Radon and progeny (Pb and Bi) in urban water-supply systems of São Paulo State,Brazil

Many water-supply systems in South America utilize the waters of the Guarani aquifer at least as part of their networks. However, there is little present knowledge in Brazil of the factors affecting Rn presence in the water supplied for end-users, despite the economic importance of Guarani aquifer. ²²²Rn analyzes of 162 water samples were performed at 8 municipalities in São Paulo State, Brazil, with the aim of investigating the major factors affecting its presence in solution. The ²²²Rn activity concentration ranged from 0.04 up to 204.9 Bq/L, with three samples exceeding the World Health Organization maximum limit of 100 Bq/L. Aeration was confirmed as the most important factor for Rn release, as expected due to its gaseous nature. Accumulation in pipes and stratification in the water column were other significant factors explaining the data obtained in some circumstances. The Rn daughters ²¹⁴Pb and ²¹⁴Bi were also determined in a set of selected samples and their presence was directly related to the occurrence of Rn dissolved in water.     

Hydrochemical relationships in groundwater from central São Paulo State, Brazil

Groundwater samples from different aquifers occurring at center/northeast portion of São Paulo State, Brazil, were collected and chemically analyzed. The waters leaching Mesozoic sediments are generally more acid (pH_average=5.9) and have lower values for total dissolved solids (TDS_average=105 mg/L) than those obtained for waters leaching Paleozoic sediments of Tubarão Group. First-degree trend surfaces revealed that the deeper tubular wells occur towards east/southeast and exploit Paleozoic sediments as well fractured/fissured diabases/basalts, whereas the tubular wells in the west/northwest region are shallower. Piper diagrams indicated that the majority of the waters are a blend of waters from different lithologies. Significant correlations were found among nitrate, chloride and bicarbonate, suggesting the occurrence of some anthropogenic inputs, whereas elevated alpha activity of geogenic ²²⁶Ra indicated the need of a broad radiometric survey in the area.     

Cenozoic tectonic events at the border of the Paraná Basin, São Paulo, Brazil

In the last decade, even in areas that had been considered tectonically stable, a great amount of Cenozoic, including the Quaternary period, structural data have been collected throughout Brazil. The main goal of this study is to describe the Cenozoic structures and tectonic evolution of an area that is located at the border of the Paraná Basin in the state of São Paulo.The research methods consisted of the analysis of: (1) brittle structure data, mainly conjugate fractures and fault slip data; (2) lineaments traced on air photos and TM Landsat and radar images; and (3) a second-order base surface map.The study area, during the Cenozoic, has been affected by five strike–slip tectonic events, which generated mainly strike–slip faults, and secondarily normal and reverse ones. The events were named, from the oldest to the youngest, E1-NE, E2-EW, E3-NW, E4-NS, and E5-NNE; and the maximum principal stresses σ1 strike approximately NE–SW, E–W, NW–SE, N–S, and NNE–SSW, respectively. Event E2-EW seems to have been contemporaneous with the deposition of the Rio Claro Formation, the most important Cenozoic deposit of probable Neogenic age, and also to have controlled the distribution of its deposits. Event E3-NW was the strongest one in the area, as is pointed out by structural data, and the maximum principal stress σ1 of event E5-NNE is partially concordant with the orientation of σH-max of well break-out data in the Paraná Basin, suggesting a Neotectonic activity for this event. Finally, discontinuities parallel and correlated to the directions of strike–slip faults of the Cenozoic events seem to have actively controlled the sculpturing of the relief in the study area.     

Soft-sediment deformation structures in late Albian to Cenomanian deposits, São Luís Basin, northern Brazil: evidence for palaeoseismicity

