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The provenance of Middle Jurassic-Cretaceous sedimentary rocks deposited in the southern Peruvian Arequipa Basin has been investigated based on the measurement of 41 Sr-Sm-Nd isotopic compositions of sedimentary rocks, 993 U-Pb zircons ages, and 202 Lu-Hf zircon isotope data. The Middle Jurassic units are dominated by Brazilian/Pampean and Grenville/Sunsas and have juvenile to evolved Hf isotopic compositions of Permian zircons. These are consistent with an Eastern Cordillera (EC) provenance. In contrast, the Late Jurassic Labra Formation presents the first appearance of Triassic-Jurassic zircons and an increase in Famatinian zircons thus suggesting a mixed provenance from the EC and/or Altiplano and the Coastal Cordillera (CC). The Gramadal Formation shows older U-Pb zircon ages, which reflect a major contribution from Precambrian sources either from the Amazon craton or the EC thus implying a change in provenance. Another change in provenance is documented for the Hualhuani Formation with sources located both in the CC and EC. Finally, the Santonian Chilcane Formation is characterized by a large contribution of Cretaceous to Famatinian zircons indicating that it was mainly sourced from the CC. Our provenance dataset associated with the depositional setting of the Middle Jurassic to Early Cretaceous formations and the cumulative curves of zircon age distribution, indicate that the Arequipa Basin was not a back-arc setting but rather a rift-like setting. Contrary to the older formations, the Chilcane Formation is dominated by contributions from the CC in a retroarc foreland basin setting. This statement further implies that the Andean basin located eastward of the volcanic arc had evolved directly from a rift to a retroarc foreland basin and implies that the control of Andean subduction on these basins might be much younger than previously thought.

Amazonian Dark Earths (ADEs) are unusually fertile soils characterised by elevated concentrations of microscopic charcoal particles, which confer their distinctive colouration. Frequent occurrences of pre-Columbian artefacts at ADE sites led to their ubiquitous classification as Anthrosols (soils of anthropic origin). However, it remains unclear how indigenous peoples created areas of high fertility in one of the most nutrient-impoverished environments on Earth. Here, we report new data from a well-studied ADE site in the Brazilian Amazon, which compel us to reconsider its anthropic origin. The amounts of phosphorus and calcium—two of the least abundant macronutrients in the region—are orders of magnitude higher in ADE profiles than in the surrounding soil. The elevated levels of phosphorus and calcium, which are often interpreted as evidence of human activity at other sites, correlate spatially with trace elements that indicate exogenous mineral sources rather than in situ deposition. Stable isotope ratios of neodymium, strontium, and radiocarbon activity of microcharcoal particles also indicate exogenous inputs from alluvial deposition of carbon and mineral elements to ADE profiles, beginning several thousands of years before the earliest evidence of soil management for plant cultivation in the region. Our data suggest that indigenous peoples harnessed natural processes of landscape formation, which led to the unique properties of ADEs, but were not responsible for their genesis. If corroborated elsewhere, this hypothesis would transform our understanding of human influence in Amazonia, opening new frontiers for the sustainable use of tropical landscapes going forward., Amazonian Dark Earth is soil that has had mysteriously high fertility since ancient times, despite the fact that surrounding soils have very low nutrients. Here the authors’ use of isotope reconstructions indicate that these soils predate human settlement and could have alluvial and burning origins.

International audience; Currently, marsupials (modern members of the Metatheria clade) are widely distributed in tropical and subtropical areas of South America, but poorly represented in the fossil record of these regions. Except for the species-rich fossiliferous localities of La Venta in Colombia, additional Miocene metatherians from tropical, equatorial South America are sparsely reported in Bolivia, Brazil, Peru, and Venezuela. Here, we introduce new metatherian remains recovered from the late middle Miocene locality of TAR-31, San Martín Department, Peru, which has been assigned to the Laventan South American Land Mammal Age (~13 Ma) by mammalian biostratigraphy. Three metatherian taxa are recognized at TAR-31: the didelphid didelphimorph ‘Thylamys’ cf. ‘T.’ colombianus, and the paucituberculatans aff. Palaeothentes and Pitheculites ipururensis sp. nov. This assemblage and the presence of a cebid primate at TAR-31 suggests predominantly humid and warm tropical conditions, with the occurrence of both forests and drier habitats in the surroundings. Comparisons with other Miocene metatherian assemblages at low and mid latitudes of South America clearly confirm close relationships between TAR-31 and La Venta (agreeing with observations based on monkeys and rodents), as well as, to a lesser extent, with Acre River local faunas and Madre de Dios (MD-67) in Brazil and Peru, respectively. The current results support the hypothesis that Western Amazonia was a single and consistent biogeographical region for land mammals over middle Miocene times, at the western edge of the Pebas Mega-Wetland System, and highlight the role of the Amazonian region concerning marsupial Neogene radiation. U-Pb analysis made on detrital zircon grains from TAR-31 gave a maximum depositional age of 17.4 ± 0.12 Ma (i.e., 4 Ma older than the biostratigraphical age), with a mixed detrital source likely comprising Precambrian (Western Amazon Craton), Neoproterozoic (Neoproterozoic mobile belts), and Phanerozoic rocks (Andes).

