Christophe Thomazo
email: christophe.thomazo@u-bourgogne.fr

Arnaud Brayard

S Elmeknassi

Emmanuelle Vennin

Nicolas Olivier

Gwénaël Caravaca

Gilles Escarguel

Emmanuel Fara

Kevin G Bylund

James F Jenks

D A Stephen

B Killingsworth

P Sansjofre

P Cartigny

Multiple sulfur isotope signals associated with the late Smithian event and the Smithian/Spathian boundary

de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

layer during the late Smithian extinction event, as opposed to reflecting the development of a lethal anoxic ocean at the global scale.

Introduction

Smithian and Smithian/Spathian boundary events

The recovery of marine and terrestrial ecosystems after the end-Permian mass extinction (EPME, ~252 Ma) is usually described as a slow and delayed process resulting from the effects of sustained or recurrent environmental stresses during the Early Triassic, such as extreme climatic warmings [START_REF] Sun | Lethally hot temperatures during the Early Triassic greenhouse[END_REF][START_REF] Romano | Climatic and biotic upheavals following the end-Permian mass extinction[END_REF], intensified watercolumn stratifications [START_REF] Horacek | Carbon isotope record of the P/T boundary and the Lower Triassic in the Southern Alps: Evidence for rapid changes in storage of organic carbon[END_REF][START_REF] Song | Large vertical δ 13 CDIC gradients in Early Triassic seas of the South China craton: Implications for oceanographic changes related to Siberian Traps volcanism[END_REF] and expansions of oceanic oxygen-minimum zones [START_REF] Algeo | Anomalous Early Triassic sediment fluxes due to elevated weathering rates and their biological consequences[END_REF][START_REF] Algeo | Terrestrial-marine teleconnections in the collapse and rebuilding of Early Triassic marine ecosystems[END_REF][START_REF] Winguth | Simulating Permian-Triassic oceanic anoxia distribution: Implications for species extinction and recovery[END_REF]. Although oxygen deficiency was probably a major biotic stressor in the thermocline and deep-ocean, shallow-marine environments were generally well-oxygenated except for brief anoxic episodes [START_REF] Algeo | The Permian-Triassic boundary at Nhi Tao, Vietnam: Evidence for recurrent influx of sulfidic watermasses to a shallow-marine carbonate platform[END_REF][START_REF] Algeo | Association of 34 S-depleted pyrite layers with negative carbonate δ 13 C excursions at the Permian-Triassic boundary: Evidence for upwelling of sulfidic deep-ocean water masses[END_REF][START_REF] Beatty | Anomalously diverse Early Triassic ichnofossil assemblages in northwest Pangea: A case for a shallow-marine habitable zone[END_REF][START_REF] Zonneveld | Diverse ichnofossil assemblages following the P-T mass extinction, lower Triassic, Alberta and British Columbia, Canada: Evidence for shallow marine refugia on the Northwestern coast of Pangaea[END_REF]. Specifically, extremely harsh environmental conditions were suggested during the late Smithian (~1.4 Ma after the Permian/Triassic boundary, PTB; Galfetti et al., 2007a) as this short time interval (~100 kyr, [START_REF] Brühwiler | High-resolution biochronology and diversity dynamics of the Early Triassic ammonoid recovery: The Smithian faunas of the Northern Indian Margin[END_REF] records a severe extinction of the nekton (e.g., [START_REF] Orchard | Conodont diversity and evolution through the latest Permian and Early Triassic upheavals[END_REF], Brayard et al., 2006[START_REF] Stanley | Evidence from ammonoids and conodonts for multiple Early Triassic mass extinctions[END_REF][START_REF] Stanley | Evidence from ammonoids and conodonts for multiple Early Triassic mass extinctions[END_REF]. Major disturbances in the global carbon cycle in the Smithian and through the Smithian/Spathian boundary (SSB) are documented by a strong negative-positive couplet of carbon isotope excursions respectively before and during the late Smithian. This couplet of excursions is documented worldwide in both carbonate (δ 13 Ccarb) and organic (δ 13 Corg) carbon reservoirs [START_REF] Payne | Large Perturbations of the Carbon Cycle During Recovery from the End-Permian Extinction[END_REF]Galfetti et al., 2007a and b;[START_REF] Tong | Early Triassic carbon isotope excursions from South China: proxies for devastation and restoration of marine ecosystems following the end-Permian mass extinction[END_REF][START_REF] Horacek | Lower Triassic δ 13 C isotope curve from shallowmarine carbonates in Japan, Panthalassa realm: Confirmation of the Tethys δ 13 C curve[END_REF][START_REF] Hermann | Organic matter and palaeoenvironmental signals during the Early Triassic biotic recovery: The Salt Range and Surghar Range records[END_REF][START_REF] Clarkson | A new high-resolution δ 13 C record for the Early Triassic: Insights from the Arabian Platform[END_REF][START_REF] Komatsu | Carbon isotopic excursions and detailed ammonoid and conodont biostratigraphies around Smithian-Spathian boundary in the Bac Thuy Formation, Vietnam[END_REF]Fig. 1). However, the magnitude differs from section to section and depends on the reservoir that has been measured (e.g., [START_REF] Meyer | δ 13 C evidence that high primary productivity delayed recovery from end-Permian mass extinction[END_REF][START_REF] Grasby | Recurrent Early Triassic ocean anoxia[END_REF][START_REF] Song | Large vertical δ 13 CDIC gradients in Early Triassic seas of the South China craton: Implications for oceanographic changes related to Siberian Traps volcanism[END_REF][START_REF] Thomazo | A diagenetic control on the Early Triassic Smithian-Spathian carbon isotopic excursions recorded in the marine settings of the Thaynes Group (Utah, USA)[END_REF]Caravaca et al., 2017a). The negative shift is usually attributed to a massive light carbon input and/or a major reorganization of the exogenous global carbon cycle, such as a decrease in the organic carbon flux buried in the sedimentary record. The negative shift has thus been linked to an episodic large-scale injection into the atmosphere of volcanic CO2 and thermogenic CH4 from the Siberian Traps [START_REF] Payne | Large Perturbations of the Carbon Cycle During Recovery from the End-Permian Extinction[END_REF][START_REF] Payne | Evidence for recurrent Early Triassic massive volcanism from quantitative interpretation of carbon isotope fluctuations[END_REF][START_REF] Meyer | δ 13 C evidence that high primary productivity delayed recovery from end-Permian mass extinction[END_REF][START_REF] Sobolev | Linking mantle plumes, large igneous provinces and environmental catastrophes[END_REF]. Alternatively, local processes such as early diagenetic reactions in pore water producing authigenic carbonates also probably participate to generate this signal [START_REF] Thomazo | A diagenetic control on the Early Triassic Smithian-Spathian carbon isotopic excursions recorded in the marine settings of the Thaynes Group (Utah, USA)[END_REF][START_REF] Zhao | Seeking a geochemical identifier for authigenic carbonate[END_REF]. The negative isotopic excursion is followed by an abrupt positive δ 13 C excursion of comparable magnitude beginning in the late Smithian and crossing the SSB. Such negative-positive swings in the carbon isotope record were suggested to characterize strong anoxic conditions (e.g., [START_REF] Retallack | Methane Release from Igneous Intrusion of Coal during Late Permian Extinction Events[END_REF][START_REF] Song | Geochemical evidence from bio-apatite for multiple oceanic anoxic events during Permian-Triassic transition and the link with end-Permian extinction and recovery[END_REF]2014a). Positive covariation of this oscillation in the δ 13 Ccarb signal with existing δ 34 SCAS records has been interpreted to reflect changes in the burial rate of sedimentary sulfides during increased marine anoxia in an ocean with an extremely small sulfate reservoir [START_REF] Song | Excursion of sulfur isotope compositions in the Lower Triassic of South Guizhou, China[END_REF]2014b). Late Smithian potential anoxic sediments were reported from various localities worldwide (e.g., [START_REF] Galfetti | Evolution of Early Triassic outer platform paleoenvironments in the Nanpanjiang Basin (South China) and their significance for the biotic recovery[END_REF][START_REF] Grasby | Recurrent Early Triassic ocean anoxia[END_REF] and anoxic conditions possibly reached ultra-shallow environments in some places (e.g., [START_REF] Wignall | Ultra-shallow-marine anoxia in an Early Triassic shallow-marine clastic ramp (Spitsbergen) and the suppression of benthic radiation[END_REF].

The late Smithian and the SSB are also marked by a major shift in climate, changing from hot to cool conditions [START_REF] Sun | Lethally hot temperatures during the Early Triassic greenhouse[END_REF][START_REF] Romano | Climatic and biotic upheavals following the end-Permian mass extinction[END_REF]. This event corresponds to major changes in marine and terrestrial organisms [START_REF] Tozer | Marine Triassic faunas of North America: Their significance for assessing plate and terrane movements[END_REF][START_REF] Dagys | Phanerozoic palinspastic reconstructions of Great Basin geotectonics (Nevada-Utah, USA)[END_REF]Galfetti et al., 2007a and b;[START_REF] Hermann | Organic matter and palaeoenvironmental signals during the Early Triassic biotic recovery: The Salt Range and Surghar Range records[END_REF]Schneebli-Hermann et al., 2012), including for instance a severe drop in taxonomic richness and disparity among ammonoids [START_REF] Stanley | Evidence from ammonoids and conodonts for multiple Early Triassic mass extinctions[END_REF][START_REF] Brayard | Guodunites, a low-palaeolatitude and trans-panthalassic Smithian (Early Triassic) ammonoid genus[END_REF][START_REF] Brosse | Ammonoid recovery after the Permian-Triassic mass extinction: a re-exploration of morphological and phylogenetic diversity patterns[END_REF], and a major restructuring of their biogeographical distributions (e.g. [START_REF] Brayard | The Early Triassic ammonoid recovery: Paleoclimatic significance of diversity gradients[END_REF][START_REF] Brayard | The biogeography of Early Triassic ammonoid faunas: Clusters, gradients, and networks[END_REF][START_REF] Jattiot | Revision of the genus Anasibirites Mojsisovics (Ammonoidea): an iconic and cosmopolitan taxon of the late Smithian (Early Triassic) extinction[END_REF]. The late Smithian extinction was at least of equal magnitude to the EPME for ammonoids (e.g., [START_REF] Brühwiler | High-resolution biochronology and diversity dynamics of the Early Triassic ammonoid recovery: The Smithian faunas of the Northern Indian Margin[END_REF][START_REF] Jattiot | Revision of the genus Anasibirites Mojsisovics (Ammonoidea): an iconic and cosmopolitan taxon of the late Smithian (Early Triassic) extinction[END_REF]. However, recent works showed that in some shallow-water settings of the Panthalassa, environmental conditions were favorable to the development of diversified and complex ecosystems during the earliest Spathian, i.e., immediately after the SSB (Brayard et al., 2017).

