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The Quadrilátero Ferrífero (QF) is a globally known region for its world-class metallic deposits. Although its Precambrian units have been vastly studied since the 1960s due to economic importance, the Cenozoic geological record represents an upcoming subject of interest. The occurrence of Cenozoic sedimentary deposits has been noticed since the end of the 19th century, but most of them are not yet fully characterized. This paper brings a complete description, mapping, 3D modeling, and simulations of the sedimentary deposit named Bandeira Basin, Serra do Tamanduá, QF. Based on field data, such as mapping and drill core database analysis, three drill cores were selected for further investigation and detailed description. The Bandeira Basin can be characterized and subdivided into three units: Unit A: found only in the southeast area and shows exclusively sediments from the Nova Lima Group; Unit B: intermediate unit that occurs in central and southeast areas, with Rio das Velhas Supergroup as a possible source of the sedimentary material; and Unit C: occurs at the top, and it is essentially colluvial deposits from Minas Supergroup units. The contacts between units are abrupt or erosive, recording successive deposition stages. The basin is thicker on its central and southwest ends and thinner on the east and north, where part of the basement outcrops. Cenozoic tectonic events were probably active in this area, controlling the sedimentary processes, with the NW-SE and NE-SW lineaments reactivated, triggering sediment deposition and migration to the deepest spot of the basin. These sediments were 3D modeled in Leapfrog Geo, the visualization of any given region of interest, in the modeled scale. This methodology allowed an assertive characterization of sedimentary filling and could be applied to other basins. This comprehension is important because these sediments are used indirectly or directly in civil projects. [ABSTRACT FROM AUTHOR]

A synthesis of the evolution of the Neoproterozoic belts or orogens surrounding the São Francisco craton (SFC) in northeastern and southeastern Brazil is presented. Emphasis is placed on recognizing the superposition of sedimentary basins, from rift to passive margin to retroarc and foreland, as well as identifying three diachronic continental collisions in the formation of the SFC. The Tonian passive margin occurs in the southern Brasília Belt with the Vazante, Canastra, and Araxá Groups. During the Tonian, island magmatic arcs and basins developed in front and behind these arcs (fore- and back-arcs). Subsequently, in the Cryogenian–Ediacaran, a retroarc foreland basin developed with part of the Araxá Group and the Ibiá Group, and finally, a foreland basin developed, which was filled by the Bambuí Group. A tectonic structure of superimposed nappes, with subhorizontal S1–2 foliation, formed between 650 and 610 Ma, is striking. In the northern Brasília Belt, there is the Stenian passive margin of the Paranoá Group, the Tonian intrusion of the Mafic–Ultramafic Complexes, and the Mara Rosa Island magmatic arc, active since the Tonian, with limited volcanic–sedimentary basins associated with the arc. A thrust–fold belt structure is prominent, with S1 foliation and late transcurrent, transpressive tectonics characterized by the Transbrasiliano (TB) lineament. The Cryogenian–Ediacaran collision between the Paranapanema and São Francisco cratons is the first collisional orogenic event to the west. In the Rio Preto belt, on the northwestern margin of the São Francisco craton, the Cryogenian–Ediacaran Canabravinha rift basin is prominent, with gravitational sediments that represent the intracontinental termination of the passive margin that occurs further northeast. The rift basin was intensely deformed at the Ediacaran–Cambrian boundary, as was the Bambuí Group. On the northern and northeastern margins of the São Francisco craton, the Riacho do Pontal and Sergipano orogens stand out, showing a comparable evolution with Tonian and Cryogenian rifts (Brejo Seco, Miaba, and Canindé); Cryogenian–Ediacaran passive margin, where the Monte Orebe ophiolite is located; and Cordilleran magmatic arcs, which developed between 620 and 610 Ma. In the Sergipano fold belt, with a better-preserved outer domain, gravitational sedimentation occurs with glacial influence. A continental collision between the SFC and the PEAL (Pernambuco-Alagoas Massif) occurred between 610 and 540 Ma, with intense deformation of nappes and thrusts, with vergence to the south and accommodation by dextral transcurrent shear zones, such as the Pernambuco Lineament (PE). The Araçuaí belt or orogen was formed at the southeastern limit of the SFC by a Tonian intracontinental rift, later superimposed by a Cryogenian–Ediacaran rift–passive margin of the Macaúbas Group, with gravitational sedimentation and glacial influence, and distally by oceanic crust. It is overlain by a retroarc basin with syn-orogenic sedimentation of the Salinas Formation, partly derived from the Rio Doce cordilleran magmatic arc and associated basins, such as the Rio Doce and Nova Venécia Groups. A third continental collision event (SF and Congo cratons), at the end of the Ediacaran (580–530 Ma), developed a thrust–fold belt that deforms the sediments of the Araçuaí Belt and penetrates the Paramirim Corridor, transitioning to the south to a dextral strike-slip shear zone that characterizes the Ribeira Belt. [ABSTRACT FROM AUTHOR]

