Fadi H Nader
email: fadi.nader@gmail.com

France Champenois

Mickaël Barbier

Mathilde Adelinet

Elisabeth Rosenberg

Pascal Houel

Jocelyne Delmas

Rudy Swennen

Diagenetic effects of compaction on reservoir properties: The case ofearly callovian "Dalle Nacrée" formation (Paris basin, France)

de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Carbonate rocks account for about half the world oil and gas reservoirs [START_REF] Warren | Dolomite: occurrence: evolution and economically important associations[END_REF]. Carbonate reservoirs are complex and their characterization is often difficult irrespective of the scale of the investigation, because they dominantly originate from heterogeneous sedimentary systems in shallow marine or continental lacustrine environments. Due to their high chemical reactivity, these sedimentary rocks undergo physical or chemical changes just after deposition till their exhumation (e.g. dissolution, cementation, neomorphism; [START_REF] Scholle | A Color Guide to the Petrography of Carbonate Rocks[END_REF][START_REF] Morad | Impact of diagenesis on the spatial and temporal distribution of reservoir quality in the Jurassic Arab D and C members offshore Abu Dhabi oilfield, United Arab Emirates[END_REF][START_REF] Nader | Multi-scale diagenesis and impacts on heterogeneity of reservoir rocks[END_REF]. Such sedimentary and diagenetic heterogeneities increase the complexity to understand the evolution of the petrophysical properties of these rocks. One main process responsible for the change of the pore network through time is compaction [START_REF] Heydari | Porosity loss, fluid flow, and mass transfer in limestone reservoirs: application to the Upper Jurassic Smackover Formation, Mississippi[END_REF]. In fact, due to the increasing litho-static pressure, the pore volume is expected to decrease with depth [START_REF] Moore | Carbonate Reservoirs: Development in Sedimentology[END_REF]and reference therein). This is not so easy to predict in carbonate rocks due to diagenesis, which could change the mechanical properties of the rocks, controlling their response to compaction (Blaise, 2012). Log signatures of carbonates are therefore not straightforward to interpret and show a wide range of values due to the influence of diagenesis, specially the commonly used sonic wave propagation velocities [START_REF] Eberli | Factors controlling elastic properties in carbonate sediments and rocks[END_REF] for Jurassic limestones of the Paris Basin see [START_REF] Brigaud | Acoustic properties of ancient shallow-marine carbonates: effects of depositional environment and diagenetic processes (Middle Jurassic, Paris Basin, France)[END_REF][START_REF] Casteleyn | An integrated study of the petrophysical properties of carbonate rocks from the Oolithe Blanche formation in the Paris Basin[END_REF][START_REF] Regnet | Acoustic and reservoir properties of microporous carbonate rocks: implication of micrite particle size and morphology[END_REF]. Hence, additional research on the compaction and associated processes occurring during burial diagenesis remains crucial and needed.

Key sedimentological, petrographic, and diagenetic data related to the Middle Jurassic carbonate rocks of the Paris Basin are provided by [START_REF] Floquet | Les systèmes sédimentaires bourguignons d'âge bathonien terminal-callovien: bull[END_REF], [START_REF] Javaux | La plate-forme parisienne et bourguignonne au Bathonien terminal et au Callovien -Dynamique sédimentaire, séquentielle et diagénétique, Place et création des réservoirs potentiels. 16[END_REF], [START_REF] Granier | Clés pour la modélisation sédimentologique de quelques réservoirs oolithiques: l'exemple du champ de Villeperdue, Bassin de Paris[END_REF][START_REF] Granier | A sedimentological model of the Callovian oolite reservoir of the Villeperdue oil field, Paris Basin[END_REF]) [START_REF] Granier | Quick look cathodoluminescence analyses and their impact on the interpretation of carbonate reservoirs. Case study of mid-Jurassic oolitic resevoirs in the Paris Basin[END_REF], [START_REF] Garcia | The validity of two biostratigraphic approaches in sequence stratigraphic correlations: brachiopod zones and marker-beds in the Jurassic[END_REF], [START_REF] Gaumet | Fondements géologiques Pour La Modélisation Stratigraphique Des Systèmes Carbonatés[END_REF], [START_REF] Guillocheau | Meso-Cenozoic geodynamic evolution of the Paris Basin: 3D stratigraphic constraints[END_REF], [START_REF] Buschaert | Widespread cementation induced by inflow of continental water in the eastern part of the Paris basin: o and C isotopic study of carbonate cements[END_REF], Brigaud et al. (2009a, b), [START_REF] Delmas | Petrophysical properties of the middle jurassic carbonates in the PICOREF sector (South champagne, Paris basin, France)[END_REF], [START_REF] Brosse | Selection and characterization of geological sites able to host a pilot-Scale CO2 storage in the Paris basin (GeoCarbone-PICOREF)[END_REF] and [START_REF] Carpentier | Impact of basin burial and exhumation on Jurassic carbonates diagenesis on both sides of a thick clay barrier (Paris Basin, NE France)[END_REF], among others. This paper aims to investigate the diagenetic influence of burial compaction on the reservoir Table 1 List of the investigated wells, including well code, current and estimated total burial depths, and thickness of the "Dalle Nacrée" Formation. The "Maximal estimated burial depth" represents the present-day burial depth in addition to the thickness eroded series. properties (porosity and permeability) of these carbonate rocks to provide eventually constraints for numerical modelling tools and workflows (e.g. [START_REF] Gonc ¸alvès | Contribution of a three-dimensional regional scale basin model to the study of the past fluid flow evolution and the present hydrology of the Paris basin, France[END_REF]Blaise, 2012). For this purpose the "Dalle Nacrée" Formation (Early Callovian) deposited in the Paris Basin was selected as a case study. This "oobioclastic" rock succession forms a characteristic limestone reservoir that has been intercepted by subsurface boreholes at burial depths ranging approximately between 1000 and 1700 m in the study area.

Well

Geological setting

The Paris Basin is a classical example of an intracratonic basin that is characterized by decreasing thermal subsidence in an extensional setting since its genesis (Pomerol, 1989;[START_REF] Guillocheau | Meso-Cenozoic geodynamic evolution of the Paris Basin: 3D stratigraphic constraints[END_REF][START_REF] Solleuz | From a mountain belt collapse to a sedimentary basin development: 2-D thermal model based on inversion of stratigraphic data in the Paris Basin[END_REF]. Superimposed, successive lithospheric processes are believed to have shaped the history of this sedimentary basin (e.g. [START_REF] Loup | Subsidence analysis in the Paris Basin: a key to Northwest European intracontinental basins?[END_REF]. [START_REF] Guillocheau | Meso-Cenozoic geodynamic evolution of the Paris Basin: 3D stratigraphic constraints[END_REF] demonstrated that the overall subsidence history of the Paris Basin, which started upon Permo-Triassic rifting, influenced the nature, geometry and hierarchy of the stratigraphic cycles constituting the basin infill. Since Middle Jurassic times, subsidence rates and accommodation spaces varied considerably together with the type of the sedimentary filling (e.g. carbonates and silici-clastics). Though, the Early Cretaceous was characterized by a compression regime, the major compression and uplift occurred after the Turonian, with three main folding events (Late Cretaceous/Senonian, Lutetian-Early Oligocene, and Burdigalian-Late Miocene). These major tectonic events are inherently associated with the geodynamic evolution of the Paris Basin [START_REF] Blès | Successive post-Variscan stress fields in the French Massif Central and its borders (Western European plate): comparison with geodynamic data[END_REF], and they resulted in significant fracturing phases which provided conduits for basinal fluids and the drivers for diagenesis. [START_REF] Lacombe | Joint analyses of calcite twins and fault slips as a key for deciphering polyphase tectonics: burgundy as a case study[END_REF][START_REF] Lacombe | Calcite twins as a key to paleostress in sedimentary basins: preliminary results from drill cores of the Paris Basin[END_REF] and [START_REF] Rocher | Intraplate paleostresses reconstructed with calcite twinning and faulting: improved method and application to the eastern Paris Basin (Lorraine, France)[END_REF] managed to reconstruct the intraplate paleostresses that prevailed in the Paris Basin and its south and eastern margins, indicating NNE-SSW extension in the late Mesozoic, N-S compression and strike-slip phases striking successively NNW and NNE during the Tertiary Pyrenean orogenesis followed by WNW extension in the Oligocene, and WNW-ESE compression attributed to the Alpine Late Miocene collision. Furthermore, [START_REF] Andre | Chronology of fracture sealing under a meteoric fluid environment: microtectonic and isotopic evidence of major Cainozoic events in the eastern Paris Basin (France)[END_REF] used microtectonics and stable oxygen and carbon isotopic analyses to demonstrate that late Jurassic to early Cretaceous extension started with a WNW-ESE direction but changed to E-W. In the Eocene, Pyrenean convergence, compression prevailed with NNE-SSW to NE-SW and finally ENE-WSW directions; while the Oligocene transition from Pyrenean to Alpine convergence, was marked by major changes in orientations and radial extension. [START_REF] Andre | Chronology of fracture sealing under a meteoric fluid environment: microtectonic and isotopic evidence of major Cainozoic events in the eastern Paris Basin (France)[END_REF] pointed out strong reactivations of bedding stylolitisation at this time. They also suggested that the Alpine convergence (since the late Miocene), witnessed a change in the directions of shortening from WNW-ESE to NNW-SSE. [START_REF] Bourgeois | Separation of rifting and lithospheric folding signatures in the NW-Alpine foreland[END_REF] associated the recent, Alpine orogeny with intraplate deformation affecting the Paris Basin, namely the "buckling" of its margins due to long-waevlength lithospheric folds striking NE. They have even postulated considerable rock uplift resulting from such folds (ca. 1000m). Hence, the Paris Basin devel-oped by stretching and thermal subsidence (Triassic and Jurassic depocentres) followed by several episodes of lithospheric folding (as of the Cretaceous times) that led to uplifted margins and erosione.g. Vosges and Black Forest areas [START_REF] Guillocheau | Meso-Cenozoic geodynamic evolution of the Paris Basin: 3D stratigraphic constraints[END_REF][START_REF] Bourgeois | Separation of rifting and lithospheric folding signatures in the NW-Alpine foreland[END_REF]. The amount and timing of such erosions remain debatable, yet, based on stratigraphic corrleations and geomorphology, up to 500 m of Late Cretaceous carbonates have been eroded along the southeastern margins of the basin (e.g. Le Roux, 1980;Fizaine, 2012). Taking into account of such eroded rock series is crucial for estimating properly the maximal burial of the "Dalle Nacrée" Formation across the Paris Basin (Table 1).

