Migration de la truite lacustre (Salmo trutta lacustris L.) dans le Léman et ses affluents

A total of 2588 adult migratory brown trout (Salmo trutta lacustris) have been tagged from 1964 to 1974 on their spawning sites, in tributaries of the western part of Lake Geneva (Switzerland). Most of the fish (96.2%) recaptured during spawning seasons in the following years have been found in the same river where they had previously been caught. Most tagged fish recaptured by fishermen were found in the western part of the Lake, near their home rivers. This tendency is very strong in autumn and winter. It still remains highly significant in spring and summer.

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Dédié à Wolfgang Geiger     

A highly reflective low cost backscattering target

A low cost biplanar reflector target has been developed and used in a system performance test of a near surface omnidirectional source and receiver. The target was constructed from sheets of closed cell plastic bubble sheeting. Theoretically, this material should have very high reflectance characteristics, and this was demonstrated by the experiment. The strongly reflecting target was located at the sea surface, and allowed the interpretation of data as the ship passed through a range of azimuthal angles. The higher than expected backscatter from the target was presumed to be due to the bubble sheeting behaving as a coherent reflector, like a thin layer of air, rather than an ensemble of individually resonating bubbles. This was verified by the data analysis. Lloyd's mirror effects were strong, because practically all of the return signals from the 10-ms continuous wave pulses were overlapping. The target strength (TS) of the reflector was strongly reduced at ranges over 100 m. The experiment shows that studies of the statistical distribution of fish school TS must consider the effects of Lloyd's mirror     

Thermoremanence in red sandstone clasts and emplacement temperature of a quaternary pyroclastic deposit (Catalan Volcanic Zone,ne Spain)

Summary The application of the progressive thermal demagnetization procedure of volcanic rock debris has been frequently used to determine the emplacement temperatures of pyroclastic deposits and thus to characterize the nature of these volcanic deposits. This debris consists of a mixture of juvenile fragments derived from the explosive fragmentation of erupting magma and an assortment of lithic clasts derived mainly from the walls of a volcanic conduit, as well as from the ground. The temperature at which the clasts were deposited can be estimated by analyzing its remanent magnetization. To do this, oriented samples of clasts are subjected to progressive thermal demagnetization and the directions of the resulting remanent vectors provide the necessary information. Clasts of basalt, andesite, limestone, pumice and homebricks have previously been used to estimate the emplacement temperatures of pyroclastic deposits. According to our data, clasts of red sandstones also seem to be good carriers of thermoremanent magnetization. We have carried out a paleomagnetic study on a Quaternary, lithic-rich, massive, pyroclastic deposit from the Puig d'Adri volcano (Catalan Volcanic Zone), which contains a large number of red sandstone clasts. It is concluded that the studied deposit cannot be considered as a lahar or as a pyroclastic surge deposit, considering both the emplacement temperature and the morphological features.Presented at 3rd Biennial Meeting on New Trends in Geomagnetism, Smolenice Castle, West Slovakia, June 22–29, 1992     

Charriage crustal,anatexie et decrochements ductiles dans les Maures orientales (Var,France) au cours de l'orogenese varisque

The kinematics of the deformational events recorded in the catazonal gneisses within the eastern part of the Maures massif (Variscan basement of Provence, southeastern France) has been established. These events can be correlated with both the metamorphic and the magmatic evolution, and the orogenic history of the eastern Maures then consists of the following stages:

1. -HP-metamorphism preserved only in relict eclogites and quartzites rich in calc-silicates,
2. -Catazonal metamorphism involving anatectic melting, broadly contemporaneous with large-scale horizontal transport towards the NNE. During this event, the lithologic units were disrupted and intensively mylonitized.
3. -Intrusion of a first generation of anatectic granitoids.
4. -A second tectonic event under epi-to mesozonal metamorphism conditions is responsible for the northward displacement of the eastern Maures relative to the western part along a sinistral strike-slip fault 4 km wide (Ramatuelle — Plan de la Tour fault) in which the early anatectic granitoids have been mylonitized. Outside the fault zone, this event is marked by upright to W-vergent open folds trending N-S, i.e. parallel to the transport direction.
5. -A moderate cataclastic reactivation of the Ramatuelle — Plan de la Tour fault with a dextral sense of shear, locally accompanied in the eastern part of the area by minor lowtemperature thrusting towards the south.
6. -Intrusion of a second generation of anatectic granites about 320 Ma ago.