Potential underlying processes

Carbon isotopic trends during the Smithian-Spathian transition have been interpreted in various ways. A first scenario suggests that emissions of 12 C-enriched carbon dioxide associated with the Siberian Traps [START_REF] Payne | Large Perturbations of the Carbon Cycle During Recovery from the End-Permian Extinction[END_REF][START_REF] Payne | Evidence for recurrent Early Triassic massive volcanism from quantitative interpretation of carbon isotope fluctuations[END_REF], causing an acidification, a warming trend and an oceanic anoxia [START_REF] Galfetti | Evolution of Early Triassic outer platform paleoenvironments in the Nanpanjiang Basin (South China) and their significance for the biotic recovery[END_REF][START_REF] Grasby | Recurrent Early Triassic ocean anoxia[END_REF]Song et al., 2014a;[START_REF] Clarkson | Dynamic anoxic ferruginous conditions during the end-Permian mass extinction and recovery[END_REF]. The subsequent enhanced burial of isotopically light organic carbon in anoxic sediments would have generated the positive δ 13 C trend documented across the SSB (Galfetti et al., 2007a). In a second model, [START_REF] Meyer | δ 13 C evidence that high primary productivity delayed recovery from end-Permian mass extinction[END_REF] argued that the positive δ 13 C shift records an increased productivity in the water column thereby generating a steeper surface-to-deep isotopic gradient. In a third alternative, [START_REF] Horacek | Carbon isotope record of the P/T boundary and the Lower Triassic in the Southern Alps: Evidence for rapid changes in storage of organic carbon[END_REF] interpreted the initial negative shift as reflecting the overturn of a previously well-stratified ocean water column causing the release of light dissolved inorganic carbon, derived from remineralized organic matter (OM) into the upper water column. Finally, local early diagenetic reactions in pore water producing 12 C-enriched authigenic carbonates during the suboxic remineralization of OM due to microbial sulfate reduction have also been suggested [START_REF] Thomazo | A diagenetic control on the Early Triassic Smithian-Spathian carbon isotopic excursions recorded in the marine settings of the Thaynes Group (Utah, USA)[END_REF][START_REF] Zhao | Seeking a geochemical identifier for authigenic carbonate[END_REF]. All these hypotheses differ in their predictions on the relative timing of the carbon isotope excursions and anoxia. The scenario of Galfetti et al.'s (2007a) implies that anoxia developed concomitantly to the positive shift during the late Smithian; the Meyer et al.'s (2011) scenario corresponds to an anoxia peaking later when δ 13 C reaches maximum values; the Horacek et al.'s (2007) model suggests that anoxia peaked just prior to the minimum in δ 13 C. Finally, the diagenetic hypothesis supports the synsedimentary co-occurrence of suboxic conditions and of the minimum δ 13 C values, which do not involve a water-column process. Therefore, the relationships between redox changes, δ 13 C fluctuations, and biotic events around the SSB needs further investigations and better discrimination between synsedimentary versus water-column chemical processes.

The biogeochemical sulfur cycle, oceanic redox conditions and sulfur isotopes

The biogeochemical sulfur cycle is a key process in regulating Earth's surface environment through the activity of several microbial metabolisms including primarily sulfate reduction, disproportionation, and sulfide oxidation. These metabolic activities transform the oxidation state of sulfur and are tightly linked to the global carbon cycle and climate, through the remineralization of organic carbon in marine sediments. The burial of oxidized (sulfate) relative to reduced (sulfide) minerals on the geological time scale, in marine sediments and sedimentary rocks, regulates marine redox conditions [START_REF] Berner | Burial of organic carbon and pyrite sulfur in sediments over Phanerozoic time: a new theory[END_REF][START_REF] Canfield | Biogeochemistry of sulfur isotopes[END_REF]. The various microbial pathways that drive the sulfur cycle can be recognized using their diagnostic stable isotopic fractionations of sulfur species [START_REF] Chambers | Fractionation of sulfur isotopes by continuous cultures of Desulfovibrio desulfuricans[END_REF][START_REF] Fry | Isotope effects associated with the anaerobic oxidation of sulfide by the purple photosynthetic bacterium, Chromatium vinosum[END_REF][START_REF] Canfield | The production of 34 S-depleted sulfide during bacterial disproportionation of elemental sulfur[END_REF][START_REF] Habicht | Sulfur isotope fractionation during bacterial sulfate reduction in organic-rich sediments[END_REF][START_REF] Habicht | Sulfur isotope fractionation during bacterial reduction and disproportionation of thiosulfate and sulfite[END_REF][START_REF] Brunner | A revised isotope fractionation model for dissimilatory sulfate reduction in sulfate reducing bacteria[END_REF]Johnston et al., 2005a;Sim et al., 2011a, b). In modern environments, the isotopic compositions of aqueous sulfide and sulfate have been successfully used to demonstrate specific biological sulfur cycling activities (e.g. Canfield et al., 2010;Fike et al., 2008[START_REF] Fike | The effect of sulfate concentration on (sub)millimeter-scale sulfide δ34S in hypersaline cyanobacterial mats over the diurnal cycle[END_REF][START_REF] Gomes | Sulfur isotope systematics of a euxinic, low-sulfate lake: evaluating the importance of the reservoir effect in modern and ancient oceans[END_REF]. In ancient sediments, the isotopic record of sulfur-bearing phases, predominantly sulfate minerals in the form of barite and CAS as well as sulfides in the form of pyrite, can be also used to trace sulfur metabolisms [START_REF] Canfield | Late Proterozoic rise in atmospheric oxygen concentration inferred from phylogenetic and sulphur-isotope studies[END_REF][START_REF] Shen | Isotopic evidence for microbial sulphate reduction in the early Archaean era[END_REF]Johnston et al., 2005b;[START_REF] Philippot | Early Archaean microorganisms preferred elemental sulfur, not sulfate[END_REF][START_REF] Leavitt | Influence of sulfate reduction rates on the Phanerozoic sulfur isotope record[END_REF] and to reconstruct the past ocean chemistry and oxidation state [START_REF] Claypool | The age curves of sulfur and oxygen isotopes in marine sulfate and their mutual interpretation[END_REF][START_REF] Canfield | Late Proterozoic rise in atmospheric oxygen concentration inferred from phylogenetic and sulphur-isotope studies[END_REF]Johnston et al., 2005b;[START_REF] Fike | Oxidation of the Ediacaran ocean[END_REF][START_REF] Gill | Parallel, high-resolution carbon and sulfur isotope records of the evolving Paleozoic marine sulfur reservoir[END_REF][START_REF] Fike | A paired sulfate-pyrite δ34S approach to understanding the evolution of the Ediacaran-Cambrian sulfur cycle[END_REF][START_REF] Hurtgen | Evaluating the relationship between the carbon and sulfur cycles in the later Cambrian ocean: an example from the Port au Port Group, western Newfoundland, Canada[END_REF][START_REF] Jones | Dynamic sulfur and carbon cycling through the end-Ordovician extinction revealed by paired sulfate-pyrite δ 34 S. Earth Planet[END_REF].

The two main components driving the long-term secular fluctuation of δ 34 S of sulfur species over geological time are variations in the net flux of sulfate reduced to sulfide, subsequently precipitated as pyrite in marine sediments, and the mean isotopic fractionation between marine sulfate and sedimentary pyrite produced during the microbial metabolic activities [START_REF] Fike | Rethinking the Ancient Sulfur Cycle[END_REF]. For example, during times of increased pyrite burial enhanced by protracted marine anoxia, the δ 34 S of marine sulfates would increase generating a positive isotopic excursion imprint in both sulfate and sulfide reservoirs. Modulation of sedimentary sulfides burial can also influence the size of the oceanic dissolved sulfate reservoir, and hence, the kinetic of sulfur isotope variations [START_REF] Bottrell | Reconstruction of changes in global sulfur cycling from marine sulfate isotopes[END_REF]. When the oceanic sulfate reservoir is small, rapid δ 34 S variations can thus be driven by relatively small flux imbalances.

Meanwhile, depositional environment and sediment remobilization can have considerable impacts on the isotopic composition of both pore water and sedimentary sulfate and sulfide phases [START_REF] Aller | Early diagenetic cycling, incineration, and burial of sedimentary organic carbon in the central Gulf of Papua (Papua New Guinea)[END_REF][START_REF] Aller | Unsteady diagenetic processes and sulfur biogeochemistry in tropical deltaic muds: implications for oceanic isotope cycles and the sedimentary record[END_REF]. Bioturbation and the local sedimentation rate can also impact the sulfur isotope records by decoupling the evolution of sedimentary pyrite δ 34 S to the overlying water column [START_REF] Pasquier | Pyrite sulfur isotopes reveal glacial-interglacial environmental changes[END_REF]. Moreover, both sulfate and pyrite sulfur isotope signals can be muted during diagenesis. Record of the δ 34 SCAS can notably be altered by circulating fluids (e.g., meteoric fluids) during diagenetic secondary carbonate precipitation and can obscure the signal of the primary oceanic sulfate isotopic composition.

Additionally, post-depositional processes can impact the δ 34 Spy records. For instance, δ 34 Spy signatures can be overprinted during late-stage diagenesis when sulfide-bearing fluids migrate through strata that contain reactive iron [START_REF] Fike | Rethinking the Ancient Sulfur Cycle[END_REF]. Due to these various possible secondary imprints on the sedimentary sulfur isotope signals, a full characterization of the depositional environment in which the sample formed is mandatory, as well as an evaluation of its connection to the open ocean, and of its diagenetic history [START_REF] Fike | Rethinking the Ancient Sulfur Cycle[END_REF].

In addition to the δ 34 S record of sulfur species, the measurement of multiple sulfur isotopes (MSI) recently becomes increasingly important to further constrain the Phanerozoic evolution of the biogeochemical sulfur cycle [START_REF] Wu | Evaluating the S-isotope fractionation associated with Phanerozoic pyrite burial[END_REF], as well as in modern environments (e.g., [START_REF] Tostevin | Multiple sulfur isotope constraints on the modern sulfur cycle[END_REF]. The use of pyrite δ 33 S in addition to δ 34 S can provide additional ways to evaluate the involvement of different sulfur metabolisms, as well as variations in sulfur fluxes through geologic time (Johnston et al., 2005a(Johnston et al., , 2005b[START_REF] Johnston | Sulfur isotope insights into microbial sulfate reduction: When microbes meet models[END_REF](Johnston et al., , 2008a, b;, b;[START_REF] Ono | Mass-dependent fractionation of quadruple stable sulfur isotope system as a new tracer of sulfur biogeochemical cycles[END_REF][START_REF] Li | Stable sulfur isotopes in the water column of the Cariaco Basin[END_REF][START_REF] Wu | Evaluating the S-isotope fractionation associated with Phanerozoic pyrite burial[END_REF][START_REF] Zerkle | Sulfur cycling in a stratified euxinic lake with moderately high sulfate: Constraints from quadruple S isotopes[END_REF][START_REF] Shen | Multiple Sisotopic evidence for episodic shoaling of anoxic water during Late Permian mass extinction[END_REF][START_REF] Leavitt | Influence of sulfate reduction rates on the Phanerozoic sulfur isotope record[END_REF][START_REF] Sansjofre | Multiple sulfur isotope evidence for massive oceanic sulfate depletion in the aftermath of Snowball Earth[END_REF]. Furthermore, MSI is a robust tool to investigate Phanerozoic paleoredox conditions even when the pyrite and contemporaneous seawater sulfate δ 34 S measurements are not paired in the same samples [START_REF] Shen | Multiple Sisotopic evidence for episodic shoaling of anoxic water during Late Permian mass extinction[END_REF][START_REF] Zhang | Widespread shoaling of sulfidic waters linked to the end-Guadalupian (Permian) mass extinction[END_REF][START_REF] Zhang | Redox chemistry changes in the Panthalassic Ocean linked to the end-Permian mass extinction and delayed Early Triassic biotic recovery[END_REF][START_REF] Saitoh | Multiple sulfur isotope records at the end-Guadalupian (Permian) at Chaotian, China: Implications for a role of bioturbation in the Phanerozoic sulfur cycle[END_REF]. For paleoenvironmental reconstructions, measurements of minor sulfur isotopes ( 33 S and 36 S) can provide additional information on local and global processes and can be helpful for differentiating between these two cases [START_REF] Johnston | Evolution of the oceanic sulfur cycle at the end of the Paleoproterozoic[END_REF][START_REF] Saitoh | Multiple sulfur isotope records at the end-Guadalupian (Permian) at Chaotian, China: Implications for a role of bioturbation in the Phanerozoic sulfur cycle[END_REF].

