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131.
M.L. Carapezza F. Barberi M. Ranaldi T. Ricci L. Tarchini J. Barrancos C. Fischer D. Granieri C. Lucchetti G. Melian N. Perez P. Tuccimei A. Vogel K. Weber 《Applied Geochemistry》2012
Gas hazard was evaluated in the three most important cold gas emission zones on the flanks of the quiescent Colli Albani volcano. These zones are located above structural highs of the buried carbonate basement which represents the main regional aquifer and the main reservoir for gas rising from depth. All extensional faults affecting the limestone reservoir represent leaking pathways along which gas rises to the surface and locally accumulates in shallow permeable horizons forming pressurized pockets that may produce gas blowout when reached by wells. The gas, mainly composed of CO2 (>90 vol.%), contains appreciable quantities of H2S (0.35–6 vol.%), and both represent a potentially high local hazard. Both gases are denser than air and accumulate near ground where they may reach hazardous concentrations, and lethal accidents frequently occur to animals watering at local ponds. In order to evaluate the rate of degassing and the related hazard, CO2 and H2S diffuse soil flux surveys have been repeatedly carried out using an accumulation chamber. The viscous gas flux of some important discrete emissions has been evaluated and the CO2 and H2S air concentration measured by portable devices and by Tunable Diode Laser profiles. The minimum potential lethal concentration of the two gases (250 ppm for H2S and 8 vol.% for CO2) is 320 times higher for CO2, whereas the CO2/H2S concentration ratio in the emitted natural gas is significantly lower (15–159). This explains why H2S reaches hazardous, even lethal, concentrations more frequently than CO2. A relevant hazard exists for both gases in the depressed zones (channels, excavations) particularly in the non-windy early hours of the day. 相似文献
132.
Ignacio?Torresi Roberto?Perez?XavierEmail author Diego?F.?A.?Bortholoto Lena?V.?S.?Monteiro 《Mineralium Deposita》2012,47(3):299-323
The Alvo 118 iron oxide–copper–gold (IOCG) deposit (170 Mt at 1.0 wt.% Cu, 0.3 g/t Au) lies in the southern sector of the
Itacaúnas Shear Belt, Carajás Mineral Province, along a WNW–ESE-striking, 60-km-long shear zone, close to the contact of the
~2.76-Ga metavolcano-sedimentary Itacaiúnas Supergroup and the basement (~3.0 Ga Xingu Complex). The Alvo 118 deposit is hosted
by mafic and felsic metavolcanic rocks and crosscutting granitoid and gabbro intrusions that have been subjected to the following
hydrothermal alteration sequence towards the ore zones: (1) poorly developed sodic alteration (albite and scapolite); (2)
potassic alteration (biotite or K-feldspar) accompanied by magnetite formation and silicification; (3) widespread, pervasive
chlorite alteration spatially associated with quartz–carbonate–sulphide infill ore breccia and vein stockworks; and (4) local
post-ore quartz–sericite alteration. The ore assemblage is dominated by chalcopyrite (~60%), bornite (~10%), hematite (~20%),
magnetite (10%) and subordinate chalcocite, native gold, Au–Ag tellurides, galena, cassiterite, F-rich apatite, xenotime,
monazite, britholite-(Y) and a gadolinite-group mineral. Fluid inclusion studies in quartz point to a fluid regime composed
of two distinct fluid types that may have probably coexisted within the timeframe of the Cu–Au mineralizing episode: a hot
(>200°C) saline (32.8‰ to 40.6 wt.% NaCl eq.) solution, represented by salt-bearing aqueous inclusions, and a lower temperature
(<200°C), low to intermediate salinity (<15 wt.% NaCl eq.) aqueous fluid defined by two-phase (LH2O + VH2O) fluid inclusions. This trend is very similar to those defined for other IOCG systems of the Carajás Mineral Province. δ
18OH2O values in equilibrium with calcite (−1.0‰ to 7.5‰ at 277°C to 344°C) overlap the lower range for primary magmatic waters,
but the more 18O-depleted values also point to the involvement of externally derived fluids, possibly of meteoric origin. Furthermore, sulphide
δ
34S values (5.1‰ to 6.3‰), together with available boron isotope and Cl/Br–Na/Cl data provide evidence for a significant component
of residual evaporative fluids (e.g., bittern fluids generated by seawater evaporation) in this scenario that, together with
magma-derived brines, would be the main sources of the highly saline fluids involved in the formation Alvo 118 IOCG deposit.
The restricted high temperature sodic alteration, the pervasive overprinting of the potassic alteration minerals by chlorite
proximal to the ore zones, ore breccias with open-space filling textures in brittle structures, microthermometric and stable
isotope data indicate, collectively, that the Alvo 118 IOCG system developed at structurally high levels and may be considered
the shallower representative of the IOCG systems of the CMP. 相似文献
133.