Soft-sediment deformation structures from the Alcântara Formation (late Albian to Cenomanian), São Luís Basin, northern Brazil, consist of (1) contorted structures, which include convolute folds, ball-and-pillow structures, concave-up paths with consolidation lamination, recumbently folded cross-stratification and irregular convolute stratification that grades into massive beds; (2) intruded structures, which include pillars, dykes, cusps and subsidence lobes; and (3) brittle structures, represented by fractures and faults displaying planes with a delicate, ragged morphology and sharp peaks. These structures result from a complex combination of processes, mostly including reverse density gradients, fluidization and liquefaction. Reverse density gradients, promoted by differential liquefaction associated with different degrees of sediment compaction, led to the genesis of convolute folds. More intense deformation promoted the development of ball-and-pillow structures, subsidence lobes and sand rolls, which are attributed to denser, and thus more compacted (less liquefied), portions that sank down into less dense, more liquefied sediments. Irregular convolute stratification that grades into massive beds would have formed at periods of maximum deformation. The subsidence of beds was accompanied by lateral current drag and fluid escape from water-saturated sands. In addition, the fractures and faults record brittle deformation penecontemporaneous with sediment deposition. All these mechanisms were triggered by a seismic agent, as suggested by a combination of criteria, including (1) the position of the study area at the edge of a major strike-slip fault zone that was reactivated several times from the Albian to the Holocene; (2) a relative increase in the degree of deformation in sites located closer to the fault zone; (3) continuity of the deformed beds over large distances (several kilometres); (4) restriction of soft-sediment deformation structures to single stratigraphic intervals bounded by entirely undeformed strata; (5) recurrence through time; and (6) similarities to many other earthquake-induced deformational structures.     

Baurusuchus salgadoensis, a New Crocodylomorpha from the Bauru Basin (Cretaceous), Brazil

Baurusuchus salgadoensis is a new baurusuchid crocodylomorph from Bauru Basin (Cretaceous), Brazil, partially preserved through a complete skull. The fossil comes from a fine sandstone sequence of Adamantina Formation, General Salgado County, São Paulo State. The sedimentary sequence where it was found, located in Fazenda Buriti, is considered Turonian-Santonian in age. The described species _Baurusuchus salgadoensis sp. nov. _ is a baurusuchid with an antorbital fenestra, double external nares with a bony septum, two well-fused supraorbitals, the supratemporal fenestrae larger than the orbits and a quadrangular-shaped laterotemporal fenestra. The position of the external nares, located on anterior and terminal portion of the rostrum together with the theropod-like lateral compression of the snout and teeth are indicators that Baurusuchus salgadoensis was a terrestrial crocodyliform. This was a carnivorous species and the lateral compression of the rostrum could be interpreted as a mechanism to increase the skull resistance forces during biting. The pointed, conical teeth, some with crenulated borders, could be used to perforate and to carve the prey. The geological context of Baurusuchus salgadoensis indicates that it probably lived in a hot and arid climate.     

A continuous multi-millennial record of surficial bivalve mollusk shells from the São Paulo Bight,Brazilian shelf

To evaluate the potential of using surficial shell accumulations for paleoenvironmental studies, an extensive time series of individually dated specimens of the marine infaunal bivalve mollusk Semele casali was assembled using amino acid racemization (AAR) ratios (n = 270) calibrated against radiocarbon ages (n = 32). The shells were collected from surface sediments at multiple sites across a sediment-starved shelf in the shallow sub-tropical São Paulo Bight (São Paulo State, Brazil). The resulting ¹⁴C-calibrated AAR time series, one of the largest AAR datasets compiled to date, ranges from modern to 10,307 cal yr BP, is right skewed, and represents a remarkably complete time series: the completeness of the Holocene record is 66% at 250-yr binning resolution and 81% at 500-yr binning resolution. Extensive time-averaging is observed for all sites across the sampled bathymetric range indicating long water depth-invariant survival of carbonate shells at the sediment surface with low net sedimentation rates. Benthic organisms collected from active depositional surfaces can provide multi-millennial time series of biomineral records and serve as a source of geochemical proxy data for reconstructing environmental and climatic trends throughout the Holocene at centennial resolution. Surface sediments can contain time-rich shell accumulations that record the entire Holocene, not just the present.     

