Serra Geral Research Articles

Full vector paleomagnetic estimation from the Paraná-Etendeka Large Igneous Province, southern Brazil: Implications on the onset of Cretaceous Normal Superchron

Comprehensive paleomagnetic study from the Paraná-Etendeka Igneous Province (PEIP), Serra Geral Formation, southern Brazil (∼ 135 Ma) adds to the scarce southern hemisphere paleomagnetic database. Twelve paleomagnetic sites from the exposed stratigraphy of the PEIP were recovered from basaltic lava flows in northern Rio Grande do Sul state. These volcanic rocks erupted between 131.5 and 135.6 Ma. The reliability of the rock magnetism data was confirmed before being accepted for paleo-intensity analysis. The Thellier-Coe paleointensity protocol was applied to 109 collected specimens, and 26 individual samples from 9 sites were selected to test for consistency of the paleointensity determinations. The new high-quality mean paleointensity value of 30.6 ± 7.2μT corresponds to a virtual dipole moment (VDM) of 5.75 ± 0.49 × 1022 Am2. These values correspond to approximately 72% of the present-day Earth's magnetic field and suggest that the Earth's magnetic field strength was slightly elevated compared to the long-term average geomagnetic field that prevailed during the Cretaceous Normal Superchron. The calculated paleomagnetic pole (Plong = −27.5° and Plat = −78.6°, A95 = 3.5°) presents an angular difference of 22° with respect to the expected pole declination with an inclination of 5°. This difference may correspond to secular variations considering the confidence cones. Our results, when compared with previous paleomagnetic data, approach the accuracy of recent models for the Cretaceous interval.

Volcano-sedimentary interactions – A key to understand Cretaceous paleoenvironments in the Paraná basin (southern Brazil)

The Lower Cretaceous in the Paraná Basin record a large volcanic event (Serra Geral Formation) that covered an active sedimentary system (Botucatu Formation), before the fragmentation of the southern Gondwana. Therefore, the fluvial-aeolian deposits underlying aeolian deposits of residual dunes, were gradually covered by volcanic flows. Intense basic and minor acidic magmatism covered an extensive continental aeolian environment. The interface between the two units shows an aeolian environment during the early stages of volcanism forming deposits and volcano-sedimentary features overlying and underlying the flows. In six outcrops on the southern portion of the current border of Paraná Basin, in Rio Grande do Sul state, these deposits and features were recognized, showing the complexity of the environment and the processes associated with lava flows and sediments. They were formed by the interaction of consolidated or unconsolidated sediments, saturated or not in the water, with basaltic or dacitic flows. Interaction features and deposits synchronous to volcanism (volcanoclastic), later or in intervals between volcanic events (epiclastic) and only cover, with absence of interactions, were identified. Through the distinctive characteristics of the interaction processes between the volcanic rocks and the sediments analyzed in the volcanic-sedimentary features and deposits, the morphology of the aeolian environment of Botucatu Formation could be, by analogy, compared to the current aeolian environments. The proposed paleoenvironment indicates a sedimentary environment with different domains, categorized by their water saturation. The different siliciclastic components found in each domain allowed the generation of different features and volcanic-sedimentary deposits evidencing aspects related to the presence or absence of water among the proposed domains.