A section investigated in the region of Paraopeba, Minas Gerais, provided detailed sedimentologic, stratigraphic and chemostratigraphic data from the Ediacaran Lagoa do Jacaré Formation, Bambuí Group, Southeast Brazil. This information allowed interpretation of tempestite facies in transgressive-regressive cycles, reinforcing the previously proposed storm-influenced sedimentation model and clarifying how it is associated with unusually high C-isotope values related to the Middle Bambuí Excursion (MIBE). Facies analysis of nine lithofacies identified at the GMD quarry based on field and petrographic descriptions showed distal tempestite facies grading upwards to a shallower, oncoidal/ooidal carbonate marine environment, then to basinal shales. The entire succession comprises a low-order transgressive hemicycle, recording the transition from a storm-influenced carbonate ramp to a siliciclastic-dominated platform. Chemostratigraphic data yielded high δ13C values ranging between +11.11‰ and +13.94‰. Our data contribute to the revision of the previously proposed interpretation and as well as to the understanding of paleoenvironmental conditions and C isotope signatures across the MIBE, near the Ediacaran-Cambrian boundary in the Bambuí Basin. [ABSTRACT FROM AUTHOR]

In east‐central Brazil, the Ediacaran‐Cambrian Bambuí Basin has the potential to provide a record of unique geochemical responses of Earth's ocean and atmosphere evolution during this key time interval. From this perspective, we studied an interval of the upper Bambuí Basin using sedimentologic, stratigraphic, and chemostratigraphic tools. The lower Cambrian Jaíba Member of the uppermost Serra da Saudade Formation is an interval of up to 60 m‐thick of carbonate rocks disposed into two shallowing upward trends. Inner to outer ramp and high‐energy shoal deposits are described, in which laminated microbialites are the prevailing sedimentary facies. REE + Y data suggest contamination by iron (oxy)hydroxides that are dissociated from the riverine detritic flux. Sedimentary iron enrichment may be related to the settling of iron nanoparticles in coastal environments, diagenetic iron mobilization, or both. MREE enrichment is caused by microbial degradation of organic matter in the iron reduction zone during the anoxic early‐diagenetic stage. Chromium isotopes yielded negatively fractionated values (δ53Cr = −0.69 to −0.27‰), probably resulting from biotic and abiotic reduction of dissolved Cr(VI) to light and less toxic Cr(III) within pores of microbial mats. The δ53Cr data of the Jaíba microbialite are thus a product of metabolic reactions in microbial mats and do not reflect seawater signal. The isotopic offset from seawater is feasible from molecular diffusion of Cr into pore water and reduction reactions occurring deep inside the mat, although the exact mechanism and consequences are not yet fully understood due to the poor preservation of metabolic reactions in the geological record. Our study suggests that Cr isotopes can be used to reconstruct Cr and other metals cycling within ancient microbial mats, and that caution should be taken when using past microbialites to infer seawater Cr records and redox state of the atmosphere and ocean. [ABSTRACT FROM AUTHOR]