Evolution and palaeoenvironment of the Bauru Basin (Upper Cretaceous,Brazil)

The Bauru Basin was one of the great Cretaceous desert basins of the world, evolved in arid zone called Southern Hot Arid Belt. Its paleobiological record consists mainly of dinosaurs, crocodiles and turtles. The Bauru Basin is an extensive region of the South American continent that includes parts of the southeast and south of Brazil, covering an area of 370,000 km². It is an interior continental basin that developed as a result of subsidence of the central-southern part of the South-American Platform during the Late Cretaceous (Coniacian–Maastrichtian). This sag basin is filled by a sandy siliciclastic sequence with a preserved maximum thickness of 480 m, deposited in semiarid to desert conditions. Its basement consists of volcanic rocks (mainly basalts) of the Lower Cretaceous (Hauterivian) Serra Geral basalt flows, of the Paraná-Etendeka Continental Flood Basalt Province. The sag basin was filled by an essentially siliciclastic psammitic sequence. In lithostratigraphic terms the sequence consists of the Caiuá and Bauru groups. The northern and northeastern edges of the basin provide a record of more proximal original deposits, such as associations of conglomeratic sand facies from alluvial fans, lakes, and intertwined distributary river systems. The progressive basin filling led to the burial of the basaltic substrate by extensive blanket sand sheets, associated with deposits of small dunes and small shallow lakes that retained mud (such as loess). Also in this intermediate context between the edges (more humid) and the interior (dry), wide sand sheet areas crossed by unconfined desert rivers (wadis) occurred. In the central axis of the elliptical basin a regional drainage system formed, flowing from northeast to southwest between the edges of the basin and the hot and dry inner periphery of the Caiuá desert (southwest). Life in the Bauru Basin flourished most in the areas with the greatest water availability, in which dinosaurs, crocodiles, turtles, fish, amphibians, molluscs, crustaceans, and charophyte algae lived. The fossil record mainly consists of transported bones and other skeletal fragments. In the northeastern and eastern marginal regions fossils are found in marginal alluvial fan deposits, broad plains of braided streams and ephemeral alkaline water lakes. In the basin interior the fossil record is related to deposits in sand sheets with braided streams, small dunes, and shallow lakes. In the great Caiuá inner desert a few smaller animals could survive (small reptiles and early mammals), sometimes leaving their footprints in dune foreset deposits. The aim of this article is to present and link the basin sedimentary evolution, palaeoecological features and palaeontological record.     

Geochronological constraints on the evolution of the Embu Complex, São Paulo, Brazil

Petrologic and geochronological work was carried out on a roadside outcrop of amphibolite facies orthogneisses near São Lourenço da Serra, about 50 km southwest of São Paulo City. These orthogneisses belong to the Embu Complex, within the Neoproterozoic Brasiliano Orogenic Cycle mobile belts of SE Brazil. The outcrop consists of predominantly foliated biotite tonalites and granodiorites, which were cut by granitic veins and pegmatites prior to final deformation. SHRIMP U/Pb measurements on zircons from one granodioritic–tonalitic gneiss indicate magmatic crystallization of the protolith at 811±13 Ma (MSWD=1.0). Zircons with dates of ca. 2000 and ca. 1000 Ma in this rock are interpreted as inherited from older crust. One zircon analyzed from the gneiss and three zircons from a discordant pegmatitic vein indicate an event at 650–700 Ma, perhaps related to the intrusion of the pegmatites. A regression of Rb–Sr whole rock data for four biotite gneisses yielded an imperfect isochron, giving an apparent age of 821±68 Ma and an elevated initial ⁸⁷Sr/⁸⁶Sr ratio of 0.719±0.005. The elevated initial ⁸⁷Sr/⁸⁶Sr ratio and the inherited zircons indicate involvement of older crust in the genesis of the gneisses. Rb–Sr feldspar and whole rock pairs yield ca. 560 Ma tielines, giving the time of final cooling below 300–350 °C, and the cessation of medium-grade metamorphism and ductile deformation. These results document a series of tectono-thermal events spanning 250 million years during the Brasiliano Orogenic Cycle. They relate to ca. 800 Ma magmatic arc activity and later allochthonous terrane assembly during closure of the Adamastor Ocean, resulting in the accretion of Western Gondwana.     

Facies analysis of tertiary alluvial fan deposits in the Jundiaí region, São Paulo, southeastern Brazil

This article presents an analysis of facies of sedimentary sequences that occur as discontinuous bodies in the Jundiaí region, west of the main Tertiary continental basins of the southeastern Brazil continental rift. Nine identified sedimentary facies, grouped into four associations, suggest the existence of an ancient alluvial fan system whose source area was the Japi mountain range (Serra do Japi). The deposits are considered Tertiary in age and chronocorrelated with those identified in the Atibaia region and at other sites up to 100 km east and northeast of Jundiaí. The depositional model adopted to explain the filling of the basin proposes that the alluvial fans, which directly derive from the source area, terminated in a braided channel longitudinal to the basin axis that flowed to northwest, in a similar configuration to that of the present day. This basin may have extended to the Atibaia region or formed a set of small basins laterally contiguous to the faults associated with the rift. Such occurrences show that the formation of rift basins was broader than the area presently occupied by the main deposits.     

