Research on travertines has increased over the past decade due to their importance to local hydrology, connections with microbial ecosystems, economic value as mineral resources, and potential as reservoir rocks. There are many unanswered questions about isotopic fractionation in different travertine settings worldwide. We use a petrological-geochemical approach to investigate the evolution of the Botijuela travertine system, positioned over similar to 3380 m above sea level, in the southwestern Antofalla Graben of the Argentine Puna, Central Andes. This travertine system offers a complete set from proximal to distal zones for understanding the origin and development of carbonate precipitation. Fluid-source analysis indicates a mixture of fresh water and hydrothermal influx, reflected in the system's mineralogical dominance of calcite, with notable variations in its geochemical composition. A conical mound in the proximal zone consists of mudstone and boundstone and preserves a geochemical halo characterized by high iron concentrations and non-equilibrium calcite precipitation. Intermediate and distal zones are dominated by high-energy facies (grainstone and rudstone), with low iron and arsenic contents, where the isotopic composition occasionally approaches equilibrium. Isotopic values (delta C-13: 2.0 to 10.4 parts per thousand; delta O-18: -8.9 to -0.7 parts per thousand VPDB) indicate fractionation triggered by CO2 degassing and evaporation with precipitation cycles in which distal-zone isotopic signatures partially overlap those of the proximal zone. The high altitude may indicate a unique condition that promotes calcite precipitation under isotopic non-equilibrium. This setting is marked by low atmospheric pressure, sudden hydraulic exhumation triggering fluid decompression and enhanced CO2 degassing, episodic hydrothermal influx, and the deposition of high-energy facies.

Carbonate precipitation in southern high-latitude environments remains poorly constrained in terms of its controlling mechanisms, particularly in continental settings where climatic extremes, volcanic substrates, and inherited glacial processes converge. Here we investigate carbonate formation in an alkaline lake hosted within Middle Pleistocene maars of the Pali Aike Volcanic Field, southern Patagonia. This setting provides a natural laboratory to investigate interactions between silicate weathering, carbon cycling, and CaCO₃ supersaturation. Mineralogical and geochemical data, including 87Sr/86Sr, δ13C, and δ18O, from carbonates, basalts, soils, sediments, and lake waters were used to constrain the processes controlling carbonate precipitation. The δ13C composition of dissolved inorganic carbon (DIC) indicates that silicate weathering involving soil-derived and atmospheric CO₂ is the primary source of carbon to the lake system. Carbonate speciation reveals a strong dominance of HCO₃− and CO₃2− over dissolved CO₂ in the lake carbon pool. Strontium isotopic compositions identify mafic rock weathering as the principal source of dissolved Ca. Combined evidence from Sr partitioning, weathering indices, aqueous geochemistry, and stable isotopes indicates carbonate precipitation under sustained supersaturation, modulated by kinetic constraints rather than simple equilibrium conditions. These results define an integrated geochemical framework in which silicate weathering intensity, carbon cycle dynamics, and precipitation kinetics jointly regulate carbonate formation, with implications for interpreting lacustrine carbonate archives in high-latitude continental systems.

Kinetics analysis is key to evaluating petroleum systems as it controls hydrocarbon generation conditions, masses, compositions and phases. In frontier basins, using kinetics from analogous source rocks introduces a significant uncertainty into petroleum system evaluations. Source rock kinetics may differ within the same basin due to variations in depositional environment and compositions. This study integrates new Rock-Eval pyrolysis, organic petrography, thermovaporisation, pyrolysis gas chromatography and both bulk and compositional phase kinetics data with forward stratigraphic modeling (FSM) and petroleum system modelling (PSM). This approach improves the understanding of the Middle Devonian to Early Mississippian atypical petroleum system of Parnaiba Basin, NE of Brazil. The analytical program was performed over 41 samples from four Organic Rich Levels (ORL's) of the Devonian Pimenteiras Formation shales. Two samples, from ORL's A and C, were selected for Compositional Phase Kinetics analysis. Alginite is the dominant maceral in more than twenty samples followed by vitrinite, zooclasts, amorphous organic matter and bituminite. Vitrinite, graptolite and bitumen reflectance values range from 0.6 to 0.8% (%Ro). Phase kinetics results show a narrow activation energy distribution (between 50 and 56 kcal/mol) in line with a homogeneous kerogen structure. Pyrolysate analysis corroborates the deposition of algal/bacterial organic matter in a dominantly marine Type II kerogen environment. Stratigraphic analysis and FSM results indicate potential for extrapolating the kinetic scheme of selected ORL's across the basin. These kinetic schemes were assigned to the 3D PSM simulator and compared with simulations using the Woodford Shale kinetic scheme. Differences of - 66,6 %, -19,5 % and -0,8 % in generated petroleum masses for ORL's A, B and C, respectively, indicate significant effects of the kinetic scheme on PSM predictions. In conclusion, incorporating locally defined kinetics parameters rather than analogue-based models improves the reliability of thermal maturity and hydrocarbon phase predictions, reducing exploration uncertainty.