The metamorphic, magmatic and tectonic evolution of the eastern Maures suggests a continuous orogenic history in an area of rapid crustal thickening by large-scale thrusting within the continental crust. This evolution may be related to the development of continental subduction during the continent/continent collision responsible for the Variscan orogeny in southern Europe.     

Age et croissance de la truite lacustre (Salmo trutta lacustris L.) du Léman

The age and growth of adult Lake Geneva trout (Salmo trutta lacustris L.) caught from 1964 to 1974 for mark-and-recapture experiments was studied by scale analysis. The median lengths of 3 years and older fish were fitted to Von Bertalanffy growth curves. Their growth rates are higher than those of the fish younger than 3 years. It is conculded that this increase of growth rate concides with beginning of life in the lake, after the downstream migration of the juvenile trout which probably takes place in the second and third summer. No general increase of growth rates between cohorts could be detected from the beginning to the end of the period studied, in spite of a serious increase of eutrophication of Lake Geneva during the same time.      

La Morte du Sauget,un ancien méandre du Rhône: bilan hydrologique et biogéochimique

The ‘Morte du Sauget’, a typical oxbow-lake in process of eutrophication and encroachment, is located in the alluvial plain of the French Upper Rhône River. Studies during 1983 have shown that, although the ‘Morte du Sauget’ is seasonally inundated by the Rhône, the impact of flooding is only temporary and is minimized by the biological activity of the waters and sediments of this system.     

Régime alimentaire des alevins de Gardons (Rutilus rutilus (L.)) dans un port du lac Léman. Comparison avec la nourriture disponible

In order to determine the food preferences of young roach, gut contents of roach fry (Rutilus rutilus (L.)) were compared with the evolution of the zooplankton community in a littoral area of Lake Geneva during June and July 1985. The food of roach fry up the age of 30 d (10–15 mm standard length) was mainly small Rotifers with some Chronomid larvae. Thereafter, Chironomid larvae constitute the major part of the diet until the fry leave the littoral zone at the age of about 45 d (15–23 mm). The relevance of classical food preference analysis is critically discussed in view of the heterogeneous spatial distribution of invertebrates observed.      

Genèse des magmas du volcanisme plio-quaternaire des Apennins

Zusammenfassung Nach einer kurzen Übersicht des Vulkanismus in der Gegend des heutigen Appeninns im oberen Jura (basischer Vulkanismus im Tiefseegraben) und im Eozän (kalkalkaliner Vulkanismus während der Tektogenese) wird der pliozäne und quartäre, durch anatektische Magmen gespeiste Vulkanismus des unter Dehnung stehenden Orogens ausführlicher behandelt. Dieser Vulkanismus äußerte sich auf der thyrrhenischen Seite des Appennins zwischen dem Arno und dem Tiber im Zusammenhang mit dem Hochdringen mehrerer kleiner Granitstöcke, deren ältester 7 Millionen Jahre alt ist, während das Alter des jüngsten nur 3 1/2 Millionen Jahre beträgt. Der Beweis wird erbracht, daß es sich um anatektische Magmen handelt, und die mutmaßliche Ursache der unvollständigen Anatexis und der Differentiation der durch diese entstandenen Magmen besprochen. Eine Hypothese zur Erklärung der Entstehung von kalireichen, femischen Differentiaten wird vorgeschlagen. Danach wird, unter Berücksichtigung der quantitativen Beziehungen der einzelnen Magmatypen, ein Gesamtbild des aktiven Vulkanismus entworfen, der gesättigte und untersättigte kalireiche Magmen längs einer 300 km langen Zone vom nördlichen Latium bis zum Vesuv förderte. Es folgt eine Diskussion über das Problem des Stammagmas dieses Vulkanismus und der dazu vorgeschlagenen Hypothesen. Geologische, magmatologische und geochemische Tatsachen machen es wahrscheinlich, daß die mediterranen Magmatypen durch eine komplexe Differentation eines tief liegenden, anatektischen Magmas entstanden sind. Zum Schluß wird der Versuch unternommen, die Entstehung und Evolution der Magmen der periappenninischen Vulkane der Insel Capraia (Toskanischer Archipel), der Pontinischen Inseln und des einzigen, östlich vom Appennin liegenden Vulkans des Monte Vulture zu erklären.