Stable isotopic constraints on Kuroko-type paleohydrothermal systems in the Mesoproterozoic Serra do Itaberaba group,São Paulo State,Brazil

Mesoproterozoic oceanic paleohydrothermal systems developed in the volcanosedimentary Serra do Itaberaba Group, which comprises part of the Ribeira fold belt. Hydrothermal alteration associated with these systems was responsible for large premetamorphic chloritic alteration halos (CZ1 rocks), overprinted by restricted premetamorphic chloritic (CZ2 rocks), argillic, and advanced argillic alterations that correspond to intensely leached rocks within feeder zones. Well-defined trends of increasing δ¹⁸O values with the progressive intensity of the alteration process are observed for igneous metabasites, metabasic hydroclastic rocks, and intermediate metamorphosed igneous and volcaniclastic rocks from CZ1. Systematic stable isotope variations evince that, in the Serra do Itaberaba metamorphosed hydrothermalized rocks, the preexisting isotope signatures of the hydrothermal systems were at least partially preserved. Highly evolved hot seawater is suggested for the genesis of the CZ1 rocks, whereas for the CZ2 rocks and marundites, the ¹⁸O fluid enrichments are interpreted as due to the major contribution of evolved seawater-derived fluids with a subordinate magmatic water component. An early near-seafloor, low-temperature alteration in a mid-ocean ridge environment was responsible for heterogeneous ¹⁸O whole-rock enrichments and followed by steady hydrothermal circulation with discharge of hot fluids, which previously underwent isotopic exchange with the ¹⁸O enriched volcanic rocks in the deeper part of the system with high temperatures and low water: rock ratios in a backarc environment. The subordinate magmatic water component derived from andesitic and rhyodacitic intrusions. The extremely high δ¹⁸O anomalies from the CZ1 rocks suggest an associated base metal massive sulfide ore body. The lower δ¹⁸O values related to the CZ2 rocks represent alteration by a higher temperature fluid, which might indicate the proximity of possible ore zones. The identification of several premetamorphic hydrothermally altered zones, similar to those of Kuroko-type base metal mineralizations, expands the mineral potential of base metal deposits in the Serra do Itaberaba Group and the volcanosedimentary sequences from the Ribeira fold belt.     

Arsenic in groundwater affected by phosphate fertilizers at São Paulo, Brazil

. This paper studies metalloid mobility in soils produced by conventional farming methods. The mobility of arsenic in soils depends on several factors including redox potential, soil mineralogy, pH, and the presence of other anions that compete with As for soil retention sites, for example, phosphate. Phosphate enhances the mobility of As in soils by competing for adsorption sites. Arsenic may accumulate in soil through the application of fertilizers. Ingestion of inorganic arsenic contained in drinking water is known to cause cancer. Studies were carried out in an area of Jundiaí, São Paulo in Brazil with high arsenic levels in natural water from domestic wells. The mobility of arsenic in the soil of Jundiaí was studied in the period 1998–2001. The application of phosphate fertilizers on a wide scale is a common agricultural practice. Based on data from the field and laboratory experiments, the deterioration of soil and groundwater quality is a result mainly of fertilizer use due to excessive P application, overdosing of soil with phosphate, and undesirable additions of arsenic in P fertilizers.     

Neoproterozoic glacial dynamics revealed by provenance of diamictites of the Bebedouro Formation, São Francisco Craton, Central Eastern Brazil

One of the main questions on Neoproterozoic geology regards the extent and dynamics of the glacial systems that are recorded in all continents. We present evidence for short transport distances and localized sediment sources for the Bebedouro Formation, which records Neoproterozoic glaciomarine sedimentation in the central-eastern São Francisco Craton (SFC), Brazil. New data are presented on clast composition, based on point counting in thin section and SHRIMP dating of pebbles and detrital zircon. Cluster analysis of clast compositional data revealed a pronounced spatial variability of clast composition on diamictite indicating the presence of individual glaciers or ice streams feeding the basin. Detrital zircon ages reveal distinct populations of Archean and Palaeoproterozoic age. The youngest detrital zircon dated at 874 ± 9 Ma constrains the maximum depositional age of these diamictites. We interpret the provenance of the glacial diamictites to be restricted to sources inside the SFC, suggesting deposition in an environment similar to ice streams from modern, high latitude glaciers.     