ABSTRACT The reflectance of vitrinite is a common thermal calibration parameter in sedimentary basins for evaluating and reconstructing thermal history. However, factors such as the scarcity of particles in Devonian and the high thermal stress reached in igneous sedimentary petroleum systems pose significant challenges to the modelling process. This study integrates organic petrography data, along with extensive X‐ray diffraction analysis (XRD), to improve the understanding of the Middle Devonian to Early Mississippian atypical petroleum system in the Parnaíba Basin, located in northeastern Brazil. The analytical program involved 54 samples for vitrinite reflectance (%Ro) and 207 samples for XRD, collected from three selected wells in the central part of the basin, covering the entire Middle Devonian to Early Mississippian sequence. Spectral decomposition on the 10Â peak ( d001 position) was conducted on the XRD data to differentiate between the authigenic smectite/illite (I/S) phase and the metamorphic detrital muscovite phase. The Kübler Index (KI), measured as full width at half maximum (FWHM ‐ ° ∆ 2θ ), was assessed in the illite and muscovite phases and converted to an equivalent %Ro for comparison with the results of calculated %Ro across three sets of 1D Petroleum System Models (PSM), which were originally calibrated using measured %Ro. The conversion ratio of smectite to illite was also calculated throughout these models. The Esquevin Index, calculated as the ratio of d 002/ d 001 reflections, was compared with KI along the profiles. The results indicate a strong correlation between KI (from the illite phase) and measured %Ro, thereby allowing KI to be used for thermal calibration. This finding suggests a progressive conversion of I/S (KI values ranging from 1.23° to 0.23° ∆2θ ) from the diagenesis zone through the anchizone to the epizone near igneous intrusions. The KI values for the muscovite phase range from 0.58° to 0.16° ∆ 2θ , supporting the detrital nature of this phase. While it does not correlate with calculated and measured %Ro, a progressive increase in metamorphism occurs along the wells, increasing both above and below igneous intrusions and suggesting muscovite recrystallisation related to the presence of magmatic intrusion. An exponential equation for the correlation between KI from illite phase and %Ro, based on the analysis of 37 pairs of KI versus measured Ro, is proposed as KI = 0.7379 Ro −0.604 ( r 2 = 0.788). These KI‐%Ro pairs of the authigenic illite phase were compared with literature data, showing a reasonable correlation with pairs obtained in regional metamorphic contexts, thus validating the use of KI as an additional thermal proxy in contact metamorphism in atypical petroleum systems.

Understanding the biotic and abiotic influences on the deposition and diagenesis of recent microbial carbonates is crucial for addressing the environmental and ecological significance of ancient organosedimentary structures. This study investigates these factors and their expression in the microstructure of Holocene tufa thrombolites from a wind-stressed freshwater lake (Lago Sarmiento, Chile) through 16S rRNA sequencing, petrology of modern and fossil deposits, and stable isotope geochemistry of water and carbonates. Carbonate precipitation in the littoral zone is linked to Rivulariaceae-rich mats, whose early induration involves extracellular polymeric substances-mediated nucleation of nanoparticles precursors to aragonite and Mg-calcite. Only remnants of these early products are preserved in fossil deposits due to diagenetic overprinting promoted by environmental factors. A syn-depositional constructive stage-interpreted as key for the stabilisation and growth of meter-sized build-ups-involves aragonite inversion to Mg-calcite, crystal size coarsening, and Mg-calcite cementation. A subsequent destructive stage-developed under increasing wave-influence as the lake-level lowered-led to spar substitution to secondary fine-grained textures (including clotted micrite), the dissolution and/or erosion of the framework, and internal sedimentation within primary and secondary pores (primarily terrigenous grains, intraclasts and peloids), partially obliterating the filamentous microfabrics. The calcified rivulariaceans and stable isotopes suggest tufa deposition under oligotrophic and relatively cold conditions (<= 12 degrees C) throughout Holocene cold/wet to warm/dry climate transitions. The resiliency of the lacustrine system likely contributes to sustaining a low-competition and high-calcification setting at millennial timescales, allowing the extensive accumulation of microbially mediated freshwater carbonates-the largest in the extratropical Southern Hemisphere. The record of Lago Sarmiento provides valuable insights into early diagenetic reworking of primary microbial textures, with implications for the identification of high-energy lacustrine systems, a setting that might be overlooked in the geologic record.