Natural fertility and intrinsic fragility of soils in the Brazilian Cerrado

This study aimed to evaluate the attributes of natural fertility and intrinsic fragility of the soils of Ivinhema River Basin (BHI), to subsidize agricultural development projects and environmental control and monitoring bodies. For this purpose, 62 soil samples were collected, at a depth of 0 to 20 cm, in areas of native vegetation belonging to the state of Mato Grosso do Sul – Brazil. The characteristic climate of the study area is of the humid mesothermal subtype (Cfa) without drought. The predominant vegetation is of the Cerrado type and the geological substrate is predominantly composed of the Serra Geral and Caiuá Formation. The samples were air-dried and the physical attributes (sand, silt, and clay) and chemical variables (pH H2O, CaCl2, KCl, ∆pH, Al3+, m%, H + Al, Ca2+, Mg2+, K+, CEC, SB, V%, OC, P, Cu, Fe, Mn, and Zn) were determined according to methodologies in Embrapa's soil analysis methods manual. The data obtained were evaluated by descriptive statistics and principal component analysis. The results showed a great variety of soils inside the basin, whose natural fertility was high for the Leptsol, Regosol, and Nitisol soils, and low for the Argiluvic Plinthosol, Petroplinthic Plinthosol, and Planosol soils. The sandy soils showed lower levels of organic carbon and negative surface loads, which shows less capacity to retain cations essential to plant nutrition and less retention of environmental contaminants if any. Regarding the textural fragility of the soils of BHI, it was possible to verify the high sensitivity of the soil to erosion and susceptibility to the contamination of groundwater or infiltrated water. The data shown in research can fill the gaps of knowledge and/or for adapting conservation practices of agricultural soils that are more susceptible to erosive processes, as well as for environmental control and monitoring bodies and/or studies of area recovery and maintenance of soil fertility.

Volcanoclastic and epiclastic diagenesis of sandstones associated with volcano-sedimentary deposits from the upper Jurassic, Lower cretaceous, Paraná Basin, southern Brazil

The opening of South Atlantic Ocean produced an immense volume of lava that covered an active aeolian system during Lower Cretaceous. The contact of Botucatu Formation sandstones with the Serra Geral volcanic flows generated a variety of volcano-sedimentary features and deposits. During volcanism, the temperature contrast between lava and wet or water-saturated sediments formed volcanoclastic features and related sedimentary deposits. In moments of magmatic quiescence, epiclastic deposits were generated due to the return of sedimentation. Volcanoclastic deposits include volcanic breccias with sandy matrix, and epiclastic deposits include conglomerates and conglomeratic sandstones with intraclasts. Quantitative petrography of the sandy matrix samples of these deposits was analyzed, in order to discuss the paragenesis of volcano-sedimentary interactions. Regular burial diagenetic processes were discussed for epiclastic sandstones and contact diagenesis processes for volcanoclastic sandstones. The original composition of volcanoclastic and epiclastic sandstones is heterogeneous. However, the main difference between them is the presence of textural fluidization indicators found in the volcanoclastic sandstones, along the lava-sediment interface. These textural characteristics indicate that the unconsolidated sediments were probably wet or saturated in water during the interaction with the volcanic flow. Epiclastic sandstones have infiltrated clays and neoformed smectites as their main diagenetic constituent due to alteration of available volcanic lithoclasts. For volcanoclastic sandstones, the formation of opal, chalcedony and megaquartz cements through burial is unlikely, due to the intergranular volume occupied by these cements, indicating near-surface early diagenetic conditions. Therefore, the mechanisms of dissolution and repreciptation of the siliceous fluids, incorporated in the system, formed mainly the chalcedony cementation. Furthermore, zeolite cementation, which occurs along the lava-sediment contact, is another important indicator of contact diagenesis for volcanoclastic sandstones. During telodiagenesis, the formation of secondary porosity by dissolution of volcanic lithoclasts and detrital K-feldspar grains was of great importance in volcanoclastic and epiclastic sandstones.

Mica in a sedimentary feature as evidence of humid conditions for a classic desert in Paraná Basin, southern Brazil

