Local and remote climatic impacts due to land use degradation in the Amazon “Arc of Deforestation”     

Maria Elisa Siqueira Silva  Gabriel Pereira  Rosmeri Porfírio da Rocha 《Theoretical and Applied Climatology》2016,124(3-4):609-620

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Geotechnical characterization of surficial high-porosity sediments in Eckernförde Bay     

A. J. Silva  H. G. Brandes  G. E. Veyera 《Geo-Marine Letters》1996,16(3):167-174

Geotechnical studies of high-porosity, finegrained sediments from Eckernförde Bay, part of the Coastal Benthic Boundary Layer program, included coring, subsampling, and on-board testing during three field experiments, and a laboratory testing program to determine the mechanical properties of the seabed. The sediments consist of high-porosity (86–94%), organic-rich (10–20%) silty clays with varying amounts of methane gas. The surface 5–10 cm are characterized by unusually high water contents (400–600%), very low shear strengths (<1 kPa), and pronounced shear thinning behavior. Below that depth sediments are somewhat more competent, exhibiting water contents of 250–300% and higher strengths (> 1 kPa).  相似文献   

Combined tidal velocity and duration asymmetries as a determinant of water transport and residual flow in Paranaguá Bay estuary     

A. Mantovanelli  E. Marone  E. T. da Silva  L. F. Lautert  M. S. Klingenfuss  V. P. Prata  Jr.  M. A. Noernberg  B. A. Knoppers  R. J. Angulo 《Estuarine, Coastal and Shelf Science》2004,59(4):523-537

Net transports of water, salt and suspended particulate matter (SPM) for a cross-section in front of the Paranaguá Harbour (Paranaguá Bay, Brazil) are presented for eight distinct tidal cycles. Data include measurements over single spring and neap tidal cycles, during both wet and dry seasons. The main drive forces of circulation and SPM dynamics are identified. Advective transport dominated under moderate to high vertical salinity stratification and weak currents, while mixing processes dominated under well-mixed conditions generated by high currents and low freshwater input. Under partially mixed conditions, both advective and mixing processes were important. The tide-induced residual circulation dictated the magnitude and direction of residual currents and net transports of water and salt, but not of SPM transport. The SPM dynamics was intrinsically related to cyclical processes of erosion, resuspension and deposition driven by tidal currents. The turbulent mixing intensity conditioned the vertical mixing of SPM. Resuspension and vertical mixing were conspicuous in spring cycles, while the horizontal advection preponderated in the neaps. Lags between maximum currents and SPM peak concentrations occurred, with more pronounced hysteresis during ebb periods.  相似文献   

3-D non-breaking regular wave interaction with submerged breakwaters     

I. J. Losada  R. Silva  M. A. Losada 《Coastal Engineering》1996,28(1-4)

Modelling of the transformation and interaction of regular wave trains with submerged permeable structures is carried out. The existing literature, is summarized relevant theories presented, and theoretical results are compared with existing laboratory data. Special attention is paid to wave reflection. The influence of wave characteristics including oblique incidence, structure geometry and porous material properties on the kinematics and dynamics over and inside the breakwater is considered. Two different models are presented: an eigenfunction expansion 3-D model and a 2-D model based on a mild-slope equation for porous media to account for breakwater slope.  相似文献   

High pressure-high temperature laboratory apparatus for the measurement of deep sea sediment physical properties     

Roger Morin  Armand J. Silva 《Ocean Engineering》1983,10(6):481-487

Laboratory equipment has been built which will measure the permeability and thermal conductivity of deep-sea sediments at their in-situ conditions of hydrostatic pressure, temperature, and void ratio. The apparatus has the capability of uniaxially consolidating a sediment sample to simulate compaction within the sediment column, while exposing the specimen to hydrostatic pressures ranging from atmospheric to 62 MPa and to temperatures from 22 to 220°C. The equipment includes a hypodermic needle mounted vertically through the base of the pressure vessel from which thermal conductivity is determined by the needle probe method. The system also features a combination of dead-weight testers which produces a small hydraulic gradient across the sample and permits the measurement of sediment permeability at large hydrostatic pressures.The physical property data generated from this apparatus will be important in understanding the mechanisms of heat transfer through the ocean floor and in analysing the coupled flow of heat and pore fluid in the vicinity of a heat source, such as a radioactive waste canister, buried in the seabed.  相似文献   

Paleontology,sedimentology and paleoenvironment of a new fossiliferous locality of the Jurassic Cañadón Asfalto Formation,Chubut Province,Argentina     

Oscar F. Gallego  Nora G. Cabaleri  Claudia Armella  Wolfgang Volkheimer  Sara C. Ballent  Sergio Martínez  Mateo D. Monferran  Diego G. Silva Nieto  Manuel A. Páez 《Journal of South American Earth Sciences》2011,31(1):54-68

A new Late Jurassic assemblage of “conchostracans”, ostracods, bivalves and caddisfly cases from the locality “Estancia La Sin Rumbo”, Chubut Province (Patagonia, Argentina) is recorded. The fossils occur in the upper part of an outcropping 45 m thick volcaniclastic lacustrine sequence of yellowish tuffs and tuffites of the Puesto Almada Member, which is the upper member of the Cañadón Asfalto Formation with U/Pb age of 161 ± 3 Ma. The sequence represents one sedimentary cycle composed of a (lower) hemicycle of expansion and a (higher) hemicycle of contraction of the water body. The invertebrates lived in small freshwater bodies during the periods of expansion of the lake. The occurrence of a great number of small spinicaudatans, associated with mud-cracks, is evidence of dry climatic conditions and suggests several local mortality events. The spinicaudatan record of the fushunograptid–orthestheriid (component of the Eosestheriopsis dianzhongensis fauna) and the presence of Congestheriella rauhuti Gallego and Shen, suggest a Late Jurassic (Oxfordian to Tithonian) age. Caddisfly cases are recorded for the first time in the Cañadón Asfalto Basin.  相似文献   

