Magma and hydrothermally driven sector collapses: The 3100 and 11,500 y. B.P. eruptions of la Grande Decouverte (la Soufrière) volcano, Guadeloupe, French West Indies

We recently reported (Boudon et al., 1984) on an eruption similar to that of May 18, 1980 at Mount St. Helens, that took place about 3100 years ago at la Soufrière, Guadeloupe. During the course of detailed geological mapping of the deposits of this event, older debris flow and blast deposits were recognized in the northern sector of the mapped area. Uncarbonized wood fragments in the debris flow have yielded ages ca. 11,500 y. B.P. The deposits extend from an amphitheater crater westward to the caribbean shore about 10 km downslope from the volcano. The deposits and crater structure suggest that they are the result of catastrophic flank failure like the event 3100 years ago. Unlike the latter activity, however, no magmatic component is found in the deposits.     

Mean turbulent properties of the stable boundary layer observed during the “coast” experiment

An acoustic Doppler sounder has been used to document the behaviour of the stable atmospheric boundary layer during the “Coast” experiment, in April-May, 1983, on a homogeneous terrain near the Dutch coast. It has been shown that kaimal's model of the spectrum of velocity in the stable surface layer can be applied and that surface-layer parameterization can be used in the whole stable surface layer. Velocity spectra have been computed between .0005 c.p.s. and .1 c.p.s. and for the stability range for z/L between 0 and 10. It is to be noted that the information has been obtained using only sodar data.     

Determination de Huit Terres Rares Dans L'Echantillon Geaochimique de Reafearence NBS 88a par Activation Neutronique Instrumentale

Les teneurs de huit éléments des terres rares (La, Ce, Nd, Sm, Eu, Tb, Yb, Lu) sont déterminées par l'analyse par l'activation neutronique instrumentale sur l'Echantillon Géochimique de Référence NBS 88a. Ces teneurs proviennent de la moyenne arithmétique de dix analyses de NBS 88a. Elles se comparent bien avec d'autres déterminations de ces éléments publiées dans la littérature. Dans la limite de la précision analytique, NBS 88a paraît homogène en ce qui concerne les terres rares.     

Evolution géochimique par dégradation et agradation des minéraux argileux dans l'hydrosphère

Résumé Les dégradations des minéraux argileux sont fréquentes dans les altérations. Elles comportent une évolution des réseaux cristallins depuis les micas et chlorites jusqu'aux minéraux ouverts comme les vermiculites et les montmorillonites par l'intermédiaire d'édifices interstratifiés. Les agradations constituent le mécanisme réciproque et sont fréquentes dans la sédimentation et la diagenèse. Elles régénèrent par cicatrisation, construction et croissance, les phyllites caractéristiques du prémétamorphisme: illite et chlorite. Ces transformations minérales dépendant des milieux naturels sont un chapitre important de la Géochimie des silicates de l'Hydrosphère.

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The clay mineral degradations are frequent during weathering. They involve an evolution of the crystal lattices, from the micas and the chlorites to the open-minerals, through the mixed-layers. The aggradations constitute the reciprocal mechanism and they are frequent during sedimentation and diagenesis. Through cicatrization, construction and growth, they regenerate the phyllites typical of premetamorphism: illite and chlorite. These mineral transformations, subject to the natural environments, are an important chapter of the Geochemistry of Hydrosphere silicates.

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Zusammenfassung Während der Verwitterungen kommt oft ein Abbau der Tonminerale vor, der sich durch die Entwicklung des Gitters von Glimmer und Chlorit, über ein Zwischenstadium von Wechsellagertonen, zu offenen Mineralen wie Vermiculit und Montmorillonit kennzeichnet. Der entgegengesetzte Vorgang spielt sich in dem, in Ablagerung und Diagenese häufigen Aufbau ab. So werden die charakteristischen Phyllosilikate der Vormetamorphose: Illit und Chlorit, durch Vernarbung, Aufbau und Anwachsen der Gitter wieder hergestellt. Diese Veränderungen, die von den Bedingungen der natürlichen Milieus abhängen, stellen ein wichtiges Kapitel der Geochemie der Hydrosphärensilikate dar.

