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Esta revisão incorpora novos dados isotópicos e químicos para correlação quimioestratigráfica de sucessões, predominantemente carbonáticas, na América do Sul (Argentina, Bolívia, Brasil, Paraguai e Uruguai). Estas sucessões, depositadas durante eventos de extensão, aparecem como espessos estratos carbonáticos/siliciclásticos em bacias epicontinentais ou foram acumulados sobre margens passivas em bordos de cratons (ex.: São Francisco, Amazonas, Bloco Rio Apa, Pampia e Río de La Plata) como três megasequências: glaciogênica, plataforma marinha carbonática (sobre diamictitos glacio-marinhos) e predominantemente continental siliciclástica. Em cinturões circunjacentes a cratons, sucessões carbonáticas contendo material vulcanoclástico/siliciclástico foram, na maioria dos casos, fortemente deformados. A idade precisa de sedimentação destas sucessões permanece em debate, mas recentes dados paleontológicos e geocronológicos têm consideravelmente restringidos os intervalos de deposição. Neste trabalho, reportamos trends isotópicos de alta resolução de C, O, Sr e S medidos em amostras bem preservadas e usamos principalmente isótopos de Sr e C em consonância com observações litostratigráficas/biostratigráficas, para estabelecer correlações detalhadas destas sucessões. Propor uma correlação quimioestratigráfica entre bacias Neoproterozoicas na América do Sul é o principal objetivo deste trabalho. This report reviews and incorporates new elemental and isotope chemostratigraphic data for correlation of Neoproterozoic carbonate-dominated successions in South America (Argentina, Bolivia, Brazil, Paraguay and Uruguay). These thick mixed carbonate/siliciclastic successions were largely deposited in epicontinental basins or accumulated on passive margins on the edges of cratons (e.g. São Francisco, Amazonia, Rio Apa Block, Pampia and Río de la Plata paleocontinents) during extensional events related to the rifting of the Rodinia Supercontinent. From the stratigraphic point of view, these successions occur as three mega-sequences: glaciogenic, marine carbonate platform (above glaciomarine diamictites or rift successions), and dominantly continental to transitional siliciclastics. In the orogenic belts surrounding cratons, carbonate-dominated successions with important volcanoclastic/siliciclastic contribution have been, in most cases, strongly deformed. The precise ages of these successions remain a matter of debate, but recently new paleontological and geochronological data have considerably constrained depositional intervals. Here, we report high-resolution C, O, Sr, and S isotope trends measured in well-preserved sample sets and mainly use Sr and C isotopes in concert with lithostratigraphic/biostratigraphic observations to provide detailed correlations of these successions. The establishing of a high-level and definite chemostratigraphic correlation between Neoproterozoic basins in South America is the main goal of this work.

Texto completo: acesso restrito. p. 199–213 Submitted by Suelen Reis (suziy.ellen@gmail.com) on 2014-04-10T15:35:52Z No. of bitstreams: 1 1-s2.0-S0301926813003057-main.pdf: 2918680 bytes, checksum: cd12440aba74da3f168db1df211dafbe (MD5) Approved for entry into archive by Rodrigo Meirelles (rodrigomei@ufba.br) on 2014-09-09T14:36:04Z (GMT) No. of bitstreams: 1 1-s2.0-S0301926813003057-main.pdf: 2918680 bytes, checksum: cd12440aba74da3f168db1df211dafbe (MD5) Made available in DSpace on 2014-09-09T14:36:04Z (GMT). No. of bitstreams: 1 1-s2.0-S0301926813003057-main.pdf: 2918680 bytes, checksum: cd12440aba74da3f168db1df211dafbe (MD5) Previous issue date: 2013 A new Re–Os radiometric age date for an organic-rich shale horizon from the Vazante Group in Brazil, coupled with geological observations, provide evidence for late Mesoproterozoic glacial episodes, conflicting with the general view of greenhouse conditions marked by a eustatic high stand at this time. Field observations of a reverse fault juxtaposing older Mesoproterozoic sedimentary rocks above younger Neoproterozoic strata provide a new stratigraphic framework and reconcile the apparent inversion of U–Pb detrital zircon ages through the succession. Combined, the geochronological, geochemical and stratigraphic evidence suggest that the Vazante Group sediments accumulated along a passive margin of the São Francisco craton and are correlative with the neighboring Paranoá Group. Biomarker, sulfur isotope and iron speciation analyses support the interpretation of a strongly stratified water column during post-glacial transgression and deposition of one of the bituminous shale horizons. The relationship of the glaciogenic Vazante Group to other late Mesoproterozoic successions, such as the non-glacial Atar Group in West Africa and Bylot Supergroup in arctic Canada, however, remains enigmatic.