The Carrancas Formation outcrops in east-central Brazil on the southern margin of the São Francisco craton where it comprises the base of the late Neoproterozoic Bambuí Group. It is overlain by the basal Ediacaran cap carbonate Sete Lagoas Formation and was for a long time considered to be glacially influenced and correlative with the glaciogenic Jequitaí Formation. New stratigraphic, isotopic and geochronologic data imply that the Carrancas Formation was instead formed by the shedding of debris from basement highs uplifted during an episode of minor continental rifting. Reddish dolostones in the upper Carrancas Formation have δ 13 C values ranging from +7.1 to +9.6‰, which is a unique C isotopic composition for the lowermost Bambuí Group but similar to values found in the Tijucuçu sequence, a pre-glacial unit in the Araçuaí fold belt on the eastern margin of the São Francisco craton. The stratigraphic position below basal Ediacaran cap carbonates and the highly positive δ 13 C values together indicate a Cryogenian interglacial age for the Carrancas Formation, with the high δ 13 C values representing the so-called Keele peak, which precedes the pre-Marinoan Trezona negative δ 13 C excursion in other well characterized Cryogenian sequences. Hence, The Carrancas Formation pre-dates de Marinoan Jequitaí Formation and represents an interval of Cryogenian stratigraphy not previously known to occur on the southern margin of São Francicso craton. Documentation of Cryogenian interglacial strata on the São Francisco craton reinforces recent revisions to the age of Bambuí Group strata and has implications for the development of the Bambuí basin. [ABSTRACT FROM AUTHOR]

In order to investigate the geochemical responses of Earth's oceans and atmosphere after a Snowball glaciation, we studied an Ediacaran cap carbonate profile pertaining to the base of the Bambuí Group (Sete Lagoas Formation) in the central portion of the São Francisco basin, east central Brazil, for trace elements (including REE + Y) and C, O, Sr, Nd, Pb and Cr isotopes. The section can be divided in three portions, from bottom to top: (i) a two-meter thick cap dolostone preserving a drop of δ 13 C values from −3.8 to −4.2‰, overlain by (ii) a ca. 123 meters-thick, reddish limestone rhythmite deposited in a tidal flat, with an important isotopic shift observed at 60 m, with δ 13 C values below averaging −5‰ and above shifting abruptly to around −0.5‰; and (iii) a topmost ca. 2 meters thick black calcarenite with positive δ 13 C (+0.9‰) and 87 Sr/ 86 Sr = 0.7076. A new, tightly constrained Pb-Pb whole rock isochron of 608 ± 19 Ma provides additional support for deposition during the early Ediacaran. We put forward a model for the deposition of the Sete Lagoas cap carbonate which starts with the glacial aftermath, when the thin cap dolostone and the basal reddish limestone were deposited due to glacier melting and subsequent sea level rise, with important mixing of glacial meltwaters with anoxic bottom waters. A decreasing trend of εNd (630Ma) values, from −6 at the base to ca. −8 at the 60 meters-mark, indicates continued input of continentally-derived detrital particles to the basin. During this phase, intermittent subaerial exposure was responsible for meteoric diagenetic alteration, which shifted 87 Sr/ 86 Sr to higher values (>0.710) and δ 18 O towards lower values. Towards the top of the sequence, the late postglacial succession is marked by marine-like REE + Y (Y/Ho = ca. 46) and lower Al and Mn contents, reflecting the diminishing of glacial meltwater input, a renewed sea level rise, and a change to more distal depositional environments, away from the coastal lines. At this moment, a vigorous input of U(VI) and 53 Cr-rich Cr(VI), reflecting in a sharp rise of U/Th ratios and positive δ 53 Cr, suggests that fully oxygenated conditions finally predominated in post-glacial surface waters in the middle to late Ediacaran. Our results add to a growing body of data for other Ediacaran cap carbonate sequences around the world (e.g. Otavi Group, Namibia and Doushantuo Formation, China) that suggest that after ca 1 Ga of anoxia (the “Boring Billion”) following the first Great Oxygenation Event, the oceans became increasingly oxygenated after the end of the Marinoan glaciation ca. 635 Ma ago, ultimately leading to the explosion of complex macroscopic life that followed this Neoproterozoic Oxygenation Event. [ABSTRACT FROM AUTHOR]

