Palaeolimnological studies and ancient maps confirm secular climate fluctuations in Amazonia

Secular Amazon discharge oscillations were investigated comparing information from ancient cartography, satellite images, palaeovegetation, sediments, anthropology and climate, focusing on the evolution of Marajó Island in the Amazon estuary. Four phases were identified. (1) 800–1200 a.d.: Amazon discharge increased gradually and eastern Marajó was a vegetation-free tidal plain with energy oscillations. (2) 1200–1350 a.d. was a dry period with lower river discharges, lower energy, increasing water salinities and maximum mangrove extension, coinciding with the extinction of chiefdoms in Marajó. (3) 1350–1540 a.d.: Amazon discharge increased rapidly, inducing a dominance of freshwater vegetation, inundation of east Marajó and likely a regional rise of relative sea-level (RSL). (4) 1540–1750 a.d.: RSL decreased, coinciding with an El Niño-related intense drought ca. 1600 a.d. Emergence of eastern Marajó was rapid and completed in the eighteenth century, under RSL stabilization to current values. The approach used provided evidence of intermittent large changes in Amazon climate, and can facilitate the prediction of future regional dynamics.     

A velocity field estimation of the Brazilian portion of the SOAM plate

With the proposition for the adoption of Geocentric Reference System for the Americas (SIRGAS) as a terrestrial reference frame for South America, the need for temporal monitoring of station coordinates used in its materialization has become apparent. This would provide a dynamic characterization of the frame. The Brazilian Network for Continuous Monitoring of GPS (RBMC) has collected high accuracy GPS measurements since 1996. The Brazilian Institute of Geography and Statistics (IBGE) maintains this network in collaboration with several universities and organizations. Most of the stations are also part of the SIRGAS network. The RBMC also contributes data to the International Terrestrial Reference System (ITRS) to densify the global frame. Two of the RBMC stations are also part of the International GPS Service (IGS). This paper reports initial results from these stations. To estimate the velocity field defined by these stations, ten IGS stations located on the border of the South American plate and in adjacent plates, along with nine RBMC stations, were used. Observations covering five groups of 15 days each were used. These groups of observations were at epochs 1997.3, 1997.9, 1998.3, 1998.9 and 1999.2. Seven IGS stations were chosen to have their coordinates constrained to those epochs. IGS products (precise ephemeris and clocks) were used to process the daily solutions, which were carried out with Bernese software. Carrier phase double differences were formed using the ionospheric-delay free observable. The troposphere was modeled using a combination of the Saastamoinen model and the Niell mapping function. A tropospheric parameter was estimated every two hours. The results of the daily baseline solutions were combined using the summation of normal equations technique, in which the final coordinates and velocities were estimated. The results were compared with various models, such as the NNR-NUVEL1 and the APKIM8.80. Velocity vectors estimated for the RBMC stations show good agreement with those two models, with rates approximately equal to 2 cm/year.     

A double structure generalized plasticity model for expansive materials

The constitutive model presented in this work is built on a conceptual approach for unsaturated expansive soils in which the fundamental characteristic is the explicit consideration of two pore levels. The distinction between the macro‐ and microstructure provides the opportunity to take into account the dominant phenomena that affect the behaviour of each structural level and the main interactions between them. The microstructure is associated with the active clay minerals, while the macrostructure accounts for the larger‐scale structure of the material. The model has been formulated considering concepts of classical and generalized plasticity theories. The generalized stress–strain rate equations are derived within a framework of multidissipative materials, which provides a consistent and formal approach when there are several sources of energy dissipation. The model is formulated in the space of stresses, suction and temperature; and has been implemented in a finite element code. The approach has been applied to explaining and reproducing the behaviour of expansive soils in a variety of problems for which experimental data are available. Three application cases are presented in this paper. Of particular interest is the modelling of an accidental overheating, that took place in a large‐scale heating test. This test allows the capabilities of the model to be checked when a complex thermo‐hydro‐mechanical (THM) path is followed. Copyright © 2005 John Wiley & Sons, Ltd.     