Therefore, the MSI composition of seawater sulfates and precipitated sulfides (i.e., pyrite) can be an important proxy to discuss the Smithian-Spathian transition processes.

Previous studies focusing on this time interval and aiming to reconstruct the biogeochemical sulfur cycle were based on analyses of pyrite framboids and trace metal elements from South China [START_REF] Tian | Reconstruction of Early Triassic ocean redox conditions based on framboidal pyrite from the Nanpanjiang Basin, South China[END_REF][START_REF] Sun | High amplitude redox changes in the late Early Triassic of South China and the Smithian-Spathian extinction[END_REF], iron mineral speciation from the Arabian margin [START_REF] Clarkson | Dynamic anoxic ferruginous conditions during the end-Permian mass extinction and recovery[END_REF], carbonate associated sulfate (CAS) δ 34 S signal from South China [START_REF] Zhang | Widespread shoaling of sulfidic waters linked to the end-Guadalupian (Permian) mass extinction[END_REF] and the western USA [START_REF] Marenco | Environmental and diagenetic variations in carbonate associated sulfate: An investigation of CAS in the Lower Triassic of the western USA[END_REF], sulfide δ 34 S signal from Japan [START_REF] Takahashi | Sulfur isotope profiles in the pelagic Panthalassic deep sea during the Permian-Triassic transition[END_REF], barite and evaporite δ 34 S signal from Italy [START_REF] Cortecci | Sulfur and oxygen isotopes in Italian marine sulfates of Permian and Triassic ages[END_REF][START_REF] Horacek | Lower Triassic sulphur isotope curve of marine sulphates from the Dolomites, N-Italy[END_REF], and paired sulfur isotopes (CAS and pyrite) signals from South Central China (Song et al., 2014b). Although the CAS δ 34 S values in recent sediments are in agreement with the sulfur isotopic composition of modern seawater sulfates [START_REF] Lyons | Sites of anomalous organic remineralization in the carbonate sediments of South Florida, USA: The sulfur cycle and carbonate-associated sulfate[END_REF], and while the record of ancient carbonates is more complete than the record of marine evaporites, the fidelity of CAS signals in rocks that have undergone variable degrees of secondary processes (e.g., early or burial diagenesis, hydrothermal alteration) needs to be carefully testified for each measured section and sample [START_REF] Present | Large Carbonate Associated Sulfate isotopic variability between brachiopods, micrite, and other sedimentary components in Late Ordovician strata[END_REF]. For instance, [START_REF] Marenco | Environmental and diagenetic variations in carbonate associated sulfate: An investigation of CAS in the Lower Triassic of the western USA[END_REF] performed δ 34 SCAS measurements on samples from the Early Triassic Moenkopi Formation of the Sonoma Foreland (western USA) basin and showed that an alteration of the isotopic signal during late stage dolomitization could not be fully excluded.

In this study, we test the existence of anoxia during the late Smithian and its relationships with the Smithian-Spathian δ 13 C curve by measuring the MSI of sedimentary sulfides and 34 S/ 32 S sulfur isotopes of CAS in the shallow water deposits of the Mineral Mountains section, Utah, USA. This section has been previously studied for its sedimentary and fossil contents, as well as for its paired carbon isotope signal [START_REF] Brayard | Transient metazoan reefs in the aftermath of the end-Permian mass extinction[END_REF][START_REF] Brayard | Early Triassic Gulliver gastropods: Spatio-temporal distribution and significance for biotic recovery after the end-Permian mass extinction[END_REF][START_REF] Hofmann | Recovery of benthic marine communities from the end-Permian mass extinction at the low latitudes of eastern Panthalassa[END_REF][START_REF] Vennin | Microbial deposits in the aftermath of the end-Permian mass extinction: A diverging case from the Mineral Mountains (Utah, USA)[END_REF][START_REF] Thomazo | A diagenetic control on the Early Triassic Smithian-Spathian carbon isotopic excursions recorded in the marine settings of the Thaynes Group (Utah, USA)[END_REF]. We discuss results of our sulfur isotope analyses in the light of detailed sedimentological constraints on depositional environments, within global C cycle perturbations typical of the late Smithian and SSB, to provide new insights into the nature of oceanic and sedimentary environmental changes at that time.

Geological setting

The Sonoma Foreland Basin

During the Permian-Triassic transition, the Sonoma orogeny led to the formation of the Sonoma Foreland Basin (SFB) (Fig. 2; [START_REF] Burchfiel | Nature and controls of Cordilleran orogenesis, western United States: Extensions of an earlier synthesis[END_REF][START_REF] Ingersoll | Subduction-related sedimentary basins of the USA Cordillera Sedimentary basins of the world[END_REF]Dickinson, 2013;Caravaca et al., 2017b). This sedimentary basin extends from the modern states of Idaho and Wyoming to Utah and eastern Nevada. The SFB was located in the northern intertropical zone on the western Pangea margin during the Early Triassic (Fig. 2).

The SFB shows detailed and well-preserved Lower Triassic fossil and sedimentary records with mainly transitional continental/marine terrigenous conglomerates and sandstones of the Moenkopi Group to shallow marine carbonates of the Thaynes Group (e.g., [START_REF] Kummel | Triassic stratigraphy of southeastern Idaho and adjacent areas[END_REF][START_REF] Kummel | Chapter 16: Paleoecology of Lower Triassic Formations of Southeastern Idaho and Adjacent Areas[END_REF][START_REF] Paull | Interpretation of Early Triassic nonmarine-marine relations[END_REF][START_REF] Lucas | The type section and age of the Timpoweap Member and stratigraphic nomenclature of the Triassic Moenkopi Group in Southwestern Utah[END_REF]. A robust, high-resolution, Smithian biostratigraphic framework based on ammonoids is available for most parts of the basin [START_REF] Brayard | Guodunites, a low-palaeolatitude and trans-panthalassic Smithian (Early Triassic) ammonoid genus[END_REF][START_REF] Brayard | Smithian ammonoid faunas from Utah: implications for Early Triassic biostratigraphy, correlation and basinal paleogeography[END_REF][START_REF] Jattiot | Revision of the genus Anasibirites Mojsisovics (Ammonoidea): an iconic and cosmopolitan taxon of the late Smithian (Early Triassic) extinction[END_REF][START_REF] Jattiot | Smithian ammonoid faunas from northeastern Nevada: implications for Early Triassic biostratigraphy and correlation within the western USA basin[END_REF][START_REF] Jenks | Smithian (Early Triassic) ammonoids from Crittenden Springs, Elko County, Nevada: Taxonomy, biostratigraphy and biogeography[END_REF].

The Mineral Mountains section

The alternating carbonates and marls of the Lower Triassic Thaynes Group (sensu [START_REF] Lucas | The type section and age of the Timpoweap Member and stratigraphic nomenclature of the Triassic Moenkopi Group in Southwestern Utah[END_REF] reflect sedimentary deposition in epicontinental marine environments and rest unconformably on middle to upper Permian rocks with a major sedimentary hiatus corresponding to the Permian-Triassic transition (e.g., [START_REF] Mckee | Stratigraphy and history of the Moenkopi Formation of Triassic age[END_REF][START_REF] Collinson | Permian-Triassic boundary in eastern Nevada and west-central Utah[END_REF].

In western and central Utah, the late Permian, Griesbachian and Dienerian are usually not observed. The historical middle and late Smithian time markers of the Thaynes Group within the SFB are respectively the Meekoceras and Anasibirites ammonoid zones, but these zones can be further subdivided (see discussion in [START_REF] Brayard | Guodunites, a low-palaeolatitude and trans-panthalassic Smithian (Early Triassic) ammonoid genus[END_REF][START_REF] Brayard | Smithian ammonoid faunas from Utah: implications for Early Triassic biostratigraphy, correlation and basinal paleogeography[END_REF][START_REF] Jattiot | Revision of the genus Anasibirites Mojsisovics (Ammonoidea): an iconic and cosmopolitan taxon of the late Smithian (Early Triassic) extinction[END_REF][START_REF] Jenks | Smithian (Early Triassic) ammonoids from Crittenden Springs, Elko County, Nevada: Taxonomy, biostratigraphy and biogeography[END_REF].

The present study has been carried out on the Smithian to Spathian sedimentary succession in the Mineral Mountains, thoroughly described for its sedimentological characteristics by [START_REF] Vennin | Microbial deposits in the aftermath of the end-Permian mass extinction: A diverging case from the Mineral Mountains (Utah, USA)[END_REF]Figs. 2, 3). The basal unit A mostly consists of microbially-dominated carbonates with sponge-microbe bioconstructions deposited on a mudflat inner ramp, intertidal to supratidal, environments evolving upward into bioclastic sediments deposited in tidal-dominated shoreface environments. Mudstone-rich sediments of the unit B are finely laminated and reflect homogenous upper offshore depositional conditions of outer to mid-ramp environments. They were episodically influenced by storm-induced events (Fig. 3). The unit including the SSB ("unit SSB") is composed of marls representing outer ramp, lower offshore, environments. This unit corresponds to the deepest deposits, below the storm wave base. The overlying unit C evolves from mudstones deposited in outer ramp (with local storm-induced deposits) to subtidal microbial carbonates deposited in outer to mid ramp environments. The evolution prior to the SSB unit thus shows a progressive deepening, whereas the lower Spathian corresponds to shallowing-upward conditions.

The local ammonoid biostratigraphy has been described in [START_REF] Brayard | Transient metazoan reefs in the aftermath of the end-Permian mass extinction[END_REF][START_REF] Brayard | Smithian ammonoid faunas from Utah: implications for Early Triassic biostratigraphy, correlation and basinal paleogeography[END_REF].

The unit A is early Smithian in age ("Vercherites undulatus beds"; V.u. in Fig. 3). The unit B is latest early to middle Smithian in age (Inyoites beaverensis and Owenites beds, respectively; I.b. and O. in Fig. 3; Unitary Association Zones UAZ3 and UAZ4 in [START_REF] Jattiot | Smithian ammonoid faunas from northeastern Nevada: implications for Early Triassic biostratigraphy and correlation within the western USA basin[END_REF]. The SSB unit mainly corresponds to the late Smithian with the occurrence of typical prionitid and xenoceltitid ammonoid assemblages (A.m. and Xe. in Fig. 3; UAZ5 and UAZ6 in [START_REF] Jattiot | Smithian ammonoid faunas from northeastern Nevada: implications for Early Triassic biostratigraphy and correlation within the western USA basin[END_REF]. Although Spathian beds are not well identified above these late Smithian assemblages, the first Spathian dominant fauna likely corresponds to a regional bivalve bloom [START_REF] Brayard | Smithian ammonoid faunas from Utah: implications for Early Triassic biostratigraphy, correlation and basinal paleogeography[END_REF][START_REF] Hofmann | Recovery of benthic marine communities from the end-Permian mass extinction at the low latitudes of eastern Panthalassa[END_REF].