The Verde River basin covers several municipalities that belong to the Brazilian state of Mato Grosso do Sul. Its source begins at about 500 m of elevation, as does its main tributary, the São Domingos River. Dozens of smaller tributaries flow into the Verde River before it joins the Paraná River at an altitude of 260 m. Sedimentary rocks, such as sandstone, dominate the local geology; however, igneous rocks, such as basalt, are also found. The weather is governed by two seasons, dry (April-September) and wet (October-March).The Verde River has undergone anthropogenic changes due to cattle farming, agriculture and, in the last decade, due to dams. Currently, there are three hydroelectric dams in the middle of the basin (Verde 4A, Verde4 and São Domingos) that compartmentalize the habitat and block the migratory paths of the local ichthyofauna.This study analyzes the relationship between the local geochemistry, indicated by the isotopic ratio in water samples (N=52), and the isotopic ratio in fish otoliths (aragonite structure) in hundreds of specimens of different species. Isotopic analysis of otoliths is recognized in scientific literature as a tool that can provide information about the geographic range of fish in their environment.The chemical analyses were performed using LA-ICP mass spectrometers (Neptune XT HR-Thermo) in the raster mode setting to track strontium levels from the core to the edge of each otolith. The 87Sr/86Sr ratio in the water samples was always higher than 0.71; however, some sections of the basin have exceeded the isotopic ratio with values over 0.72, for example, the very first segment of the upper Verde River (0.7260), the upper and lower São Domingos River (0.7272), the Verde River after receiving water from São Domingos River, and most tributaries of the lower Verde River basin. Both the Paraná River and the middle Verde River, upstream of the São Domingos reservoir, had 87Sr/86Sr ratios of below 0.72, the latter section being where we caught most of the fish.The results for 87Sr/86Sr obtained on the edge of the otolith showed consistent correspondence to the values in the water of the sites where the fish were captured. This indicates that the isotopic proportions of strontium obtained in otoliths all the way from the core to the edge must be related to the environments in which the animals grew up, which is the basis for tracing the individual spatial range. Supported by this correlation, we are now analyzing the potential, the previous (in the fish lifespan scale) and the current migratory and dispersal paths for the ichthyofauna. Considering all points, we expect that our results will contribute to a better understanding and management of the regional migratory ichthyofauna in the future.

The syn-orogenic Miocene deposits of the Patagonian Foreland System were the focus of numerous works in the latest years, due to their central role in the comprehension of the tectono-stratigraphy and tectonic evolution related to the Patagonian Andean growth. In this work we present a chronostratigraphic scheme based on magnetostratigraphy and U[sbnd]Pb geochronology for one of the syn-orogenic successions of the Patagonian Foreland System: the Paso del Sapo Basin. The sequence is constrained to an age of >14.9 to 14.9–14.6 Ma for the basal alluvial systems of La Pava Formation, with mean sedimentation rates of 4.2 cm/kyr; of 14.6 to 12.8–12.7 Ma for the lacustrine - deltaic environments of the lower Collón Cura Formation, with sedimentation rates ranging from 1.6 to 26.0 cm/kyr; and of 12.8–12.7 to 14.9 to

The development of analytical tools to determine the origin of fishes is useful to better understand patterns of habitat use and to monitor, manage, and control fisheries, including certification of food origin. The application of isotopic analyses to study calcified structures of fishes (scales, vertebrae, and otoliths) may provide robust information about the fish geographic origin and environmental living conditions. In this study, we used Sr and C isotopic markers recorded in otoliths of wild and farmed commercialized pirarucu (Arapaima spp.) to evaluate their prediction potential to trace the fishes origin. Wild and farmed fish specimens, as well as food used for feeding pirarucu in captivity, were collected from different sites. Isotope composition of otoliths performed by isotope-ratio mass spectrometry (IRMS; δ13C) and femtosecond laser ablation multi-collector inductively coupled plasma mass spectrometry (LAfs-MC-ICPMS; 87Sr∕86Sr) were compared to the isotopic composition of water and of the food given to the fishes in the farms. Wild fish specimens that lived in environments with the largest fluctuation of river water Sr isotope ratios over time presented the largest Sr isotope variations in otoliths. A quadratic discriminant analysis on otolith isotopic composition provided 58 % of correct classification for fish production (wild and farmed) and 76 % of correct classification for the fish region. Classification accuracy for region varied between 100 % and 29 % for the Madeira and the Lower Amazon fishes, respectively. Overall, this preliminary trial is not yet fully developed to be applied as a commercial traceability tool. However, given the importance of Arapaima spp. for food security and the generation of economic resources for millions of people in the Amazon basin, further analyses are needed to increase the discrimination performance of these biogeographical tags.

Karst processes are of primary importance for the generation of secondary porosity and permeability in carbonate reservoirs and aquifers. The topic investigated in this study are the effects of the facies and stratigraphy of different layers on the vertical distribution of solution cavities formed by hypogenic fluids in a carbonate sequence. This work uses the Toca da Boa Vista (TBV) and Toca da Barriguda (TBR) caves as analogues of carbonate reservoirs that are affected by karst processes. These are two different caves that are 400 m apart but exhibit the same geological characteristics and occur in the Neoproterozoic Salitre Formation (700-560 Ma), Sao Francisco Craton, Brazil. These caves form the longest cave system in South America, with conduits of lengths ∼107 km (TBV) and ∼34 km (TBR). Previous studies of these caves indicated their hypogene origins. These caves developed by an ascending fluid flow, mainly along fractures. The fluid then flowed laterally and was influenced by the following five stratigraphic units, from the bottom to the top: (1) cross-bedded oolitic grainstone, (2) fine grainstone with chert nodules, (3) microbial carbonate, (4) interbedded fine siliciclastics and marls, and (5) crystalline grainstone interfingered with chert layers. Units 4 and 5 formed a stratigraphic seal. Units 1, 2, and 3 below the seal supported the lateral redistribution of flow and respective conduit development. Therefore, these units exhibit a high degree of karstification. Veins related to the first fluid phases that compose a hydrothermal mineral assemblage cut across these units. We conclude that stratigraphic control is important for determining the architecture of the hypogenic cave system at the local scale.

International audience; Since 2012, we have investigated a stratigraphic section encompassing the late Eocene–earliest Oligocene interval at Shapaja (Tarapoto area, Peruvian Amazonia, ca. 7°S), through paleontological and geological fieldwork. The measured sedimentary series (120 m-thick [West] plus 90 m-thick [East]), assigned to the upper member of the Pozo Formation, records fluvial micro-conglomeratic lenses intercalated with floodplain and evaporite-rich fine red deposits, estuarine/coastal-plain tidally-influenced fine sandstones, and oxbow lake nodule-rich blue clays. This sedimentary shift coincides locally with the demise of the large Eocene coastal-plain wetland known as Pozo System. The late Eocene–early Oligocene Shapaja section was extensively sampled for chemostratigraphy (δ13C on dispersed organic matter and pedogenic carbonate nodules), which in turn allowed for refining the location of the Eocene-Oligocene Transition (EOT) and other climatic events recognized at a global scale (i.e., Oi-1 and Oi-1a). The section has yielded nine fossil localities with plant remains (leaves, wood, charophytes, and palynomorphs), mollusks, decapods, and/or vertebrates (selachians, actinopterygians, lungfishes, amphibians, sauropsids, and mammals), documenting ~130 distinct taxa. Four localities of the upper member of the Pozo Formation at Shapaja predate the EOT, one is clearly within the EOT, while four are earliest/early Oligocene in age. The small leaf impressions found along the Shapaja section could be indicative of dry and/or seasonal conditions for this region throughout and after the EOT. Monkeys, indicative of tropical rainforest environments, are only recorded in a latest Eocene locality (TAR-21). Two biotic turnovers are perceptible in the selachian, metatherian, and rodent communities, well before the EOT [~35–36 Ma] and a few hundred thousand years after the EOT [~33 Ma]. The latter turnover seems to be primarily related to a global sea-level drop (ichthyofauna: marine-littoral elements replaced by obligate freshwater taxa) and/or the onset of a drier and more seasonal climate in early Oligocene times (terrestrial components). Changes in the structure of the Shapaja paleocommunities were mostly driven by the flexural subsidence during the late Eocene, and then globally driven by the earliest Oligocene climatic deterioration.