An epicontinental sea covered the Paris Basin during Bathonian-Callovian times, which developed whithin subtropical latitudes (25-30 • N) (Fig. 1; [START_REF] Enay | Synthèse paléogéographique du Jurassique franc ¸ais, Document du Laboratoire de Géologie de Lyon[END_REF]Thierry and Barrier, 2000;Brigaud et al., 2009b). Overlying an aggradational Bathonian carbonate platform, consisting of ooids and bioclastic shoals (Oolithe Blanche) and carbonate muds (Calcaire de Comblanchien), shallow marine bioclastic and oolitic sands prevailed. These facies mark the end of a transgressive succession; they are overlain by the Middle Callovian maximum flooding surface [START_REF] Guillocheau | Meso-Cenozoic geodynamic evolution of the Paris Basin: 3D stratigraphic constraints[END_REF]. During the latest Bathonian-Early Callovian, the Paris Basin was, subsequently, characterized by oobioclastic ramp settings [START_REF] Garcia | Bathonian-Callovian Paris Basin-Subalpine Basin intercorrelations along an Ardennes-Ardèche cross-section[END_REF][START_REF] Gaumet | Fondements géologiques Pour La Modélisation Stratigraphique Des Systèmes Carbonatés[END_REF]Brigaud et al., 2009a,b). The Callovian witnessed a major carbonate productivity crisis at the Bathonian/Callovian boundary, in relation to the break-up of the Pangea supercontinent as well as global warming and associated transgression.

The study area concerns the Early Callovian oobioclastic facies and is located in the southeastern part of the Paris Basin (Yonne, Aube, and Haute-Marne; France). It comprises fives boreholes (Table 1): i.e. the Arrentières (ART) borehole situated towards the southeastern margin of the basin contrary to the Saint-Martin-de-Bossenay (SMB), Gisy-les-Nobles (GN), Grange-le-Bocage (GLB) and Avon-la-Pèze boreholes (AP) which are located in the deeper central part of the basin, to the west (Fig. 2). These boreholes intercept the Early Callovian "Dalle Nacrée" Formation with thicknesses varying between 13 and 22 m (GLB and AP, respectively; Table 1). The thicknesses recorded in the marginal Arrentières (ART) borehole and the further basinward Saint-Martin-de-Bossenay (SMB) borehole are very similar (19 and 21m, respectively). The maximum thickness of this formation reaches some 30 m in the Villeperdue oilfield (toward the centre of the Paris Basin; Fig. 3).

The term "Dalle Nacrée" is an old name that was given to a rock succession (mainly reservoirs) representing two sequences that are refered to as "Pierre de Dijon-Corton" and "Pierre de Ladoix", from bottom to top [START_REF] Floquet | Les systèmes sédimentaires bourguignons d'âge bathonien terminal-callovien: bull[END_REF][START_REF] Javaux | La plate-forme parisienne et bourguignonne au Bathonien terminal et au Callovien -Dynamique sédimentaire, séquentielle et diagénétique, Place et création des réservoirs potentiels. 16[END_REF][START_REF] Garcia | Bathonian-Callovian Paris Basin-Subalpine Basin intercorrelations along an Ardennes-Ardèche cross-section[END_REF][START_REF] Thierry | Les ammonites du Callovien-Oxfordien des sondages Andra dans l'Est du bassin de Paris: synthèse biochronostratigraphique, intérêts paléoécologique et paléobiogéographique[END_REF]. The two latter rock units are sometimes termed together as "Calcaires d'Etrochey" [START_REF] Purser | Plates-formes carbonatées exemple du Jurassique moyen du Bassin de Paris, Dynamique et méthodes d'étude des bassins sédimentaires[END_REF][START_REF] Gaumet | Fondements géologiques Pour La Modélisation Stratigraphique Des Systèmes Carbonatés[END_REF]. Stratigraphically, this formation is attributed to the upper part of the Middle Jurassic -Late Bathonian to/or Early Callovian [START_REF] Thierry | Dalle Nacrée. Synthèse Géologique du Bassin de Paris[END_REF][START_REF] Gaumet | Stratigraphic control upon depositional facies, geometries and profiles across the Bathonian-Callovian carbonate platform in Burgundy[END_REF]ca. between 166.1-163.5 Ma;Gradstein et al., 2012). It is underlain by the Late Bathonian "Comblanchien", and overlain by the Middle Callovian "Marnes de Massingy". The latter, marl deposits make a relatively thick seal- [START_REF] Purser | Plates-formes carbonatées exemple du Jurassique moyen du Bassin de Paris, Dynamique et méthodes d'étude des bassins sédimentaires[END_REF], [START_REF] Enay | Synthèse paléogéographique du Jurassique franc ¸ais, Document du Laboratoire de Géologie de Lyon[END_REF] and [START_REF] Thierry | Late Sinemurian, Middle Toarcian, Middle Callovian, Early Kimmeridgian, Early Tithonian[END_REF].

ing unit that disconnects the Early Callovian limestones from the Late Jurassic limestone reservoirs. The "Dalle Nacrée" mainly consists of bioclastic or oolitic limestones, interpreted to be deposited in a medium to high energy subtidal environment with local pools of low energy [START_REF] Thierry | Dalle Nacrée. Synthèse Géologique du Bassin de Paris[END_REF][START_REF] Granier | A sedimentological model of the Callovian oolite reservoir of the Villeperdue oil field, Paris Basin[END_REF]. The Pierre de Dijon-Corton and Pierre de Ladoix strata are rich in bryozoans, echinoids, crinoids, coral debris, bivalves, brachiopods, ammonites and occasionally green algae [START_REF] Javaux | La plate-forme parisienne et bourguignonne au Bathonien terminal et au Callovien -Dynamique sédimentaire, séquentielle et diagénétique, Place et création des réservoirs potentiels. 16[END_REF][START_REF] Gaumet | Fondements géologiques Pour La Modélisation Stratigraphique Des Systèmes Carbonatés[END_REF][START_REF] Guillocheau | Meso-Cenozoic geodynamic evolution of the Paris Basin: 3D stratigraphic constraints[END_REF][START_REF] Thierry | Les ammonites du Callovien-Oxfordien des sondages Andra dans l'Est du bassin de Paris: synthèse biochronostratigraphique, intérêts paléoécologique et paléobiogéographique[END_REF]Brigaud et al., 2009b).

One of the major hydrocarbon discoveries in the "Dalle Nacrée" Formation is the Villeperdue oilfieldwith a reserve of some 100 million barrelslocated about 100 km east of Paris City. There, the "Dalle Nacrée" occurs at a burial depth of about 1800 m (below ground level). Its thickness ranges between 20 and 30 m. It has been subdivided into three units [START_REF] Granier | Clés pour la modélisation sédimentologique de quelques réservoirs oolithiques: l'exemple du champ de Villeperdue, Bassin de Paris[END_REF]. From bottom to top the following units are differentiated: 1) a unit dominated by radial ooids, 2) a unit characterized by concentric ooids and 3) a unit composed of micritic ooids. These units also represent three shallowing-upward parasequences of the lowermost "Callovian" transgressive system tract. They are separated by major regional sedimentary discontinuities (hardground, oolite gravel and oolite pebble layers), which have been generated by allocyclic processes, and were interpreted as time-lines by [START_REF] Granier | A sedimentological model of the Callovian oolite reservoir of the Villeperdue oil field, Paris Basin[END_REF]. These discontinuities permitted subdividing the "Dalle Nacrée" Formation into three reservoir units corresponding to distinct ooid textures which also were observed in well logs [START_REF] Granier | Quick look cathodoluminescence analyses and their impact on the interpretation of carbonate reservoirs. Case study of mid-Jurassic oolitic resevoirs in the Paris Basin[END_REF]. The three main reservoir units can be subdivised further into sub-units called "pseudo-parasequences" on the basis of local discontinuities of autocyclic origin, in relation to the migration of oolitic sedimentary bodies [START_REF] Granier | Clés pour la modélisation sédimentologique de quelques réservoirs oolithiques: l'exemple du champ de Villeperdue, Bassin de Paris[END_REF]. Noteworthy is that the "Dalle Nacrée" reservoirs have been affected by a variety of diagenetic processes early after deposition and later during further burial [START_REF] Javaux | La plate-forme parisienne et bourguignonne au Bathonien terminal et au Callovien -Dynamique sédimentaire, séquentielle et diagénétique, Place et création des réservoirs potentiels. 16[END_REF][START_REF] Carpentier | Impact of basin burial and exhumation on Jurassic carbonates diagenesis on both sides of a thick clay barrier (Paris Basin, NE France)[END_REF]. Diagenesis has therefore major impacts on the reservoir properties and overall heterogeneities of this formation.

Methods

Petrography

Based on the availability of well cores and total thickness of the Dalle Nacrée Formation, samples were prepared mainly from three boreholes (ART1, AP2, and GN1; Tables 1 and2). Targets of sampling were horizons with the best apparent reservoir properties in the available boreholes (the depth of the samples are given in Table 2). Only a few, representative, samples were collected from the remaining cores of SMB18 and GLB1. A total of 41 plugs (1-inch in diameter) were taken horizontally and vertically from the available well cores to make thin sections, which were impregnated with blue epoxy to identify the pore space. The latter were stained with alizarin red-S and potassium ferricyanide to differentiate carbonate minerals also based on their ferroan nature [START_REF] Dickson | Carbonate identification and genesis as revealed by staining[END_REF].

