Extreme values and meteorology

Summary The basic ideas of univariate extremes and some applications are described in the paper; some references are made to multivariate extremes and stochastic processes of extremes.

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Zusammenfassung Es werden einige grundlegende Ideen zu univariaten Extremen und ihren Anwendungen beschrieben. Multivariate Extreme und stochastische Prozesse von Extremen werden ebenfalls besprochen.

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Vertical Profiles of Turbulence Parameters in the Thermal Internal Boundary Layer

Boundary-Layer Meteorology - The correct simulation of pollutant dispersion in coastal regions demands understanding the turbulence structure of the thermal internal boundary layer (TIBL), which...     

Landslide risk analysis in the area North of Lisbon (Portugal): evaluation of direct and indirect costs resulting from a motorway disruption by slope movements

A risk analysis is developed for a test site located in the area north of Lisbon using a scenario of a temporary interruption of the motorway A9 due to a landslide of rotational or translational type. Landslide susceptibility is assessed at the regional scale independently for rotational and translational slides, comparing the landslide distribution with a set of assumed independent landslide predisposing factors. Susceptibility models are validated and classified through the computation of prediction rate curves based on the temporal partition of the landslide data sets. Landslide hazard maps are based on a scenario of future landslide occurrence for the next 27 years. These maps allow the definition of two critical areas on the motorway A9 with regards to landslide susceptibility. Direct costs associated with both critical spots are assessed taking into account the probable affected area of the motorway, and the reconstruction costs. Indirect costs derived from the traffic interruption are evaluated considering the alternatives paths to the motorway, and include costs resulting from: (1) additional fuel consumption; (2) decrease in tollgate income; and (3) loss of productive time. Results show that indirect costs may be 24 to 43 times higher than direct costs, assuming a temporary interruption of the motorway for 6 months.     

The Archean BIF-hosted Cuiabá Gold deposit, Quadrilátero Ferrífero, Minas Gerais, Brazil

The Cuiabá Gold Deposit is located in the northern part of the Quadrilátero Ferrífero, Minas Gerais State, Brazil. The region constitutes an Archean granite–greenstone terrane composed of a basement complex (ca. 3.2 Ga), the Rio das Velhas Supergroup greenstone sequence, and related granitoids (3.0–2.7 Ga), which are overlain by the Proterozoic supracrustal sequences of the Minas (< 2.6–2.1  Ga) and Espinhaço (1.7 Ga) supergroups.The stratigraphy of the Cuiabá area is part of the Nova Lima Group, which forms the lower part of the Rio das Velhas Supergroup. The lithological succession of the mine area comprises, from bottom to top, lower mafic metavolcanics intercalated with carbonaceous metasedimentary rocks, the gold-bearing Cuiabá-Banded Iron Formation (BIF), upper mafic metavolcanics and volcanoclastics and metasedimentary rocks. The metamorphism reached the greenschist facies. Tectonic structures of the deposit area are genetically related to deformation phases D₁, D₂, D₃, which took place under crustal compression representing one progressive deformational event (E_n).The bulk of the economic-grade gold mineralization is related to six main ore shoots, contained within the Cuiabá BIF horizon, which range in thickness between 1 and 6 m. The BIF-hosted gold orebodies (> 4 ppm Au) represent sulfide-rich segments of the Cuiabá BIF, which grade laterally into non-economic mineralized or barren iron formation. Transitions from sulfide-rich to sulfide-poor BIF are indicated by decreasing gold grades from over 60 ppm to values below the fire assay detection limit in sulfide-poor portions. The deposit is “gold-only”, and shows a characteristic association of Au with Ag, As, Sb and low base-metal contents. The gold is fine grained (up to 60 μm), and is generally associated with sulfide layers, occurring as inclusions, in fractures or along grain boundaries of pyrite, the predominant sulfide mineral (> 90 vol.%). Gold is characterized by an average fineness of 0.840 and a large range of fineness (0.759 to 0.941).The country rocks to the mineralized BIF show strong sericite, carbonate and chlorite alteration, typical of greenschist facies metamorphic conditions. Textures observed on microscopic to mine scales indicate that the mineralized Cuiabá BIF is the result of sulfidation involving pervasive replacement of Fe-carbonates (siderite–ankerite) by Fe-sulfides. Gold mineralization at Cuiabá shows various features reported for Archean gold–lode deposits including the: (1) association of gold mineralization with Fe-rich host rocks; (2) strong structural control of the gold orebodies, showing remarkable down-plunge continuity (> 3 km) relative to strike length and width (up to 20 m); (3) epigenetic nature of the mineralization, with sulfidation as the major wall–rock alteration and directly associated with gold deposition; (4) geochemical signature, with mineralization showing consistent metal associations (Au–Ag–As–Sb and low base metal), which is compatible with metamorphic fluids.     