The initial infill of the Patagonian Broken Foreland is related to Miocene, syn-orogenic, volcaniclastic successions accommodated in intermontane basins. In the last years several works have paid attention to these successions due to their role in the comprehension of the timing of deformation, the relationship between arc volcanism and the environmental signals, and the climate changes related to the growth of the orogen. In this paper we perform the U-Pb geochronology and the sedimentologic and paleosols analyses of a Miocene, synorogenic, volcaniclastic succession (La Pava Formation) located at the northern part of Patagonian Broken Foreland. The results indicate that the syn-kinematic sedimentation (evidenced by growth strata and progressive unconformities) proceeded between ~19 Ma to ~14 Ma, associated with arc-derived volcaniclastic deposits, under alluvial conditions with profuse paleosols development. The facies analysis combined with the paleosols and provenance studies indicate episodic and cyclic supply of pyroclastic materials, which were mainly deliveredfrom the catchment area of the system, affected by explosive volcanism. A succession of stacked paleosols was recorded into 3 sections, bounded by unconformities, which record from Alfisols-like, Vertisol-like to Andisolslikepaleosols. Paleosols variations were related to the effects of tectonic events, climate changes or to the increase of volcanic supply in comparison to soil-forming processes. The results obtained in this work are considered substantial to unravel the tectonic, volcanic and paleoclimatic framework of the North Patagonian Andes. Fil: D'Elia, Leandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; Argentina Fil: Bilmes, Andrés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto Patagónico de Geología y Paleontología; Argentina Fil: Varela, Augusto Nicolás. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; Argentina Fil: Bucher, Joaquin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; Argentina Fil: López, Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; Argentina Fil: García, Micaela Romina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; Argentina Fil: Ventura Santos, Roberto. Universidade Do Brasilia. Instituto de Geociencias; Brasil Fil: Hauser, Natalia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidade Do Brasilia. Instituto de Geociencias; Brasil Fil: Naipauer, Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geocronología y Geología Isotópica. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geocronología y Geología Isotópica; Argentina Fil: Sato, Ana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; Argentina Fil: Franzese, Juan Rafael. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Geológicas. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Centro de Investigaciones Geológicas; Argentina

A simple and quick method for simultaneous purification of Cu, Zn and Mo and accurate and precise measurement of their isotopic composition in geological samples using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) has been developed. The method involves the use of a single chromatographic column filled with the anion exchange resin AG-MP-1 for complex matrix removal and further purification of these three elements. The external standard-sample-standard bracketing (SSB) procedure combined to internal standard addition was used for accurate mass bias correction and precise Cu, Zn and Mo isotopic ratio measurements. The method was applied to different geological materials, as granodiorite (GSP 2-USGS), limestone (JLS-1, Japan), Buffalo River Sediments (NIST SRM - 8704) and sediments from Amazon River Basin. The mean precision for these samples was: 0.08 ‰ for δ65/63Cu; 0.05 ‰ for δ66/67Zn and 0.04 ‰ for δ98/95Mo. The main advantage is that the proposed method is simple and rapid, and carries out the quantitative recovery of elements of different atomic masses and at very low concentration ranges, mainly for Mo. In addition, optimizations made the calibration and correction of instrumental mass bias easier, leading to consistent results with other methods that are currently published. The comparison of isotopic compositions of Cu and Mo obtained for granodiorite with respect to data reported in the literature demonstrate that the simpler and multi-element method developed in this study can be properly used within the required limits of accuracy as a multi-proxy tool in isotope geochemistry.

International audience; The northern part of South America has undergone several major changes in its tectonic setting since the Triassic, evolving from rifting to the development of a retroarc-foreland basin on its Andean margin, leading to margin extension and continental uplift following the breakup between Africa and South America. So far, it is unclear when and how these geodynamic events affected the paleo-Amazonian drainage. In this study, we investigate the provenance of Triassic–Eocene sedimentary rocks deposited in the northern Peruvian Amazonian basin, based on their Sr-Nd isotopic compositions and U-Pb zircon dating. The Triassic–Jurassic samples have εNd(0) values ranging from −7.9 to −10.0 and main U-Pb zircon peaks at 0.9–1.3 Ga (31–33%) and 0.5–0.7 Ga (21–28%) that suggest a mixed clastic supply from the Western and Eastern Cordillera or craton within a rift to post rift setting. Samples from the Albian–Maastrichtian interval yield much lower εNd(0) values (−16.8 to −18.6) and a dominance of zircon grains derived from terranes in the easternmost Brazilian Shield (Ventuari-Tapajos (2.0–1.82 Ga), Rio Negro-Jurena (1.82–1.54 Ga) and Rondonia San Ignacio (1.54–1.3 Ga), thus indicating a cratonic source for these sedimentary rocks. Finally, the early Paleocene–Eocene sedimentary rocks record the first arrival of Andean detritus in the Amazonian retroarc foreland, with εNd(0) values ranging between −5.6 to −12.0 and up to 16% of the zircon grains yielding ages younger than 120 Ma. Together with recently published studies, these provenance data document the existence of a long-lived Aptian–Maastrichtian continent-wide cratonic drainage in the northern part of South America. This cratonic drainage developed in response to the late Cretaceous uplift of the northeastern part of the South America craton likely driven by geodynamic processes related to post rift opening of the Atlantic Equatorial Ocean. The formation of a late Maastrichtian–early Paleocene mountain chain in the Peruvian Andes associated with the onset of provenance from the Andean orogenic belt led to a shift of the Amazon drainage pattern. Hence, the earliest Andean-Amazonian rivers are no younger than late Maastrichtian-early Paleocene.