Mariano Bonomo Alejandro Fabián Zucol Beatriz Gutiérrez Téllez Andrea Coradeghini María Susana Vigna 《Journal of Paleolimnology》2009,41(2):273-296
This paper presents results of interdisciplinary palaeoenvironmental research carried out on a sediment sequence from the
Nutria Mansa 1 archaeological site. This late Holocene site is located in the Pampean plains, Argentina. Siliceous microfossils
were recorded (i.e. phytoliths, diatoms, chrysophytes, sponges) and micro-charcoal was analyzed. In addition, fauna identified
at the site were correlated with regional palaeoclimatic evidence. Based on the microfossil associations, we concluded that
the human occupations occurred beside a fluvial and brackish-freshwater lacustrine setting. Grass communities were located
on its margins that developed under a warm temperate climate with evidence for dryness and marked seasonality in part of the
record. Although some stratigraphic and faunal evidence indicates a possible temperature increase, these fluctuations were
not sufficient to extirpate mammals of arid and cold environments. 相似文献
134.
Rafael P. Fernandez Martin Kaufmann Beatriz M. Toselli 《Journal of Atmospheric and Solar》2009,71(8-9):805-815
The relative importance of different processes and transitions in the appearance of non-LTE populations for the fundamental levels of ozone was studied by quantifying the kinetic law of every process and transition that affect each level population. The vibrational temperatures and the relative contribution of every transition are presented as a function of altitude. The results show that the appearance of non-LTE populations for the fundamental levels is not produced by a direct imbalance between absorption and emission but as a consequence of imbalanced collisional transitions provoked by the overpopulation of O3(0 v2 0) levels. This fact confirms that the relaxation cascade drives through the bending mode ν2. 相似文献
135.
An overview of laboratory apparatuses to measure seismic attenuation in reservoir rocks 总被引:1,自引:0,他引:1
Beatriz Quintal Nicola Tisato Erik H. Saenger Claudio Madonna 《Geophysical Prospecting》2014,62(6):1211-1223
Intrinsic wave attenuation at seismic frequencies is strongly dependent on rock permeability, fluid properties, and saturation. However, in order to use attenuation as an attribute to extract information on rock/fluid properties from seismic data, experimental studies on attenuation are necessary for a better understanding of physical mechanisms that are dominant at those frequencies. An appropriate laboratory methodology to measure attenuation at seismic frequencies is the forced oscillation method, but technical challenges kept this technique from being widely used. There is a need for the standardization of devices employing this method, and a comparison of existing setups is a step towards it. Here we summarize the apparatuses based on the forced oscillation method that were built in the last 30 years and were used to measure frequency‐dependent attenuation in fluid‐saturated and/or dry reservoir rocks under small strains (10?8–10?5). We list and discuss important technical aspects to be taken into account when working with these devices or in the course of designing a new one. We also present a summary of the attenuation measurements in reservoir rock samples performed with these apparatuses so far. 相似文献
136.
137.
Tidal effects on phytoplankton assemblages in a near‐pristine estuary: a trait‐based approach for the case of a shallow tropical ecosystem in Brazil
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Gleyci A. O. Moser Fernanda Reinhardt Piedras Anna Beatriz J. Oaquim Daiana S. Souza Suzana G. Leles Domênica T. de Lima Ana Beatriz A. Ramos Cássia de O. Farias Alexandre M. Fernandes 《Marine Ecology》2017,38(4)
The study of near‐pristine estuaries can be used as a tool for mitigation projects of harmful effects in anthropogenic eutrophic systems, since one can analyze the effect of temporal and spatial variations generated mainly by natural forces. Phytoplankton taxonomy has been used as a classical indicator to assess changes in transitional water communities, however alternative methods based on morphological, behavioral and physiological traits offer the opportunity to compare sites or moments with different taxonomic compositions. Our goal, in this context, is to evaluate phytoplankton community short‐term and seasonal variability in a near‐pristine estuary, Barra Grande estuary (Ilha Grande, RJ, Brazil), through species functional traits and thus community functional diversity. Samplings were carried out in a mooring in complete tidal cycles, seasonally during 2012. Our results showed a diverse phytoplankton community with 38 frequent and abundant taxa, marked by density variation (1.2 × 10.4–2 × 10.7 cell L?1) in depth, with abundance inversely related to tidal currents. The functional structure of the phytoplankton community measured by functional diversity (FD), varied seasonally in and across a gradient of tidal energy. A core community, mainly represented by flagellates and dinoflagellates, occurred in all observations and was highly functional (high FD), exploiting a variety of habitats. The chain‐forming diatoms were associated with high tidal energy, and occurred in higher densities during summer. Phytoplankton cell size, cell shape, and the ability to form colonies are extremely plastic traits that can be regulated by the environment, however, isolated tychopelagic diatoms were present in the study area across all seasons, with higher contributions in autumn and winter, reflecting the shallow characteristic of this system. During the winter, an exposed sandbar was formed, and the lack of connection with the ocean resulted in an abundance of riverine and brackish water taxa. In this near‐pristine estuary the densities and occurrences of HAB phytoplankton are low. Trait‐based analyses add information about community structure, which can be impacted by anthropogenic actions in urbanized coastal systems. Thus the information provided by this study regarding phytoplankton functional diversity and its relation to nutrients and hydrography in Barra Grande Estuary can be applied as a baseline model for the development of public policies. 相似文献
138.
