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Abstract: Sedimentary successions of palustrine deposits from the Forez Graben recorded changes in depositional and hydrological conditions throughout the Middle to Late Miocene of France. Paleontological, mineralogical and geochemical data combined with mass-balance calculation allowed the identification of modern, diagenetic and eogenetic stages of authigenic precipitation within the sedimentary pile. Stratigraphic log contains six clay- and sand-rich sequences, some associated with freshwater ostracods. δ13C, δ18O values and Sr isotopic ratios of whole-rock samples and ostracods indicate that the Montrond-les-Bains upper sequence (8 to 175mbs) is a continental lake system that recorded continental weather condition (15 to 25°C) during the upper Miocene time. Geochemical changes permit the estimation of variations of evaporation-inflow changes (E/I: 8 to 75% and δ18Orainfall −6 to −8‰) associated with two sequences. δ18O and E/I progressive changes were related to runoff to colder climate conditions. Large E/I values in below 100mbs are associated with the appearance of authigenic calcite and dolomite precipitation. Euhedral dolomite seems to be related to desiccation period that induced capillary pumping of water undersaturated with respect to calcite but saturated for dolomite. The lower part of the Middle Miocene sedimentary series (175 to 300mbs) hosts continental deposits with scarce fossil, a larger proportion of dolomite and massive pyrite levels related to mixed eogenetic and diagenetic precipitation. Scarce preserved “eogenetic levels” with unrealistic E/I ratios suggest either δ18O values similar to the upper section but with temperature lower than 15°C, or a similar temperature but very low δ18Orainfall. Calculated δ18OH2O values have to be as low as −15‰. δ18OH2O values are similar to present-day melted snow. This stable isotope suggests episodes of regional warming melting surrounding snow, and able to mobilize as well as deposit thick sand levels. Eogenetic to diagenetic calcite, dolomite and pyrite precipitation involves S and Mg-fluid influxes associated with methanogenic process (eogenesis) mixed with recrystallized pyrite and dolomite with diagenetic fluid circulation. [Copyright &y& Elsevier]

Summary: Hydrochemical and stable isotopic (2H, 18O) data were used to characterize the groundwater flow and major chemical features within a complex fractured volcanic aquifer system, the Argnat basin, which is located in the Chaîne des Puys (French Massif Central). From 10 sampling points, the study of the transfer into the saturated zone from upstream to downstream, given the geological context and topography, allows to estimate the role of supply from high and low altitudes to the recharge processes. This work shows the existence of different types of supply between pahoehoe and a’a flows. Therefore, the morphology of volcanic flows impacts the chemical and isotopic signatures of groundwater, enhancing or reducing the influence of the unsaturated zone on the pathways of infiltrated water. Pahoehoe flows imply horizontal water flows of low discharge at the top of the lava whereas a’a flows seems to be much more heterogeneous and locally able to promote the existence of perched water bodies and further vertical circulations. Taking into account these two types of behaviour, a conceptual scheme of the functioning of this heterogeneous environment is proposed, which will help towards a sustainable management of volcanic aquifers in relation with the . [ABSTRACT FROM AUTHOR]