Un Pachyerymnoceras arabique dans le Callovien supérieur du Dahar (Sud tunisien), nouvel élément de datation du membre Ghomrassène (formation Tataouine) ; corrélations avec l'Arabie Saoudite et le Moyen-Orient

The first ammonite discovered at the base of the Ghomrassène Member of the Tataouine Formation belongs to a species of Pachyerymnoceras from the Latest Callovian (Solidum Zone) of the Arabian province. The underlying Krechem el Miit Member is also dated Late Callovian, with a fauna of Pachyerymnoceras from the Lower Athleta Zone in Algeria. The associated faunas (echinids, brachiopods) are the same, as well as the faunas of the overlying Ksar Haddada Member, which is dated also Late Callovian, referring to the brachiopods faunal succession in Saudi Arabia. Correlations with other areas in Tunisia, Saudi Arabia and Middle East underline the same sedimentary evolution during a second-order transgressive half-cycle. To cite this article: R. Enay et al., C. R. Geoscience 334 (2002) 1157–1167.

Résumé

La première ammonite découverte à la base du membre Ghomrassène de la formation Tataouine est un Pachyerymnoceras de la partie supérieure du Callovien supérieur (Zone à Solidum) de la province arabique. Le membre Krechem el Miit sous-jacent est aussi daté du Callovien supérieur par des Pachyerymnoceras connus dans la partie inférieure de la Zone à Athleta en Algérie. La faune associée (échinides, brachiopodes) est la même que celle du membre Ksar Haddada sus-jacent, daté également du Callovien supérieur par référence à la succession des brachiopodes en Arabie Saoudite. Les corrélations avec les autres régions de Tunisie, l'Arabie Saoudite et le Moyen-Orient mettent en évidence une même évolution sédimentaire au cours d'un demi-cycle transgressif de deuxième ordre. Pour citer cet article : R. Enay et al., C. R. Geoscience 334 (2002) 1157–1167.     

Le provincialisme sud-caraibe à l'Aptien inférieur. Sa signification dans le cadre de l'Evolution geodynamique du domaine Caraibe et de l'Atlantique central

Stratigraphic and palaeontologic data from the Lower Cretaceous of Venezuela and the critical revision of the previous results on the whole Caribbean Lower Aptian, show that the South Caribbean region is characterized by an endemic Rudist fauna while some micropalaeontological components have an african affinity. Consequently a South Caribbean palaeobiogeographic province is to be distinguished from a Northern one known to have some European characters. These results fit well with palaeogeographic and palaeotectonic reconstructions concerning both the Caribbean as well as the Central Atlantic areas. New palaeogeographic and palaeoceanographic implications are considered.     

Apport de la gravimétrie à l'étude de la structure du bassin des Triffa (Maroc nord-oriental) : implications hydrogéologiques

Various techniques (horizontal and vertical derivatives, upward continuation, Euler deconvolution) have been applied to the gravity data from the Triffa's plain and the north flank of the Beni-Snassen massif to delineate various major geological structures such as faults and basins. These results allow the production of a structural map showing the fault systems for the survey area. This map forms the basis for planning future hydrogeological research in this region. To cite this article: D. Khattach et al., C. R. Geoscience 336 (2004).     

Paléoclimat des Petites Antilles depuis 4000 ans BP : l'enregistrement de la lagune de Grand-Case à Saint-Martin

A 2.5-m-thick sequence of lake sediments at the Étang de Grand-Case, Saint Martin (French West Indies) is studied here. Significant hydrological budget fluctuations allows distinction of three main climatic periods: (1) an overall dry period (4200 BP–2300 BP), characterised by carbonated mud, gypsum and storm sand layers; (2) a wet phase (2300 BP–1150 BP) dominated by organic mud; and (3) a more complex phase (1150 BP to present), with detrital inputs due to human activities. Comparison with other regional high-resolution records shows that similar climate modifications typify the whole Mesoamerican and Caribbean area. The climatic phenomena that are implicated in the variations of both precipitation and hurricane frequency over the Lesser Antilles are due to the latitudinal displacement of the inter-tropical convergence zone. These data give new support to the hypothesis of the existence of a correlation between peopling phases and climate variations in the Caribbean as previously proposed by some archaeologists. To cite this article: P. Bertran et al., C. R. Geoscience 336 (2004).     

Découverte des roches à affinité ophiolitique dans la chaîne panafricaine au Cameroun : les talcschistes de Ngoung, Lamal Pougue et Bibodi Lamal

Outcrops of talc schists extending over >1 km have been discovered within the garnet- and muscovite-bearing mica schist of the Pan-African belt near Yaoundé (Cameroon). Mineralogical studies show that a metamorphism of the upper greenschist facies was prolonged by hydrothermal reactions. This latter led to the transformation of hornblendites into talc schists. Chemically, talc schists and relicts of hornblendite remind ultrabasic rocks, and REE patterns point to E-MORB and peridotite. It is thus suggested that the talc schists and relicts of hornblendite may correspond to slices of a dismembered Pan-African ophiolite set. To cite this article: C. Nkoumbou et al., C. R. Geoscience 338 (2006).     