In Paraná Basin, oriented mica appears into horizontal layered fine sediments feature defined as geodes with sediments. Mica is identified as biotite in a volcano-sedimentary context of Botucatu and Serra Geral formations. Throughout the accomplishment of multiple analyses such as petrography, rock chemical evaluation, Rare Earth Elements (REE) values and also the Chemical Index of Alteration (CIA) some contributions for local paleoenvironment and paleoweathering for the classic Botucatu paleodesert is proposed. Since biotite is not regular in sediments of a desert environment, the mica presence suggests that it was transported by aqueous input and deposited within the provided spaces. The arrangement of these sediments as planar cross-stratification also confirms that this process is water dependent, otherwise the preservation of the layers' horizontality would not be preserved. The REE results of negative Ce (Cerium) anomaly in some features, geochemically implies the contribution of water column during deposition. Some geodes are intensely silicified, and in these, there is a relative preservation of Ce attributed to an intense siliceous cementation, avoiding the oxidation of Ce. Despite some differences in Ce values, these features hold similar REE patterns and CIA values indicating similar provenance for the geodes’ sediments and they were probably deposited under similar chemical conditions. The Ce difference between the slightly silicified and intensely silicified geodes shows local conditions for the values, influenced by the presence of water presence and silicification.

Classifying micropollutants by environmental risk in groundwater using screening analysis associated to a hybrid multicriteria method combining (Q)SAR tools, fuzzy AHP and ELECTRE

This study aimed to evaluate and monitor pesticides in groundwater of the Serra Geral aquifer, located in the Paraná Basin 3 (southern Brazil), using Liquid Chromatography coupled with a Quadrupole-Time-of-Flight Mass Spectrometer (LC-QTOF MS). A total of 117 samples, collected in three different moments, were analyzed over 36 months. Groundwater samples from 35 wells and four surface water points were monitored in each sampling campaign. A pesticide screening methodology was proposed with the tentative identification of 1607 pesticides and pesticide metabolites. The application of the proposed methodology resulted in the verification of 29 pesticides and pesticide metabolites, 7 as confirmed analytes and 22 as suspect compounds. (Q)SAR in silico predictions and GUS index calculation provided data on the potential environmental risk of the identified compounds, with eight endpoints considered. After in silico predictions, an alternative hybrid multicriteria method was applied, combining the weighting of endpoints of fuzzy AHP and micropollutants classification by environmental risk using ELECTRE. The fuzzy AHP results indicated the greatest importance of mutagenicity among the eight evaluated indicators, while the scarce influence of the physicochemical properties on the environmental risk suggested their exclusion from the model. Accordingly, the ELECTRE results highlighted the prevalence of thiamethoxam and carbendazim as the most dangerous for the environment. The application of the proposed method enabled the selection of the compounds that must be monitored, considering mutagenicity and toxicity predictions for environmental risk analysis.

Relationship between precipitation events and groundwater recharge of the Serra Geral Aquifer System in an experimental watershed located in the municipality of Caxias do Sul, RS: Brazil

Relationship between precipitation events and groundwater recharge of the Serra Geral Aquifer System in an experimental watershed located in the municipality of Caxias do Sul, RS: Brazil

Lower Campanian palynoflora from the Araçatuba Formation (Bauru Group), Southeastern Brazil

This paper presents the first record of a rich palynoflora within the Bauru Group (Cretaceous of southeastern Brazil). The Bauru Group is rich in animal fossils, but has been virtually barren in palynomorphs. There are only two previous palynological works from the Bauru Group: (1) that of the São Carlos Formation, whose outcrop is located outside the formal boundary of the Bauru Basin, and (2) the extremely poor and poorly preserved palynoflora from a coprolite of the Marília Formation. The material studied here, from the Araçatuba Formation, is the only one palyniferous sample from a groundwater well drilled in the central-west region of the state of São Paulo. The Araçatuba Formation, constituted by swamp deposits, rests directly on the basalts of the Serra Geral Group. The Araçatuba palynoflora contains index palynomorphs – Cretacaeiporites polygonalis, C. scabratus and Hexaporotricolpites emelianovi – signifying an early Campanian age. Moreover, the absence of Santonian indices and of older ages, confirms attribution to the lower Campanian. In paleoclimatic terms, the assemblage suggests aridity, given the abundance of ephedroid pollen grains and the low frequency of pteridophytic spores. The occurrence of spores of water ferns confirms the paludal setting. The aqueous environment is also suggested by the occurrence of zooclasts derived from crustacean eggs. However, the virtual absence of phytoplankton may indicate the ephemeral nature of the water body.