Tropical wetlands are vital for global climate regulation, but their sensitivity to climatic variability makes them vulnerable to hydrological disruptions. The Brazilian Pantanal is the world's largest continental wetland and an ecological and climatic hotspot. Its long-term resilience is poorly constrained due to limited sedimentological and geochemical records, unconsolidated siliciclastic deposits, and intense redoximorphic processes. This study offers an unprecedented paleoclimatic reconstruction of the Nhecolandia region using an 11.8 m sediment core from Meio Lake (Nhumirim Farm, Embrapa Pantanal). We integrate X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS), principal component analysis (PCA), and multiple chemical weathering proxies (Rb/Sr, Ba/Sr, and the Chemical Proxy of Alteration-CPA). The sedimentary succession records two warmer intervals separated by a cooler one, with shifts in hydrological conditions, indicating a structured paleoclimate and hydrological regime. Correlation with paleoclimate records from Serra da Bodoquena suggests regional synchronicity, implying the Pantanal may function as an integrated climate system modulated by orbital forcing and tropical atmospheric circulation. However, the chronology is inferred from lithostratigraphic correlation and requires validation through absolute dating. Comparison with recent rainfall data (1984-2019) reveals a departure from the long-term hydrological pattern, with no return to past wetter conditions. These findings point to a potential climatic tipping point, emphasizing the need for integrated mitigation and conservation strategies to preserve Pantanal's ecological functions and long-term climate resilience.

The rise in atmospheric CO2 demands the need for scalable carbon removal strategies. Carbon capture and storage (CCS) through mineralization in Ca-and Mg-rich basalts represents a robust and long-term approach for permanently sequestering CO2 as stable carbonate minerals. The Pali Aike Volcanic Field in southern Patagonia, a basaltic province of geological significance, remains underexplored for CCS applications. Its location in the Magallanes region, a center for green hydrogen development, highlights its strategic value for CO2 storage. This work presents the first laboratory-scale CO2 injection experiments conducted on continental basalts from southern South America. Powdered basalt samples were reacted with water and supercritical CO2 for 1, 7, 10, 15, 30, and 100 days, and both aqueous and solid phases were analyzed to track geochemical and mineralogical changes. ICP-OES analyses revealed rapid basalt dissolution from day one, releasing major cations (Na, K, Ca, Mg) and increasing pH, which favored carbonate precipitation. By day 30, XRD and SEM confirmed calcite formation. Carbon isotope data (delta C-13(carb) =-3.3 parts per thousand to-7.3 parts per thousand; delta C-13(DIC) =similar to-36 parts per thousand to-31 parts per thousand) indicate that carbonates formed predominantly from reactions between the CO2-rich solution and basalt. These results highlight the reactivity of Patagonian basalts and provide essential baseline data for CCS. With its abundance of mafic rocks and proximity to renewable energy facilities, the Pali Aike Volcanic Field represents a strategic site for CO2 mineralization and future studies, enhancing the global inventory of long-term storage regions.

The sedimentation in the alkaline lakes could be understood as a product of intrinsic and extrinsic factors’ interaction, where both can exert influence with alternating or progressive predominance due to the large-scale geochemical scenario, promoted by the tectonic and geomorphological settings, the climate and hydrology, the sedimentation, and the environments of deposition. Sedimentological studies of modern carbonate deposits in extreme environments provide access to a better understanding of physical-chemical reactions under the intense influence of natural conditions of desert climate, such as UV radiation, temperature variation, altitude, and heavy winds. Modern carbonate environments, where alkaline lakes are forming under comparable geomorphological, biological, climatic, volcanic, and tectonics characteristics as those during the formation of the Aptian Pre-Salt lakes on the Brazilian continental shelf, are possible analogues to improve our understanding of the physical-chemical processes involved the formation of ancient carbonate deposits. Nevertheless, it is difficult to study a single modern example, which fulfils all the criteria required to define a realistic evolutionary model for the Aptian equivalent. Thus, we have selected for our evaluation several modern alkaline lake locations, which form under variable environmental conditions, e.g., the Pantanal, Central Brazil, and Patagonia, Chile. These environments present vastly different conditions, which can furnish important insights, and taken together provide fundamental information to decipher relationships between the inorganic and organic processes involved in carbonate reservoir formation. In the Pantanal region, thousands of lakes are distributed throughout one of the largest fan river systems. Microbial activity in many of these water bodies mediates the production of carbonates associated with authigenic clay mineral precipitation, e.g., smectite. In Chile’s Patagonia Torres Del Paine region, the Sarmiento and Amarga lakes are located in an area of glacial regression, which represents an environment with recent microbialite formation in a cold and arid climate. Additionally, in this cold, arid region, Lake Pali Aike, situated in the crater of a dormant volcano, is potentially an interesting case study. Each of these three different regions is characterized by extreme environmental conditions, such as a desert climate with high temperatures during the day and very low temperatures at night, strong winds, and a high incidence of solar radiation. The primary goal of integrating studies of these three distinctly diverse environments located in varying geological settings is to develop an actualistic facies model representing the ancient conditions of the various Pre-Salt lacustrine depositional environments, ranging from deep subaqueous, intermediate subaqueous, shallow subaqueous, and subaerial systems.

