The use of the marine biotic index AMBI in the assessment of the ecological status of the Obidos lagoon (Portugal)     

Carvalho S  Gaspar MB  Moura A  Vale C  Antunes P  Gil O  da Fonseca LC  Falcão M 《Marine pollution bulletin》2006,52(11):1414-1424

This study reports the longitudinal distribution of sediment properties, including inorganic and organic contaminants, and the structure of the benthic community in Obidos lagoon, a coastal system permanently connected to the sea and with negligible freshwater sources. Sediments from the upper to central lagoon consist of fine particles (91%) and from the lower lagoon of sands (94%). Chemical composition is strongly correlated to the percentage of fine particles. Contamination is relatively low in those sediments suggesting the effect of diffuse sources. The increase in organic matter content from down- to upstream areas was associated with the dominance of opportunistic species, while sensitive and indifferent species to organic enrichment were mainly associated to the clean sandy downstream area. The marine biotic index (AMBI) was suitable for the discrimination of the biological and environmental gradients in the Obidos lagoon and was highly related with the gradient of organic matter content in this system.  相似文献   

Deep-sea Fe-Mn Crusts from the Northeast Atlantic Ocean: Composition and Resource Considerations     

Susana Bolhão Muiños  James R. Hein  Martin Frank  José Hipólito Monteiro  Luís Gaspar  Tracey Conrad 《Marine Georesources & Geotechnology》2013,31(1):40-70

Eighteen deep-sea ferromanganese crusts (Fe-Mn crusts) from 10 seamounts in the northeast Atlantic were studied. Samples were recovered from water depths of ～1,200 to ～4,600 m from seamounts near Madeira, the Canary and Azores islands, and one sample from the western Mediterranean Sea.

The mineralogical and chemical compositions of the samples indicate that the crusts are typical continental margin, hydrogenetic Fe-Mn crusts. The Fe-Mn crusts exhibit a Co + Cu + Ni maximum of 0.96 wt%. Platinum-group element contents analyzed for five samples showed Pt contents from 153 to 512 ppb.

The resource potential of Fe-Mn crusts within and adjacent to the Portuguese Exclusive Economic Zone (EEZ) is evaluated to be comparable to that of crusts in the central Pacific, indicating that these Atlantic deposits may be an important future resource.  相似文献   

Inshore/offshore gradients of imposex and organotin contamination in Nassarius reticulatus (L.) along the Portuguese coast     

Rato M  Gaspar MB  Takahashi S  Yano S  Tanabe S  Barroso C 《Marine pollution bulletin》2008,56(7):1323-1331

Imposex and organotin (OT) tissue contamination of the netted whelk Nassarius reticulatus (L.) were assessed in the continental shelves around the main estuaries of the central coast of Portugal (Lisbon: Tagus estuary; Setúbal: Sado estuary) and the main coastal lagoon in the Southern of Portugal (Faro: Ria Formosa). Pollution levels were higher in areas of more intense boat traffic and shipyard activities and imposex showed a clear decreasing gradient from the estuaries to the offshore, in relation to a similar gradient of tissue contamination by tributyltin. Remarkably, imposex was extensively spread over the adjacent continental shelves of Tagus and Sado estuaries. The current work shows that TBT pollution is undoubtedly a matter of concern not only for the above estuaries where harbours are implanted but also for the adjacent continental shelves, regardless the massive dilution of contaminants that may occur in these deeper areas.  相似文献   

Imposex in Hexaplex (Trunculariopsis) trunculus (Gastropoda: Muricidae) from the Ria Formosa lagoon (Algarve coast-southern Portugal)     

Vasconcelos P  Gaspar MB  Castro M 《Marine pollution bulletin》2006,52(3):337-341

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Petrology of kamafugites and kimberlites from the Alto Paranaíba Alkaline Province, Minas Gerais, Brazil     

Ana Araujo  Richard W. Carlson  José C. Gaspar  Luiz A. Bizzi 《Contributions to Mineralogy and Petrology》2001,142(2):163-177