Morro Agudo is the largest known Mississippi-Valley Type deposit (MVT) in Brazil with original estimated reserves of 18.3 Mt @ 5.08% Zn and 1.75% Pb of which 3.92 Mt@ 4% Zn and 1.45% Pb remained in 2017. In spite of having been mined for more than 30 years, a comprehensive study of Morro Agudo metallogenic features was still lacking in the international literature. This deposit is hosted within the 250 km long Vazante Sequence, a N-S-trending Mesoproterozoic-Neoproterozoic carbonate-dominant sedimentary sequence thrusted over Neoproterozoic rocks during the Brasiliano Orogeny. Sulfide bodies in Morro Agudo are restricted to the Morro do Calcario Formation as a 1300 m long ore envelope averaging 9 m thick, comprising stacked up stratabound orebodies that thin out down dip and are limited to the NE by the Main Fault. Five orebodies are described: (a) Breccia-hosted orebody “GHI”, (b) Sphalerite-rich doloarenite orebody “JK”, (c) Galena-rich doloarenite orebody “L”; (d) Lower replaced stratiform orebody “M”; (e) Upper replaced stratiform orebody “N”. Comparison of these orebodies reveals mineral zonation patterns and variations in Zn-Pb grade consistent with sulfide textural relationships. These relationships indicate five mineralization styles that provide spatial and timing constraints for Morro Agudo; (a) Stratiform sulfides, (b) Massive Ore, (c) Laminated Ore, (d) Breccia-hosted Ore, (e) Late stage fracture-filling Ore. Carbon and oxygen stable isotope data for each mineralization style shows a pattern of mixing of signatures of mineralizing fluids and barren host rocks and supports our interpretation that these mineralization styles occurred in more than one stage of ore formation. The ore was later offset by a set of strike slip normal faults associated with compression related to the Brasiliano Orogeny, of which the Main Fault (Falha Principal) is the most important because it limits the deposit to the NE. Previous interpretation of upper orebodies as part of a SEDEX system is revisited in the present work. In our model, data used to support a syngenetic origin for Morro Agudo, such as synsedimentary structures, Pb isotopes in sulfides and fluid inclusion data indicate a younger, barren generation of sulfides deposited long before Zn-Pb mineralization, during sedimentation of the Morro do Calcario Formation in the Mesoproterozoic. These early sulfides were preserved in cherts and as massive pyrite beds that were later overprinted by sphalerite and galena. Overprinting thus mixed Meso and Neoproterozoic Pb isotopic sources and led to a long standing argument over whether the Morro Agudo ores were syngenetic or epigenetic. This interpretation is also in agreement with the current classification of the Vazante Sequence as containing imbricated Neoproterozoic and Mesoproterozoic sedimentary rocks. Based on our work of sulfide textural relationships, stable isotopes, whole-rock geochemistry and previously published data, we argue that Morro Agudo ores formed by at least two stages of percolation of mildly hot hydrothermal fluid in the Neoproterozoic. The primary reason for sulfide precipitation is interpreted to be mixing of mildly-hot, metal-bearing basinal brines and seawater/connate waters.

Carbonates of the Salitre Formation, Irece Basin, Brazil, have been the focus of extensive stratigraphic and structural studies for several decades. Besides hosting phosphorites deposits, these rocks are analogues to fractured and certified oil reservoirs, such as those of the Cretaceous pre-salt oil system offshore Brazil. The present study presents an integration of X-Ray Diffraction (XRD), Quantitative Evaluation of Minerals by Scanning Electron Microscopy (QEMScan), Optical Petrography, Cathodoluminescence (CL), and Charge Contrast Imaging (CCI) data that allows a high-resolution characterization of the mineralogy within the carbonate units. In addition, we also present carbon and oxygen stable isotope data to identify possible origins of the associated fluids. The mineral characterization revealed that calcite (50–70%), quartz (20–30%) and dolomite (10–20%) are the main post-sedimentary mineral phases found in veins, vesicle structures and cement of the carbonate units. The mineral phases of veins were formed by the interaction with hydrothermal fluids, which had an important role in the dissolution, karstification, and remobilization of carbonate units. Isotopic analysis shows that δ13C and δ18O are more negative in veins and vesicles when compared to host rock, indicating that there is no effective isotopic exchange between the host rock and the filled structures and that these structures were filled with hydrothermal fluids from an external source.