The Palmital Shear Zone, located in the southern Ribeira Orogen, is a NW-SE oriented crustal-scale shear zone that marks the tectonic boundary between two contrasting geological terranes: the Luis Alves Microplate (LAM) to the west and the Paranagua Terrane (PT) to the east. This study aims to characterize the Palmital SZ through multi-scale structural analysis and geophysical data, to elucidate its tectonic evolution during the amalgamation of the southwestern Gondwana continent. The Palmital SZ is identified by contrasting anomalies between the adjacent geological terranes. The PT is characterized by negative magnetic anomalies, while the LAM exhibits positive magnetic anomalies. Towards the offshore, this magnetic signature contrast extends into the shallow portion of the Brazilian continental margin. The study area presents mafic granulites and type-A granites from the LAM, and ortho- and paragneisses basement intruded by syn-collisional granites belonging to the PT. The tectonic fabric of the PT is characterized by a gneissic foliation (S1) trending NE-SW and a mylonitic foliation (S2). The S2 exhibits proto-to ultra-mylonitic fabrics, trending NNW-SSE with subvertical dip and two stretching lineation orientations: the southern domain displays sub-horizontal plunge, while the central-northern domain, low to moderate plunge to NNE. Microstructural analysis of the mylonitic foliation (S2) indicates deformation conditions of low temperature (<= 450 degrees C), equivalent to greenschist facies, transitioning from ductile to ductilebrittle regime. Kinematic criteria such as S-C shear bands, quartz oblique foliation, asymmetric feldspar porphyroclasts and mica fish, document sinistral kinematics of the Palmital SZ. Structural, geological and geophysical evidences suggest that the Palmital SZ originated and evolved as a suture juxtaposing latterally the PT Neoproterozoic units with the Paleoproterozoic units of the LAM during the Brasiliano Orogeny. The Palmital SZ progressed from a transpressional deformation to transtensional deformation phase, registering an oblique continental collision.

Ice ages have profoundly influenced Earth's climate, reshaping both biotic and abiotic systems. Understanding their signatures in the sedimentary record is key to assessing the mechanisms and consequences of extreme climate changes, offering valuable insights into ancient climate dynamics. In this study, we explore the paleoclimatic and paleoenvironmental aspects of a Middle Pennsylvanian succession composed of thin-bedded, mudrich facies from the Campo do Tenente Formation (eastern Parana Basin, Brazil), which was deposited at mid- to high paleolatitudes during the late Paleozoic ice age (LPIA). Our multiproxy approach, adapted from methods used in the study of Quaternary glaciations, integrates sedimentological and geochemical data. Five outcrops near Campo do Tenente and Lapa (southern Brazil) were surveyed, where vertical logs up to 17 m thick were measured. In one of these logs (Campo do Tenente Quarry) we performed systematic sampling and ice-rafted debris (IRD) counting. Seven sedimentary facies including diamictite, rhythmite and shale with varying amounts of IRD were defined and grouped into three associations formed by 1) diluted turbidity currents, 2) rainout, and 3) mud settling. Sr/Ba paleosalinity data suggest low salinity conditions, trending toward freshwater at the top of the succession, indicating a depositional environment with salinity fluctuations, possibly near a marine transitional zone. While the alternation of different facies with variable amounts of IRD suggest cyclicity controlled by ice-margin fluctuation, paleoweathering proxies (CIA, CIW, CPA, MIA, TiO2) show low variability, indicating persistent cold temperate conditions that do not follow facies changes or IRD amount variations. We propose that glacial advance-retreat cycles were driven primarily by second-order climatic factors, which are not well captured by traditional geochemical proxies. These findings support the temperate nature of ice masses at the Parana Basin margins during the Pennsylvanian and highlight the significant role of local drivers in shaping glacial behavior. On a broader scale, our results align with recent perspectives that suggest glaciation and deglaciation events during the LPIA occurred asynchronously and had a much more dynamic character than previously thought.

