Journal of South American Earth Sciences最新文献

Brazil is the seventh-largest phosphate producer globally, contributing to almost 3% of total production. Approximately 20% of the country's phosphate output comes from sedimentary sources, while the remaining 80% is of magmatic origin. The growing demand for phosphate has sparked increased interest in identifying new deposits. In northwestern Brazil, a phosphate rocks in the São Benedito Formation, part of the Alto Tapajós Group in the Apuí region of Amazonia, has attracted attention.

Twelve outcrops were collected for mineral and chemical analysis, solubility testing in aqueous media, standard tests using citric acid, and P₂O₅ release kinetics. The raw material consists of compacted gray quartz sandstone containing fluorapatite, glauconite, and siderite. The raw samples exhibited total P₂O₅ content of up to 6%. Additional elements were assessed, with only CaO and Fe₂O₃ showing total contents reaching 8.05 wt% and 6.65 wt%, respectively. Kinetic extraction in a 2% citric acid solution revealed a positive correlation between soluble and total contents of CaO and P₂O₅ indicating apatite composition. The elements showed solubility exceeding 60% within the first 30 min and reaching 100% after 180 min. However, as the fluorapatite and siderite dissolved, the citric acid solution became saturated, halting the dissolution process. These results indicate effectiveness in solubilizing phosphate in samples with less than 4 to 5 wt% of P₂O₅, meeting the minimum requirements established by the Brazilian Ministry of Agriculture. These characteristics suggest that the São Benedito Formation phosphate rocks have agronomic value for use as direct/natural fertilizers in Brazil's tropical acidic soils.

Benthic foraminifera are valuable tools for understanding the dynamics of methane seepage worldwide. This study was conducted to characterize the filtration levels of surface samples from 18 stations within a filtration field on the outer continental shelf of the Colombian Caribbean margin. The characterization was based on variables of benthic foraminifera (wall types, spatial distribution of abundances, and associations of dominant species), shell modifications (overgrowth, dissolution, and fragmentation), multivariate statistics, and models explaining the relationships between foraminifera populations and species with levels of filtration activity. Four activity zones were identified. The assemblage of Quinqueloculina candeiana, Triloculina trigonula, Lagenammina difflugiformis, Criboelphidium poeyanum, and Criboelphidium sp. represented low activity; the assemblage of Lobatula ungeriana, Cibicidoides mundulus, and Cibicidoides pseudoungerianus represented moderate filtration; and the assemblage of Liebusella soldanii, Bigenerina irregularis, and Reophax agglutinatus represented moderate–high filtration, whereas high filtration was identified for the assemblage of Cibicidoides mundulus and other hyaline species. Moreover, the type of substrate, methane transport, and physiological adaptations such as symbiosis affected the abundances of these species in different filtration zones, indicating a preference for greater abundances of benthic foraminifera in zones of moderate activity. Furthermore, the δ¹³C values of three species, Criboelphidium poeyanum (−0.17 to −3.85 PDB), Quinqueloculina candeiana (0.02‰ to −1.18‰ PDB), and Lobatula ungeriana (1.99‰ to −3.03‰ PDB), reflected isotopic signals related to CO₂ plumes that preserved the effects of hydrocarbon oxidation and microbial gas. The response of the species was associated with their living depth. Finally, a redundancy analysis demonstrated that the benthic foraminifera populations examined in this study respond primarily to the type of substrate, salinity, and gas seepage.

In the Seridó Pegmatite Province (SPP) there are thousands of granitic pegmatite intrusions, including unzoned and barren, and zoned and mineralized ones. The whole rock chemical analysis of pegmatite is usually unfeasible because of its large grain size. However, fine-grained aplites syn crystallized with pegmatites should allow them to be used as proxies to assess pegmatite melt differentiation. We selected 15 representative aplite occurrences within unzoned pegmatite intrusions, including 7 intrusions with the grayish muscovite-aplite type and 8 with the reddish magnetite-aplite type. We also used for new trace element analysis samples of medium-to coarse-grained facies of host unzoned pegmatites. These pegmatites occur as NE-SW and N-S dykes and sills intruding mica schist and paragneiss from the Seridó Belt. Both aplite types contain along with quartz and feldspars accessory apatite, zircon, monazite, and xenotime. Tourmaline, muscovite, and garnet occur in the grayish aplites, whereas biotite and opaque minerals occur in the reddish aplites. The grayish aplites are slightly to strong peraluminous, while the reddish aplites are slightly metaluminous to slightly peraluminous. The reddish aplites and their host pegmatites are enriched in Ba, Sr, U and Th, while the grayish aplites and their host pegmatites are enriched in B, Li and Cs. The K/Rb ratios of the aplites varies from 11 to 44 with similar ranges in both reddish and grayish aplites. Normalized to the average upper continental crust composition, both aplite types present positive anomalies of Rb, Pb, U, and Hf, and negative anomalies of Ba, Sr and Ti. K, Nb and Ta show variable enrichment and depletion. They usually show HREE enrichment in relation to LREE and negative Eu anomaly, but positive Eu anomaly and tetrad patterns occur in few samples. In the normative QAP diagram the aplites show a wide range of compositions with a trend from quartz-plagioclase-rich tonalite to quartz-poor K-feldspars-rich alkali granite. Such trend is inverted in relation to the characteristic trends of melt differentiation by crystal fractionation. The albite/K-feldspar ratio of aplites shows a wide distribution range that would be related to the compositional variety of the partially melted protoliths and/or the variation in melting rate during prograde anatexis. The trace element compositions of the medium-to coarse-grained facies of the unzoned pegmatites are very similar to those of the coexisting aplites. The obtained data using aplites as a proxy for their host pegmatites precludes a unique line of melt descent at the origin of the SPP aplites and unzoned pegmatites and thus strongly support an anatectic origin from different sources.