Mafic rocks representative of the alkaline magmatism of the Alto Paranaíba Province in southwestern Minas Gerais, Brazil were studied by means of petrography, mineral, whole-rock and isotope geochemistry with the objective of better understanding this Cretaceous magmatism and the characteristics of the magma sources. Because of the variety and complexity of lithotypes examined in this research and the paucity of detailed studies of these Brazilian rocks in the literature, this study also attempts to establish parameters that allow for a clear distinction between kimberlite and kamafugite. Fifty-two occurrences are described and classified as kimberlite or kamafugite. Among the kamafugites, both ugandite (characterized by the presence of leucite) and mafurite (with kalsilite) end members have been characterized. Mineral compositions were found to be efficient in distinguishing between kimberlites, mafurites and ugandites in the province, primarily on the basis of phlogopite composition. The Re-Os isotope systematics permitted a better understanding of the relation of the sublithospheric mantle source to the magmatism in the region. Kimberlites, mafurites and ugandites have different ¹⁸⁷Os/¹⁸⁸Os ratios (0.117 to 0.129, 0.127 to 0.145 and 0.142 to 0.147, respectively). The Rb-Sr and Sm-Nd isotope systematics failed to indicate first-order differences between kamafugites and kimberlites, whilst ²⁰⁶Pb/²⁰⁴Pb ratios for the kimberlites are higher than those for the other rock types. Kimberlite and kamafugite isotopic compositions appear to be related to the mixture of at least two dominant mantle components: one with an isotopic signature similar to that of lithospheric peridotites, i.e., with ¹⁸⁷Os/¹⁸⁸Os ratios of the order of 0.118, similar to those observed in mantle-derived xenoliths entrained in kimberlites intruded in the Kaapvaal, Wyoming, and Siberian cratons; another with higher ¹⁸⁷Os/¹⁸⁸Os ratios of the order of 0.135, within the range of ratios reported for pyroxenite veins in alpine-type peridotites and ocean island basalts. Different melting depths of heterogeneous lithospheric sources by a mantle plume are suggested to explain the isotopic characteristics of the Alto Paranaíba Alkaline Province alkaline rocks.  相似文献   

The phlogopites from the Jacupiranga carbonatite intrusions   总被引：1，自引：0，他引：1  

Dr. José C. Gaspar  Prof. Peter J. Wyllie 《Mineralogy and Petrology》1987,36(2):121-134

Summary Electron microprobe analyses of phlogopites from five carbonatite intrusions (C₁ oldest, to C₅ youngest) constituting the carbonatite plug in the Jacupiranga complex support previous conclusions based on magnetite analyses that C₂ to C₅ represent a trend of differentiation, and that C₁ has different chemical characteristics. All analyzed grains are zoned but no systematic zoning trends occur. The FeO/(FeO + MgO) ratio is very low (0.065 to 1.2), MgO is high (22.5 to 28.2%), TiO₂ is very low (up to 0.44w%), BaO may be very high (up to 10.3 w%), and Na₂O may be as high as 2.77 w%. With decreasing age from C₂ to C₅, MgO increases. Phlogopites from a banded reaction rock between carbonatite and jacupirangite are similar to, but not related to the phlogopites of the adjacent carbonatite. Compared with other carbonatite micas, the MgO-rich, TiO₂-poor Jacupiranga phlogopites present one of the less evolved compositions, similar to those in mantle peridotites. Carbonatite micas are generally lower in TiO₂ than BaO-rich micas from other rocks.

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Die Phlogopite der Karbonatitintrusionen von Jacupiranga und ihre petrogenetische Bedeutung

Zusammenfassung Mikrosondenanalysen von Phlogopiten aus fünf verschiedenen Karbonatitintrusionen (C₁ am ältesten, C₅ am jüngsten) des Jacupiranga-Komplexes unterstützen die früheren Schlüsse aus Magnetitanalysen, daß C₂ bis C₅ durch eine kontinuierliche magmatische Differentiation voneinander abgeleitet werden können, während C₁ andere geochemische Charakteristika aufweist. Alle analysierten Phlogopite sind zoniert, jedoch ohne jede systematische Tendenz in der Zonierung. Das FeO/(FeO + MgO)-Verhältnis ist sehr niedrig (0.065 bis 0.12), TiO₂ ist niedrig (unter 0.44 Gew.-%), BaO kann mit bis zu 10.3 Gew.-% sehr hoch sein, und Na₂O kann 2.77 Gew.% erreichen. Mit abnehmendem Alter von C₂ nach C₅ steigt der Gehalt an MgO an, während BaO abnimmt. Phlogopite aus einem gebänderten Reaktionsgestein zwischen Karbonatit und Jacupirangit sind ähnlich zusammengesetzt wie die benachbarten Karbonatite, mit diesen jedoch nicht verwandt. Verglichen mit Glimmern anderer Karbonatitvorkommen zählen jene von Jacupiranga zu den am wenigsten entwickelten auf Grund ihrer hohen MgO-Gehalte bei gleichzeitiger TiO₂-Armut. Sie weisen eine ähnliche Zusammensetzung wie Glimmer aus Mantelperidotiten auf. Bei gleichen BaO-Gehalten sind Glimmer aus anderen Karbonatiten generell ärmer an TiO₂.