p. 71 - 83 Submitted by Ana Valéria de Jesus Moura (anavaleria_131@hotmail.com) on 2012-01-10T19:18:01Z No. of bitstreams: 1 0895981110000416-main.pdf: 2060599 bytes, checksum: f1ab9079c334ca980deb2aa5bbb75add (MD5) Made available in DSpace on 2012-01-10T19:18:01Z (GMT). No. of bitstreams: 1 0895981110000416-main.pdf: 2060599 bytes, checksum: f1ab9079c334ca980deb2aa5bbb75add (MD5) Previous issue date: 2010 This paper aims at establishing a tectonic and temporal framework to characterize the metallogenic processes that contributed to the origin of the mineral provinces in the northern São Francisco Craton. Many Archean mineralizations (eg. massive sulfide zinc, lead, zinc and copper, besides magnesiteetalc, ironetitaniumevanadium, iron, chromite and manganese) were generated before the assembly of the Craton. Deposits of chromite, nickel, gold and emerald were produced during the Paleoproterozoic orogenic cycle, when the Craton was amalgamated into the Atlantica paleocontinent. An extension event is recorded in the Neoproterozoic, during the breakup of Rodinia, associated with deposits of phosphorite and uranium. Kimberlite diamond and gold mineralization were generated during the Brasiliano orogenic cycle, coeval with the amalgamation of West Gondwana. A long-lasting and rather uniform crustal stress is recorded in the area during the Cambrian period. Resetting of the isotopic and magnetic systems that affected the Neoproterozoic sediments of the Irecê Basin at about 520 Ma was attributed to the regional-scale fluid migration and mineralization in the aftermath of the Brasiliano orogenic cycle.

texto completo: acesso restrito. p. 143–167 Submitted by Suelen Reis (suziy.ellen@gmail.com) on 2014-03-11T13:54:17Z No. of bitstreams: 1 1-s2.0-S0009254106004232-main.pdf: 3815885 bytes, checksum: f5996941265d84fcc0220d7671aa8c16 (MD5) Approved for entry into archive by Rodrigo Meirelles (rodrigomei@ufba.br) on 2014-09-09T16:05:28Z (GMT) No. of bitstreams: 1 1-s2.0-S0009254106004232-main.pdf: 3815885 bytes, checksum: f5996941265d84fcc0220d7671aa8c16 (MD5) Made available in DSpace on 2014-09-09T16:05:28Z (GMT). No. of bitstreams: 1 1-s2.0-S0009254106004232-main.pdf: 3815885 bytes, checksum: f5996941265d84fcc0220d7671aa8c16 (MD5) Previous issue date: 2007 The Neoproterozoic successions of South America largely accumulated during extensional events associated with the breakup of Rodinia. These units are preserved as thick carbonate and siliciclastic strata in epicontinental seaways and shallow marine environments on passive cratonal margins, which have been intensely deformed in mobile belts surrounding the craton. Volcaniclastic and siliciclastic materials are associated with some of the marginal fold belts. Three mega-sequences are represented in the cratonal area: glaciogenic, carbonate and molasse. At least two transgressive-regressive sea level cycles occurred during the evolution of the carbonate mega-sequence, which lies above iron-cemented glacio-marine diamictite of probable Sturtian age. We report high resolution carbon, oxygen, strontium and sulfur isotope trends from analyses of well-preserved sample sets and use principally strontium and carbon isotopes from the best preserved samples in concert with lithostratigraphic and biostratigraphic observations to provide detailed correlations of the South American Neoproterozoic successions. Lead–zinc deposits, some of which with important metal reserves seem to be restricted to the Sturtian carbonate succession and associated with a sequence boundary at the end of the first transgressive–regressive cycle. Phosphate deposits are found in both Sturtian and Varangerian/Marinoan carbonate successions, above glaciogenic sequences.

