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

Isotopic measurements on groundwaters have been carried out on the Valréas Miocene aquifer. A strong isotopic contrast exists between the recharge area and the confined aquifer, suggesting limited hydraulic communications between these two portions. In the confined aquifer, radiometric velocities are 10 to 12 times smaller (0.2–0.4 m·yr⁻¹) than hydraulic velocities (≈2.2 m·yr⁻¹). The overexploitation of the resource can have entailed a major change in the hydraulic gradients leading to a perturbation of the system and a gradual attenuation of the hydraulic barrier, which may threaten the sustainability and the quality of the resource.

The Saint-Lawrence Lowlands correspond to the Cambrian–Early Ordovician passive margin of the Iapetus Ocean, overlain by Ordovician deposits of the Appalachian foreland. A structural and palaeostress study of this platform near Quebec City allowed reconstructing its tectonic evolution since the Palaeozoic. The collapse of the Iapetus margin (NW–SE extension) has induced N040 normal faults. Appalachian compressions (WNW and north–south) have reactivated these border faults, and induced strike-slip faults trending N090 and N140. During the Mesozoic, NNE to NNW extensions have reactivated N090 and N040 faults. The following NE–SW compression has been active until today.

The Aı̈t Kandoula basin is known for its abundance of micromammal fauna. The systematic study of the fauna of two layers of the Afoud section (AF6 and AF5), highlights the presence of two new species: Myocricetodon afoudensis nov. sp. and Myocricetodon jaegeri nov. sp. These two layers are respectively dated at 10.1 and 6.3 Ma by magnetostratigraphic correlation.

Bone gnawing modifications by rodents at a large scale is a taphonomical feature usually found in Plio-Pleistocene assemblages. We report for the first time such a case within the 26-Myr-old karstic fissure filling assemblage of Pech-Desse (phosphorites of Quercy, Upper Oligocene, MP 28). A selection is observed on small ungulate long bones and other elements with a similar size. As predation evidences are also numerous on these taxa, and because some similar gnawed bones have been observed within the contemporaneous locality of Pech-du-Fraysse, we propose a secondary intervention of theridomyid rodents (maybe Archaeomys) on a carnivore laird.

The mount Manengouba is a polygenic volcanic complex of the Cameroon line, which was built in the Quaternary, between 1.55 and 0 Ma, during three stages. The first stage, from 1.55 to 0.7 Ma, corresponds to the building of the Elengoum volcano. The second, between 0.7 and 0.56 Ma, points to the collapse of the Elengoum summit. The third, from 0.56 to 0 Ma, fits with the erection of the Eboga volcano and its caldera sinking, and, from 0.48 Ma, with the adventive fissural activity. The products define an alkaline sodic series, from nepheline-bearing basalts to trachytes. All the lavas evolved by fractional crystallization in a periodically replenished magmatic chamber.

The observation with the scanning electron microscope of polished, etched sections of Palaeozoic limestones enables the discovery of calcareous micro- and nannofossils, which can be attributed to the Incertae Sedis family Ovummuridae Munnecke, Servais and Vachard, 2000. These microfossils are only preserved in Konservat-Lagerstätten without late diagenetic overprint. New findings are made in sections of the Upper Silurian of the Barrandian area, Czech Republic, the Upper Carboniferous of the Donetz basin, Ukraine, the Lower Permian of the Ural mountains, Russia, and the Upper Permian of the Hindu Kush, Afghanistan. The Ovummuridae, which were totally unknown up to now, were possibly very abundant in carbonate platforms of all Palaeozoic periods, at least from the Silurian onward.

The Valea Morii Cu–Au ore deposit (Apuseni mountains, Romania) is characterised by a spatial association of a porphyry copper (Cu±Au) with a low-sulfidation epithermal deposit (Au). Microthermometric and sulphur isotopic data, obtained on both porphyry and epithermal veins, express a telescoping between these two types of mineralization, which can be explained either by an erosion phenomenon during the hydrothermal activity or by a collapse of the upper part of the hydrothermal system.

Solute transfer in soils may create sharp concentration fronts. The numerical modeling of these fronts remains a difficult problem. The proposed one-dimensional model (Wamos-T) is robust and well adapted to these problems. It is based on operator splitting: discontinuous finite elements combined with a slope limiting procedure is used to discretize the advective term, the dispersive and reactive terms of the transport equation being solved by an implicit finite differences scheme. Compared to a widely used finite element method (Hydrus-1D), Wamos-T provides more accurate results when sharp fronts occur.

A new rhyolitic tuff outcrop has been discovered in southern Corsica, at Francolu. It shares a calc-alkaline affinity with nearby, previously known, rhyolitic Balistra tuff and dacitic ignimbritic Tre Paduli tuff. A weighted mean age of 19.3±0.5 Ma has been obtained using the K–Ar method on tuff glasses from these three formations. Synchronous emplacement is also indicated by the coherent reverse palaeomagnetic directions, which further imply that only about half of the Corsica–Sardinia rotation was completed at 19 Ma.

The Peille earthquake (M_w=3.4) occurred on 1st November 1999, 15 km to the north of the cities of Nice, Monaco and Menton. This event was very well recorded by 20 seismological stations located between 6 and 50 km from the epicenter. We used a non-linear location method and showed that the earthquake occurred at shallow depth (3±1.5 km) close to the Peille–Laghet fault trace. Moreover the computed focal mechanism is consistent with the left lateral strike slip movement of this fault. An empirical Green's function deconvolution showed that the rupture occurred on a fault portion smaller than 600 m long. This earthquake was also the occasion to point out remarkable site effect amplifications in some areas of the city of Nice.