Dental anthropological data may provide valuable information about an individual's life, including age at death, health, signs of violence, ancestry, diet features, intentional modifications, and geographic origin. These pieces of information may be further detailed by diet and residential mobility estimates provided by isotopic analyses. The use of isotope data in the modern population is strongly dependent on the diverse origin of food supply, thus requiring an updated and location-specific database. In this study, we have analyzed the isotopic ratio of strontium, carbon, and nitrogen in enamel and dentin collagen of third molars individuals from three main cities in Brazil. Besides the isotope data, we have also surveyed their diet in adolescence habits to develop models to be applied for forensic studies in the Brazilian territory. We show that the forensic value of the place of origin estimation based 87Sr/86Sr levels is reduced in these highly urbanized samples. Among the outliers, most individuals are older than the mean age (25.1) or had water from wells in childhood. The sample's diet has a robust C4 presence and mean trophic levels consistent with the declared high frequency of chicken, meat, and dairy products, also compatible with the high consumption of sugar, rice, and beans in the local culture. Individuals with special diets, either by choice or therapeutic needs, were potential outliers among the group. Our results also contribute to the international human tissues isotopic database and can contribute for human identification of Brazilians or foreigners with distinct isotopic signatures. Los datos dentales pueden proporcionar información valiosa sobre la vida de una persona, incluida la edad, la salud, los signos de violencia, la ascendencia, la dieta, las modificaciones intencionales y el origen geográfico. Esta información se puede detallar más mediante la estimación de la dieta y la movilidad residencial, proporcionada por el análisis isotópico. El uso de datos isotópicos en la población moderna está estrechamente relacionado con el origen diverso de los alimentos, por lo que requiere una base de datos actualizada y específica de la ubicación. En este estudio, analizamos la proporción de isótopos de estroncio, carbono y nitrógeno en el colágeno de la dentina y el esmalte del tercer molar de individuos de tres grandes ciudades de Brasil. Además de los datos isotópicos, también se recopilaron datos sobre hábitos alimentarios para el desarrollo de modelos para ser aplicados en estudios forenses en territorio brasileño. Los resultados mostraron que el valor forense de la estimación del lugar de origen basado en los niveles de 87Sr / 86Sr se reduce en estas muestras altamente urbanizadas. Entre los valores atípicos, la mayoría de las personas son mayores que el promedio (25,1) o consumieron agua de pozo en la infancia. La dieta de la muestra tiene una presencia robusta de C4 y niveles tróficos medios relacionados con la alta frecuencia de pollo, carne y productos lácteos en la dieta declarada, también compatible con el alto consumo de azúcar, arroz y frijoles en el cultivo local. Los individuos con dietas especiales, por elección o necesidad terapéutica, eran posibles valores atípicos entre el grupo. Los resultados también contribuyen a la base de datos internacional de isótopos de tejidos humanos, contribuyendo a la identificación humana de brasileños o extranjeros con firmas isotópicas distintas. Dados odontológicos podem fornecer informações valiosas sobre a vida de um indivíduo, incluindo idade, saúde, sinais de violência, ancestralidade, dieta, modificações intencionais e origem geográfica. Essas informações podem ser mais detalhadas pela estimativa de dieta e mobilidade residencial, fornecidas por análise isotópica. O uso de dados isotópicos na população moderna é fortemente relacionado à origem diversificada dos alimentos, exigindo, portanto, um banco de dados atualizado e específico para o local. Neste estudo, analisamos a razão isotópica de estrôncio, carbono e nitrogênio no colágeno da dentina e esmalte de terceiros molares de indivíduos de três grandes cidades do Brasil. Além dos dados de isótopos, também foram coletados dados de hábitos alimentares para o desenvolvimento de modelos a serem aplicados em estudos forenses em território brasileiro. Os resultados mostraram que o valor forense da estimativa de local de origem com base nos níveis 87Sr/86Sr é reduzido nessas amostras altamente urbanizadas. Entre os outliers, a maioria dos indivíduos tem idade superior à média (25,1) ou consumiu água de poço na infância. A dieta da amostra tem uma presença robusta de C4 e níveis tróficos médios relacionados à alta frequência de frango, carne e laticínios na dieta declarada, compatíveis também com o alto consumo de açúcar, arroz e feijão na cultura local. Indivíduos com dietas especiais, por opção ou necessidade terapêutica, foram potenciais outliers entre o grupo. Os resultados também contribuem para o banco de dados isotópicos internacionais de tecidos humanos, contribuindo para identificação humana de brasileiros, ou estrangeiros com assinaturas isotópicas distintas.

The impacts of river damming on aquatic fauna are assessed and then integrated across hierarchical scales, portrayed as nested circles. The outer circles characterize the studied site for habitat disturbance and hydrologic regime during the construction and filling phases. The inner circles characterize the construction and filling phase zones for water quality parameters and aquatic fauna. The procedure for integrating the impacts comprises two consecutive stages: in the task stage, inner circles are characterized through field and laboratory work involving sampling and analyses of water aliquots and aquatic fauna; in the impact assessment stage, circle data are processed in ecological and statistical algorithms, which allow identification of changes in abundance and composition of aquatic fauna communities and their integration with changes in water quality parameters across the construction and filling phase zones. The integrative assessment of river damming impacts on aquatic fauna was carried out in the Sabor River dam (Portugal). This dam created two reservoirs: primary and secondary. Changes in water quality caused by dam construction and stream water impoundment were significant, marked by increases in temperature and electric conductivity downstream, accumulation of phosphorus and nitrogen in the reservoirs triggering the growth of algae and the increase of chlorophyll a, and drop of transparency. These changes were aggravated in the secondary reservoir. The consequences of water deterioration for aquatic fauna were severe, marked by abrupt declines of native fish species and invasion of exotic species even upwards the reservoirs. The ecological status determined from ecological quality ratios of benthic macroinvertebrate assemblages were also affected, changing from good-fair in the unaffected watercourses to fair-poor in the lakes.

Giant piston cores recovered from shallow depths ( 87 Sr/ 86 Sr seawater variation through geological times. Depth-to-age conversion of the magnetic susceptibility logs was implemented based on the identification of correlative peaks between cores and the developed 87 Sr/ 86 Sr age model. The influence of Northern Hemisphere glaciation is reflected in these new stratigraphic logs by a gradual increase from ∼2.7 Ma in the lower signal of magnetic susceptibility (below background level), to values approaching the arithmetic means, likely reflecting an overall increase in terrigenous input. The Rio Grande Rise cores have very low Plio-Pleistocene sedimentation rates (∼0.4–0.8 cm/ka), similar to gravity cores from the oligotrophic subtropical South Atlantic (below ∼2000 mbsl), and for which an inverse correlation between carbonate content and magnetic susceptibility was established. The coring depths on the Rio Grande Rise encompass strong gradients in oxygen concentration and other seawater parameters that define today's AAIW/UCDW transition. Depth-dependent variation in sedimentation rates since the onset of Northern Hemisphere glaciation coincides with the incursion of intermediate waters (UCDW, AAIW) in response to the overall reduction of NADW export to the Southern Ocean. Background levels of magnetic susceptibility in the cores suggest that this variation is mainly attributed to terrigenous input. The source region of this material has yet to be traced by considering in particular the mineral composition and paramagnetic properties of the detrital clays.

