LMWOA (low molecular weight organic acid) exudation by salt marsh plants: Natural variation and response to Cu contamination     

Ana P. Mucha  C. Marisa R. Almeida  Adriano A. Bordalo  M. Teresa S.D. Vasconcelos 《Estuarine, Coastal and Shelf Science》2010

This work aimed to evaluate, in vitro, the capability of roots of two salt marsh plants to release low molecular weight organic acids (LMWOAs) and to ascertain whether Cu contamination would stimulate or not organic acids exudation. The sea rush Juncus maritimus and the sea-club rush Scirpus maritimus, both from the lower Douro river estuary (NW Portugal), were used. Plants were collected seasonally, four times a year in 2004, during low tide. After sampling, plant roots were washed for removal of adherent particles and immersed for 2 h in a solution that matched salinity (3) and pH (7.5) of the pore water from the same location to obtain plant exudates. In one of the seasons, similar experiments were carried out but spiking the solution with different amounts of Cu in order to embrace the range between 0 and 1600 nM. In the final solutions as well as in sediment pore water LMWOAs were determined by high performance liquid chromatography. Plants were able to release, in a short period of time, relatively high amounts of LMWOAs (oxalate, citrate, malate, malonate, and succinate). In the sediment pore water oxalate, succinate and acetate were also detected. Therefore, plant roots probably contributed to the presence of some of these organic compounds in pore water. Exudation differed between the plant species and also showed some seasonally variation, particularly for S. maritimus. The release of oxalate by J. maritimus increased with Cu increase in the media. However, exudation of the other LMWOAs did not seem to be stimulated by Cu contamination in the media. This fact is compatible with the existence of alternative internal mechanisms for Cu detoxification, as denoted by the fact that in media contaminated with Cu both plant species accumulated relatively high amounts (29–83%) of the initially dissolved Cu. This study expands our knowledge on the contribution of globally dominant salt marsh plants to the release of LMWOAs into the environment.  相似文献   

A constitutive model for mechanical and chemo‐mechanical compaction in sedimentary basins and finite element analysis          下载免费PDF全文

A. Brüch  S. Maghous  F.L.B. Ribeiro  L. Dormieux 《国际地质力学数值与分析法杂志》2016,40(16):2238-2270

Compaction and associated fluid flow are fundamental processes in sedimentary basin deformation. Purely mechanical compaction originates mainly from pore fluid expulsion and rearrangement of solid particles during burial, while chemo‐mechanical compaction results from Intergranular Pressure‐Solution (IPS) and represents a major mechanism of deformation in sedimentary basins during diagenesis. The aim of the present contribution is to provide a comprehensive 3D framework for constitutive and numerical modeling of purely mechanical and chemo‐mechanical compaction in sedimentary basins. Extending the concepts that have been previously proposed for the modeling of purely mechanical compaction in finite poroplasticity, deformation by IPS is addressed herein by means of additional viscoplastic terms in the state equations of the porous material. The finite element model integrates the poroplastic and poroviscoplastic components of deformation at large strains. The corresponding implementation allows for numerical simulation of sediments accretion/erosion periods by progressive activation/deactivation of the gravity forces within a fictitious closed material system. Validation of the numerical approach is assessed by means of comparison with closed‐form solutions derived in the context of a simplified compaction model. The last part of the paper presents the results of numerical basin simulation performed in one dimensional setting, demonstrating the ability of the modeling to capture the main features in elastoplastic and viscoplastic compaction. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Paleoweathering features in the Sergi Formation (Jurassic-Cretaceous), northeastern Brazil,and implications for hydrocarbon exploration     

Cristina Pierini  Ana M. Mizusaki  Nuno Pimentel  Ubiratan F. Faccini  Claiton M.S. Scherer 《Journal of South American Earth Sciences》2010,29(2):412-426

