Modelling diffusion in a heterogeneous rock matrix with a time-domain Lagrangian method and an inversion procedureModélisation de la diffusion dans une matrice rocheuse hétérogène par une méthode lagrangienne dans le domaine des temps et une procédure d'inversion

A Lagrangian method in time domain is proposed to solve transport by diffusion over large grids such as those extracted from autoradiographs of rock samples. The method is rapid and well suited to simulate out-diffusion experiments in a heterogeneous rock matrix. By coupling with a Gauss–Newton optimiser, it is possible to identify automatically the diffusion coefficients of porous areas in the matrix. This offers a more comprehensive view of a potential transport of contaminants, e.g., after a leak from an underground repository site. To cite this article: F. Delay et al., C. R. Geoscience 334 (2002) 967–973.     

Early and late Holocene water-level fluctuations of Lake Annecy, France: sediment and pollen evidence and climatic implications

Early and late Holocene water-level changes in Lake Annecy, France, were reconstructed from a sediment sequence from Annecy. Two early Holocene successive rises in lake level at ca. 8900-8700 BP are recorded. Another increase in lake level, beginning at ca. 780 BP, is documented. The higher lake-level conditions in Lake Annecy during the 9th millennium BP, i.e. between the Preboreal oscillation and the 8200 yr event, appear to coincide with a more widespread cooling period which has been recorded in western Europe, in the Greenland ice-sheet and the North Atlantic ocean. The rise in lake level at ca. 780 BP can be related to the early Little Ice Age.     

Present-day deformation of the Dauphine Alpine and Subalpine massifs (SE France)

The positions of 20 geodetic points surveyed in 1946-1952 by the Institut Géographique National in the Grenoble area (western Alps) were remeasured in 1993-1994 using GPS. We evaluate the displacements of the common points of the networks between the two surveys, and calculate the strain-rate tensors for different sets of three adjacent points. The significant N70° shortening direction observed at the boundary of the Belledonne and Taillefer massifs suggests that the dextral strike-slip motion between the External Crystalline Massifs (ECM) and the Subalpine domain is still active. Geological evidence suggests that this deformation, which is compatible with the few focal mechanisms available for the area, occurred throughout the late Neogene. Our data also suggest a roughly 3-5 mm yr⁻¹ active shortening concentrated at the external front of the Subalpine chains. This thrust motion results in a principal axis of compression orientated N130°, oblique to the direction of shortening observed in the ECM. This change in direction is also seen in in situ stress measurements. This motion may mark the southward continuation of the active fault observed in the Jura mountains by Jouanne, Ménard & Darmendrail (1995).     

Draa Sfar, Morocco: A Visean (331 Ma) pyrrhotite-rich, polymetallic volcanogenic massive sulphide deposit in a Hercynian sediment-dominant terrane

Draa Sfar is a Visean, stratabound, volcanogenic massive sulphide ore deposit hosted by a Hercynian carbonaceous, black shale-rich succession of the Jebilet terrane, Morocco. The ore deposit contains 10 Mt grading 5.3 wt.% Zn, 2 wt.% Pb, and 0.3 wt.% Cu within two main massive sulphides orebodies, Tazakourt (Zn-rich) and Sidi M'Barek (Zn–Cu rich). Pyrrhotite is by far the dominant sulphide (70 to 95% of total sulphides), sphalerite is fairly abundant, chalcopyrite and galena are accessory, pyrite, arsenopyrite and bismuth minerals are rare. Pyrrhotite is monoclinic and mineralogical criteria indicate that it is of primary origin and not formed during metamorphism. Its composition is very homogeneous, close to Fe₇S₈, and its absolute magnetic susceptibility is 2.10^− 3 SI/g. Ar–Ar dating of hydrothermal sericites from a coherent rhyolite flow or dome within the immediate deposit footwall indicates an age of 331.7 ± 7.9 Ma for the Draa Sfar deposit and rhyolite volcanism.The Draa Sfar deposit has undergone a low-grade regional metamorphic event that caused pervasive recrystallization, followed by a ductile–brittle deformation event that has locally imparted a mylonitic texture to the sulphides and, in part, is responsible for the elongated and sheet-like morphology of the sulphide orebodies. Lead isotope data fall into two compositional end-members. The least radiogenic end-member, (²⁰⁶Pb/²⁰⁴Pb = 18.28), is characteristic of the Tazakourt orebody, whereas the more radiogenic end-member (²⁰⁶Pb/²⁰⁴Pb  18.80) is associated with the Sidi M'Barek orebody, giving a mixing trend between the two end-members. Lead isotope compositions at Draa Sfar testify to a significant continental crust source for the base metals, but are different than those of the Hajar and South Iberian Pyrite Belt VMS deposits.The abundance of pyrrhotite versus pyrite in the orebodies is attributed to low fO₂ conditions and neither a high temperature nor a low aH₂S (below 10^− 3) is required. The highly anoxic conditions required to stabilize pyrrhotite over pyrite are consistent with formation of the deposit within a restricted, sediment-starved, anoxic basin characterized by the deposition of carbonaceous, pelagic sediments along the flank of a rhyolitic flow-dome complex that was buried by pelitic sediments. Deposition of sulphides likely occurred at and below the seafloor within anoxic and carbonaceous muds.Draa Sfar and other Moroccan volcanogenic massive sulphide deposits occur in an epicontinental volcanic domain within the outer zone of the Hercynian belt and formed within a sedimentary environment that has a high pelagic component. In spite of the diachronous emplacement between the IPB deposits (late Devonian to Visean) and Moroccan deposits (Dinantian), all were formed around 340 ± 10 Ma following a major phase of the Devonian compression.     