The Bambuí Group is a lithostratigraphic unit that comprises a mixed carbonate-siliciclastic platform deposited in a foreland basin. It is a 1st order sequence that filled the São Francisco Basin during the Ediacaran-Cambrian in southeast Brazil. The Lagoa do Jacaré Formation is the second carbonate unit of the Bambuí Group and is related to a 2nd-order regressive hemicycle composed of dark gray shallow water carbonates with high positive ẟ1³C values (>+10‰) related to the upper part of the Middle Bambuí Excursion (MIBE). We described four outcrops in the center-north of Minas Gerais state (Paraopeba, Curvelo, Montes Claros and Ubaí areas) coupled with ẟ13C and ẟ18O, and SEM-EDS analysis in order to support detailed facies analyses. One seismic line and three well logs in the south part of the Januária High were also used to define the stratigraphic framework of the Lagoa do Jacaré Formation in the Bambuí Foreland Basin system. Eight facies were interpreted from the outcrop data and grouped into five facies associations, that represent peritidal zone (FA1), ooidal sand shoals (FA5), tempestites of mid ramp (FA3), fine-grained carbonate of outer ramp (FA4), and fine-grained siliciclastic from offshore (FA2). The strong presence of terrigenous material (quartz, feldspars, muscovite, biotite, apatite) with some authigenic/diagenetic minerals (pyrite, titanite, rutile) in all facies are the main petrographic aspect of the studied carbonate rocks, related to high sedimentary input and some events during early diagenesis. FA1 with lower mean values of ẟ1³C (+9‰) predominates in the north, meanwhile FA3 is the main association in the south with higher ẟ1³C mean values (+12‰). This difference is probably related to the stratigraphic differences between the basal section (at south) and upper section (at north) of the Lagoa do Jacaré Formation. The Januária High was the main controlling element for the deposition of the carbonate ramp in the north sector of the basin, close to the Ubaí and Montes Claros cities. Probably, this structural high also played an important role as source area in the forebulge sector, uplifted by flexure due to the orogeny of the Brasília and Araçuaí (still in development) Belts (∼540-520 Ma). To the east, a N–S carbonate ramp system was developed in the back-bulge sector according to the main paleocurrents measurements. This ramp is related to a 300 m thickness section of the Lagoa do Jacaré Formation that was firstly identified and correlated to the successions on the surface using well logs, possibly registering at the top the decreasing in the ẟ1³C values, after the main stages of the MIBE probably in close association with Ediacaran-Cambrian boundary, related to the assembling of the Gondwana Supercontinent recorded in this region of southeast Brazil. • The Lagoa do Jacaré Formation (LJF) has more than 300 m of thickness. • The LJF deposited in a homoclinal carbonate ramp in the central Bambuí Basin. • The LJF increase in thickness from Januária High to Montes Claros. • a remarkable assemblage of siliciclastic minerals was first identified in the LJF. • The LJF was deposited in the back-bulge and forebulge of a foreland basin system. [ABSTRACT FROM AUTHOR]

• Middle Bambuí positive δ13C excursion (MIBE) in a restricted basin. • Higher δ13C carb , δ13C org , and δ34S signals during the MIBE. • δ13C carb and 87Sr/86Sr anomalies in the restricted Bambuí Basin. • Methanogenesis in sulfate-depleted oceans during the MIBE. • A heterogeneous biogeochemical landscape during the Ediacaran-Cambrian transition. The Ediacaran-Cambrian Bambuí Group in Brazil records an anomalously positive excursion in carbonate carbon isotopes (δ13C carb) with a sustained plateau of ca. +15‰ (aka the Middle Bambuí Excursion–MIBE). Considering that the δ13C carb signals in Ediacaran-Cambrian seawaters do not typically exceed +6‰, the MIBE therefore represents a profound carbon cycle anomaly in Earth's history. Although intensive studies have been done on the Bambuí Group, origins of the MIBE remain enigmatic. In order to better constrain the biogeochemical carbon and sulfur cycles during the MIBE, high-resolution chemostratigraphic analysis was conducted for both the plateau (i.e., Lagoa do Jacaré Formation) and the recovery part (i.e., lower Serra da Saudade Formation) of the MIBE. Chemostratigraphic profiles reveal remarkably different values in δ13C carb , δ13C org , δ18O carb , and δ34S pyrite between these two studied MIBE intervals. The new data show that the plateau of the MIBE is characterized by coupled higher δ13C carb , higher δ13C org, and higher δ34S pyrite signals compared with the recovery part of the MIBE. Based on multiple lines of sedimentological, geochemical, and model evidence, we propose that the possibilities of enhanced organic carbon burial and porewater methanogenesis are insufficient to explain the MIBE. Instead, local or regional controlling factors, including water-column methanogenesis, low-sulfate conditions, and enhanced carbonate recycling in a restricted basin may have played a role, independently or in unison, in generating this profound positive δ13C carb excursion. Therefore, the MIBE may reflect a regional event, instead of a global carbon cycle anomaly. We caution against the use of the MIBE in chemostratigraphic correlations on a global scale or any other attempt to infer global carbon cycling at that time. The biogeochemical landscape of the late Ediacaran-Cambrian basins and ocean margins may be more heterogeneous than previously thought. [ABSTRACT FROM AUTHOR]