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From the regulation of space to the space of regulation

For about ten years, economic geography has enjoyed a renewal. Many researchers have found anchorage in different theoretical currents in order to analyse current economic changes. Regulation theory has been particularly inspirational in these considerations. This article represents a balance between different axes of research in regional economics, and their encounters with regulationist ideas. The main schools of thought are presented in chronological order with the prominent actors and the research results underlining the principal elements from each school. Finally, some prospects for the future are outlined. This revised version was published online in July 2006 with corrections to the Cover Date.     

Barium and strontium uptake into larval protoconchs and statoliths of the marine neogastropod Kelletia kelletii

The trace elemental composition of calcified larval hard parts may serve as useful tags of natal origin for invertebrate population studies. We examine whether the trace metal barium (Ba) deposits into the calcium carbonate matrix of molluscan larval statolith and protoconch in proportion to seawater Ba concentration at two temperatures (11.5 and 17°C). We also examine strontium (Sr) uptake as a function of temperature. Using encapsulated larvae of the marine gastropod, Kelletia kelletii, reared in the laboratory under controlled conditions, we demonstrate a significant inverse effect of temperature and a positive effect of seawater Ba/Ca ratio on Ba incorporation into larval carbonates. Ba/Ca partition coefficients (D_Ba) in protoconch were 1.13 at 11.4°C and 0.88 at 17.1°C, while D_Ba in larval statolith measured 1.58 at 11.4°C and 1.29 at 17.1°C. Strontium incorporation into statoliths is also inversely affected by temperature, but there was a significant positive effect of temperature on Sr incorporation into protoconch. These data suggest larval statoliths and protoconchs can meaningfully record variation in seawater physical and chemical properties, and, hence, have potential as natural tags of natal origin.     

The seismological picture of the inner core: structure and rotation

This paper presents a review of recent results concerning the structure and the rotation of the inner core, as inferred from seismological observations. We first focus on the apparent hemispherical pattern of the inner core structure, observed in both the anisotropy and the heterogeneity of the uppermost layers, whereas isotropic velocities seem to be homogeneous in a broad wavelength domain. Then we present results on the radial variations of the attenuation and its possible anisotropy, for which viscoelasticity and wave scattering provide complementary explanations. Linked to these results is a discussion about the detection of the PKJKP phase, which propagates as S-wave inside the inner core. Finally, the seismological observations of a possible inner core rotation are discussed; recent results seem to favour rotation rates below 0.2° yr^?1.     

Gymnospermes s.l. du Jurassique supérieur du massif Manamana,Sud-Ouest de Madagascar: une nouvelle paléoflore gondwanienne

Fossil plants from Upper Jurassic sediments belonging to the Gymnosperms s.l. have been studied in the Manamana massif from the southwestern part of Madagascar. The levels are Upper Oxfordian in age on the basis of the palaeontological content, especially with ammonites. The majority of fossil plants are devoided of organic matter but in some cases collodion peels have been made to present epidermal characters. The cuticle of Brachyphyllum madagascariense nov. sp. has been observed with scanning electron microscope (SEM). This new flora is constituted by Pteridospermales and Coniferales. Fragmentary fronds of Pteridospermales have been collected of Pachypteris sp. A and Pachypteris sp. B. Some epidermal characters are described. Coniferales are represented by leafy stems. The diagnosis of Brachyphyllum madagascariense nov. sp. is given with morphological and epidermal characters. Others conifers have been determined: Brachyphyllum sp. A, Brachyphyllum sp. B, Elatocladus sp., Cupressinocladus sp., Cyparissidium sp.. Araucarites sp. remains are probably isolated fertile scales of a female cone. Complete cones of Conites sp. are also present.Comparisons of the systematic composition are made with other Gondwana floras of the same age from Antarctica, South America, Madagascar, India, South Africa, New Zealand and Australia. This flora shows xerophytic adaptations. With the Filicales described by Appert (1973a, b) from the same localities, it is now the most diverse flora from the Upper Jurassic of Madagascar, despite the lack of Cycadales, Bennettitales and Angiosperms.