Analysis of Long-Term Anisotropic Convergence in Drifts Excavated in Callovo-Oxfordian Claystone

The main purpose of this paper is to analyze the convergence measurements in drifts of the Underground Research Laboratory (URL) of the French National Radioactive Waste Management Agency (Andra), excavated in Callovo-Oxfordian claystone. These measurements show an anisotropic closure, which depends on the drift orientations with respect to the horizontal in situ stresses. This anisotropic character of the deformation is taken into account by assuming that the drifts section evolves following an elliptical shape. The characteristics of the deformed elliptical section are evaluated following the methodology proposed by Vu et al. (Rock Mech Rock Eng 46:231–246, 2013). Then, using the semi-empirical law proposed by Sulem et al. (Int J Rock Mech Min Sci Geomech Abstr 24:145–154, 1987), the convergence evolution is fitted independently for each axis of the ellipse. This method allows to distinguish two effects: the face advance and the time-dependent behavior of the ground. The results for the two drift orientations (along the major horizontal stress and perpendicular to it) show very close values for the parameters describing the time-dependent properties of the ground, the distance of influence of the face, and the extent of the decompressed zone around the drift. Finally, the model is validated by keeping these parameters as constants and by simulating the convergence data on a new drift. It is shown that with a period of about 40 days of convergence monitoring, the model can provide valuable insights for predictions of the convergence evolution in the long term.     

Sur les inocérames de Tercis (Landes,France) : le meilleur outil corrélatif entre Europe et Amérique du Nord autour de la limite Campanien–Maastrichtien

Four hundred inoceramids have been collected in the geological site at Tercis, where the Campanian–Maastrichtian boundary has been recently defined. At Tercis, a distinct drop of the adult size of inoceramids is observed between levels 111 and 117 and two turnovers of faunal composition were documented between levels 94 and 96 and between levels 111 and 117; the latter interval encompasses the stage boundary. The recognised inoceramid assemblages are very close to those known from North America, allowing better correlation than before between the two domains in the interval 77–70 Ma. The presence of these faunas perfectly located in the section leads to consider the Tercis section as the best known reference for this fossil group, the surprisingly good correlative potential of which has still to be considered in many areas.     

Spatial and Temporal Variations of Trace Element Contents in Xanthoria Parietina Thalli Collected in a Highly Industrialized Area in Northern France as an Element for a Future Epidemiological Study

This work was made in Dunkirk, which is located on the French coast, in the north, near Belgium and Great Britain. The study concerned the industrial and urban surroundings of Dunkirk and Dunkirk itself. Objectives of our study is (1) to monitor spatial patterns and temporal trends (1995–2003) of trace element (As, Cd, Hg, Ni, Pb, V, Zn) deposition and (2) to make a first evaluation of exposed population to highest metals concentrations. This work is the first step of future epidemiological investigation. In 1995, the high lead concentrations were due to industrial emissions and to traffic. Zinc and arsenic concentrations were also high and widespread in the entire studied zone, but higher near industrial area. Mercury concentrations were limited in the western part and clearly revealed the impact of waste incinerator. We did not find any significant difference between trace element contents in lichens between 1995 and 2003 except for mercury, which decreased. In 2003, the contamination by lead was more focused in the biggest metallurgical plant, which is now the predominant source for this element. The traffic impact decreased, but there was still lead remaining. For the other elements the highest concentrations were observed near the industrial zone. Highest contaminations concern 25–33% of the population, who live near industrial zone in districts where annual average incomes are the lowest. Those results confirm the needs for a further epidemiological study, which could take place in priority where population is the most exposed.