the Archean sulfur cycle that require negative Δ 33 S sulfate could reflect a secular change in the nature of atmospheric composition and/or photochemical processes affecting sulfur isotopes from early to late Archean time, or suggest that the previously-studied barites record a different suite of processes associated with a unique and rare depositional environment, and/or that early diagenetic and metasomatic sulfur cycling commonly controls pyrite MAF signatures. Our recent CAS results further indicate that Neoarchean atmospheric processes could have produced sulfate with a positive Δ 33 S value, and therefore the mechanisms that lead to positive-MAF sulfate need to be further explored to better constrain the composition of the Archean atmosphere.

Figure 1

 1 Figure 1 Structural cross-section through the Campbellrand platform (top) and geologic map (bottom) of the Kaapvaal Craton showing the cross-section transect through the surface exposures of the Late Archean Transvaal Supergroup, and the two structural sub-basins, Griqualand West and Transvaal. Stratigraphic sections and sample locations for this study are shown. Modified

Figure 2

 2 Figure 2 δ 13 C and δ 18 O data of carbonate in samples that were also analyzed for sulfur isotopes. The symbols represent the various collection locations with squares indicating cores, circles indicating outcrops, open symbols are for samples from the Transvaal area and filled symbols are for samples for Griqualand West. 2SD is 0.25‰ for δ 13 C and 0.85‰ for δ 18 O.

Figure 3

 3 Figure 3 Cross-plots of Δ 33 S vs. δ 34 S values. The symbols represent the various collection locations with squares indicating cores, circles indicating outcrops, open symbols are for previous data (Paris et al., 2014) and filled symbols are for new data.) Errors are plotted as 2sd.

Figure 4

 4 Figure 4 Cross-plots showing 1/[CAS] (g of carbonate/µg of sulfate) vs. Δ 33 S with linear (A) or logarithmic x-axis (B). The "Py" arrow in Fig. 4 points to a sample that was drilled over a pyrite nodule and contained the highest sulfate content (>8000 ppm), the lowest δ 34 S, and a negative Δ 33 S value. Panel B shows the most enriched data points that correspond to the samples drilled over pyrite (Py). The symbols represent the various collection locations with squares indicating cores, circles indicated outcrops, open symbols are for previously published values[START_REF] Paris | Neoarchean carbonateassociated sulfate records positive Δ33S anomalies[END_REF].Errors are plotted as 2sd.

Figure 5

 5 Figure 5 Stratigraphic sections of the outcrops and cores across the Campbellrand-Malmani platform showing the Δ 33 S values. The sections are shown relative to an arbitrary datum at the

Figure 6

 6 Figure 6 Sulfur K-edge XANES spectra of carbonate samples. The vertical line indicates the location of the sulfate peak.

Fig. 7

 7 Fig. 7 Cross-plots showing Δ 33 S vs. δ 34 S values for the top (Gamohaan-Koegelbeen formation, A) and base of the platform (Reivilo formation, B) both from this study and from Paris et al. (2014).

  . Within the Reivilo formation, pyrites with negative Δ 33 S values and very negative δ 34 S values seem to indicate that there was a process with a distinct MAF law (oval, Fig.7), and not a simple MDF process with initial sulfate containing a negative Δ 33 S. Therefore, we suggest that these pyrites could derive from atmospherically-derived negative Δ 33 S reduced sulfur with positive Δ 33 S sulfide derived from sulfate to make pyrite (ferrous sulfide reacting with elemental sulfur to make pyrite, Rickard 1975).This positive Δ 33 S atmospheric sulfate hypothesis leaves us with the challenge of explaining the possibility of a 33 S-enrichment in sulfate that contradicts the barite record. Laboratory and numerical experiments have produced different fractionations including some showing that oxidized S-phases can carry a positive Δ 33 S. Overall, no lab experiment seems to directly capture the Archean relationship observed between δ 34 S, Δ 33 S and Δ 36 S (Δ 36 S/ Δ 33 S ~1 in sediments),which demonstrates that open and critical questions remain about the underlying MAF-generating process.

	5.3 Can atmospheric processes generate positive sulfate?

Table 1

 1 Relative proportions of sulfur species determined from XANES spectra

	samples	CAS	SO4-ester	gypsum	barite sulfonate sulfoxide pyrite	S8	kerogen type 1	kerogen type 2	methio nine
	GKP 1175 d	29	12	28	_	2	_	3	3	13	6	4
	WJG3 40	7	9	_	2	1	10	10	12	6	21	21
	SAC 1966	34	27	_	9	15.0	3	_	_	6	6	_
	WJG1 56.15a	43	27	_	8	8	_	_	_	7	5	_
	WJG9 48a	33	27	_	11	14	_	_	_	8	4	_
	WB98 969'54''a 48	26	_	5	_	_	_	_	10	7	2
	WJG3 51	_	_		_		_	no fit	_	_	_	_
	Appendix: data repository
	Supplementary information (Figs. S1 to S6)

Acknowledgments

We thank Dr. LaFlamme, Dr. Marin-Carbonne and one anonymous reviewer for their helpful reviews and Prof. Ono for handling the editorial process. Altogether, they helped us improve this article. We thank Prof. Beukes for his help in accessing the cores and for feedback on the geological context. Use of the Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. Financial support was received from the NSF (grant EAR-1349858 attributed to WWF and JFA). WWF acknowledges support from the Simons Foundation Collaboration on the Origins of Life.