Eastern Paris Basin Research Articles

A Bajocian event of global coral reef growth: Record from northern Switzerland

Following the extinction event at the Triassic – Jurassic boundary and during the Pliensbachian – Toarcian events, coral reef builders were severely affected, and the number of reef domains during the early Middle Jurassic was at an all-time low. However, new and updated data seem to show that corals were more widespread than previously thought, particularly during the Bajocian (170–168 Ma), but biostratigraphic markers are lacking to constrain the precise timing of reef evolution of this interval. A recently discovered 40 m-thick carbonate unit in northern Switzerland, on the northern Tethys margin, documents this rapid growth. Two cores from this unit display a reef with a high number of specimen but a low coral diversity, dated as Bajocian, which likely grew at a considerable water depth (upper limit of the mesophotic zone or 20–30 m). Additionally, it developed on top of clay mineral-rich accumulation characterised by low relief. Twelve different coral genera were identified, with a strong predominance of Periseris, Isastrea, Thamnasteria and Dendraraea. In the absence of other biostratigraphic markers, palynomorphs were used to provide accurate dating, which shows that palynology is a powerful tool for dating reef deposits. The results show reef growth during the early Bajocian, in the Sauzei and Humphriesianum ammonite zones, based on the palynological data, yielding similar ages to other Bajocian reef localities in the Eastern Paris Basin in France and Luxembourg dated simultaneously. These results indicate that the Middle Jurassic and more specifically the last two ammonite zones of the early Bajocian were periods suitable for coral reef builders, and that global regrowth of coral reefs occurred more rapidly than expected. A new Bajocian reef distribution is presented, showing no reefs at latitudes below 15°. This distribution pattern is probably due to the fact that water temperature was too elevated (> 25 °C) towards the equator for corals, which prevented reef growth. This would tend to favour a scenario in which the global climate, in particular temperature, is a determining factor for coral reef growth.

Multi-stage micrite diagenesis in the late Jurassic of the Eastern Paris Basin: petrophysical and mechanical properties for engineering purposes

Abstract The Calcaires du Barrois Formation is a succession of dominantly micritic limestone of Kimmeridgian to Tithonian age, outcropping in the eastern part of the Paris Basin. This is an active karstic aquifer of interest to Andra (French National Agency for Radioactive Waste Management), who are studying the feasibility of a deep geological repository of radioactive waste in an underground research laboratory located approximately 450 m below the surface. Surface installations of the Industrial Centre for Geological Disposal project are planned in the upstream recharge zone of the aquifer. It is of primary interest to characterize the Calcaires du Barrois Formation to provide guidelines for the planning and sizing of these facilities, to minimize the impact on the aquifer system. An integrated study was designed for this purpose, linking petrography (thin section and scanning electron microscopy), carbon and oxygen stable isotope geochemistry, X-ray diffraction, petrophysics and geomechanics. It is based on the analysis of three key cored wells penetrating the formation at different relative depths. The Calcaires du Barrois have undergone several stages of diagenesis that have defined the current properties. Unconformities associated with the Jurassic–Cretaceous transition led to prolonged early subaerial exposures during which freshwater flowed efficiently through the upper half of the formation. Through mineralogical stabilization, among other processes, microporosity was preserved in micrites in this interval consisting of clean limestone with thin marl layers. The lower half of the formation, more argillaceous, was not or was only slightly affected by this early meteoric diagenesis, and recrystallization and cementation of micrites occurred during burial diagenesis, involving chemical compaction. Later, during the return to the surface associated to the Cenozoic orogens, another phase of meteoric diagenesis affected the uppermost few metres below the outcropping portions of the formation, but without modifying significantly the previously acquired petrophysical properties. Consequently, an intra-formational boundary was progressively developed at around 75 m (from the top reference). This boundary separates (1) a lower half of the Calcaires du Barrois with dense and tight micrites, showing high Young's modulus values, and a moderate intensity of fractures, from (2) an upper half with microporous micrites showing low Young's modulus values, and almost devoid of fractures. A transitional zone of about 30 m thick, with intermediate properties, sitting above this boundary and below the only thin metre-scale macroporous grainstone level of the formation, accommodated most of the deformation linked to the Cenozoic Western European orogens and is intensively fractured. The current hydrogeological model considers a purely sedimentological boundary to delimit two sub-aquifers within the Calcaires du Barrois Formation. This will have to be reappraised since it is here demonstrated that the real boundary is located significantly higher in the formation and is inherited from a multi-stage diagenetic history. These findings will complement and influence planning for the Industrial Centre's project.

