210Pb-derived chronology in sediment cores evidencing the anthropogenic occupation history at Corumbataí River basin, Brazil

Activity profiles of excess ²¹⁰Pb combined with chemical data determined in two sediment cores from Corumbataí River basin, São Paulo State, Brazil, provided new insights into the reconstruction of historical inputs of anthropogenic constituents, contributing to improving management strategies of the hydrological resources in the basin since most of the municipalities extensively utilize the waters of Corumbataí River and tributaries for drinking purposes, among other uses. Excellent significant relationships between loss on ignition (LOI) and organic matter were found for sediments of both analyzed profiles. Silica was found to be inversely related to organic matter at both analyzed profiles: its decrease accompanied an increase in the specific surface of the sediments. This relationship was confirmed by a great number of inverse significant correlations among silica and oxides Na₂O, K₂O, CaO, MgO, Al₂O₃, P₂O₅, Fe₂O₃, MnO, and TiO₂. It was possible to identify the role of organic matter on adsorption of several oxides/elements in the core sediments profiles. Apparent sediment mass accumulation rates corresponding to 224 and 802 mg cm⁻² year⁻¹ were obtained, and are compatible with field evidence, indicating a higher value associated with sand mining activities interfering with the natural/normal sedimentation process, due to modifications of the channel drainage.     

Pedo‐Geochemical Signatures of Archeological Sites in the Tapirapé‐Aquiri National Forest in Marabá, Amazonia,Brazil

The present study aims to interpret the occupation of terra firme (nonflooded uplands) archeological sites located at Tapirapé‐Aquiri National Forest in the Brazilian state of Pará, through an integrated analysis of pedological, archeological, and geochemical data. We focus on seven archaeological sites, selected among 22 identified in the region. Radiocarbon and thermoluminescence dating indicate distinct periods of occupation over the past ∼6000 years, and the pedo‐geochemical data identify intra‐ and inter‐site differences in soil. Archaeological, chronometric, and pedo‐geochemical data provide a basis for the functional classification of archeological sites found in the region and help to identify specific human activity areas. The results lead us to infer that many of the archeological sites were the result of multiple occupations that left a persistent pedological signature on the landscape.     

Contrasting metamorphic conditions in the Neoproterozoic collision-related Nappes south of São Francisco Craton, SE Brazil

Metamorphic conditions are described for three major tectonic entities on the basis of geothermobarometry in a huge Neoproterozoic nappe complex that verges toward the southern border of the São Francisco craton. The uppermost Socorro-Guaxupé Nappe, represented by its granulite facies basal portion, yields a maximum temperature and pressure of 890 °C and 11 kbar. Its metamorphic evolution is consistent with heating at the base of the crust as a result of an abnormally high geothermal gradient, probably due to underplating by the lithospheric mantle. The underlying Três Pontas-Varginha Nappe yields two somewhat distinct P–T paths, both characterized by peak assemblages in the kyanite stability field. The basal kyanite-bearing granulites show higher peak pressure values (15 kbar at 840 °C) and a trajectory that continues in the kyanite stability field, whereas the upper sillimanite granulites show higher temperatures (880 °C at 13 kbar) and a steeper path toward the sillimanite stability field. Data for the Carmo da Cachoeira nappe reveal a steep trajectory, in which the elevated maximum pressure (18.5 kbar at 820 °C) was obtained from a garnet amphibolite that lies along its basal contact. The inverted metamorphic pattern previously observed across these sequences is confirmed by our thermobarometric data, which reveal that the highest temperatures were attained toward the top of the pile.     

Chemical variations and significance of phosphates from the Fregeneda-Almendra pegmatite field, Central Iberian Zone (Spain and Portugal)

Granitic pegmatites are widespread within a schist-metagreywacke complex in the Fregeneda-Almendra area (Central Iberian Zone). They intrude pre-Ordovician metasedimentary rocks and show a zonal distribution relative to the Meda-Penedono-Lumbrales granitic complex, from barren bodies to those enriched in Li, F, Sn, Nb>Ta, P and Be. Based on mineralogical criteria, these pegmatites are classified into three main categories: barren, intermediate and rare-element pegmatites, with each type including various subtypes. Phosphates are present in many pegmatites that usually occur as fine-grained accessory minerals. The most complex association of such minerals includes numerous Fe–Mn phosphates that occur in intermediate pegmatites. Al-phosphates are characteristic of Li-rich pegmatites. Electron microprobe analyses of representative phosphates reflect compositional differences depending on the pegmatite type. The Fe/(Fe+Mn) ratio of phosphates tends to decrease as the evolution degree of the pegmatites increases.     

Assessing drought in the drylands of northeast Brazil under regional warming exceeding 4 °C

Natural Hazards - Historically, during periods of extreme drought, food security in the drylands of the semiarid region of Northeast Brazil (NEB) is under severe risk due to agricultural collapse....     