Emplacement dynamics of the plumbing system and lava pile of the Paraná Magmatic Province in Morro da Igreja, Santa Catarina, Brazil

The mechanisms of magma ascent, transport and emplacement of the volcanic pile from LIPs are key issues regarding the understanding of the complex construction of volcanic systems and magma transport through the crust. The integrated approach of morphology of the volcanic and subvolcanic bodies, whole rock geochemistry and ASM data provides a robust tool to unravel the flow dynamics of the volcanic bodies and the sequence of the magmatic events. Such approach allows building up a model of construction of the lava pile considering the role played by the plumbing system. This paper investigates the emplacement mechanism of sill and lava flows of the Serra Geral Group (SGG), in the southern part of Mesozoic Paraná-Etendeka Magmatic Province (PEMP) in Brazil. Geologic and geochemical analysis were integrated with anisotropy of magnetic susceptibility (AMS), anisotropy of anhysteretic remanent magnetization (AARM) and rock magnetism experiments on 14 sampling sites in the Morro da Igreja region, top of the lava pile in Santa Catarina. The area is composed of low-Ti basaltic (with predominance of rubbly pahoehoe) and silicic lava flows, both intruded by a tabular sill that reaches a few hundred meters wide. The mafic lava flows are composed of Gramado, Urubici and Esmeralda magma-type basalts and andesite basalts. The silicic lava flows are massive or foliated, classified as Palmas type dacites. The sill has regular columnar joints and is classified as Esmeralda type. Magnetic mineralogy data suggests magnetite or Ti-poor magnetite as the main magnetic mineral for all the igneous rocks, and AARM results show anomalous fabric for the lava flows and normal or intermediate fabric for the sill. Besides the anomalous fabric sites, AMS data provide reliable directional data to infer flow direction for the sill, with initial propagation towards NE, followed by a preferential SE direction of magma flow. For the silicic rocks, the presence of vertical and inclined magnetic foliation suggest a lava dome geometry. The dynamics of the magmatic flow of the sill and lava flows associated with the compositional characteristics of the rocks allows stablishing the stratigraphy of the magmatic events in the area as well as the proposition of an emplacement model for the sequence.

Behavior of molecular maturity parameters in overmature shales affected by diabase intrusion (Irati Formation, Paraná Basin – Brazil)

Molecular parameters based on saturated and aromatic compounds are important tools to access thermal maturation, but the behavior of these compounds is affected by different rates of heating. This study used samples from the Irati Formation, one of the most important source rocks in the Paraná Basin, to assess the behavior of commonly used maturation parameters in overmature rocks, in conditions of high heating rates. The Irati Formation belongs to an atypical hydrocarbon generation system. It was matured by heat of the magmatic intrusions related to volcanism of the Serra Geral Group. The main objective of this work is to evaluate how the heat of a diabase intrusion affected the distribution of the saturated and aromatic biomarker parameters, relating to the intrusive rock distance. For this purpose, eleven shale samples from the borehole CBM-002-ST-RS of the Santa Terezinha field were analyzed. The samples were located at a maximum distance of 46.4 m from a 35.32 m-thick diabase intrusion. For the better understanding of each parameter behavior, was established four different zones according to their trends: maturity correlation, equilibrium, reversal and high thermal stress. The maturity correlation zone is where the progression of the parameter's values are correlated to the increase in maturation towards the base of the profile. The saturated parameters, such as Ts/(Ts + Tm), M30/(M30 + H30) and C29Ts/(C29Ts + H29) marked the increase in maturation of the samples more distant from the intrusion, and the aromatic parameters, such as MPI-1, MPR, DMDBTR 2.4/1.4 and TA(I)/TA(I + II), show an increase in maturation at the intermediate-distance samples. The ratio of Tric/H30 marked the increase of maturation in the largest number of samples. The parameters that reach equilibrium in the beginning of oils window entered the profile already in the equilibrium zone, such as 20S/(20S + 20R), 22S/(22S + 22R) and ββ/(αα + ββ). Furthermore, most parameters presented a reversal zone after the equilibrium or the maturity correlation zone, where they showed an inverse pattern with increase in maturation value. Finally, all parameters presented a chaotic distribution in the samples closest to the intrusion (starting at an average distance of 11 m from the intrusion), this behavior characterize the high thermal stress zone.

