Phases d'érosion—comblement de la vallée de la Papenoo et volcanisme subrécent à Tahiti,en relation avec l'évolution des iles de la Société (Pacifique Sud)

A detailed mapping and data from borings support the conclusion that there is a late lava flow inside the Papenoo valley, the main valley of Tahiti island. This last volcanic manifestation which took place 400,000 years ago came after the phase of erosion corresponding to the Illinoian glacial period. It is one of the four phases of erosion followed by filling observed in the cross section of the Papenoo valley.     

Sur l'origine et l'âge des levées sédimentaires profondes: Cas du delta sous-marin du Rhône (Méditerranée nord-occidentale)

The interpretation of sedimentological and geochronological results lead us to the conclusion that the sedimentary levees flanking the deep-sea channels of the Rhône deep-sea fan are made up of various kinds of turbidites originating from different coastal areas and were deposited during the Quaternary glacial epochs.     

Sur l'existence d'une topographie antérécifale dans la région de Tuléar (côte sud ouest de Madagascar)

The outline of the Pleistocene coastal geomorphology in the Tuléar area (Madagascar) can be redrawn from the analysis of the setting and characteristics of present-day coral reefs. Initial outer reef tracts, which grew in Tatsimian times (according to Battistini's terminology), followed in their development the river pattern, since they settled upon the divides between valleys instead of growing uniformly on the outer shelf. These primary reef chains coalesced subsequently. Inner reefs and coral banks also followed, although not so closely, the river pattern.     

La “zonale” Biscaye-Labrador: mise en évidence de cisaillements dextres antérieurs à l'ouverture de l'Atlantique Nord

The study of recent geological and geophysical data, collected west of France, allows of delineating a large fracture zone, with a 130° N dextral slip, between Ireland and Aquitaine (France). This zone belongs to a wider structure which extended from Labrador to Spain and which sheared the Caledonian and Hercynian systems before the opening of the North Atlantic.     

Prélèvements systématiques et caractérisation des réflecteurs acoustiques: nouvelle étape dans la compréhension de la géologie de la Méditerranée occidentale

A sampling survey in the Ligurian Sea and north of the Balearic Islands (Mediterranean Sea) brought back samples containing the following elements: (1) lithified Quaternary crust and deep-lying corals; (2) Early Pliocene marls corresponding to reflector level M in some cases; (3) red sediments tentatively assimilated with the Messinian continental equivalent; (4) rocks coming from the basement; (5) volcanic rocks.For the first time, basalts with olivine were discovered in the Algero-Provencal Abyssal Plain.A volcano 500 m high was sampled by dredging north of Minorca.     

Etude de la variabilité des teneurs en Hg,Cu, Zn et Pb de trois espèces de mollusques de l'étang de Berre (France)

The bioaccumulation of Hg, Cu, Zn and Pb ions was studied in three mollusc species at three sites in the Berre lagoon (Marseille, France), which have been selected according to their hydrodynamic conditions. The degree of the contamination of these mollusc populations was calculated in order to determine the levels of the metal ions present. The uptake of metal ions was regularly monitored for two successive years; the causes of the high variability was observed throughout the two years for all the species studied are discussed.     

Distribution et écologie des Méduses (Cnidaria) du golfe de Tunis (Méditerranée sud occidentale)

The Medusae of Tunis Gulf (25 species) are qualitatively the third zooplanktonic group after Tintinnids and Copepods. Anthomedusae (eight species), Trachymedusae (five species) and Leptomedusae (four species) represent the major part among the 20 species of Hydromedusae identified during our study (December 1993–November 1995). However, the Limnomedusae (two species) and the Narcomedusae (one species) are poorly represented. In the Bay of Tunis, Obelia spp., the most common and dominant species, command the quantitative fluctuations of Hydromedusae and reach exceptionally the density of 25 800 ind. m^–3. Within the Scyphomedusae (five species), Pelagia noctiluca is the most common species which outbreaks in winter and autumn. Tunis Gulf seems to be composed of two jellyfish communities; the first one is composed of endogenous species showing a constant period of blooming like Olindias, Cladonema, Aurelia, Cotylorhiza and Rhizostoma and sometimes permanent like Obelia spp. and Clytia spp.; the second is represented by exogenous species considered as “visitors” like Velella, Sminthea or Pelagia whose presence on the coast is dependent on local and particular winds and currents.     