• Extensive new Ba isotopic survey of modern barites. • First Proterozoic Ba isotopic results. • Provides genetic model for enigmatic post-Marinoan barite formation. • Provides evidence for stratified post-Marinoan ocean. • Provides arguments for why barite horizons are confined to Marinoan and not Sturtian or Paleoproterozoic strata. Measurements of triple oxygen isotope ratios in barite horizons within post-Marinoan cap carbonates have provided some of the most compelling evidence that the Marinoan glaciation was a Snowball Earth event. However, the origin of these barite horizons remains unresolved. To constrain the Ba sources, and thus formation mechanisms of these horizons, we analyzed the Ba isotope composition of post-Marinoan barite deposits from Northwest Canada, Northern Norway, Brazil and South China. We augment these analyses with a Ba isotope survey of almost 100 modern and ancient additional barite measurements, including samples from pelagic (or 'marine'), hydrothermal, terrestrial, Proterozoic stratiform and cold seep environments. Unlike modern cold seep or terrestrial barites, we find that globally-distributed post-Marinoan barites exhibit a relatively narrow isotopic range, suggesting a well-mixed, effectively limitless Ba source. Moreover, post-Marinoan deposits exhibit a similar mean Ba isotope composition to modern marine barites, which we interpret as evidence of a marine Ba source. Considered alongside existing geochemical, geological, and new Ba isotope survey data, we conclude that Ba in barite horizons was sourced from a well-mixed, Ba-replete but SO 4 -poor reservoir that accumulated during the Marinoan Snowball Earth interval. This deep Ba reservoir was then transported upward—either by ocean circulation or dolomitization of underlying cap carbonates—and was brought into contact with continental weathering-derived sulfate in a post-glacial meltwater surface layer. Thus, in addition to providing a plausible mechanism for generating globally-synchronous deposition of post-Marinoan barite horizons that reconciles all existing geochemical and geological data, our results demonstrate the utility of Ba isotopes to interrogate the origin of enigmatic barite deposits throughout the sedimentary record. [ABSTRACT FROM AUTHOR]

We apply trace element analysis of syn -sedimentary pyrite to track the redox and nutrient variations in the Ediacaran-Cambrian Bambuí Group of eastern Brazil. Sedimentary pyrite from black shales interleaved within the basal cap carbonate of the 635–600 Ma Pedro Leopoldo Member, deposited in an open marine setting connected to the global sea, preserve high Mo up to >200 ppm, erratic enrichment of micronutrients such as Cu, Ni, Ba, Zn and uniform enrichment of Se. This indicates the importance of oxidative continental weathering and development of an enhanced Redox Sensitive Elements (RSE) dissolved reservoir on the aftermath of the Marinoan glaciation, with atmospheric O 2 levels, calculated from Se/Co ratios of pyrites, around 2.5–3.5 wt%. A shallow oxic layer over deep euxinic realms made possible by high concentrations of dissolved sulfate was probably maintained up to the late Ediacaran, during deposition of the Cloudina-bearing Lagoa Santa Member (585–540 Ma). Upsection, however, radical shifts to muted Mo concentrations and overall low micronutrient concentrations are recorded in the Serra de Santa Helena Formation, with O 2 levels plunging below 1 wt%. This indicates the development of ferruginous bottom water conditions in a sulfate-poor setting, due to restriction of the basin by the encircling Brasiliano mountains that formed Gondwana. The restricted, oxygen-poor and nutrient-depleted conditions caused the demise of complex life forms and hampered the development of typical Ediacaran-Cambrian ecosystems. Basin re-connection might have occurred during deposition of the Lagoa do Jacaré Formation, with independent proxies such as local tidal facies indicating a return to more ventilated conditions in the upper Bambuí Group. Our results highlight the importance of basin restriction and connection over coupled redox-nutrients variations during the development of Ediacaran-Cambrian ecosystems. • Sedimentary pyrite trace element concentrations of the Bambuí Group. • Basin restriction and connection controls coupled redox-nutrients variations. • Radical shifts in nutrient and oxygen levels in the Ediacaran-Cambrian transition. • Redox-nutrient variations control the development of complex life forms. [ABSTRACT FROM AUTHOR]

