The effect of an oil drilling operation on the trace metal concentrations in offshore bottom sediments of the Campos Basin oil field,SE Brazil     

Rezende CE  Lacerda LD  Ovalle AR  Souza CM  Gobo AA  Santos DO 《Marine pollution bulletin》2002,44(7):680-684

The concentrations of Al, Fe, Mn, Zn, Cu, Pb, Ni, Cr, Ba, V, Sn and As in offshore bottom sediments from the Bacia de Campos oil field, SE Brazil, were measured at the beginning and at 7 months after completion of the drilling operation. Concentrations of Al, Fe, Ba, Cr, Ni and Zn were significantly higher closer to the drilling site compared to stations far from the site. Average concentrations of Al, Cu, and in particular of Ni, were significantly higher at the end of the drilling operation than at the beginning. Comparison between drilling area sediments with control sediments of the continental platform, however, showed no significant difference in trace metal concentrations. Under the operation conditions of this drilling event, the results show that while changes in some trace metal concentrations do occur during drilling operations, they are not significantly large to be distinguished from natural variability of the local background concentrations.  相似文献   

Geomorphological controls on coastal vegetation at the Virginia Coast Reserve     

Bruce P. Hayden  Marcio C. F. V. Santos  Guofan Shao  R. Craig Kochel 《Geomorphology》1995,13(1-4)

The establishment and succession of vegetation on migrating, low-profile barrier islands is greatly affected by the physical hydrogeomorphological processes that regulate island topography, saline and fresh groundwater table surfaces. Apart from the physical destruction of plants by overwash processes, fluctuations in water table elevations and variations in groundwater salinity, both spatially and temporally, also appear to have significant impact on the nature and distribution of vegetation on these islands. Species composition, community structure and biodiversity on the Virginia barrier islands are controlled by the same processes that give rise to landforms and maintain their form. These processes include marine water inundations, groundwater salinity variations and changes in depth to the fresh-water table. Land surface elevation, landform morphology and position on the barrier island determine exposure to high tides, storm surges, sand burial, and the extent of the fresh-water reserves.In this article, the underpinnings of a Long-term Ecological Research Program in which 25 geologists, geomorphologists, climatologists, and ecologists have a common research plan is presented and several examples of the product of this research partnership dealing with geomorphological and hydrologic controls on vegetation dynamics are detailed. Among the aspects of ecological dynamics examined in terms of geomorphological processes are vegetation zonation, succession, disturbance, and ecosystem state change.  相似文献   

Floor design in underground coal mines   总被引：1，自引：0，他引：1  

C. Faria Santos  Z. T. Bieniawski 《Rock Mechanics and Rock Engineering》1989,22(4):249-271

Summary Floor failure and excessive heave in underground coal mines can jeopardize the stability of the whole structure, including the roof and pillars, due to differential settlements and redistribution of stress concentrations. Besides, floor failure is detrimental to haulageway operation and can lead to unacceptable conditions of high deformation. Thus, the design of any underground opening must consider roof/pillar and floor as one structural system.This paper presents guidelines for the design of mine floors, including the necessary field and laboratory investigations and the determination of the bearing capacity of floor strata. The design methodology is based essentially on a modified Hoek-Brown rock mass strength criterion. The main modifications are the introduction of the concept of the point of critical energy release to account for the long term strength, the inclusion of tensile strength and the adoption of a lithostatic state of stress in the rock mass. The determination of the dimensionless parametersm ands result from correlations with the RMR (rock mass rating) of the Geomechanics Clasification. Nine case histories, both in longwall and room and pillar coal mining, were analyzed with the proposed methodology.  相似文献   

Salt tectonics,a controlling factor on the development of the Marseilles and Grand-Rhone sedimentary ridges,Gulf of Lions,western Mediterranean Sea     

Antonio Tadeu dos Reis  Christian Gorini  Alain Mauffret  Wiktor Weibull 《Comptes Rendus Geoscience》2004,336(2):143-150

