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International audience; Fragments of filled wood‐borings were recently discovered from the Eocene–Oligocene Conglomerate and Sandstone Formation of the Malzieu Basin (Lozère, southern France). Propagation phase‐contrast X‐ray synchrotron microtomography (PPC‐SRμCT) was used to characterize their hidden inner structures. Virtual 2D sections and 3D reconstructions show that the inner microstructures of borings display a mudstone–wackestone siliceous matrix including tiny coprolites. The hexagonal cross‐section of these coprolites is characteristic of termite faecal pellets. Morphology and dimensions of the coprolites share strong similarities with those of extant Kalotermitidae (drywood termites). The depositional environment is interpreted as a fluvial valley in which the lenticular sandstone and conglomerate lenses correspond to channels. This discovery complements the record of Palaeogene termites which remain poor in France and throughout the world.

Argillites are one of the geological formations studied by IRSN for their confining properties for isolation of radioactive wastes. One of the main objectives is the study of water transport through rocks with very low water content and very low hydraulic conductivity by modeling of natural tracer profiles. This paper presents the protocol developed for and applied to the acquisition of data for chloride content in interstitial water of the Toarcian argillites at the Tournemire site (Southern France). This protocol is based on laboratory diffusion experiments and on modeling. Experimental data obtained during the transient and steady-state parts of diffusion experiments enable, respectively, the assessment of the diffusion coefficient and the determination of Cl concentration in pore water. Using this protocol, profiles with depth for both of these data sets have been acquired along the geological sequence. Taking into account the present knowledge of the geological and hydrogeological history of the Tournemire massif, a conceptual model granting the main role for mass transport to diffusion has been proposed. According to this conceptual model, a one-dimensional numerical model was built for simulating the mass transport of chloride through the sedimentary column, over 53 Ma. The good agreement between experimental data and calculated values for both diffusion coefficients and concentrations of chloride confirms that diffusion is likely the main process for mass transport in the massif. This model was also tested with the deuterium content of interstitial water, applying variable concentrations at the aquifer system boundaries for reflecting the thermal dependency of isotopic composition in precipitation. These simulations also reveal the likely important role of heterogeneities, such as fractures, in the variability of tracer concentrations with regards to a simple diffusion profile. © 2004 Elsevier B.V. All rights reserved.

After the previous lacking evidence allowed the interpretation of a non-deposition episod, the newly recorded mammal fauna from Puycelci (Tarn, SW France, close South to the Quercy paleokarstic area) now shows the MP 26 standard level (Late Oligocene, Early Chattian) being represented within the Eastern Aquitaine molassic basin filling. According to the evolutionary stage of known mammal lineages, the most significant Puycelci fossils are the Issiodoromys pauffiensis rodent and the Metriotherium cf. sarelense nov. sp. (described in this paper) artiodactyl ungulate. This new dating exemplifies the improvement of the mammalian biochronologic record as regards both the Quercy paleokarst and the surrounding lacustrine Tertiary basins W, S, and S-E to the Quercy, as well as, directly E and N-E, the smaller tectonic Tertiary basins within the crystalline Massif Central basement. The updated record shows the strong extension in time of the paleokarstic data, down to the Middle and Early Eocene, and up to the Early Miocene. Regarding the classically reported Late Eocene to Late Oligocene span, as well in the paleokarst and the peripheral basins, the available biochronological data now attains a valuable density level, the variation of which is significant. On one side there are periods (Late Eocene, Early Oligocene, Early Late Oligocene) with high biochronologic density, allowing improved time resolution using evolutionary stages within mammalian lineages (e.g. numerical ages). Such periods corresponds to almost continuous sedimentary processes, with only possible short breaks. On the other side, there are periods with unreported data, shared in the paleokarst and peripheral basins (Late Oligocene as best example). Such periods may well correspond to some non-deposition episods as once alleged by geologists. Then the surrounding biochronologic data would bear constraining value regarding these episods.