Beatriz González-Fernández Mónica Meléndez-Asensio Eduardo Menéndez-Casares 《Environmental Earth Sciences》2009,59(4):913-928
Chemical and isotopic analyses of groundwater from the carbonated Jurassic aquifers in the Gijón-Villaviciosa basin (Asturias,
northern Spain) were carried out. Nine springs were sampled to determine major cations and anions, as well as the stable isotopes
of the water molecule (δ2H and δ18O) and sulphate (δ34S) values. Also, δ34S values from gypsum coming both from Triassic rocks and bottom of Jurassic sequence were also determined. The results obtained
were used to classify the waters with a genetic criteria in three groups: (1) waters with a high gypsum influence, with sulphate
coming from Jurassic gypsum, (2) waters without gypsum influence, where sulphate source could be atmospheric deposition from
industrial processes and marine aerosol, and (3) waters with some gypsum influence, in which sulphate origin could be a combination
of different sources. In relation to recharge, δ2H and δ18O values were close to those of Global Meteoric Water Line and fit a local line that suggests a meteoric origin. The estimated
elevations for spring recharge are in agreement with those obtained from hydrogeological maps. 相似文献
139.
Elisabete S. Braga Vitor C. Chiozzini Gláucia B.B. Berbel João C.C. Maluf Valquíria M.C. Aguiar Marcela Charo Daniel Molina Sílvia I. Romero Beatriz B. Eichler 《Continental Shelf Research》2008
Nutrient distributions observed at some depths along the continental shelf from 27°05′S (Brazil) to 39°31′S (Argentina) in winter, 2003 and summer, 2004 related to salinity and dissolved oxygen (mL L−1) and saturation (%) data showed remarkable influences of fresh water discharge over the coastal region and in front of the La Plata estuary. In the southern portion of the study area different processes were verified. Upwelling processes caused by ocean dynamics typical of shelf break areas, eddies related to surface dynamics and regeneration processes confirmed by the increase of nutrients and the decrease of dissolved and saturation oxygen data were verified. High silicate concentrations in the surface waters were identified related to low salinities (minimum of 21.22 in winter and 21.96 in summer), confirming the importance of freshwater inputs in this region, especially in winter. Silicate concentration range showed values between 0.00 and 83.52 μM during winter and from 0.00 to 41.16 μM during summer. Phosphate concentrations worked as a secondary trace of terrestrial input and their values varied from 0.00 to 3.30 μM in winter and from 0.03 to 2.26 μM in summer; however, in shallow waters, phosphate indicated more clearly the fresh water influence. The most important information given by nitrate concentrations was the presence of water from SACW upwelling that represents a new source of nutrients for marine primary production. Nitrate maximum values reached 41.96 μM in winter and 33.10 μM in summer. At a depth ∼800 m, high nitrate, phosphate and silicate concentrations were related to Malvinas Current Waters, Subantarctic Shallow Waters and Antarctic Atlantic Intermediate Waters (AAIW). Dissolved oxygen varied from 3.41 to 7.06 mL L−1 in winter and from 2.65 to 6.85 mL L−1 in summer. The percentage of dissolved oxygen saturation in the waters showed values between 48% and 113% in winter and from 46% to135% in summer. The most important primary production was verified in the summer, and situations of undersaturation were mainly observed below 50 m depth and at some points near the coast. The anti-correlation between nutrients and dissolved oxygen which showed evident undersaturation also revealed important potential sites of remineralization processes. The nutrient behaviours showed some aspects of the processes that occur over the Southwestern South Atlantic continental shelf and in their land–sea interfaces between Mar del Plata and Itajaí. 相似文献
140.
Summary Estimates of hourly global irradiance based on geostationary satellite data with a resolution of several (2 to 10) kilometres
reproduce ground-measured values with a Root Mean Square Error (RMSE) of typically 20% to 25%. The different components of
this RMSE have been enumerated by several authors but, due to the lack of adequate measurements, their respective importance
is not well settled. In the present study we attempt to quantify these components from a practical point of view, that is
from the point of view of users having to rely on time/site specific irradiance data. We conclude that the intrinsic, or “effective”
RMSE is more along the line of 12%. This effective RMSE is the measure of the methodological imprecision (satellite-to-irradiance
conversion models). The remaining part of the overall RMSE is the amount by which spatially averaged satellite-derived estimates
are, by their very nature, bound to differ from ground-measured local insolation.
Received August 15, 1997 Revised March 4, 1998 相似文献