Extreme environments, such as hypersaline habitats, hot springs, deep-sea hydrothermal vents, glaciers, and permafrost, provide diverse ecological niches for studying microbial evolution. However, knowledge of microbial communities in extreme environments at high southern latitudes remains limited, aside from Antarctica. Laguna Timone is a hypersaline crater lake located in a Pleistocene maar of the Pali Aike Volcanic Field, southern Patagonia; the lake was formed during basaltic eruptions in a periglacial setting. Here, we report the first integrative characterization of microbial communities from biofilms and microbial mats in this lake using high-throughput 16S rRNA and ITS gene sequencing, along with mineralogical and hydrochemical analyses of water, sediments, and carbonates. Bacterial communities were dominated by the genera Enterobacterales ASV1, Pseudomonas, Oscillatoria, Nodularia, and Belliella, with site-specific assemblages. Fungal communities included Laetinaevia, Ilyonectria, Thelebolus, Plectosphaerella, and Acrostalagmus, each showing distinct distribution patterns. These baseline data contribute to understanding microbial dynamics in hypersaline maar environments and support future investigations. This integrative approach highlights key microbe–mineral relationships and underscores the potential of Laguna Timone as a natural laboratory for exploring biosignature formation and microbial adaptation in chemically extreme environments, both on early Earth and potentially beyond.

The 87Sr/86Sr ratio stands as a crucial isotopic marker for the paleogeographic and paleoenvironmental reconstruction of Aptian carbonate sequences in the offshore Campos and Santos basins in Brazil, as well as the Namibe basin in Angola. It facilitates the identification of distinct stratigraphic successions and alterations in the basin's source areas, allowing for valuable geological correlations and interpretations on both margins. Furthermore, it can indicate diagenetic processes, hydrothermal events involving chemical mobility, and textural modifications associated with regional tectonic events linked to the evolution of the South Atlantic rift. In isotopic dilution analyses, the quality of the results is ensured by eliminating interferences and ensuring a stable signal during spectrometric reading, where the 87Sr/86Sr ratios have analytical precision between the 5th and 6th decimal place. However, samples with a significant compositional variation, such as laminations, microstructures, microveins, or even with clastic minerals, may yield scrambled distinct signals during the grinding and homogenization processes, making it difficult to recognize subtle variations. Strontium isotope analyses by laser ablation coupled to multi-collector ICP-MS Neptune Plus, obtained through the in situ 87Sr/86Sr method have great potential and broad applicability in cases where the search for gentle isotopic signal variations is relevant, such as in the study of drilling cores. By using integrated petrographic information, it has become possible to perform high-resolution analyses, addressing different components of the crystalline system, with strontium intensities ranging from 200 mg/L to ~ 6000 mg/L. The speed of the analyses, from sampling rock fragments to performing laser-based analyses, provides a large volume of results in a relatively short period of time, facilitating correlations between stratigraphic intervals. The in situ 87Sr/86Sr method has analytical precision between the 4th and 5th decimal place, with sufficient sensitivity to characterize different groups defined by ratios in the ranges of 0.712 - 0.714 (predominantly continental), 0.710 - 0.711 (mixed), and 0.709 - 0.710 (marine influence). Its application in the study of pre-salt carbonates brings a significant advancement in recognizing the environment, and its genetic and diagenetic processes, with great potential to advance our understanding of chemostratigraphy and unravel the transition between continental and marine environments in the early stages of the South Atlantic Ocean's history.

On geological timescales, the volume of CO2 in the atmosphere is influenced by processes such as silicate weathering. In particular, the weathering of basaltic rocks increase the availability of divalent cations such as Mg2+ and Ca2+ in natural waters enabling carbonate formation under atmospheric conditions. Therefore, the existence of carbonate deposits in basaltic provinces provides an excellent opportunity to contribute for the regional environmental record. The Pali Aike Volcanic Field consist of basaltic rocks that covers an area of ca. 4500 km2 in southernmost South America, which were sourced from a deep Mantle source since ca. 4 Ma until the Holocene. The Laguna Timone is a maar filled by a brine developed after explosive volcanic eruptions and constitutes an endorheic hydrological system where carbonate precipitation (calcite and magnesium calcite) is controlled by enrichment of Ca2+ and Mg2+ ions released during the weathering of alkaline basalts. X- ray fluorescence analyses in basaltic rocks reveal high concentration of elements such as CaO (9.73 - 10.57 wt.%) and MgO (9.49-12.76 wt.%). X-ray diffraction results verify that basalts contain pyroxene (Na, Ca) (Mg, Fe, Al) (Al, Si)2O6, olivine (Fe, Mg)2SiO4 and plagioclase NaAlSi3O8-CaAl2Si2O8 which are suitable phases for the mineral carbonation process. The δ13C DIC values of lake range between −12‰ and −16‰ while for the water of the river values of -7‰. These isotopic ratios are associated to three possible sources/processes: weathering of silicates by carbonic acid, atmospheric CO2 and degradation of organic matter. Furthermore, Sr isotope ratios of carbonates (tufa fragments and thin crust in pebbles) define a range between 0.70408 and 0.70475 which is discussed on basis of the data of basaltic rocks (0.70316 to 0.70351) and top soils (0.705382) in the PAVF. Although the Sr isotope ratios of carbonates are indicative of their derivation from the weathering of basalts an exogenous input from relatively enriched 87Sr material is required, this could be associated to 87Sr leached from the top soils and transported by strong wind. Contrastingly a carbonate vein preserved in the tuff ring deposit of the maar has Sr isotope ratios ranging from 0.70265 to 0.70314, similar to the compositional range of the Mantle xenoliths (0.70264 to 0.70431) and basalts. These data indicate that primary sources of carbonates in the lake are related to in-situ weathering of mafic and ultramafic rocks.