p.346–361 Submitted by Ana Valéria de Jesus Moura (anavaleria_131@hotmail.com) on 2012-01-13T12:32:35Z No. of bitstreams: 1 S1342937X06001985-main.pdf: 2869794 bytes, checksum: 3ceabc4f60938ee86c2d118b04156918 (MD5) Made available in DSpace on 2012-01-13T12:32:35Z (GMT). No. of bitstreams: 1 S1342937X06001985-main.pdf: 2869794 bytes, checksum: 3ceabc4f60938ee86c2d118b04156918 (MD5) Previous issue date: 2007 The cratonic blocks of South America have been accreted from 2.2 to 1.9 Ga, and all of these blocks have been previously involved in the assembly and breakup of the Paleoproterozoic Atlantica, the Mesoproterozoic to Neoproterozoic Rodinia, and the Neoproterozoic to Phanerozoic West Gondwana continents. Several mineralization phases have sequentially taken place during Atlantica evolution, involving Au, U, Cr, W, and Sn. During Rodinia assembly and breakup and Gondwana formation, the crust-dominated metallogenic processes have been overriding, responsible for several mineral deposits, including Au, Pd, Sn, Ni, Cu, Zn, Mn, Fe, Pb, U, P2O5, Ta, W, Li, Be and precious stones. During Rodinia breakup, epicontinental carbonate-siliciclastic basins were deposited, which host important non-ferrous base metal deposits of Cu–Co and Pb–Zn–Ag in Africa and South America. Isotope Pb–Pb analyses of sulfides from the non-ferrous deposits unambiguously indicate an upper crustal source for the metals. A genetic model for these deposits involves extensional faults driving the circulation of hydrothermal mineralizing fluids from the Archean/Paleoproterozoic basement to the Neoproterozoic sedimentary cover. These relations demonstrate the individuality of metal associations of every sediment-hosted Neoproterozoic base-metal deposit of West Gondwana has been highly influenced by the mineralogical and chemical composition of the underlying igneous and metaigneous rocks.

RESTRITO Submitted by Santiago Fabio (fabio.ssantiago@hotmail.com) on 2012-07-10T15:35:46Z No. of bitstreams: 1 GG.pdf: 1133804 bytes, checksum: ae51a47d0d030047211f4318f71000f0 (MD5) Made available in DSpace on 2012-07-10T15:35:46Z (GMT). No. of bitstreams: 1 GG.pdf: 1133804 bytes, checksum: ae51a47d0d030047211f4318f71000f0 (MD5) Previous issue date: 2006 The Lapa Formation is a thick carbonate sequence (∼900 m) that constitutes the upper part of the Vazante Group on the São Francisco craton, Brazil. It conformably overlies a previously unrecognized glacial diamictite unit of poorly constrained age. The sequence, above the glacial unconformity, consists predominantly of organic-rich shale, subtidal rhythmic dolomicrites and microbialaminites, and intertidal stromatolites. Four boreholes, spanning different depositional settings, were sampled at high-resolution and investigated for their petrographic and chemical criteria to evaluate their degree of preservation. The δ13C and δ18O values of well preserved Lapa carbonate microsamples range from −8.2‰ to 3.3‰ (VPDB) and from −13.6‰ to −0.9‰ (VPDB), respectively. Each of the δ13C profiles of the investigated cores reveals two strong negative excursions of up to 8‰, an event in post-glacial dolomicrites immediately above the glaciogenic unit and a 10 m interval of organic-rich shale, and a second near the top of the sequence associated with a shale interval. Based on the observation of dropstones and sedimentary iron formation in the underlying diamictite, as well as the distinguishable carbon isotope trends, the Lapa Formation is considered as a cap carbonate lithofacies. The age of the Lapa Formation is presently unknown but the least radiogenic 87Sr/86Sr value (∼0.7068), associated with a negative carbon isotope excursion, matches that from the Rasthof Formation in Namiba on the Congo craton, which is radiometrically constrained to be younger than ca. 750 Ma.

