Tracing source and evolution of suspended particles in the Rio Negro Basin (Brazil) using chemical species of iron

Suspended solids found in porewaters obtained in waterlogged soil sequences that included representative laterite–podzol transitions, associated brooks and major rivers of the Rio Negro watershed (Brazil) were studied using electron paramagnetic resonance (EPR) and Fourier-transform infrared spectroscopies. The main goal was to ascertain sources and track the evolution of suspended matter using a ubiquitous chemical species, FeIII complexed to organic matter (FeOM). Three size fractions were separated by tangential-flow (ultra)filtration: particulate (> 0.2 μm), dense (P) and light (Ps), and colloidal (5 kD < Col. < 0.2 μm) fractions. Quantitative results were acquired for Col. and Ps fractions which are predominantly organic in nature.FeOM concentration (in ‰ dry weight) was determined to be relatively low in suspended solids found in black waters from podzol porewaters and brooks whereas in the main rivers it was several times higher. FeOM concentrations were also correlated with Fe(II)/Fe(III) ratios in solution; these ratios were high in podzol porewaters and low in the rivers. Considering that organic complexation of Fe(II) is minor when compared to that of Fe(III), two interpretations were proposed to account for the above observation. First, [FeOM] was assumed to be distributed along a mixing line, with the clear waters from laterites and the black waters from podzols being its end-members. Consequently, [FeOM] can be used to trace the source of suspended material. Second, dissolved Fe(II) from podzol areas was considered to be progressively oxidized as pore waters move towards the mainstream. According to this mechanism, iron is complexed by organic matter or precipitated as oxides, thus producing an evolution of colloidal matter. As a result of these mechanisms' action, both the high production of Fe(II) and organic matter at the waterlogged podzol–laterite transition areas are major factors affecting iron export in the Rio Negro watershed.     

Geology and geochronology of the Betara region in south-southeastern Brazil: Evidence for possible Statherian (1.80–1.75 Ga) and Calymmian (1.50–1.45 Ga) extension events

The results of geological mapping, chemical analysis and radiometric dating of metabasic rocks of Betara Formation, and mapping and dating of those present in the Betara basement nucleus together with mylonitic granodiorite and syenogranite are reported here. U–Pb analysis of bulk zircon fractions from the metabasic rocks of the basement nucleus yielded a Statherian age of 1790 ± 22 Ma, while the metabasic rocks from the upper part of the Betara Formation yielded a Calymmian age between 1500 and 1450 Ma. This age is a minimum for the deposition of the Betara Formation. The older metabasic rocks are associated with post-tectonic, possibly anorogenic syenogranite, while the younger ones are gabbro or very porphyritic ankaramite whose REE patterns are consistent with crystallization from an N-MORB parent magma. The observations and data point to the probable events associated with extensional processes of the end of Paleoproterozoic and early Mesoproterozoic. Similar registers of Statherian (1.80–1.75 Ga) and Calymmian (1.50–1.45 Ga) extensional events are recorded in other parts of the South American and African continents. The Neoproterozoic witnessed the formation and junction of the tectonic slices which formed the Apiaí domain during the assemblage of western Gondwana.     

Collision of the Ganges–Brahmaputra Delta with the Burma Arc: Implications for earthquake hazard

We take a fresh look at the topography, structure and seismicity of the Ganges–Brahmaputra Delta (GBD)–Burma Arc collision zone in order to reevaluate the nature of the accretionary prism and its seismic potential. The GBD, the world's largest delta, has been built from sediments eroded from the Himalayan collision. These sediments prograded the continental margin of the Indian subcontinent by  400 km, forming a huge sediment pile that is now entering the Burma Arc subduction zone. Subduction of oceanic lithosphere with > 20 km sediment thickness is fueling the growth of an active accretionary prism exposed on land. The prism starts at an apex south of the GBD shelf edge at  18°N and widens northwards to form a broad triangle that may be up to 300 km wide at its northern limit. The front of the prism is blind, buried by the GBD sediments. Thus, the deformation front extends 100 km west of the surface fold belt beneath the Comilla Tract, which is uplifted by 3–4 m relative to the delta. This accretionary prism has the lowest surface slope of any active subduction zone. The gradient of the prism is only  0.1°, rising to  0.5° in the forearc region to the east. This low slope is consistent with the high level of overpressure found in the subsurface, and indicates a very weak detachment. Since its onset, the collision of the GBD and Burma Arc has expanded westward at  2 cm/yr, and propagated southwards at  5 cm/yr. Seismic hazard in the GBD is largely unknown. Intermediate-size earthquakes are associated with surface ruptures and fold growth in the external part of the prism. However, the possibility of large subduction ruptures has not been accounted for, and may be higher than generally believed. Although sediment-clogged systems are thought to not be able to sustain the stresses and strain-weakening behavior required for great earthquakes, some of the largest known earthquakes have occurred in heavily-sedimented subduction zones. A large earthquake in 1762 ruptured  250 km of the southern part of the GBD, suggesting large earthquakes are possible there. A large, but poorly documented earthquake in 1548 damaged population centers at the northern and southern ends of the onshore prism, and is the only known candidate for a rupture of the plate boundary along the subaerial part of the GBD–Burma Arc collision zone.     

Recent theoretical results on coronal heating

The scenario of magnetohydrodynamic turbulence in connection with coronal active regions has been actively investigated in recent years. According to this viewpoint, a turbulent regime is driven by footpoint motions and the incoming energy is efficiently transferred to small scales due to a direct energy cascade. The development of fine scales to enhance the dissipation of either waves or DC currents is therefore a natural outcome of turbulent models. Numerical integrations of the reduced magnetohydrodynamic equations are performed to simulate the dynamics of coronal loops driven at their bases by footpoint motions. These simulations show that a stationary turbulent regime is reached after a few photospheric times, displaying a broadband power spectrum and a dissipation rate consistent with the energy loss rates of the plasma confined in these loops. Also, the functional dependence of the stationary heating rate with the physical parameters of the problem is obtained, which might be useful for an observational test of this theoretical framework.     