The role of the Antofagasta–Calama Lineament in ore deposit deformation in the Andes of northern Chile

During the Late Jurassic–Early Oligocene interval, widespread hydrothermal copper mineralization events occurred in association with the geological evolution of the southern segment of the central Andes, giving rise to four NS-trending metallogenic belts of eastward-decreasing age: Late Jurassic, Early Cretaceous, Late Paleocene–Early Eocene, and Late Eocene–Early Oligocene. The Antofagasta–Calama Lineament (ACL) consists of an important dextral strike-slip NE-trending fault system. Deformation along the ACL system is evidenced by a right-lateral displacement of the Late Paleocene–Early Eocene metallogenic belts. Furthermore, clockwise rotation of the Early Cretaceous Mantos Blancos copper deposit and the Late Paleocene Lomas Bayas porphyry copper occurred. In the Late Eocene–Early Oligocene metallogenic belt, a sigmoidal deflection and a clockwise rotation is observed in the ACL. The ACL is thought to have controlled the emplacement of Early Oligocene porphyry copper deposits (34–37 Ma; Toki, Genoveva, Quetena, and Opache), whereas it deflected the Late Eocene porphyry copper belt (41–44 Ma; Esperanza, Telégrafo, Centinela, and Polo Sur ore deposits). These observations suggest that right-lateral displacement of the ACL was active during the Early Oligocene. We propose that the described structural features need to be considered in future exploration programs within this extensively gravel-covered region of northern Chile.     

Treatment of a Trifluraline Effluent by Means of Oxidation‐Coagulation with Fe(VI) and Combined Fenton Processes

The amination water (AW) effluent stream from the industrial production of the trifluraline herbicide was submitted to an oxidation‐coagulation treatment with potassium ferrate, combined with advanced oxidation processes. The experimental results obtained by analysis of variance (ANOVA) for the oxidation‐coagulation‐Fenton process, evaluating the variables pH (A), Fe(VI) concentration (B), and H₂O₂ concentration (C), demonstrated that the regression equation resulting from the Response Surface Methodology (RSM) experimental design, for the quadratic model, was η_Abs (%) = 36.9– 21.58A + 8.37A² + 1.36B + 0.92B² + 1.08C + 1.52C² + 1.27AB – 1.34AC + 1.33BC. The maximum absorptiometric color reduction occurred at pH 3, with corresponding maximum amounts of iron and hydrogen peroxide. The absorptiometric color and COD reduction were 96% and 57%, respectively. For the oxidation‐coagulation‐photo‐Fenton process, the analyzed variables were pH (A), Fe(VI) concentration (B), H₂O₂ concentration (C), and temperature (D). The regression equation resulting from the quadratic model was η_Abs (%) = 38.3 – 20.2A + 8.12A² – 0.27B + 3.73B² + 0.3C + 3.6C² + 1.67D + 3.1D² + 1.72AB + 0.51AC – 1.82AD + 0.74BC – 1.11BD + 0.03CD. The ANOVA response showed that the highest absorptiometric color reduction occurred at pH 3, with respective maximum amounts of iron and hydrogen peroxide at 60°C. The maximum efficiencies achieved by the proposed treatment process for the trifluraline effluent stream were 95% and 85%, for absorptiometric color and COD reduction, respectively.     

Leaf breakdown in two tropical streams: Differences between single and mixed species packs

We assessed leaf breakdown of five native riparian species from Brazilian Cerrado (Myrcia guyanensis, Ocotea sp., Miconia chartacea, Protium brasiliense, and Protium heptaphyllum), incubated in single and mixed species packs in two headwater streams with different physico-chemical properties in the Espinhaço Mountain range (Southeastern Brazil). Leaves were placed in plastic litter bags (15 cm×20 cm, 10 mm mesh size) and the experiments were carried out during the dry seasons of 2003 and 2004. Leaf nitrogen and phosphorus contents were similar in all species, but polyphenolic contents were different (P<0.001). M. guyanensis showed higher polyphenolics content (8.48% g⁻¹ dry mass) and leaf toughness. Individually, higher breakdown rates were found in M. guyanensis at Indaiá stream (k=0.0063±0.0005 d⁻¹) and in Ocotea sp. at Garcia stream (k=0.0088±0.0006 d⁻¹). However, P. brasiliense and P. heptaphyllum showed lower breakdown rates at Indaiá and Garcia streams (Indaiá: k=0.0020±0.0002 and 0.0019±0.0001 d⁻¹; Garcia: k=0.0042±0.0001 and 0.0040±0.0002 d⁻¹). Single and mixed breakdown processes of each species were not statistically different on both streams. However, all species showed higher breakdown rates at Garcia stream (P<0.01). These results suggest that leaf breakdown is not altered when litter benthic patches are composed by a mixture of species in the same proportions that they occur on riparian leaf falls.     