p. 263–304 Submitted by Ana Valéria de Jesus Moura (anavaleria_131@hotmail.com) on 2012-01-26T15:59:26Z No. of bitstreams: 1 S016913680500020X-main.pdf: 2085935 bytes, checksum: ca02adfba2f94589150a37f9ca97e874 (MD5) Made available in DSpace on 2012-01-26T15:59:26Z (GMT). No. of bitstreams: 1 S016913680500020X-main.pdf: 2085935 bytes, checksum: ca02adfba2f94589150a37f9ca97e874 (MD5) Previous issue date: 2005 The Proterozoic sediment-hosted Zn–(Pb) sulfide and non-sulfide deposits of the São Francisco Craton, Brazil, are partially syn-diagenetic and epigenetic and were probably formed during extensional events. The majority of the deposits occur within shallow water dolomites. The Pb isotopic data of sulfides are relatively homogeneous for individual deposits and plot above the upper crust evolution curve of the Plumbotectonic model. Some of the deposits are characterized by highly radiogenic lead (206Pb/204Pb ≥ 21) originating from the highly radioactive crust of the São Francisco Craton. Pb and S isotopic data suggest the sources of metal and sulfur for the deposits to be the basement rocks and seawater sulfates in the sediments, respectively. The relatively high temperatures of formation (100 to 250 °C) and moderate salinity (3% to 20% NaCl equiv.) of the primary fluid inclusions in the sphalerite crystals suggest the participation of basinal mineralizing fluids in ore formation. The steep paleo-geothermal gradient generated by the radioactively enriched basement rocks probably assisted in heating up the circulating mineralizing fluids.

Texto completo: acesso restrito. p. 303–329 Submitted by Edileide Reis (leyde-landy@hotmail.com) on 2014-02-05T14:23:11Z No. of bitstreams: 1 Aroldo Misi.pdf: 1475684 bytes, checksum: 2cf690d3f8ad6bc11020176429d6cd67 (MD5) Approved for entry into archive by Rodrigo Meirelles (rodrigomei@ufba.br) on 2015-10-09T18:46:34Z (GMT) No. of bitstreams: 1 Aroldo Misi.pdf: 1475684 bytes, checksum: 2cf690d3f8ad6bc11020176429d6cd67 (MD5) Made available in DSpace on 2015-10-09T18:46:34Z (GMT). No. of bitstreams: 1 Aroldo Misi.pdf: 1475684 bytes, checksum: 2cf690d3f8ad6bc11020176429d6cd67 (MD5) Previous issue date: 2001 The Vazante Formation consists of approximately 1700 m of mainly microbial mats and stromatolitic reefal lenses that were deposited on shallow marine platform and have been entirely dolomitized. Samples representing different dolomite generations were taken from three boreholes covering the entire spectrum of the Vazante carbonates. Dolomites can be classified, based on petrography and geochemistry, into four generations ranging in crystal size between ∼4 μm (almost micritic) and 3 mm and occurring as both replacements and cements. The Sr/Ca molar ratios, calculated for the dolomitizing fluid (0.0006–0.0138), suggest a contribution from a non-marine, possibly meteoric, water component. The δ18O and δ13C values vary from −0.1 to −14.3‰ (PDB) and 0.2 to −2.3‰ (PDB), respectively. Fluid-inclusion study suggests that dolomitization must have commenced at a temperature lower than about 50 °C. A mixing-zone model of dolomitization for Dolomites I–III satisfies the constraints from elemental chemistry, δ18O, 87Sr/86Sr and fluid inclusions. The petrographic and chemical criteria of the latest generation, Dolomite IV, reflect conditions of deep burial environment at temperatures above 120–130 °C. The δ13C values show only small variations at the base of the formation, followed by a major negative plunge (∼4‰) at the top, this plunge correlated with the Sturtian glacial phase. In contrast to C-isotopes, only few samples may have retained their near-primary 87Sr/86Sr values of 0.70614–0.70734. The lowest 87Sr/86Sr value (0.70614), from fibrous cement in the upper part of the formation, correlates with the negative δ13C shift and is also consistent with the Sr-isotope signature proposed for the glacial Sturtian seawater. The δ34S values, obtained from sulfates trapped in carbonates, range between 10.8 and 16.9‰ with a jump to 21.3‰ in the overlying formation. All isotope signals are within the range suggested for the early Neoproterozoic seawater, but the Precambrian baseline is poorly known and additional work is required to confirm this tentative assignment.

