Reconstructing fluid-flow events in Lower-Triassic sandstones of the eastern Paris Basin by elemental tracing and isotopic dating of nanometric illite crystals

International audienceLower- to Middle-Triassic sandstones from eastern Paris Basin were buried to a maximum depth of 2500 m at a paleo-temperature of about 100 °C. They contain extensive amounts of authigenic platy and filamentous illite particles similar to those reported in reservoirs generally buried at 3000 to 5000 m and subjected to temperatures of 120 to 150 °C. To evaluate this unexpected occurrence, such sandstones were collected from drill cores between 1825 and 2000 m depth, and nanometric-sized sub-fractions were separated. The illite crystals were identified by XRD, observed by SEM and TEM, analyzed for their major, trace, rare-earth elements and oxygen isotope compositions, and dated by K-Ar and Rb-Sr.Illite particles display varied growth features in the rock pore space and on authigenic quartz and adularia that they postdate. TEM-EDS crystal-chemical in situ data show that the illite lath/fiber and platelet morphologies correspond at least to two populations with varied interlayer charges: between 0.7 and 0.9 in the former and between 0.8 and 1.0 in the latter, the Fe/Fe+Mg ratio being higher in the platelets. Except for the deeper conglomerate, the PAAS-normalized REE patterns of the illite crystals are bell-shaped, enriched in middle REEs. Ca-carbonates and Ca-phosphates were detected together with illite in the separates. These soluble components yield 87Sr/86Sr ratios that are not strictly in chemical equilibrium with the illite crystals, suggesting successive fluids flows with different chemical compositions. The K-Ar data of finer <0.05 μm illite separates confirm two crystallization events at 179.4 ± 4.5 and 149.4 ± 2.5 Ma during the Early and Late Jurassic. The slightly coarser fractions contain also earlier crystallized or detrital K-bearing minerals characterized by lower δ18O values. The δ18O of the finest authigenic illite separates tends to decrease slightly with depth, from 18.2 (± 0.2) to 16.3 (± 0.2) ‰, suggesting different but contemporaneous crystallization conditions deeper in the section.The illite platelets and filaments crystallized in changing physical-chemical crystallization conditions induced by fluids flows through the host-rock pore system. These flow events were probably driven by repetitive rifting episodes of the North Atlantic Ocean, although located several hundreds kilometers away from eastern Paris Basin, and/or by fracturing events in the nearby basement of the Vosges Massif. Complex relationships between geodynamical events, thermal anomalies, and advective fluids confirm that remote tectonic activities can impact quiescent basins, even if located far from tectono-thermal activities, by discrete and long-distance fluid flows

Impact of a 70°C temperature on an ordinary Portland cement paste/claystone interface: An in situ experiment

International audienceRadioactive wastes in future underground disposal sites will induce a temperature increase at the interface between the cementitious materials and the host rock. To understand the evolution of Portland cement in this environment, an in situ specific device was developed in the Underground Research Laboratory in Tournemire (France). OPC cement paste was put into contact with clayey rock under water-saturated conditions at 70°C. The initial temperature increase led to ettringite dissolution and siliceous katoite precipitation, without monosulfoaluminate formation. After one year of interaction, partial decalcification and diffuse carbonation (calcite precipitation) was observed over 800 μm in the cement paste. At the interface, a layer constituted of phillipsite (zeolite), tobermorite (well-crystallised C-S-H), and C-(A)-S-H had formed. Globally, porosity decreased at both sides of the interface. Geochemical modelling supports the experimental results, especially the coexistence of tobermorite and phillipsite at 70°C, minerals never observed before in concrete/clay interface experiments

Evolution of porewater composition through time in limestone aquifers: Salinity and D/H of fluid inclusion water in authigenic minerals (Jurassic of the eastern Paris basin, France)

International audiencePast water circulations can significantly reduce the porosity and permeability of marine limestones. This is particularly the case in the Middle (Bathonian/Bajocian) to Upper (Oxfordian) Jurassic limestones from the eastern border of the Paris Basin. The knowledge of the timing, the temperature and composition of paleowaters is essential to model the hydrological evolution in this area where the Callovian–Oxfordian claystones are studied for the storage of nuclear wastes. In this way, fluid inclusions hosted in low-temperature (< 60°C) authigenic calcite, quartz and celestite crystals were analyzed by Raman spectroscopy and mass spectrometry to determine the chlorinity and D/H ratios. Chlorinity measurements (mmol Cl per liter of water) in fluid inclusions trapped in authigenic crystals during the late Jurassic/early Cretaceous period revealed unexpected high values, up to 3800 mmol l− 1, indicating that brines were involved in some of the diagenetic crystallization processes. By contrast, fluid inclusions in calcite cements of Cenozoic age within the Oxfordian limestones have low Cl concentration (less than 150 mmol l− 1), thus showing that a dilution event caused by water infiltrations during the Cretaceous uplift of this part of the basin has flushed out the original saline porewater. By coupling δD of fluid inclusion with δ18O of calcite crystals, we estimate that calcite precipitation occurred at temperatures between 25 and 53°C. The hydrogen isotope composition of calcite-forming water is different between the Middle Jurassic (δD ranging from − 20 to − 35.8‰V-SMOW) and the overlying Oxfordian limestone (δD from − 59.5 to − 44.8‰V-SMOW). Present-day groundwaters are also of distinct composition on both sides of the Oxfordian claystones, indicating that limestone aquifers underwent independent hydrologic evolutions since the early diagenetic Jurassic cementation

