Coupling of tectonic factors and precipitation variability as a driver of Late Quaternary aggradation in Northeast Brazil

The coupling between tectonic factors and climate processes is a key element in understanding landscape evolution. However, few studies address this issue in the context of unglaciated tropical areas in passive continental margins. Thus, this research aimed to understand the origins and evolution of the geomorphological landscape in the eastern sector of Northeast Brazil along the Late Quaternary, between the Last Interstadial (Marine Isotopic State 3) and the Upper Holocene. The morphostratigraphic approach, coupled with sedimentological analyses and optically stimulated luminescence dating of sediments, showed that the depositional record stored in the landscape ranges from at least 60 000 years BP until the Upper Holocene. Depositional intervals suggest that there were moments of climatic instability followed by moments of relative geomorphological quiescence. Such active moments coincide chronologically with Heinrich and Dansgaard-Oeschger events, which are likely linked to changes in paleo-pluviosity that might respond to the dismantling of elluvial covers and colluvial deposition in the area. Likewise, reworking of hillslope materials led to increased deposition in the fluvial realm. In addition, such deposits might have been affected by the neotectonic complexity of the area, responsible for the creation of non-concatenated accommodation spaces, indicating a dynamics of uplifting and subsidence of blocks typical of passive margin taphrogenic environments. Therefore, the formative processes that led to the Late Quaternary deposition of sediments in a platform margin context reflect a coupling between tectonic and climatic factors. The former, driven by precipitation variability on a regional scale, triggered fluvial and high-energy hillslope processes that resulted in ubiquitous valley floor and piedmont aggradation, whereas the latter led to the dismantling of local base levels, transforming depositional units into new denudational landforms subject to the current climate dynamics. © 2020 John Wiley & Sons, Ltd.     

Use of geothermal methods in outlining deep groundwater flow systems in Paleozoic interior basins of Brazil

Results of regional-scale geothermal studies are presented, providing new insights into the characteristics of deep groundwater flow systems in the Paleozoic sedimentary basins in the Amazon, Paraná and Parnaíba regions of Brazil. The study makes use mainly of bottom-hole temperature data sets for oil wells, the depths of which vary from 1,000 to 4,000 m. The techniques employed in data analysis have allowed identification of non-linear features in vertical distributions of temperature, produced by deep groundwater flows in the study area. According to the results obtained, vertical velocities of subsurface flows are found to fall in the range 10^?10 to 10^?9 m/s, while the horizontal velocities are significantly higher, of the order 10^?8 m/s. Identification of large-scale down flows has allowed inferences as to the existence of lateral movements of groundwater. The basins in the Amazon region are found to be characterized by widespread down flow of groundwater, implying the existence of distributed recharge systems operating on regional scales. There is a systematic decrease in horizontal velocities along the direction from west to east. This feature is considered indicative of gravity driven flows induced by episodes of uplift, since Miocene times, in the Andean region.     

Potential of the LASH model for water resources management in data-scarce basins: a case study of the Fragata River basin,southern Brazil

ABSTRACT

The objective of this study was to evaluate, based on a data-scarce basin in southern Brazil, the potential of the Lavras Simulation of Hydrology (LASH) model for estimating daily streamflows, annual streamflow indicators and the flow–duration curve. It was also used to simulate the different runoff components and their consistency with the basin physiographical characteristics. The statistical measures indicated that LASH can be considered suitable according to widely used classifications and when compared with other studies involving hydrological models. LASH also showed satisfactory results for annual indicators, especially for maximum and average annual streamflows, as well as for the flow–duration curve. It was found that the model was consistent with the basin characteristics when simulating runoff components. The results obtained in this study allowed us to conclude that the LASH model has the potential to aid practitioners in water resources management of basins with scarce data and similar soil and land-use conditions.

Editor A. Castellarin; Associate editor Y. Gyasi-Agyei     

Ordinary kriging and indicator kriging in the cartography of trace elements contamination in São Domingos mining site (Alentejo, Portugal)

The abandoned pyrite mine of São Domingos, in the southeast Portugal is still an acid mine drainage generator and a source for trace elements pollution. This study aims to evaluate and map the soils and sediments chemical pollution. With this purpose three test sites located in the vicinities of the mine were sampled for soils, sediments and mining waste materials. The samples were analysed for pH, organic carbon, iron oxides and total content of As, Cu, Cr, Hg, Pb, Sb, U, Zn, Mn, S, Fe Al, Ca, K, Mg and P. The hyperspectral image of the test sites was acquired using the aero transported sensor HymapTM. Chemical analysis and hyperspectral images data were processed to estimate the contamination maps by multivariate data analysis, ordinary kriging, cokriging and indicator kriging methodologies.The test sites located downstream the mine open pit, are highly contaminated mainly in As, Hg, Pb and Sb, but no contamination was found in the third test site, upstream the mining site. The acid mining drainage seems to be the main spreading agent of chemical contaminants mostly originating from the mine waste materials. Factorial analysis and the geostatistical methodologies allowed several approaches for the contamination cartography of mining areas.     