Impact of far-field glacially-induced stresses on fault stability in the eastern Paris Basin

Stable Continental Regions (SCR) feature very low seismicity levels, but historical seismicity reveals that these areas can experience large damaging earthquakes of magnitude up to Mw ≈ 7, on faults that were previously undocumented or thought to be stable. Glacial Isostatic Adjustment (GIA) is commonly considered as a factor of SCR deformation and stress perturbations that can trigger fault failure in formerly glaciated areas. Studies suggest that fault reactivation due to GIA may not only be restricted to glaciated areas, but could also occur in their periphery, several hundreds of kilometers away from the former glaciations. In this study, we model GIA associated to the Alpine, Massif Central, Celtic and Scandinavian glaciations from the last glacial cycle, in order to estimate the impact of this process on fault stability in the eastern Paris Basin, an area featuring very low strain rates and seismic activity, but of particular interest due to the proposed construction of a radioactive waste disposal facility. Our computations predict stress perturbations far (hundreds of kilometers away) from the ice loads, of similar amplitude to those in areas where fault reactivation has been observed (1–8 MPa at LGM, 0.8–2 MPa at present-day in our study area). We also show that the interaction between several GIA systems can impact the timing of maximum fault destabilization in a different way than common models considering only a single ice load. The computed far-field glacially-induced stress perturbations remain small compared to ambient crustal stresses, but they are large enough to potentially destabilize faults close to Andersonian geometries, with known faults in the eastern Paris Basin meeting these criteria, mainly in the Marne and Saint-Martin-de-Bossenay fault systems. Yet, there is no known evidence of Quaternary fault activity in the Paris Basin, and discrepancies between the localization of potentially unstable faults due to GIA and seismically active areas in northern France suggests that other processes must be at play.

Last glacial maximum cooling of 9 °C in continental Europe from a 40 kyr-long noble gas paleothermometry record

The Last Glacial Maximum (LGM; ∼26–18 kyr ago) is a time interval of great climatic interest characterized by substantial global cooling driven by radiative forcings and feedbacks associated with orbital changes, lower atmospheric CO2, and large ice sheets. However, reliable proxies of continental paleotemperatures are scarce and often qualitative, which has limited our understanding of the spatial structure of past climate changes. Here, we present a quantitative noble gas temperature (NGT) record of the last ∼40 kyr from the Albian aquifer in Eastern Paris Basin (France, ∼48°N). Our NGT data indicate that the mean annual surface temperature was ∼5 °C during the Marine Isotope Stage 3 (MIS3; ∼40–30 kyr ago), before cooling to ∼2 °C during the LGM, and warming to ∼11 °C in the Holocene, which closely matches modern ground surface temperatures in Eastern France. Combined with water stable isotope analyses, NGT data indicate δD/NGT and δ18O/NGT transfer functions of +1.6 ± 0.4‰/°C and +0.18 ± 0.04‰/°C, respectively. Our noble-gas derived LGM cooling of ∼9 °C (relative to the Holocene) is consistent with previous studies of noble gas paleothermometry in European groundwaters but larger than the low-to-mid latitude estimate of 5.8 ± 0.6 °C derived from a compilation of noble gas records, which supports the notion that continental LGM cooling was more extreme at higher latitudes. While an LGM cooling of ∼9 °C in Eastern France appears compatible with recent data assimilation studies, this value is greater than most estimates from current-generation climate model simulations of the LGM. Comparing our estimate for the temperature in Eastern France during MIS3 (6.4 ± 0.5 °C) with GCM outputs presents a promising avenue to further evaluate climate model simulations and constrain European climate evolution over the last glacial cycle.

Far-field brittle deformation record in the eastern Paris Basin (France)

AbstractJurassic carbonate strata in the eastern Paris Basin exhibit several generations of faults, tension gashes and stylolites. Although their relative chronology can sometimes be determined according to cross-cutting relationships, the duration of major deformation phases and their influence on fluid flow and carbonate cementation are still uncertain. This contribution aims to clarify the timing of brittle deformation and associated calcite cementation. Tension gashes filled by calcite in Jurassic carbonates were sampled in outcrops and boreholes and dated through U–Pb geochronology. Almost all the sampled fractures were cemented during the Cenozoic period. Continuous deformation spread from c. 50 to 30 Ma. Tension gashes oriented N10° to N20° dated at 48–43 Ma show the main Pyrenean contractional stage. A second set of calcites were dated at c. 35–33 Ma and document a Late Eocene – Oligocene extension. A transition from the compressional to the extensional regime is expressed by tension gashes dated between 43 and 35 Ma. Finally, tension gashes oriented N150° to N175°, dated between 32 and 18 Ma, may result from the propagation of the horizontal stress generated by the Alpine orogen or by late Pyrenean deformation. Clumped isotope thermometry on five samples revealed both low crystallization temperatures (from 27 to 53 °C) and the meteoric origin of calcite-precipitating fluids. Our research therefore documents a continuous fracturing from Ypresian to Rupelian times, and less expressed brittle deformation during the Miocene period.