Petrographic analyses under conventional polarized microscope, fluorescence (Nikon Eclipse LV100 POL microscope) and cathodoluminescence (CL, NIKON eclipse ME600) consisted firstly of characterizing the overall components, matrix phases and porosity distribution of the investigated thin sections. The limestone textures have been described using the [START_REF] Dunham | Classification of carbonate rocks according to depositional texture[END_REF] modified by [START_REF] Embry | A late devonian reef tract on northeastern banks island[END_REF] classification, and the porosity according to [START_REF] Choquette | Geological nomenclature and classification of porosity in sedimentary cabonates[END_REF]. Cement (chemical diagenetic) phases were described principally based on the classification of [START_REF] Flügel | Microfacies of Carbonate Rocks[END_REF]. All thin sections were scanned and analyzed with JMicroVision © (version 1.2.7, [START_REF] Roduit | JMicroVision: Image Analysis Toolbox for Measuring and Quantifying Components of High-definition Images[END_REF] to quantify porosity, amount of grains, micrite and different kinds of cement. Matlab ® scripts, developed by [START_REF] Claes | A 3D classification for mathematical pore shape description in complex carbonate reservoir rocks[END_REF], were used to determine porosity, overall cement and grain percentages for each thin section, based on segmentation and digital point counting (500 points, 1000 simulations for each thin section). Both scripts were run with Matlab version 7.9.0.529 (R2009b) Copyright © 1984-2013 and make use of the Matlab Image Processing Toolbox TM .

Petrophysics and image analysis

Micro-Computed Tomography (CT) allowed to carry out a 3D quantitative and qualitative investigation of the pore space at a high resolution. In this study, this technique was used to determine the interconnectivity of pores. Four samples were scanned with CT: i.e. samples GN1 2, AP2 8, ART1 6 and SMB18 2. The CT equipment installed at IFPEN is a microtomograph X Nanotom from PHOENIX X-ray (German made). A Hamamatsu flat detector (110 × 110 mm) was used in the setup. Acquisition parameters for the rock samples were the following: 6 mm diameter sample, source object distance 12 mm, source-detector distance 200 mm, pixel size 3 m, 1100 × 1100 field of view, 90 KV (second scan for sample ART1 6 at 70KV), 170 A, 0.2 • angular step, Cu 0.1 mm filter, 2h30 acquisition time. ImageJ © is a public domain Java image processing program that can display, edit, analyze, process, save and print 8-bit, 16-bit and 32-bit images. The program can adjust the threshold and calculate the area, mean (= grey level, = macroporosity), minima, maxima and standard deviation of total stacks of CT slices using the "Stack" plugin. The acquired CT-values contribute to the calculation of average total macroporosity (> 3 m) for each sample. Avizo ® (version 6.0.0 XL, 2009) was used as a 3D analysis software from Mercury Computer Systems SAS for scientific and industrial data visualization. The resulting images and videos after segmentation gave a clear overview of potentially connected pore-clusters; each of which was represented by a distinct colour.

He-injection porosity and classical water-saturation permeability measurements (Table 3) were applied on the same samples that were analyzed by MICP (since the latter is a destructive technique). Mercury Injection Capillary Pressure (MICP) measurements were performed at IFPEN and provide a percentage of the measured porosity and permeability (Table 3). MICP was executed with a AutoPore IV of Micromeritics Instrument Corporation on 22 samples from the available wells (Table 3). This mercury porosimeter of 60000 psi (∼4000 bar) covers a pore throat size range of approximately 0.003 m to 360 m. It involves the intrusion of mercury (i.e. a non-wetting liquid) at a high pressure, and constant increasing rate, into the investigated sample. The injected volume allows the determination of the pore throat and bulk (Hg) porosity. Finaly, more detailed permeability values (Table 3) were calculated based on Sawnson's empirical equation correlating permeability with Mercury Injection Capillary Pressure [START_REF] Swanson | A simple correlation between permeabilities and mercury capillary pressures[END_REF].

Geochemistry

Various diagenetic phases were carefully sampled (using a dentist micro-drill) for measuring their carbon and oxygen stable isotopic composition (33 samples; Table 4) at the University of Erlangen -Germany (Institute of Geology and Mineralogy). For this purpose the carbonate powders were reacted with 100% phosphoric acid (density > 1.9; [START_REF] Wachter | Exchange of oxygen isotopes in carbon dioxidephosphoric (correction of phosporic) acid systems[END_REF] at 75 • C in an online carbonate preparation line (Carbo-Kielsingle sample acid bath) connected to a ThermoFinnigan 252 mass-spectrometer (Thermo Electron Corp., Waltham, MA, USA). All values are reported in per mil relative to Vienna Pee Dee belemnite standard (‰V-PDB) by assigning a ␦ 13 C value of +1.95‰ and a ␦ 18 O value of -2.20‰ to National Bureau Standards (NBS) 19. Oxygen isotopic compositions of dolomites were corrected using the fractionation factors given by [START_REF] Rosenbaum | An isotopic study of siderites, dolomites and ankerites at high temperatures[END_REF]. Reproducibility based on replicate analysis of laboratory standards is better than ±0.02‰ for ␦ 13 C and ±0.03‰ for ␦ 18 O.

Numerical modelling

EasyTrace software (version 4.7 R1, July 2013; © 1992-2013, IFP Energie nouvelles) was used for the statistical analyses of quantitative petrographic data. EasyTrace is an 1D multi-disciplinary data processing and editing tool, featuring advanced spreadsheets and a wide range of functionalities for analysing and editing well data. Burial modelling was achieved by means of the software TemisFlow TM 1D (Beicip-Franlab, IFP Energies nouvelles). The input stratigraphic data included thickness, age of deposition and erosion, as well as lithological parameters. With this software, the burial/thermal history at each investigated well locations were constructed resulting in the evolution of associated pressure and temperature (discussed below). ) and grainstone (C to F) microfacies in the "Dalle Nacrée" (Early Callovian), with a varying degree of compaction (Paris Basin) (view under parallel polarized light, PPL): A) sutured grain contacts indicating some degree of compaction (GLB1 well). B) continuous stylolite and fracturing related to further compaction (AP2 well). C) From grains barely touching each other to point and plane-parallel grain contacts;D) from point/plane-parallel to concavoconvex grain-to-grain contacts, deformed to slightly spalled grain coatings, partial grain fracturing of more resistant grains; E) all grains touching each other with sutured and interpenetrating grain-to-grain contacts, still some free space left between grains, spalled coated grains; F) barely free space left between grains; sutured grain-to-grain contacts; abundant spalled coated grains, well-developed individual and stylolite swarms cutting through grains.

Results

Petrography

Rock textures

Two main limestone textures can be distinguished based on petrographic analyses, namely wackestones and grainstones (Fig. 4). The wackestone microfacies (mainly found in wells GLB1 and AP2) is characterized by an initial micrite matrix ( > 50%) that was partially replaced by microsparite. Detrital components of the wackestone are merely subrounded bioclasts ( > 30%) with sizes ranging from 400 to 4000 m. Subordinated framework components ( < 30%) are (well) rounded ooids (400-600 m), well rounded pellets (100 m) and subrounded mudclasts (300 m).

The grainstone microfacies (found in wells SMB18, GN1, AP2 and ART1) is characterized by a considerable amount of calcite cement ( > 30%). Only occasionally, minor amounts of micrite (<10%) have been observed within the rock textures (e.g. ART1 well). This facies contains rounded to well-rounded ooids (>40%), sub-rounded bioclasts and pellets (both ∼20%), and rare sub-rounded mudclasts ( < 10%). The ooids have a uniform size in ART1 and GN1 (∼ 400 m) while they can go up to 1500 m in the other wells. The bioclasts have sizes ranging from 300 to 1500 m, pellets extent from 100 to 300 m, and mudclasts are ∼300 m in size.

Chemical diagenetic phases

Five major chemical diagnetic phases have been observed, namely: syntaxial overgrowth cement, microsparite, blocky/equant calcite cements, dolomite cement and pyrite. The presented description of the (chemical) diagenetic phases primarily follows [START_REF] Flügel | Microfacies of Carbonate Rocks[END_REF] i.e. cement described by fabrics and types. Since this paper focuses on the blocky calcite cement, they have been further subdivided on the basis of their cathodoluminescence characteristics (i.e. BC1, BC2, BC3, see below) (cf. [START_REF] Carpentier | Impact of basin burial and exhumation on Jurassic carbonates diagenesis on both sides of a thick clay barrier (Paris Basin, NE France)[END_REF].

Syntaxial overgrowth calcite cement, 400-2000 m in size, is commonly found around echinoderm fragments in grainstones, displaying a cloudy to limpid fabric (Fig. 5). Occasionally, this cement displays a poikilotopic fabric, engulfing grains through its growth (Fig. 5A). Based on the investigated thin sections, this phase is characterized by a zoned pattern under cathodoluminescence (CL). Accordingly, three zones have been distinguished, i.e. nonluminescent, limpid bright orange, and dull, dark to light brown CL-zones (Fig. 5B). Systematically, in almost all investigated thin sections, the contact between the two first zones is irregular and reflects a corrosive stage. Under fluorescence (FL) these three zones show respectively, light brown, bright greenish yellow and zoned green to greenish black colours (Fig. 5D). Upon staining the first two phases show a pink colour indicating pure calcite, while the last phase is purple (Fig. 5C), indicating the presence of ferroan calcite [START_REF] Dickson | Carbonate identification and genesis as revealed by staining[END_REF]. The syntaxial calcite cement is rare and poorly developed in the wackestone facies (AP2 and GBL1 wells) as well as in the grainstones of the ART1 well. In AP2, GBL1 and ART1 wackestones, only the two first CL-zones (described above) are present. On the contrary, all three zones are present in the grainstones. Where the syntaxial calcite cement appears to be best developed, it can account up to ∼23% of the bulk sample (e.g. in cores of the GN1 well).