Paleoweathering in the Sergi Formation has been classified and analyzed to ascertain its origin and relationship with stratigraphic evolution. The Sergi Formation belongs to the pre-rift sequence of the Recôncavo Basin (northeastern Brazil) and comprises a complex association of eolian and fluvial sandstones and lacustrine mudstones. This formation can be subdivided into three depositional sequences bounded by regional unconformities. Four paleoweathering types, each one related to a distinct origin, have been described in the Sergi Formation: (1) textural mottling, which is distinguished by alternating rock colors as a result of the iron oxide mobilization within mineral phases that evolved under alternating oxidation (yellowish, brownish and reddish shades) and reduction (grayish or greenish hues) conditions; (2) non-textural mottling, which displays a discoloration pattern that is independent of the original rock texture; (3) carbonate concentrations, usually related to carbonate nodule formation, which display a massive internal structure that reveals their origin through continuous growth or crystallization; and (4) banded carbonates (silicified), associated with the beginning of regular surface formation due to the chemical precipitation of carbonates within lacustrine environments. Both mottling color motifs and carbonate accumulation usually represent groundwater oscillation rather than pedogenesis. Only carbonate intraclasts and banded carbonate (silicified) have their origin ascribed to pedogenesis sensu stricto, although the carbonate intraclasts do not represent soil deposits in situ, but calcretes eroded from areas close to channels, and the banded carbonates (silicified) have strong diagenetic modifications. Therefore, it is reasonable to assume that fluvial and meteoric water have controlled paleoweathering evolution as well as deposition, yet both aspects are ruled by the same mechanisms (relief, sedimentation rate and, above all, climate).  相似文献   

The last deglaciation in the Picos de Europa National Park (Cantabrian Mountains,northern Spain)     

Ana Moreno  Blas L. Valero‐Garcés  Montserrat Jiménez‐Sánchez  María José Domínguez‐Cuesta  M. Pilar Mata  Ana Navas  Penélope González‐Sampériz  Heather Stoll  Pedro Farias  Mario Morellón  J. Pablo Corella  Mayte Rico 《第四纪科学杂志》2010,25(7):1076-1091

A sedimentological and geochemical study of the Lago Enol sequence (Cantabrian Mountains, northern Spain), together with detailed geomorphological mapping, provides a first record of glacier evolution and climate change over the last 40 ka in the Picos de Europa National Park. The Enol glacier retreated from its maximum extent prior to 40 ka BP as demonstrated by the onset of proglacial lacustrine sedimentation in two glaciated depressions: the Comella hollow to the north (before 40 ka BP) and the Lago Enol (before 38 ka BP). These results support previous evidence that the maximum extent of southern European glaciers occurred earlier than in northern Europe. Alternation of homogeneous and laminated proglacial sediments during the glacier retreat illustrate a dynamic glacial evolution during the Marine Isotope Stage (MIS) 3 (40–26 ka BP). A slight warming is detected at 26 ka ago with the change from proglacial sediments (in a lake located in contact to the glacier) to glaciolacustrine sedimentation (in a non‐contact or distal lake). Finally, the onset of organic‐rich sediments took place at 18 ka ago. This last transition occurred in two phases, similarly to the North Atlantic Last Termination, suggesting a link between North Atlantic Deep Water formation oscillations and palaeohydrological variability in the Cantabrian Mountains. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Methodological issues involved in the definition of the marine sector     

Ana Luiza Cortez 《GeoJournal》1988,16(3):247-255

Recently, the debate surrounding the United Nations Convention in the Law of the Sea (UNCLOS) and the Exclusive Economic Zones (EEZ) has been extended to the realm of economic growth and planning. Although coastal states are making efforts to determine what resources they have in their EEZs, little is known about the exact contribution those resources are making or potentially could make to enhanced economic growth. This paper suggests an accounting framework, based on existing literature, which explicity delineates the industries that should be considered a part of the marine sector. Criteria are suggested to help determine exactly where a particular industry falls. Several methodological issues are discussed in detail.The views expressed here are those of the author and do not necessarily represent those of the United Nations.  相似文献   

