Comptes Rendus de l'Académie des Sciences - Series IIA - Earth and Planetary Science最新文献

The Rhéouis and Boudinar Eocene outcrops located along the Tunisian ‘north–south axis’ show continental deposits similar to those already described in the west-central and meridional Atlas in the Jebel Chaambi and Chebket Bouloufa. The field investigations of these levels conduct to the discovery of Bulimes' terrestrial Gastropods known in the Mediterranean domain. The presence of palygorskite in the clay minerals confirms the emerged tendency of these deposits. The continental palaeogeography might have been induced by the Triassic halokinetic movements along the Atlasic anticlines.

The Earth's atmosphere evolution through geological times has induced significant changes in its composition. The properties of today's atmosphere, due in particular to the presence of oxygen, show strong evidence of the Sun–Earth relationship. The influence of solar activity will be presented, concerning the neutral and ionised atmosphere including the magnetosphere, the thermosphere down to the troposphere, and climate as well as the various consequences on our environment (space weather).

Pyramidelloides dolini n. sp., older strongly sculptured eulimid, is described from the Middle Eocene of southwestern Alabama (Gosport Sand). This new species probably had a planktotrophic larval stage similar to the recent Indo-West-Pacific species. Relationship with the species of the genus Palisadia is discussed. Geographic distributions of both the fossil and the recent species of the genera Pyramidelloides and Palisadia support finally a classic pattern in tropical marine biogeography: a discontinuous geographic range between Indo-Pacific and Caribbean provinces.

The present study characterizes the effluents of the ‘Maroc Phosphore’ factories III and IV (of Jorf Lasfar coastal zone). The results show that the effluent (Cs/l) is very acid, very phosphate-rich, high in suspended matter and calcium-rich. Hydrological parameters indicate an important content of phosphates, especially in the stations located in the South of Cs/l. Tissues of mussel Mytilus galloprovincialis from the Jorf Lasfar zone present high concentrations of Cd and Cu.

Pterosaurs were hitherto represented in the abundant and varied Late Campanian–Early Maastrichtian vertebrate assemblages of southern France by very scanty remains, which did not allow an identification at the family level. An incomplete cervical vertebra from a locality of that age at Cruzy (Hérault, southern France) is described and identified as belonging to an azhdarchid pterosaur with an estimated wingspan of about 3 m.

Numerous Miocene to Quaternary occurrences of adakites and adakitic rocks are identified among the calc-alkaline magmatism from the Western Philippines. These rocks are associated with three different geodynamic frameworks, i.e. subduction, rifting (Macolod Corridor in Luzon) and collision (Palawan indentation of the Philippine archipelago). Slab, lower crust and sediment melting, coupled with assimilation-fractional crystallization, and mantle metasomatism by magmatic liquids are responsible for the generation of these rocks. The occurrence of the adakite–gold–copper relationship makes these areas good metallogenic exploration targets.

The Rio Magno unit (eastern Corsica) is represented by an Apenninic-type (Internal Ligurides) ophiolitic sequence: N-MORB basalts, Lower Cretaceous Palombini-bearing limestones, Middle Cretaceous flysch. In addition, it is unaffected by HP–LT alpine metamorphism. These peculiar features further support the hypothesis of close geodynamical relationships between the Corsican and Northern Apenninic ophiolites. We suggest that, in the Jurassic Piedmont-Ligurian oceanic basin, the Rio Magno and Internal Ligurides ophiolitic sequences represent a continuous, internal, oceanic palaeodomain. Afterwards, during Late Cretaceous–Late Eocene, they underwent a similar orogenic evolution, escaping from deep involvement during the subduction beneath the European continental margin.

The phenomena of decarbonatation and recarbonatation of the apatite have been studied on calcareous phosphate (Kasrik, Turkey) characterized by low contents of phosphate (14.6 % P₂O₅), sulfur (traces), organic matter (0.15 % C), chlorine (0.01 %) and magnesium (0.5 % MgO). The phosphate phase is made up of a carbonatofluoroapatite in which parameter a of the apatite lattice is equal to 9.341 Å. Thermograms show an important endothermicity, due to the loss of water and to the dissociation of carbonate. The exothermicity effect, connected with the burning of organic matter, compensates partly the endothermicity (the ore samples are crushed to a grain size of 400 μm). The calcination is operated in a muffle furnace at 950 ° and 1 000 °C for about 1 h. After roasting, quenching, washing and attriting, the calcined product is treated by gaseous CO₂. During the calcination, parameter a increases from 9.341 to 9.351 Å, and after recarbonatation decreases from 9.351 to 9.347 Å, corresponding to a decrease of the apatitic CO₂ from 3.8 to 1.1 % and then to an increase to 2.1 %. In final analysis, it appears that the phenomena of thermal decarbonatation and, then, of recarbonatation after cooling, present important consequences on ore beneficiation technologies.

Structural and metallogenic studies of the Ifri copper deposit (western High Atlas, Morocco) demonstrate that a great part of the mineralization was linked to a stockwork developed during a Late-Variscan NNW-verging shearing event. With this significant result, the until now accepted syngenetic character for this mineralization has to be reconsidered and allows to suggest a new guide of prospection for this kind of deposit.

Some anomalous transient electric signals in the ULF band, the so-called SES, are claimed to be earthquake precursors. However, their origin remains widely unknown. Anomalous signals having the same characteristics as the SES have been observed at the ‘Centre de recherche géophysique’ (CRG), Garchy (France) and their origin has now been clearly identified with the leakage of electric and phone networks of the CRG. They can be generated by two electrochemical mechanisms of the metallic electrode polarization: the galvanic cell and the AC electrolytic cell. These two mechanisms were controlled by field experiments, and their existence can be generalized and extrapolated to different scales. Any lack of insulation of grounded metallic bodies (underground electric and phone networks, pipelines, gas and water metallic conduits, railways, grounded towers of high power electric lines etc.) could lead to the generation of DC signals looking like the so-called SES. The greatest care must then be taken when claiming the existence of electric precursors of seismic or volcanic significance.