The Early Triassic is marked by a global long-term rise in sea level with several second-and third-order transgressive-regressive (T-R) sequences [START_REF] Haq | Chronology of Fluctuating Sea Levels Since the Triassic[END_REF]. Within the SFB, a Spathian T-R cycle is recognized together with two older T-R cycles that developed during the Griesbachian-Dienerian and the Smithian (e.g., [START_REF] Paull | Interpretation of Early Triassic nonmarine-marine relations[END_REF][START_REF] Lucas | The type section and age of the Timpoweap Member and stratigraphic nomenclature of the Triassic Moenkopi Group in Southwestern Utah[END_REF]. The Smithian transgression proceeded southward in a complex pathway resulting from the multifaceted subsidence of the basin and paleotopographic highs within and on each side of the basin (e.g. [START_REF] Lucas | The type section and age of the Timpoweap Member and stratigraphic nomenclature of the Triassic Moenkopi Group in Southwestern Utah[END_REF]Caravaca et al., 2017b). The maximum extent of this transgression within the basin was reached during the late Smithian [START_REF] Paull | Interpretation of Early Triassic nonmarine-marine relations[END_REF][START_REF] Lucas | The type section and age of the Timpoweap Member and stratigraphic nomenclature of the Triassic Moenkopi Group in Southwestern Utah[END_REF][START_REF] Brayard | Smithian ammonoid faunas from Utah: implications for Early Triassic biostratigraphy, correlation and basinal paleogeography[END_REF]. It corresponds to the deepest environmental conditions recorded at Mineral Mountains, i.e., the unit SSB [START_REF] Vennin | Microbial deposits in the aftermath of the end-Permian mass extinction: A diverging case from the Mineral Mountains (Utah, USA)[END_REF].

Methods

A total of 34 bulk rock samples of the Mineral Mountains section were investigated for their major and trace elements, carbonate carbon isotopes, sulfide major ( 32 S, 33 S) and minor ( 33 S, 36 S) sulfur isotopes and CAS major sulfur isotopes (Table 1). All measurements were performed on bulk rock samples which were at start powdered to < 60 μm using a ring and puck mill at the Biogéosciences Laboratory, Dijon, France.

Carbonate carbon isotopes

Carbonate carbon isotope analyses (δ 13 Ccarb) were carried out at the Biogéosciences Laboratory, Dijon, France. The samples (90 to 300 µg) were loaded into septum screwed glass tubes, flushed via the autosampler with He to remove atmospheric gases. Each sample was reacted with 500 μl of >100% phosphoric acid at 90°C for 17 min using an online carbonate preparation line coupled to an IsoPrime stable isotope ratio mass spectrometer (Isoprime, Manchester, UK). Inorganic carbonate content was quantified manometrically from the CO2 yield; all isotopic values are reported in the standard δ-notation in permil (‰) relative to VPDB by assigning a δ 13 C value of +1.95‰ to the NBS19 international standard.

The long-term reproducibility of the NBS19 replicate analyses (three months) is better than ± 0.09‰ (1σ) for carbon isotopes. H3PO4 blank tests were performed and evolved CO2 was below the detection limit of our online-IRMS system.

Sulfide isotopes

Sulfide sulfur was retrieved using a conventional wet chemical extraction at the Biogéosciences Laboratory, Dijon, France. Acid volatile sulfide (AVS), representing monosulfides, and chromium reducible sulfur (CRS) consisting primarily of pyrite were extracted sequentially. First, AVS was liberated using cold concentrated HCl for 2 hours. If any, resulting hydrogen sulfide was precipitated as Ag2S with a 0.3 M AgNO3 solution.

Subsequently, CRS was released using a hot and acidic 1.0 M CrCl2 solution [START_REF] Canfield | The use of chromium reduction in the analysis of reduced inorganic sulfur in sediments and shales[END_REF]. The resulting H2S was precipitated as Ag2S. After centrifugation, the silver sulfide precipitate was washed several times with deionized distilled water and dried at 50°C for 48 hours in an oven and weighted. Mass balance was used to calculate the amount of AVS and CRS. Concentrations in ppm are reported individually in Table 1 (note that monosulfides were below the detection limit in all samples). The silver sulfides were then fluorinated to produce SF6 and analyzed for their multiple sulfur isotope compositions at the Stable Isotope Laboratory of the Institut de Physique du Globe de Paris, France. The isotope compositions were determined by dual-inlet gas-source mass spectrometry monitoring ion beams at m/z of 127, 128, 129, and 131 using a ThermoScientific MAT 253 gas source mass spectrometer [START_REF] Labidi | Determination of multiple sulfur isotopes in glasses: A reappraisal of the MORB δ 34 S[END_REF]. Sulfur isotope ratios are reported in conventional delta notation with respect to VCDT as Eq. ( 1): (1) where i is either 3, 4 or 6; and as Eqs. ( 2) and (3) for capital delta notation (following Johnston et al., 2008a):

(2)

(3)

The δ 34 S values are presented with an analytical reproducibility of ≤0.1‰. We used values for IAEA-S2 on the Vienna Cañon Diablo Troilite (VCDT) normalization of 5.224‰, 0.030‰ and -0.203‰ for δ 34 S, Δ 33 S, and Δ 36 S, respectively. Based on duplicate and triplicate analyses, uncertainties on Δ 33 S and Δ 36 S values by the SF6 technique are estimated at 0.01‰ and 0.2‰ in 2σ, respectively.

Ten samples have been successfully cross calibrated (Table 1, Fig. 4) for their δ 34 Spy with measurements performed at the Biogéosciences Laboratory, Dijon, France, on SO2 molecules via combustion of ~500 µg of silver sulfide homogeneously mixed with an equal amount of tungsten trioxide using a Vario PYRO cube (Elementar GmbH) connected online via an open split device to an IsoPrime IRMS system (Isoprime, Manchester, UK).

International standards IAEA-S-1, IAEA-S-2 and IAEA-S-3 were used for calibration assuming δ 34 S values of -0.3‰, +22.7‰ and -32.3‰ (VCDT), respectively. Analytical reproducibility was better than ± 0.3‰ (1σ) based on replicates for standard materials and samples.

CAS sulfur isotopes

CAS sulfur was retrieved using a wet chemical extraction at the Laboratory Géosciences Océan, Brest, France. Fifty grams of carbonate samples (with carbonate contents typically >70 wt. % of the total rock) were powdered, soluble sulfates being leached by a 1.7 M NaCl solution for 4 hours, followed by four rinses in deionized water. This step was repeated five times and the powder was then dissolved in 4 N HCl (12 h). The acidified samples were then filtered, on a 0.45-μm nitrocellulose paper and an excess of 250 g.l -1 of BaCl2 solution was added to the filtrate to precipitate BaSO4. After centrifugation, the barium sulfate precipitate was washed several times with deionized distilled water and dried at 60°C for 24 hours in an oven. δ 34 S measurements were performed at the Biogéosciences Laboratory, Dijon, France, on SO2 molecules via combustion of ~500 µg of barium sulfate homogeneously mixed with 1/3 of vanadium pentoxyde using a Vario PYRO cube (Elementar GmbH) connected online via an open split device to an IsoPrime IRMS system (Isoprime, Manchester, UK). International standard NBS 127 was used for calibration assuming a δ 34 S value of +20.3‰ on the VCDT scale. Isotope results are reported in the standard delta notation against the Vienna Cañon Diablo Troilite standard (VCDT). Analytical reproducibility was better than ± 0.3‰ (1σ) based on replicates for standard materials.

Major and trace elements

Major and trace elements analyses were performed on selected samples by ICP-MS at the Activation Laboratory (Actlabs) in Ancaster, Canada. The method used is Lithium Metaborate/Tetraborate Fusion ICP and ICP-MS. Reproducibility was estimated by seven replicate analyses of laboratory standards, and is better than 2% (1σ) for major and trace elements.

Petrographic observations

Photonic observations of Mineral Mountains samples were performed using a Leica MZ205c at the Biogéosciences Laboratory, Dijon. High-resolution images were obtained with a JEOL JSM 6400F Field Emission SEM equipped with an Oxford INCA Energy 300 X-ray Energy Dispersive Spectrometer (EDS) system for all chemical analyses at the ARCEN platform (Laboratory Institut Carnot de Bourgogne in Dijon, Université de Bourgogne, France). The thin sections were prepared for SEM analyses and were subsequently coated with ~10 nm of graphite using a High Resolution Ion Beam Coater GATAN 681. The high-resolution images were taken in back-scatter electron imaging mode to enhance the compositional contrast. These facilities were used to identify rock textures and to examine pyrite morphologies in samples from the studied section.

Results and discussion

Carbonate carbon isotopes

Except for samples MI169, MI197, MI202 and MI209, the δ 13 Ccarb values presented in this work have already been reported in [START_REF] Thomazo | A diagenetic control on the Early Triassic Smithian-Spathian carbon isotopic excursions recorded in the marine settings of the Thaynes Group (Utah, USA)[END_REF]. All data are consistent with the expected δ 13 Ccarb decrease (by ∼3‰) during the middle Smithian followed by an abrupt increase (of ∼4‰) through the late Smithian and the SSB (Fig. 3). Samples from the upper part of unit A and from unit B (from 50.8 to 104.2 m) display a significant correlation of the δ 13 Ccarb signal with the Mn content and Mn/Sr ratio (see figure 3 in [START_REF] Thomazo | A diagenetic control on the Early Triassic Smithian-Spathian carbon isotopic excursions recorded in the marine settings of the Thaynes Group (Utah, USA)[END_REF]. In this work, we also observe a covariation between the δ 13 Ccarb and the Mg/(Mg+Ca) ratios (Fig. 5). There is however no covariation between the δ 13 Ccarb and δ 13 Corg signals at MI throughout the units B, SSB and C (see figure 3 in [START_REF] Thomazo | A diagenetic control on the Early Triassic Smithian-Spathian carbon isotopic excursions recorded in the marine settings of the Thaynes Group (Utah, USA)[END_REF]. Low δ 13 Ccarb values (∼-3‰) associated with high Mn/Sr and high Mg/(Mg+Ca) ratios are interpreted to reflect early diagenetic authigenic precipitation of dolomicrites within reducing, Mn-bearing, 12 C enriched, fluids produced during the bacterially mediated degradation of OM close to the sediment water interface [START_REF] Gilleaudeau | Carbon isotope records in a Mesoproterozoic epicratonic sea: carbon cycling in a low-oxygen world[END_REF][START_REF] Schrag | Authigenic carbonate and the history of the global carbon cycle[END_REF][START_REF] Thomazo | A diagenetic control on the Early Triassic Smithian-Spathian carbon isotopic excursions recorded in the marine settings of the Thaynes Group (Utah, USA)[END_REF].

Major and trace elements

The Mg/(Mg+Ca) ratio varies from 0.01 to 0.13 with a mean value of 0.04 ± 0.03 (1σ) (Table 1). The units A and B exhibit high ratios of 0.05 ± 0.03 and 0.05 ± 0.02 (1σ), respectively. The unit C displays the lowest Mg/(Mg+Ca) ratio with an average of 0.02 ± 0.01 (1σ). Mg/(Mg+Ca) ratios decrease within the unit SSB (Fig. 3) and most likely provide a direct record of the relative amount of dolomicrite versus carbonates in the samples. Indeed, the carbonate concentration is strongly correlated to the sum of Ca plus Mg contents (Fig. 6, r = +0.90, p < 0.01, n = 32). The dolomitization most likely occurred early in the studied section leading to the formation of nano to micro-meter-sized granular structures, poorly preserved spherical dolomite and euhedral rhombs (Fig. 7A, 7B and 7C). Dolomite is often observed in association with sheet-like mat and microbial structures. The formation of these morphologies and structures has been interpreted as reflecting, microbially mediated, early precipitation of dolomites [START_REF] Lin | Characterization of the Microbial Dolomite of the Upper Sinian Dengying Formation in the Hanyuan Area of Sichuan Province, China[END_REF] and their evolution into crystalline dolomite may be explained by subsequent burial diagenesis [START_REF] Rodriguez-Blanco | A route for the direct crystallization of dolomite[END_REF].

