Determination par activation neutronique des rapports Cl/Br des inclusions fluides de divers gypses. Correlation avec les donnees de la microcryoscopie et interpretations genetiques

Gypsum contains liquid inclusions which fill mainly primary cavities. Analysis of inclusions may give some information about the mineral formation process. In places, diagenetic solutions have filled secondary cavities along cleavage planes or replaced initial liquid inclusions in primary cavities; the presence of such secondary inclusions must, therefore, be taken into consideration. This study presents our results on the Cl/Br ratio of liquid inclusions in gypsum. The Cl/Br ratio is practically constant in present sea water, and has been measured in many different types of waters. The Br content of halite has also been extensively studied to trace the compositional changes of a salt-depositing brine. In gypsum Br is present only in microscopic fluid inclusions. For this reason we used the neutron-activation method. We adopted the technique in order to prevent any contamination and obtain directly Cl/Br ratio within 10% accuracy. In order to ascertain that liquid inclusions reside mainly in primary cavities of gypsum, we selected our samples only after microscopic observation. Fifty-eight samples from different types of gypsum were analysed. The salinities of the inclusions, obtained through the data on freezing, and the Cl/Br ratio, obtained through activation-analysis, give us clues as to the nature of the fluids depositing the gypsum. Recent gypsum deposits from French salt-pans of Mediterranean and Atlantic coasts were sampled. The latter has apparently been diagenetically altered by meteoric water; the salinity of many inclusions having been changed while the Cl/Br ratio (315 and 350) in both remains close to the value of present sea water (#300). Liquid inclusions of Recent crystals from New Caledonia, deposited in mangrove swamps are enriched in Br (Cl/Br = 150 and 200). The enrichment might be related to the presence of abundant organic materials. Inclusions in crystals from Sebkha el Melah (Tunisia) also show high Br content (Cl/Br = 194). In this case, the brine was highly concentrated and was saturated with NaCl. The Upper Miocene gypsum from Sicily was studied to test the various models for the genesis of this important evaporite formation of the Mediterranean. Freezing data show some decrease of salinities, probably by groundwater diagenesis, but the Br content is high. The Cl/Br ratio is 175, and this value is similar to that of Sebkha el Melah. Samples from three thick Eocene and Oligocene sequences near Paris and in the South of France were studied. Freezing data and Cl/Br ratio of their inclusions indicate that those gypsum deposits have crystallized in marine environments receiving considerable influx of river-waters.     

Magnitude-Intensity Relationships in the Ibero-Magrebhian Region

In this paper we present magnitude (Ms) – magnitude(mb) and magnitude-intensity relationships which areconsidered the most adequate in the Ibero-Maghrebianregion. This work is based on selected samples ofrecently revised events with magnitude mb assigned bythe Instituto Geográfico Nacional (I.G.N.) and Msassigned by I.S.C and N.E.I.C., and isoseismal mapsfrom 142 events. Using these data, we have obtainedone magnitude (Ms) – magnitude (mb) relationship, twomagnitude (mb and Ms) assignment relationships viaepicentral intensity (I₀), and ten magnitude (mb andMs) assignments relationships via macroseismicinformation: four using Ambraseys' methodology (1985)and six using the isoseismal area of degree III, IV and VI.According to the obtained results it could be concluded that historical magnitude assignment with lesser uncertainties are those obtained via macroseismic information using magnitude-intensity relationships with Ambraseys' methodology (1985). The magnitude-isoseismal area assignment relationships have, in most cases, great differences depending on the degree of the isoseismal area used. Magnitude assignments via epicentral intensity have the highest uncertainties. Geographic regionalization of the relationshipshas been studied but the highest correlations and statistical significance are obtained when we fit all the Ibero-Maghrebian region data.Finally we have used the results obtained in this workto assign magnitude to some important historicalearthquakes in the Ibero-Maghrebian region: the 1755Lisbon earthquake, the 1680 Málaga earthquake, the1829 Torrevieja earthquake and the 1884 Arenas del Reyearthquake. According to our relationships andmethodology we have assigned an Ms value of 9.3 ±0.6 to the 1755 Lisbon earthquake (its mb magnitudecannot be estimated due to the saturation of the mbscale), an mb value of 6.3 ±0.4 and an Ms valueof 6.9 ± 0.6 to the 1829 Torrevieja earthquake, anmb value of 6.2 ± 0.4 and an Ms value of 6.4 ±0.6 to the 1680 Málaga earthquake and an mb valueof 6.1 ± 0.4 and an Ms value of 6.5 ± 0.6 tothe 1884 Arenas del Rey earthquake.     