Predictive Mapping of Prospectivity in the Gurupi Orogenic Gold Belt,North–Northeast Brazil: An Example of District-Scale Mineral System Approach to Exploration Targeting

The Gurupi Belt hosts a Paleoproterozoic gold province located in north–northeastern Brazil, at the borders of Pará and Maranhão states. It is considered to be an extension of the prolific West African Craton’s Birimian gold province into South America. Additionally, the belt has been the object of recent mineral exploration programs with significant resource discoveries. This study presents the results of predictive mapping using up-to-date mineral system concepts and recently finished regional-scale geological mapping, stream sediment and airborne geophysical surveys conducted by the Geological Survey of Brazil. We relate gold mineralization to an initially enriched crust, metamorphism, deep fluid pathways, structurally controlled damage zones and hydrothermal alteration. Prospective targets were generated using only regional public datasets and knowledge-driven targeting technique. This work did not incorporate any known gold deposits, yet it predicted the largest known deposits and their satellite targets. Besides, high prospective targets mapped almost 40% of known primary gold occurrences within 7% of the project area. This work allowed considerable search area reduction and identification of new target areas, thus collaborating on reducing costs, time and risk of mineral exploration. Results indicate that we achieved an efficient understanding of the geological processes related to the Gurupi Belt mineral system.     

Erratum to: Climate change projections over three metropolitan regions in Southeast Brazil using the non-hydrostatic Eta regional climate model at 5-km resolution

Theoretical and Applied Climatology -     

Resource partitioning among air‐breathing marine predators: are body size and mouth diameter the major determinants?

Although the body size of consumers may be a determinant factor in structuring food webs, recent evidence indicates that body size may fail to fully explain differences in the resource use patterns of predators in some situations. Here we compared the trophic niche of three sympatric and sexually dimorphic air‐breathing marine predators (the South American sea lion, Otaria flavescens, the South American fur seal, Arctocephalus australis, and the Magellanic penguin, Spheniscus magellanicus) in three areas of the Southwestern Atlantic Ocean (Río de la Plata and adjoining areas, Northern Patagonia and Southern Patagonia), in order to assess the importance of body size and mouth diameter in determining resource partitioning. Body weight and palate/bill breadth were used to characterize the morphology of each sex and species, whereas the trophic niche was assessed through the use of stable isotope ratios of carbon and nitrogen. The quantitative method Stable Isotope Bayesian Ellipses in R (SIBER) was used to compute the area of the Bayesian ellipses and the overlap of the isotopic niches. The results showed that morphological similarity was significantly correlated with isotopic distance between groups within the δ¹³C–δ¹⁵N bi‐plot space in the Río de la Plata area, but not in Northern and Southern Patagonia. Furthermore, resource partitioning between groups changed regionally, and some morphologically distinct groups exhibited a large trophic overlap in certain areas, such as the case of male penguins and male sea lions in Southern Patagonia. Conversely, female sea lions always overlapped with the much larger males of the same species, but never overlapped with the morphologically similar male fur seals. These results indicate that body size and mouth diameter are just two of the factors involved in resource partitioning within the guild of air‐breathing predators considered here, and for whom – under certain environmental conditions – other factors are more important than morphology.     

Estuarine flooding in urban areas: enhancing vulnerability assessment

The assessment of vulnerability provides valuable knowledge in the risk assessment steps of a risk governance process. Given the multiscale, multilevel, and multisectorial aspects of flood risk, the diversified entities that directly and indirectly intervene in risk management require specific outputs from the assessment studies. Urban areas in estuarine margins are particularly exposed and vulnerable to flooding. Such interface conditions are found in the Old City Centre of the Seixal, located in the Tagus estuary, Portugal. Here, two distinct methodologies were applied for the assessment of territorial vulnerability. A regional, lower-scale, methodology explores the application of the statistical procedure based on the SoVI^® at the statistical block level. A second, local and higher-scale, methodology is based in data collected through field matrices at the building and statistical sub-block level. Comparison of results revealed that the lower-scale assessment provides information on the vulnerability drivers at the regional and municipal level. Nevertheless, only at a higher-scale, it is possible to characterize and differentiate the smaller geographical units of analysis that compose the Old City Centre of Seixal. The lower-scale vulnerability assessment allows a strategic response, based on adaptation measures such as spatial planning, institutional capacity building and public awareness. The local level assessment provides more accurate knowledge to support local emergency planning and the allocation of operational and material resources at the urban level. Nevertheless, rather than antagonistic, both models can be considered as complementary, having in mind the requirements of an holistic flood risk governance model.

     

Variation in the mobilization of mercury into Black-winged Stilt Himantopus himantopus chicks in coastal saltpans,as revealed by stable isotopes

Causes of variation in mobilization of mercury into Black-winged Stilt Himantopus himantopus chicks were studied through analysis of stable isotope ratios of carbon and nitrogen. Blood and breast feathers were collected from chicks in coastal saltpans during successive breeding seasons. Detritus samples and potential prey (macroinvertebrates) were also collected. Total mercury concentrations and stable isotope signatures were measured using atomic absorption spectroscopy and isotope ratio mass spectrometry respectively. Mercury levels in Chironomidae, Corixidae and Hydrophilidae correlated with mercury levels in chick feathers. Differences of δ¹⁵N signatures between macroinvertebrate groups indicated that they belong to different trophic levels. δ¹⁵N signatures of invertebrates correlated with mercury levels in invertebrates and chicks, but not with δ¹⁵N signatures in chicks. Between-group and between-site differences of δ¹⁵N signatures and mercury levels in invertebrates suggested that they contribute differently to mercury mobilization into chicks, and their relative contribution depends on prey availability in each site. Inter-site differences in the biomagnification factor reinforced that idea. δ¹³C signatures in invertebrates marked a larger range of carbon sources than just detritus. Variation of water inflow regime and prey availability may cause between-group and between-site differences of δ¹³C signatures in prey. Discrepancies between feather and blood for δ¹³C signatures in Praias-Sado and Vaia suggested that temporal variation of prey availability may be the main factor affecting mercury mobilization into chicks in both those cases, since their water inflow regimes are the same. The lowest levels of δ¹³C signatures in Vau suggested that water inflow regime may be the main factor in this case, since no discrepancy existed in δ¹³C signatures between blood and feather.