Blooms of cyanobacteria (Microcystis aeruginosa) are becoming increasingly recurrent in the A Baxe dam reservoir (Galicia, Northern Spain) as a result of increasing levels of different anthropogenic pressues in the Umia catchment. The aim of this study is to develop a model that allows us to detect the spatial level where the main problems that trigger eutrophication occur. We used Mike Basin coupled with Load Calculator to model and visualize spatially explicit results of stream flow and N and P export. The results indicate increase in nitrogen (N) and phosphorus (P) concentrations that trigger eutrophication.High concentrations of nutrients at the Upper Umia derive from livestock, while at the Lower Umia the origin is sewage, highlighting impacts from diffuse pollution and point source pollution in different areas of the basin. Cyanobacteria blooms result from the influence of both contaminant sources, being also triggered by local environmental conditions such as temperature, solar radiation or flow rate. This model will be useful for predicting possible changes, alterations and evolutions that occur in the watershed, that can help ensure compliance with the Water Framework Directive. In addition to the model developed, the results indicate the need for the implementation of management practices in order to reduce the blooms of cyanobacteria (green systems for wastewater in rural areas, riparian forest restoration, etc.). Some sub-basins, such as the Gallo sub-basin, require immediate action since they are major contributors of nutrients to the main river as a result of the low carrying capacity of local waste water treatment plants.

Delineating the controls on hydroclimate throughout Brazil is essential to assessing potential impact of global climate change on water resources and biogeography. An increasing number of monsoon reconstructions from δ 18 O records provide insight into variations in regional monsoon intensity over the last millennium. The strength, however, of δ 18 O as a proxy of regional climate limits its ability to reflect local conditions, highlighting the need for comparable reconstructions of local moisture conditions. Here, speleothem 87 Sr/ 86 Sr values are developed as a paleo-moisture proxy in central Brazil to complement existing δ 18 O-based reconstructions of regional monsoon intensity. Speleothem 87 Sr/ 86 Sr values are resolved using laser ablation and conventional solution mass spectrometry at high resolution relative to existing (non- δ 18 O-based) paleo-moisture reconstructions to allow comparisons of centennial variability in paleo-monsoon intensity and paleo-moisture conditions. Variations in speleothem 87 Sr/ 86 Sr values from Tamboril Cave are interpreted to reflect varying extents of water interaction with the carbonate host rock, with more interaction resulting in greater evolution of water isotope values from those initially acquired from the soil to those of the carbonate bedrock. Increasing speleothem 87 Sr/ 86 Sr values over the last millennium suggest progressively less interaction with the carbonate host rock likely resulting from higher infiltration rates, expected under wetter conditions. Increasingly wetter conditions over the last millennium are consistent with an overall trend of increasing monsoon intensity (decreasing δ 18 O values) preserved in many existing δ 18 O records from the region. Such a trend, however, is absent in δ 18 O records from our site (central Brazil) and Cristal Cave (southeast Brazil), suggesting the existence of divergent (relevant to δ 18 O precip ) shifts in the climate patterns within and outside the core monsoon region.

Changes in insolation driven by precession and obliquity are considered the major driver of tropical precipitation on orbital time scales, and responsible for vegetation and physical landscape changes during the Late Holocene over tropical South America. Here we investigate the environmental changes in the karst region of Chapada do Apodi - Northeastern Brazil (NEB), using a multi-proxy approach including carbon (δ13C), oxygen (δ18O) and strontium (87Sr/86Sr) isotopic analyses on speleothems from different caves, carbonate bedrock, and clastic cave deposits. This approach reveals that the balance between soil formation and erosion and their alternating impact on vegetation and precipitation changes occurred in response to variations in the position and intensity of the Intertropical Convergence Zone (ITCZ) over the region. The high δ13C and δ18O and low 87Sr/86Sr values at 4,200 yrs BP indicate a massive episode of soil erosion, resulting in the exposure of carbonate bedrocks over a large area of the karst terrain. This event marks the beginning of the Meghalayan chronozone, characterized as the aridification of this region, decline in soil production, drying out of underground drainages, and increased dominance of dry-adapted flora species, characteristic of a more open vegetation (caatinga). We investigated if the Holocene climatic changes affected human occupation in the NEB and found that the overall demographic course is virtually identical to the well-established curve characterized by population deflation during Middle Holocene.

Banded Iron Formations (BIFs) from the Carajas Mineral Province (CMP), southeastern Amazonian Craton, are the protolith of the world-class iron deposits of the CMP. Besides being one of the largest iron ore deposits in the world, they recorded important paleoenvironmental and regional geodynamic markers across the Neoarchean-Paleoproterozoic transition. We investigate the secular variation of geochemical signature, from several deposit of Carajas Province. The low contents of Al2O3 and of 19 other immobile trace elements (e.g., Zr, Th, Hf, Ti) in 26 high-resolution detritus-free BIF samples indicate their detritus- free nature. Their positive shale-normalized (subscript SN) La and Gd anomalies are similar to those of modern seawater; whereas their Y/Ho ratios are higher. These BIF samples also display large positive chondrite-normalized (subscript CN) Eu anomalies, reflecting the influence of high-temperature hydrothermal vents and bottom solutions. In contrast to modern seawater and to most other Neoarchean/Paleoproterozoic detritus-free BIFs, the Carajas BIFs do not show the typical heavy rare earth element (REE) enrichment relative to light REE; instead they do show variable light to heavy REE fractionation trends (YbSN/PrSN ratios: 0.05–4.91). The Th/U ratios of both bulk BIFs and mesobands are generally lower than the upper-crustal ratio. Although the bulk BIFs show mostly chondritic values, the individual Fe and Si bands exhibit distinctly higher ratios. The general absence of negative CeSN anomalies attests for rather reducing paleoenvironmental conditions. Unlike the great majority of the data which lack negative anomalies of Ce, a few samples do display such anomalies, which may be compatible to the oxidizing conditions shown by the low Th/U ratios of most the Carajas BIFs. Such low Th/U ratios may register terrestrial weathering conditions, which cause preferential U input into the oceans in response to the oxidation of immobile U4+ to more mobile U6+.