The population of the Polish countryside: Demography and living conditions

Despite substantial rural-urban migration, 38.1 percent of the population of Poland still live in the countryside and the total numbers are only 0.9mln fewer than in 1946. At present the rural population is increasing and the rate of natural increase (though falling) is higher than in the towns though the productive age group is smaller. However, these human resources are not being properly used and the results can be seen in terms of economic inefficiency, low living standards and a high level of state support. Loss of jobs in factories and state farms results in welfare payments by the state and considerable 'hidden unemployment' on small family farms where profitability is constrained by inefficient use of labour. Poverty among the rural population is evident through a collapse of house building and considerable domestic overcrowding. However, conditions vary considerably across the country and this must be reflected in the economic and social policies drawn up for the new administrative regions introduced in 1999. This revised version was published online in July 2006 with corrections to the Cover Date.     

Size Fractionation (Dissolved, Colloidal and Particulate) of Trace Metals in the Thur River, Switzerland

The distribution of some trace metals (Cu, Zn, Ni, Co,Fe, Mn) and of DOC over a particulate (> 1 m),a colloidal (size < 0.45 m and molecular weight > 10 kD) and an ultrafiltered fraction (< 10 kD)was determined at several sites on the Thur River,Switzerland, at various times of the year. Thecomplexation of Cu by strong ligands in theultrafiltrate and in the conventional filtrate (<0.45 m) was compared using a ligand-exchange/CSV method.The <0.45 m concentrations of Cu (from anaverage of 7 nM to 24 nM), Zn (<5–23 nM), Ni (5–13 nM),Co (1.5–3 nM) and Mn (7–92 nM)increased downstream. The major part of Cu, Zn, Niand Co usually occurred in the ultrafiltratefraction at all sites, whereas Fe and Mn were mostlyin the particulate fraction, under conditions of lowsuspended matter content (< 10 mg L^-1) in theriver. The percentage of metal in the colloidalfraction, with respect to the 0.45-m filtrate,decreased in the order: Cu (median 11%) > Zn Ni(median 5–6%) > Mn Co (median < 5%). DOCalso consisted mostly of molecules in the < 10 kDrange.Cu was strongly complexed by natural organic ligandsin all filtrate and ultrafiltrate samples. A largepart of the strong Cu binding ligands consisted ofcompounds in the < 10 kD range, but colloidalligands with similar properties also occurred. Cu wasdistributed among the dissolved and the colloidalligands, roughly in proportion to organic carbon.The colloidal fraction (as defined here) did notincrease in its proportional amount downstream and wasonly of limited significance in transporting traceelements in the Thur River under low discharge conditions.     

Deglacial palaeoclimate at Puerto del Hambre,subantarctic Patagonia,Chile

The primary objective of this study is to further substantiate multistep climatic forcing of late‐glacial vegetation in southern South America. A secondary objective is to establish the age of deglaciation in Estrecho de Magallanes–Bahía Inútil. Pollen assemblages at 2‐cm intervals in a core of the mire at Puerto del Hambre (53°36′21″S, 70°55′53″W) provide the basis for reconstructing the vegetation and a detailed account of palaeoclimate in subantarctic Patagonia. Chronology over the 262‐cm length of core is regulated by 20 AMS radiocarbon dates between 14 455 and 10 089 ¹⁴C yr BP. Of 13 pollen assemblage zones, the earliest representing the Oldest Dryas chronozone (14 455–13 000 ¹⁴C yr BP) records impoverished steppe with decreasing frequencies and loss of southern beech (Nothofagus). Successive 100‐yr‐long episodes of grass/herbs and of heath (Empetrum/Ericaceae) before 14 000 ¹⁴C yr BP infer deglacial successional communities under a climate of increased continentality prior to the establishment of grass‐dominated steppe. The Bølling–Allerød (13 000–11 000 ¹⁴C yr BP) is characterised by mesic grassland under moderating climate that with abrupt change to heath dominance after 12 000 ¹⁴C yr BP was warmer and not as humid. At the time of the Younger Dryas (11 000–10 000 ¹⁴C yr BP), grass steppe expanded with a return of colder, more humid climate. Later, with gradual warming, communities were invaded by southern beech. The Puerto del Hambre record parallels multistep, deglacial palaeoclimatic sequences reported elsewhere in the Southern Andes and at Taylor Dome in Antarctica. Deglaciation of Estrecho de Magallanes–Bahía Inútil is dated close to 14 455 ¹⁴C yr BP, invalidating earlier dates of between 15 800 and 16 590 ¹⁴C yr BP. Copyright © 2000 John Wiley & Sons, Ltd.     