Microsparite calcite appears under three forms with distinct genetic characteristics. First, a microsparite cement phase is observed around grains, showing an isopachous fabric (Figs. 6A,B,C). Here, it often marks the transition between the grains and blocky calcite cement. A similar type of cement appears replacing mud in grains and matrix (Figs. 6A,B). Other microsparite calcite cements are found filling dissolved grains (Figs. 6D,E,F). These show equant mosaic microcrystalline fabrics, although occasionally drusy mosaic fabric is observed (e.g. in cores of the AP2 well) when enough space for precipitation was available (Fig. 6E,F). The euhedral microsparite crystals are transparent and are between 50 and 300 m in size. They show a pink colour upon staining. Under CL two distinct zones can be differentiated: a first nonluminescent black phase, and a second thin, bright orange phase (Figs. 6B,D). Under FL, the two CL zones correspond to light brown and bright green-yellow phases, respectively (Fig. 6F). Microsparite calcite phases are present in every well and always show the two described CL and FL zones. Their presence range from ∼5% in ART1 to ∼31% in GLB1, where they replace considerably the mud matrix.

Blocky cements consist of clear subhedral calcite crystals ranging from 200 to 1500 m in size without a preferred orientation (Fig. 7). Upon staining, their colour appear purple (Figs. 7C,E), indicating a ferroan nature [START_REF] Dickson | Carbonate identification and genesis as revealed by staining[END_REF]. The blocky calcite cement shows three major CL-zones: 1) a dull, dark brown zone (BC1), followed by 2) a dull bright orange (BC2) and 3) a dull dark orangelight brown zones (BC3; Figs. 7B,D,F). The latter two zones are most frequent and correspond respectively to green to greenish black colours under fluorescence. Blocky calcite cements are found in spalled coated grains and microfractures within grains. The first zone (BC1) with dull CL-pattern is mainly present in ART1 well, while it is absent or present in minor proportions in the other wells. Its presence ranges from ∼26% in grainstones to ∼7% in wackestones. In the former microfacies, it precipitated between grains and inside molds, where it is characterized by some sharp edged crystals (Fig. 7). In wackestones, it fills up some molds and interparticle space in the matrix. Dolomite cement has also been found in the investigated samples (in open pores), showing a more turbid pattern compared to the clearer blocky calcite cements. The subhedral crystals show two cleavage directions at 120 • and vary in size from 200 to 1000 m. The unimodal dolomite cement has a dull, dark brownblack appearance under CL (Figs. 7B,F) and greenish black under FL. Staining results in a blue colour, typical of ferroan dolomite. This blocky dolomite is found only in the ART1 grainstones (ranging from ∼5 to ∼19%).

Both framboidal and euhedral pyrite crystals are found in micritic/organic-rich parts of the mud matrix, ooids and bioclasts. In lesser amounts, they are found in the microsparite in the proximity of organic-rich mud, creating a lining effect between microsparite and micrite in clasts. The framboidal or euhedral nature cannot easily be determined due to the general small size of the crystals. More specifically, in SMB18 euhedral crystals develop Fig. 6. Photomicrographs under parallel polarized light (PPL), cathodoluminescence (CL), and fluorescence (FL) illustrating the microsparite in the "Dalle Nacrée" wells (Paris Basin): A, B) microsparite cement filling up a dissolved gastropod and replacing micrite matrix (GLB1 well); C) microsparite cement surrounding a partially recrystallized pellet creating an isopachous fabric (GN1 well); D) microsparite cement filling up the inner side of a gastropod shell and creating a transition between shell and blocky calcite cement (AP2 well); E, F) microsparite cement primarily filling up a dissolved grain, followed by blocky calcite cement with a drusy outline (XPL, Fl; AP2 well).

solely in clasts while the framboidal form crystallizes in clasts, microsparite, and blocky calcite cement. In GLB1, pyrite fills up some foraminiferal molds. The pyrite crystals are largest in SMB18 grainstone but most abundant in AP2 wackestone. Commonly, a similar proportion (5%) of pyrite is present in samples of the different studied wells.

The quantitative estimations of the various documented (chemical) diagenetic phases in the available thin sections are presented in Table 2 (based on point-counting with JMicroVision, see Methods). The two key wells, ART1 and AP2-representing the margin and depocentre of Paris Basin, respectivelyshow similar percentages of grains (ca. 40%) in grain-supported and mud-supported rock textures. ART1 samples show particularly higher contents of blocky calcite cements and dolomite cements, averaging respectively around 20% and 12% of bulk samples. The highest amounts of syntaxial overgrowth calcite cement (up to 24%) have been recorded in GN1 well cores. Based on these observations, blocky cements appear to prevail in grain-supported "Dalle Nacrée" facies on the south-east margin of the Paris Basin, while higher contents of syntaxial overgrowth calcite cements are recorded in the central part of the basin.

Matlab scripts (automated image analysissee Methods) were also used to quantify grains and overall cements as well as porosity (Table 2). The results for grains and total cement content estimations on thin sections with this technique are systematically, respectively higher and lower compared to the point-counting results obtained by means of JMicroVision (see Table 2). Still the same trends can be deduced based on the results acquired by both methods. Matlab results would be better for overall quantitative characterization, since they take into account the whole thin section surfaces.

Physical diagenetic events

The effects of burial compaction were defined qualitatively in wackestones and grainstones based on petrographic analysis. Overall, the wackestone facies, which are characterized by a mud matrix, seldom reveal evidence of mechanical compaction. The effects of compaction are better expressed in the grainstone facies. Different degrees of compaction can be, hence, discriminated based on different textural features, such as gentle point and plane-parallel grain-to-grain contacts to pressure solution stylolites (Table 2).

Two degrees of compaction are defined for the wackestones (which are mainly found in the wells towards the centre of the Paris Basin). These are expressed in order of increasing compaction by: (1) sutured grain contacts, individual (micro)stylolites, and small stylolite swarms (Fig. 4A; Table 2) and (2) thick stylolite swarms and fracturing in the matrix without affecting the grains (Fig. 4B; Table 2).

Grainstones across the basin show compactional diagenetic products grouped in four categories representing increasing compaction (Table 2). These are, respectively: (1) mild packing of grains (from barely touching each other to point and planeparallel grain contacts; Fig. 4C); (2) moderate packing of grains (from point/plane-parallel to concavo-convex grain-to-grain contacts), deformed to slightly spalled grain coatings, and partial grain fracturing (Fig. 4D); (3) sutured grain contacts and interpenetrating grain-to-grain contacts, spalled coated grains, complete grain fracturing, discontinuous microstylolite development (Fig. 4E); and (4) well-developed individual and stylolite swarms cutting through grains, abundant sutured grain-to-grain contacts and spalled coated grains (Fig. 4F).

Accordingly, the two key boreholes representing the southeastern margin and central zone of the Paris Basin (ART1 and AP2, respectively) show relatively distinct degrees of compactions (Table 2). For example, about 25% of the 16 investigated thin sections of ART1 borehole (at a variety of depths) show welldevelopped individual stylolites (degree #4, above); whereas grain-to-grain sutured contracts are more frequent, consisting the major evidence of compaction (in about 60% of investigated thin sections). On the other hand, 40% of the 15 investigated sections of AP2 (located towards the centre of the basin) revealed the highest compaction degrees in wackestones and grainstones. Furthermore, 46% of these 15 sections revealed the lowest compaction degree. These latter sections are characterized by 14.2% of syntaxial calcite cement, whereas this cement represent only ∼10% of the highest compacted sections (Table 2). Therefore, it can concluded that overall compaction is more important in the centre rather than on the margin of the Paris Basin within the "Dalle Nacrée" facies. But, the results also show that when present, the syntaxial calcite cement somehow prevented the mechanical compaction even in the basin centre.

2D visual porosity

Porosity percentages are classically acquired by methods like point counting (using JMicroVision and Matlab; Table 2). Inter-and intragranular solution enhanced pore types (vuggy porosity) are principally present in the grainstone facies (Fig. 8). Ooid cortices could contain some isolated microporosity (Fig. 9). Furthermore, the ART1 grainstones contain some intergranular microporosity, at the boundaries with cement (Fig. 9D). The dolomite cement fills up solution-enhanced pores, indicating dissolution before the emplacement of this diagenetic phase. In samples GN1 and SMB18, dissolution prevailed and has evolved into vugs (∼2 to ∼30%), yet they appear not to be considerably cemented. The investigated wackestones included only limited occurences of vugs, particularly found along opened-stylolites (up to ∼3%).

Quantitative petrographic analysis revealed that the highest porosity values (ca. 20-30%) exist in the grain-supported rock textures (devoid of mud-matrix) that are found towards the centre of the Paris Basin, where relatively high amounts of early calcite cements prevaile.g. microsparite in SMB18 samples and syntaxial overgrowth calcite in GN1; Table 2). Samples from the AP2 borehole have very low porosity values (average around 6%). Here again porosity is highest (ca. 20%) where syntaxial overgrowth cement is very abundant (17-22%; Table 2). ART1 cores revealed very low porosity values (average around 2%; Table 2), in well cemented grain-supported rock textures. Relatively lower values of porosity were achieved by Matlab calculations, yet the main trends are similar to the ones presented above (see Table 2). For the sake of homogenization and overall characterization, the Matlab values are preferentially used.

3D analytical porosity and permeability

Porosity and permeability measurements are better achieved on 3D samples (i.e. plugs) by means of a series of techniques such as He-porosimetery, MICP (Hg) and CT (see Methods). He-Porosity and MICP (Hg) porosity values are significantly different than those estimated for the same samples by quantitative image analysis on 2D thin sections (compare Tables 2 and3). Yet again, similar trends can be found. The highest He-Porosity and Hg-Porosity values vary between 11 and 14% and they are found in GN1 samples. He-porosity values for AP2 cores are in the order of 7%, whereas those for ART1 cluster around 8% (Table 3).

Permeability values are, in general, very low ( < 1 mD; Table 3). This is not the case for GN1 samples which are characterized by 18-30 mD. Only one sample from the SMB18 borehole has been used for permeability analyses. This sample is representative of the only available piece of the corebased on the related well logs. It also gave a relatively high permeability value (ca. 20 mD) compared to all other samples, which is not surprising taking into account the above observations with respect to the porosity distribution. Most of the other samples are either over-cemented grainstones (e.g. ART1) and wackestones (e.g. AP2), and hence have very low permeability values (< 1mD; Table 3).