The origin of enriched mantle beneath São Miguel, Azores

Lavas from the island of São Miguel, Azores Archipelago have long been known to display large radiogenic isotopic variability, that ranges from “depleted” isotopic signatures (e.g. high ε_Nd ∼ +5) in the west, typical of many ocean island basalts, to more “enriched” compositions (e.g. low ε_Nd ∼ +1) in the east. Here, we further characterise the geochemistry of lavas from this remarkable locality, focussing on the nature and origin of the enriched source. Our new isotope data define a striking, linear array in Nd and Hf isotope space that points towards an unusual, enriched composition below the mantle array. This distinctive Hf-Nd isotope signature is associated with elevated values of all three radiogenic Pb isotope ratios. Although the enriched component has certain geochemical similarities to both terrigenous sediments and some samples of the continental mantle lithosphere, such comparisons do not stand closer examination. In the absence of a clear, modern analogue we explore the isotope evolution of some simple, model melt compositions to investigate plausible means of producing an appropriate enriched component. Nd-Hf isotope characteristics provide the tightest constraints and can be reproduced by an ancient (∼3 Ga), modest-degree melt (∼2%) from a garnet peridotite source. Currently, modest-degree melts from garnet-bearing sources are found forming some major oceanic islands. Subduction, isolation and later mixing of small amounts (<5%) of such basaltic material with more ubiquitous ambient mantle can account for the isotopic characteristics of the enriched São Miguel source. Yet the incompatible element ratios of the enriched São Miguel lavas do not show “recycled” signatures of near-surface alteration nor subduction zone dehydration. Thus, we infer that the enriched component was originally under-plated basalt, intruded into oceanic mantle lithosphere rather than forming the island edifice itself. Since the extreme isotope compositions of São Miguel reflect unextraordinary, albeit ancient, magmatic fractionation, the general rarity of such signatures indicates the efficiency of mantle processes in homogenising or hiding similar sources.     

Territorial exclusion and violence: the case of the state of São Paulo, Brazil

If we had to point out one single feature to define Brazilian cities today, it would be the existence of a dual built environment: a landscape produced by private entrepreneurs and contained within the framework of detailed urban legislation, and another one, three times greater, self-produced by the poor and eternally situated in an intermediate zone between the legal and the illegal. In addition to being an expression of economic and social disparities, this contrast has profound implications on the form and functioning of the cities. The sprawl of the precarious peripheries has lead to an absurd disconnection of poorly urbanized spaces and the city center where jobs, cultural and economic opportunities are concentrated. The effects of this persistent territorial exclusion are devastating and occur in both the peripheries and the city center. The purpose of this paper is to explore the nexus between the precarious and risky urbanization which took place in Brazilian cities and the urban violence that seems to be the most recent and visible face of this model, using the concrete example of different cities in the state of São Paulo. In order to construct the links it is first important to understand how patterns of economic development and population trends have contributed to the generation of risk urbanization and how planning and urban management policies interact with it.     

Climate-induced sediment-palaeosol cycles in a Late Cretaceous dry aeolian sand sheet: Marília Formation (North-West Bauru Basin, Brazil)