Breaking effects of a Pyrenean compressive tectonic phase are recognised in northern Pyrenean foreland, such as in the Quercy Jurassic limestone platform. The age of this phase still remains poorly constrained. In the so-called Quercy phosphorites area, within the Prajoux–Memerlin paleokarst system near the city of Cajarc, a clay filling shows a strike slip fault effect, close to N–S direction. According to an analysis of the mammal fauna and inferred chronology of the polyphased paleokarst infilling, the age of the faulted clay is late Middle Eocene, with a mammal age estimate of 41.5 Ma. This provides reliable precise floor-age constraining for the involved sismo-tectonic paroxysm, seemingly related to the Pyrenean tectonic compressive phase.

International audience

[1] On the basis of chloride concentrations of pore water in the Tournemire massif (part 1), a conceptual model for mass transport in argillites by diffusion is proposed. From this conceptual model and current knowledge of the geological history of the massif, one-dimensional numerical simulations are formulated for chloride transport in Tournemire massif over the past 53 Ma. Good agreement between experimental data and calculated values for both diffusion coefficients and concentrations of chloride confirms that diffusion is the main process for mass transport in the massif. This model is also tested using deuterium contents of pore water, applying variable concentrations to meteoric water (circulating in system boundary layers) based on the thermal dependency of its isotopic composition. These simulations reveal the likely important role of lithologic heterogeneities, such as fractures, in the horizontal distribution of tracer concentrations.

Paleogeography and Tertiary sedimentation on the basement, north of the Rieupeyroux Ridge (Aveyron, Central Massif). During Tertiary era, several sedimentary stages have succeeded one another north of Rieupeyroux Ridge. The first deposits are preserved in a tectonic fault graben directed by the Sillon houiller. They are proceeding from the erosion of kaolinite weathered mantle on the basement. Then, fluviatile spreading had taken place (Paleocene ?). At last, during Ludian, a wide zone of sedimentation in rivers, swamps and lakes spreads out., Durant le Tertiaire, plusieurs épisodes sédimentaires se sont succédés en Rouergue au nord de la dorsale de Rieupeyroux. Les premiers dépôts sont conservés dans un fossé guidé par le Sillon houiller. Ils sont issus du démantèlement de manteaux d'altération à kaolinite sur le socle. Puis viennent des épandages fluvatiles (Paléocènes ?). Enfin, au Ludien, s'est installée une vaste zone de sédimentation lacustre palustre et fluviatile., Paleogeografía y sedimentación sobre el zócalo, al norte de los cerros de Rieupeyroux (Aveyron, Massif Central) . Durante el Terciario, numerosos sedimentarios episodios se sucedián en el Rouergue, al norte de los cerros de Rieupeyroux. Los primeros sedimentos son conservados en una fossa tectónica dirigida por el Sillon houiller. Provinieron de la erosión de una cubierta alterata de caolinita sobre el zócalo. Después, llegan depósitos fluviátiles (Paleocenos ?). A la postre, durante el Ludiense se extendía una larga zona de sedimentación lacustre, palustre y fluviátil., Simon-Coinçon Régine. Plateaux et bassins du socle du Rouergue au nord de Rieupeyroux (Aveyron) : paléogéographie et sédimentation tertiaire. In: Revue géographique des Pyrénées et du Sud-Ouest, tome 55, fascicule 1, 1984. Géographie physique. pp. 57-69.

Carte géomorphologique d'un secteur des Prépyrénées, basses montagnes ne dépassant pas 753 m d'altitude. Des plis d âge et de style différents affectent trois zones structurales : zone sous-pyrénéenne où alternent calcaires et marnes, zone cénomanienne (flysch et conglomérats), zone nord-pyrénéenne (calcaires et dolomies). En contrebas d'une surface d'aplanissement fini-tertiaire s'insinuent des couloirs villafranchiens eux-mêmes défoncés par les vallées du pleistocene moyen et récent ou les dépressions karstiques. Plusieurs unités physiographiques sont caractérisées, en particulier en ce qui concerne l'évolution des versants. Le réseau hydrographique, surimposé, est influencé par le karst (grotte et rivière souterraine du Mas d'Azil)., Carcenac Claude, Simon-Coinçon Régine, Taillefer François. Carte géomorphologique du Mas-d'Azil SE. Notice. In: Revue géographique des Pyrénées et du Sud-Ouest, tome 40, fascicule 4, 1969. pp. 329-351.