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With 7 figures  相似文献   

The origin of diamonds in western Minas Gerais,Brazil     

G. M. Gonzaga  N. A. Teixeira  J. C. Gaspar 《Mineralium Deposita》1994,29(5):414-421

Important diamond mineralized alluvium/colluvium occurs in western Minas Gerais (WMG) in the Brasília Orogenic Belt (700-450 my). Diamonds are geographically related to glacial and periglacial sediments (Upper Proterozoic and Permo-Carboniferous), wadi and debris flow conglomerates (Lower Cretaceous and Upper Cretaceous), and ultramafic alkaline rocks (intrusive and extrusive, including kimberlites, leucitites, kamafugites, carbonatites, etc.) of Cretaceous age. Petrological data indicate that the rocks originally petrographically classified as kimberlites present mineralogical, chemical, and isotopical differences with Group I and II kimberlites and more closely resemble kamafugites. The Brasília Orogenic Belt presents features of a Wilson Cycle implying that WMG does not fulfil the geotectonic and geothermometric requisites to host primary diamond sources. An analysis of field relations and sedimentology in WMG shows that the majority of the diamonds have been transported by glacial events from the São Francisco Craton further east.  相似文献   

Kamafugitic diatremes: facies characterisation and genesis—examples from the Goiás Alkaline Province, Brazil     

Tereza Cristina Junqueira-Brod  Jos Affonso Brod  Jos Carlos Gaspar  Hardy Jost 《Lithos》2004,76(1-4):261-282

This paper describes the internal organisation of two diatremes (Águas Emendadas and Neuzinha) and one small breccia-filled conduit (Tigre) in the central portion of the Late Cretaceous Goiás Alkaline Province (GAP), central Brazil, and explores the criteria for facies recognition. The GAP kamafugitic diatremes are emplaced into Carboniferous sandstones of the Aquidauana Formation, at the northern margin of the Paraná Basin. They are usually elliptical structures, not longer than 900 m, filled with breccia and partially covered by thin kamafugitic to basanitic lava flows. The breccias are dominated by juvenile pyroclasts, with subordinate amounts of cognate fragments and xenoliths. In addition to variations in ash and lapilli proportions, juvenile fragment types may be used to discriminate genetic processes and the corresponding pyroclastic deposits.

An extensive field, textural and compositional dataset was analysed by multivariate statistical techniques. Combined with field observations, this allowed us to define a set of facies for kamafugitic diatremes, and, more importantly, to understand the internal structure of the studied bodies and to cross-correlate them. Seven distinct facies were recognised. The Fluidised Conduit Facies (FCF) represents high-energy, strongly fluidised but only moderately fragmented systems. It occurs in a confined environment, and is typical of deeper parts of the conduit, before the actual diatreme level is reached by the ascending fluidised magma. Large amounts of spinning droplets are formed within this region. The Fluidised Conduit–Diatreme Facies (FCDF) is characteristic of intermediate depths in the conduit, where highly fluidised and highly fragmented systems produce large amounts of ash. Spinning droplets decrease in abundance, ordinary juvenile fragments become very common, and xenoliths from the country rock in the immediate vicinity of the diatreme are present. The Fluidised Fragmented Facies (FFF) and the Magmatic Fluidised Facies (MFF) produce very heterogeneous deposits that dominate the shallower part of the system, making up most of the diatreme-filling materials. The Fluidised Fragmented Facies can be distinguished by much higher degrees of fluidisation, fragmentation and system energy. It occupies the internal part of the diatreme and is characterised by the common presence of tuff pockets, tuff fragments, and accretionary and armoured lapilli. The Magmatic Fluidised Facies typically occupies the outer portion of the diatreme and can be distinguished from the Fluidised Fragmented Facies by the dominance of lapilli over ash and by the presence of abundant wrapped fragments. The Magmatic Facies (MF) and the Coherent Magmatic Facies (CMF) are volumetrically subordinate and represent late stages, when less fluidised and less fragmented material, or even coherent magma erupts relatively passively, in the aftermath of the main explosive stage that generated the diatreme. The Border Facies is defined by the increased abundance of material from the immediate country rock. At Águas Emendadas and Neuzinha this facies is marked by the presence of fragments of peperite-like rock, formed by the interaction of the fluidised magma with friable sandstone.  相似文献   