Aeolian sand sheets, which are characterized by low relief surfaces that lack dunes, are common in arid and semi‐arid climatic settings. The surface of an aeolian sand sheet can either be stable and subject to pedogenetic effects, or unstable such that it is affected by deflation or sedimentation. The Marília Formation (Late Cretaceous) may be interpreted as an ancient aeolian sand sheet area, where alternating phases of stability and instability of the accumulation surface have been recorded. Detailed field studies were carried out in several sections of the Marília Formation, where cyclic alternations of palaeosols and aeolian deposits were evident, using palaeopedological and facies analysis methods, supported in the laboratory by the analysis of rock samples, cut and polished in slabs, thin sections, scanning electron microscope images and X‐ray diffraction data from the clay minerals. The deposits comprise three lithofacies that, in order of abundance, are characterized by: (i) translatent wind‐ripple strata; (ii) flood deposits; and (iii) ephemeral river channel deposits. Palaeosols constitute, on average, 65% of the vertical succession. Three types of palaeosols (pedotypes) are recognized: (i) Aridisols; (ii) Entisols; and (iii) Vertisols. Erosional surfaces due to aeolian deflation divide the top of the palaeosol profiles from the overlying aeolian deposits. The palaeoenvironmental interpretation of the deposits and the palaeosols allows the depositional system of the Marília Formation to be defined as a flat area, dominated by aeolian sedimentation, with subordinate ephemeral river sedimentation, and characterized by a dry climatic setting with occasional rainfall. The climate is the main forcing factor controlling the alternation between episodes of active sedimentation and periods of palaeosol development. A climate‐controlled model is proposed in which: (i) the palaeosols are indicative of a stable surface that is developed during the more humid climatic phases; and (ii) the erosional surfaces and the overlying aeolian sediments attest to periods of deflation and subsequent sedimentation, thereby increasing the availability of sediment during the drier climatic phases. The ephemeral fluvial deposits mark the more humid climatic conditions and contribute to the lagged sediment influx caused during the drier periods by the erosion of previously stored sediment.     

Geochemistry of groundwater from a rhyolite aquifer,Northwest Iran

Chemical data on groundwater composition in rhyolitic hard rock aquifers with limited global occurrence are rarely found. In this research geochemistry of Mahabad Rhyolite Aquifer, NW Iran, was studied considering major ions, silica and trace elements measured in wet and dry seasons. Based on the results, the mean silica content was 18 mg l^?1, less than the average of the rhyolitic waters. However, the relatively higher electrical conductivity (EC) of 418 µS cm^?1 was measured. Based on a PHREEQCI model, the weathering of the silicate minerals and dissolution of carbonated intercalations turns groundwater dominantly into Ca–HCO₃ type, enhancing EC, pH and silica concentration along the flow path. Trace elements of Sr, Ba and Pb were measured at highest concentrations, the later with an average value of 83 ppb exceeds the drinking guidelines. Cluster analysis confirms biotite weathering and barite dissolution as the main sources of the trace elements in the groundwater. The results signify geochemical features of rhyolitic groundwater which can be a useful tracer of mixing in flow systems containing variety of aquifers including rhyolites.     

Geochemistry of contaminated komatiites from the Umburanas greenstone belt,Bahia State,Brazil

The late Archaean Umburanas greenstone belt (UGB) is located in the São Francisco Craton, southwest of Bahia State, Brazil. The lower unit of UGB comprises basal komatiite lavas and tholeiitic basalts intercalated with felsic volcanic rocks. The regional crystalline basement rocks, the Gavião block, predominantly consist of granitic, granodioritic and migmatitic gneiss along with tonalite-trondhjemite-granodiorite (TTG) associations.Petrographic studies of UGB komatiites reveal characteristic spinifex igneous texture although primary mineralogy is rarely preserved. Based on textural relationships, komatiites are divided into cumulate, spinifex, and massive types. The MgO content varies in the range 31.5–40.4 wt%. The MgO–SiO₂ negative correlation in komatiites suggests olivine fractionation trend. The UGB komatiites are of Al-undepleted type, characterized by Al₂O₃/TiO₂ (21–48) ratio, enriched in highly incompatible LILE relative to moderately incompatible HFSE and distinct negative Nb, Sr and Eu anomalies. Also shows depletion of light rare earths, convex-downward rare earth patterns typically not observed in komatiites world-wide, and primitive mantle normalized Gd/Yb (1.03–1.23) and La/Sm (2.36–4.99) ratios. The negative Eu anomaly is attributed to the circulation of H₂O-rich fluid, whereas the negative Nb and Sr anomalies are attributed to contamination from granitic basement rocks of the Gavião block.The UGB komatiites are most likely derived from adiabatic decompressional melting of a mantle plume. The melting took place at liquidus temperatures in the range 1572–1711 °C, which is consistent with mantle-plume origin invoked for several other komatiites in Archaean greenstone belts elsewhere. The melts were more likely generated at a depth shallower than 100 km (pressure < 2.5 GPa) where garnet was absent in the source mineralogy. Geochemical characteristics suggest contamination of primary melts with granitic basement rocks either during ascent of melt or during emplacement of magma in a continental basin setting. Greenschist to low-T amphibolite facies metamorphism at ∼2Ga may also have played a role in modifying the original komatiite petrography and composition.     