Impact of Far-Field Glacially-Induced Stresses on Fault Stability in the Eastern Paris Basin

Impact of Far-Field Glacially-Induced Stresses on Fault Stability in the Eastern Paris Basin

Origin of 87Sr enrichment in calcite cements in Jurassic limestones (Eastern Paris Basin, France)

In this contribution, the origin of fluids having cemented the Jurassic limestones in the eastern part of the Paris Basin is discussed through the isotopic composition (δ18O, δ13C, 87Sr/86Sr) of authigenic calcite crystals filling vugs and fractures. The Upper and Middle Jurassic limestones, overlying and underlying the Callovian-Oxfordian claystones, experienced dissolution and crystallization leading to a succession of calcite cements depleted in 18O and enriched in 87Sr compared to the bulk host limestone isotope composition. These isotopic shifts originate from the flow of allochthonous basinal fluids through the fracture network that developed during the main tectonic deformation events. Mixing between the allochthonous fluids and the autochthonous local porewaters is attested by variable 87Sr/86Sr in diagenetic calcite. 87Sr-enriched fluids that precipitated calcite cements strongly impact the 87Sr/86Sr ratio of present-day groundwaters in Jurassic limestones and may have modified the Callovian-Oxfordian porewater isotope composition.

The heteromorph ammonite genus Ancyloceras (Ancyloceratidae) in the Paris Basin (lower Aptian, Lower Cretaceous, NE France)

In the present work, we examine a sample of 54 specimens of the heteromorph ammonite genus Ancyloceras d’Orbigny, 1842 from the Argiles à Plicatules Formation (lower Aptian, Lower Cretaceous) of the eastern Paris Basin (NE France). The results are as follows: (1) the sample is regarded as monospecific and assigned to the well-named species Ancyloceras varians d’Orbigny, 1842; (2) its variability is continuous and concerns as well as adult size, coiling and shell ornamentation. Adult size varies by a factor of two from one individual to another. The angle between the proversum and the retroversum is variable. The ornamentation on the spiral and the proversum varies between robust morphotype with trituberculate strong ribs separated by few smooth intercalaries ribs and slender morphotype with feebly tuberculate ribs. There are no arguments in favor of sexual dimorphism in Ancyloceras varians.

Sedimentary architecture, depositional facies and diagenetic response to intracratonic deformation and climate change inferred from outcrops for a pivotal period (Jurassic/Cretaceous boundary, Paris Basin, France)

The aim of this study is to decipher the respective influences of geodynamic and climate disturbances at the Jurassic/Cretaceous boundary on sedimentary facies and carbonate diagenesis in a stable intracratonic basin using isotopic geochemistry and subsidence quantification. Fourteen lithofacies were deposited in a (1) carbonate platform and (2) a delta plain environment. Climate change from cool and wet to warm and semi-arid conditions during the early Tithonian influenced the syn-sedimentary dolomitization process within the carbonate platform during the mid-Tithonian. Architecture and facies reconstructions well-constrained the Jurassic-Cretaceous Unconformity (JCU), which was an important local structural episode marked by (1) an 80 m uplift in the eastern Paris Basin and by (2) the formation of a NW–SE low wavelength 15 km-wide and 30 km-long flexure. This first tectonic event tended to maintain brine ponds and supratidal marsh environments in the platform during the late Tithonian and early Berriasian, forming Purbeckian facies and associated dolomitic facies. A major depositional change occurred between the early and late Berriasian from shallow carbonate platform environments to fluviatile-deltaic clastic deposits (Wealden facies). This facies change is underlain by a major unconformity corresponding to the Ryazanian unconformity. It is marked (1) by erosion processes, karstification of the carbonate substrate, and the development of ferruginous weathering products (goethite), followed by (2) incision processes in a fluvial-deltaic environment. This unconformity is consecutive to a 40 m uplift in the eastern Paris Basin. The rifting phase in the Bay of Biscay, in the Pyrenean Zone, and in the Artic-North Atlantic together with the opening of the Ligurian Sea had a major influence on the northern part of France by causing uplifts (120 m from the Tithonian) and flexuring. Geodynamics played a major role in carbonate demise in the Paris Basin leading to exposure and karstification of the carbonate platform. Added to the generalized uplift, western Tethyan cool and humid conditions from the late Berriasian caused terrigenous influx into large-scale marine domains which was detrimental and unfavorable to carbonate growth.