Introdução. Coleções didáticas são instrumentos importantes de apoio e suporte aos processos de ensino e aprendizagem, que tanto podem ser utilizados em contextos de sala de aula, ou mesmo para fins de pesquisa. Permitem aos usuários o contato e a interação com materiais representativos de um determinado objeto de estudo. Objetivo e Métodos. Mediante a curadoria e caracterização de um acervo de 30 amostras de rochas carbonáticas, selecionadas dentre um total de 100 amostras coletadas nas seis províncias espeleológicas conhecidas no estado da Bahia, foi construída uma coleção didática sobre rochas carbonáticas e o carste nesse estado. As amostras foram fotografadas e descritas macro e microscopicamente. Também foram realizadas análises por Fluorescência e Difração de Raios X. Resultados e Conclusão. O acervo didático é aqui apresentado e descrito, ficando assim disponível para utilização em diferentes contextos e servindo como um recurso didático disponível para pesquisa, educação em Geociências e popularização das Ciências da Terra.

Carbonate accumulation processes in modern non-marine systems producing tufa and travertine deposits have gained relevance in recent years due to their importance as possible analogues to the hydrocarbon reservoirs of the Brazilian and African Pre-Salt. The biotic/abiotic genesis of these carbonates is related to the fact that these rocks create favorable situations for the proliferation of benthic microbial communities, which can influence the genesis of travertine and/or its final form. The aim of this study is to characterize the carbonate deposits and the biotic influence in the Botijuela travertine systems, located on the western margin of the Salar de Antofalla in the Puna region of Argentina. Descriptions of morphological features and sedimentary facies in the outcrops, thin-slice petrography, mineralogical analysis by X-ray diffraction (XRD), chemical analysis by X-ray fluorescence (XRF), and stable isotopes of C and O (V-DPB) were done. The Botijuela was divided into two active systems: Vega Verde and Vega Blanca. The vent of the first one is a conical mound (~15m) with a length of 530 m, and the second one is a fissure ridge with fractures with a length of 325m, also with two fossilized travertine systems, named I and II. At the proximal depositional zone of Vega Verde, the system presents carbonate facies of mudstones with bubbles, shrub-boundstones, and oncoidal (~0.5cm diameter) rudstones. The fractures of Vega Blanca in the proximal zone present halite and subsequent development of carbonate pools (transversal 2–7 cm) and big oncoids (~2 cm in diameter). Dams and barrages in the pools present botryoids in areas that show subaerial exposure. Oncoids and dendriform shrubs are well developed in the proximal-intermediate depositional zones in low-slope areas. Intermediate zones of both systems are characterized by higher-energy carbonate facies: crenulated mudstones, oncoidal grainstones, and rudstones. The distal area of Vega Verde presents rudstones with detrital fragments, diatoms, and ostracods that interbed with siliciclastic sediments of the Antofalla Salar basin. Vega Blanca presents bigger (~15cm) transversal carbonate pools with oncoids and botryoids at the dams. Mineralogically, the systems are mainly calcite, and calcite low in Mg. Geochemically, Vega Verde shows a content of CaO of ~51.05% and Vega Blanca ~46.63%, with average loss of ignition values of ~40% for both. Vega Verde proximal zone is characterized by a high Fe-As-Pb content (Fe2O3 ~4.3%, Pb-As 0.5 to 1.7%) with an isotopic signature of δ13C (1.97-10.84) and δ18O (-0.67-8.91). In comparation, Vega Blanca systems show averagely higher values of SiO2 (I~10.79% -, II~5.17%) and Na2O (I~ 0.32; II~1.47%), with isotopical signatures for system I of δ13C (5.31~14.78) and δ18O (-4.86~ -0.24), for system II of δ13C (6.34~15.36) and δ18O (-3.20~ -0.71). Signatures indicate a water hypogene origin with δ13C fractionation enrichment towards the Antofalla basin. Geochemical data allows us to infer that the systems have a different water origin. Overall, high-resolution facies analysis of travertine systems and their integration with their geochemical framework and tectonic setting constitute a step forward regarding the environmental distribution of microbially related deposits and the comprehension of their main constraints.