Petrogenesis of early paleozoic peralkaline rhyolites from the Macedo de Cavaleiros region (NE Portugal)     

M. Luisa Ribeiro 《International Journal of Earth Sciences》1987,76(1):147-168

The petrology and geochemistry of Variscan peralkaline gneisses from NE Portugal, discovered in 1962, is presented. Major and trace element data for the oversaturated sequence of the Macedo de Cavaleiros area depict some specific geochemical patterns: high Fe₂O₃ ^(t) (even higher than in the Ethiopian Main Rift), high REE concentrations and small Eu anomalies. Field and petrographical observations also suggest that liquid immiscibility has played an important petrogenetic role in the crystallization trends. The alternating pyroxenefeldsparhematite-rich bands observed in outcrop are interpreted as resulting from fluctuating fO₂ conditions. Petrological and geochemical data show that these pantelleritic and comenditic rocks are the end members of an alkaline-transitional basaltic sequence, by which they are overlain. An uppermost sequence of oceanic tholeiitic basalts completes the picture of an evolving rift environment, where mantle processes generate crustal thinning and eventually oceanic crust.

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Zusammenfassung Petrologie und Geochemie variszischer peralkaliner Gneisse aus Nordostportugal, 1962 entdeckt, werden dargestellt. Die Haupt- und Spurenelementanalysen dieser übersättigen Gesteine weisen Besonderheiten auf, wie z. B. die hohen Fe203-Gehalte, die selbst noch die des »Ethiopian Main Rift« übersteigen, die hohen Konzentrationen an Seltenen Erdelementen und die kleine negative Eu-Anomalie. Geländegeologie und Petrographie suggerieren, da\ die liquid-magmatische Entmischung eine wichtige petrogenetische Rolle im Kristallisationsablauf spielte. Im Aufschlu\ wird eine Wechsellagerung von Pyroxen-Feldspat- und Hämatit-reichen Schichten beobachtet, die hier als Folge von fO2-Schwankungen erklärt wird. Die petrologischen und geochemischen Daten zeigen, da\ die pantelleritischen und comenditischen Gesteine die letzten Glieder in einer Abfolge vom alkalinen übergangstyp darstellen... Die vulkanische Abfolge im Gebiet von Macedo de Cavaleiros endet mit tholeiitischen Basalten, die damit das Bild der magmatischen Entwicklung in einem Rift-Bereich, in dem Mantelprozesse eine Krustenverdünnung in einem Rift-Bereich, in dem Mantelprozesse eine Krustenverdünnung und die Bildung ozeanischer Kruste bewirkten, vervollständigen.

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Résumé L'auteur présente la pétrologie et la géochimie des gneiss varisques peralcalins du nord-est du Portugal, découverts en 1962. Les analyses des éléments majeurs et en traces dans ces roches sursaturées montrent quelques caractéristiques spéciales comme la haute teneur en Fe₂O₃ (t) (supérieure mÊme à celles de l'»Ethiopian Main Rift«), la haute concentration en terres rares et la faible anomalie négative de Eu. La géologie de terrain et les observations pétrographiques suggèrent aussi que l'imiscibilité entre liquides a joué un rÔle pétrogénétique important au cours de la cristallisation. Les alternances de bandes alternativement riches en pyroxène-feldspath et en hématite, observées sur les affleurements, sont interprétées comme le résultat de la fluctuation de fO₂. Les données pétrologiques et géochimiques montrent que les roches pantéléritiques et comenditiques représentent les derniers termes d'une séquence du type alcalintransitionel qui les surmonte. La séquence volcanique dans le secteur de Macedo de Calvaleiros se termine par des basaltes tholéiitiques qui complètent le cadre d'une environnement d'un zone de »rift« dans laquelle les processus mantéliques ont déterminé l'amincissement crustal et la formation d'une croûte océanique.

