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

Isotopic investigations of reindeer, one of the main meat resources for Upper Palaeolithic humans of southwestern France, led to palaeoecological hypotheses that need modern equivalents to be tested. A relevant reference modern population is aimed with the Kaminuriak caribou. Amounts of carbon-13 and nitrogen-15 measured on collagen from teeth roots reflect a short-term record representative of different time life periods of the animal. Reindeer winter diet based on lichen consumption and body protein recycling seems pictured with characteristic isotopic signatures.

A detailed geophysical survey has been carried out in the Armorican massif. Magnetic and radiometric data have been simultaneously recorded. The studied area offers a short cross-section through the major domains of the Variscan collision belt. Geophysical maps have been correlated with a regional geological map drawn within the framework of the project (Armor2, GéoFrance 3D). Geological contours could be revisited and continuity of some structural features are evident. Radiometric maps allowed identifying the geochemical content of K, U and Th within volcano-sedimentary units. Magnetic geological formations are followed beneath the Neogene sedimentary cover and offshore.

Microdioritic intrusives crosscut the Hercynian structures of the Jbilet massif in the western Morocco. Their mineralogical, petrological and geochemical compositions display the main characteristics of calc-alkaline magmas and any of the alkaline ones. This magmatic event occurred at ca 255 Ma, as indicated by the ⁴⁰K–⁴⁰Ar age of fresh kaersutite crystals, but seven ages for whole-rock samples, scattered between 231 and 180 Ma, reflect the general rejuvenation of the ages linked to a latter penetrative alteration event of their feldspars and groundmass.

The borders of the Central High Atlas chain showed different structural styles, as revealed by the interpretation of recently acquired surface geology and sub-surface data. Structures, characterizing thick and thin skin tectonics, are variable from west to east and from south to north, while both shortening and deformation intensities decrease in the same directions. These differences are essentially related to the attitude of inherited Hercynian fault pattern and to the Mesozoic development of the Central High Atlas.

Fractal geometry concepts are applied to analyse hard rock fracturing and the associated river network. The study area is located in the Ivory Coast (region of Man). Analyses point out that fracture network is plane filling, with D≈2 at all scales. The river network displays a rupture scale. This difference is interpreted in terms of geological constraints undergone by the river network according to the scale.

Within the populations of the gradual lineage including Contusotruncana fornicata (Plummer) (Globotruncanidae), the spiral heights increase with time. The speed of this increase is linked to the asymmetries in the distributions of the index used to measure the spiral heights. The succession of these asymmetries shows an evolutionary process, combining gradualist continuity and discontinuities by successive evolutional jumps. These two coexisting modes could be induced by genetic mechanisms evoked for phyletic gradualism and punctualism respectively.

The bathymetric maps from the western part of the Gibraltar Strait indicate the occurrence of a shoal between –56 and –200 m depth. During the Late Glacial Maximum (21–19 kyr BP), this shoal was the main island of an archipelago lying between Europe and Africa. The island (14 km × 5 km) was set in the middle of a narrow pass in the western part of the present strait, opening westward into an inner sea. This island was submerged around 11 kyr BP. This location, the palaeolandscapes for the Late Glacial period, and the time of submergence exactly fit the Atlantis description given by Plato in the ‘Timaeus’. The ‘mighty power which unprovoked made an expedition against the whole of Europe and Asia’ could be the irrupting culture of northern Europe pushed to the south by the rough climates of the Late Glacial Maximum.

The Cu, Zn, Cd, Pb concentrations and Pb isotopic compositions are determined in mussel flesh from Sète harbour (Hérault) and the Thau lagoon. The mussels were sampled in specific places near industrial piers, boat workshops, a fertiliser factory and at the harbour extremities. The spatial variations in concentrations are linked to the industrial inputs. The interest of this study is that Pb isotopic compositions in the soft parts constrain the lead sources, by comparison with industrial products and natural endmember signatures, and identify water movements in the harbour.

Two major dykes of basalts, microgabbros, olivine dolerites (continental tholeiites), and of camptonites and benmoreites (alkaline rocks) are respectively exposed in the Mayo Oulo–Léré and Babouri–Figuil Early Cretaceous half-grabens (Northern Cameroon–Southern Chad). The tholeiites were probably derived from an asthenospheric source in connection with a lithospheric thinning occurring between Santonian and Eocene times. In contrast, the alkaline rocks may be derived from a deeper metasomatized mantle source.

The Tithonian–Berriasian series of the western Basse Provence carbonate platform (southeast France) is made of the stacking of very high frequency elementary depositional sequences, of metric scale, generally shallowing upward and frequently with emergent caps. The study of this series brings a better understanding of the controlling factors of these sequences. Fischer plots built from the sequence thicknesses and analogous diagrams built from the palaeodepths data suggest that the variations of positive accommodation do not exclusively control the development of these sequences. Variations of neritic carbonate production and/or accumulation have a considerable importance as far as they directly modify the ratio positive accommodation/sedimentary supplies.