The study focuses on the deposition of freshwater lacustrine tufa in recently deglaciated areas, specifically in Lago Sarmiento. Lago Sarmiento is a large (water volume of ca. 9 km3 and a maximum depth of ca. 310 m), alkaline and oligotrophic lake situated on folded, mudstone-rich turbiditic deposits from the Upper Cretaceous. The lake margin features a semicontinuous tufa section, reaching up to approximately 10 meters in thickness. This section comprises variably amalgamated tufa mounds that can merge into terraces or be arranged as isolated mounds, domes, and V-shaped build-ups of metric sizes. The deposits are irregular, displaying a clotted to slightly dendritic fabric, and high porosity. Vugs within them are filled with authigenic materials (peloids and gastropods) and terrigenous grains (quartz + plagioclase ± Fe-Mg silicates). Microbialites records are discernible at the microscale within the tufa framework. These records consist of variably micritized and/or eroded shrubs composed of fascicular Mg-calcite (mostly 6 - 8.5 mol% MgCO3) encrusting filamentous structures interpreted as formed after the calcification of EPS around radially organized cyanobacteria of the genus Rivularia, as deduced from 16S rRNA analysis in a microbial mat sample. Scant framboidal pyrite is observed in SEM images, suggesting minimal contributions of sulfate-reducing bacteria to carbonate precipitation. Stable isotope analysis of the tufa (δ13C and δ18O) and lake waters (δ2H, δ18O, and δ13C-DIC) indicates that the positive δ13C tufa composition results from variable amounts of CO2 degassing and microbial photosynthesis over a lake DIC pool that remained near isotopic equilibrium with atmospheric CO2. The slightly negative δ18O tufa composition is interpreted as precipitation during warm/dry periods in the Holocene. Lake water chemistry is characterized by relatively low Mg/Ca molar ratios (0.51 – 1.8), intermediate alkalinity (6 – 11.6 meq/L), and low Ca/Alk ratios (0.1 – 0.59 meq/L). In lakes with similar water chemistry, the supply of Ca+2 and Mg+2 is required to achieve carbonate saturation, e.g., through groundwater discharge. A distinctive record of tufa filling fractures in the mudstones that compose the bedrock is identified in the uppermost portions of the lacustrine tufa section, resembling a seepage system that fed the lake. The putative "seepage carbonates" include thicker infills (up to 20 cm) with microfabrics similar to lacustrine tufa, as well as thin (> 2 cm) and laminated cements with syntaxial crystal growth, arranged as interconnected vein-like structures. The "seepage carbonates" exhibit higher aragonite content, Sr/Ca ratio, and lower content of Mg in calcite than the lacustrine tufa. However, the similar δ13C and δ18O composition among both groups suggest the precipitation of the former in sub-lacustrine conditions. In-situ 87Sr/86Sr analysis of lacustrine tufa formed in opposed margins of the lake reveals strong heterogeneity in the source of Sr, with 87Sr/86Sr compositions spanning between those of the bedrock (~0.7075) and Holocene volcanism in southern Patagonia (~0.7050). These findings indicate complex interactions between intrabasinal and extrabasinal sources, climate, and microbial mediation that influenced the multi-episodic growth of the tufa deposits after the local retreat of the glaciers approximately 12.5 ka BP.

Botijuela travertine system is located at the western edge of the Salar de Antofalla at 3433 meters above sea level, the area shows several hot springs still active and several fossilized carbonate deposits. One of the main outcrops of this area is Vega Verde, which develops in a north-south direction where the carbonate deposits start from a vent and reach the Salar de Antofalla basin. In this place, it was possible to observe the development of several microbial ecosystems: non-lithified and lithified microbial mats in the closest area to the vent, as well as cyanobacterial biofilms and lithified stromatolites in the mixing zone between freshwater and thalassic water. In this work, we present the geochemical and mineralogical characterization of these microbial ecosystems. Mineralogically, the lithified ecosystems were composed mainly of calcite, and a less extended Mg-bearing calcite, aragonite, gypsum, and halite. Stable Isotopes C & O analyses showed that the samples from the vent presented an isotopic signature related to hydrothermal origin with δ13C (2,05 – 7,82) and δ18O (-6,59- -9,77) values. While the stromatolite from the Salar de Antofalla (in the mixing zone) showed high δ18O (0,8-1,12) and δ13C (7,63-13,26) values, which suggests that the evaporation process is the main fractionation force. Although is considered that the main processes driving the travertine mineral precipitation are degassing and evaporation, petrological and SEM analyses showed that microbial activity appears to be contributing to the sedimentological textures of Vega Verde samples rocks. Moreover, the mineral morphologies and carbonate growth structures found in the SEM rock samples were also found in the in vitro carbonate precipitation experiments, but exclusively when microbial mats were present, and not in the negative control. These results suggest a strong influence of hydrothermal flows, evaporation process, and microbiological mediation during the Vega Verde carbonate systems formation.

