Serra Geral Research Articles

Platinum-group element geochemistry of the Paraná flood basalts – Modelling metallogenesis in rifting continental plume environments

The 135 Ma Paraná-Etendeka Large Igneous Province (PELIP) is one of the largest areas of continental flood basalt (CFB) volcanism in the world and is widely agreed to be a product of intracontinental melts related to thermal anomalies from the Tristan mantle plume. The province rifted during the break-up of Gondwana, as the plume transitioned into an oceanic geodynamic environment. This study reports analyses of plume-derived basalts from the Brazilian side of the PELIP (the Serra Geral Group) to investigate major, trace and platinum-group element (PGE) abundances in an evolving plume-rift metallogenic setting, with the aim of contextualising metallogenic controls alongside existing magmatic interpretations of the region. The chalcophile geochemistry of these basalts defines three distinct metallogenic groupings that fit with three modern multi-element magma classifications for Serra Geral lavas. In this scheme, Type 4 lavas have a distinctive PGE-poor signature, Type 1 (Central-Northern) lavas are enriched in Pd, Au and Cu, and Type 1 (Southern) lavas are enriched in Ru and Rh. Our trace element melt modelling indicates that the compositional variations result from changes in the melting regime between the garnet and spinel stability fields, in response to the thinning and ‘unlidding’ of the rifting continent above. This process imposes progressively shallower melting depths and higher degrees of partial melting. Accordingly, Type 4 magmas formed from small degree melts, reducing the likelihood of sulphide exhaustion/chalcophile acquisition at source. Type 1 (Central-Northern) magmas incorporated components of the sub-continental lithospheric mantle (SCLM) in higher-degree partial melts; the SCLM was heterogeneously enriched via metasomatism prior to plume melting, and this produced enrichment in volatile metals (Pd, Cu, and Au) in these magmas. In contrast, the Ru-Rh enrichment in Type 1 (Southern) lavas is attributed to increased spinel-group mineral and sulphide incorporation from the mantle into higher degree partial melts close to the continental rift zone. Our models confirm the importance of contributions from SCLM melts in precious metal mineral systems within CFB provinces, and reinforce the role of heterogeneous metasomatic enrichment underneath cratons in boosting intracontinental prospectivity with respect to ore deposits.

Proposed method for the evaluation of water productivity in fractured aquifers

Due to the poor understanding of fractured aquifer systems, the choice of the best locations for the installation of productive wells in these aquifers is a challenge for hydrogeology. The present work aims to propose and apply a method to evaluate the water productivity of the Serra Geral Aquifer System (SGAS) in northern Paraná. Environmental factors that influence the aquifer productivity were defined and weights were assigned, ranging from 1 to 5, as well as ranges and classes that varied from 1 to 10. Using data from wells and structural lineaments identified in the area, maps of estimates were prepared using the ordinary kriging method. The maps were then multiplied by the previously assigned weights and classes, generating the water productivity map (FAPI). Multiple Linear Regression (MLR) was applied to validate the assigned weights and obtain the SGAS water productivity equation. The FAPI map indicates that the majority of the study area (58%) has low water productivity, followed by medium productivity (27.7%). The other classes represented low percentages in the area. The MLR demonstrated that the weights assigned were mostly correct, with the exception of the weight of the Specific Capacity factor which could be lower. Despite this, the model generated was considered representative (p < 0.05; R2 = 0.85). It was also possible to suggest areas more favorable to the location of tubular wells in the study area. Finally, the proposed method and the FAPI map are considered innovative and important tools for urban and environmental planning, aiming at better management of water resources.

Structural, hydrogeological and hydrochemical characterization of aquifers in the Paraná Basin: An integrated literature review

The Paraná Basin in Brazil is of vital importance and because of a large groundwater reservoir and the high exploitation of this resource by the population a structural and hydrogeochemical knowledge is needed. Objectives: 1) Analyze studies that address the structural, hydrogeological and hydrochemical characterization of aquifers in the Paraná Basin; 2) Highlight the main techniques used in the respective studies and the scientific development arising from the use of these techniques for a better hydrochemical and structural understanding of the Paraná Basin. Methodology: Tracing lineaments from satellite image and field work are the main techniques used for structural characterization. For hydrochemical analyses, factorial methods physical-chemical analyses are used. Results: the most common chemical types of groundwater that circulate in the sedimentary and volcanic units of the Paraná Basin, which include the Pirambóia, Irati, Rio Bonito, Botucatu and Serra Geral formations are calciumbicarbonates, calcium-magnesian bicarbonates, calcium-sodium bicarbonates and sodium-sulphate-chloride bicarbonates. Sodium-sulfated waters are not found in the Serra Geral Formation, except when they come from the sedimentary units. Sodium and sulfate are not expected ions in basalt weathering, and therefore a greater understanding is needed on structural communication by means of faults that occur between the Serra Geral Aquifer System (SGAS) and the mesozoic and permian sedimentary aquifers and aquitards that contribute for unexpected ions in the SGAS. Conclusion: The Paraná Basin is a reason for interest in geological studies in Brazil because of its link to several areas of interest in geosciences, which include hydrochemistry, stratigraphy, paleontology and hydrogeology.