Les promesses de l'écosystème nucléaire

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Methods for PDO olive oils traceability: state of art and discussion about the possible contribution of strontium isotopic tool

International audienceOlive oil represents an important ingredient in the Mediterranean diet and is appreciated both for nutritional and sensory properties, often related to geographical origin and cultivar of olive fruits employed. Fraudsters trying to seek financial gain can adulterate the product causing economic repercussions and, sometimes sanitary risks.The “protected designation of origin” (PDO) label insures a relative protection of both consumers and honest producers,since it prescribes production techniques and specific geographical origin, but one of the main problems is to set downobjective tools to control these specifications. We reviewed numerous studies using various analytical tools to discriminate PDO olive oils’ geographical origin depending on volatiles compounds, fatty acid and triacylglycerol composition, trace elements, and/or stable isotope ratios, but we highlighted that, despite their efficiency, none of them could provide an irrefutable identification. However, 87Sr/86Sr signature revealed to be an optimal geographicalfingerprint in the same purpose for other food products like cereals, orange juice, coffee or alcoholic beverages. Such 87Sr/86Sr studies do not exist on olive oils, probably because of analytical issues, but we propose that developing complementary 87Sr/86Sr studies could be a promising tool to reenforce the characterization of PDO olive oils

Management of dredged marine sediments in southern France : main keys to large-scale beneficial re-use

International audienceFifty million cubic meters of marine sediments are dredged each year in France in order to maintain and develop harbor activities and sustain the economy of littoral territories. Because of anthropogenic activities in and around these harbours, sediments are often enriched in pollutants that can be released when sediments are dredged and induce a risk for human and environment. French regulations come to govern the management of dredged marine sediments, considering them ‘safe’ and possibly to be dumped at sea or contaminated’ and needed to be treated on land as waste. However, sediments can be considered as valuable resources but they remain today lowly reused. This poster provides an overview of the technical and regulatory aspects elated to dredged marine sediment management in France and aims to determine why dredged marine sediments are not fully utilized as a resource and whether these barriers can be overcome. The regulation for the management of dredged material is complex and lies at the intersection of the European framework directives on water (WFD), waste and marine strategy. While WFD provides for European reference values for priority substances, there are no common European standards for sediments. Dredged sediments are mainly composed of particles with heterogeneous grain size that can be used in applications ranging from building materials to plant growing media. The organic matter and heavy metals potentially present can also be used for beneficial purposes. There are several reasons why not all dredged sediment is used. These include the irregular composition of dredged sediments, the frequent presence of pollutants in the sediments and the high cost associated with reusing dredged sediments compared to other sources. The variable nature of dredged sediments means that materials made from them have different attributes. High processing costs are also a barrier to the reuse of dredged sediments. Steps required to prepare dredged sediments for reuse result in higher prices than for similar resources. These barriers lead to a low demand for dredged sediments. This demand can be stimulated by overnment incentives and a good regulatory framework. Cost would decrease with the increasing reuse of dredged sediments, as processes would become more efficient and new treatment methods would be tried. National regulations could help streamline this process by standardizing sediment composition tests, removing the classification of dredged sediments as ”waste” and creating a regulated market for dredged sediments, thereby creating a promising economic sector

Geochemical Tracing of Potential Hydraulic Connections between Groundwater and Run-Off Water in Northeastern Kansas, USA

This study is focused on establishing the extent of potential hydraulic connections of local lowland aquifers with the run-off waters of a nearby creek and two major rivers in and around Fort Riley in northeastern Kansas, USA. It is based on collective evidence by combining the contents of several major and trace elements of the waters with their oxygen, hydrogen and Sr isotopic compositions. The area of investigation is located a few miles to the west of the Kansas Konza Prairie, which is a United States designated site for regular monitoring of ecological and environmental configurations. The δ18O and δD of the run-off waters from the two rivers and the creek, and of the ground waters from local aquifers are almost identical. Relative to the General Meteoric Water Line, the δ18O-δD data have a tendency to deviate towards relatively lower δ18O values, as do generally the sub-surface waters of intra-continental basins. The observed stable isotope compositions for these waters preclude any significant impact by either an evapo-transpiration process by the vegetation, or an interaction with immediate mineral-rock matrices. The 87Sr/86Sr ratios of the aquifer waters collected from wells close to the Kansas River were markedly different from those of the river waters, confirming a lack of hydraulic interactions between the aquifers and the river. On the contrary, ground waters from wells at a relative distance from the Kansas River have 87Sr/86Sr ratios, Sr contents and Sr/Ca ratios that are similar to those of the river water, suggesting a hydraulic connection between these aquifers and the river, as well as a lack of any impact of the vegetation. An underground water supply from nearby Summer Hill located to the north of the study area has also been detected, except for its western border where no interactions occurred apparently between the aquifer waters and the reservoir rocks, or with the creek and river waters. The 87Sr/86Sr signatures of the ground waters suggest also a major east-west flow system in the study area that can be divided into three entities, together with a supplementary north-south trend along the Threemile creek towards the Kansas River