The early evolution of the South Atlantic Ocean following the Cretaceous break-up of Gondwana is extensively recorded in rift basins along the conjugate margins of Africa and Brazil. For the Brazil side, divergent views of the source and pathway of the initial seawater incursion persist due to a paucity of recognized transitional sequences that document marine transgressive deposits over the continental interior. To address this, we conducted a high-resolution sedimentological and geochemical study through a core in the Campos Basin that encompasses the key lithologic switch from lacustrine carbonate to marine evaporite settings. Steroid lipid biomarkers, derived from pelagophyte marine algae, make a striking appearance in concert with a pronounced negative shift of 87Sr/86Sr ratios and coincident with the appearance of anhydrite. Importantly, the sulfur-sequestered biomarkers reveal a dynamic system where redox-stratified and anoxic conditions were amplified along with a deepening chemocline through the marine transition. During the break-up of Gondwana, a marine invasion from the proto-South Atlantic Ocean about 116 million years ago transformed the paleoecosystem of the Campos Basin, as revealed by the analysis of lipid biomarkers and carbonate isotopes from the east coast of Brazil

We present new petrographic, whole-rock geochemistry, and SHRIMP U - Pb zircon geochronological data of metabasic rocks interlayered as sills in the metasedimentary units of the Perau and Betara formations, Votuverava Group, Southern Ribeira Belt, Brazil. These formations overlie similar to 1.8 Ga Paleoproterozoic metagranitoids that represent basement inliers from the Paranapanema Craton. Petrography and whole-rock geochemistry allow the recognition of four groups, ranging from primitive to evolved compositions: i) cumulatic metadolerites (G1), ii) isotropic metadolerites (G2), iii) ortho-amphibolites (G3); and iv) ferroan ortho-amphibolites (G4). They exhibit tholeiitic subalkali basaltic composition, near-flat REE patterns, and signatures between N- and E-MORB. Fractional crystallization under low fO2 conditions is the main petrogenetic process controlling the magmatic evolution, as observed by Ti/V and Cr/Y ratio and tholeiitic trends. Crustal contamination signatures are observed through negative Nb anomaly, Th/Nb-Ti/V proxies trends, LILE enrichment, and, also, assimilated xenocryst zircons aged similar to 2.2 Ga. REE and trace element systematics indicate that the basic magmas were generated by similar to 20-10% partial melting of a model asthenospheric mantle source within spinel facies. TiO2/Yb-Nb/Yb and Nb/Yb-Zr/Yb ratio proxies and P-MORB metabasic rocks, previously described in the literature within the Votuverava Group, suggest a plume-influenced melt. A new SHRIMP U - Pb zircon age of 1448 +/- 11 Ma was determined for an ortho-amphibolite sample (G3 group). We propose an intracontinental tectonic setting for the genesis of the metadolerites whitin the Perau and Betara formations, suggesting that this extensional event is associated with the Paranapanema Craton rifting. Furthermore, the genesis of the studied metabasic rocks could be associated with a regional extensional event during Calymmian times (similar to 1.5-1.45 Ga), which generated basic magmatism in several other cratons, such as the Congo, S & atilde;o Francisco, Siberian, Laurentian, and China cratons, linked to the break-up of the Columbia Supercontinent.

Tufas are freshwater carbonate rocks that form in continental environments through a combination of physical, chemical, and biological processes. This study investigates the role of microorganisms in the precipitation of Quaternary tufa deposits in the Serra da Bodoquena Formation, in the Bonito region. Two sites along the Mimoso River, named Ta & iacute;ka and Mimosa, characterized by the pool-barrage-cascade depositional subenvironment, were selected for this study. Four distinct facies were identified: stromatolitic boundstones, phytoherm boundstones of algae, phytoherm boundstones of bryophytes, and phytoclastic rudstones. These facies were observed in diverse hydrological settings, including fast-flowing waters, such as waterfalls and cascades, as well as slow-flowing areas, such as pools and dams. The delta 18O depletion indicated a meteoric origin for the fluid involved in carbonate precipitation. The low delta 13C values were attributed to photosynthetic processes and the contribution of light carbon-enriched groundwater. The presence of Oocardium stratum and calcified organic mucilage from extracellular polymeric substance (EPS) corroborates the significant role of microorganisms in tufa formation, particularly in stromatolitic boundstones and phytoherm boundstones of algae. Rapid CO2 degassing significantly contributes to mineralization in fast-flowing waters. Micro-CT results offer detailed insights into the relationship between mechanical processes and biological influences in shaping porosity characteristics. The findings of this study significantly enhance our understanding of the role of microorganisms in tufa formation, highlighting the complex interplay between biotic and abiotic processes in the development of different tufa facies. Moreover, the insights gained from this study provide valuable implications for interpreting tufa deposits worldwide.