La dispersion des apports de la Gironde sur le plateau continental. Données in situ,satellitales et numériques

Coastal waters are generally a product of mixing between continental and oceanic originated water masses. Near river mouth areas, as in the Gironde estuary, oceanic waters are modified by the influence of freshwater discharge that introduces suspended and dissolved substances, including pollutants. Within PNOC (Programme National d'Oceanographie Côtière) our objective is to determine the extent of the influence of the Gironde estuary on to the Aquitanian continental shelf. Several cruises for collecting hydrological data have been carried out in this area. The data of every cruise were coupled with a NOAA-11 satellite passage. The recorded images have been analysed and were compared with the results given by a 3D mathematical model. The interaction among different dynamical factors (density, wind-driven and tidal circulation) controls the mixing and the transport of low salinity waters.     

Morphologie et sedimentologie de la pente externe de la partie nord du Grand Recif ed Tulear (SW de Madagascar). Nature et repartition des elements organogenes libres. (Morphology and sedimentology of the outer slope of the northern part of the “Grand Recif” of tulear (Madagascar). Nature and distribution of free organic elements.)

The Tuléar area lies on the southwest coast of Madagascar. The Tropic of Capricorn runs across the center of the Bay of Tuléar which is closed by a barrier reef called the “Grand Récif”. Other reef tracts can be found in this bay: fringing reefs, inner reefs, coral islets, coral banks.This paper is the result of a study of the outer side of the area called the “shipwreck sector”, which extends just in front of the city of Tuléar, in the northern part of the Grand Récif. The investigations were made by diving as deep as 50 m and below this depth by dredging down to 150 m. The outer slope consists of several zones, the succession of which forms the elements of a morphological model.The numerical values of sedimentological indices and sedimentary facies were obtained by means of an I.B.M. 360/44 or a C.I.I. computer; they do not vary independently but derive from each other. A sedimentary sequence is defined as a precise succession of facies which continues to be modified during the transfer of sediments inside the sedimentary sequence. The numerical values of the indices of a given facies show coherent variations which point to the evolution of the sediments during their transfer. The successions and relations of different sequences form the sedimentological model. The combination of terms in the morphological and sedimentological models allows the morpho-sedimentary model to be defined. This model can be integrated into one elaborated for the Tuléar area as a whole.Generally, two sequences extend on the outer slope. The first one is the spur and groove sequence that starts with an accumulated facies of gravel in the surf zone. The shifting facies of sands in which a very evolved material is included, mark the transition to the stable facies of accumulation. In this sequence wave action plays a central part. The second sequence is formed by sedimentary deposits of the coral flagstone (deep coral flagstone forward the reef). They are characterized by the presence of free or loose organic elements. These elements derive from calcareous algea. They are chiefly made of rhodolite nodules, rhodolite pseudonodules and Lithothamnion particles mixed with sand very rich in Foraminifera.The nature, distribution and percentage of these elements were studied as a function of the depth where they were found and, therefore, of the distance from the reef front. These free organogenic elements are typical of the outer slope of coral-reef tracts beaten by heavy swells.     

Données géomorphologiques sur la région de Fresh Creek,Ile Andros (Bahama)

