Spatial Analysis of Airborne Geophysical Data Applied to Geological Mapping and Mineral Prospecting in the Serra Leste Region, Carajás Mineral Province, Brazil

The Serra Leste region, located in the northeast portion of Carajás Mineral Province (PA), hosts important chrome-PGE, Au–Pd–Pt, Cu–Mo–Au, iron, and manganese deposits and occurrences related to different geological settings. We present a regional prospective model with focus on PGE mineralizations based on airborne geophysics (magnetometry, gamma-ray spectrometry and time domain electromagnetometry) and geological data. Geological and geophysics data analysis indicate a plausible correspondence between areas with meta-mafic–ultramafic rocks and low values in gamma spectrometry, mainly for the thorium channel. The meta-ultramafic units of the complexes, the main host rock of the PGE mineralization, are well defined by analytic signal from the anomalous magnetic field and by the apparent conductance anomalies derived from the GEOTEM system. The combination of the derivative products with updated geological data of the Serra Leste region and PGE-Luanga deposit enable to establish a regional prospective model for PGE and the identification of new targets within the studied area.     

Fate characteristics of nitrogen in runoff from a small agricultural watershed on the south of Huaihe River in China

Qualitative and quantitative evolution of the Swarna estuary, during the past 38 years (1967–2005), has been analysed by integrating the results of field surveys, satellite images, hydrodynamic modelling and topographic data in GIS context. Significant changes in erosion/accretion patterns of the estuarine banks, inlet configuration and adjacent spits, and origin, morphology, orientation and areal extent of fifteen braided islands have been estimated. Hydrodynamics of the region is studied through modelling, and probable flow pattern that is responsible for morphological changes is discussed. The simulated flow patterns indicate that current speeds are of the order of 10–20 cm/s inside the estuary and of the order of 40 cm/s at the mouth. The Right bank (Rb) of the estuary is subject to net erosion and the Left bank (Lb) is subject to net accretion. On an average, 20–30% of the area of all braided islands would be flooded, if the water level rises by 0.7 to 1.0 m. Islands of this estuary are morphologically very dynamic (migrating towards north, northeast and southwest directions) and subject to net accretion, whereas only one island (i.e., the Padu) has lost its major portion of landmass. A conceptual inverse distance weighted (IDW) interpolation model has been generated and evaluated possible flooding on the estuarine shoals and braided islands, due to heavy rainfall and/or sea-level rise. The model reveals that the possibility of flooding will be higher for those islands which are located close to the Rb than those close to the Lb.     

Architecture of the deep critical zone in the Río Icacos watershed (Luquillo Critical Zone Observatory,Puerto Rico) inferred from drilling and ground penetrating radar (GPR)

In the critical zone, surficial bedrock interactions result in the formation of a mantle of chemically‐ and physically‐altered material defined here as regolith. In the watershed of the Río Icacos, an upland river draining the Luquillo Mountains in tropical Puerto Rico, we explored the influence of lithology (quartz diorite versus hornfels‐facies volcaniclastic rock) on weathering. Regolith profiles were studied by drilling boreholes and imaging the subsurface using ground penetrating radar (GPR). Overall, the regolith structure is not laterally continuous but rather is punctuated by zones of deep fractures that host in situ weathering, corestones, and colluvial material. GPR images of these vertical zones show reflectors at 15–20 m depth. Thus, the architecture of the critical zone in the upper Luquillo Mountains is highly dependent on lithology and its influence on fracture development. At the highest elevations where hornfels overlies quartz diorite, positive feedbacks occur when the water table drops so that oxidative weathering of biotite in the more felsic rock creates microfractures and allows deeper infiltration of meteoric waters. Such exposure results in some of the fastest weathering rocks in the world and may contribute to formation of the knickpoint in the Río Icacos watershed. This work represents the first study combining GPR and drilling to look at the structure of the deep critical zone and demonstrates: (1) the importance of combining direct methods (such as drilling) with indirect methods (such as GPR) to understand the architecture of the critical zone in tropical systems; (2) the interplay of the surficial stress regime, lithology and climate in dictating the architecture of weathering. Copyright © 2016 John Wiley & Sons, Ltd.     