Numerical modeling and 3D-gravity inversion of the Vargeão impact structure formed in a mixed basalt/sandstone target, Paraná Basin, Brazil

Terrestrial impact structures formed in basaltic targets are suitable analogues for analyzing cratering processes in other planetary bodies where basalt is abundant. However, such structures are remarkably scarce on Earth. The Vargeão impact structure in the Santa Catarina state, Brazil, is one of the rare cases of such structures. It was formed in the Paraná-Etendeka Large Igneous Province, in the region that currently corresponds to the Paraná Basin, in southern Brazil. Local stratigraphy comprises volcanic rocks of the Jurassic-Cretaceous Serra Geral Formation, mostly basalts intermixed with rhyodacites, lying on top of sandstones of the Piramboia (Triassic) and Botucatu (Jurassic) formations. We analyzed the dynamics of crater formation through numerical simulations, focusing on the resistance to deformation under high pressure of a very tick basalt (>1 km) layer overlaying clastic sedimentary sequences. We then compared the crater morphology obtained from the model with the results of a 3D-gravity inversion based on the Preconditioned Conjugate Gradient (PCG) algorithm. We used this method to estimate the depth of the sandstones underneath the basaltic layer, and to better understand the complex structural relationship between both lithologies, especially in the central uplift area. Our results showed that the Vargeão crater was likely formed in ca. 130 sec., by a projectile of approximately 1,400 m in diameter, which produced a transient crater of ~14 km diameter, with a subdued topographic high at the center. We also point out that the negative Bouguer anomaly observed at the center was a consequence of the structural uplift of the sandstones by ~500 m, together with pre-Triassic sedimentary sequences underneath the sandstones. Both models support the formation of a final crater with a relatively subtle central peak.

Lithosphere of South American intracratonic basins: Electromagnetic and potential field data reveal cratons, terranes, and sutures

A magnetotelluric survey comprising 18 broadband stations disposed along a 450 km-long profile was carried out at the transition between the Chaco-Paraná (CPB) and the Paraná (PB) intracratonic basins in northeastern Argentina. Three-dimensional inversions of the responses show that the CPB and southern PB lithospheres are resistive (~103 Ω m) down to 120 km, but with distinct crustal and upper mantle electrical properties. Also, Bouguer gravity and density anomalies are positive at CPB, whereas they are negative at PB. We associate the CPB lithosphere with the Paleoproterozoic Rio Tebicuary craton and the southern PB lithosphere with an ancient and buried piece of craton, the Southern Paraná craton. Geochemical data of mantle xenoliths from the Cenozoic alkaline/carbonatitic province within the Rio Tebicuary craton suggest a subcontinental lithospheric mantle affected by metasomatic processes, which explains its lower resistivity (reaching values as low as 300 Ω m) and higher density (#Mg = 0.87). In contrast, the Southern Paraná craton is more resistive (>103 Ω m) and less dense, suggesting a de-hydrated, depleted, and thicker craton. These cratons are separated by a crustal conductor (15 to 20 km depth; 1–10 Ω m) that we interpret as a southward continuation of a linear anomaly (Paraná Axial Anomaly) defined in former induction studies within the PB in Brazil. Hence, we redefined the trace of this conductive lineament: instead of bending towards the Torres Syncline, it continues inside the CPB. We propose the lineament to be an Early Neoproterozoic suture zone that controlled the location of maximum subsidence in the intracratonic basins during the Paleozoic. In the Early Cretaceous, the Paraná Axial Anomaly was the site of maximum extrusion and deposition of Serra Geral basalts. This anomaly separates compositionally distinct cratonic lithospheres along its path. Melting of this heterogeneous and enriched mantle created the Paraná igneous province.