Serra Geral fractured aquifer and the uncertainties of geospatial models: A case study in the caxias fault zone

In hydrogeology, geospatial interpolators are commonly used to simulate water table distribution, contaminant concentrations and aquifer vulnerability. However, few are the studies that demonstrate which interpolator best suits the dataset. This study targets on this knowledge gap by assessing the geospatial dependency influence, the scale influence and the intrinsic uncertainties of the score over the deterministic and stochastic models in the Serra Geral Fractured Aquifer System. The hydrogeological parameters considered as reference for this assessment were the Potentiometric Surface, Fracture Flow Zones, Static Level, Discharge, Transmissivity and Specific Capacity. The Potentiometric Surface and Fracture Flow Zones parameters have demonstrated a strong spatial dependence on the geomorphology and regional lithostratigraphy, whilst the Static Level, Discharge, Transmissivity and Specific Capacity have showed less spatial dependence and with the worst scores of the consistency indexes. The scale of this study has had little influence on the geospatial models. When using interpolation to generate geospatial models, one should perform an evaluation of the spatial dependency, the mean bias, the shared variance score between observed and simulated dataset and the statistical difference between the scores of the Pearson Correlation prior to choose the most adequate interpolator.

Where are they from and where are they going? Detecting areas of endemism, distribution patterns and conservation status of the order Spirostreptida in Brazil (Diplopoda, Juliformia)

Millipedes are well-known for their limited dispersal abilities with species restricted to mountains, islands, and patches of forest being important models for formulating and testing biogeographic hypotheses. The order Spirostreptida is composed of nearly 1300 species distributed across the Afrotropical, Oriental, and Neotropical regions. The order is divided into the suborders Cambalidea and Spirostreptidea with the families Pseudonannolenidae (Cambalidea) and Spirostreptidae (Spirostreptidea) occurring in Brazil. To date, there have been no studies on the biogeography of Neotropical Spirostreptida. We employed a multi-approach analysis with Parsimony Analysis of Endemicity, Endemicity Analysis, and Infomap, to detect areas of endemism and patterns of distribution of the order in Brazil. Six areas of endemism are proposed for the 133 Brazilian species: Northern Serra Geral, Southeastern mountain ranges, Cerrado and Atlantic Forest zone, Eastern Cerrado and Serra do Espinhaço, Pantanal, and Southern Amazon and Cerrado zone. Most endemic areas fall within the Atlantic Forest, which has been previously shown to be an important area of endemism for many invertebrate taxa. The richest biomes are the Atlantic Forest with 75 species and the Cerrado with 55 species, while the least rich biomes are the Caatinga with six species and the Pampa with three species. Although the southeastern region of Brazil has the highest species richness, it also has the highest concentration of threatened species. Based on International Union for Conservation of Nature (IUCN) criteria, most Brazilian Spirostreptida are either endangered or critically endangered, with the highest concentration of endangered taxa occurring in the Atlantic Forest biome.

Monitoring groundwater storage in a fractured volcanic aquifer system.

The use of groundwater resources is under increasing pressure to meet the demands of the society. Despite this, the understanding of its availability is still limited when compared to other water reserves. The aquifer studied was the volcanic Serra Geral Aquifer System (SASG) located in a humid subtropical region. This research aims to explore in a pioneering way the large-scale hydrogeological processes taking place at the SASG using a unique and complementary tool of intensive field monitoring, remote sensing data, and hydrological modeling. Results showed a fast response of groundwater levels to rainfall, with an average of 29days of lag times. We also identified areas in the southern region of the basin with higher depletion rates, with GRACE results indicating a negative trend (- 57mmyear-1) associated with a major recharge event that occurred in the region before the period monitored. Also, the interflow calculated using the MGB hydrological model showed that the flow within the limits between the soil and the volcanic rocks (different in hydraulic conductivity) varies spatially, influencing the baseflow of rivers as for slopes and soil capacity to store water.