The images acquired with CT are convenient to determine the nature of the pores and their spatial relationships (Fig. 9). Sample GN1, representing the best reservoir rocks of the investigated "Dalle Nacrée" Formation towards the centre of Paris Basin, shows two major clusters of pores that are well connected, illustrating an efficient pore network (Fig. 9A). Sample SMB18 displays individual, unconnected pores (Fig. 9B). Sample AP2 has a more locally occurring cluster surrounded by several individual pores (Fig. 9C). These latter pores are isolated by matrix mud and or cements. Further work is proposed to investigate the microporous character of the grains in this sample. These could play a major role in enhancing the overall permeability. Sample ART1 shows pervasive cementa- tion of the initial intra-and intergranular pore space (Fig. 9D). The actual, effective porous space is almost non-existing.

Geochemistry

A limited amount of oxygen and carbon stable isotopic analyses (n = 33; Table 4) was carried out and preferentially focused on some of the major (chemical) diagenetic phases. These analyses were applied on micro-sampled bivalve shells, bryozoan echinoderms (n = 13), syntaxial calcite cement (n = 3), microsparite/recrystallized grains (n = 9) and blocky calcite and dolomite cements (n = 8). The values range from -11.81‰ to -1.84‰ for ␦ 18 O V-PDB and from +1.08 to +2.74‰ for ␦ 13 C V-PDB (Fig. 10). The ␦ 18 O V-PDB and the ␦ 13 C V-PDB stable isotopes of the bivalve shells, bryozoans and echinoderms display a broad range of values from -8.41‰ to -1.84‰ and from +1.42‰ to +2.62‰, respectively. The syntaxial calcite cement exhibits ␦ 18 O V-PDB and the ␦ 13 C V-PDB ranging from -5.41‰ to -3.51‰ and from +1.78‰ to +2.22‰, respectively. Microsparite and recrystallized grains display a significant scatter of ␦ 18 O V-PDB values from -8.22‰ to -1.94‰ and a narrow range of ␦ 13 C V-PDB values from +1.84‰ to +2.74‰. The blocky calcite cements exhibit the most extended range of ␦ 18 O V-PDB values (ca. from -11.81‰ to -2.13‰), but they possess a restricted range of ␦ 13 C V-PDB values (+1.08‰ to +2.71‰) without any distinctive clustering with regard to the CL-zones defined above.

Burial history

The five investigated wells are located in two different regions of the Paris Basin (Fig. 2), which have been affected by distinct burial evolutions. One-dimensional burial/thermal modelling was carried out for all five wells in order to investigate the burial histories of the margin and the basin centre (Fig. 11). The constructed models are, firstly, based on the actual, present day structural configuration of the sedimentary basin (and its stratigraphic sequences) at the location of each well (e.g. [START_REF] Faure | Kinematic and petroleum modeling of the alberta foothills and adjacent forelandwest of calgary[END_REF]. Then, the software (TemisFlow TM , see Methods) was used to simulate the structural evolution of the basin through time. Hence, the various geological rock successions can be removed backward in time following a step by step approach (i.e. "backstripping"). The input parameters consist of the present-day depths of the various rock units with corresponding geological ages as reported from boreholes. These consist of some 22 different formations (from the surface ground level to the base Middle Triassic rock unit; Fig. 12). Accordingly, the stratigraphic thicknesses of these formations were calculated. Erosion events are then inserted (with estimations of the duration and eroded thicknesses). The lithologies and paleo-bathymetries (invoking sub-arial exposures if present) are also valuable input data. Geothermal gradients are defined principally based on the bottom hole temperatures and existing geothermometers. [START_REF] Gaulier | Modeling present and past thermal regimes in the paris basin: petroleum implications[END_REF] constructed a numerical basin model to constrain the present and past thermal regimes in the Paris Basin. For instance, the values of present day thermal gradients for the Liassic series were suggested to be around 55-65 • C/km. Results of Fig. 10. A. Oxygen and carbon stable isotopic compositions of the "Dalle Nacrée" Formation (Paris Basin) consitutents and diagenetic phases (standardized to V-PDB). Samples are from the five investigated wells (GN1, GLB1, SMB18, AP2, and ART1). The blue rectangles represent seawater calcite of Middle Jurassic (dotted line [START_REF] Veizer | 87Sr/86Sr, ␦13C and ␦18O evolution of phanerozoic seawater[END_REF] and Jurassic bivalves isotopic values (solid line; [START_REF] Anderson | The stable isotopic records of fossils from the Peterborough Member Oxford Clay Formation (Jurassic), UK: paleoenvironmental implications[END_REF][START_REF] Wierzbowski | Reconstruction of late Bajocian-Bathonian marine palaeoenvironments using carbon and oxygen isotope ratios of calcareous fossils from the Polish Jura Chain (central Poland) Palaeogeography[END_REF]. The yellow rectangle represents the range of the blocky calcite cement of Mid-to Late Jurassic limestone [START_REF] Buschaert | Widespread cementation induced by inflow of continental water in the eastern part of the Paris basin: o and C isotopic study of carbonate cements[END_REF]. B. Fractionation diagram of [START_REF] Friedman | Compilation of stable isotope fractionation factors of. geochemical interest[END_REF] showing the temperature evolution of the Jurrasic seawater in the case if this latter is responsible for the crystallization of each cement. See (A) for colour legend. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.) clay mineralogy and fluid inclusion studies are generally used, as well, to calibrate the thermicity of basin modelse.g. [START_REF] Guilhaumou | Détermination de paléotempératures dans les roches mères du bassin de Paris: etude d'inclusions fluides et implications pour l'histoire thermique du bassin[END_REF] investigated the varying thermal conditions during the Paris Basin history. Deep temperatures were also esti-mated in the Paris Basin by means of tectonic-heat flow modelling [START_REF] Bonté | Deep Temperatures in the Paris Basin Using Tectonic-heat Flow Modelling European Geothermal Congress EGC[END_REF]. For this work, we have compiled results and data from the literature and used IFPEN data to undertake the 1D basin models. The primary objective was set to compare the burial [START_REF] Flügel | Microfacies of Carbonate Rocks[END_REF][START_REF] Bonté | Deep Temperatures in the Paris Basin Using Tectonic-heat Flow Modelling European Geothermal Congress EGC[END_REF].

Through all constructed models, deposition T 0 was set to start at the beginning of the Anisian, Middle Triassic (∼240 Ma).Thermal models, which represent the central part of the Paris Basin, show that the maximum present-day temperature and pressure values for the "Dalle Nacrée" Formation are around 77 • C (350K • ) and 1.4 × 10 7 Pa (Fig. 11A). The ART1 well model is characterized by lower overall pressure and temperature values recorded for the "Dalle Nacrée" Formation compared to those recorded in the other studied wells (Fig. 11B). At this well, the temperature and pressure reached mean values between 33 and 42 • C (306 to 315K • ) and between 5 and 6 × 10 6 Pa, at present day (Fig. 11B).

A B

Fig. 13. Simplified paragenesis sequences of the "Dalle Nacrée" Formation (Paris Basin), based on petrographic analysis of GN1, GLB1, SMB18, AP2, and ART1 well cores: A) paragenesis sequence of the investigated limestones in the central part of the basin (especially based on investigations of AP2 and GN1 well cores); B) paragenesis sequence of the equivalent limestones in the margin of the basin (based on ART1 well).

The burial histories of the ART1 and GN1wells are further described, since they represent the basin margin and centre, respectively (Fig. 12). Burial of deposited sediments appears to have taken place at slow rate until the Middle Jurassic (Dogger; around 180Ma). Burial rate subsequently increased until the Late Jurassic (Fig. 12). The burial rate slowed down again in GN1 until the Cenozoic times (Fig. 12A), while it remained stable, with almost no further considerable burial at ART1 throughout the Cretaceous (Fig. 12B). According to the 1D modelling, the "Dalle Nacrée" Forma-tion in ART1 and GN1 wells reached maximum burial depth around the Cretaceous-Paleogene boundary (70Ma; Fig. 13). Before that, the maximum burial depth of the "Dalle Nacrée" at ART1 borehole took place relatively early (about 150Ma) in the Late Jurassic (at ca. 600m; Fig. 12B). At the same time (150 Ma), the "Dalle Nacrée" was at a depth of 815 m at the GN1 borehole (Fig. 12A). Besides, burial continued at GN1 to reach a maximum depth in the order of 1600 m around the Cretaceous-Paleogene boundary (70Ma). Hence, continuous burial occurred until the Cenozoic boundary in the centre of Fig. 14. Photomicrographs under PPL/CPL and CL illustrating the paragenesis of the "Dalle Nacrée" grainstones at the margin of the Paris Basin (ART1 well): A) early syntaxial cement surrounded by a micritic coating; B) poikilotopic syntaxial cement with cloudy appearance incorporating several ooids with isopachous microsparite cement; C) isopachous microsparite cement showing pre-burial characteristics as it penetrates another grain; microsparite continues forming during early mechanical compaction; blocky calcite cement fills up remaining space between spalled coatings and grains; D) non-luminescent/luminescent zoned syntaxial calcite cement; E) bioclastic grainstone with microsparitic calcite, a ferroan/non-ferroan blocky calcite cement and a ferroan dolomite; F) microsparite phases lining pores after an early dissolution phase; blocky calcite cement was originally well developed showing different zones under CL; a late dissolution event affected the blocky calcite cement, which created space for the dolomite cement to crystallize (CL).

the Paris Basin, with 200 m to 1000 m additional burial depth than that of the margin at ART1 (from 150Ma to around 70Ma, respectively). Significant uplift and erosional events especially affected the margin throughout the Cenozoic (discussed above). The "Dalle Nacrée" oobioclastic limestone intercepted by the ART1 borehole has been structurally at lower burial depth with respect to its equivalent strata existing in the centre of the Paris Basin. Since the Late Jurassic, the oobioclastic limestone remained at a relatively stable burial depth at the margin, while the same formation in the centre of the basin underwent further burial.

