Anne-Marie Bodergat

Distribution of Recent Ostracoda in Ise and Mikawa Bays, Pacific Coast of Central Japan

The relationship between shallow marine environments and ostracod species in Ise and Mikawa Bays on the Pacific coast of central Japan is discussed on the basis of 28 surface sediment samples collected in summer, 1984. The distribution of benthonic ostracod species is influenced by various parameters of the marine environment. Among them the salinity and the distribution of sediment materials are especially important elements that strongly characterize habitats of benthonic organisms in the bay. In this study the distribution of the main ostracod associations is also considered in relation to several other environmental parameters. Particular attention is paid to the effects of water pollution on the environment and the ostracod fauna, since the bay areas we investigated are located close to large industrial cities.

Chemical composition of Leptocythere psammophila (Crustacea: Ostracoda) as influenced by winter metabolism and summer supplies

Leptocythere psammophila is well known for the ecophenotypic variations of the ornamentation of its carapace. To test the respective influences of the environmental parameters on its ornamentation, 41 living specimens were collected in the Baltic Sea, the North Sea and in the English Channel during spring, summer and winter (April 1987, September and December 1988). The carbonate carapaces of these specimens were analyzed by means of electron microprobe. Thirteen elements were detected. Statistical comparisons of means and variances were performed using classical F and t-tests. Data were submitted to Normalized Principal Component Analysis and Discriminant Analysis. There are no significant differences between chemical composition of the carapaces from the different stations. However, the variability of Baltic Sea specimens is lower than that of other stations. Nonetheless, strong and significant differences appear when samples are gathered by season. The chemical composition of summer individuals is controlled by variations in water salinity and in fine grain terrigenous sediment supply. The composition of winter samples is related to the incorporation of Mg. In the case of spring specimens, both these factors have to be considered. Discriminant analysis between winter and non-winter samples sets correctly 84% of the individuals. The wrongly classified specimens are interpreted as ostracods that did not molt during the season of sampling. By attributing them to their possible season of molting, the result of the Normalized Principal Component Analysis improves. Differences in ornamentation are slight. They occur between the samples from the Baltic Sea and those from the other stations. The former have larger and less numerous punctations and lack the smooth surface in the anteroventral part of the carapace. The punctation diameter is more variable during summer than during spring. In the range of environments investigated, ornamentation of the carapace of L. psammophila seems unaffected by the seasonal environmental variations whereas its composition exhibits strong differences.

Tide versus eutrophication. Impact on ostracods populations structure of Mikawa Bay (Japan)

Abstract In Mikawa Bay where red tides blooms occur during summer, eutrophication is a very well known process. We examine its effects on distribution of recent ostracods populations. Two synthetic parameters are analyzed : abundance and species diversity. We are able to discriminate two main groups of stations : a correspondence and a cluster analysis allow us to constitute three classes containing both species and stations. Typical open marine species are located near the mouth of the bay and the brackish ones in the inner part of the bay. Influence of tidal currents is evident in the deepest part of the bay. Effects of cutrophication process could occur in the inner part of the bay. Nevertheless it does not seem to be the main factor that controls the structure of the ostracodes population.

Signification écologique des associations d'ostracodes de la coupe de Kritika (Pliocène supérieur, Rhodes, Grèce)

Resume Les populations dostracodes ont ete etudiees dans 19 prelevements effectues dans la serie lithologique a caractere marin du Pliocene superieur de la coupe de Kritika (Ile de Rhodes, Grece). 124 especes dostracodes appartenant a 44 genres ont ete reconnues. Les associations de ces especes revelent deux milieux de vie : le premier (50–100 m) a la base fait partie de letage circalittoral, le deuxieme (5–25 m) appartient a letage infralittoral. Les pourcentages de chacune des especes sont compares dans les differents prelevements, ainsi que les indices biocoenotiques (richesse specifique, abondance, taux de renouvellement et equitabilite). A la base de la coupe, Costa edwardsii et Bosquetina rhodiensis dominent nettement. Les indices biocoenotiques indiquent un biotope dont les conditions denvironnement sont stables. Le facteur principal de lanalyse des correspondances binaires oppose ces echantillons a ceux dans lesquels ces deux especes sont absentes. En effet, a partir dun niveau a terriers, C. edwarsii et B. rhodiensis disparaissent et le renouvellement faunistique est de 100 % ; ceci traduit de nouvelles conditions denvironnement destabilisees ulterieurement, puis interrompues par un episode dhypoxie.