The Mn/Sr ratio varies from 0.2 to 12.4 with a mean value of 2.2 ± 3.2 (1σ) (Table 1).

The units A and C show the smallest ratios with average values of 0.9 ± 0.6 and 1.1 ± 0.8 (1σ), respectively, whereas units B and SSB display highest ratios with respective average values of 6.8 ± 4.4 and 6.0 ± 8.0. Samples MI97 to MI127 (from 56 to 107.7 m), encompassing the units B, SSB and the lowermost samples of the unit C (Fig. 3) show Mn/Sr values > 2. Due to the high responsiveness of the Mn/Sr ratio to record reducing fluids during diagenesis (Kaufman and Knoll, 1995), samples with Mn/Sr > 2 are considered here to have undergone significant water-rock interactions during early diagenetic secondary processes [START_REF] Pakhomova | Fluxes of iron and manganese across the sediment-water interface under various redox conditions[END_REF][START_REF] Thomazo | A diagenetic control on the Early Triassic Smithian-Spathian carbon isotopic excursions recorded in the marine settings of the Thaynes Group (Utah, USA)[END_REF].

Sulfur sulfide concentrations vary throughout the section, from 15 to 1329 ppm with a mean value of 216 ± 301 ppm (1σ) (Table 1). These concentrations vary over a short time scale and a well-defined trend across sedimentary deposits is not recognized. The Unit A shows the strongest variations encompassing the total range of values, with a mean value of 163 ± 339 ppm (1σ). The microbial deposits from unit A are remarkably poor in sulfides (only 48 ± 25 ppm; 1σ) compared to calcarenite and siltstones from the same unit or samples from overlying units. Unit B shows the highest mean value, 474 ± 290 ppm (1σ), while the unit SSB exhibits the lowest mean value, 131 ± 124 ppm (1σ). Concentrations in the unit C are similar to those of the unit A, with a mean value of 206 ± 257 ppm (1σ).

Only nine samples yielded enough materials for CAS quantification of sulfate contents.

The concentrations vary from 23 to 72 ppm with a mean value of 35 ± 17 ppm (1σ). This dataset is restricted and we did not attempt to outline any special trend along the section.

The TOC concentrations show variations from 0.02 to 0.37 wt. % with a mean value of 0.114 ± 0.099 wt. % (1σ) (Fig. 3, Table 1). Units B, SSB and C exhibit similar TOC concentrations with average values of 0.09 ± 0.04, 0.06 and 0.06 ± 0.02 wt. % (1σ), respectively. Strongest variations in TOC content are observed in unit A and encompass the highest mean value: 0.169 ± 0.115 wt. % (1σ). Within this unit, the microbial deposits show a lower TOC concentration (0.04 ± 0.026 wt. %; 1σ) than the overlying calcarenite and siltstones (0.218 ± 0.094 wt. %; 1σ). A clear maximum in TOC content is documented atop the unit A, between MI72a and MI83 (Fig. 3). This maximum is associated with a negative carbon isotope shift in δ 13 Ccarb (Fig. 3) and δ 13 Corg values (down to -30.46‰; [START_REF] Thomazo | A diagenetic control on the Early Triassic Smithian-Spathian carbon isotopic excursions recorded in the marine settings of the Thaynes Group (Utah, USA)[END_REF]. Given the shallow depositional settings and the absence of evidence for anoxia in the water column [START_REF] Vennin | Microbial deposits in the aftermath of the end-Permian mass extinction: A diverging case from the Mineral Mountains (Utah, USA)[END_REF][START_REF] Thomazo | A diagenetic control on the Early Triassic Smithian-Spathian carbon isotopic excursions recorded in the marine settings of the Thaynes Group (Utah, USA)[END_REF], these features may be interpreted as corresponding to a major perturbation of the global carbon cycle. It can result from a CO2 released from volcanogenic [START_REF] Sobolev | Linking mantle plumes, large igneous provinces and environmental catastrophes[END_REF] or thermogenic sources [START_REF] Payne | Evidence for recurrent Early Triassic massive volcanism from quantitative interpretation of carbon isotope fluctuations[END_REF]. However, changes in productivity and preservation of organic matter (i.e. the biological pump) due to increasing temperatures (Fig. 3; [START_REF] Sun | Lethally hot temperatures during the Early Triassic greenhouse[END_REF][START_REF] Romano | Climatic and biotic upheavals following the end-Permian mass extinction[END_REF] or changes in the relative contribution of the TOC between terrestrial and marine OM (Caravaca et al., 2017a) may also explain this signal.

The S/C ratio fluctuates from 0.02 to 1.56 with a mean value of 0.38 ± 0.45 (1σ) (Fig. 3, Table 1). Units B, SSB and C show the highest ratios with values of 0.69 ± 0.37, 0.36 and 0.69 ± 0.36 (1σ), respectively. Excluding MI83 (S/C = 0.74; similar to values observed in units B, SSB and C), unit A displays the lowest ratios with a mean of 0.07 ± 0.36 (1σ). S/C ratio fluctuations in the units B, SSB and C are controlled by variations in the S content, whereas unit A samples (except MI83) do not exhibit any covariation with either the TOC or S content. The behavior of the sulfur and carbon contents through the section suggest that the activity of microbial sulfate reduction (MSR) activity and ensuing sulfur sulfide precipitations were probably not limited by sedimentary OM availability.

Sulfide MSI results

The δ 34 Spy signal of sedimentary pyrites is highly variable with values ranging from -21.2‰ to +46.7‰ (Fig. 3, Table 1). Positive values are recorded in units A, SSB and C. The unit A shows positive, little variable, δ 34 Spy values with an average isotopic composition of 12.2 ± 5.0‰ (1σ). The unit B documents strictly negative δ 34 Spy values with an average isotopic composition of -14.2 ± 6.8‰ (1σ). SSB samples yield positive δ 34 Spy values of +22.9‰ and +4.2‰. The unit C exhibits mostly positive δ 34 Spy values but cover an extended range of values (-3.0‰ to 46.7‰) with short time scale variations (mean δ 34 Spy is 4.5 ± 16.4‰; 1σ; Fig. 3).

Overall, the ∆ 33 Spy signal varies from -0.01‰ to +0.12‰ with an average value of 0.05 ± 0.04‰ (1σ) (Fig. 3, Table 1). At its base, unit A shows values close to zero with an average isotopic composition of 0.02 ± 0.03‰ (Table 1, Fig. 3). More positive values are recorded in units B, SSB and C with average values of 0.08 ± 0.03‰, 0.06 ± 0.00‰ and 0.06 ± 0.04‰ (1σ), respectively. Small-scale variations of the ∆ 33 Spy signal (from 0.00‰ to 0.12 ‰) are recorded in unit C between 139.2 m and 148.3 m (Fig. 3). In this section, there is no evidence of secondary hydrothermal or metamorphic alteration of the MSI record based on petrographic observations of the samples. Instead, the lack of covariation between the δ 34 Spy and sulfides content in all units (Table 1) and the observation of pyrite (FeS2) in the form of framboids suggest that microbial sulfur cycling had a dominant role on the δ 34 Spy signal, rather than the influence of secondary processes such as thermochemical sulfate reduction [START_REF] Machel | Products and distinguishing criteria of bacterial and thermochemical sulfate reduction[END_REF].

Interpretations of the sulfide MSI signal

Most previous studies focusing on the Smithian-Spathian transition considered the oceanic sulfur cycle under a steady state hypothesis where sulfides are precipitated after MSR under open-system conditions (here defined as oceanic sulfate supply > microbial sulfate reduction). However, at Mineral Mountains, this hypothesis cannot account for the highmagnitude (from -21.2‰ to +46.7‰) and rapid (probably ≪50 kyr; see [START_REF] Brühwiler | High-resolution biochronology and diversity dynamics of the Early Triassic ammonoid recovery: The Smithian faunas of the Northern Indian Margin[END_REF] swings in δ 34 Spy values between the units A and B and between units B and SSB. The most positive ∆ 33 Spy values (up to +0.12‰) are also significantly above expected ∆ 33 Spy under a steady state approximation [START_REF] Wu | Evaluating the S-isotope fractionation associated with Phanerozoic pyrite burial[END_REF]. Instead, we suggest here that the observed high-magnitude and rapid swings in δ 34 Spy values can reflect deviations from the canonical Phanerozoic δ 34 Spy value (-20‰) produced under steady state open-system conditions (as observed in unit B) to either (i) a Rayleigh-type distillation of the residual pore water sulfate pool, or (ii) a partial or complete re-oxidation of the reduced sulfur pools produced during MSR (units A, SSB and C) (see Fike et al., 2015 and references therein). Taking into account the positive δ 34 Spy values in units A, SSB and C, hypotheses (i) and (ii) have fundamentally different paleoenvironments implications. If a Rayleigh distillation drove increasing δ 34 Spy values, this implies that the residual sulfate pool might have evolved during the course of sulfate reduction in a closed system with a disconnection between the pore water and the overlying seawater [START_REF] Fike | Rethinking the Ancient Sulfur Cycle[END_REF]. On the contrary, pyrites with heavy δ 34 S that precipitated in shallow marine settings characterized by frequent and repeated abiotic oxidative reworking due to physical (e.g., through storm or tide activity) or biological (e.g. bioturbation) mixing of sediments can be produced during abiotic oxidation of sulfides (fractionation up to 5‰; [START_REF] Fry | Sulfur isotope effects associated with oxidation of sulfide by O2 in aqueous solution[END_REF]. The pyrite 34 S enrichment is in this case controlled by unsteady diagenetic processes and primarily reflects the efficiency of solute diffusion (pumping) and re-precipitation (refluxing) in the suboxic zone [START_REF] Aller | Early diagenetic cycling, incineration, and burial of sedimentary organic carbon in the central Gulf of Papua (Papua New Guinea)[END_REF][START_REF] Aller | Unsteady diagenetic processes and sulfur biogeochemistry in tropical deltaic muds: implications for oceanic isotope cycles and the sedimentary record[END_REF][START_REF] Gao | Enriched pyrite δ 34 S signals in modern tropical deltaic muds[END_REF]. Transport conditions and sedimentary dynamics indeed play a major role on the observed sulfur isotope pattern by promoting exchanges of sulfur and iron pools between the reduced deep layers and oxidized surface layers of unconsolidated sediments as shown in both the modern [START_REF] Aller | Unsteady diagenetic processes and sulfur biogeochemistry in tropical deltaic muds: implications for oceanic isotope cycles and the sedimentary record[END_REF] and the geological sedimentary record [START_REF] Pasquier | Pyrite sulfur isotopes reveal glacial-interglacial environmental changes[END_REF].

This process can result in geochemical records that preserve small or negative isotopic offsets between sulfate and sulfide [START_REF] Sansjofre | Multiple sulfur isotope evidence for massive oceanic sulfate depletion in the aftermath of Snowball Earth[END_REF]; these differences can be substantially less than the isotopic fractionation associated with microbial sulfur cycling in sediments [START_REF] Fike | Rethinking the Ancient Sulfur Cycle[END_REF]. Finally, observed swings in δ 34 Spy values can also reflect variations in the fractionation with reduced MSR ε 34 associated with lowering sulfate concentrations or increasing cell-specific reduction rates [START_REF] Leavitt | Influence of sulfate reduction rates on the Phanerozoic sulfur isotope record[END_REF].