Avaliação hidrogeológica quali-quantitativa do aquífero fraturado Serra Geral, localizado no noroeste do Rio Grande do Sul

Um dos maiores aquíferos do Rio Grande do Sul é o aquífero fraturado Serra Geral. Ele corresponde a uma importante fonte de abastecimento de água para 46% dos municípios. Este estudo objetiva avaliar a influência do sistema de fraturas do sistema aquífero Serra Geral na produtividade e na qualidade das águas subterrâneas. Testes estatísticos, integrando parâmetros estruturais, hidrodinâmicos e hidroquímicos, foram realizados utilizando o programa estatístico PAST. A área de estudo abrange o município de Frederico Westphalen. A maior parte (75%) das captações do município não ultrapassa 186 m de profundidade. As captações que interceptam mais de uma zona de fratura têm maior capacidade específica (até 19,8 m3/h/m) e são menos profundas do que as que interceptam uma única zona de fratura. As vazões são da ordem dos 8 m3/h. Os poços próximos aos maiores lineamentos interceptam frequentemente várias zonas de fraturas e apresentam: estradas de água, nível dinâmico e estático menos profundos, maior vazão e maior capacidade específica em relação aos poços próximos a lineamentos menores. Os níveis piezométricos indicam tendência regional de escoamento de oeste para leste e nordeste. Predominam águas bicarbonatadas sódicas, sendo mais carbonatadas e mais cloretadas as águas de poços que interceptam uma única zona de fratura. O pH, entre 7 e 9,9, aumenta com a proximidade dos lineamentos e com o aumento da profundidade da captação. Apesar de 78% das águas apresentarem qualidade nos padrões de potabilidade para consumo humano, há poços com concentrações de ferro total e de fluoreto acima do permissível. Há indícios de contribuição de águas salinizadas de aquíferos mais profundos (fluxo ascendente) em poços que exploram o sistema aquífero SG.

Resurfaced paleodunes from the Botucatu erg amid Cretaceous Paraná volcanics

Extensive exposure of Cretaceous paleodunes partly covered by basaltic rocks is a rare surficial structure in the geomorphology of continents. The Paraná Basin offers the opportunity in southernmost Brazil to study the relationships between the major Botucatu paleoerg-turned into the Guarani Aquifer (1.2 million km2) and the overlying, first flows from the Paraná Volcanic Province (1 million km2). We describe the Inhanduí Paleodune Field (IPDF; 15,000 km2) preserved by the first two (up to six) flows of the Paraná Volcanic Province. The field was exposed by erosion of volcanic overburden in Fronteira Oeste of southernmost Brazil. A plan view of the field is examined in the extensive grasslands and rice crops of the pampas. Observational geology from satellite images was followed by field description, gammaspectrometry, petrography and whole-rock geochemistry. Results show that bedforms include thousands of varied individual and compound paleodunes, including crescentic (barchane), linear, circle (blowout), and complex forms. Cerro do Jarau was considered an impact crater, and is here characterized as a compound paleodune. The paleoerg sand was silicified and deformed by hot water from the Guarani aquifer and the explosion of vapor in IPDF. The active dunes were flooded with tholeiitic lavas; heating by residual heat from volcanism (raised geothermal gradient) led to sand injection into overlying volcanic rocks. Silicification accompanied and followed the injection process. The Botucatu Formation includes the paleodunes and was the source bed of the sand injectites (Novo Hamburgo Complex) into the overlying volcanic group. We thus uncovered the processes associated with the flooding of a major, active erg by lavas from a large volcanic province. Hyperdry climate prevailed in the sandy Botucatu desert and continued in the rocky Serra Geral desert. The studied geological relationships are unique in the geological records; their understanding fosters the correct description of geological evolution of other terrains where some of the parameters are present.

Raw materials and functional designs of Fishtail projectile points from southern Brazil