First Jurassic occurence of Enoploclytia M’Coy, 1849 (Crustacea: Decapoda: Erymidae)

Among the Erymidae Van Straelen, 1925, known as early as the Late Permian (Changhsingian) and widespread in the Jurassic, the genus Enoploclytia M’Coy, 1849 seems to have a late appearance because of its lack before the Cretaceous. Until now, the oldest representative was E. augustobonae Devillez, Charbonnier, Hyžný and Leroy, 2016 from the Early Cretaceous (Barremian) of the eastern Paris basin (France). However, a new fossil collected in Normandy (France), showing the typical carapace groove pattern of Enoploclytia, attests the presence of the genus in the Late Jurassic (Oxfordian).

Origin and influence of the superficial structure on the morphogenesis (Eocene plateaux of the eastern Paris Basin)

The concept of superficial structure relates to surficial deformations that are determined neither by tectonic deformation nor by surface geomorphic processes sensu stricto. This work addresses two mechanisms leading to structural surface disturbances in the Lutetian strata of the Eocene plateaux of the eastern Paris Basin. Firstly, mechanical release which is associated with stress-relief during Quaternary valley downcutting. It results in lateral spreading of the middle Lutetian limestone, and subsequent sub-erosion of underlying sands may cause valley-side cambering. Secondly, ghost-rock karstification in the phreatic zone which is leading to surficial collapse of the upper Lutetian cover. Geological structure (thickness and porosity of the middle Lutetian limestone) and valley-side slopes stratigraphy (position of the upper Ypresian sand) control the spatial distribution of these processes. Ghost-rock karstification, conditioned by tectonic joints is confined to the west; to the east, cambering processes occur where upper Ypresian sand aquifer and alluvial aquifer are connected. During the Quaternary, periglacial conditions account for cambering processes and also for a second phase of karstification within an aquifer perched in the active layer, and from mechanical release joints. Resultant morphological features are then inherited and cambering is even a fossil process where upper Ypresian sand crops out above the valley floor. Consequently, large-scale landforms, derived from the superficial structure, are essentially inactive.

High resolution ion microprobe investigation of the δ18O of carbonate cements (Jurassic, Paris Basin, France): New insights and pending questions

The scope of this work is to investigate, at a high resolution, the oxygen isotope composition (δ18Ocarb) of diagenetic products (synsedimentary and burial calcite cements) in shallow-marine carbonates. SIMS (Secondary Ion Mass Spectrometry) microprobe analyses were performed on thin sections from Oxfordian and Kimmeridgian Formations of the eastern Paris Basin and compared to data obtained on the same diagenetic products by conventional mass spectrometry (acid digestion). Hereby obtained, δ18O are similar, but the SIMS dataset displays a larger range of values.The isotopic zonation obtained by SIMS transects through sequences of cements filling pores, reveals an (expected) isotopic depletion from older stage synsedimentary calcites to younger stage blocky calcites and that follows the CL (cathodoluminescence) zonation. SIMS analyses however show that synsedimentary cements precipitated in intra-skeletal pores, have heavier δ18O than their inter-particle counterparts, with an offset of +4‰V-PDB, despite similar petrographical characteristics. This difference is maintained in the δ18O of the first stages of blocky calcite cements, intra-skeletal blocky calcites showing heavier δ18O than the time equivalent and petrographically identical inter-particle calcites, with an offset of +5‰V-PDB. These offsets are tentatively explained by the precipitation of cements under non-equilibrium conditions in intra-skeletal pores, where organic matter decay may have played a key role, acting notably on the pH.The occurrence of isolated micro-diagenetic environments, co-existing at the thin section scale, is tentatively proposed as an explanation to these small scale and high amplitude δ18O heterogeneities. These results may question the sampling strategy for future works. Microdrilling may miss the observed range of variation, but averaging the values may not necessarily lead to real misinterpretations if a critical selection of samples is performed, targeting potentially similar micro-diagenetic environments and avoiding potentially specific ones, i.e. closed intra-skeletal pores.These results also definitely underscore the need for additional experiments to improve the reliability of SIMS, in order to develop the use of this very high resolution technique for carbonate diagenesis studies.