Superposition de la tectonique éburnéenne et panafricaine dans les granitoïdes de la bordure nord du craton ouest africain, boutonniére de Zenaga, Anti-Atlas central, Maroc

The Zenaga Inlier shows a comprehensive record of the Eburnian and Pan-African Orogenies. The Eburnian is characterised by high-temperature regional metamorphism and complex magmatism. The early (Azguemerzi) granodiorite has an isotopic mantle signature and was emplaced diapirically during the Eburnian Orogeny causing local thermal metamorphism. The foliation observed in this granitoid is a result of the interference between its primary syn-emplacement foliation and the regional foliation under amphibolite-facies conditions. The northern part of Zenaga has been intruded by the leucocratic granites of Tazenakht. These granites are cut by mylonites and phyllonites, corresponding to the Pan-African shear zones and accompanied with sub-greenschist-facies metamorphism during the Pan-African Orogeny. The deformation was the result of a regional sinistral transpressive event. This study in the northern part of the West African Craton shows the superposition of the Pan-African on the Eburnian Orogeny and the presence of a major fault in the Anti-Atlas.     

Série du marégraphe de Marseille : mesures de températures de surface de la mer de 1895 à 1956 : une correction

In 2007, a daily temperature series, which has been collected from 1885 to 1967 at the Marseilles tide recorder, was published here. Upon the available information provided by the data managing office, they were considered as sea-surface temperatures. Unfortunately they were not but air temperature inside the building. In the present paper, the authors correct this error by studying the true seawater temperature series which had been dug out after the publication of the precedent paper. The study of this slightly shorter series (1895–1956) leads to close conclusions. Along these 61 years, the warming trend of the surface seawater rises to +1.6 °C, to +1.3 °C if only January to May and December are selected and +2.2 °C during the June to November period. In the first half part of the series (1895–1925), the average value of each month distributions (except January) and annual minimal (except 1956) are significantly lower than along the second (1925–1956).     

Dépliage 3-D des anticlinaux bordant le synclinal fermé de la vallée des Ponts, Jura central, Suisse

The Ponts valley syncline is a closed basin within the Neuchâtel Jura fold and thrust belt. This syncline, apparently uplifted to an altitude of around 1000m is closed in the SW by an anticline with an oblique WNW-ESE direction. The 3-D geometry of the entire structure is examined and unfolded in detail. This syncline is filled with an unexpectedly thick series (~400m) of Tertiairy Molasse, as revealed by the CS-AMT (controlled source audio-magneto-telluric) and a reflexion seismic line. The latter also documents internal compressional structures within the well layered upper freshwater Molasse series. The 3-D configuration of the top Malm limestones has been constructed for the entire area based on new detailed geologic and structural mapping, hundreds of dip measurements, as well as geophysical data. The Malm marker bed displays three distinct types of structures: 1) Thrust faults with shallow dips, vergent to the NW and/or SE that are associated with folds interpreted as fault bend folds; 2) high angle inverse faults, mostly with a SE vergence are interpreted as inverted normal faults, inherited from a modest Oligo-Miocene extensional phase in a NW-SE direction; and 3) tear faults with a dominant N-S direction, probably inherited from an Oligocene extensional phase in association with the opening of the Rhine and Bresse grabens. Tear faults accommodate important lateral changes in fold geometry during the Late Miocene main folding-and-thrusting phase. All deformations are easily explained in an entirely thin-skinned fashion, taking place above a thick detachment horizon within Triassic evaporite series.Manuscrit reçu le 31 mars 2003 Révision acceptée le 23 juin 2004     

Enregistrement de phénomènes de resédimentation au cours du Maastrichtien supérieur et du Paléocène supérieur (J. Serj, Tunisie atlasique) : apport micropaléontologique et signature tectono-eustatique

Sedimentological and biostratigraphic analysis of Campanian–Maastrichtian reduced series of the J. Serj permitted to characterize two episodes of submarine erosion. The first is pre-Upper Maastrichtian (Rosita contusa zone), the second is pre-Upper Palaeocene (Morozovella velascoensis zone). Thus, two type-1 boundary surfaces are distinguished. These surfaces limit three stratigraphic intervals in apparent continuity. Syn-sedimentary tectonic activity is attested by gravity deposits or processes (conglomerates, slumps). To cite this article: A. Amri et al., C. R. Geoscience 337 (2005).     

Preuves de la discordance de l'Ordovicien supérieur dans la zone axiale des Pyrénées : exemple du dôme de la Garonne (Espagne,France)

The geological mapping of the Garonne Dome had already shown an angular unconformity between the Upper Ordovician and the underlying series. This paper presents data from a nearby location, Planelh deth Pas Estret, southeast of the Garonne Dome, where the unconformity can be seen at outcrop scale. The unconformity angles amount to up to 20°. This unconformity is interpreted as a result of an extensional event of pre-Upper Ordovician age. To cite this article: J. Garc??a-Sansegundo et al., C. R. Geoscience 336 (2004).     