Discussion

Paragenesis

The various diagenetic phases (chemical and physical) that are described above, were chronologically organized based on petrographic analyses (e.g. cross-cutting relationship) for each borehole.

Hence, several paragenetic sequences have been proposed that finally were grouped into two overall sequences (Fig. 13). The first paragenesis represents the four boreholes that are located further towards the centre of Paris Basin (i.e. AP2, GN1, SMB18 and GLB1; Fig. 13A).The second paragenetic sequence is representative of the southeastern margin of the basin, at the locality of the ART1 borehole (Fig. 13B).

In general, both paragenetic sequences similarly illustrate the diagenetic processes that occurred after deposition and during burial. Hence, the deposition of mud-and mostly grain-supported sediments was followed by micritization and syntaxial overgrowth calcite cementation in pre-burial settings. The first distinction between the margin and the basin paragenetic sequences concerns the syntaxial overgrowth calcite cement. In both settings, this cement developed relatively early before shallow burial (mechanical compaction) and precipitated throughout shallow burial. Yet, this cement is considerably more abundant in basinal well cores, such as GN1 samples (Table 2), and spans well through the deep Fig. 15. Photomicrographs illustrating the paragenesis of the "Dalle Nacrée" grainstones in the central part of the Paris Basin (SMB18, GN1 and AP2 wells): A) aragonitic shell of gastropod that was recrystallized into calcite, followed respectively by microsparitic calcite lining the pores and by blocky cement (AP2 well -FL/CPL); B) large syntaxial cement that has precipitated before mechanical compaction; microsparite replaced mud in ooids; inter-/intragranular pores turned into vugs (GN1 well -CPL); C) microsparite cement surrounding grains and replacing mud in ooids. Blocky cement fills up free space created by mechanical compaction; pyrite crystals present in mud and replacing microsparite cement (AP2 well -CPL/FL); D) microsparite cement around grains and replacing mud in ooids, intergranular pores are filled with blocky cement. Partially dissolved grain due to chemical compaction (AP2 well -PPL); E) stylolitization during late chemical compaction (AP2 -PPL); F) late dissolution (diss.) phase affecting the more resistant syntaxial cement creating vuggy porosity (GN1well -CPL).

burial settings (Fig. 13A). In both marginal and basinal boreholes, the microsparite calcite cements occurred after a first phase of dissolution during shallow burial. Pyrite may have formed before, but it certainly did precipitate at the same time as some of the microsparite cements (based on its selective occurrences on microsparites, see above). Following mechanical compaction, pressure solution affected the sediments and is taken here to represent "deeper burial" settings (Fig. 13). For the marginal ART1 core, the emplacement of some blocky calcite cements (BC1) appears to have started before considerable compaction (Fig. 13B). The BC1 phase with dull CL pattern has been found primarily in ART1 well core, and it could have formed at the same time when syntaxial overgrowth cement continued to grow (i.e. third zone of syntaxial cement, with dull CL pattern, see above) in some areas situated deeper in the basin (e.g. GN1). [START_REF] Carpentier | Impact of basin burial and exhumation on Jurassic carbonates diagenesis on both sides of a thick clay barrier (Paris Basin, NE France)[END_REF] also observed contemporaneous syntaxial cements and blocky calcitebased on similar cathdodoluminescence patterns. Furthermore, the syntaxial overgrowth calcite cements have been demonstrated to precipitate for a long time overlapping most of the other diagenetic phases (e.g. [START_REF] Javaux | La plate-forme parisienne et bourguignonne au Bathonien terminal et au Callovien -Dynamique sédimentaire, séquentielle et diagénétique, Place et création des réservoirs potentiels. 16[END_REF]. This has been more or less observed in this study in the "Dalle Nacrée" grainstones, especially in the deeper part of the Paris Basin. ART1 well core has also the peculiarity of including dolomite cement (that developed after a phase of dissolution), which has not been observed in the other wells (Fig. 13B). Finally, both areas of the Paris Basin appear to have been affected by further dissolution, preferentially along existing stylolites.

Although there exists a scatter in terms of ␦ 18 O V-PDB between the samples of the different boreholes (from -11.81‰ to -1.84‰ for ␦ 18 O V-PDB ), the heaviest isotopic compositions of the calcitic marine components are similar to that of the Bathonian and other Mid-Jurassic marine calcite bivalve shells reported in literature (Fig. 10, [START_REF] Anderson | The stable isotopic records of fossils from the Peterborough Member Oxford Clay Formation (Jurassic), UK: paleoenvironmental implications[END_REF][START_REF] Veizer | 87Sr/86Sr, ␦13C and ␦18O evolution of phanerozoic seawater[END_REF][START_REF] Wierzbowski | Reconstruction of late Bajocian-Bathonian marine palaeoenvironments using carbon and oxygen isotope ratios of calcareous fossils from the Polish Jura Chain (central Poland) Palaeogeography[END_REF]. The ␦ 13 C values of most of the samples (Fig. 10) fit with reported bulk rock data from Middle to Late Jurassic carbonates from the Paris Basin [START_REF] Buschaert | Widespread cementation induced by inflow of continental water in the eastern part of the Paris basin: o and C isotopic study of carbonate cements[END_REF][START_REF] Vincent | Geodynamic control on carbonate diagenesis: petrographic and isotopic investigation of the Upper Jurassic formations of the Paris Basin (France)[END_REF]Brigaud et al., 2009a).

The initial shells of some allochems (e.g. mollusks) are believed to have leached very early in the diagenetic history, probably after micritization, creating space for later cements. In wackestone facies, dissolution may also have affected the poorly developed (first) non-luminescent growth zone of the syntaxial calcite cement, which is surrounded by an early micritic coating, suggesting it to be syn-depositional. The cloudy character of the syntaxial cement may be due to incorporation of impurities during its crystallization, a process typical of near-surface marine, vadose-marine or meteoric-phreatic environments according to [START_REF] Flügel | Microfacies of Carbonate Rocks[END_REF]. The syntaxial cement also shows a poikilotopic texture incorporating intact grains pointing to a crystallization before considerable mechanical compaction (Fig. 14B).

Hence, a first dissolution episode is suggested to have developed molds and enhanced intergranular porosity, which are filled by fine sediments and microsparite (Fig. 13). CL-zoned microsparites in wackestones and syntaxial calcite cements in grainstones may suggest a synchronous precipitation under shallow burial condi-tions [START_REF] Horbury | Meteoric phreatic diagenesis in cyclic late Dinantian carbonates, northwest England[END_REF][START_REF] Chapoulie | Apport de la cathodoluminescence à haute résolution à l'étude de la diagenèse météorique dans la formation sédimentaires carbonatés[END_REF]. It can also indicate recrystallization giving rise to microsparite during the emplacement of the syntaxial cement phase. These two phases exhibit also similar values for ␦ 18 O V-PDB and ␦ 13 C V-PDB , pointing to precipitation/recrystallization from a common parent fluid. The ␦ 18 O V-PDB isotopic composition are lighter than the Bathonian seawater calcites suggesting either an increase in temperature of the initial seawater and/or a meteoric water influx. In the former case, considering the isotopic compositions of the microsparite and the syntaxial calcite cement, these phases would have formed at temperatures between 24 • C and 68 • C (Fig. 10B). Based on the 1D burial model (Fig. 11), the temperature prevailing at the "Dalle Nacrée" in ART1 borehole, reached around 42 • C by Late Jurassic times. Further recrystallization at deeper burial may have re-set the ␦ 18 O signature (for instance at the Cretaceous-Paleogene boundary). The black and bright orange zoned CL-pattern of the microsparite cement may indicate fluctuation in the chemistry of the fluids, such as often recorded in meteoric fluids during shallow burial [START_REF] Meyers | Isotope geochemistry of regionally extensive calcite cement zones and marine components in Mississippian Limestone, New Mexico[END_REF][START_REF] Barnaby | Redox conditions of calcite cementation interpreted from Mn and Fe contents of authigenic calcites[END_REF][START_REF] Franck | Chronostratigraphic significance of cathodoluminescence zoning in syntaxial cement: mississippian lake valley formation new Mexico[END_REF]. Moreover, the presence of small euhedral pyrite crystals associated with the microsparite may suggest slightly reducing conditions.

The petrography and luminescence patterns of the blocky calcite cement suggest precipitation in a burial setting (c.f. [START_REF] Vincent | Geodynamic control on carbonate diagenesis: petrographic and isotopic investigation of the Upper Jurassic formations of the Paris Basin (France)[END_REF]Brigaud et al., 2009a,b;[START_REF] Carpentier | Impact of basin burial and exhumation on Jurassic carbonates diagenesis on both sides of a thick clay barrier (Paris Basin, NE France)[END_REF]. Blocky calcite cement fill up free space around spalled coated grains and fractures created by mechanical compaction. Thus, it is believed to be a syn-to post compactional product. Analysed blocky calcite cements show a broad range of ␦ 18 O V-PDB values (-11.81‰ to -2.13‰) and a relatively restricted range of ␦ 13 C V-PDB values (+1.08‰ to +2.71‰), similar to reported results of equivalent blocky calcite cements from the other Middle/Late Jurassic carbonates of the Paris Basin (␦ 18 O V-PDB values: -12.9‰ to -3.3‰; ␦ 13 C V-PDB : +1‰ to +3‰; Brigaud et al., 2009a). More precisely, the blocky calcite cements of the ART1 borehole show ␦ 18 O V-PDB values in the order of -7.5‰, while most of the blocky calcite cements of other wells (towards the centre of the basin) have lower ␦ 18 O V-PDB values tending towards -2‰ (similar to original marine signaturewith one exception, see Table 4). This cement exhibits, indeed, the lightest values in terms of oxygen isotopes (even if scattered) and are consistent with blocky calcite observed in other Mid-Jurassic carbonate rocks of the Paris Basin [START_REF] Buschaert | Widespread cementation induced by inflow of continental water in the eastern part of the Paris basin: o and C isotopic study of carbonate cements[END_REF]Brigaud et al., 2009a). Such scattered signature may result from a continuous precipitation through time with increasing temperatures of the parent fluids and/or a meteoric input as well (e.g. [START_REF] Carpentier | Impact of basin burial and exhumation on Jurassic carbonates diagenesis on both sides of a thick clay barrier (Paris Basin, NE France)[END_REF]. This latter hypothesis has been demonstrated by recent research, particularly for the Late Jurassic limestones overlying the Callovian-Oxfordian marls. Yet, the "Dalle Nacrée" limestones are below this efficient permeability barrier which would not allow paleo-fluid circulations as proposed for the Oxfordian and Kimmeridgian carbonates. Such disconnection has been proven by distinct isotopic signatures of cements above and below the Callovian-Oxfordian marls, with the latter remaining those of unmodified marine calcite [START_REF] Buschaert | Widespread cementation induced by inflow of continental water in the eastern part of the Paris basin: o and C isotopic study of carbonate cements[END_REF]. Considerable meteoric input is also difficult to demonstrate since the observed ␦ 13 C values of the blocky calcite cements in the investigated cores remain buffered by the host rock (i.e. within the range of original marine calcite).