A geomorphological study of the east coast of Andros (Fresh Creek area) shows the existence of a paleotopography represented by low-altitude hills (few metres). This paleotopography is protected by the presence of a calcitic Quaternary crust which covers Pleistocene calcarenite.In the western part of the area, there are long woody axes, oriented NE-SW, parallel to the channels of the creek. They end at two kilometres from the coast, along which is a second kind of lower hills, orthogonal to the first.The first axes can be interpreted as megaripples as seen at the present time on modern deposits (on the Great Bahama Bank) and fossilized by the upper crust. The second direction is made by accretion ripples along the coast.The surface of the Bahamian calcarenite has been studied. The Bahamian karst presents two topographical forms: “blue holes” like those outside the island, which are 60–80 m in diameter and both sparse and deep; and “washtub” dolines; these are numerous and shallow, and, from low altitude, exhibit a honeycombed aspect on the surface. This karstic topography with dolines and blue holes is also seen through the water of the Creek the hard bottom of which is covered only here and there with a few centimetres of sediments. Hence, there is a submerged karstic topography, made of the same elements as the aerial karst, but submerged by the Holocene transgression. The present karstic relief, in relation with the different eustatic levels of the Quaternary, has begun 120,000 years ago, according to the isotopic ages, and might be composed by different steps, difficult to show now, in the topography.The blue holes in the interior of the island of young and little evolved karst, were formed more by solution than by collapse of the karstic caves, because of the absence of a real river to drain the Andros shelf at the time of low sea levels. Blue holes of the inside of the island, as they are called, with submarine openings, have the same salinity as the water of the creek (17.5 g/l). The dolines with very low salinity (0.7 g/l to 3.8 g/l) are filled with stromatolites and charophytes, slowly forming sediments made up essentially of high-magnesian calcite.It seems that the Andros Island karst can be compared with that of the Yucatan, where there are round and deep open pits, called cenote, of which the Bahamian equivalent would be the blue holes which were drowned by the Holocene transgression.     

Lamprey (Geotria australis; Agnatha) reddening syndrome in Southland rivers,New Zealand 2011–2013: laboratory findings and epidemiology,including the incidental detection of an atypical Aeromonas salmonicida

From 2011, lamprey (Geotria australis) populations in Southland, New Zealand have been affected by reddening along the length of the body and increased mortalities, termed lamprey reddening syndrome (LRS). Molecular testing, bacteriology, histopathology and epidemiology were used to determine if an infectious agent was present and to increase the understanding of this syndrome. An atypical Aeromonas salmonicida was detected from affected lamprey in 2011. This organism has not previously been reported from New Zealand. Investigative molecular testing indicated the organism was an uncharacterised, unculturable, atypical A. salmonicida and a likely incidental finding. Histopathology did not indicate an infectious process was involved, but suggested the reddening may be due to blunt trauma. Epidemiological investigation found the Mokoreta River had a significantly higher prevalence of LRS than others in the Southland region, but there was no clear reason why. To date, no infectious aetiology for this syndrome has been identified.     

Interactions between tectonics and fluid circulations in an inverted hyper-extended basin: Example of mesozoic carbonate rocks of the western North Pyrenean Zone (Chaînons Béarnais,France)

Interactions between fracturing, fluid circulations and fluid chemistry in hyper-extended margins are still poorly described as most of them are located offshore, buried underneath post-rift sediments. The southern Aquitaine basin and the northern Pyrenees constitute an appropriate case study to investigate these interactions since a model of hyper extended margin with mantle exhumation during the Lower Cretaceous subsequently inverted was recently proposed. From a field study, we here describe three main sets of fractures (set 1 to set 3). They are correlated with main stages of the geodynamic evolution of the basin corresponding to the Liassic rifting, the Aptian-Cenomanian hyper-extension, and the Pyrenean compression. Petrographic observations, Raman and micro-thermometry analysis on fluid inclusions, ICP-MS, and isotope analysis permitted to determine chemistries, temperatures, redox conditions, gas compositions, oxygen and carbon isotopic signatures, and REE contents of parent fluids for cements precipitated during each episode. In particular saddle dolomite and chlorite precipitated in set 2 fractures during the hyper-extension corresponding to the thermal peak at temperatures higher than 300 °C. The isotopic signature, the high CO₂ content, the occurrence of H₂S and the high salinity of parent fluids suggest ascending magmatic fluids percolating across Triassic evaporites. The late and post hyper-extensional phase is characterized by hydraulic brecciation in dolomitic formations, a decrease in temperature and salinity, a decrease in magmatic contribution in parent fluids, a closing of the diagenetic system during burial and a switch to reducing conditions during the precipitation of quartz, pyrite and calcite. The Pyrenean compressive phase associated with the third fracturing stage induced a reopening of the diagenetic system and favored a return to oxidizing conditions and infiltrations of meteoric fluids.