Multicriteria Geologic Data Analysis for Mineral Favorability Mapping: Application to a Metal Sulphide Mineralized Area,Ribeira Valley Metallogenic Province,Brazil

GIS techniques have been used in the evaluation of favorability for base-metal mineralization in an area comprising the Cerro Azul and Apiaí quadrangles (SG.22-X-B-IV and V, scale 1:100.000), Ribeira Valley, São Paulo and Paraná States, Brazil. Methods have been employed for selection and weighting of prospective variables when applying GIS techniques to a digital database consisting of geological, geochemical and airborne geophysics, and mineral occurrence information. The exploration variable selection and analysis were based on two mineralization models: (1) Panelas type, vein-type carbonate hosted, and (2) Perau type, sedimentary-exhalative. The overlay was performed by weighted linear combination (WLC) and order weighted average (OWA) methods. Both methods proved suitable for the study area, yielding similar results. The ordered weighted averaging analysis provided the best results, with favorability maps showing a large number of classes occupying relatively minor areas. In comparison, the weighted linear combination analysis produced more coherent results but without details for minor areas. The prospective parameters obtained are considered suitable for both Perau and Panelas types. Both methods are inexpensive, and are suitable for selection of prospective areas during geological surveys in areas similar to the studied one.     

Vertically persistent sedimentary facies boundaries along growth anticlines and climate-controlled sedimentation in the thrust-sheet-top South Pyrenean Tremp-Graus Foreland Basin

Compression of the thrust sheet underlying the central South Pyrenean Tremp-Graus Foreland Basin led to weak folding of the overlying basin fill during deposition of Eocene sediments. From the distribution of sedimentary facies and the presence of these folds, it is interpreted that thrusting of deep-seated competent units was accommodated by weak synsedimentary folding with a shorter wavelength at shallower levels. This led to differential subsidence at the surface but no unconformities are observed. The slower subsidence along the active anticlines locally influenced the distribution of sedimentary facies: lateral boundaries between different sedimentary facies are found to extend (sub)vertically up to more than 60 metres within narrow zones a few 100 m to 1.5 km wide. The growth folds thus led intermittently to the fixation of the position of facies boundaries, including a fixation of the coastline, over long periods (104 to 105 years). Sediment transport paths were also influenced by the slight folding of the surface. The orientation of the weak ‘en echelon’ anticlines and of related facies boundaries agrees with the inferred compressional pattern during the Eocene. Explanations for the regular occurrence of 50–60 m thick sedimentary cycles in terms of tectonic pulses or orbitally driven climatic changes and resulting pulses in sediment yield are discussed. For cycles of shorter length (10–15 m), with durations of the order of tens of thousands of years, it is inferred that these are due to regular climatic changes, probably related to orbital forcing, and resulting cyclic alternations of arid and wet periods. Such periodic changes of climate would have caused the intermittent waxing and waning of coarse-grained sediment     

UGC 7388: A galaxy with two tidal loops

We present the results of our spectroscopic and morphological studies of the galaxy UGC 7388 with the 8.1-m Gemini North telescope. Judging by its observed characteristics, UGC 7388 is a giant late-type spiral galaxy seen nearly edge-on. The main body of the galaxy is surrounded by two faint (μ _B ～ 24 ^m /□″ and μ _B ～ 25 _· ^m 5/□″) extended (～ 20–30 kpc) loop-like structures. A large-scale rotation of the brighter loop about the main galaxy has been detected. We discuss the assumption that the tidal disruption of a relatively massive companion is observed in the case of UGC 7388. A detailed study and modeling of the observed structure of this unique galaxy can give important information about the influence of the absorption of massive companions on the galactic disks and about the structure of the dark halo around UGC 7388.     