Effects of infauna harvesting on tidal flats of a coastal lagoon (Ria Formosa, Portugal): implications on phosphorus dynamics     

Falcão M  Caetano M  Serpa D  Gaspar M  Vale C 《Marine environmental research》2006,61(2):136-148

The systematic collection of benthic organisms in tidal flats of coastal lagoons should be taken into account for the management of these systems, once sediment disturbance affects biogeochemical processes by favouring pore water renewal during tidal inundation. The objective of the present work was to evaluate the effects of infauna harvesting on the phosphorus dynamics of muddy and sandy intertidal areas in the Ria Formosa. Sediment cores and overlying water were collected during August 2000 and February 2001 from reworked and undisturbed sediment before and after flooding. Results obtained showed that during the first minutes of flooding there was a marked decrease of phosphate in pore water of disturbed sediments. However, phosphate tidal fluxes from sandy sediment were clearly higher (17 nmol cm(-2) d(-1) in summer and 3 nmol cm(-2) d(-1) in winter) than in muddy sediment (0.4 nmol cm(-2) d(-1) in summer and -0.01 nmol cm(-2) d(-1) in winter). After muddy sediment disturbance concentrations of iron oxides increased quickly (from 5 to 16 micromol g(-1)) and phosphate was sorbed onto these iron oxides, resulting in a buffering of phosphate pore water concentrations at low values in the oxidized sediment zone. The estimated P-output from muddy sediment decreased one to two orders of magnitude after sediment disturbance in contrast to sandy sediments in which the impact of infauna harvesting was minimal. Consequently, the P-cycle is influenced by the disruption of muddy habitats in tide-driven systems. Such information could be useful for the management of the lagoon.  相似文献   

The 9th of July 1998 Faial Island (Azores,North Atlantic) seismic sequence   总被引：2，自引：0，他引：2  

L. Matias  N. A. Dias  I. Morais  D. Vales  F. Carrilho  J. Madeira  J. L. Gaspar  L. Senos  A. B. Silveira 《Journal of Seismology》2007,11(3):275-298

The Faial earthquake (M _L 5.8) that occurred on the 9th of July, 1998, in the Azores region (north Atlantic), caused nine casualties and severe destruction affecting more than 5,000 people. The main shock was located at sea, 10 km NE of the Faial Island, and triggered a seismic sequence that lasted for several weeks and was characterized by an unusual high p-value of 1.40 for the modified Omori law. We present here the results of a joint inversion of hypocenters and 1D velocity model performed on the data collected by the permanent network complemented with a temporary network installed shortly after the occurrence of the main event. The 1D velocity model shows a heterogeneous upper crust, testified by the observed differences in site effects at the stations, while the middle crust from ∼2.5 to 8 km in depth is quite homogeneous. The Moho is located at a depth of about 12–13 km and the Vp/Vs ratio is found to be around 1.78. The events at depth are mainly concentrated in the middle-lower crust (8–12 km), while their spatial distribution shows a main cluster, visible after relocation, SSE trending. This direction of elongation is consistent with one of the fault planes (N151°E) of the centroid moment tensor (CMT) solution for the main shock. The same plane is the preferred main shock fault plane inferred after a Coulomb failure function analysis on the aftershock distribution. The main event relocation points to a focal depth shallower than 5 km. The aftershocks pattern shows that several fault systems were reactivated by the stress perturbation induced by the main shock. Besides the two main tectonic directions, trending WNW–ESE and NNW–SSE, observed in the tectonics of Faial, Pico, and S. Jorge, there is also evidence of a new tectonic direction trending WSW–ENE.  相似文献