This study analyses the lithic landscape and the selection of rocks used to manufacture Fishtail points (FP) in southern Brazil, their designs, and some functional aspects. In order to identify the offer of lithic resources, we carried out several surveys throughout 15 months in 47 counties in the Southern Brazil covered by the Botucatú - Serra Geral Vulcano Sedimentary Complex. The lithic composition of numerous hill slopes, fallen rocks, and accumulations of pebbles and boulders in the riversides was evaluated. The results show that basalts (including a small proportion of andesites and rhyodacites-rhyolites), and silicified sandstones, are ubiquitous in the landscape. Conversely, non-translucent cherts are scarce, so their acquisition would have been time-consuming. However, these local cherts were the rocks mostly used to manufacture these points, being another example of the selectivity for high quality rocks by Paleoamerican hunter-gatherers. The same cherts selected in southern Brazil to produce the FP were used to manufacture other point-types by local hunter-gatherers of the early and middle Holocene grouped in the so-called “Umbú Tradition”. Not a single FP of the entire collection analyzed here was made from silicified limestones, which is one of the most common raw materials among the Uruguayan FPs, nor were they made from quartzites as were most of the FPs of the Pampean plains.&#x0D; Regarding to the designs of these projectiles, some morphotypes appear to have been designed to produce multiple injuries through successive thrusts and withdrawals in the bodies of the prey, while in others, the design seems to have favoured penetration and fixation on the prey, suggesting in this case, a single shot technique for each projectile. As the maintenance process unfolded, especially for points below ~ 80 mm in length, they show features that negatively impacted their efficiency, including distinct asymmetries, somewhat open front angles, a decrease in the cutting perimeter and cross-sectional area, an increase in the bevel angle of the blade edges, and a tendency to a conical cross-section. Behaviours intended to counteract these problems were maximizing the length of the leading edge, maintaining the symmetry and the triangular blade resting on straight shoulders, and maintaining the aerodynamic properties as much as it were possible, in order to improve their lethality and the fixation capacity.&#x0D; Beyond these rejuvenation processes, three different morphotypes of points appear to be included within the sample. The first includes points over 120 mm and ~ 80 g in weight, with triangular or slightly lanceolate limbs, which mostly present straight shoulders, but there are also examples of rounded shoulders. The second design corresponds to projectiles between 110 and 87 mm and ~30 g in weight, with triangular or slightly lanceolate blades and straight shoulders. The third design presents the classic shape of these projectiles, with a fish silhouette, with maximum lengths below 90 mm, with a more robust and conceptually different design, where the angles of the edges of the blades and of the shoulders are equal, perhaps with the intention to facilitate the spear withdrawal to produce multiple injuries.

The effects of basaltic lava flows on the petrophysical properties and diagenesis of interbedded aeolian sandstones: an example from the Cretaceous Paraná Basin, Brazil

An analysis of the petrophysical and diagenetic effects of the emplacement of Cretaceous basaltic lava flows (Serra Geral Formation) on aeolian sandstones (Botucatu Formation) has been undertaken on core samples from the Paraná Basin, Brazil. Between 0.1 and 1 m from the contact zone, acoustic wave velocities and porosities in sandstones show a significantly wider scatter than those located &gt;1 m away from the lava contact. Higher P-wave values (average 3759.3 m s −1 ) occur between 0.1 and 1 m from the lava contact in contrast to those areas &gt;1 m away (average 3376.8 m s −1 ), whilst the average porosity is 6.5% near the contact (0.1–1 m) and 10.7% away from the contact (&gt;1 m). Petrographical evaluation reveals two diagenetic pathways responsible for modification of the petrophysical properties: early hydrothermal Mg-rich authigenesis (Type 1) and early chemical dissolution (Type 2). Type 3 diagenesis occurs away from the lava–sediment contact (&gt;1 m), with the appearance of poikilitic calcite and smectite. The sandstone samples associated with Type 1 and Type 2 diagenesis display a decrease in porosity and increased acoustic velocities in relation to Type 3, while Type 3 samples show little or no variation in reservoir properties. The lava-induced diagenetic effects at the sandstone–lava contacts (0.1–1 m) may form a baffle or seal to fluids around the margins of the sandstone bodies. Therefore, whilst diagenesis associated with lava emplacement may hinder reservoir quality around the margins, the original reservoir properties are preserved within these large sandstone bodies. Supplementary material: Petrophysical and petrographical data are available at https://doi.org/10.6084/m9.figshare.c.5244473

Determining sediment provenance history in a Gondwanan erg: Botucatu formation, Northern Paraná Basin, Brazil

The Lower Cretaceous Botucatu Formation comprises a dry-aeolian system developed in western Gondwana and preserved within the Paraná Basin of central South America. Multiproxy provenance analysis (detrital zircon UPb dating, heavy mineral, petrographic and granulometric analysis) was undertaken along two 500 km transects of the northern Paraná Basin (NW and NE transects). To assess the provenance variation within the aeolian stratigraphy, samples were taken from the base and top of the Botucatu Formation and from sandstones interbedded with volcanics in the overlying Serra Geral Formation. Granulometric analysis shows a mean fine- to very fine-grained sand. The bulk petrography yields an average composition of Q91F6L2, and heavy mineral analysis gives a mean of 86% of zircon-tourmaline-rutile, demonstrating the overall polycyclic nature of the sediment. The discrete occurrence of garnet, apatite and epidote indicates local sediment input points, providing indirect evidence for point-sourced fluvial input into an overall dry aeolian system. Detrital zircon UPb LA-ICP-MS dating demonstrates a dominant Cambrian to Late Neoproterozoic (520–750 Ma) population with subsidiary Tonian-Stenian (0.9–1.2 Ga) and Orosirian-Rhyacian (1.9–2.3 Ga) contributions. The Botucatu Formation along the northern basin margin displays similar provenance to the southern part of the basin, pointing to a predominance of recycling processes within the basin. Statistical plots illustrate the detrital zircon age variability - recording an upward decrease in the age proportion of Permian and Tonian-Stenian populations and an increase in Cambrian-Late Neoproterozoic dates towards the top. Such variability can be related to the recycling of distinct Paraná Basin strata. The proportion of Cambrian-Late Neoproterozoic dates increases in the NE, indicating a possible input from the Ribeira Belt granitoids. Similar to major-scale dune-fields, Botucatu erg register variable sand sources there are possibly linked with coexisting depositional systems. In summary, the northern Botucatu erg is mostly fed by local sources reworked from underlying Paraná Basin units, with little direct input from basement sources and limited impact of regional wind-pattern variability.

