A framework for an optimised groundwater monitoring network and aggregated indicators

The implementation of the Water Framework Directive (EU 2000) requires a groundwater quality monitoring. It is used for characterisation of the ‘good’ chemical status of each groundwater body and for the restoration or protection purposes of those bodies already at ‘good’ status. Interpretative aspects are lying in the design of monitoring network and in the way of building global indicators. Attention is given here to the global chemical status of the groundwater bodies and to the role of diffuse pollution, much of which is brought via groundwater to surface water. Monitoring ‘local’ pollution associated with individual sites is not addressed. Groundwater bodies with different contrasted hydrogeology conditions, land use and topography have been considered to establish an approach for choosing an optimised monitoring network. Then, a quality assessment system has been developed and applied for qualifying the general status of each groundwater body. The use of non-dimensional indexes allows us to process with all kinds of chemical parameters in a normalised way and, by means of adequate aggregation rules, to qualify the general quality status of a groundwater body. The obtained diagnostic, even if not fully validated, is closely linked to the pragmatic objectives contained in the EU Water Directive.     

Neogene upper‐crustal cooling of the Olympus range (northern Aegean): major role of Hellenic back‐arc extension over propagation of the North Anatolia Fault Zone

The North Anatolian Fault Zone (NAFZ) is one of the most hazardous active faults on Earth, yet its Pliocene space‐time propagation across the north Aegean domain remains poorly constrained. We use low‐temperature multi‐thermochronology and inverse thermal modelling to quantify the cooling history of the upper crust across the Olympus range. This range is located in the footwall of a system of normal faults traditionally interpreted as resulting from superposed Middle–Late Miocene N–S stretching, related to the back‐arc extension of the Hellenic subduction zone, and a Pliocene‐Quaternary transtensional field, attributed to the south‐westward propagation of the NAFZ. We find that accelerated exhumational cooling occurred between 12 and 6 Ma at rates of 15–35 °C Ma^?1 and decreased to <3 °C Ma^?1 by 8–6 Ma. The absence of significant Plio‐Pleistocene cooling across Olympus suggests that crustal exhumation there is driven by late Miocene back‐arc extension, while the impact of the NAFZ remains limited.     

Seismic hazard assessment in the Ionian Islands based on observed macroseismic intensities

Catalogues of actual observed intensities are constructed for three towns in the Ionian Islands. They are used for seismic hazard assessment and the results are compared with those obtained by standard approaches; that is, by statistics applied to the data computed from epicentral parameters. The results show that seismic hazard is better assessed using observed rather than computed data, but preparation of the local catalogue presents non-trivial difficulties.     

Field and petrological evidence for a Late Palaeozoic (Upper Carboniferous–Permian) age of the Erfaulet orthogneiss (Gran Paradiso,western Alps)

In the Gran Paradiso massif (western Alps), the boundary between the Erfaulet orthogneiss and the overlying metasediments (Money Complex) is interpreted as a Late Palaeozoic intrusive contact. Major arguments in favour of this hypothesis are: (i) the obliquity of the sedimentary layering with respect to the contact; (ii) the presence of aplitic dykes within the Money Complex; (iii) the lack of a mylonitic zone; and (iv) rare relics of an early generation of garnet in the Money metasediments, interpreted as evidence of the contact metamorphism of the Erfaulet granite. To cite this article: B. Le Bayon, M. Ballèvre, C. R. Geoscience 336 (2004).     

Détermination indirecte des limites d'Atterberg par gravimétrie dynamique

This study presents a new method for Atterberg limits measurements using dynamic drying. Indeed, for some polluted clays, or clay mixtures, classical methods cannot be used. The principle of liquid $(W_{\mathrm{L}})$ and plasticity $(W_{\mathrm{P}})$ limits determination by this method is presented. Experimental values for classical clays are close to those obtained with Casagrande's methods, allowing for larger physical mud characterisation. To cite this article: C. Proust et al., C. R. Geoscience 336 (2004).     

Biotites and associated minerals as markers of magmatic fractionation and deuteric equilibration in granites

Analyses of 80 biotite, alkali feldspar, oligoclase, hornblende, Fe-Ti oxide separates from the coarse-grained granites of a late-hercynian epizonal diapir, the Ploumanac'h complex, Brittany, show that these minerals display a regular concentric cryptic layering related to fractional crystallization. The Ca, Mg, Ba, Sr, Cr, V content of minerals decreases as the Na, Fe, and Rb content increases. Biotites become more dioctahedral towards the outer residual syenogranite, with a correlative K deficiency. Trioctahedral biotites from the inner accumulative monzogranite are secondarily oxidized with a gain of Fe³⁺ and a loss of OH. This alteration id due to the percolation of exsolved fluids rich in H₂O and containing a small amount of CO₂, F, S, Cl. During this autometamorphic stage, trace elements like Rb, Sr are completely redistributed on the scale of hand specimens, with a restricted range of partition coefficients between biotite, perthite and oligoclase. This equilibration occurred at a temperature about 550 ° C and a fluid pressure about 1,000 bars, with f _H2_O probably less than 500 bars. A later stage of fluid circulation along fractures brings up a slight Li metasomatism. Biotites are a sensitive marker of both magmatic and postmagmatic stages of subsolvus or ‘wet’ plutonites.     