Le rôle des plantes dans le transfert du silicium à la surface des continentsThe role of plants in the transfer of silicon at the surface of the continents

Silicon is the most abundant element after oxygen in the lithosphere (27 wt%). Plants and soil microorganisms are important contributors to the weathering of silicates. Plants are able to accumulate several percent of Si in the biomass. The importance of plants in the rates of Si output to surface waters is discussed in this paper. To cite this article: J.-D. Meunier, C. R. Geoscience 335 (2003).     

Distribution des thanatocénoses récentes de radiolaires dans l'Atlantique nord-oriental et le sud de la mer de Norvège

The relative abundance of five groups of radiolarian species (nasselarians and spumellarians) in the thanatocoenoses within the recent sediments from 64^oN to the Equator is described. Four types of thanatocoenoses of Radiolarians and several subtypes are distinguished and in the broadest sense four major faunal zones can be delimited: north of 60^oN, a subarctic zone, a boreal zone, a subtropical zone whose boundary runs approximately along 45^oN and, south of 13^oN, a tropical zone. The correlations between the faunal provinces and climatic belts are more gradual in the low and intermediate latitudes than in the high latitudes     

Assimilation de données dans un modèle d'écosystème marin de la mer Ligure

The objective is to explore the potentialities of sequential statistical estimation methods to assimilate observations in a primary production biological model coupled to a vertical 1D hydrodynamical model characterised by a k–l turbulent closure. The assimilation method is derived from the SEEK filter (Singular Evolutive Extended Kalman filter), which uses an error subspace represented by multivariate empirical orthogonal functions (EOFs). Real data assimilation experiments collected at sea have been realised to reconstruct the variability of the Ligurian Sea ecosystem during the FRONTAL field experiment. To cite this article: S. Magri et al., C. R. Geoscience 337 (2005).     

Sedimentation et volcanisme synsédimentaire de la série de base de l'adoudounien infra-cambrien à travers deux exemples de l'Anti-Atlas du Maroc

The Adoudounian Basal Series within the western part of the Moroccan Anti-Atlas Mountains was deposited in a varying palæogeographical setting. The first deposits of volcaniclastic and carbonate sediments accumulated in small shallow basins under tectonic control. Then, sedimentation became siliciclastic and volcano-detrital with coastal and deltaic sedimentation in the western area and lagoon-lacustrine in the eastern area. Synsedimentary alkaline volcanism, associated with normal faulting, indicates a within-plate extensional tectonic regime related to rifting, which affected the northern margin of the West African Craton, during Late Neoproterozoic-Early Cambrian times.     

Datation Ar/Ar de la province magmatique de l’Atlantique central dans le Sud-Ouest algérien

⁴⁰Ar/³⁹Ar step-heating analyses performed on plagioclase separates from seven doleritic basalts (four sills, one dyke and two lava flows) from southwestern Algeria display disturbed age spectra, reflecting various contributions of alteration by sericite and/or excess argon. Weighted mean ages corresponding to the less altered plagioclase fractions yielded minimum ages ranging from 192.7 ± 3.0 to 197.9 ± 2.0 Ma and a minimum date of 198.9 ± 1.8 Ma was obtained on a saddle-shaped age spectrum (excess argon). These ages are in accordance with those previously obtained on the CAMP province and partly in agreement with the peak activity of the CAMP at 198 Ma, highlighted in the neighbouring Taoudenni basin (Mali). In Algeria, the eastern boundary of the CAMP seems to coincide with the Pan-African suture zone.     

Répartitions comparées de foraminifères planctoniques du Crétacé moyen dans la téthys et la mer boréale par rapport à une zonéologie macropaléontologique

Cette note donne une présentation des résultats obtenus par le Groupe de Travail européen des foraminifères planctoniques de 1976 à 1978.The results obtained by the European MCE working group on planktic foraminifera are summarized. A total of 49 species were revised, referable to the genera Planomalina, Rotalipora, Hedbergella, Whiteinella, Archaeoglobigerina, Praeglobotruncana, Dicarinella and Marginotruncana.     

L'ouverture et le développement du bassin de Morondava (Madagascar) du Carbonifère supérieur au Jurassique moyen. Données stratigraphiques, sédimentaires, paléontologiques et structurales

In the western part of Madagascar, the Morondava Basin shows the Malagasy Karoo series, made of Late Carboniferous-Mid-Permian (Sakoa), Late Permian-Mid-Triassic (Sakamena) and Late Triassic-Mid-Jurassic (Isalo) sequences. The sedimentary facies are mainly aerial and clastic in the series, and the marine conditions are fully established after Lower Jurassic times, when the strait between Africa and Madagascar was flooded.The Karoo basins where these series were deposited are mainly hemi-grabens. Their filling proceeded from west to east and from south to north. Distinction between the southern and northern part of the Morondava Basin suggests that development of the basin was controlled by old crustal weakness zones trending north-northwest-south-southeast and north-northeast-south-southwest.