An abandoned estuary within Marajó Island: Implications for late Quaternary paleogeography of northern Brazil

Several previous studies have recognized paleochannels as the most typical geomorphologic features imprinted in the modern landscape of Marajó Island, northern Brazil. A characterization of these paleochannels by detailed mapping has not yet been accomplished, despite their great potential for helping reconstructing the succession of events responsible for the origin and evolution of the drainage system at the mouth of the Amazon River during the Quaternary. The present study aims to provide a detailed mapping and characterization of these paleochannels using remote sensing (i.e., SRTM, Landsat 5-TM, and Landsat 7-ETM+), integrated with sedimentological and radiocarbon data obtained from outcrops and cores. The mapped paleochannels allowed for the first time correlation of the channel-like morphologies with fining-upward sedimentary successions, typical of channel deposits. The study focuses on the Lake Arari area located in the northeast of Marajó Island, where a complex fluvial network dominated by a funnel-shaped structure attributed to a Late Pleistocene paleoestuarine system was recognized. The inner estuary was connected to three fluvial channels that ran from the east-southeast throughout an area currently occupied by Marajó Bay, implying that this bay did not exist when the estuarine system was active. Separation of the eastern side of Marajó Island due to tectonic causes related to capture of Tocantins River by northeastward-orientated faults would have interrupted the fluvial inflow, ultimately causing the abandonment of the estuarine system. Today, the central part of the funnel-shaped structure related to the Late Pleistocene paleoestuary is occupied by Lake Arari, where sediments started to accumulate no earlier than the mid-Holocene. It is proposed that this lake might have developed from the Late Pleistocene estuary as the fluvial inflow was cut off during the detachment of Marajó Island. Marajó Island serves as an example of a very dynamic site of changing landscapes throughout the Quaternary as a result of tectonic activity.     

The NW Scotland earthquake swarm of 1974

Summary. A swarm of earthquakes occurred in the Kintail area of NW Scotland in 1974 August with magnitudes up to M_L = 4.6 and reported intensities up to VI MM. One earthquake of the series was recorded by about 60 temporary stations of the LISPB refraction experiment in addition to the permanent LOWNET network. This allowed the determination of an accurate epicentre for that event which was then used as a control event to locate other earthquakes of the Kintail series. The events of that swarm had a strikeslip focal mechanism and seemed to be associated with the Strathconon Fault.     

Late pleistocene and holocene loess deposits of the Southeastern Buenos Aires province,Argentina

The Late Pleistocene and Holocene loess deposits of the SE Buenos Aires province are composed of four allostratigraphic units that represent four episodes of loess deposition. The first and the second episodes occurred in Late Pleistocene times. The second episode was followed by a soil forming interval (Early Holocene to Mid-Holocene times). The third episode took place at about 5000 yr BP, after the Holocene sea-level maximum when marine regression began. The fourth episode constitutes a historical event of only local significance.Loess shows a fairly constant granulometric and mineralogical composition. The modal fraction consists of very fine sand and coarse silt (3 to 5 phi). They are classified as sandy silts or silty sands. Three grain-size subpopulations are differentiated: coarse, medium and fine. The medium-size subpopulation, which is the most important, consists of most of the very fine sand and coarse silt. It is thought to be transported by modified saltation and short-term suspension during local dust-storms.The mineralogical composition of loess consists of a volcaniclastic assemblage derived mainly from reworked pyroclastic deposits, primary tephras and volcaniclastic sediments. The source area of these materials was located in the lower Colorado river valley about 400 km SW of the studied area. There was also a direct supply by volcanic ash falls.     

Concentration of anionic detergents in Rio Grande water (South Brazil)

The concentration of anionic detergents, polyphosphates, ammonia, seston and dissolved oxygen have been determined in a small bay near the principal sewage discharge of the city of Rio Grande. The results show great variations in the concentrations, as a function of the time of the day. The highest concentrations in anionic detergents were observed between 09.00 and 10.00 in the morning, and from 18.00 to 21.00. The other parameters present an erratic distribution, except the dissolved oxygen, showing a net increase in the second half of the sampling period.