p. 302-305 Submitted by Ana Valéria de Jesus Moura (anavaleria_131@hotmail.com) on 2011-09-09T13:12:28Z No. of bitstreams: 1 10647-35962-1-PB.pdf: 2214213 bytes, checksum: 33ee842d48602ada35981ac07a2c8305 (MD5) Made available in DSpace on 2011-09-09T13:12:28Z (GMT). No. of bitstreams: 1 10647-35962-1-PB.pdf: 2214213 bytes, checksum: 33ee842d48602ada35981ac07a2c8305 (MD5) Previous issue date: 2000-06 ntegrated studies carried out on the Proterozoic sediment-hosted Pb-Zn sulfide deposits of the São Francisco Craton, Brazil, allowed the estimation of (1) ages of the host sequences, (2) timing of mineralization, (3) possible sources of met al and sulfur, (4) temperature and salinity range of mineralizing solutions, (5) sources of fluids and (6) possible mechanisms of fluid flow. Contrary to the deposits from other Proterozoic basins, the Brazilian deposits do not contain world class met al reserves. This can probably be attributed to the lack of sufficient investments in exploration and mining development research activities. However, the sulfide deposits of the São Francisco Craton do share several important geological, structural, isotopic and fluid characteristics with some of the giant deposit types. Using these data we develop a more realistic met allogenic model for the Proterozoic sediment-hosted Pb-Zn sulfide deposits.

p. 315-317 Submitted by Ana Valéria de Jesus Moura (anavaleria_131@hotmail.com) on 2011-09-09T13:25:35Z No. of bitstreams: 1 10650-35965-1-PB.pdf: 648069 bytes, checksum: fded09c47a370c7fd708ee275dd10069 (MD5) Made available in DSpace on 2011-09-09T13:25:35Z (GMT). No. of bitstreams: 1 10650-35965-1-PB.pdf: 648069 bytes, checksum: fded09c47a370c7fd708ee275dd10069 (MD5) Previous issue date: 2000-06 The Pb-Zn (Ag) mineralizations of Nova Redenção, Una-Utinga Basin, are hosted by dolarenites, dolomicrites and siliceousferruginous breccias of the Salitre Formation, Una Group. An ore reserve of about 2.5 Mt, with average grade of 6,1% Pb, 0,5% Zn, 32 ppm Ag and 10 ppm of Cd has been estimated by Companhia de Pesquisa de Recursos Minerais (CPRM) in the main sector of the deposit. The mineralization is composed mainly of galena and sphalerite, which occur in different ways (disseminated, stratabound, oolith and brecciacement, filling stilolytes/pockets, and veins). The orebodies are directly associated with N50°W trending regional fractures and faults, which are thought to represent deep basement structures reactivated during and after the Neoproterozoic carbonate basin sedimentation. Relationships between sulfides and the shallow sedimentation facies are striking. Several evidences of early-formed sulfates have been observed, including length-slow or lutecite-type microcrystalline quartz, aggregates of quartz with gypsum structure, microcrystalline pseudo-fibrous silica nodules, indicating both a lithostratigraphic and a sedimentary facies control. The study of primary fluid inclusions in sphalerites contemporaneous to galena showed the presence of moderate to high (around 24.3wt% eq. NaCl) aqueous solutions, containing Ca, K and Mg salts. The homogenization temperatures (TH) have a mean value of 185°C. Previous sulfur isotopic studies (d34S) (Misi et al. 1999) in cogenetic galenasphalerite pairs also indicated temperatures in the range 140°-180°C. Sulfur isotopic data in sulfides and sulfates suggested that sulfur was derived from seawater, possibly by thermochemical reduction (Misi et al. 1999). The characteristics of the mineralization along with the obtained fluid inclusion and isotopic data permit to suggest the following met allogenic model for the Nova Redenfao deposit: high concentration of met al brines have migrated throughout deep reactivated structures of the basement, forming sulfides by thermochemical reduction of sulfur present in the basin. The stratigraphic and sedimentary facies control is indicated by the presence of sulfates formed probably by sea-water evaporation in shallow zones of sedimentation.