Anthropogenic heavy metal signatures for the fast growing urban area of Natal (NE-Brazil)

In this study the effect of anthropogenic discharges on the heavy metal content in the Potengi–Jundiai river system near the fast growing city of Natal, NE-Brazil, is investigated. Due to the multiple anthropogenic source character without any predominating anthropogenic heavy metal discharge the area of Natal may serve as a characteristic place for the study of the impact of the fast growing Brazilian cities on the environment. In general the sediments of the Rio Potengi–Jundiai river system in the studied area are not severely polluted. However, close to waste water drain pipes a characteristic anthropogenic heavy metal signature is visible in enhanced Zn, Pb, Cu and Cd values relative to reference elements such as Al and Fe. Sources are domestic and animal waste, combustion products and hydrocarbons. These heavy metals are probably mainly bound to organic matter. The elements Sn, Hg and Ag in part also belong to the anthropogenic heavy metal signature. The elements Cr, Ni and V are characteristic of weathering heavy minerals in crystalline rocks exposed in the catchment area of the river system and are not significantly added from anthropogenic sources. These heavy metals are most likely predominantly bound to oxides and represent the pristine geogenic background of the system. They can thus be used as reference elements to monitor incipient accumulation of Zn, Pb, Cu and Cd due to anthropogenic input. The element characteristics found here match with those found in other fast growing urban areas such as the Sao Paulo metropolitan area.     

A three-scale model for pH-dependent steady flows in 1:1 clays

A new three-scale model to describe the coupling between electro-chemistry and hydrodynamics in non-swelling kaolinite clays in steady-state conditions is proposed. The medium is characterized by three separate nano-micro and macroscopic length scales. At the pore (micro)-scale the portrait of the clay consists of micro-pores saturated by an aqueous solution containing four monovalent ions (Na⁺, H⁺, Cl⁻, OH⁻) and charged solid particles surrounded by thin electrical double layers. The movement of the ions is governed by the Nernst–Planck equations and the influence of the double layers upon the hydrodynamics is modeled by a slip boundary condition in the tangential velocity governed by the Stokes problem. To capture the correct form of the interface condition we invoke the nanoscopic modeling of the thin electrical double layer based on Poisson–Boltzmann problem with varying surface charge density ruled by the protonation/deprotonation reactions which occur at the surface of the particles. The two-scale nano/micro model is homogenized to the macroscale leading to a precise derivation of effective governing equations. The macroscopic model is discretized by the finite volume method and applied to numerically simulate desalination of a clay sample induced by an external electrical field generated by the placement of electrodes. Numerical results indicate strong pH-dependence of the electrokinetics.     

Genetic and metamorphic conditions constrained by fluid inclusions from Paleoproterozoic (c. 1.8 Ga) magnesite ore deposits, NE Brazil

Precambrian magnesite occurrences hosted by metadolomites from the Orós belt, Ceará, Brazil, are part of a greenschist–amphibolite, metavolcano-sedimentary terrain, dated at 1.8 Ga, cut by Meso- to Neoproterozoic Brasiliano granites and Neoproterozoic basic sills. These rocks were affected by a shear zone between 580 and 500 Ma. The magnesite-bearing marbles can be grouped as medium-grained (1–9 mm) at the Riacho Fundo ore deposit or sparry magnesite (1–15 cm) at the Cabeça de Negro ore deposit. The sparry magnesite shows textural characteristics related to original sedimentary structures. Both types of magnesite-bearing marbles contain aqueous and aqueous-carbonic fluid inclusions that yield homogenization temperatures between 170 and 370 °C. Applying a pressure correction, these temperatures are compatible with the evolution from greenschist to amphibolite facies metamorphic conditions, as described in previous work on the Orós region. It also agrees with data in specialized literature on the metamorphism of carbonate rocks. Fluid inclusion distribution, composition, and physical-chemical characteristics suggest temperature increase, probably related to metamorphism on these rocks. The medium-grained magnesite records partial contamination of CO₂-rich inclusions by relict carbonaceous material (bitumen, hydrocarbons?) that favors, but does not confirm, a syngenetic sedimentary origin and could have caused the lowering of CO₂ melting point in these inclusions. Therefore, though textural evidence points to a sedimentary-diagenetic model, fluid inclusions record conditions of a metamorphic event.     

Short‐term dynamics in fish assemblage structure on a sheltered sandy beach in Guanabara Bay,Southeastern Brazil

Short‐term dynamics in juvenile fish assemblage structure were studied to test whether the most abundant species show temporal segregation, in order to assess whether selected environmental variables could predict species groupings, and to examine the stability of sunset–day–sunrise–night differences. Samplings were collected at 3‐h intervals over 48 h on a seasonal basis between spring 2005 and winter 2006. Fish species richness and abundance were higher in spring, and the lowest values occurred in winter. Harengula clupeola occurred mainly in spring, whereas Atherinella brasiliensis peaked in summer and autumn. On the other hand, Trachinotus carolinus, Umbrina coroides and Mugil liza were abundant in winter. Although temperature, salinity and dissolved oxygen were not found to have a strong effect on the abundance patterns of most species, they did appear to have a significant influence on assemblage groupings, according to canonical correspondence analysis and Spearman rank correlation. There is no consistency of diel usage patterns by a given species across seasons. The relative abundance differed between the time of day, which differed among the seasons; this further complicates an understanding of the dynamics of an assemblage. Studies of diel changes that pooled the sampling period as day or night can miss important changes that occur in a short time scale, such as a 3‐h period.