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After a short survey of the volcanic activity around the chain of the Apennines during the upper Jurassic (basic and submarine ophiolitic volcanism) and during the Eocene (calc-alkaline volcanism of the early tectonic stages), a more detailed picture of plio-quaternary volcanism derived from anatectic magma during the distensive stage of orogenesis is given. This volcanic activity has taken place on the tyrrhenian side of the Apennines between the Arno and Tiber rivers and is connected with the uplift of some little granitic stocks, ranging between 7 m. y. and 3,5 m. y. Some arguments on the anatectic origin of magma, on its differentiation and on the possible causes of the incomplete anatexis are reported. An hypothesis is proposed to explain the genesis of some highly mafic and alkaline differenciates. A general picture is also given of the volcanic activity derived from saturated or undersaturated alkaline magma, along a zone of 300 km from northern Latium to Vesuvius. The parental magma origin of this volcanism and the several hypotheses regarding this problem are discussed. The geological, magmatological and geochemical data make probable the hypothesis that the mediterranean volcanic rocks were produced by a complex mechanism of differentiation of a deep-seated anatectic magma. Finally, some hypotheses on the origin and the evolution of magmas of the periapenninian volcanoes are given (Capraia and Pontine islands, and M. Vulture, the latter being the only recent volcano localized on the eastern side of the Apennines).

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Résumé Après une vue d'ensemble de l'activité volcanique dans la région de la chaîne des Apennins à la fin du Jurassique (volcanisme basique sousmarin) et au cours de l'Eocène (volcanisme alcali-calcique [calco-alcalin] pendant la tectogénèse), le volcanisme Pliocène et Quaternaire, nourri par des magmas anatectiques pendant le stade distensive de l'orogénèse est traité. Ce volcanisme du côté tyrrhénien de l'Apennin, entre l'Arno et le Tibre, est lié à la mise en place de plusieurs petits stocks granitiques, dont le plus vieux a 7 millions d'années, le plus récent n'en a que 3 1/2 millions.Il est prouvé que ce sont des magmas anatectiques; la raison pour l'anatexie régionale, la différenciation des magmas est traité. Une hypothèse qui pourrait expliquer l'origine des roches fémiques et potassiques est donné.Une vue plus générale du volcanisme actif, produisant des magmas potassiques saturés et sous-saturés le long d'une zone de 300 km du nord du Latium au Vsesuve est donné, bien regardant les relations quantitatives entre les types différents de magma. Le problème du magma primaire de cette activité volcanique et plusieurs hypothèses sont discutés. Des raisons géologiques, magmatologiques et géochimiques font supposer que les types de magma méditerrané sont dérivés par différenciation d'un magma d'anatexie resté en profondeur. Reste enfin à expliquer l'origine et l'évolution des magmas trouvés dans les volcans périapennins de l'île Capraia (Archipel Toscan), des îles Pontiennes et du Monte Vulture, seul volcan du côté oriental de la chaîne des Apennins.

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L'événement intraviséen dans la zone moldanubienne de la chaîne varisque d'Europe: les données des formations volcano-sédimentaires dévono-dinantiennes du Massif Central Français,des Vosges du Sud (France) et de la Forêt Noire (R.F.A.)