Des mammifères de l'Aquitanien inférieur à La Roche-Blanche-Gergovie (Puy-de-Dôme, France), révélateurs de l'activité post-oligocène du rift en Limagne de Clermont

Abstract Recently discovered mammal-bearing layers near La Roche-Blanche-Gergovie, Clermont-Ferrand basin (France) make it possible to attribute an Early Miocene age (Aquitanian, MN1) to the upper part of these series, hitherto considered as Late Oligocene. Palaeoenvironmental inferences are drawn from the micro-mammal fauna, from a complete and connected posterior leg of Mesaceratherium pauliacense as well as from ostracod community-bearing beds. Up-dating of the mammal faunas from old mammal localities in the Clermont basin and recently discovered ones point out, for the first time, a narrow subsident channel, near the Western Limagne main fault, testifying that the rift activity continued during Aquitanian times.

Âges et environnements des Couches rouges d'Anoual (Jurassique moyen et Crétacé inférieur, Haut-Atlas oriental, Maroc)

Lithology, sedimentology and palaeoenvironments allow a lithostratigraphic subdivision of the Red beds into five formations. A marine episode identified near the top of the first formation is Early Bathonian in age. An erosional unconformity overlies this marine level just below the Lower Cretaceous deposits. It could be related to a large sedimentary gap between the Lower Bathonian and the Lower Cretaceous series.

Les ostracodes et l'évolution paléogéographiqueau quaternaire récent du site d'Ashtart (golfe de gabès, tunisie orientale)

Resume Vingt-sept echantillons ont ete preleves dans le bassindAshtart, en Mer Pelagienne, le long de la carotte KST 100. Letude de lostracofaune, permet de reconnaitre quatre associations specifiques pour la periode setendant sur les 27 000 dernieres annees; la premiere correspond a la regression du Wurm III et les trois autres a la transgression versilienne.

Pliensbachian magnetostratigraphy: new data from Paris Basin (France)

Sampling of an industrial drill string from the northeastern Paris Basin (Montcornet, France) provides early Jurassic magnetostratigraphic data coupled with biochronological control. About 375 paleomagnetic samples were obtained from a 145 m thick series of Pliensbachian rocks. A composite demagnetization thermal up to 300°C and an alternating field up to 80 mT were used to separate the magnetic components. A low unblocking temperature component (<250°C) with an inclination of about 64° is interpreted as a present-day field overprint. The characteristic remanent component with both normal and reversed antipodal directions was isolated between 5 and 50 mT. Twenty-nine polarity intervals were recognized. Correlation of these new results from the Paris Basin with data from the Breggia Gorge section (Ticino, southern Alps, Switzerland), which is generally considered as the reference section for Pliensbachian magnetostratigraphy, reveals almost identical patterns of magnetic polarity reversals. However, the correlation implies significant paleontological age discrepancies. Revised age assignments of biostratigraphic data of Breggia as well as an objective evaluation of the uncertainties on zonal boundaries in both Breggia and Moncornet resolve the initial discrepancies between magnetostratigraphic correlations and biostratigraphic ages. Hence, the sequence of magnetic reversals is significantly strengthened and the age calibration is notably improved for the Pliensbachian, a stage for which sections combining adequate magnetic signal and biostratigraphic constraints are still very few.

Biostratigraphical Scale in the Toarcian of the Paris Basin (France) by Means of Ostracod Associations

Stratigraphical and paleontological studies on the edges of the Paris Basin enable us to recognize five ostracod species associations during the Toarcian. These associations, as a result of an evolutionary trend, allow us to propose a biostratigraphical scale.

Anisotropie chimique de la carapace des ostracodes, Exemple de Leptocythere psammophila

The chemical composition of the shell of Leptocythere psammophila has been determined by means of an electron microprobe. Twelve elements have been analyzed at 30 points that had exactly the same position on 39 valves. Statistical analysis of the results reveals that all specimens present a significant anisotropy in the distribution of one or several elements. Antero-posterior differences are the more common. Variations between inner and outer parts of the shell are less frequent. The elements involved in biological pathways (P, Na, S, Mg, Ca) have a heterogenous distribution. Elements associated with mineral inclusions (Al, Si, Mn, Fe) have a more homogeneous distribution.