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

Halitherium taulannense nov. sp., a new Upper Eocene dugongid, is described on the basis of a well-preserved cranium and mandible that belong to different specimens. It represents the earliest species of an Oligocene and essentially European genus. It comes from the ‘Alpes-de-Haute-Provence’, in southeastern France. It provides much information about the cranial morphology of an Eocene dugongid and diversification of the first sirenians during Eocene time.

This paper presents preliminary results for three GPR profiles acquired across the Wellington active strike-slip fault within the Wellington urban area. In this sector, it is suggested that the subsurface geometry (8–10 m) of the fault comprises two main deforming strands that bound narrow transpressive and transtensive sections. The location of fault planes interpreted from radargrams closely corresponds with the inferred location of the main fault at the ground surface. Despite noise due to the urban settings, GPR proved to be a technique capable of locating fault strands, thus potentially providing useful data in targeting areas for palaeoseismic studies, such as trenching.

Four new taxa are described. Three of them are attributed to the extant Phrynops group: a primitive member, unidentified within the group or related to the large extant Phrynops forms; a primitive member of the Acanthochelys subgroup, small extant members of the group; a more evolved member, although still primitive, of the large extant Phrynops. The fourth is either a representative of an extinct group or a form related to the extant Chelus group. The presence of the second taxon in older Patagonian localities, as early as Lower Albian, indicates that the diversification of the extant groups was achieved as early as the Lower Cretaceous.

The basalts exposed around the Lago General Carrera–Buenos Aires display a wide range of chemical compositions. These include: Cretaceous calc-alkaline magmas typical of the Andean arc, Eocene to Quaternary intraplate alkali magmas and Quaternary magmas, the geochemical signature of which shows similarities with those of Chile ridge MORB. Such diversity is related to the evolution of the subduction processes below Patagonia, starting with a ‘normal’ subduction regime, followed by collision–subduction of the active Farallon–Aluk and Chile ridges together with the development of ‘asthenospheric windows’ during the Eocene and since the Upper Miocene respectively.

Synthetic crystals of mono-silicated fluor–britholite doped with rare earth elements have been prepared. The stoichiometry of the compound has been determined by means of microprobe analyses. Single crystal Laue diffraction and luminescence measurements reveal the covalent character of the rare-earth channel anion bond, thus explaining the stability of such compounds in the natural environment.

The meandrous leveed channels of the Nile Cone show clear evidence of avulsions. Their sedimentary architecture is founded on numerous stacked lens-shaped acoustic units. In the areas of the distal fan, lobe deposits are apparent from multichannel imagery. Huge debris flow deposits, sometimes associated with pockmarks, are recognized. Mud volcanoes and gas seeping are closely associated with faulting. In the East, a very long north-trending channel, originating from the Egyptian coast, merges with a network of channels, very probably originating from the Levantine coasts. Both networks outlet in the sedimentary basin located south of Cyprus.

The discovery of a new fossiliferous locality yielding a type of marine fish-fauna that was up to now unknown, is reported from the pre-evaporitic Messinian of Hurchillo, near Orihuela (Alicante Province, Spain). In fact, with more than 60% of the studied material, Sardina? crassa (Sauvage) is predominant. This species is surprisingly associated with Myctophids, which make up almost 13% of the fish fauna. Such a community indicates that the fossiliferous locality was generated in a shallow, sublittoral environment, which was nevertheless connected to the open sea from which the Myctophids were drifted by currents.

A long and slender wing metacarpal from the Late Oxfordian Sables de Glos of Cordebugle (Calvados, Normandy) clearly belongs to a pterodactyloid pterosaur, with an estimated wingspan of at least 2.30 m. This is currently one of the earliest records of a representative of the Pterodactyloidea.

The purpose of this study is to investigate the fluxes of total suspended solids (TSS) in the Têt River system (1 380 km²). On the basis of a great number of measurements, we estimate the mean annual sediment flux at the mouth to be about 53 546 t·yr⁻¹ (nearly 40 t·km⁻²·yr⁻¹) for the period 1980–1999 (average annual water discharge 10.4 m³·s⁻¹). Almost all suspended sediment loads are transported during brief flash floods that mainly occur during autumnal heavy downpours. The scarceness of these events leads to a very large inter-annual variability of the river sediment fluxes (from 1 to more than 100). Despite the damming of the river in the central part of its drainage basin, the observed sediment fluxes are more important downstream the dam than upstream. This can be explained by low sediment retention behind the dam, by greater erosion rates in the downstream part of the basin, filled with crumbly Plio-Quaternary formations, and by heavy storms located in the fore land.

A zincian ilmenite paragenesis is found in metapelites from a contact metamorphic zone (central Jebilet, Morocco) induced by the emplacement of microgranitic intrusions. The zincian ilmenite is mainly preserved in syntectonic andalusite porphyroblasts. The growth of zincian ilmenite is related either to sphalerite breakdown during prograde metamorphism, or to the pervasive flow of a mineralizing fluid within the metapelites. The chlorine-rich fluid carried zinc and other metals leached in the microgranites, during its flow to discharge zones which were probably the Jebilet sulfide deposits.