The Borborema Province of northeast Brazil occupies a strategic position in the central portion of West Gondwana, linking three of its major cratonic constituents: the São Francisco- Congo, Amazon, and West Africa cratons. The southern portion of the province, the Riacho do Pontal fold belt, comprises an association of exhalative rocks with metabasalts having transitional mid-oceanic ridge basalt geochemistry (Monte Orebe Complex) that suggests the preservation of remnants of Neoproterozoic oceanic crust. This view is supported by geophysical data: the Riacho do Pontal fold belt corresponds to the inflexion of a paired positive-negative Bouguer anomaly similar to other Precambrian suture zones. Sm-Nd isotope data for the metabasalts yield a whole-rock isochron age of 819 ± 120 Ma with an initial εNd(t) = +4.4, indicating derivation from a depleted mantle source. The onset of subduction within the Borborema Province (ca. 630 Ma) caused the inversion of basins and obduction of slices of oceanic crust. In this scenario, the Riacho do Pontal fold belt represents a complete late Neoproterozoic plate tectonics cycle involving the collision of the São Francisco craton (lower plate) with the Pernambuco-Alagoas block (upper plate). This interpretation challenges current views that the Borborema Province has acted as a coherent block since Paleoproterozoic time (part of the Atlantica supercontinent), suggesting instead a dynamic setting, where multiple plates interacted during the Proterozoic. The Monte Orebe ophiolite provides a link with other Cryogenian oceanic crust occurrences in central Brazil and West Africa, indicating the preservation of a transcontinental Neoproterozoic suture zone in the heart of West Gondwana. [ABSTRACT FROM AUTHOR]

Abstract: Remnants of a Neoproterozoic glaciation in east central Brazil are represented by thin diamictite layers (Jequitaí Formation and correlative units), locally overlying striated pavements on the São Francisco craton. The diamictites are covered by the Sete Lagoas Formation of the basal Bambuí Group, which is generally accepted to be a typical cap carbonate sequence. Although most authors have preferred a mid-Cryogenian (post-Sturtian) age for it, based mainly on Pb-Pb whole rock data, the Sete Lagoas Formation bears lithostratigraphic and isotopic characteristics that are identical to early Ediacaran cap carbonates worldwide, including a basal thin (0–10m) pale and flinty cap dolostone, preserving a drop in δ13C values from around −3.2‰ to −4.5‰ with associated δ18O around −5‰, and crystal-fan facies interpreted as aragonite pseudomorphs. Ediacaran zircons have been recovered from the middle of the Sete Lagoas Formation, constraining the deposition of its upper half to be younger than 610Ma (). Although there is an unconformity below the point where the zircons were collected, it is short-lived, as suggested by the identical, typically Ediacaran 87Sr/86Sr values above and below (0.7074–0.7076). Carbonate clasts from the Jequitaí Formation and correlative diamictite-bearing units in the fold belts that surround the São Francisco craton (Canabravinha and Serra do Catuni formations) display similar ranges in δ13C (−6.7 to +2.6‰), suggesting the erosion of a pre-glacial carbonate platform with negative δ13C values (i.e. the Islay and/or Trezona anomalies). The cratonic Carrancas Formation, on the other hand, yielded pale dolostone clasts with δ13C in a small range between −4.2 and −3.4‰, and δ18O values around −6.5‰. These clasts could be derived from the cap dolostone unit itself, in which case the Carrancas Formation would represent resedimented basal Sete Lagoas Formation and imply that sections of the Sete Lagoas Formation sitting atop the Carrancas Formation are incomplete. The base-truncated sections have confused previous attempts to correlate the Sete Lagoas Formation with other cap carbonate successions. In light of the available lithostratigraphic, isotopic and U-Pb zircon data, we propose that the Sete Lagoas Formation represents a basal Ediacaran cap carbonate sequence (∼635–610Ma) deposited after the Marinoan glaciation in east central Brazil. [Copyright &y& Elsevier]