Predicting catchment sediment yield in Mediterranean environments: the importance of sediment sources and connectivity in Italian drainage basins

Predicting sediment yield at the catchment scale is one of the main challenges in geomorphologic research. The application of both physics‐based models and regression models has until now not provided very satisfying results for prediction of sediment yield for medium to large sized catchments (c. >50 km²). The explanation for this lies in a combination of the large data requirements of most models and a lack of knowledge to describe all processes and process interactions at the catchment scale. In particular, point sources of sediment (e.g. gullies, mass movements), connectivity and sediment transport remain difficult to describe in most models. From reservoir sedimentation data of 44 Italian catchments, it appeared that there was a (non‐significant) positive relation between catchment area and sediment yield. This is in contrast to what is generally expected from the theory of decreasing sediment delivery rates with increasing catchment area. Furthermore, this positive relation suggests that processes other than upland erosion are responsible for catchment sediment yield. Here we explore the potential of the Factorial Scoring Model (FSM) and the Pacific Southwest Interagency Committee (PSIAC) model to predict sediment yield, and indicate the most important sediment sources. In these models different factors are used to characterize a drainage basin in terms of sensitivity to erosion and connectivity. In both models an index is calculated that is related to sediment yield. The FSM explained between 36 and 61 per cent of the variation in sediment yield, and the PSIAC model between 57 and 62 per cent, depending on the factors used to characterize the catchments. The FSM model performed best based on a factor to describe gullies, lithology, landslides, catchment shape and vegetation. Topography and catchment area did not explain additional variance. In particular, the addition of the landslide factor resulted in a significantly increased model performance. The FSM and PSIAC model both performed better than a spatially distributed model describing water erosion and sediment transport, which was applied to the same catchments but explained only between 20 and 51 per cent of the variation in sediment yield. Model results confirmed the hypothesis that processes other than upland erosion are probably responsible for sediment yield in the Italian catchments. A promising future development of the models is by the use of detailed spatially distributed data to determine the scores, decrease model subjectivity and provide spatially distributed output. Copyright © 2006 John Wiley & Sons, Ltd.     

Municipal initiatives for managing dunes in coastal residential areas: a case study of Avalon, New Jersey, USA

The characteristics of foredunes created in a municipal management program on a developed barrier island are evaluated to identify how landforms used as protection structures can be natural in appearance and function yet compatible with human values. Shoreline management zones include a naturally evolving, undeveloped segment; a noneroding, developed segment; eroding and noneroding segments of an “improved beach” where dunes have been built by artificial nourishment; and a privately built, artificially nourished dune on the shoreline of an inlet.A disastrous storm in 1962 resulted in an aggressive program for building dunes using sand fences, vegetation plantings, purchase of undeveloped lots, and sediment backpassing to maintain beach widths and dune elevations. The present nourished and shaped foredune in the improved beach is higher, wider, and closer to the berm crest than the natural dune. Restricted inputs of aeolian sand keep the surface flat and poorly vegetated. A stable section of this engineered shore has a wider beach, and sand fences have created a higher foredune with greater topographic diversity. The cross shore zonation of vegetation here is more typical of natural dunes, but the environmental gradient is much narrower. The privately built dune is low, narrow, and located where it could not be created naturally. Foreshore and aeolian sediments in the undeveloped segment and the improved beach are similar in mean grain size (0.16–0.21 mm) and sorting (0.31–0.39φ), but sediment on the surface of the nourished dune is coarser (28.1% gravel) with a more poorly sorted sand fraction (1.30φ) representing lag elements on the deflation surface.Willingness to enhance beaches and dunes for protection has reduced insurance premiums and allowed the municipality to qualify for funds from the Federal Emergency Management Agency (FEMA) to replace lost sediment, thus placing an economic value on dunes. Success of the management program is attributed to: (i) timing property-purchase and dune-building programs to periods immediately after storms (causing residents to accept high dunes that restrict access or views); (ii) instituting a vigorous education program (reminding residents of hazards during nonstorm periods); (iii) maintaining control over local sediment supplies (to keep pace with erosion and create new shoreline environments); (iv) investing private and municipal economic resources in landforms (qualifying them for external funds for replacement); and (v) maintaining, augmenting, or simply tolerating biodiversity and natural processes (retaining a natural heritage).     