A seawater origin would imply burial temperatures ranging from 25 • C till 83 • C to explain oxygen isotope values of the blocky calcite ranging between -11.81‰ and -2.13‰ V-PDB (Fig. 10B). Although such condition might have occurred in the centre of the Paris Basin by Paleogene times (check Fig. 11), it cannot be projected for its margin (ART1), which appears to have been less deeply buried (maximum temperature: ∼56 • C (+/-5 • C) at ∼1700m). Note that, compared to the oxygen isotopic signatures of similar blocky cements from the other wells, those of ART1 show the lightest values (even if they were the less buried). Fluids which might have affected the "Dalle Nacrée" in the centre of the basin under different geothermal conditions, might be the same that affected the adjacent margin under localized hydrothermal conditions. Based on the less compacted rock texture at the ART1 borehole, it is enticing to suggest warmer, extrinsic fluids, responsible for the blocky calcite pervasive cementation. [START_REF] Gigoux | Evidence for an Early Cretaceous mineralizing event above the basement/sediment unconformity in the intracratonic Paris Basin: paragenetic sequence and Sm-Nd dating of the world-class Pierre-Perthuis stratabound fluorite deposit[END_REF] suggested that a significant geothermal event took place at the southeastern part of the Paris Basin in the Early Cretaceous times. This could have certainly affected cementation.

An additional dissolution episode partially affected the blocky calcite cements at the ART1 borehole, as the latter shows sharp random edges and remnant crystals occurring in the subsequently formed dolomite cement. The dolomite cement postdates the blocky calcite cement, and fills most of the remaining pore space. Dissolution also created vugs along stylolites. It is unclear if these vugs are another product of the dissolution event preceding dolomitization or the result of a separate, later dissolution phase, which is observed in all well cores.

Diagenetic effects of burial compaction

According to the observations and the discussion above, all the grainstone facies of the "Dalle Nacrée" underwent similar deposition and eogenesis, involving early marine and/or meteoric precipitation, recrystallization and dissolution. However, burial diagenesis appears to be slightly different in the depocentre (SMB18, GN1, AP2 wells) compared to the basin margin (ART1 well). The investigated grainstones from the ART1 borehole show considerable amounts of burial blocky calcite cement and dolomite cement (Table 2; Fig. 13B) compared to the grainstones from the other wells, that are characterized by higher degrees of chemical compaction (as presented above; Table 2). The deeply buried grainstones could also be organized in two groups based on burial diagenesis. A first group (e.g. GN1), has considerable amount of syntaxial overgrowth calcite cement (∼20%; formed in early to shallow burial settings) that appears to have preserved the grains from being packed during compaction. The second group lacks relatively early cement and show strongly compacted rock textures (Fig. 4E). Dolomitization, which is observed in the ART1 borehole, and which has been documented in other studies (e. [START_REF] Jacquemyn | Sedimentpetrologische En Diagenetische Studie Van Jura Reservoirgesteenten in Het Bekken Van Parijs: De Villeperdue Gevallenstudie[END_REF]Brigaud et al., 2009a,b;[START_REF] Carpentier | Impact of basin burial and exhumation on Jurassic carbonates diagenesis on both sides of a thick clay barrier (Paris Basin, NE France)[END_REF], is not within the scope of this present study. Still, it is interesting to note that no similar dolomite cements were found in the GN1, SMB18 and AP2 grainstones, which show relatively higher current bulk porosity. One can suggest that the origin of the dolomitizing fluids that have affected the ART1 grainstones may have been the deeper part of the basin, especially since the produced dolomite is ferroan (implying precipitation from reducing fluids most probably during excessive burial). The time span of crystallization of these dolomites, deduced from the proposed paragenesis (Fig. 13B), indicate that they have formed relatively late when the burial depth difference between the basin centre and margin was very large. More work and additional data are needed to refine the genesis of the dolomites.

Porosity evolution

Pre-compactional and syn-to post-compactional, major dissolution episodes are believed to have affected the studied "Dalle Nacrée" limestones (Figs. 13A,B). First, the pre-compactional dissolution was probably caused by Jurassic calcite seawater (for aragonitic shells) and/or meteoric-related fluids in a shallow-burial eogenetic environment, creating space for precipitation of latter cements. Here, early meteoric water influx during synsedimentary emersive episodes might apply as well (see [START_REF] Javaux | La plate-forme parisienne et bourguignonne au Bathonien terminal et au Callovien -Dynamique sédimentaire, séquentielle et diagénétique, Place et création des réservoirs potentiels. 16[END_REF][START_REF] Carpentier | Impact of basin burial and exhumation on Jurassic carbonates diagenesis on both sides of a thick clay barrier (Paris Basin, NE France)[END_REF]. The exact timing of a later, syn-to post-compactional dissolution phase is uncertain. The dissolution might have started during late compaction by the expulsion of fluids from the deeper parts of the basin, and migration along high permeability pathways (e.g. stylolites, bedding planes) or, eventually, by telogenetic meteoric fluids circulations. This dissolution phase mainly caused porosity along stylolites in the wackestone facies and vuggy porosity in the grainstone facies in the deeper part of the basin (centre) where burial was maximal. Consequently, the two major dissolution episodes (except for some dissolution associated with the emplacement of dolomites in ART1 well core), could be considered to have happened before burial (Callovian) and later on, after major burial, most probably by the time of uplift, as of Turonian [START_REF] Guillocheau | Meso-Cenozoic geodynamic evolution of the Paris Basin: 3D stratigraphic constraints[END_REF]. Within these two time periods, the overall porosity of the "Dalle Nacrée" reservoirs was mainly controlled by burial diagenesis (physical and chemical) (Fig. 15).

'Pre-burial' refers to the time before major (or deep) burial, yet including shallow burial (e.g. mechanical compaction). Stylolites and blocky calcite cements are interpreted as evidence of deep, late burial (Fig. 13). Pre-burial porosity is defined, here, as the porosity that existed before the emplacement of the (burial) blocky calcite cement (i.e. pre-burial = bulkblocky calcite/dolomite cements). Calculations are based on point-counting results (i.e. quantitative petrographic analyses of thin sections), taking into account intergranular porosity and cement distributions (e.g. [START_REF] Heydari | Porosity loss, fluid flow, and mass transfer in limestone reservoirs: application to the Upper Jurassic Smackover Formation, Mississippi[END_REF]. The deduced pre-burial porosity values of the "Dalle Nacrée" reservoirs show a negative correlation with the proposed degrees of compaction (Fig. 16A). In other words, the pre-burial porosity decreases with the increasing degrees of compaction (1-4; Fig. 16A). Petrographic observations showed that the syntaxial calcite cement started to precipitate during early diagenesis, so it could play a role in framework preservation against compaction (e.g. [START_REF] Morad | Impact of diagenesis on the spatial and temporal distribution of reservoir quality in the Jurassic Arab D and C members offshore Abu Dhabi oilfield, United Arab Emirates[END_REF][START_REF] Nader | Quantification of diagenesis impact on reservoir properties of the Jurassic Arab D and C members (offshore[END_REF]. Blocky calcite cement precipitated before considerable burial in the ART1 borehole, filling up inter-granular pore space before textural packing during mechanical compaction. Pervasive cementation destroyed the remaining porosity during further burial. Image analysis demonstrates that GN1 samples have the highest amount of syntaxial cement and highest porosity percentages (Fig. 9A; Table 2) -resulting in connected pore clusters, while ART1 samples have the highest amount of blocky calcite cement marked by lower porosity values (Table 2). Furthermore, data analysis showed that the proportion of blocky calcite cement decreases with the amount of syntaxial calcite cement (Fig. 16B). This could be explained by different diagenetic conditions required for the precipitation of these two types of cements. In addition, the further growth of early syntaxial calcite cement occluding porosity, hampering blocky cement to precipitate later on. Finally, the take home message is that where syntaxial calcite cement prevails in the basin centre, lower amounts of blocky calcite and higher porosities are found. On the basin margin, abundant amounts of blocky calcite are found together with the lowest porosity values.