Metallogenetic model for the Buritirama Mn-carbonate rocks. [Display omitted] • The dolomitic marbles associated with the Buritirama Formation record a likely marine geochemical signature. • δ13C values of dolomitic marbles are thought to be an expression of the Lomagundi Carbon Isotopic Excursion. • Geochemistry and isotopes data of Mn-Carbonate rocks indicate a multi-stage metallogenetic model involving the manganese marine cycle. The Mn-bearing Buritirama Formation is composed of clastic and chemical metasedimentary rocks representing a Rhyacian platformal basin (ca. 2.18–2.06 Ga) that limits the northern border of the Archean-Paleoproterozoic Carajás domain with the Paleoproterozoic Bacajá domain in the southern Amazon Craton, northern Brazil. The Buritirama Formation is divided into three main stratigraphic units. The Lower and Upper units consist of a basal quartzite followed by carbonate–silicate rocks (marls), dolomitic marbles (dolostone) and minor biotite schist while the Intermediate Unit consists of Mn-carbonate rocks topped by a supergene Mn-oxide deposit (Cenozoic age). These rocks were deformed and metamorphosed during the Transamazonian event (ca. 2.06 Ga). Geochemical data from dolomitic marbles (Lower Unit) exhibit negative Ce anomalies, high Y/Ho ratios (ca. 48) and seawater-like REE + Y patterns that reinforce an open platform setting for the Buritirama basin. Positive δ13C values (+3.2‰ to +5.0‰ V-PDB) for dolomitic marbles are considered to be an expression of the Lomagundi Carbon Isotopic Excursion. The metallogenesis of Mn-carbonate rocks is evaluated based on redox-sensitive trace elements (e.g. Zn and Ni), PAAS-normalized REE + Y patterns and δ13C values (−2.56‰ to +0.15‰ V-PDB) and point out to a classical multi-stage redox-controlled Mn-model involving: i) a primary hydrothermal fluid source related to ocean vents and/or normal faults; ii) microbially-mediated reduction of Mn-oxides particles at the ocean bottom; and iii) reactions between Mn2+ and CO 3 2− (organic matter and seawater related), giving rise to diagenetic Mn-carbonates. The Rhyacian age, Mn deposits, and presence of Lomagundi-like δ13C allows to correlate the Buritirama Formation with the Águas Claras Formation within the Carajás domain further south, thus establishing an important metalliferous event that was up to now largely overlooked within the southern Amazon Craton. [ABSTRACT FROM AUTHOR]

The Serra da Saudade Formation is part of the Bambuí Group, a cratonic cover from the western São Francisco craton. It is composed by siliciclastic sediments deposited in a foreland basin during a transgressive event. The Serra da Saudade Formation is mainly represented by rhythmites, siltstones (locally glauconitic) and rare sandstones. The glauconitic siltstone was deposited during a maximum flooding surface and sediment starvation, which allowed high concentrations of probable volcanic-sourced potassium. The interpretation of the depositional age of the Bambui Group had multiple turnovers in the last decades. Finding and dating synsedimentary volcanic rocks is essential to solve this conundrum. This paper presents the first U-Pb direct dating of the Bambuí Group from zircon grains recovered from a volcaniclastic layer interbedded with glauconitic siltstones from the upper Serra da Saudade Formation. A total of 107 U-Pb ages were obtained by LA-ICP-MS and plotted into a Concordia diagram. The provenance signature comprises a wide range of detrital zircon ages (1.0–2.8 Ga). These data represent inherited zircon grains incorporated into the magma during magmatic activity that produced the volcanic sediment, or to dilution and reworking of volcanic ashes that mixed to fine-grained clastic sediments prior to deposition. A significant amount of 10 highly concordant, prismatic zircon grains clustered into a well constrained age of 520.2 ± 5.3 Ma, which represent the explosive volcanic eruption age, and by extent, the depositional age of the upper Serra da Saudade Formation. Since the currently final thrust stacking ages from the Brasilia Belt and the Araçuaí Belt are dated ca. 600 and 540 Ma, respectively, one must carefully look for the real age of the deformation event that affected the Bambuí Group over the São Francisco craton. Image 1 • Stratigraphy, petrography and geochronology of Serra da Saudade Formation, Bambuí Group. • The glauconitic siltstone was deposited in a foreland basin during low sedimentation rates and related to volcanic processes. • The volcanoclastic layer described in the upper Bambuí Group reveals a sedimentation age of 520.2 ± 5.3 Ma. • The Bambuí Group spanned the Ediacaran-Cambrian boundary and was deformed during the Cambrian Period. [ABSTRACT FROM AUTHOR]