Resumé L'existence d'une phase tectonique intraviséenne dans la chaîne varisque d'Europe a été admise par divers auteurs. Le présent travail apporte des précisions sur la nature de cet événement dans le Nord du Massif Central, les Vosges et la Forêt Noire, c'est à dire dans la zone interne varisque. Des données nouvelles concernent les Vosges et la Forêt Noire. Dans le domaine étudié, cet événement géodynamique n'est pas phcatif et se caractérise par une période d'instabilité au cours du Viséen supérieur qui conduit à d'importants phénomènes de resédimentation, résultats de l'érosion de paléoreliefs. Cette période d'instabilité se prolonge au cours du Viséen supérieur où une emersion généralisée se produit dans la zone moldanubienne. Dans les zones externes septentrionales, la déformation synmétamorphique qui se déplace vers l'extérieur de la chaîne est contemporaine de cet événement. Dans le massif armoricain (zone externe), il se traduit par des mouvements décrochants. Cet événement s'explique par un épaississement crustal, conséquence directe de la collision varisque et se traduit par un soulèvement qui précède la phase de déformation paroxysmale d'âge tardi-viséen et carbonifère supérieur.

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The existence of an Intravisean tectonic phase in the variscan belt of Europe is admitted by some authors. The present work specifies the characteristics of such an event in the northern part of the French Massif Central, in the Vosges mountains and in the Black Forest, i.e. in the internal variscan zone. New data are given for the Vosges and the Black Forest. In the considered domain the geodynamic event does not have a folding effect. It leads to a period of instability during Late Visean, inducing important resedimentation processes as a result of erosion of the paleoreliefs. A generalized emersion of the Moldanubian Zone occurs at the same time. This event coincides with the migration toward the North of the syn-metamorphic deformation in the extern parts of the belt. In the Armorican Massif (external zone) strike slip faults are active during the same period. That event can be explained by the crustal thickening resulting from the variscan collision. The uplift preceds the paroxysmal Late Visean and Upper Carboniferous tectonic phase.

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Zusammenfassung Verschiedene Autoren vertreten die Meinung, daß das mitteleuropäische Variszikum innerhalb des Visé von einer tektonischen Phase betroffen wurde. Die gegenwärtige Arbeit soll eine genauere Vorstellung von den Ereignissen geben, welche sich um diese Zeit im nördlichen Zentralmassiv, den Vogesen und dem Schwarzwald abspielten. Innerhalb des angeführten Bereiches läßt sich nirgends eine Faltung beobachten. Es handelt sich vielmehr um ein geodynarmsches Ereignis, welches sich im obereren Visé als eine Periode der Instabilität mit sehr beachtlichen Erosionen einerseits und ebenso bedeutenden Resedimentationen andererseits äußert. Diese Zeit der Instabilität mündet noch im Laufe des obersten Visé in einer allgemeinen Heraushebung des Moldanubikums. Das Intra-Visé Ereignis ist zeitgleich mit der nordwärtigen Wanderung der synmetamorphen Deformation in den externen Zonen. Im armorikanischen Massiv fällt es anscheinend mit bedeutenden Blattverschiebungen zusammen. Offensichtlich steht hinter den Vorgängen als Ursache eine relativ plötzliche Krustenverdickung im Zusammenhang mit der variszischen Kollision. Die Heraushebung geht der paroxysmalen Deformation im späten Visé bzw. frühen Oberkarbon voraus.

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Structure et fonctionnement des écosystèmes du haut Rhône français. VII. Le complexe hydrographique de la Lône des Pêcheurs (un ancien méandre du Rhône)

The hydrological analysis of one of the old meanders of the french upper Rhône, called the ‘Lône des Pêcheurs’, is carried out from September 1976 to November 1977. The principal components analysis of the physico-chemical characteristics of the water shows an ecological tripartition along the longitudinal axe of the ‘lône’, according to the mixing processus of two types of waters, the one influenced by the lateral underflow, the other flowing in from the Rhône, and related with the overflow. Partitional analogies are also noted between the structure of phytoplanctonic community and the hydrological environment.