Contrasting patterns of precipitation seasonality during the Holocene in the south‐ and north‐central Mediterranean

Pollen‐based quantitative estimates of seasonal precipitation from Lake Pergusa and lake‐level data from Lake Preola in Sicily (southern Italy) allow three successive periods to be distinguished within the Holocene: an early Holocene period before ca. 9800 cal a BP with rather dry climate conditions in winter and summer, a mid‐Holocene period between ca. 9800 and 4500 cal a BP with maximum winter and summer wetness, and a late Holocene period after 4500 cal a BP with declining winter and summer wetness. This evolution observed in the south‐central Mediterranean shows strong similarities to that recognized in the eastern Mediterranean. But, it contrasts with that reconstructed in north‐central Italy, where the mid‐Holocene appears to be characterized by a winter (summer) precipitation maximum (minimum), while the late Holocene coincided with a decrease (increase) in winter (summer) precipitation. Maximum precipitation at ca. 10 000–4500 cal a BP may have resulted from (i) increased local convection in response to a Holocene insolation maximum at 10 000 cal a BP and then (ii) the gradual weakening of the Hadley cell activity, which allowed the winter rainy westerlies to reach the Mediterranean area more frequently. After 4500 cal a BP, changes in precipitation seasonality may reflect non‐linear responses to orbitally driven insolation decrease in addition to seasonal and inter‐hemispheric changes of insolation. Copyright © 2011 John Wiley & Sons, Ltd.     

High-temperature emplacement of the Cerro Galán and Toconquis Group ignimbrites (Puna plateau,NW Argentina) determined by TRM analyses

Estimates of pyroclastic flow emplacement temperatures in the Cerro Galán ignimbrite and Toconquis Group ignimbrites were determined using thermal remanent magnetization of lithic clasts embedded within the deposits. These ignimbrites belong to the Cerro Galán volcanic system, one of the largest calderas in the world, in the Puna plateau, NW Argentina. Temperature estimates for the 2.08-Ma Cerro Galán ignimbrite are retrieved from 40 sites in 14 localities (176 measured clasts), distributed at different distances from the caldera and different stratigraphic heights. Additionally, temperature estimates were obtained from 27 sample sites (125 measured clasts) from seven ignimbrite units forming the older Toconquis Group (5.60–4.51 Ma), mainly outcropping along a type section at Rio Las Pitas, Vega Real Grande. The paleomagnetic data obtained by progressive thermal demagnetization show that the clasts of the Cerro Galán ignimbrite have one single magnetic component, oriented close to the expected geomagnetic field at the time of emplacement. Results show therefore that most of the clasts acquired a new magnetization oriented parallel to the magnetic field at the moment of the ignimbrite deposition, suggesting that the clasts were heated up to or above the highest blocking temperature (T _b) of the magnetic minerals (T _b = 580°C for magnetite; T _b = 600–630°C for hematite). We obtained similar emplacement temperature estimations for six out of the seven volcanic units belonging to the Toconquis Group, with the exception of one unit (Lower Merihuaca), where we found two distinct magnetic components. The estimation of emplacement temperatures in this latter case is constrained at 580–610°C, which are lower than the other ignimbrites. These estimations are also in agreement with the lowest pre-eruptive magma temperatures calculated for the same unit (i.e., 790°C; hornblende–plagioclase thermometer; Folkes et al. 2011b). We conclude that the Cerro Galán ignimbrite and Toconquis Group ignimbrites were emplaced at temperatures equal to or higher than 620°C, except for Lower Merihuaca unit emplaced at lower temperatures. The homogeneity of high temperatures from proximal to distal facies in the Cerro Galán ignimbrite provides constraints for the emplacement model, marked by a relatively low eruption column, low levels of turbulence, air entrainment, surface–water interaction, and a high level of topographic confinement, all ensuring minimal heat loss.     

Investigating the Halogen Chemistry From High-Latitude Nighttime Stratospheric Measurements of OClO and NO2

Two cases of simultaneous nighttime measurements of NO₂ and OClO in the winter polar stratosphere are analyzed in order to test our present knowledge of halogen chemistry in the presence of high amount of NO₂ at low temperature. Comparisons with Lagrangian model calculations using several hypotheses are performed. First simulations, using the admitted constant rates of chemical reaction, strongly underestimate the measured OClO while the NO₂ profiles are correctly reproduced. If uncertainties in actinic fluxes calculations are taken into account, simulation results do not show a significant reduction of the underestimation. A better agreement can be achieved if the formation of unstable isomers of ClONO₂ and of BrONO₂ occurs in the cold conditions of the polar stratosphere. An approximate value of the branching ratios of the channels leading to ClONO₂ and ClOONO, and to BrONO₂ and BrOONO, necessary to reproduce both OClO and NO₂ is given and discussed.