Molecular indicators for palaeoenvironmental change in a Messinian evaporitic sequence (Vena del Gesso, Italy). II: High-resolution variations in abundances and 13C contents of free and sulphur-bound carbon skeletons in a single marl bed

The extractable organic matter of 10 immature samples from a marl bed of one evaporitic cycle of the Vena del Gesso sediments (Gessoso-solfifera Fm., Messinian, Italy) was analyzed quantitatively for free hydrocarbons and organic sulphur compounds. Nickel boride was used as a desulphurizing agent to recover sulphur-bound lipids from the polar and asphaltene fractions. Carbon isotopic compositions (delta vs PDB) of free hydrocarbons and of S-bound hydrocarbons were also measured. Relationships between these carbon skeletons, precursor biolipids, and the organisms producing them could then be examined. Concentrations of S-bound lipids and free hydrocarbons and their delta values were plotted vs depth in the marl bed and the profiles were interpreted in terms of variations in source organisms, 13 C contents of the carbon source, and environmentally induced changes in isotopic fractionation. The overall range of delta values measured was 24.7%, from -11.6% for a component derived from green sulphur bacteria (Chlorobiaceae) to -36.3% for a lipid derived from purple sulphur bacteria (Chromatiaceae). Deconvolution of mixtures of components deriving from multiple sources (green and purple sulphur bacteria, coccolithophorids, microalgae and higher plants) was sometimes possible because both quantitative and isotopic data were available and because either the free or S-bound pool sometimes appeared to contain material from a single source. Several free n-alkanes and S-bound lipids appeared to be specific products of upper-water-column primary producers (i.e. algae and cyanobacteria). Others derived from anaerobic photoautotrophs and from heterotrophic protozoa (ciliates), which apparently fed partly on Chlorobiaceae. Four groups of n-alkanes produced by algae or cyanobacteria were also recognized based on systematic variations of abundance and isotopic composition with depth. For hydrocarbons probably derived from microalgae, isotopic variations are well correlated with those of total organic carbon. A resistant aliphatic biomacromolecule produced by microalgae is, therefore, probably an important component of the kerogen. These variations reflect changes in the depositional environment and early diagenetic transformations. Changes in the concentrations of S-bound lipids induced by variations in conditions favourable for sulphurization were discriminated from those related to variations in primary producer assemblages. The water column of the lagoonal basin was stratified and photic zone anoxia occurred during the early and middle stages of marl deposition. During the last stage of the marl deposition the stratification collapsed due to a significant shallowing of the water column. Contributions from anaerobic photoautotrophs were apparently associated with variations in depth of the chemocline.     

Assessment of loess as parent material for agroecological potential

Due to its physical and chemical properties, areas with a loess mantle of proper thickness favour arable farming. Loess as a parent material promotes the formation of soils of good structure, nutrient supply and water budget. The ongoing land evaluation project places particular emphasis on the consideration of parent material in its scoring system as soil and climatic parameters are assessed in conjunction with the grain size composition of subsurface material and soil texture.A test area most suitable for the presentation of the method seems to be a sandy alluvial fan with loess mantle and this circumstance allows the contrasting of the agroecological potentials of soils developed on the two parent materials of different nature.The favourable water storage properties of loess make this deposit particularly valuable under the conditions of climatic aridification. The geographical information system applied here is capable of simulating the agroecological potential changes caused by reduced precipitation, increased evaporation and dropping groundwater levels.The research for this paper was carried out as part of the MEDALUS II (Mediterranean Desertification and Land Use) collaborative research project. MEDALUS II was funded by the EC under its Environment Progamme, contract no. EV5V 0128/0166. A grant was also provided by the OTKA (Hungarian National Science Foundation), project no 1278. The support is gratefully acknowledged.     

Spatiotemporal changes in cadmium contamination in the Seine estuary (France)

Cadmium (Cd) is among the major contaminants in the Seine estuary. In the biota, the RNO (Réseau National d’Observation, the French Mussel-Watch) has shown that Cd concentrations in mussels living at the mouth of the estuary are related to changes in inputs to this area of phosphogypsum, a calcium sulphate that is a by-product of the phosphoric acid naturally enriched with Cd. In the water column, Cd concentrations at several key estuary sites show a very marked trend toward decreased contamination in the particles as well as in the dissolved phase. The behavior of Cd in the estuary has been studied between 1991 and 1998 in the framework of the scientific program Seine-Aval. This program has highlighted punctual Cd inputs in the estuarine water column. The partition of Cd between the dissolved and the particulate phase, previously described in various estuaries, is characterized by an intense phenomenon of solubilization in the mixing zone freshwater-seawater, but the colloidal Cd fraction remains low along the whole salinity gradient, about 5% to 10% of the apparent dissolved fraction. Although the decrease of inputs induced a fall of Cd concentrations in the water column, laboratory experiments show that the estuarine particles are far from being exhausted in Cd. Despite continuous efforts to reduce the urban and industrial inputs into the estuarine and coastal waters, the Seine estuary still remains very contaminated by Cd.     

The 2011 submarine volcanic eruption in El Hierro (Canary Islands)

Forty years after the Teneguía Volcano (La Palma, 1971), a submarine eruption took place off the town of La Restinga, south of El Hierro, the smallest and youngest island of the Canarian Archipelago. Precursors allowed an early detection of the event and its approximate location, suggesting it was submarine. Uncertainties derived from insufficient scientific information available to the authorities during the eruption, leading to disproportionate civil protection measures, which had an impact on the island's economy—based primarily on tourism—while residents experienced extra fear and distress.