Bonebeds, concentrations of fossilized vertebrates, provide valuable insights into paleoecological, biostratigraphic, and macroevolutionary contexts, though they are often influenced by taphonomic processes. Brazilian Triassic rocks are notable for such fossil assemblages. Among these, the Várzea do Agudo site is remarkable for its abundance of fossils of the traversodontidae cynodont Exaeretodon riograndensis. Initial studies suggested that biogenic factors, especially scavenging and predation, were key to the formation of these bonebeds. This study aims to describe a new fossiliferous concentration from this site, analyzing the taphonomic and biostratinomic processes involved in its genesis. Our findings indicate that multiple factors, including biogenic actions and environmental conditions such as floodplain dynamics, contributed to the accumulation and preservation of the abundant bonebeds. This integrative approach enhances our understanding of the paleoecology of Exaeretodon riograndensis, which was probably a gregarious animal, and the environmental context of Hyperodapedon Assemblage Zone.

The main objective of this article is to determine the completeness magnitude (CM) of the earthquake catalog for Argentina and neighbouring countries from 1524 to 2024. The CM was evaluated from a stable estimate of the average rate of earthquake occurrence and the temporal distribution of seismicity using the Stepp and Temporal Course of Earthquake Frequency (TCEF) methods. These methods provide an innovative approach to the analysis of the completeness level in the study area. Temporal variations of the CM in the past were also investigated, since no records were available before the 16th century.

The catalogue was filtered and homogeneized to moment magnitude (Mw). Results from the Stepp method showed that the CM significantly improved from 1960, whereas the TCEF method indicated a decrease of the CM from 1964. The Gutenberg and Richter (G-R) recurrence parameters a and b were also estimated for the entire catalog using the CM obtained from both methods, and for the cortical, intermediate and deep events using only the Stepp completeness. The b value obtained for the entire catalogue is 0.75 with the Stepp method and 0.66 with the TCEF method, very similar to the regional values determined in previous studies. It is necessary to highlight that the proposed approach provides a preliminary step for estimating the seismic hazard of the study area. The integration of other methods will help to improve some limitations, contributing to a complete assessment of the earthquake catalogue.

Halysites catenularius Linnaeus is reported from the Silurian strata that form outcrop in the Rancho Placeritos (San Antonio dolostone) located west of Hermosillo, capital of Sonora, Mexico. In this region, a sequence of Paleozoic sedimentary rocks of ages ranging from the Upper Ordovician to the Lower Mississippian is exposed. Halysites catenularius is identified as a reef buildings tabulate coral associated with calcareous algae, sponges, rugose corals, other tabulate corals, bryozoans, brachiopods and, pelmatozoans. The biota developed in shallow tropical seas from southwest of the North American craton, which was located near the paleoecuatorial line. The Silurian platform deposits of Sonora correlate with localities in the southern United States of America and northern Mexico (Sonora and Chihuahua) that were part of the margin of the North American craton. The description of Halysites catenularius contributes to the knowledge of the biota of the lower Paleozoic of Mexico, particularly the Silurian.

The concept of baseline is crucial for assessing natural water conditions and detecting anthropogenic influences in groundwater systems. This research proposes a methodology to define a geochemical baseline using the groundwater flow theory to develop a conceptual model, distinct from most methodologies that primarily rely on statistical techniques. The proposed methodology comprises three phases: defining a conceptual model, defining a geochemical baseline based on hydrogeochemical characterization, and identifying anthropogenic sources. This approach enhances understanding of hydrogeologic processes such as water-rock interactions, exchanges with other water bodies, redox conditions, and groundwater flow by integrating information about geology, structural geology, base level of discharge, hydrological connectivity, topography, and water table. The methodology was applied in the southern region of Mexico, specifically in the Comitán-Montebello lakes watershed characterized by complex features like the karst system and interactions with surface water bodies, providing relevant insights into the hydrogeological setting. It is a cost-effective approach that improves understanding of hydrogeological processes in data-scarce areas, thereby supporting the establishment of geochemical baselines.