Application of a statistical water-table model reveals connections between dunes and vegetation at Doñana

We present a simple statistical model of the water-table fluctuations based on a set of multiple regressions for a dune slack of the Doñana National Park, and its utility to understand some ecological processes. The variation in the coefficients of the regressions for different locations allows discrimination between different zones in the dune slack, and explains the spatial pattern of heath vegetation observed in the stabilized sands. Model simulations were compared with an existing sparse data set of water-table levels, and suggests possible mechanisms responsible for the catastrophic pine tree mortality, which happened during the drought of 1979–83.     

Response of benthic opportunistic polychaetes and amphipods index to different perturbations in coastal oligotrophic areas (Canary archipelago,North East Atlantic Ocean)

Oligotrophic areas harbour low macrofaunal abundance and patchy distribution. In these areas it is necessary to test the reliability of biological indicators, especially those based on taxonomic sufficiency where the level of identification is balanced against the need for ecological information and could affect the efficiency of bioindicators. The BOPA (benthic opportunistic polychaetes and amphipods) index was applied in five coastal areas subjected to different perturbations (aquaculture, harbour, brine, sewage, and thermal pollution) in the Canary archipelago, an oligotrophic area of the Atlantic Ocean. Significant differences in the BOPA index between impact and control sites were only found in the area affected by a harbour. Perturbations such as aquaculture, brine or sewage discharge produce only a weak response of the BOPA index, whereas no effects were observed at thermal pollution‐impacted locations. The BOPA index should be used with caution to establish the ecological status of coastal water bodies in the Canary Islands, since it was only reliable in strongly impacted regions (enlargement harbour works), but did not respond clearly to other man‐induced perturbations.     

Indicators of Great Basin rangeland health

Early-warning indicators of rangeland health can be used to estimate the functional integrity of a site and may allow sustainable management of desert rangelands. The utility of several vegetation canopy-based indicators of rangeland health at 32 Great Basin rangeland locations was investigated. The indicators were originally developed in rangelands of the Chihuahuan Desert. Soil resources are lost through wind and water-driven erosion mainly from areas unprotected by plant canopies (i.e. bare soil). Study sites in Idaho had the smallest bare patches, followed by sites in Oregon. The more arid Great Basin Sagebrush Zone sites in Utah had the largest bare patches. Several vegetational indicators including percent cover by vegetation, percent cover by life-form, percent cover by sagebrush, and percent cover by resilient species were negatively related to mean bare patch size and are potential indicators of Great Basin rangeland condition. Plant community composition and the range of bare patch sizes were different at sites in the three locations in Idaho, Oregon and Utah. Therefore, expected indicator values are location specific and should not be extrapolated to other locations. The condition of study sites were often ranked differently by different indicators. Therefore, the condition of rangeland sites should be evaluated using several indicators.     

Spatial concentration and variability of rainfall in the Iguaçu River Basin,State of Paraná−Brazil

The analysis of rainfall as an environmental factor that influences landscape dynamics is an important and ongoing topic of discussion. This discussion can be centred on the discovery of impacts caused by the increase or decrease in rainfall frequency and intensity. From this perspective, this study sought to analyse the rainfall variability in the Iguaçu River basin, located in the State of Paraná, southern Brazil. The main objective was focused on the temporal-spatial rainfall distribution in the study area and its interaction with landscape dynamics (different land uses). Precipitation data for the period 1988−2018 were obtained from the ‘Águas Paraná’ Institute. To calculate the Concentration Index−CI values of the study area, data analysis was performed using the ‘R’ software with Climatol and Precindicon subroutines of the software, and analysis of Landsat 8 satellite images through ArcGIS. The results indicated that there was a well-defined spatial variability in the study area, as the CIs defined higher rainfall concentrations upstream from the river basin and lower rainfall concentrations downstream—implying that these processes may be strongly associated with land use.