Intraseasonal variability of greenhouse gas emission factors from biomass burning in the Brazilian Cerrado

Abstract. Landscape fires, often referred to as biomass burning (BB), emit substantial amounts of (greenhouse) gases and aerosols into the atmosphere each year. Frequently burning savannas, mostly in Africa, Australia, and South America are responsible for over 60 % of total BB carbon emissions. Compared to many other sources of emissions, fires have a strong seasonality. Previous research has identified the mitigation potential of prescribed fires in savanna ecosystems; by burning cured fuels early in the dry season when landscape conditions still provide moist buffers against fire spread, fires are in general smaller, patchier, and less intense. While it is widely accepted that burned area (BA) and the total carbon consumed are lower when fires are ignited early in the dry season, little is known about the intraseasonal variability of emission factors (EFs). This is important because potentially, higher EFs in the early dry season (EDS) could offset some of the carbon benefits of EDS burning. Also, a better understanding of EF intraseasonal variability may improve large-scale BB assessments, which to date rely on temporally static EFs. We used a sampling system mounted on an unmanned aerial vehicle (UAV) to sample BB smoke in the Estação Ecológica Serra Geral do Tocantins in the Brazilian states of Tocantins and Bahia. The protected area contains all major Cerrado vegetation types found in Brazil, and EDS burning has been implemented since 2014. Over 800 smoke samples were collected and analysed during the EDS of 2018 and late dry season (LDS) of 2017 and 2018. The samples were analysed using cavity ring-down spectroscopy, and the carbon balance method was used to estimate CO2, CO, CH4, and N2O EFs. Observed EF averages and standard deviations were 1651 (±50) g kg−1 for CO2, 57.9 (±28.2) g kg−1 for CO, 0.97 (±0.82) g kg−1 for CH4, and 0.096 (±0.174) g kg−1 for N2O. Averaged over all measured fire prone Cerrado types, the modified combustion efficiency (MCE) was slightly higher in the LDS (0.961 versus 0.956), and the CO and CH4 were 10 % and 2.3 % lower in the LDS compared to the EDS. However, these differences were not statistically significant using a two-tailed t test with unequal variance at a 90 % significance level. The seasonal effect was larger in more wood-dominated vegetation types. N2O EFs showed a more complex seasonal dependency, with opposite intraseasonal trends for savannas that were dominated by grasses versus those with abundant shrubs. We found that the N2O EF for the open Cerrado was less than half the EF suggested by literature compilations for savannas. This may indicate a substantial overestimation of the contribution of fires in the N2O budget. Overall, our data imply that in this region, seasonal variability in greenhouse gas emission factors may offset only a small fraction of the carbon mitigation gains in fire abatement programmes.

Influence of environmental and morphological parameters on the microfauna community present in phytotelmata of a bromeliad in a fragment of Atlantic Forest, southern Brazil

Bromeliads are important epiphytes due to their abundance in the Neotropical region and morphological complexity. Their compact and imbricated leaf bases form water storage cisterns that promote important resources for colonization by several prokaryotic and eukaryotic microorganisms. Due to the lack of knowledge about these environments, the objective of the study was to investigate which physical-chemical and ecological parameters exert effects on the biological richness present in the cisterns of Vriesea platynema. The study was carried out in the Center for Research and Nature Conservation (CPCN – Pró-Mata), in the Serra Geral plateau, northeastern Rio Grande do Sul, Brazil. Active searches were performed for 10 trees with bromeliads fixed at two heights (&amp;lt; 1.5 m and &amp;gt; 2.5 m). For each bromeliad individual, the height in relation to the ground, the diameter and depth of the central cistern, water temperature, number of lateral cisterns and number of adjacent bromeliads, were measured. A total of 23 taxa were identified in the phytotelmata of V. platynema, with Philodina, Lambornella, Paramecium, Tetrahymena and Diptera larvae being the most representative groups. The richness of organisms in the phytotelmata presented a positive correlation with water temperature (p = 0.01), and the number of adjacent bromeliads (p = 0.05), indicating that physicochemical and ecological factors could influence the richness of bromeliad biota.