In order to discriminate among these mechanisms, the use of the minor isotope of sulfur ( 33 S) in combination with the δ 34 Spy signal has been previously successfully applied to various Phanerozoic sediments by some authors (e.g. [START_REF] Shen | Multiple Sisotopic evidence for episodic shoaling of anoxic water during Late Permian mass extinction[END_REF][START_REF] Zhang | Widespread shoaling of sulfidic waters linked to the end-Guadalupian (Permian) mass extinction[END_REF][START_REF] Zhang | Redox chemistry changes in the Panthalassic Ocean linked to the end-Permian mass extinction and delayed Early Triassic biotic recovery[END_REF][START_REF] Saitoh | Multiple sulfur isotope records at the end-Guadalupian (Permian) at Chaotian, China: Implications for a role of bioturbation in the Phanerozoic sulfur cycle[END_REF]. MSI analyses were first applied to the EPME context by [START_REF] Shen | Multiple Sisotopic evidence for episodic shoaling of anoxic water during Late Permian mass extinction[END_REF]. They analyzed carbonate rocks across the PTB at the GSSP Meishan section, South China and based on a negative ∆ 33 Spy shift, they suggested that the episodic shoaling of anoxic deep-water caused the EPME. Recently, [START_REF] Zhang | Widespread shoaling of sulfidic waters linked to the end-Guadalupian (Permian) mass extinction[END_REF] analyzed the quadruple sulfur isotopic composition of carbonates across the end-Guadalupian extinction from two sections in South China. They also suggested that the shoaling of sulfidic deep-waters contributed to this extinction based on negative ∆ 33 Spy signatures. Both studies interpreted negative ∆ 33 Spy signals as indicating the mixing of 34 S-enriched and 34 S-depleted sulfur from two different sources. The shutdown of bioturbation in the sediments caused by shoaling of toxic (anoxic/sulfidic) deep-waters was put forward to support this interpretation. However, this inference was challenged by [START_REF] Saitoh | Multiple sulfur isotope records at the end-Guadalupian (Permian) at Chaotian, China: Implications for a role of bioturbation in the Phanerozoic sulfur cycle[END_REF]. Based on an additional MSI record of the end-Guadalupian event at Choatian, China, these authors proposed that in shallow marine limestones deposited in oxic conditions, a negative ∆ 33 Spy shift can be also recorded and reflects the mixing of two distinct types of pyrites precipitating from MSR in an open and closed system. They subsequently suggested that bioturbation at Chaotian promoted MSR and enhanced pyrite burial within the sediments. Thus, while these studies both agreed on the mixing of different pools of sulfides to account for observed negative ∆ 33 Spy shifts, the link with the bioturbation intensity and ensuing redox conditions was interpreted in opposite ways.

In the frame of these previous works, we report here the first MSI record across the Smithian and the SSB (Fig. 8). The measured MSI correlate remarkably with the lithostratigraphic units of the Mineral Mountains section and its δ 13 Ccarb record (Fig. 3). We notably document steadily high ∆ 33 Spy values associated with low negative δ 34 Spyr in unit B, while unit A shows low ∆ 33 Spy values associated with positive δ 34 Spy. In the units SSB and C, the ∆ 33 Spy signal remains high and is associated with positive δ 34 Spy. Strong small-scale fluctuations of the MSI signal are recorded in the unit C (Fig. 3).

In vitro laboratory experiments have shown that the MSI values of hydrogen sulfide produced during MSR under non-limiting sulfate conditions is higher in ∆ 33 Spy and lower in δ 34 Spy compared to the substrate [START_REF] Johnston | Sulfur isotope insights into microbial sulfate reduction: When microbes meet models[END_REF]Sim et al, 2011aSim et al, , 2011b)). Therefore, the high ∆ 33 Spy values associated with low negative δ 34 Spy values of unit B (data in quadrant II of figure 8) relative to contemporaneous seawater sulfate estimated by model calculation [START_REF] Wu | Evaluating the S-isotope fractionation associated with Phanerozoic pyrite burial[END_REF] is consistent with sulfate reduction in an open system (i.e. sulfate supply > sulfate reduction) with respect to sulfate. This is supported by evidence that most sulfides of unit B are small pyrite framboids (Fig. 7C) congruent with MSR activity. Moreover, the likely absence of an anoxic water column [START_REF] Thomazo | A diagenetic control on the Early Triassic Smithian-Spathian carbon isotopic excursions recorded in the marine settings of the Thaynes Group (Utah, USA)[END_REF] and the abundant occurrences of bioturbations and storm events (Figs. 3,7A) recorded during the deposition of the unit B suggest that pyrites precipitated synsedimentarily and that sediments were continuously replenished in sulfates. In other words, the connectivity of the sedimentary pore water, where MSR proceeded with the overlying water column, was probably strong during the deposition of unit B. This MSI signal corresponds to an open system sulfate reduction. We hypothesize that this connection was favored by a sustained sedimentary remobilization. Additionally, we estimate that sulfur isotope fractionations during MSR in the unit B of Mineral Mountains reflect values of 34 ε and 33 λ of 44.8‰ and 0.512, respectively, based on the sedimentary sulfides and seawater sulfate isotopic compositions proposed by [START_REF] Wu | Evaluating the S-isotope fractionation associated with Phanerozoic pyrite burial[END_REF]Fig. 8).

The δ 34 Spy values of the unit SSB and most of unit C show highly positive values associated with positive ∆ 33 Spy (Fig. 3, Table 1). These data mostly occurred in the quadrant I of the figure 8 and fall above the regression line expected during open-system MSR.

Therefore, these positive δ 34 Spy and ∆ 33 S values cannot be solely explained by variations in MSR (a decrease in the MSR fractionation being accompanied by a decrease in the ∆ 33 S signal; [START_REF] Bradley | Patterns of sulfur isotope fractionation during microbial sulfate reduction[END_REF] or sulfur disproportionation activities [START_REF] Shen | Multiple Sisotopic evidence for episodic shoaling of anoxic water during Late Permian mass extinction[END_REF][START_REF] Sim | Sulfur isotope evidence for low and fluctuating sulfate levels in the Late Devonian ocean and the potential link with the mass extinction event[END_REF][START_REF] Zhang | Widespread shoaling of sulfidic waters linked to the end-Guadalupian (Permian) mass extinction[END_REF]. In order to infer potential underlying mechanisms, we superimposed on figure 8 (i) the mixing line of the sedimentary sulfide and seawater sulfate endmembers, as well as the expected isotopic compositions of accumulative sulfides produced during sulfate reduction in a closed system. Arrows in figure 8 show the evolution of the residual sulfate and instantaneous sulfides during a closed-system Rayleigh distillation.

Isotopic data from the unit SSB and the lower part of unit C are largely consistent with the range of values in a closed system Rayleigh distillation (including the mixing line between accumulative sulfides and open system sulfides, Fig. 8). Importantly, they cannot be explained by the mixing of sulfides produced during sulfate reduction in an open system and produced during quantitative sulfate reduction in a closed system. Moreover, very highly 34 Senriched (and positive ∆ 33 Spy) sulfides in parts of units SSB and C may reflect (i) the evolution of the residual sulfate reservoirs from which sulfides precipitated and subsequent MSR, or (ii) the precipitation of super heavy pyrite (i.e., δ 34 Spy > δ 34 SCAS). Both of these hypotheses are in accordance with a closed-system Rayleigh distillation model. However, we cannot fully exclude here that the heaviest pyrite signal also reflect an H2S pool produced under low sulfate concentration, where some of the H2S would have been partially oxidized under aerobic conditions with an attendant effect resulting in sulfate that is lighter than the H2S available for capture as pyrite [START_REF] Ries | Superheavy pyrite ( 34 Spyr > 34 SCAS) in the terminal Proterozoic Nama Group, southern Namibia: A consequence of low seawater sulfate at the dawn of animal life[END_REF]. Further analyses using secondary-ion mass spectrometry will help to better address cumulative versus instantaneous isotopic effects associated with these processes in a future study. The sulfides of the units SSB and C are pyrite framboids of various sizes (Figs. 7E and7F) consistent with MSR activity. According to the record of trace elements [START_REF] Thomazo | A diagenetic control on the Early Triassic Smithian-Spathian carbon isotopic excursions recorded in the marine settings of the Thaynes Group (Utah, USA)[END_REF], these sediments were deposited under oxic conditions. A collapse in bioturbation and storm event occurrences are visible during the late Smithian and at the SSB (Figs. 2,5D). We therefore suggest that pyrites of unit SSB and C precipitated synsedimentarily in pore water with a limited sulfate availability due to a rapid disconnection of top-layer sediments with the overlying seawater sulfate reservoir. Such a marked change may result from the absence of bioturbations at that time (see stratigraphic variations of bioturbation intensity in, Fig. 3 and illustration of non-biotic and nonbioturbated mudstones from the SSB unit in, Fig. 7D). This disappearance was coeval to, and could have been a consequence of, the global late Smithian event, which for instance corresponds to a major diversity loss in nektonic organisms (e.g., [START_REF] Brayard | Guodunites, a low-palaeolatitude and trans-panthalassic Smithian (Early Triassic) ammonoid genus[END_REF][START_REF] Jattiot | Revision of the genus Anasibirites Mojsisovics (Ammonoidea): an iconic and cosmopolitan taxon of the late Smithian (Early Triassic) extinction[END_REF]. It may have also been generated by a strong increase in the sedimentation rate [START_REF] Pasquier | Pyrite sulfur isotopes reveal glacial-interglacial environmental changes[END_REF], as observed regionally during the SSB and lower Spathian (Caravaca et al., 2017b).

Finally, most of the samples from the unit A show MSI values in-between quadrant I and IV of figure 8, close to, or aligned with, the mixing line between two different pools ( 34 Senriched and 34 S-depleted sulfur) of pyrites precipitating from MSR in an open and closed systems. In this case, when MSR occurs in an open system with respect to sulfates, pyrites with substantially low δ 34 Spy and high ∆ 33 Spy values are formed. In contrast, when sulfate reduction goes to completion in a closed system, the sulfates are fully reduced and the δ 34 Spy and ∆ 33 Spy values of the precipitated pyrites become equal to those of sulfates [START_REF] Shen | Multiple Sisotopic evidence for episodic shoaling of anoxic water during Late Permian mass extinction[END_REF][START_REF] Sim | Sulfur isotope evidence for low and fluctuating sulfate levels in the Late Devonian ocean and the potential link with the mass extinction event[END_REF][START_REF] Zhang | Widespread shoaling of sulfidic waters linked to the end-Guadalupian (Permian) mass extinction[END_REF][START_REF] Saitoh | Multiple sulfur isotope records at the end-Guadalupian (Permian) at Chaotian, China: Implications for a role of bioturbation in the Phanerozoic sulfur cycle[END_REF]. The unit A samples are mainly composed of dolomicrites and microbial limestones deposited in very shallow water environments (Fig. 3). Burrows observed in the unit A may indicate that bioturbation activity supplied sulfates into the limestone deposits and promoted MSR leading to the low δ 34 Spy and high ∆ 33 Spy values. However, the TOC in unit A is largely higher than in the unit B. The sulfate reduction rate in the unit A may have been even higher than in unit B and perhaps also to the rate of diffusive sulfate supply into the sediments due to the large amount of available OM [START_REF] Ohmoto | Biogeochemistry of Sulfur and the Mechanisms of Sulfide-Sulfate Mineralization in Archean Oceans[END_REF][START_REF] Ohmoto | Sulfur and carbon isotopes[END_REF] promoting "seawater sulfate like" δ 34 S and ∆ 33 S values. Therefore, the observed variations in the δ 34 Spy and ∆ 33 Spy values in unit A probably better reflect the rate of mixing between the two types of pyrites. Because unit A contained microbial limestones and dolomicrites corresponding to the development of complex microbial ecosystems with the possible involvement of microbial sulfide oxidizers, the processes that led to its MSI signal may also have been more complex by involving several cycles of oxidation-reduction reactions (e.g., [START_REF] Canfield | Animal evolution, bioturbation, and the sulfate concentration of the oceans[END_REF][START_REF] Zerkle | Fractionation of multiple sulfur isotopes during phototrophic oxidation of sulfide and elemental sulfur by a green sulfur bacterium[END_REF][START_REF] Zerkle | Sulfur isotope values in the sulfidic Frasassi cave system, central Italy: A case study of a chemolithotrophic S-based ecosystem[END_REF][START_REF] Johnston | Multiple sulfur isotopes and the evolution of Earth's surface sulfur cycle[END_REF][START_REF] Fike | Rethinking the Ancient Sulfur Cycle[END_REF].