Shrimp U–Pb zircon dating and palynology of bentonitic layers from the Permian Irati Formation, Paraná Basin, Brazil

This paper presents the first SHRIMP zircon age data from bentonitic ash fall layers intercalated with the Irati sedimentary rocks, as well as palynofossils retrieved from the PETROBRAS-Six mine, Paraná State, southern Brazil. The Permian Irati Formation is one the most important oil source horizons within the Paraná Basin, and consists mainly of siltstones, gray claystones, as well as organic-rich claystones intercalated with limestones. Zircon morphology based on cathodoluminescence images includes two different populations: a dominant population of euhedral, prismatic, elongate to acicular grains which are most likely related to an ash fall volcanism; and a population of rounded to large prismatic grains, that were interpreted as detrital grains. SHRIMP analysis performed on the euhedral and prismatic grains revealed an age of ca. 278.4 ± 2.2 Ma (7 points with 95% confidence) interpreted as the crystallization age of the volcanic eruption. Based on this new dating, the Irati Formation should be placed on the Lower Permian (Cisuralian), Artinskian in age, modifying substantially the traditional ages previously attributed to this unit. The palynofossils from this level include key species of the Lueckisporites virkkiae Zone (such as L. virkkiae, L. densicorpus, L. stenotaeniatus, Weylandites lucifer, Alisporites splendens). Typical species of this zone also occur in African and other South American (Argentina) Permian strata, allowing stratigraphical correlations. The origin of the ash falls is not clearly defined. It may be related either to calc-alkaline arc magmatism associated to the Sanrafaelica Orogeny (275 and 250 Ma) or to bimodal volcanic events associated to an early intracontinental rift developed within southwestern Gondwana at ca. 278 My. The dating of this unit is significative to calibrate biostratigraphic schemes along the Paraná Basin, as well as equivalent zones in Gondwana areas, mainly in its Occidental portion.     

The copper–gold and gold deposits of the Neoproterozoic Mara Rosa magmatic arc, central Brazil

Mineral exploration in the Neoproterozoic Goiás Magmatic Arc, central Brazil, dates back to the beginning of the 1970s. The Goiás Magmatic Arc extends for more than 1000 km in the western and northern parts of Goiás, into Tocantins, and disappears under the Phanerozoic Parnaíba Basin. Two main areas of Neoproterozoic juvenile crust, the Arenópolis and the Mara Rosa arcs, are identified. They lie in the southern and northern sectors of the Goiás Arc, respectively, and are relatively well studied.The Goiás Magmatic Arc dominantly comprises tonalitic/dioritic orthogneisses and narrow NNE-striking volcano-sedimentary belts. Recent U–Pb zircon data indicate crystallization of the tonalite protoliths in two main episodes: the older between ca. 890 and 790 Ma and the younger at 670–600 Ma. Nd isotopic data indicate the very primitive nature of the original magmas, with T_DM model ages mostly within the interval between 0.9 and 1.0 Ga and _Nd(T) values between +3.0 and +4.6. In the Chapada–Mara Rosa area, the supracrustal rocks form three individual NNE belts, known as the eastern, central and western belts, separated from each other by metatonalites/metadiorites.Gold and Cu–Au deposits of the Mara Rosa area occur in four main associations: (i) Au–Ag–Ba (e.g., Zacarias), which are interpreted as stratiform, disseminated volcanogenic deposits, (ii) Cu–Au (e.g., Chapada) which has been interpreted either as volcanogenic or as a porphyry-type deposit, (iii) Au-only deposits (e.g., Posse), interpreted as an epigenetic disseminated deposit controlled by a mesozonal shear zone and (iv) Au–Cu–Bi (e.g., the Mundinho occurrence), which are considered as vein-type deposits controlled by magnetite-rich diorites.The gold and Cu–Au deposits located within the Goiás Magmatic Arc can be spatially and temporally related to the magmatic evolution of a collisional belt or, in other words, to an orogenic gold deposit model. These models are based on the continuous evolution of collisional plates, which can be subdivided into four stages with distinct magmatic characteristics: (i) subduction stage, (ii) syntectonic collisional magmatism stage, (iii) post-tectonic collisional magmatism stage and (iv) post-orogenic extension stage.     

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.

     

How geological origin influences the quality of sand and the environmental impacts of its mining,Bahia state,Northeastern Brazil

The highly increasing demand for sand in Northeastern Brazil, due to governmental economic incentive focused to this region, has necessitated the opening of new extraction mines, generally without adequate environmental control. This study aimed to assess several sand extraction activities in the Recôncavo territory, Bahia state—area with high variability in sedimentary deposits—by evaluating the quality of the sand and the extraction impacts according to the geological basement. The methodology consisted of field research, using satellite images and maps for characterization, application of the environmental and economic impact checklists, and analysis of organic matter, particle size distribution, and salt content in 35 samples from different sand mines. The sands were classified as white sand (from Neossols/weathered aeolian sandstones), brown sand (from mature soils), and river sand. A strong relation between the geological origin and sand type and quality was established. Although the river sand appears to be the best option for extraction with regards to sand quality and low environmental impacts, the white sand derived from Jurassic sandstones is intensively extracted due to easy access, availability of wide deposits, and visual quality and homogeneity. However, the white sand has an inadequate particle distribution due to its poor gradation (aeolian selection of fine particle) and high environmental impacts due to its location in wet tropical ecosystem dominated by the Atlantic forest and the erosion of sandy soils. We demonstrated that the knowledge of lithology is fundamental for mapping new potential sand mines and minimizing the generated impacts.