The Marseilles (also called Marseilles/Planier) and Grand Rhone sedimentary ridges, offshore the Gulf of Lions, western Mediterranean Sea, are generated by sediment spillover funnelled by the Marseilles and Grand-Rhone canyons, respectively. We show that the Marseilles and Grand-Rhone canyon directions are tectonically conditioned by Plio-Quaternary salt-induced sea-floor relief. Overburden extension in the area created an assemblage of listric faults running parallel to the strike of the continental margin. This salt-induced topography resulted in accentuated fault scarps impacting the sea-floor morphology and forcing submarine valleys to deflect to the east. Gravity-induced extension equally influenced the morphological pattern of the valley overbanking deposits. Sediment spillover occurred on both flanks of the canyons, but because active faulting generated space accommodation for overflow deposits, it inhibited the development of typical levee morphology along the canyons' left flanks. To cite this article: A.T. dos Reis, C. R. Geoscience 336 (2004).  相似文献   

Proposal for selection of control,preventive and rehabilitation measures based on degradation land level and geoindicators in the fortaleza metropolitan region,State of Ceará, Brazil     

Lázaro Valentin Zuquette  Jaime Quintas dos Santos Collares  Osni José Pejon 《Environmental Geology》2007,52(5):899-922

Preventive, controlling, rehabilitative and corrective measures to improve the environmental quality of the hydrographic basins of the Fortaleza metropolitan region in the state of Ceará (Brazil) are presented based on geological and geotechnical data, land degradation rates and sources, and other geoindicators. The region is affected by coastal and stream erosion, gravitational mass movement, dunes, silting, and water pollution, sanitary landfills in inappropriate sites, decommissioned and abandoned aggregate mining, and swamp areas. Geoindicators were used to classify each of the 12 hydrographic basins as possessing low (4), intermediate (3), or high (5) degradation levels. A group of 59 environmental management measures related to ecological, bioengineering, mechanical, policy and administrative, agricultural and clean-up methods was selected. From this general group a set of 31 measures was chosen considering goals, efficacy for specific environmental problems, suitability for large or small areas, behavior under different annual climatic conditions, environmental problems of the region, geological and geotechnical limitations and degradation level of the basins. A set of the more suitable geoindicators was selected for monitoring efficiency of the measures for each basin.  相似文献   

3-D electromagnetic imaging of a Palaeozoic plate-tectonic boundary segment in SW Iberian Variscides (S Alentejo, Portugal)     

N. Vieira da Silva  A. Mateus  F.A. Monteiro Santos  E.P. Almeida  J. Pous 《Tectonophysics》2007,445(1-2):98

In SW Iberian Variscides, the boundary between the South Portuguese Zone (SPZ) and the Ossa Morena Zone (OMZ) corresponds to a major tectonic suture that includes the Beja Acebuches Ophiolite Complex (BAOC) and the Pulo do Lobo Antiform Terrane (PLAT). Three sub-parallel and approximately equidistant MT profiles were performed, covering a critical area of this Palaeozoic plate-tectonic boundary in Portugal; the profiles, running roughly along an NE–SW direction, are sub-perpendicular to the main Variscan tectonic features. Results of the three-dimensional (3-D) modelling of MT data allow to generate, for the first time, a 3-D electromagnetic imaging of the OMZ–SPZ boundary, which reveals different conductive and resistive domains that display morphological variations in depth and are intersected by two major sub-vertical corridors; these corridors coincide roughly with the NE–SW, Messejana strike–slip fault zone and with the WNW–ESE, Ferreira–Ficalho thrust fault zone. The distribution of the shallow resistive domains is consistent with the lithological and structural features observed and mapped, integrating the expected electrical features produced by igneous intrusions and metamorphic sequences of variable nature and age. The development in depth of these resistive domains suggests that: (1) a significant vertical displacement along an early tectonic structure, subsequently re-taken by the Messejana fault-zone in Late-Variscan times, has to be considered to explain differences in deepness of the base of the Precambrian–Cambrian metamorphic pile; (2) hidden, syn- to late-collision igneous bodies intrude the meta-sedimentary sequences of PLAT; (3) the roots of BAOC are inferred from 12 km depth onwards, forming a moderate resistive band located between two middle-crust conductive layers extended to the north (in OMZ) and to the south (in SPZ). These conductive layers overlap the Iberian Reflective Body (evidenced by the available seismic reflection data) and are interpreted as part of an important middle-crust décollement developed immediately above or coinciding with the top of a graphite-bearing granulitic basement.  相似文献   