p. 47-65 Submitted by Ana Valéria de Jesus Moura (anavaleria_131@hotmail.com) on 2012-01-23T17:15:44Z No. of bitstreams: 1 S1342937X0570126X-main.pdf: 1967218 bytes, checksum: 7266d6bc53bafa83043e421d29708a29 (MD5) Made available in DSpace on 2012-01-23T17:15:44Z (GMT). No. of bitstreams: 1 S1342937X0570126X-main.pdf: 1967218 bytes, checksum: 7266d6bc53bafa83043e421d29708a29 (MD5) Previous issue date: 1999 Integrated studies of seven Proterozoic sediment-hosted, Pb-211-Ag sulfide deposits of Brazil, permit the estimation of the age of the hosting sequence and the mineralization, the nature of the sulfur and metal sources, the temperature range of sulfide formation and the environment of deposition. These deposits can be classified into three groups, according to their ages. (a) Archean to Paleoproterozoic: the Boquira deposit, in Bahia state, consists of stratiform massive and disseminated sulfides hosted by parametamorphic sequences of grunnerite-cummingtonite+magnetite that represent a silicate facies of the Boquira Formation (BF). Lead isotope data of galena samples indicate a time Span between 2.7 and 2.5 Ga for ore formation, in agreement with the stratigraphic position of the BE The relatively heavy sulfur isotope compositions for the disseminated and stratiform sulfides (+8.3 to +12.8 %O CDT)suggest a sedimentary source for the sulfur. (b) Paleo to Mesoproterozoic: stratiform and stratabound sulfides in association with growth faults are present in the Canoas mine (Ribeira, in Parana state) and in the Caboclo mineralization (Bahia state). They are hosted by calcsilicates and amphibolites in the Canoas deposit, whereas in the Caboclo area the mineralization is associated with hydrothermally altered dolarenites at the base of the 1.2 Ga Caboclo Formation. The interpreted Pb-Pb age of the Canoas mineralization is coeval with the 1.7 Ga host rocks. Sulfur isotopic data for Canoas sulfides (+1.2 to +16 %O CDT) suggest a sea water source for the sulfur. The range between -21.1 and +8.8 %O CDT for the Caboclo sulfides could suggest the action of bacterial reduction of seawater sulfates, but this interpretation is not conclusive. (c) Neoproterozoic: stratiform and stratabound sulfide deposits formed during the complex diagenetic history of the host carbonate rocks from tlieMorro Agudo (Bambui Group), Ired and Nova RedenCIo (Una Group), yield heavy sulfur isotope values (+18.9 to +39.4 %O CDT). The uniform heavy isotope composition of the barites from these deposits (+25.1 to +40.9 %a) reflect their origin from Neoproterozoic seawater sulfates. The latestage, and most important, metallic concentrations represent sulfur scavenged from pre-existing sulfides or from direct reduction of evaporitic sulfate minerals. Lead isotope data from the Bambui Group suggest focused fluid circulation from diverse Proterozoic sediment sources, that probably was responsible for metal transport to the site of sulfide precipitation. (d) Late Proterozoic to Early Paleozoic: lead-zinc sulfides (+pyrite and chalcopyrite) of Santa Maria deposits, in Rio Grande do Sul, form the matrix of arkosic sandstones and conglomerates, and are closely associated with regional faults forming graben structures. Intermediate volcanic rocks are intercalated with the basal siliciclastic members. Lead isotope age of the mineralization (0.59 Ga) is coeval with the host rocks. Sulfur isotopic values between -3.6 and +4.1 are compatible with a deep source for the sulfur.

Texto completo: acesso restrito. p.87–100 Submitted by Suelen Reis (suelen_suzane@hotmail.com) on 2013-01-30T14:23:23Z No. of bitstreams: 1 Misi.pdf: 2104937 bytes, checksum: dae3326343dfa94be452f0114d8265ec (MD5) Made available in DSpace on 2013-01-30T14:23:23Z (GMT). No. of bitstreams: 1 Misi.pdf: 2104937 bytes, checksum: dae3326343dfa94be452f0114d8265ec (MD5) Previous issue date: 1998 The Una Group, Irecê Basin (Bahia state) is correlative with the better known Bambuí Group of the São Francisco Basin (Minas Gerais state); these basins are remnants of widespread carbonate platform that covers > 300 000 km2 of the São Francisco Craton in Brazil. The Irecê area contains a well-controlled stratigraphic succession hosting economic phosphate deposits and sulfide mineralization. Una Group strata comprise a basal siliciclastic sequence, mostly composed of glacial diamictites (Bebedouro Formation), followed by a carbonate succession that is several hundred meters thick, the Salitre Formation. An angular unconformity separates the two units. The carbonates of the Salitre Formation are characterized by 87Sr/86Sr ratios ranging between 0.70745 and 0.71776, and δ13C values ranging between −4.4 and +9.4‰ PDB. The carbonates also contain beds and nodules of barite and gypsum with highly positive δ34S values (+25.2 to +32.8‰ CDT). The ‘best preserved’ carbonate samples selected on the basis of their Mn and Sr concentrations as well as their ratios, yield 87Sr/86Sr values of 0.70745–0.70765. Comparison of these values with the secular strontium isotopic curve for the Neoproterozoic seawater suggests a 600 (to 670) Ma age for the Salitre Formation and for its correlative units in the São Francisco Basin.