Osteoderms of Montealtosuchus arrudacamposi (Crocodyliformes,Peirosauridae) from the Turonian-Santonian (Upper Cretaceous) of Bauru Basin,Brazil

The skin of Crocodyliformes is characterized by osteoderms of various sizes and shapes. It plays roles in defence, thermoregulation, sexual attraction, calcium reserves, and locomotion. This study presents the morphometric characteristics of osteoderms preserved in the nuchal, dorsal, ventral and appendicular shield of Montealtosuchus arrudacamposi, a Peirosauridae crocodyliform from the Turonian-Santonian (Upper Cretaceous) of Adamantina Formation, Bauru Basin, Brazil. The results of the analysis show that its dermal shield had protective and thermoregulatory functions and a well-defined mechanical function allowing terrestrial locomotion and enabling good agility and capacity for movement.     

Geochemistry of rare earth elements in bottom sediments of the Brazil Basin, Atlantic Ocean

The sedimentation and ore formation were studied in sediments from nine stations located in the 24°W profile in the Brazil Basin of the Atlantic Ocean. The sediments are represented by mio- and hemipelagic muds, which are variably enriched in hydrothermal iron and manganese oxyhydroxides. As compared to the sediments from other basins of the Atlantic Ocean, these rocks are marked by extremely high manganese contents (up to 1.33%) and maximal enrichment in Ce. It was shown that the positive Ce anomaly is related to the REE accumulation on iron oxyhydroxides. Influence of hydrothermal source leads to the decrease of Ce anomaly and LREE/HREE ratio. In the reduced sediments, preservation of positive Ce anomaly and/or its disappearance was observed after iron and manganese reduction. The REE contents were determined for the first time in the Ethmodiscus oozes of the Brazil Basin. Ore deposits of the Brazil Basin are represented by ferromanganese crust and ferromanganese nodules. Judging from the contents of iron, manganese, rare, and trace elements, these formations are ascribed to the sedimentation (hydrogenic) deposits. They are characterized by a notable positive Ce anomaly in the REE pattern. The extremely high Ce content (up to 96% of total REE) was discovered for the first time in the buried nodules (Mn/Fe = 0.88).     

Geochemical and stable isotopic evolution of the Guarani Aquifer System in the state of São Paulo, Brazil

The purpose of this report is to explain geochemical and stable isotopes trends in the Brazilian unit of the Guarani Aquifer System (Botucatu and Piramboia aquifers) in S?o Paulo State, Brazil. Trends of dissolved species concentrations and geochemical modeling indicated a significant role of cation exchange and dissolution of carbonates in downgradient evolution of groundwater chemistry. Loss of calcium by the exchange for sodium drives dissolution of carbonates and results in Na–HCO₃ type of groundwater. The cation-exchange front moves downgradient at probably much slower rate compared to the velocity of groundwater flow and at present is located near to the cities of Sert?ozinho and águas de Santa Barbara (wells PZ-34 and PZ-148, respectively) in a shallow confined area, 50–70 km from the recharge zone. Part of the sodium probably enters the Guarani Aquifer System. together with chloride and sulfate from the underlying Piramboia Formation by diffusion related to the dissolution of evaporates like halite and gypsum. High concentrations of fluorine (up to 13.3 mg/L) can be explained by dissolution of mineral fluoride also driven by cation exchange. However, it is unclear if the dissolution takes place directly in the Guarani Aquifer System or in the overlying basaltic Serra Geral Formation. There is depletion in δ ²H and δ ¹⁸O values in groundwater downgradient. Values of δ ¹³C(DIC) are enriched downgradient, indicating dissolution of calcite under closed system conditions. Values of δ ¹³C(DIC) in deep geothermal wells are very high (>–6.0‰) and probably indicate isotopic exchange with carbonates with δ ¹³C about –3.0‰. Future work should be based on evaluation of vertical fluxes and potential for penetration of contamination to the Guarani Aquifer System. Electronic Publication