Quaternary thermokarst and thermal erosion features in northern France: origin and palaeoenvironments

A thermokarst is a collapse feature resulting from the thawing of ice‐rich permafrost or of massive ice of various origins. Little attention has been paid to the sedimentary fabric resulting from this type of collapse, except for glaciotectonic features. In western Europe, two palaeo‐forms are commonly studied: lithalsas and ice‐wedge casts. Collapsed pingos are much rarer. Very few papers have compiled present‐day and fossil data. Here, field data collected from quarries in the eastern Paris Basin were analysed, providing useful records of thermokarst collapses in alluvial calcareous silts, sands, and gravels. These forms have a circular shape when viewed on satellite images. Permafrost is attested regionally by the recurrent occurrence of meter‐sized pattern grounds at the surface of the chalk and of ice‐wedge casts. Traces of segregation and reticulate ice are common. These features are primarily connected to a major interstadial, c. 150 ka BP, orbitally forced and commonly associated with a major glacial retreat. They occur both in drained and waterlogged situations, resulting in a specific pattern of deformation. They are controlled by the brittle and plastic behaviour of sediments and resemble passive glaciotectonism. Normal and reverse faults, with the offset decreasing downward, are common, and those with local shear are reported. Lithalsas, seasonal frost blisters, spring frost blisters and perhaps pingos seem to have formed. Most of these deformations correspond to thermokarst sinkholes bordered by gravitational collapse faults. The offset of these faults increases towards the surface, and the faults have been recurrently confused with neotectonism triggered by palaeo‐earthquakes. However, there are no faults beneath the observed deformation features, and the region lacks recorded seismic activity over the last century. Our data may be helpful in interpreting similar structures elsewhere.

Vertical distribution of helium and 40 Ar/ 36 Ar in porewaters of the Eastern Paris Basin (Bure/Haute-Marne): constraints on transport processes through the sedimentary sequence

Abstract As part of its ongoing project on repositories for high-activity, long-lived radioactive waste, a 2000 m deep borehole was drilled by the French Nuclear Waste Agency (ANDRA) in the layered structure of alternating aquifers and aquitards of the Eastern Paris Basin. Among the information retrieved from this borehole, the vertical distribution of chloride in porewaters showed that, in addition to vertical diffusion, lateral advection in the aquifers plays a major part in transporting chlorine away from the study area. Helium concentrations were also measured in porewaters along the borehole. Because the helium input function is different from that of chlorine, it represents an excellent alternative tracer to further constrain transport characteristics. We applied an advection–diffusion model to the helium profiles with the appropriate source term for 4 He based on U–Th measured concentrations of uranium and thorium. 40 Ar/ 36 Ar data, which were available along the whole sequence, were also simulated. The modelled and measured 4 He profiles were in good agreement, indicating that the transport parameters used for the chlorine simulations were robust. 40 Ar/ 36 Ar simulations also gave coherent results and confirmed that most of the radiogenic 40 Ar remained trapped in the rocks (primarily in clays and feldspars).

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

Lower- to Middle-Triassic sandstones from eastern Paris Basin were buried to a maximum depth of 2500m 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 –5000m and subjected to temperatures of 120 to –150°C. To evaluate this unexpected occurrence, such sandstones were collected from drill cores between 1825 and 2000m 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 for the former and between 0.8 and 1.0 for 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 <0.05μm illite separates confirm two crystallization events at 179.4±4.5 and 149.4±2.5Ma 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.

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)

Past 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 3800mmoll−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 150mmoll−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.

Methanogenic microbial community of the Eastern Paris Basin: Potential for energy production from organic-rich shales

Shallow, thermally immature organic-rich shales represent considerable resources in the Paris Basin (France). We investigated the presence of methanogenic consortia (i.e., syntrophic bacteria and methanogens) in the Lower Toarcian Paper Shales formation, to link geochemical and lithological properties of the rocks to the spatial distribution of microbial communities. The presence of methanogenic microbial populations, demonstrated via their growth in enrichment cultures, occurs throughout most of the rock layers, and may be explained by the transport of organics and microorganisms within the formation. The enriched consortia were able to utilize the organic matter of the rock as sole carbon source in microcosm, indicating a strong potential of these microbial communities for methanogenesis in situ.