Investigation of U–Th–Ra and Th–Ra–Th radioactive disequilibria in volcanic rocks from Trindade and Martin Vaz Islands (Brazil; Southern Atlantic Ocean)     

Rosana N. Santos  Leila S. Marques 《Journal of Volcanology and Geothermal Research》2007

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Overseas garbage pollution on beaches of northeast Brazil     

Santos IR  Friedrich AC  Barretto FP 《Marine pollution bulletin》2005,50(7):782-786

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Hydrogeological investigation in Santiago Island (Cabo Verde) using magnetotellurics and VLF methods   总被引：2，自引：0，他引：2  

Fernando A. Monteiro Santos  Eugnio P. Almeida  Mota Gomes  Antnio Pina 《Journal of African Earth Sciences》2006,45(4-5):421-430

A geoelectromagnetic research was carried out in the Santa Cruz region (Santiago Island, Cabo Verde) during June 2004. The survey comprised MT soundings and VLF profiles. The main purpose of the MT profile, carried out across three important valleys associated with freshwater aquifers, was to study the tectonic structures correlated to seawater infiltration. The VLF method was used inside of the valleys for investigating shallow structures related to the aquifer contamination by seawater.Numerical modelling shows that the ocean effect is not important for MT data collected at periods shorter than 1 s. The MT data were inverted using a two-dimensional approach, to obtain the sub-superficial electrical conductivity distribution. The VLF data were processed applying the Karous–Hjelt filters to obtain the equivalent current distribution and inverted using 2-D approach. The results obtained in one of the most important valleys show anomalous current concentration/low resistivity (<20 Ω m) areas at depths greater than 40 m that may correspond to an increase in seawater content.The MT data modelling show that the deep zones beneath the valley are strongly fractured representing good pathways for seawater circulation. The depth of the conductive zones increases from south to north, suggesting a northward decreasing of the seawater infiltration effect. This observation correlates very well with in situ geochemical observations.  相似文献   

The Imataca Complex, NW Amazonian Craton,Venezuela： Crustal evolution and integration of geochronological and petrological coolinghistories     

ColomboC.G.Tassinari JoseM.U.Munha WilsonTeixeira TeresaPalacios AllenP.Nutman CesarSosaS. AdjairP.Santos BrunoO.Calado 《《幕》》2004,27(1):3-12

SHRIMP U/Pb-zircon data and Nd mean crustal residence ages indicate that the lmataca Complex developed from an Archean (≥3.2Ga) continental protolith which has undergone considerable isotopic disturbance plus and juvenile accretion during late-Archean (-2.8Ga) times. Transamazonian granulites experienced peak metamorphic conditions of 750-800℃, 6-8kbar with associated transpressive thrusting and tectonic imbrication. Geochronology on zircon, pyroxene and garnet constrains the timing of peak metamorphism at 1.98-2.05Ga. Diffusion modeling of Fe-Mg exchange between biotite inclusions and host garnet yields (near metamorphic peak) cooling rates of 50-100℃/Ma, with petrological cooling rates being generally consistent with cooling rates determined from geochronology. Combining the retrograde P-T path with cooling rates suggests that after the metamorphic peak, large portions of the lmataca Complex were exhumed from 30 to 17km at a rate of 7-2km/Ma.After this, exhumation rates progressively decreased as the rocks approached the surface. Rapid overall upliftlerosion had ceased when the rocks passed below 600-550℃ at 2.01-1.96 Ga ago. Observed variations in mineral cooling ages are interpreted as to reflect episodic differential tectonic exhumation within major fault systems. Inferred (maximum) ages of fault re-activation generally coincide with major continental accretion events in the Amazonian Craton and reflect long-term thermal evolution of the lmataca terrane, as conditioned by variable response to continued continental convergence during the Proterozoic.  相似文献