Understanding regional groundwater flow using water-rock interaction processes and anthropic signatures in a fractured volcanic aquifer

This research evaluated the hydrochemistry of a fractured volcanic aquifer at Paraná 3 Basin, in the western region of the state of Paraná, southern Brazil. Geochemical rock data from the literature were used to describe the distinctive characteristics of the principal geological units in the area, Pitanga and Paranapanema Formations, both belonging to the Serra Geral Group. Data from x-ray diffraction were obtained to deepen the study of hydrogeochemical processes. Previous studies did not consider the differences in the lithogeochemistry of the group, in the terms contemplated in this research. In addition, the research also approaches the evaluation of the flow depth contribution in the groundwater chemistry and the analysis of hydrogeochemistry processes. For this analysis, a set of chemical data was utilized on 35 groundwater samples from water supply boreholes at Paraná 3 Basin. From shallow to deep flow, there was an increase in pH, electrical conductivity, total dissolved solids, total alkalinity and a decrease in CO2. These parameters exert the main physical-chemical groundwater controls, which are identified by changes in the major ions along the flow lines, as well as by variations in trace elements. The water-rock interaction becomes increasingly evident in the intermediate and deep flows, standing the higher alkalinity, pH, electrical conductivity, total dissolved solids (TDS) and most of the trace elements at Pitanga Formation. Pitanga Formation presents higher medians of alkalinity (95.5 mg.L-1), electrical conductivity (225 μS.cm-1) and TDS (140.0 mg.L-1) than Paranapanema Formation (57.0 mg.L-1; 130 μS.cm-1 and 90.0 mg.L-1, respectively). Furthermore, the pH distribution shows greater values starting at the 60% percentile in Pitanga Formation (8.24), compared to Paranapanema (8.10). Despite such differences, it was not possible to distinguish the geological units with the hydrochemical characterization, probably because both units are mainly represented by rocks of basic composition, with a similar mineralogical basis. The shallow hydrogeochemical processes are characterized by the weathering of Fe–Mg silicates and plagioclase, changing to a predominance of ion exchange in deeper flows. Calcite precipitation is a secondary process, associated with calcium consumption towards deeper flows. Anthropic influences are mainly observed with more elevated concentrations of NO3-, PO43-, Cl- and K+, occurring in the entire basin, and they are strongly evidenced by the correlation between Cl- and NO3- in most samples.

Ferns and Lycophytes from the Estação Ecológica Serra Geral do Tocantins: a contribution to the flora of the Jalapão, Brazil

Abstract This study contributes to the flora of ferns and lycophytes, also referred to as pteridophytes, from the Estação Ecológica Serra Geral do Tocantins (EESGT), which is part of the Jalapão region in Tocantins. Although Jalapão is one of the largest protected areas in the Cerrado vegetation of Northern Brazil, its biodiversity has, thus far, been poorly reported in the literature. Therefore, fieldwork was recently carried out at EESGT in different habitats. Our collections and data from digital repositories included 31 ferns and four lycophyte species belonging to 20 genera of 15 families. Despite occupying only a small fraction of the landscape, forests concentrate most pteridophyte diversity, reinforcing their importance for the conservation of this group within the Cerrado. Eleven species are new records for Tocantins, one is new for Bahia, and one was recently described (Anemia areniticola). In addition to a list of all taxa, we provide illustrations and an identification key to encourage further studies on this often-neglected component of Cerrado flora.