Determination of reaeration‐rate coefficient by modified tracer gas technique     

Pétrick Anderson Soares  Guilherme Faht  Adilson Pinheiro  Marcos Rivail da Silva  Evelyn Zucco 《水文研究》2013,27(19):2710-2720

The modified tracer gas technique is used to determine the reaeration coefficient in six different water bodies of the Itajaí River basin, three with rural land use and three in urban areas. Propane was used as the tracer gas and Rhodamine WT as the conservative tracer, providing information on dilution, mixing and dispersion. Liquefied petroleum gas was used instead of high purity propane, aimed at reducing the costs associated with the field trials. Reaeration‐rate coefficients observed in the field ranged from 25.8 to 367.7 d^?1. Two data sets could be observed where smaller streams had substantially larger coefficients of between 133.1 and 367.7 d^?1, while the larger streams had values ??ranging from 25.8 to 54.5 d^?1. Five empirical equations were evaluated by comparing the values ??obtained in the field. The equations proposed by Tsivolgou and Wallace and Tsivoglou and Neal showed greater adherence to the values ??determined in the tests. Reaeration‐rate coefficients obtained in the field were correlated with the hydrodynamic characteristics of the watercourses, thus establishing a mathematical function through which to obtain estimates for future evaluations. The R² value obtained using this equation was 0.959, indicating a high correlation between the calculated values ??and those estimated in the field. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Deformation of a pervasively molten middle crust: insights from the neoproterozoic Ribeira‐Araçuaí orogen (SE Brazil)     

Alain Vauchez  Marcos Egydio‐Silva  Marly Babinski  Andra Tommasi  Alexandre Uhlein  Dunyi Liu 《地学学报》2007,19(4):278-286

Pervasive melting of the middle crust, as inferred in Tibet and the Altiplano, probably influences the deformation of the lithosphere. To constrain strain distribution in a pervasively molten crust, we analysed the deformation in an eroded analogue of these orogens. The Ribeira‐Araçuaí orogen (SE Brazil) comprises a stack of allochthons containing large volumes of anatectic and magmatic rocks. The upper allochton (∼300 km long, 50–100 km wide and >10 km thick) involves peraluminous diatexites and leucogranites resulting from partial melting of the middle crust. It overlies another allochthon containing huge early‐ to syn‐collisional plutons intruding metasediments. Both anatexites and magmatic intrusions display a pervasive strain‐induced magmatic fabric. Homogeneous strain distribution suggests inefficient localization. U–Pb ages of ∼575 Ma imply that anatexite melting was synchronous to the early‐ to syn‐collisional magmatism. Similarity in ages magmatic and solid‐state fabrics indicates that intrusions and anatexites deformed coherently with solid‐state rocks while still molten, in response to a combination of gravity‐driven and collision‐driven deformation.  相似文献   

Crustal growth of the central-eastern Paleoproterozoic domain,SW Amazonian craton: Juvenile accretion vs. reworking     

Moacir José Buenano Macambira  Marcelo Lacerda Vasquez  Daniela Cristina Costa da Silva  Marco Antonio Galarza  Carlos Eduardo de Mesquita Barros  Julielson de Freitas Camelo 《Journal of South American Earth Sciences》2009,27(4):235-246

The Trans-Amazonian cycle was an important rock-forming event in South America, generating voluminous juvenile and reworked fractions of continental crust. The Bacajá domain, in the southern sector of the Maroni-Itacaiúnas Province in the Amazonian craton, is an example of the Trans-Amazonian terranes adjacent to the Archean Carajás block. Zircon Pb-evaporation and whole-rock Sm–Nd analyses were carried out on representative samples of six lithological units, and allowed the proposal of a comprehensive tectonic-magmatic evolutionary sequence for the central and eastern parts of this domain, from the Neoarchean to the Rhyacian. Gneisses with ages of ca. 2.67 and 2.44 Ga are the oldest rocks recorded in the region, and probably represent remnants of island and continental arcs. The Três Palmeiras succession, emplaced between 2.36 and 2.34 Ga, hosts gold deposits and represents the first record of Siderian supracrustal rocks in the Amazonian craton. It was probably part of an island arc/ocean floor accreted to a craton margin. Rhyacian granitogenesis lasted for ca. 140 My (2.22–2.08 Ga), marking different stages of the Trans-Amazonian cycle. The first stage is represented by continental arc granitoids formed by melting of Archean crust at 2.22–2.18 Ga. The second is characterized by the production of juvenile material between 2.16 and 2.13 Ga. The third and final stage at ca. 2.08 Ga is represented by a large volume of granitoids originated from either juvenile material or reworked crust during compressive stresses. Nd isotopes reveal that juvenile rocks dominated in the northern part of the domain, whereas those formed from reworked crust predominate in the south. The present-day configuration of the Bacajá domain results from collision against the Archean Carajás block at the end of the Trans-Amazonian cycle.  相似文献   

Effects of shock‐induced incongruent melting within Earth’s crust: the case of biotite melting     

Dailto Silva  Cristiano Lana  Gary Stevens  Carlos R. Souza Filho 《地学学报》2011,23(4):225-231

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