Hydrogeological compartmentalization and connection of the Guarani (GAS) and Serra Geral (SGAS) aquifer systems from a multiscale perspective: a case study in southern Brazil

The Guarani (GAS) and Serra Geral (SGAS) aquifer systems are the main groundwater sources in southern Brazil. We investigated the crucial relationship between the primary, intergranular pore system in the GAS and the secondary pore system associated with fractures in the SGAS in order to understand better the compartmentalization and connection, water storage, and productivity of both aquifers. Data from 375 wells that produce from both aquifers was used to evaluate the hydrodynamic characteristics of the GAS-SGAS contact. The integration of data using remote sensing, structural data, and thin section analysis support interpretations about the compartmentalization and potential connection of the aquifers. Fault zones trending NW, EW, and NNE demarcate six structural blocks in which the GAS-SGAS contact varies more than 400 m in elevation. Thin section analysis of sandstone texture and composition allowed us to determine the relationship between the type of porosity and cement type and content. The surface demarcating the Guarani-Serra Geral contact is highly productive in 93% of the wells that reach both aquifers. The integration of our results allowed us to propose a conceptual hydrogeological model for the GAS and SGAS aquifers in the study area.

Morphometric and structural diagnosis of fault reactivation in the Cenozoic: a case study of the Blumenau-Soledade Lineament in southern Brazil

Abstract The hypothesis that geomorphometric parameters and structural-geological features are diagnostic of reactivation of the Blumenau-Soledade Lineament in central-western Santa Catarina, Brazil was tested by confronting data on asymmetry, elongation, morphological markers, drainage patterns, and river anomalies of the Pelotinhas catchment and structural data for the Serra Geral Group (Parana Basin). The results indicate reactivation of the lineament as a dextral strike-slip fault, as the cause of an associated morphostructure characterized by an escarpment along the left bank of the river as well as being responsible for catchment asymmetry and morphometric anomalies. Although fault data indicate paleostress correlatable to regional tectonic events described in the literature, we propose that the earliest paleostress pulse possibly was active during the Paleocene-Eocene transition, with σ1 oriented NE-SW and σ3 NW-SE. In the early Paleogene, the stress system evolved as an extensional pulse. During the Paleogene and early Neogene, the paleostress field rotated with reorientation of the σ1 axis between NNW and NNE. The current tectonic regime was established between the Late Pleistocene and Holocene, with compressional stress σ1 oriented approximately WNW-ESE and σ3 NNE-SSW, as it generally occurs in the South American Plate.

Contamination susceptibility of Serra Geral Aquifer at municipal scale in Brazil

Abstract In the present work we intend to discuss groundwater contamination and its susceptibility in Serra Geral Aquifer, in Brazil. For this purpose, a list of data concerning the wells located in the study region was elaborated, obtained from the Groundwater Information System (GIS) of the Geological Survey of Brazil. Moreover, data on land use occupancy from United States Geological Survey (USGS) images was constructed. In order to determine local susceptibility to contamination, cross-referencing data was obtained based on the susceptibility index (SI) as well as from methodologies and the pollutant origin and surcharge hydraulically (POSH) system. The results pointed that the SI of the municipality of Sarandi (Brazil, RS) ranged from very low (37%) to high (76%) contamination susceptibility. Included on these, 12% is in the very low range, 17,6% in low, 13% in moderate to low, 13,2% in moderate to high, and 44% in high contamination susceptibility. Furthermore, potential sources of pollutant load are concentrated in areas where the contamination SI has scored from moderate to high. It is concluded that the methodologies used are important tools that benefits and facilitate environmental impact assessments, enabling management for the purpose of protecting and preserving water resources in general.

