Rayleigh-wave phase velocities in French Polynesia

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Rayleigh-wave phase velocities are investigated in the period range 17–100 s by the two-station method over several paths covering most of French Polynesia. Our results confirm the validity of theoretical models obtained through regionalization of data pertaining to longer paths. They also exhibit a 2–3.5 per cent anisotropy, with the axis of maximum velocity oriented in the direction of spreading of the plate. Part of this anisotropy is, however, due to the presence of the Tuamotu archipelago; when this is removed, the remaining anisotropy (about 1.5 per cent) correlates with the present direction of spreading, indicating that a relaxation of the anisotropy has taken place since the East Pacific ridge jump. Finally, the presence of the Tuamotu Islands explains anomalous waveshapes for surface waves travelling in their vicinity, due to multipathing through their faster structure.     

The Amsterdam-St. Paul volcanic province,and the formation of low Al tholeiitic andesites

The island of St. Paul in the Indian Ocean is located on the axis of the southeastern branch of the Indian Ocean Rise, as is the similar volcano of Amsterdam, 80 km to the north. Both volcanoes and possibly part of the local ridge are formed of a high-alumina plagioclase tholeiite making this a distinctive volcanic province. Lavas with Al₂O₂ contents of 12 to 22% are directly related by plagioclase fractionation. Residual rocks are a distinctive low silica, low alumina, potassic andesite with andesine and even olligoclase feldspar. Parallel lines of evolution exist in the sea floor plagioclase tholeiites, which differ only in slightly lower tenor of Sr and potassium group elements, and in the Steens Mountain tholeiites of Oregon, which differ in their significantly higher Sr and K group elements     

MORPHOLOGIES OF IRON CRYSTALS FROM THE HAVERÖ METEORITE

Studies of unpolished chips of the Haverö meteorite using the scanning electron microscope (SEM) and the electron microprobe (EMP), show two types of metallic iron particles: A, discrete convex globules of 5 to 50 microns made up of lamellae and interlocked grains, evenly interspersed among the matrix; B, flattened contorted crystals, less than one micron, lining the iron globules and cavities in the silicates or forming rounded spiny bodies. This second type of iron is interpreted, according to the current theory, as resulting from the in situ reduction of iron-magnesium silicates     

Biogéographie des ammonites jurassiques et reconstitution palinspastique de la Téthys

Résumé

— La distribution géographique des ammonites jurassiques est régie par deux causes fondamentales : l’écologie et l’histoire évolutive (événements vicariants). L’analyse conjointe de ces deux facteurs permet de reconnaître : d’une part des taxons dont la distribution est essentiellement contrôlée par des contraintes écologiques (Phylloce-ratinae et Lytoceratinae, liés à des environnements océaniques profonds; Clydoniceratidae et Proplanulitinae liés à des plates-formes assez superficielles); d’autre part des taxons dont l’histoire évolutive est associée à des événements vicariants (Ammonitina liasiques euro-boréales et Cardioceratidae-Kosmoceratidae boréaux du Jurassique moyen).

Les exemples développés ici permettent d’analyser en terme de paléobiogéographie la position de l’Europe centro-méridionale (Bulgarie, Hongrie, Roumanie) incluse au Jurassique dans la bordure nord-téthy-sienne. Il est montré que Phylloceratinae et Lytoceratinae sont très abondants dans les régions supposées profondes à cette époque (sphéno-chasme des monts d’Apuseni, sillon Dobrogeo-Caucasien), alors qu’elles sont très rares sur la plate-forme moësienne. La même remarque est valable pour les plates-formes moyennes-orientales de la marge sud (Israël, Arabie Saoudite).

Lorsque l’on tente d’établir des reconstructions palinspastiques basées sur la paléobiogéographie, on constate que les taxons qui ont une histoire évolutive originale fournissent de meilleures informations paléogéographiques que les formes ubiquistes ou celles à préférences écologiques accusées. Les données brutes de répartition des faunes d’ammonites ne sont donc pas des arguments absolus pour corroborer les reconstructions. Les analyses fauniques, conduites avec une approche qualitative et quantitative, doivent tenir compte de données extra-biologiques telles que la distribution des faciès et des unités structurales; enfin, le niveau d’intervention — local, régional, global — conditionne fortement les possibilités d’interprétation des résultats.     