CAS sulfur isotopes results

Only nine samples over the twenty initially selected as part of this study yielded enough material for CAS isotopic analyses. Results are therefore not subdivided with respect to units of the studied section. No temporal trend can be documented. The δ 34 S values of CAS vary between +19.5‰ and +34.8‰ (mean value of +25.9 ± 6.3‰, 1σ) (Fig. 3, Table 1).

Results indicate a strong relationship between δ 34 SCAS and the Mg/(Mg+Ca) ratio (r = -0.64, p = 0.06, n = 9, including all samples but increasing to r = -0.84, p < 0.01, n = 8, without MI163, Fig. 9A), and between the δ 34 SCAS and the Mn/Sr ratio (r = -0.75, p < 0.02, n = 9, Fig. 9B).

Limestones with low Mg/(Mg+Ca) ratios show δ 34 SCAS of around +35‰, whereas dolomicrites with high Mg/(Mg+Ca) ratios exhibit 32 S-enriched sulfur isotope compositions around +20‰. There are no significant correlations between δ 34 SCAS and carbonate concentration, δ 13 Ccarb, δ 34 Spy and CAS concentrations (Table 1).

Fidelity and comparisons with other documented δ 34 S signals from the Smithian-Spathian transition.

The observed range of δ 34 SCAS values are in agreement with previous measurements from Spathian strata of the Moenkopi Formation, in the southernmost part of the SFB, that yield values between +25‰ and +38‰ [START_REF] Marenco | Environmental and diagenetic variations in carbonate associated sulfate: An investigation of CAS in the Lower Triassic of the western USA[END_REF], and more generally with most Spathian sulfate δ 34 S values falling between +25‰ and +30‰ VCDT (e.g., [START_REF] Cortecci | Sulfur and oxygen isotopes in Italian marine sulfates of Permian and Triassic ages[END_REF][START_REF] Holser | Gradual and Abrupt Shifts in Ocean Chemistry During Phanerozoic Time[END_REF][START_REF] Holser | Events near the Permian-Triassic boundary[END_REF][START_REF] Holser | Geochemical cycles of carbon and sulfur[END_REF][START_REF] Strauss | The isotopic composition of sedimentary sulfur through time[END_REF][START_REF] Luo | Isotopic evidence for an anomalously low oceanic sulfate concentration following end-Permian mass extinction[END_REF]Song et al., 2014b). Highly 34 S-enriched sulfates are characteristic of the Early Triassic with maximum values of about +35‰ compared with values of ∼+10‰ in the late Permian [START_REF] Holser | Catastrophic chemical events in the history of the ocean[END_REF][START_REF] Claypool | The age curves of sulfur and oxygen isotopes in marine sulfate and their mutual interpretation[END_REF][START_REF] Cortecci | Sulfur and oxygen isotopes in Italian marine sulfates of Permian and Triassic ages[END_REF][START_REF] Wilgus | A stable isotope study of Permian and Triassic marine evaporite and carbonate rocks[END_REF][START_REF] Scholle | Carbon and Sulfur Isotope Stratigraphy of the Permian and Adjacent Intervals[END_REF][START_REF] Strauss | The isotopic composition of sedimentary sulfur through time[END_REF][START_REF] Kampschulte | The sulfur isotopic evolution of Phanerozoic seawater based on the analysis of structurally substituted sulfate in carbonates[END_REF]Longinelli and Flora, 2010;Song et al., 2014b). However, the exact timing of the positive +35‰ maximum during the Early Triassic differs from study to study with some authors suggesting that this maximum is restricted to the Spathian [START_REF] Wilgus | A stable isotope study of Permian and Triassic marine evaporite and carbonate rocks[END_REF][START_REF] Marenco | Environmental and diagenetic variations in carbonate associated sulfate: An investigation of CAS in the Lower Triassic of the western USA[END_REF] or occurs across or immediately above the PTB [START_REF] Newton | Large shifts in the isotopic composition of seawater sulphate across the Permo-Triassic boundary in northern Italy[END_REF][START_REF] Gorjan | Paleoredox, biotic and sulfur-isotopic changes associated with the end-Permian mass extinction in the western Tethys[END_REF][START_REF] Luo | Isotopic evidence for an anomalously low oceanic sulfate concentration following end-Permian mass extinction[END_REF][START_REF] Horacek | Lower Triassic sulphur isotope curve of marine sulphates from the Dolomites, N-Italy[END_REF]Song et al., 2014b). Interestingly, some of the Early Triassic δ 34 SCAS records show large and rapid variations within a section [START_REF] Newton | Large shifts in the isotopic composition of seawater sulphate across the Permo-Triassic boundary in northern Italy[END_REF][START_REF] Riccardi | Sulfur isotopic evidence for chemocline upward excursions during the end-Permian mass extinction[END_REF][START_REF] Luo | Isotopic evidence for an anomalously low oceanic sulfate concentration following end-Permian mass extinction[END_REF]Song et al., 2014b). These behaviors have been interpreted to reflect a drawdown in seawater sulfate concentration associated with a shortened residence time. Coupled variations in the carbon and sulfur cycles are suggested and might be traced back using the δ 13 C and δ 34 S records when such paleoenvironmental conditions developed. Covariations between δ 13 C and δ 34 S signals during periods of low seawater sulfate concentration have been hypothesized for the Early Triassic in South China [START_REF] Luo | Isotopic evidence for an anomalously low oceanic sulfate concentration following end-Permian mass extinction[END_REF]Song et al., 2014b), but also during the Paleozoic [START_REF] Gill | Parallel, high-resolution carbon and sulfur isotope records of the evolving Paleozoic marine sulfur reservoir[END_REF][START_REF] Gill | Geochemical evidence for widespread euxinia in the Later Cambrian ocean[END_REF] and the Cretaceous [START_REF] Adams | Volcanic triggering of a biogeochemical cascade during Oceanic Anoxic Event 2[END_REF]. Such a relationship between the δ 34 SCAS and δ 13 Ccarb signals cannot be identified in our dataset.

Several authors postulated that a gradient in sulfate δ 34 S potentially developed within water column depth during the Early Triassic [START_REF] Newton | Large shifts in the isotopic composition of seawater sulphate across the Permo-Triassic boundary in northern Italy[END_REF][START_REF] Kump | Massive release of hydrogen sulfide to the surface ocean and atmosphere during intervals of oceanic anoxia[END_REF][START_REF] Riccardi | Sulfur isotopic evidence for chemocline upward excursions during the end-Permian mass extinction[END_REF][START_REF] Marenco | Sulfur isotope geochemistry and the end Permian mass extinction[END_REF]. The advection of deep 34 S-enriched sulfate water masses that formed during periods of prolonged global deep-ocean anoxia into shallow water environments may explain variable sulfate δ 34 S and deleterious biotic conditions due to ensuing shallow marine euxinia [START_REF] Isozaki | Permo-Triassic Boundary Superanoxia and Stratified Superocean: Records from Lost Deep Sea[END_REF][START_REF] Newton | Large shifts in the isotopic composition of seawater sulphate across the Permo-Triassic boundary in northern Italy[END_REF][START_REF] Grice | Photic Zone Euxinia During the Permian-Triassic Superanoxic Event[END_REF][START_REF] Kump | Massive release of hydrogen sulfide to the surface ocean and atmosphere during intervals of oceanic anoxia[END_REF][START_REF] Riccardi | Sulfur isotopic evidence for chemocline upward excursions during the end-Permian mass extinction[END_REF][START_REF] Marenco | Sulfur isotope geochemistry and the end Permian mass extinction[END_REF]. The observed stratigraphic variations in Mg/(Mg+Ca) ratios (Fig. 3) and the negative correlation between the degree of dolomitization and the δ 34 SCAS (Fig. 9A) suggest that the dolomitization process and associated δ 34 SCAS could be facies-dependent, with shallowest sediments experiencing a higher degree of dolomitization compared to deepest sediments. These observations are consistent with the hypothesis of a gradient in sulfate δ 34 S, with the dolomitized samples recording the lower δ 34 SCAS. However, (i) a water column anoxia is not documented at Mineral Mountains and the advection of anoxic water masses to the shallowest part of the SFB is not kineticallysupported by the carbon isotopes record [START_REF] Thomazo | A diagenetic control on the Early Triassic Smithian-Spathian carbon isotopic excursions recorded in the marine settings of the Thaynes Group (Utah, USA)[END_REF], and (ii) the relationships observed between the δ 34 SCAS and both Mg/(Mg+Ca) and Mn/Sr ratios (Fig. 9A and9B) indicate that the sulfur isotope signal of CAS mostly reflects variations in early diagenetic processes including the degree of dolomitization. Accordingly, we postulate that only samples exhibiting Mn/Sr below 0.5 record primary CAS-derived δ 34 S sulfate with values between +32.4‰ and +34.8‰. This approximation is in agreement with the estimates by [START_REF] Marenco | Environmental and diagenetic variations in carbonate associated sulfate: An investigation of CAS in the Lower Triassic of the western USA[END_REF] interpreting a weaker altered signal in the Moenkopi Formation of the southern SFB, which exhibits sulfate δ 34 S values between +31‰ and +38‰.

Nevertheless, several early diagenetic reactions associated with secondary fluids can be deduced from the δ 34 SCAS record at Mineral Mountains. Indeed, during early diagenesis, the MSR activity tends to produce a 34 S-enriched CAS record [START_REF] Marenco | Environmental and diagenetic variations in carbonate associated sulfate: An investigation of CAS in the Lower Triassic of the western USA[END_REF], especially if reduction occurred under a Rayleigh-type distillation in a closed system with respect to sulfates, as deduced from the MSI signal in samples from units SSB and C (Fig. 8).

However, because OM fuels MSR a positive relationship between TOC and δ 34 SCAS and an increasing S/C ratio associated with 34 S-enriched CAS might be expected [START_REF] Raiswell | The iron biogeochemical cycle past and present[END_REF]. No such relationship between the δ 34 SCAS and TOC or between the δ 34 SCAS and S/C can be documented using our restricted available data set.

In the unit C (between MI159 and MI169) significant small-scale δ 34 SCAS variations (15‰ in amplitude) are also observed independently of the TOC, S/C ratio and paired δ 34 S of pyrites. Such high-frequency fluctuations of the δ 34 SCAS signal are difficult to explain by secular variations in seawater sulfate sulfur isotopic composition in a steady-state global sulfur cycle. Indeed, these variations are much more rapid (≪50 kyr, [START_REF] Brühwiler | High-resolution biochronology and diversity dynamics of the Early Triassic ammonoid recovery: The Smithian faunas of the Northern Indian Margin[END_REF] than the sulfate residence time in the ocean (i.e., 13 Myr in the modern ocean, Kah et al., 2004; but probably reduced to 1.3 Myr during the Triassic due to lower sulfate concentration, [START_REF] Horita | Chemical evolution of seawater during the Phanerozoic[END_REF]. Rapid changes of the δ 34 SCAS signal during the Griesbachian to Smithian interval have nonetheless been interpreted to reflect very low sulfate concentrations (≤4 mM) with a residence time of oceanic sulfate reduced to ≤200 kyr (Song et al., 2014b). Thus, a partial influence of a global signal cannot be completely discarded in our case.