Several studies have reported Miocene shallow-marine incursions in the Pebas Megawetland system (Western Amazonia) based on paleontological and sedimentological evidence. Only a few publications restricted to Middle and Late Miocene fossils outcropping in the Iquitos (Peru), Benjamin Constant and Eirunepe (Brazil) areas have provided isotopic evidence to test these incursions. In this study, we present new carbon, oxygen, and strontium (87Sr/86Sr ratios) isotopic data of macrofossils (pacu and ray teeth, crab claws and oysters), and microfossils (ostracods and foraminifera) from reported lower to lower upper Miocene sedimentary rocks of Western and Eastern Amazonian (Peru and Brazil), mainly from shallow-marine deposits. It was also analyzed present-day organisms from distinct environments (beach, sea, riverine, and estuary) and compared these results with Miocene fossils. While C and O isotopic compositions indicate that Western Amazonia fossils display an isotopic composition similar to the present-day continental, limnic and riverine, environments (−17‰ to −5.61‰ for δ13C and − 10.14‰ to −1.92‰ for δ18O), Eastern Amazonia fossils display C and O isotopic compositions comparable to those from seawater environments (−2.53‰ to −0.72‰ for δ13C and − 4.85‰ to −1.76‰ for δ18O). We further used the 87Sr/86Sr isotopic composition of the fossils to estimate paleosalinity conditions. The 87Sr/86Sr isotopic compositions indicates that Eastern Amazonian water bodies of the Pirabas Formation (Marajo Basin) varied from mesohaline to marine conditions. In contrast, Early Miocene Western Amazonian water bodies of the Pebas Megawetland System (PMWS) are characterized by freshwater conditions. Nonetheless, in Middle and Early Late Miocene, oligohaline conditions are found in the Peruvian part of the PMWS. Paleosalinity estimates of the Brazilian part of the PMWS are less constrained and might indicate a salinity range between freshwater or oligohaline conditions. Our isotopic data suggest the PMWS was occasionally submitted to oligohaline conditions during Middle and Early Late Miocene shallow-marine incursions. We suggest that Miocene shallow-marine incursions in Western Amazonia at this time were characterized by transitional paleoenvironments, reconciling isotopic, sedimentological and paleontological evidences.

Rocks of the Vazante Group in the Morro Agudo region (SE-Brazil) integrate a thick clay-carbonate sequence composed of twelve sedimentary facies and four facies associations (FAs), deposited in a mixed marine passive margin environment. This work carried out systematic isotope analyses of δ13C and δ18O on the two upper stratigraphic units of the Vazante Group (Morro do Calcario and Serra da Lapa formations) and on the Serra do Landim Formation. Despite the pervasive secondary dolomitization and hydrothermal overprint, most samples can be classified as least-altered dolostone, with some exceptions. Samples of Serra do Landim Formation are the ones with the highest degree of alteration, together with a small group of dolomites collected in a sphalerite-mineralized zone, at the top of the Morro do Calcario Formation. The isotopic profiles and the facies analysis showed the Morro do Calcario Formation presents homogeneous values of δ13C, and the Serra da Lapa Formation negative values of δ13C at the base, upwards inflected towards positive values. These coupled data suggest a significant change of environment in the depositional setting and conditions between these two formations, passing from calmer and stable (Morro do Calcario) to energetic and disturbed (Serra da Lapa). The strong negative values of δ13C, namely Lapa anomaly, are associated with diamictite facies below thick layer of carbonates, suggesting the influence of the Sturtian glacial event, in the lower Serra da Lapa Formation. The Lapa anomaly is the best chemostratigraphic marker throughout the sequence and guides the regional correlation of the Vazante Group. The basal diamictites of the Serra da Lapa Formation include dolomitic fragments of Morro do Calcario facies, indicating an intra-basinal source. Based on the isotopic profile correlation, it is inferred that the upper units (Morro do Calcario and Serra da Lapa formations) of the north and south portions of the Vazante Group were deposited in the same basin, or in connected basins, possibly separated, in part, by the Rio Escuro basement High.

Paleovegetation studies in Brazil have been mostly based on pollen analysis and geochemical proxies in lacustrine and soil records. These records, however, are sparsely located in the continent and, in most of the cases, centered over the Holocene, giving a minor picture of past vegetation since the Last Glacial Maximum. Stalagmites have been long used as recorders of paleoprecipitation and monsoon activity over time in tropical and subtropical South America by using δ 18 O analyses, but recently they also showed the potential to record past vegetation and soil changes through the combined use of δ 13 C and 87Sr/86Sr. We utilize this new approach to determine the periods of paleovegetation transition and soil development in the Cerrado (Brazilian savanna) biome from central Brazil. Our results show a coherent period of transition from sparser vegetation and shallower soil above the cave to denser vegetation and thicker soil since the last deglaciation circa 15 ka BP. The timing of this transition is different from the multiproxy evidence found in the Caatinga (dry forest) biome, in northeastern Brazil, circa 4.2 ka BP, resulting in a period of paleovegetation seesaw pattern between central and northeastern regions of Brazil. Additionally, atmospheric pCO2 and temperature variations may have played a major role on the paleovegetation transition in the Cerrado region whereas precipitation linked to the Intertropical Convergence Zone was the major modulator of paleovegetation in the Caatinga.

Samples dredged from the Cruzeiro do Sul Lineament exhibit ferromanganese crusts precipitated above phosphate-rich substrates (phosphorites, phosphate-impregnated volcanic rocks and older phosphatized ferromanganese crusts). Co-chronology of the crusts, paleontological data and 87Sr/86Sr ratios of the phosphatized substrate indicate that the last phosphatization event in the region happened between 17.6 and 14.6 Ma ago. When the event ceased, oxic conditions were resumed and hydrogenetic crust precipitation started at a maximum rate of 1.6–3.0 mm/Ma, forming layers of Fe-vernadite above the phosphorites. These crusts differ in composition from crusts that formed prior to the phosphatization, which were impregnated by carbonate fluorapatite and recrystallized forming a 10 A Mn-phase, in expense of a lower crystallinity Mn-phase. Mn/Fe ratios of non-phosphatized crusts vary from 1.05 to 1.41. The Mn/Fe ratios as well as the metal content (Co = 0.65–1.04 wt%, Zn = 0.04–0.06 wt%, Cu = 0.02–0.06 wt% and Ni = 0.29–0.48 wt%) are similar to hydrogenetic crusts described in other parts of the world.