Future changes in Central Europe heat waves expected to mostly follow summer mean warming

Daily output from the PRUDENCE ensemble of regional climate simulations for the end of the twentieth and twenty-first centuries over Europe is used to show that the increasing intensity of the most damaging summer heat waves over Central Europe is mostly due to higher base summer temperatures. In this context, base temperature is defined as the mean of the seasonal cycle component for those calendar days when regional heat waves occur and is close, albeit not identical, to the mean temperature for July–August. Although 36–47% of future Central Europe July and August days at the end of the twenty-first century are projected to be extreme according to the present day climatology, specific changes in deseasonalized heat wave anomalies are projected to be relatively small. Instead, changes in summer base temperatures appear much larger, clearly identifiable and of the same order of magnitude as changes in the whole magnitude of heat waves. Our results bear important consequences for the predictability of central European heat wave intensity under global warming conditions.     

Interaction of multiple ice streams on the Malin Shelf during deglaciation of the last British–Irish Ice Sheet

The Malin Shelf, off north-west Ireland, was an important zone of confluence for marine-based ice streams of the former British–Irish Ice Sheet (BIIS). Legacy geophysical datasets are used to construct models of the seismic character, relative age and distribution of shelf sediments and landforms. Buried and surface landform assemblages provide evidence that during deglaciation of the Late Devensian BIIS, the region was occupied not by a single Hebrides Ice Stream as previously proposed, but by four discrete ice streams, here referred to as the Sea of the Hebrides (SHIS), Inner Hebrides, North Channel and Tory Island ice streams. Our observations of stratigraphic relationships between the deposits of these ice streams indicate physical interactions between them during shelf deglaciation. We interpret an initial dominant cross-shelf flow along the SHIS impeding cross-shelf ice flow from other ice sheet sectors. Following withdrawal of the SHIS grounding line from the shelf edge to mid-shelf bathymetric highs during deglaciation, a reconfiguration of ice sheet flow paths allowed the expansion of smaller cross-shelf ice streams draining central Scotland and north-western Ireland. This internal dynamic behaviour provides a possible physical analogue for time-transgressive flow patterns reported for outlets draining the West Antarctic Ice Sheet.     

Pluri-decadal evolution of rock glaciers surface velocity and its impact on sediment export rates towards high alpine torrents

The acceleration of surface velocities observed over the last two decades on monitored rock glaciers worldwide is a widespread signal of the probable control of warming air temperatures on long-term permafrost creep. Yet, the actual consequences of this acceleration on sediment availability in high mountain catchments have never been properly estimated at the pluri-decadal scale. The present study evaluates the sediment transfer activity between five rock glaciers located in the western European Alps and the headwaters of the torrential channels they are respectively connected to. It reposes on the orthorectification of aerial images available generally from the 1960s to the mid-2010, to reconstruct time-series of (i) horizontal surface velocities and (ii) frontal erosion rates. Values of horizontal velocity are retrieved by tracking the displacement of boulders on the surface of rock glaciers between consecutive images while erosion rates affecting the fronts are calculated by combining these values of displacement with the geometry of the front (mean width and rock glacier thickness) derived from recent high-resolution digital elevation models. Results confirm the general acceleration of rock glaciers surface velocities since the 1970s and indicate that this accelerating trend is causing an increase in the erosion rates calculated at the front of most studied rock glaciers. In some cases and over specific periods however, the acceleration resulted in the advance of the whole landforms over their own sediments, leading to a comparatively low sediment export towards the torrents.     

Variograms of Order ω: A Tool to Validate a Bivariate Distribution Model

The multigaussian model is used in mining geostatistics to simulate the spatial distribution of grades or to estimate the recoverable reserves of an ore deposit. Checking the suitability of such model to the available data often constitutes a critical step of the geostatistical study. In general, the marginal distribution is not a problem because the data can be transformed to normal scores, so the check is usually restricted to the bivariate distributions. In this work, several tests for diagnosing the two-point normality of a set of Gaussian data are reviewed and commented. An additional criterion is proposed, based on the comparison between the usual variogram and the variograms of lower order: the latter are defined as half the mean absolute increments of the attribute raised to a power between 0 and 2. This criterion is then extended to other bivariate models, namely the bigamma, Hermitian and Laguerrian models. The concepts are illustrated on two real data-sets. Finally, some conditions to ensure the internal consistency of the variogram under a given model are given.