气象卫星云图的多分辨小波分解及人工神经网络降水估计研究

采用多分辨小波分析对卫星图象进行预处理 ,在保留其特征信息的同时 ,减小了数据量 ,改善了神经网络训练过程的收敛性能 ,提高了处理速度。采用这一方法根据 GOES- 8的红外亮温图象和气象雷达资料对巴西圣保罗州中部的降水量估计进行了试验 ,取得了良好的效果。     

Estimating Buoyancy Heat Flux Using the Surface Renewal Technique over Four Amazonian Forest Sites in Brazil

The surface renewal (SR) method was applied for the first time to measurements of air temperature over four Amazonian forest sites and different seasons in order to obtain estimates of buoyancy heat flux. The required calibration of this method against eddy covariance resulted in a value for a specific parameter that is close to the range reported in other studies, contributing to the generalization of the SR method to different kinds of canopies. The comparison with fluxes obtained using the eddy covariance technique revealed a good match between the two methods for different sites, heights and seasons. Sites with high levels of non-stationarity in the signals of temperature and wind speed presented higher scatter in the regression with fluxes from eddy covariance. For a particular site with previously reported influence of low-frequency motions, the regression was only satisfactory, i.e., slope parameter close to unity and small offset, when oscillations with periods longer than $\approx $ ≈ 13 min were filtered out. The SR method has a great potential due to the simplicity of the instrumentation required. However, care should be taken when measuring under the influence of mesoscale motions, which can lead to high levels of non-stationarity, compromising the fundamental concepts of the SR theory.     

Typical source areas of May 1998 flow-like mass movements in the Campania region, Southern Italy

Flow-like mass movements in granular materials are among the most serious natural hazards, systematically producing huge amounts of damage and numerous victims, especially when involving volcanic soils. This is the case of the events in Southern Italy in May 1998, when rainfall triggered many destructive landslides along the slopes of a carbonate massif mantled by pyroclastic soils. Due to the complexity of the occurred phenomena, a shared interpretation of their triggering stage is still not available.

As a contribution to the topic, the paper initially discusses the geological and geomorphological features of the massif combining them in three hillslopes models. The models are then associated to the hydrogeological features and anthropogenic factors in order to define six typical landslides source areas that are not casually distributed on the massif. The study subsequently focuses on the most frequent type of source areas, associated to the largest unstable soil volumes and longest run-out distances. For these source areas, the triggering mechanism is discussed, with an example of geotechnical validation being proposed for a well monitored mountain basin. The geotechnical modelling at site scale confirms the geological analyses at massif scale and provides further insights into the events, thus highlighting the potential of a multidisciplinary approach for the interpretation of very complex slope instability phenomena.     

Failure analysis of the granite for a dam foundation

This paper presents the numerical and experimental investigation of a dam foundation. The site consists of granite and especially weathered granite. Numerical and analytical analyses have been conducted to evaluate suitability of the granite for a dam foundation. Mohr–Coulomb failure criterion has been used to calculate the compressive strength of the rock mass. Finite element implementation of Mohr–Coulomb criterion has been used for deformation and settlement analysis. Packer testing and in-situ estimation of rock mass deformability using the Goodman jack have been performed. The results of the evaluations show that very small normal and differential settlements can be expected in structural regions due to dam construction, and the compacted concrete dam can safely be constructed on either the competent granite or the weathered granite. However, the dam foundation on the weathered granite has high conductivity potential problems for the reservoir.     

Evolution of a Callovian-Oxfordian carbonate margin in the Neuquén Basin of west-central Argentina: facies, architecture, depositional sequences and global sea-level changes

This paper reviews a detailed stratigraphic and sedimentologic study of a carbonate complex developed on the foreland side of the Neuquén Embayment, a protected shallow-water epicratonic site behind the active edge of the South American plate. Superb outcrops at the core of basement-involved Andean structures expose the shelf-to-basin transition and reveal with clarity the external and the internal architecture of the depositional sequences and component system tracts. Platform carbonates are largely represented by ooid and mainly rhodoid grainstones, with associated patches of coral framestone. The deeper platform and slope facies are composed of oncoidal and skeletal micritic limestones with scattered coral-sponge-algal build-ups. The overall composition and facies pattern bears resemblance to other Late Jurassic carbonate complexes form Europe and with the Smackover Formation from the Gulf Coast Basin of North America.

Analysis based on mapping of the stratal patterns and facies associations in outcrops allowed the recognition of four depositional sequences. Timing provided by ammonite biochronology suggests that eustatic fluctuations were a major factor influencing the carbonate-margin architecture, and regulated episodes of condensed sedimentation, shifts of the depositional belts, and development of stratigraphic discontinuities. The onset and the end of carbonate sedimentation were associated with episodes of marine retreat and accumulation of evaporites and eolian-fluvial deposits at basin-centre locations. However, most of the marine fluctuations recorded within the carbonate complex were insufficient to expose the shelf break (Type 2), and accordingly lowstand system tracts are poorly represented. On the shelf the transgressive system tracts are represented by thin grain-supported carbonate blankets. These taper out downslope into omission surfaces or are replaced by patches of small sponge buildups. Highstand system-tract organization changes through time, reflecting changes in productivity and accomodation, presumably tied to second-order sea-level changes. Callovian highstand accumulation featured a catch-up carbonate system and produced a thin-aggradational ramp configuration, whereas conditions during middle-late Oxfordian allowed a keep-up system and produced outbuilding depositional geometries with steeper slopes.