The Vilariça River (located in the northeast of Portugal) is inserted in an agricultural basin and it was chosen to replace the spawning grounds for fish, that was lost due to the construction of dams in the Sabor River. Thus, it is essential to study the effect of agricultural practices on water quality and in the health status of fish. The barbel (Luciobarbus bocagei) and Douro nase (Pseudochondrostoma duriense) were the selected species and the work was developed in two seasons (Summer 2016 and Winter 2017). For that, the histopathological changes of fish gill were used as biomarkers, through a semi-quantitative approach that considers the injuries severity. And the water quality assessment criteria followed the methodologies proposed for classifying the status of surface water bodies from Portugal. The current study showed severe histopathological changes in both species and both seasons, and the water was classified as polluted and extremely polluted in Summer and Winter respectively. The pollution in Summer was due to high temperatures, low dissolved oxygen and major concentration of As and Mn, and in Winter is due to the high concentration of Total Suspended Solids, nitrites and Cd. The increase of values of physico-chemical parameters on the water was caused by the less streamflow and excessive agricultural fertilization in Summer which arrive the river by irrigation, and by the erosion of soil particles with heavy metals associated in Winter. Also, the canonical analysis showed that physico-chemical parameters concentrations in Summer justify the major prevalence of aneurism in barbel and exudate in nase and Winter the major prevalence of hypertrophy in barbel. In conclusion, the study showed that the gill injuries of barbel and Douro nase was correlated with the water quality and it is influenced by seasonal agricultural practices and the flow regime.

The Itataia phosphate-uranium deposit is located in Santa Quiteria, in central Ceara State, northeastern Brazil. Mineralization has occurred in different stages and involves quartz leaching (episyenitization), brecciation and microcrystalline phase formation of concretionary apatite. The last constitutes the main mineral of Itatiaia uranium ore, namely collophane. Collophanite ore occurs in massive bodies, lenses, breccia zones, veins or episyenite in marble layers, calc-silicate rocks and gneisses of the Itataia Group. There are two accepted theories on the origin of the earliest mineralization phase of Itataia ore: syngenetic (primary) – where the ore is derived from a continental source and then deposited in marine and coastal environments; and epigenetic (secondary) – whereby the fluids are of magmatic, metamorphic and meteoric origin. The characterization of pre- or post-deformational mineralization is controversial, since the features of the ore are interpreted as deformation. This investigation conducted isotopic studies and chemical analyses of minerals in marbles and calc-silicate rocks of the Alcantil and Barrigas Formations (Itataia Group), as well as petrographic and structural studies. Analysis of the thin sections shows at least three phosphate mineral phases associated with uranium mineralizaton: (1) A prismatic fluorapatite phase associated with chess-board albite, arfvedsonite and ferro-eckermannite; (2) a second fluorapatite phase with fibrous radial or colloform habits that replaces calcium carbonate in marble, especially along fractures, with minerals such as quartz, chlorite and zeolite also identified in calc-silicate rocks; and (3) an younger phosphate phase of botryoidal apatite (fluorapatite and hydroxyapatite) related with clay minerals and probably others calcium and aluminum phosphates. Detailed isotopic analysis carried out perpendicularly to the mineralized levels and veins in the marble revealed significant variation in isotopic ratios. Mineralized zones exhibit a decrease in δ13C and δ18O isotope values and a higher 87Sr/86Sr ratio toward the center of the vein. In conjunction with petrographic studies, these changes contesting the hypothesis of a sedimentary origin for uranium and suggest a radiogenic Sr input by alkaline to peralkaline fluids from fertile granites of the end of Brasiliano/Pan-African orogeny, located outside the deposit. The origin of the phosphorous is associated with phosphorite deposits in the same depositional environment of the neoproterozoic supracrustal quartz-pelite-carbonate sediments of the Itataia Group. Considering the studies conducted here and available geological data, three main mineralizing events can be identified in Itataia: (1) an initial high temperature event connected with a sodium metasomatism-related uranium episode, taking place in Borborema Province and its African counterpart; (2) a second lower temperature stage, consisting of a multiphase cataclastic/hydrothermal event limited to fault and paleokarst zones; and (3) a third and final event, developed in frankly oxidizing conditions. The last two involving mixing of hydrothermal and meteoric fluids.

Brazil was the main destination of enslaved Africans during the eighteenth and nineteenth centuries in the New World. We have analyzed isotopes of carbon, nitrogen and strontium in the enamel and dentin of teeth derived from remains of 41 enslaved Africans excavated in Pretos Novos cemetery (Rio de Janeiro) and Se de Salvador cathedral (Salvador) in order to investigate aspects related to the geographical origins and dietary habits in Africa in these two groups with differing histories. Strontium isotope results indicate a wide range of geographical origin for the analyzed individuals of both cemeteries, being significantly wider in Pretos Novos. Carbon and nitrogen isotopes results suggest that the diet of most individuals was based on plants. Only 26% probably had access to a significant amount of animal protein. The results also show that while some individuals were consuming C3 plants such as yams and manioc, others had a diet based more on C4 plants such as sorghum, millet and maize. Interpreted in conjunction with archaeological and historical evidence, the findings of this study, including the high variability of 87Sr/86Sr, δ13C and δ15N values, contribute to the process of reconstructing the dramatic history of slavery in Brazil and in the Americas.

Landfills stabilization stages depend on parameters such as the age of the landfill, the refuse composition, and the confinement level of the buried material. In the absence of free oxygen, redox reactions (e.g., SO42-, NO3-) and methanogenesis control the decomposition of organic matter. Landfill’s stabilization stage is usually assessed by parameters such as pH, biochemical oxygen demand, chemical oxygen demand, dissolved organic carbon, and biogas composition. This study evaluates the stabilization stage of a 50-year-old tropical landfill located in Central Brazil based on physicochemical parameters, dissolved carbon isotope data (δ13C), redox reactions, and concentration of released gases CO2 and CH4. We show that seasonal variations of these parameters are modified by rainwater inflow, which carries free-oxygen into the landfill. An increase in free-oxygen leads to a 13C-depletion in carbon isotopic composition of dissolved CO2 and an increase in redox-dependent species such as Fe3+, SO42-, and NO3-. Our data show that most of the landfill has reached the methanogenic stage and that periodic oxygen input by rainwater affects methane production. The studied site is a complex chemical system in which organic matter degradation occurs by aerobic, anaerobic, and methanogenic processes, depending on the recharge susceptibility.