Twenty years of Belgian North Sea aerial surveillance: a quantitative analysis of results confirms effectiveness of international oil pollution legislation

Over the years many policy measures have been taken to prevent illegal oil discharges from ships, like the MARPOL 73/78 Convention (1983) and the Bonn Agreement (1969/1983). However, the number of discharges remained high, leading to chronic oiling of seabirds and sensitive coastlines, therefore further measures were taken. The aim of this study is to quantify the effectiveness of two key legislative regulations: the IMO-designation of the North Sea as MARPOL Special Area which took effect in 1999, and the adoption of the EU Directive on Port Reception Facilities in 2000. Under study is the heavily navigated Belgian Surveillance Area, monitored since 1991, characterised by shallow waters with ecologically important sandbanks. The aerial surveillance data from 1991 to 2010 show a stepwise decrease in ship-source oil pollution. Three time periods can be distinguished with two turning points coinciding with the actual implementation of these key legislative measures, confirming their effectiveness.     

Sur lesStaurastrum du lac Léman

Among the Desmids which have been observed in the plankton of the lake of Geneva, organisms having 4 processes have been discovered. Their frequency in the water samples and the results of in vitro studies on their progeny when cultivated in several environmental conditions, allow us to consider these organisms as a form ofStaurastrum sebaldi. The triradiate organisms have been incorrectly named and one must now consider three different species.      

Deep-sea submersible survey in the Suruga, Sagami and Japan Trenches: preliminary results of the 1985 Kaiko cruise, Leg 2

Nine submersible dives were made in three trenches off central Japan, between 2990 and 5900 m of water depth. Our observations confirm the interpretation that Daiichi-Kashima Seamount is a Cretaceous guyot formed on the Pacific plate that has traveled into the Japan Trench. We also confirmed the previous interpretation of a large normal fault that splits the seamount in two halves, the lower one being now subducting beneath the Japan margin. Compressional deformation was identified within the lower part of the inner slope in front of the seamount. The pattern of deformation that affects Quaternary sediments is in agreement with the present kinematics of the convergence between the Pacific plate and Japan. Deep-water (5700 m) clam colonies are associated with advection of fluids, driven by the subduction-related overpressures. In the northern slope of the Boso Canyon, along the Sagami Trough system (Philippine Sea plate-Japan boundary), the deformation affecting a thick upper Miocene to lower Pliocene sequence indicates two directions of shortening: a N175°E direction which is consistent with the present relative motion along the Sagami Trough (N285–N300°E) and a N30°E direction which could be related to a more northerly direction of convergence that occured during the early Quaternary and earlier.     

Role of suspended sediments on the distribution of PCB in the Seine Estuary (France)

PCB (polychlorinated biphenyls) contamination and its relationship to SPM (suspended particulate material) have been studied in the Seine Estuary, which is heavily polluted by these persistent and hydrophobic man-made chemicals. Two sampling cruises have been performed during different freshwater discharge conditions. PCB and SPM concentrations, as well as grain-size distributions in the particulate material have been determined. Water samples have been collected at fixed positions during a tidal cycle, and along transects within the estuary.PCB concentrations vary from 2 ng 1⁻¹ in the marine zone to 250 ng 1⁻¹ within the estuary, and reach 1.3 × 10³ ng 1⁻¹ in the turbidity maximum zone. During a tidal cycle, low PCB concentrations are observed at high water, and are in the same range in February as in July. High PCB contamination is observed at low water, but PCB concentrations are about five times higher in February. SPM and PCB variations are well correlated in both periods of observations. Higher PCB contamination during February is explained by higher SPM inputs, mainly due to particles of riverine origin. The transport of PCB within the estuary depends on the quantity and the grainsize composition of suspended material, which varies according to freshwater discharge and tidal amplitude.