Serra Geral Group Plumbing System and 3D Geological Framework in Southern Paraná-Etendeka LIP (Brazil), Part II: Coupling 3d=D Geologic and Magnetic Models

Serra Geral Group Plumbing System and 3D Geological Framework in Southern Paraná-Etendeka LIP (Brazil), Part II: Coupling 3d=D Geologic and Magnetic Models

Serra Geral Group Plumbing System and 3D Geological Framework in Southern Paraná-Etendeka Lip (Brazil), Part I: Revealed from Borehole, Geochemical and Petrophysical Data

Serra Geral Group Plumbing System and 3D Geological Framework in Southern Paraná-Etendeka Lip (Brazil), Part I: Revealed from Borehole, Geochemical and Petrophysical Data

The consequences of debris flows in Brazil: a historical analysis based on recorded events in the last 100 years

This study aims at providing an overview of the socioeconomic consequences that debris-flow events have caused in Brazil, positioning the country in the international scenario and identifying areas where targeted actions are necessary. The analysis is conducted by calculating the debris-flow mortality rate (MR) and by using the so-called F-N plots (frequency of events that have caused N or more fatalities vs. the number of fatalities), based on a compilation of debris-flow-related disasters from 1920 to 2021. In total, 45 debris-flow events were documented in the considered period, responsible for 5771 fatalities and more than 5.5 billion USD in economic losses. The Serra do Mar Mountain Range is the main site of reported debris-flow occurrences (64.5%), followed by Serra da Mantiqueira (13.3%), and Serra Geral (13.3%). Southeast Brazil (SEB) is the region most affected by debris-flow events, due to the highest population density and the development of several cities in hilly areas, such as Petrópolis (Rio de Janeiro state) and Cubatão (São Paulo state). The debris-flow MR of SEB is higher than any other region in Brazil, pushing the national debris-flow MR upwards, and the F-N curve of SEB consolidates the region as the one with the highest risk to the phenomenon, indicating a higher probability of fatal events. The F-N plots further show that debris-flow events in Brazil represent a higher societal risk than in countries such as China, Japan and Italy. While there are differences in country size and the scale effect should be considered, these results highlight the urgent need for investments in disaster prevention and preparedness programs.

GEOLOGY OF THE FRONTEIRA OESTE RIFT, SOUTHERNMOST BRAZIL – A FIELD GUIDE

The Fronteira Oeste Rift located in the state of Rio Grande do Sul, southern Brazil, covers an area of 15,000 km2 and constitutes both a rhombohedral structural province and a paleohot spring field. These major features can be observed during a two-day field trip. A 4x4 vehicle is recommended. The weather is cold (freezing), humid climate during winter and hot (35 °C), varying from humid to dry during summer-. Excellent access to the outcrops is possible through paved and unpaved roads. Outcrops described in this field guide are stratigraphically located above the Botucatu Formation (paleoerg) and below the Serra Geral Group (volcanics) of the Paraná Basin. Sandstones of the Botucatu Formation were quickly filled by rainwater and after covered by a basalt (Mata Olho Flow) and a quartz andesite (Catalán Flow), thus originating the Guarani Paleoaquifer. The third Cordillera Flow (basaltic andesite) occurs in places, eventually covered by the Muralha Flow (basaltic andesite). Two additional basaltic andesites (UR13 and Coxilha Flows) were described in a drill hole. Aquifer heating by raised geothermal gradient led to pre-compaction cementation of sandstones by iron-rich minerals. Eolian quartz-rich sediments were deformed and hydrothermally altered in the composite paleodunes, showing thousands of circular, elliptical and curvilinear structures. Compaction caused upward motion of hot water + liquefied sand leading to the formation of many sand injectites and extrudites. Simultaneous doming of overlying rocks caused both large- and small-scale rhombi in sandstones and volcanic rocks. Post-compaction silicification occurred together with the formation of a myriad of 0.1-1.0 m-large hydrothermal vents at the surface of the paleoerg and also the first three lava flows. Features resulting from these processes can be visited, as described in this Geological Field Guide. A shorter geotrail is also described.

Stochastic simulation of the Serra Geral Aquifer System in the state of Rio Grande do Sul, Brazil

Stochastic simulation of the Serra Geral Aquifer System in the state of Rio Grande do Sul, Brazil