Origin of Micropores In Late Jurassic (Oxfordian) Micrites of the Eastern Paris Basin, France

Abstract: Porous micritic facies, either primary chalks or resulting from secondary destructive micritization, can constitute important hydrocarbon or water reservoirs. Characterization of reservoir properties and the understanding of factors which controlled the distribution of porosity are of primary interest to evaluate the prospective reserves. Middle and late Oxfordian limestones of the eastern Paris Basin show several horizons with porosities higher than 20%. The porosity is mainly microporous and located either within secondary micritized grains or in the micritic matrix. Using SEM, cathodoluminescence, as well as confocal microscopy, stable oxygen and carbon isotope ratios, and petrophysical measurements, a scenario for the evolution of the micropores is proposed. Lime mudstones to packstones constitute the majority of the high-porosity facies (HPFs). Inner lagoonal deposits are more micritized and thus more porous than grainstones, and facies rich in leiolitic oncoids and echinoid clasts are less impacted by micritization. Micritization was responsible for an increase of the intragranular porosity in most grain types. During both eogenesis and shallow burial, mineralogical stabilization dissolved aragonitic particles and allowed precipitation of calcite rhombs. This process was probably enhanced below surfaces of subaerial exposure. During burial, Ostwald ripening allowed the growth of larger micrite crystals at the expense of smaller ones during early Berriasian and late Aptian recharges of deep aquifers when the northern margin of the basin was exposed. Overgrowths on micrite crystals were more important in intervals strongly affected by chemical compaction, which favored oversaturation of waters with respect to calcite. In low-porosity horizons (LPFs), the dense micritic texture of oncoids and the monocrystalline architecture of echinoid clasts prevented an intense micritization, while the strong chemical compaction enhanced poronecrosis. Telogenetic fracturing created new fluid pathways that favored inputs of meteoric fluid in porous micrite and allowed the continuation of Ostwald ripening during Cenozoic times. As a whole, mesogenetic inputs of waters undersaturated with respect to calcite in deep aquifers during exposure of basin margins are a more efficient process than early subaerial exposure for enhancing aggrading neomorphism and appearance of microporous micrites. Initial mineralogical heterogeneities also impact the intensity of chemical compaction and thus the stratigraphical distribution of microporous limestones.

Deciphering the history of climate and sea level in the Kimmeridgian deposits of Bure (eastern Paris Basin)

Abstract An integrated stratigraphic study was conducted on a Kimmeridgian succession of 3rd-order cycles including marls and limestones in a shelf context at Bure (Paris Basin). The study was possible due to the exceptional opportunity provided by well-boring activities related to the construction of an underground laboratory of the French National Agency for Radioactive Waste Management (ANDRA). Studies of macrofossils, microfossils, sedimentology, clay mineralogy, isotopic composition (C, O) of shells and organic molecular geochemistry lead to a detailed description of the stratigraphic column, which allows us to address the history of sea-level and climate changes. Six transgressive–regressive cycles are recognised in the studied Kimmeridgian succession. In these 3rd-order cycles, the deepest environments are systematically represented by marls and organic-rich sediments whilst the shallowest are represented by limestones. These cycles do not correspond to changes in temperatures or carbonate production rates at a regional or global scale. On the contrary, long-term palaeontological, sedimentological, and geochemical changes during the Early Kimmeridgian are interpreted as climatically induced. These climatic changes are considered as responsible for bringing significant granular carbonate production to an end, in contrast to carbonate mud that was deposited in alternation with marls throughout the Late Kimmeridgian.

GIS-based variability of building materials towards the Île-de-France cuesta (Paris Basin, France): inventory, distribution, uses and relationship with the environment

Abstract The Pays rémois in the eastern Paris Basin is an administrative area of 1394 km 2 ; in the surroundings of Reims (France). Two main geological substrata are separated by the Île-de-France cuesta: the Tertiary substratum in the western part is composed of various types of geomaterials (clay, sandstone, limestone, burrstone), whereas the substratum in the eastern part is composed only of Cretaceous Chalk. A field survey in each commune of the Pays rémois identified 26 building materials documented in a Geographic Information System database (GIS-database) that includes information about them (lithology, petrographical and petrophysical data, weathering) and the corresponding buildings (e.g. town, georeferenced data, building type, position on the façade). The spatial analysis of the building materials’ distribution (Standard Deviational Ellipse) with GIS identifies their uses and the criteria established for the selection of the materials: availability, efficiency, workability and durability. Some lithologies were preferred for particular buildings or selected for their efficiency in specific positions. The study also defines the relation between the stones’ origin (local and non-local stones) and their application. This database is useful to establish stone replacement strategies in the Pays rémois .