Hidrogeomorfologia em confluência fluvial obtusa, Guarapuava, Paraná

As misturas sólidas e líquidas no curso fluvial são intensificadas em áreas de confluência de rios condicionadas principalmente pela abertura angular da junção. O conhecimento da dinâmica hidrossedimentológica em junções de leito rochoso com diferentes aberturas angulares é fundamental para entendimento do ajustamento morfológico nas confluências e subsidiar ações de preservação e conservação dos ecossistemas fluviais. Nesse sentido, o presente trabalho apresenta os resultados de um estudo hidrogeomorfológico sobre confluência fluvial com ângulo de junção obtuso (&gt;100º), em rio de planalto com leito rochoso, na Formação Serra Geral. A pesquisa avaliou segmento fluvial a montante e jusante do rio das Pedras e no tributário rio das Pombas, em Guarapuava, Paraná, por meio de observações e mensurações das características morfológicas e hidráulicas largura, profundidade do talvegue, declividade do leito e vazão em margens plenas. O ajustamento morfológico em confluências obtusas é peculiar, uma vez que o ângulo de junção fluvial condiciona uma dinâmica específica de fluxo, erosão, transporte e deposição de sedimentos, resultado principalmente de sua associação com a natureza geológica do leito fluvial e os tipos de uso e manejo da terra a montante da confluência. Hydrogeomorphology of an obtuse fluvial confluence, Guarapuava, Paraná A B S T R A C TSolid and liquid mixtures in river courses intensify in areas of river confluence, conditioned mainly by the angular opening of the junction. Knowledge of hydrosedimentological dynamics in bedrock junctions with different angular openings is essential for understanding morphological adjustment at confluences and for supporting actions for the preservation and conservation of river ecosystems. For this reason, this article presents the results of a hydrogeomorphologic study on a river confluence with an obtuse junction angle (&gt;100º), in a plateau bedrock river, in the Serra Geral Formation. The research evaluated a fluvial segment upstream and downstream of the Pedras River and in the Pombas River tributary, in Guarapuava, Paraná, through observations and measurements of morphological and hydraulic characteristics, width, talweg depth, bed declivity and bankfull flow. Morphological adjustment in obtuse confluences is peculiar in that the fluvial junction angle conditions specific flow, erosion, sediment transport and deposition dynamics, mainly resulting from its association with the geological nature of the river bed and types of land use and management upstream of the confluence. Keywords: Fluvial channel stability, bedrock, fluvial morphology.

Lithostratigraphy of the Serra Geral Formation in the northern portion of the Paraná-Etendeka Igneous Province: A tool for tracking Early Cretaceous paleoenvironmental changes

A detailed lithofacies analysis in Continental Flood Basalt Provinces allows the comprehension of their evolution and paleoenvironmental significance. In the northern portion of the Paraná-Etendeka Igneous Province (PEIP), in Brazil (Uberlândia-Araguari area), a volcanological and stratigraphic approach provided evidence that the basaltic volcanic succession is not monotonous, involving different lava flow morphologies and architecture. The volcanic succession reaches a thickness of ca. 300 m and includes four lithofacies associations: pillow lavas, compound pahoehoe, simple pahoehoe, and sediment-matrix basalt breccia. Pillow lavas, simple pahoehoe, and compound pahoehoe characterize the onset of volcanic activity in the area. Sediment-matrix basalt breccia and thick simple pahoehoe lavas occur in upper stratigraphic levels. Some of these thick igneous bodies can represent invasive lavas or shallow intrusions. In the study area, the common presence of volcanic deposits and structures formed in wet conditions is evidenced by the occurrence of pillow lavas, undulatory columns, and interleaved lacustrine and fluvial sedimentary rocks. These deposits reflect different environmental conditions from those previously described as arid in other portions of the PEIP. Low-temperature post-depositional alteration has affected the volcanic and sedimentary rocks of the study area, obliterating many of the primary sedimentary structures. The subaerial and subaqueous lavas are chemically similar, and compatible with high-TiO2 Pitanga magma type. The Uberlândia-Araguari area and the southern part of the PEIP have a similar stratigraphic style both characterized by the dominance of compound pahoehoe lavas at the base and by an intermittent volcanism, which is evidenced by the intercalation of sedimentary deposits with lavas.

Investigação geotécnica de taludes rochosos por meio da análise estrutural: estudo de caso da BR-116, Rio Grande do Sul

A BR-116, localizada no nordeste do estado do Rio Grande do Sul, atravessa a Escarpa da Serra Geral, composta de derrames ácidos e básicos da Formação Serra Geral. Diversos movimentos de massa são observados na rodovia, relacionados com a queda e os deslizamentos de blocos dos taludes rochosos. Como hipótese, pretendeu-se verificar se as famílias de fraturas tectônicas regionais causam os movimentos de massa nos taludes da BR-116. O objetivo desta pesquisa foi aperfeiçoar os métodos de investigação geotécnica, correlacionando a Geologia Estrutural com a estabilidade de taludes rochosos. Entre os métodos utilizados estão o sensoriamento remoto e a análise de lineamentos estruturais, a análise estrutural geométrica e a análise geotécnica dos maciços rochosos (identificação de possíveis planos de ruptura e cálculo de seus fatores de segurança). Os resultados dos lineamentos estruturais regionais indicam o predomínio da direção ENE, seguida pelas direções subordinadas NE e WNW. Em relação às fraturas de alto ângulo analisadas em campo, caracterizou-se um máximo com direção N50-70E, similar ao observado regionalmente. A interpretação do diagrama de movimentos de massa indica que 75% dos movimentos que podem ocorrer na BR-116 seriam causados por deslizamentos em cunha, e o restante são planares, com predomínio de descontinuidades de alto ângulo. A direção máxima dos lineamentos (N70-90E) pode causar movimentos em seis dos sete taludes estudados, e o segundo máximo (N60-80W) condiciona deslizamentos em quatro dos sete pontos. Essa evidência mostra que as estruturas provenientes dos lineamentos regionais são as que mais podem gerar movimentos de massa.