New zircon U-Pb geochronology (SHRIMP) and geochemistry combined with geochronology (LA-ICP-MS) of titanite data are provided to investigate the metallic sources (whether igneous or sedimentary) and the temporal evolution of one of the most relevant Precambrian metallogenic provinces of the South American Platform, the Seridó Mineral Province. The granites of Serra de João do Vale pluton, calc-silicate “skarnoid” rocks and paragneiss related to the Bonito W-Mo-Cu exoskarn deposit were investigated. It was analyzed titanites of magmatic (Serra de João do Vale), hydrothermal (calc-silicate rocks) and metamorphic (paragneiss) origin. The magmatic titanite is wedge-shaped with larger grain size (up to 250 μm), richer in HFSE elements, Al and Fe, and manifests negative Eu anomalies (Eu/Eu × averaging 0.31–0.60). The hydrothermal titanite is found alongside epidote and calcite, have subhedral shapes and medium grain size (up to 150 μm). The metamorphic titanite is anhedral, generally smaller than 100 μm and appear as thin coronae in ilmenite or as inclusions in biotite. Both metasomatic and metamorphic titanites manifest positive Eu anomalies (Eu/Eu × averaging 1.20 and 1.06, respectively) and are enriched in Ti, Rb and U in relation to the magmatic. Conventional mineral thermobarometry (Al-in-titanite independent barometer, and Zr-in-titanite thermobarometer) provided pressures between 400 and 550 MPa and temperatures between 720 and 787 °C for the crystallization history of the granite, coeval with the regional peak metamorphism at 568–624 °C and 300–500 MPa (Ti in biotite independent barometer and biotite-muscovite thermobarometer). Conditions for the titanite-epidote calc-silicate assemblage were constrained through thermodynamic modelling in NCKFMAST + COH pseudosection at 439 ± 35 °C and 190 ± 50 MPa. The zircon U-Pb age registered the magmatism between 585.5 and 580.5 Ma. Titanite U-Pb ages from granite and calc-silicate rocks timed the closure of U-Pb system at the isotherm of 550 °C between 562 and 557 Ma. (20 m.y. after the intrusion), which marks the metasomatic process. The average W content in paragneisses and calc-silicate titanites (35.8–35.5 ppm) is 4 times higher than in the granite (6.76 ppm), reaching a maximum of 328 ppm. Mo and Cu mirrors this behavior, with concentrations that exceed nearly double that of titanites from Serra de João do Vale granites, peaking at 308 ppm of Mo and 162 ppm of Cu. Metal contents in titanite disclose the metasiliciclastic rocks of the Jucurutu Formation as, at least partially, a source of metals (mainly for W, but also Cu and Mo) in the skarn mineralization during the terrane exhumation at the end of Ediacaran period.

Naturally fractured volcanic rocks represent a globally significant potential hydrocarbon reservoirs and can also be used for CO₂ storage; however, the study of volcanic reservoirs in Brazil is limited. Although numerous volcanic reservoir types have been classified, relatively few studies are dedicated to the weathering of crust-like reservoirs, i.e., volcanic rocks undergoing subaerially alteration by weathering prior to deep burial. This study aims to characterize a volcanic weathered crust reservoir analog located in the coastal zone of the Pernambuco Basin, NE Brazil. We applied a multiscale approach motivated by the expressive potential of volcanic rocks as reservoirs in this marginal basin and considered their implications for CO₂ geological storage projects. The deformational aspects observed in this analog have also been observed in other volcanic rocks that crop out in the coastal zone, thus, the data provided here can guide future characterization of both onshore and offshore reservoirs. We focused on an 80 m wide outcrop and employed geometric and topological analysis of two-dimensional fracture networks to investigate the influence of regional fault zone control on the fracture permeability tensors. The parameters of fracture systems were studied using terrestrial gravimetric data, orthophoto mosaic obtained by an unmanned aerial vehicle (UAV), petrography, and outcrop-based structural data. The investigated outcrop includes porphyritic trachytes with euhedral sanidine crystals and minor quartz phenocrysts, sourced from the Ipojuca Magmatic Suite. The residual Bouguer map indicates the influence of at least two regional rift fault zones, i.e., NW-SE (strike-slip) and NE-SW (normal) trending systems, in the studied rocks. These trachytic rocks exhibited a marked dissolution of sanidine phenocrysts and matrix, columnar disjunctions, and natural fractures, causing the porosity and permeability of the reservoir analog to increase. Geometric and topological analyses showed that the south-central sector of the outcrop exhibits heightened connectivity within the fracture network. Furthermore, the principal fracture permeability is controlled by the primary families of the fracture network and regional fault zones. Our results demonstrate that the fracture network observed in the volcanic reservoir analog was influenced by the post-rift tectonic reactivation of Cretaceous structures within the Pernambuco Basin. The secondary porosity resulting from weathering and subsequent dissolution of the primary constituents and fractures of the rocks studied demonstrates the potential for the exploration of these reservoirs as models for known occurrences of volcanic rocks in the onshore and offshore domains of the Pernambuco Basin.