Finally, the strong correlation between the δ 34 SCAS and the degree of dolomitization and the Mn/Sr ratio, as well as the identification of a closed system Rayleigh-type distillation of sulfur species, makes a compelling case for synsedimentary early diagenetic processes as the main control for the CAS sulfur isotope signal observed at Mineral Mountains.

Perspectives on the use of MSI record in its sedimentological context

The Mineral Mountains MSI signal is slightly different from previous observations for the sedimentary sulfur cycle associated with bioturbation during the Phanerozoic. In [START_REF] Shen | Multiple Sisotopic evidence for episodic shoaling of anoxic water during Late Permian mass extinction[END_REF], negative sulfide ∆ 33 S values measured across the PTB were suggested to reflect the mixing of two types of pyrite formed during both an open system and a quantitative closed system MSR. [START_REF] Shen | Multiple Sisotopic evidence for episodic shoaling of anoxic water during Late Permian mass extinction[END_REF] linked this mixing to a shutdown of bioturbation resulting from the shoaling of anoxic deep waters that led to the EPME. According to this model, the pore water exchanged continuously with oceanic sulfate under oxic conditions because of the enhanced bioturbation (associated with low δ 34 S and high ∆ 33 S). On the contrary, bioturbation would have disappeared during anoxia and the sulfate supply into sediments was suppressed, leading to quantitative pore water sulfate reduction (high δ 34 Spy and low ∆ 33 Spy). A similar scenario was proposed by [START_REF] Zhang | Widespread shoaling of sulfidic waters linked to the end-Guadalupian (Permian) mass extinction[END_REF], who interpreted negative ∆ 33 S-δ 34 S values of pyrites around the PTB as corresponding to pyrites produced in a shoaling sulfidic water column. More recently, these interpretations have been challenged by [START_REF] Saitoh | Multiple sulfur isotope records at the end-Guadalupian (Permian) at Chaotian, China: Implications for a role of bioturbation in the Phanerozoic sulfur cycle[END_REF] based on the MSI record across the Guadalupian-Lopingian (Late Permian) boundary at Chaotian (China). They showed that the setting of pore water sediments under oxic conditions are not always an open system with respect to sulfates, even if bioturbation is associated. Indeed, MSR is well known for its role in promoting the precipitation of early diagenetic authigenic carbonates and secondary carbonates such as dolostones with low δ 13 Ccarb values through the consumption of excess protons [START_REF] Vasconcelos | Microbial mediation of modern dolomite precipitation and diagenesis under anoxic conditions (Lagoa Vermelha, Rio de Janeiro, Brazil)[END_REF][START_REF] Zhang | Dissolved sulfidecatalyzed precipitation of disordered dolomite: Implications for the formation mechanism of sedimentary dolomite[END_REF][START_REF] Thomazo | A diagenetic control on the Early Triassic Smithian-Spathian carbon isotopic excursions recorded in the marine settings of the Thaynes Group (Utah, USA)[END_REF], within reducing Mn-bearing, 12 C-enriched, fluids produced during the bacterially mediated degradation of OM in the suboxic/anoxic zone.

On the contrary, during the deposition of both unit SSB and the lower part of unit C, the disappearance of bioturbation (see stratigraphic variations of bioturbation intensity in Fig. 3 and illustration of non-biotic and non-bioturbated mudstones from the SSB unit in Fig. 7D), , may have strongly reduced the pore water replenishment in sulfates, therefore leading to; (i) reduced in situ sulfide precipitation, (ii) MSI signatures typical of a closed system Rayleightype distillation, and (iii) reduced early diagenetic remineralization processes (i.e., lower Mn/Sr and lower Mg/(Mg+Ca) ratios, higher δ 13 Ccarb) due to the shortage in oxidant availability.

The relationship between secular trends in bioturbation patterns and the sedimentary geochemical signatures observed at Mineral Mountains, together with the absence of anoxia, support the primary influence of local processes as an important driver of isotopic trends observed before and across the SSB. Worldwide correlation of the Smithian-Spathian δ 13 C signal (Fig. 1) is more easily explained by modifications of the global carbon cycle if the primary driver of the muted δ 13 Ccarb and δ 34 Spy signatures across the SSB reflects the collapse of biogenic sediment mixing and subsequent changes in the connectivity of sedimentary pore waters with the overlying water column. These have likely influenced the geochemical properties of sediments over large distances and may have also generated a global pattern [START_REF] Hofmann | Loss of the sedimentary mixed layer as a result of the end-Permian extinction[END_REF][START_REF] Pasquier | Pyrite sulfur isotopes reveal glacial-interglacial environmental changes[END_REF]. If these hypotheses are confirmed, they also suggest that many commonly used proxies to infer Early Triassic seawater anoxia may rather reflect the poor sediment oxygenation arising from the extinction of organisms performing bioturbation.

Finally, the use of MSI geochemistry, together with strong sedimentological constraints, show that changes in the sulfur cycle before and across the SSB at Mineral Mountains is most probably a local consequence of the late Smithian extinction event rather than recording the development of a lethal global anoxic ocean. Therefore, the data reported in this study demonstrate that the sulfide MSI signal can be a valuable proxy for assessing local paleoenvironmental and sedimentological processes throughout Earth history.

Conclusions

The study of the multiple sulfur isotope records before and across the SSB at Mineral Mountains provides new insights into the Early Triassic sulfur cycle and its temporal and mechanistic relationships with local sedimentological conditions, the δ 13 C curve variations and the decrease in diversity and abundance among benthic organisms. We notably show that:

1. The ∆ 33 S-δ 34 S signals reflect the operation of MSR in two different regimes. Before the late Smithian, open system sulfate reduction in sediments pore water connected to the seawater is prevailing, while during the late Smithian and after the SSB, a closed-system, sulfate-limited, Rayleigh-type distillation is recorded in the MSI signals.

2. No change in the oxygenation of the water column accompanied this evolution of the MSI record and all pyrite framboids formed in the sediment pore water were precipitated under an overlying oxygenated water column.

3. The connection of pore waters to the overlying water column is locally controlled by sedimentological conditions such as bioturbation intensity and sedimentation rate. This led to a constant replenishment in pore water sulfates during the middle Smithian, and an impoverishment during the late Smithian and across the SSB. Finally, we suggest that the muted sulfur isotope record at Mineral Mountains is a consequence of the late Smithian extinction and the associated loss of the sedimentary mixed layer. Future isotopic studies on other sections across the SSB in various sedimentological contexts should be used to further test in detail these inferences and help to improve our understanding of the importance of local synsedimentary processes for paleoenvironmental reconstructions during the EPME recovery and, more generally, over geological times.

among localities is primarily based on high-resolution ammonoid zonations (see synthesis in [START_REF] Jenks | Biostratigraphy of Triassic Ammonoids[END_REF]. Anasibirites multiformis beds; Xe: Xenoceltitidae "gen. indet." A. beds (see [START_REF] Brayard | Smithian ammonoid faunas from Utah: implications for Early Triassic biostratigraphy, correlation and basinal paleogeography[END_REF][START_REF] Jattiot | Revision of the genus Anasibirites Mojsisovics (Ammonoidea): an iconic and cosmopolitan taxon of the late Smithian (Early Triassic) extinction[END_REF]. Relative variations of sea surface temperatures are depicted using color gradient and underlined a major cooling event across the Smithian/Spathian Boundary (interpreted from [START_REF] Sun | Lethally hot temperatures during the Early Triassic greenhouse[END_REF][START_REF] Romano | Climatic and biotic upheavals following the end-Permian mass extinction[END_REF]. A prolonged absence of bioturbation occurred in the SSB and lower unit C intervals. These deposits correspond to mud outer ramp lower offshore environment [START_REF] Vennin | Microbial deposits in the aftermath of the end-Permian mass extinction: A diverging case from the Mineral Mountains (Utah, USA)[END_REF]. Below and above, the depositional environment is the same but shows a more intense bioturbation.

III.

IV.

Fig. 8

  Therefore, the development of anoxic conditions and consequent shutdown of bioturbation are not required to produce negative ∆ 33 Spy values and processes linking the sedimentary sulfur cycle to bioturbation are more complicated than previously thought. Contrasting with Saitoh et al. (2017) we established here (Fig. 8, Section 4.3) a strong relationship between bioturbation and the MSI signal recorded within the permanently oxic bottom water conditions that developed at Mineral Mountains across the SSB. Bioturbation, which is a necessary driver to sustain intense iron and sulfur cycling in marine sediments through the suboxic zone (Van de Velde et al., 2016), likely continuously supplied sulfates into the sediments and stimulates the sulfate reduction and in situ sulfide precipitation in the sediments during the deposition of the middle Smithian unit B. During this period, open system MSR activity from pore water fluids connected to oceanic waters is in accordance with (i) the higher average concentration of sulfides, (ii) the observation of pyrite (FeS2) in the form of framboids, and (iii) the MSI signatures. Moreover, unit B records low δ 13 Ccarb values associated with high Mn/Sr and high Mg/(Mg+Ca) ratios. Such variations are in agreement with a strong influence of the MSR activity on the geochemistry of the sediments.

4.

  Both the C and S isotope signals at Mineral Mountains are therefore best explained by the extent to which MSR and associated early diagenetic remineralization proceeded within the sediments.

Fig. 2 :

 2 Fig. 2: (A) Early Triassic paleogeographic map and location of the Sonoma Foreland Basin

Fig. 3 :

 3 Fig. 3: Mineral Mountains section with corresponding lithological units and

Fig. 4 :

 4 Fig. 4: Cross calibration between SO2-EA-IRMS and SF6-IRMS on the δ 34 S values of 10

Fig. 5 :

 5 Fig. 5: Relationship between the δ 13 Ccarb (VPDB, ‰) and the Mg/(Mg+Ca) ratio in units A, B,

Fig. 6 :

 6 Fig. 6: Correlation relationship between the carbonate content (in wt. %) and the sum of

Fig. 7 :

 7 Fig. 7: Selected thin sections from the Mineral Mountains section under a photonic and

Fig. 8 :

 8 Fig. 8: Graphic showing the sulfides δ 34 S and ∆ 33 S relationship in units A, B, SSB and C. The

  Fig.2

  Fig.3

  Fig.4

  Fig.5

  Fig.

  Fig.9

Acknowledgments

This work is a contribution to the ANR project AFTER (ANR-13-JS06-0001-01) and was also supported by the French "Investissements d'Avenir" program, project ISITE-BFC (ANR-15-IDEX-03), and by the FEDER Bourgogne Franche-Comté. The Mineral Mountains section is located on US public land under the stewardship of the Bureau of Land Management (BLM) of the US Department of the Interior; their management and access to this land is greatly acknowledged. Maud Boyet is warmly acknowledged for her initial work on REE.

Rémi Laffont is acknowledged for his work on the statistical analysis of the results.

Fig. 9: Relationships between the δ 34 SCAS (VCDT, ‰) and the Mg/(Mg+Ca) ratio (A), and the Mn/Sr ratio (B) in units A, B, SSB and C.