A PHOTOGRAPHIC ATLAS OF THE ARCHITECTURE, FLOW GEOMETRY AND MORPHOLOGY, AND FACIES OF SERRA GERAL GROUP (PARANÁ IGNEOUS PROVINCE) IN THE STATE OF PARANÁ, BRAZIL

The rocks that make up the Serra Geral Group spread over approximately 100,000 km2 of the State of Parana, which represent about 10% of the Parana Igneous Province. The geologic mapping of the Serra Geral Group in the State of Parana was carried on from 2003 to 2018, and revealed a great diversity of features and facies of basic and acidic lava lows, as well as the presence of interbedded volcaniclastic deposits. This paper presents an inventory of this geodiversity along with brief descriptions, a wealth of photographic documentation, and the georeferenced location of each outcrop, making it easy to access the documented sites, in order to assist the development of scientiic research in this geologic compartment, which occupies nearly half of the Parana territory. The processes responsible for the lithologic features are interpreted in compliance to the knowledge accumulated on the various continental basaltic provinces by many researchers, including the authors of this paper, so to build up a genetic system for the Serra Geral Group more complete and coherent with the paleogeography of Gondwana in its initial breakup stage. In the early Cretaceous, during ca. 1.2 Ma with the paroxysm at 134.7 Ma, a huge magma amount, which is estimated at least in 600,000 km3, lowed over the thick sedimentary Paleozoic sequence of the Parana Basin, stacking up a volcanic sequence. The interaction between the rising magma with the sedimentary sequence up to 7,000 m thick, gave rise also to thousands of intrusive bodies, such as sills and dikes, almost all of a basic nature. Furthermore, the ascending magma interacting with aquifer systems gave rise to explosive volcanism – hydrovolcanism – which produced many maic volcaniclastic deposits MVDs, interbedded to the basic lows. Thus, in South America, during this relatively short lapse of time, basic and acidic lows covered the Parana Basin, being reported in Brazil, Argentina, Paraguay, and Uruguay under diverse names. In the present article, it will be simply referred as Serra Geral Group (SGG). The lithological inventory represented by the present photographic atlas comprises diagnostic features of basalt, andesi-basalt, rhyolite and dacite lava lows, maic volcaniclastic deposits MVDs, and dykes of basic composition.

Estimation of soil loss by the USLE model in a mountain basin in the south of Santa Catarina state, Brazil

Water erosion is a factor of soil degradation that is triggered by the impact of raindrops originated by intense rainfall disaggregating the soil, followed by the carrying of particles by surface runoff. In the erosion process, in addition to soil loss, nutrients, fertilizers, and pesticides are carried resulting in water courses and water pollution. Erosion can have a major impact on agricultural production, when soil use and management techniques are not used. Therefore, this study aimed to evaluate the soil loss in the Malacara river basin, which is a sub-basin of the Mampituba river basin characterized by a contrasting relief, with high altitudes in the escarps of Serra Geral and floodplain. The method used for the development of this research was the application of the Universal Soil Loss Equation (USLE). USLE soil loss estimation requires the following factors: rainfall erosivity (R), soil erodibility (K), slope length (L), slope steepness (S), soil use and management (C), and erosion control practice factor (P). The estimated rainfall erosivity was 5,754.2 MJ mm ha-1 h-1 year-1. Erodibility was determined for the soils present in the basin, highlighting a high value for gleysoil. The topographic factor (LS) showed values from 0 to greater than 20, which corresponds to the low to very high runoff potential. The floodplain showed lower runoff rates, while for the locations close to the enclosed valleys in the Malacara canyon, the runoff potential varied from high to very high. The soil use and management factors and conservation practices (CP) obtained a maximum value of 0.404, corresponding to the exposed soil; the second most representative class was agricultural areas, with a value of 0.145. The soil loss in the Malacara river basin varied from 0 to more than 200 t ha-1 year-1. In fact, 87.38% of the area presents a degree of sheet erosion normal to slight and, only 2.94% of the area has a high or very high degree of erosion. Moreover, due to the relief characteristics with shallow soils and intense rainfall in mountainous basins, knowing and understanding soil losses due to erosion is crucial for the adequate management of water resources in river basins.