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Optical absorption and electron spin resonance in blue and green natural beryl     

Ana Regina Blak  Sadao Isotani  Shigueo Watanabe 《Physics and Chemistry of Minerals》1982,8(4):161-166

A comparative study of blue and green beryl crystals (from the region of Governador Valadares, Minas Gerais, Brazil) using electron paramagnetic resonance (EPR) and optical absorption (OA) spectroscopy is reported. The EPR spectra show that Fe³⁺ in blue beryl occupies a substitutional Al³⁺ site and in green beryl is localized in the structural channels between two O₆ planes. On the other hand the infrared spectra show that the alkali content in the blue beryl is mostly at substitutional and/or interstitial sites and in green beryl is mostly in the structural channels. The OA spectra show two types of Fe²⁺. Thermal treatments above 200° C in green beryl cause the reduction of Fe³⁺ into Fe²⁺ accompanied by a change of color to blue. The blue beryl color does not change on heating. The kinetics of the thermal conversion of Fe³⁺ into Fe²⁺ is composed of two first order processes; the first one has an activation energy ΔE ₁=0.30 eV and the second one has an activation energy ΔE ₂=0.46 eV.  相似文献   

Quantitative analysis of soft-bottom molluscs in the Bellingshausen Sea and around Peter I Island   总被引：2，自引：0，他引：2  

Jesús S. Troncoso  Cristian Aldea  Patrick Arnaud  Ana Ramos  & Francisco García 《Polar research》2007,26(2):126-134

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Source, path and receiver effects on seismic surface waves     

Ana M. G. Ferreira  John H. Woodhouse 《Geophysical Journal International》2007,168(1):109-132

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The impact of hurricanes on sedimenting particulate matter in the semi-arid Bahía de La Paz,Gulf of California     

Norman Silverberg  Evgueni Shumilin  Fernando Aguirre-Bahena  Ana Patricia Rodríguez-Castañeda  Dmitry Sapozhnikov 《Continental Shelf Research》2007

From 2002 through 2004, time-series sediment trap samples were collected from a depth of 410 m in Cuenca Alfonso, Bahía de La Paz, on the SW coast of the Gulf of California. The instrument recorded the impact of the local passage of hurricanes “Ignacio” (24–26 August) and “Marty” (21–23 September) in 2003. These two events accounted for 82% of the total rainfall measured in 2003, equivalent to the annual average precipitation in years without hurricanes. Mean total mass fluxes (TMFs) of 2.88 and 3.58 g m⁻² d⁻¹ were measured during the week of each hurricane as well as the following week. This may have been enough to produce a lamina in the underlying sediment with characteristics peculiar to such events. The terrigenous component was particularly abundant, with notably higher concentrations of Fe, Sc, Co and Cs and REEs. In contrast, TMFs throughout 2002–2004 (excluding the hurricane periods) averaged only 0.73 g m⁻² d⁻¹ and had a larger marine biogenic component. The extraordinary elemental fluxes during the 29 days of hurricane-influenced sedimentation represented a great proportion of the totals over an entire “normal” year: Co (67.8%) >Sc (62.6) >Fe (59.6) >Cs (53.4)>Lu (51.5)>La (51.3)>Yb (51.0)>Ce (49.5) >Tb (48.4) >Sm (44.7)>Cr (36.5) >Ca (31.0)>Eu (25.4%). The terrigenous fraction was calculated using (a) TMF minus the sum of CaCO₃, biogenic silica and organic matter and (b) the ratio of Sc in the trap samples to the average in the Earth's crust. The latter was consistently smaller, but the two methods offered similar results following hurricanes (78% vs. 63%, respectively). For normal sedimentation, however, the difference method yielded values twice as large as the Sc method (58% vs. 30%) This suggests that the mineralogy of the terrigenous fraction may also vary, with unsorted dessert soil being carried to sea by the powerful flash floods associated with hurricanes. Eolian supply of particles, particularly Sc-free quartz grains, possibly from beyond the limited fluvial drainage basin, apparently dominates normal sedimentation.  相似文献