Burial diagenesis and fluid flow (basin to margin)

The investigated wells intercepting the "Dalle Nacrée" Formation (Early Callovian) towards the centre and at the southeastern margin of the Paris Basin revealed different burial histories as well as distinct diagenetic evolutions. The hypothesis proposed here concerns the effects of differential compaction on reservoirs due to distinct burial histories. It also involves basinal fluid flow and evolution during burial. Meteoric water influx towards the centre of the basin due to geodynamic movements during the Early Cretaceous as suggested by [START_REF] Vincent | Geodynamic control on carbonate diagenesis: petrographic and isotopic investigation of the Upper Jurassic formations of the Paris Basin (France)[END_REF]), Brigaud et al. (2009a,b) and [START_REF] Carpentier | Impact of basin burial and exhumation on Jurassic carbonates diagenesis on both sides of a thick clay barrier (Paris Basin, NE France)[END_REF] might have affected the "Dalle Nacrée" later on during further burial and telogenesis. It is difficult to support such paleo-fluid circulation at the beginning of burial (before major compaction and regional uplift) with the overlying, thick layer of Callovian-Oxfordian marl which must have acted as an efficient seal, as discussed above (see also [START_REF] Buschaert | Widespread cementation induced by inflow of continental water in the eastern part of the Paris basin: o and C isotopic study of carbonate cements[END_REF]. While the grainstones of the "Dalle Nacrée" Formation were further compacted in the deeper part of the basin, similar less buried facies were affected by massive blocky calcite cementation in marginal settings. It is believed that the early compaction of the grainstone in the deeper part of the basin has induced fluid migration toward the marginal part of the basin (Fig. 17). Subsequently, it led to a massive calcite cementation of the porous facies (grainstone). The inter-granular porosity of the unpacked grain-textures was "filled up" by pervasive cementation, at a time of probable high geothermal or even hydrothermal activities in the southeastern margin of the Paris Basin (e.g. [START_REF] Gigoux | Evidence for an Early Cretaceous mineralizing event above the basement/sediment unconformity in the intracratonic Paris Basin: paragenetic sequence and Sm-Nd dating of the world-class Pierre-Perthuis stratabound fluorite deposit[END_REF]. Alternatively, with a higher ambient temperatures (due to high geothermal conditions), the grainstones might have also been rapidly cemented from in-situ marine-related formation waters. Hence, reservoir heterogeneities occur on a basin scale and relates to distinct burial evolution and associated fluid flow. This implies that the "Dalle Nacrée" grainsupported reservoirs are continuous from the centre of the Paris Basin to its margin (covering some 150 km in length). [START_REF] Gaumet | Stratigraphic control upon depositional facies, geometries and profiles across the Bathonian-Callovian carbonate platform in Burgundy[END_REF] and [START_REF] Gaumet | Fondements géologiques Pour La Modélisation Stratigraphique Des Systèmes Carbonatés[END_REF] showed that such continuous facies do exist between the Loire (to the west) and the Ardennes (to the northeast) with distances exceeding 200 km. There exist some muddy intercalations and textural variabilities, but in general the reservoirs seems to be somehow continuous and would allow basin-scale fluid migrations. It is precisely the specific diagenetic time frame (shallow to relatively deep burial) that is of interest to this paper. We suggest that the differential compaction not only led to textural differentiation of the "Dalle Nacrée" sediments but also resulted in paleo-circulation of fluids in a confined reservoir/aquifer causing subsequent pervasive cementations along the margin of the basin.

Conclusion

The investigated boreholes of the "Dalle Nacrée" Formation (Early Callovian) in the Paris Basin were separated into two groups based on their position and distinct burial evolution. The evolution of pressure and temperature in function of time showed that the strata intercepted by the ART1 well underwent less burial than those sampled in the SMB18, GN1, AP2 and GLB1 wells. These latter wells are situated in the central part of the Paris Basin. Maximal burial was achieved at the Cretaceous-Paleogene boundary (∼70Ma), with 1700 m in the ART1 well (situated on the margin of the Paris Basin) and 2800 m in GN1, used herein as a case reperesntative for the deeper buried wells.

The petrographic analyses of the "Dalle Nacrée" core samples led to the construction and interpretation of the degree of compaction and diagenetic evolution for each investigated rock texture, namely wackestones and grainstones. The wackestones (GLB1 and AP2 wells) show relatively lower porosity values. The grainstones possess a solution enhanced, inter-and intragranular to vuggy porosity. The grainstones of the ART1 well samples are characterized by a cementation reducing inter-and intra-granular porosity.

Syntaxial calcite cement appears early in the paragenetic sequences, but occurs in lower amounts in ART1 thin sections, based on the statistical analysis and quantitative petrography.

Blocky calcite cements are more abundant in this well and appear to have slightly preceded deep burial diagenesis, compared to the other wells that are located towards the centre of the Paris Basin. A post-compactional ferroan dolomite cement was only found in ART1 well cores.

Differentail burial history across sedimentary basin centre-tomargin, such as observed in the studied area of the Paris Basin, affect paleo-fluid flow and subsequently carbonate diagenesis. Therefore, the reservoir properties differ according to the position within the basin, resulting in cross-basinal heterogeneities. The "Dalle Nacrée" reservoirs demonstrate higher compaction at the centre of the Paris Basin compared to the southern margin. Good reservoirs, located near the centre of the basin, show considerable amounts of early syntaxial overgrowth cement (preserving intergranular porosity during mechanical compaction), and may have been later on affected by dissolution, fracturing and stylolite relaxation. Equivalent reservoirs located along the basin margin (e.g. ART1 well) have been occluded by blocky calcite cement during burial. The fluids responsible for this cementation are believed to be most probably compaction-driven from the centre of the basin.

Fig. 1 .

 1 Fig. 1. (A) Paleogeographic map of Eurasia and the Tethys domain during the Bathonian-Callovian times. (B) Enlarged map showing the paleogeographic configuration of the Paris Basin. These maps are from Brigaud et al. (2009a) based on a compilation from[START_REF] Purser | Plates-formes carbonatées exemple du Jurassique moyen du Bassin de Paris, Dynamique et méthodes d'étude des bassins sédimentaires[END_REF],[START_REF] Enay | Synthèse paléogéographique du Jurassique franc ¸ais, Document du Laboratoire de Géologie de Lyon[END_REF] and[START_REF] Thierry | Late Sinemurian, Middle Toarcian, Middle Callovian, Early Kimmeridgian, Early Tithonian[END_REF].

Fig. 2 .

 2 Fig. 2. Geological map of the Paris Basin with indication of the locations of the investigated wells (map from Delmas et al., 2002).

Fig. 3 .

 3 Fig. 3. WNW-ESE lithostratigraphic cross-section through the Middle Jurassic rock series of the Paris Basin (from Delmas et al., 2010; Houel and Delmas, 2013). The inset map shows the location of the cross-section across the Paris Basin.

Fig. 4 .

 4 Fig.4. Photomicrographs showing typical wackestone (A/B) and grainstone (C to F) microfacies in the "Dalle Nacrée" (Early Callovian), with a varying degree of compaction (Paris Basin) (view under parallel polarized light, PPL): A) sutured grain contacts indicating some degree of compaction (GLB1 well). B) continuous stylolite and fracturing related to further compaction (AP2 well). C) From grains barely touching each other to point and plane-parallel grain contacts;D) from point/plane-parallel to concavoconvex grain-to-grain contacts, deformed to slightly spalled grain coatings, partial grain fracturing of more resistant grains; E) all grains touching each other with sutured and interpenetrating grain-to-grain contacts, still some free space left between grains, spalled coated grains; F) barely free space left between grains; sutured grain-to-grain contacts; abundant spalled coated grains, well-developed individual and stylolite swarms cutting through grains.

Fig. 5 .

 5 Fig. 5. Photomicrographs illustrating the syntaxial calcite cement in the "Dalle Nacrée" well cores (Paris Basin): A, B) well developed syntaxial cement around echinoderm fragments followed by blocky cement (GN1 well) under parallel polarized light (PPL) and CL; C, D) cloudy poikilotopic cement around a broken crinoid plate (SMB18 well) under parallel polarized light (PPL) and fluorescence (FL).

Fig. 7 .

 7 Fig. 7. Photomicrographs showing blocky calcite and dolomite cement in the "Dalle Nacrée" well cores (Paris Basin): A, B) three phases of blocky calcite cement filling up the inside of a mollusc, while the interparticle space is filled with dolomite cement (unstained thin section from ART1 well), under PPL and CL, respectively; C) to the left blocky calcite cement filling up a fracture through a composite ooid and to the right dolomite cement filling up an another fractured composite ooid (ART1 wellstained, under PPL); (D) blocky calcite cement filling up different fractures (GLB1 well); E, F) blocky calcite and dolomite cement (ART1 well -CL), stained under PPL and CL, respectively.

Fig. 8 .

 8 Fig. 8. Pore types in grainstones from the "Dalle Nacrée" well cores (Paris Basin): A) interparticle porosity to vuggy porosity (SMB18 well -PPL); B) combination of interparticle, intraparticle and vuggy porosity between ooids (GN1 well -PPL); C) grainstone with intergranular porosity and later vuggy porosity along stylolite (ART1 well -PPL); D) possible locations for intercrystalline microporosity between subhedral blocky calcite cement crystals (GN1 well -FL).

Fig. 9 .

 9 Fig. 9. Porosity visualization acquired with CT and ImageJ for four samples, from wells GN1 (A), SMB18 (B), AP2 (C), and ART1 (D), respectively. The cubes are 1.5 × 1.5 × 1.5 mm and the image in (D) is 1.5 × 1.5 mm. See text for details.

Fig. 11 .

 11 Fig. 11. Pressure (in Pa) and temperature (in • C) evolution with time for the investigated wells, separating centre from marginal areas in the Paris Basin (A and B, respectively), based on 1D burial models (TemisFlow, IFP Energies nouvelles). Numerical burial modelling involves backstripping from the present-day structural configuration and calculations of thermal and pressure conditions in various time steps. The input stratigraphic data included thickness, age of deposition and erosion, as well as lithological parameters.

Fig. 12 .

 12 Fig. 12. Comparision between typical 1D burial models of the centre (A, GN1 well) and margin (B, ART1 well) of the Paris Basin (simulated by TemisFlow, IFP Energies nouvelles). The reported stratigraphic units are as follows: 1) Anisian-Scythian, 2) Ladinian, 3) Carnian, 4) Norian, 5) Rhaetian, 6) Hettangian -Sinemurian, 7) Domerian, 8) Toarcian, 9) Early Bajocian, 10) LateBajocian, 11) Bathonian, 12) Callovian (Dalle Nacrée), 13) Sequanian, 14) Oxfordian, 15) Kimmeridgian, 16) Tithonian, 17) Barremian, 18) Aptian, 19) Albian, 20) Albian Gault Shales, 21-22) Late Cretaceous Chalk. For further information on the various formations and litho-stratigraphic units for the Jurassic refer to Fig.3. evolutions in the basin centre and margin. A 3D basin model would certainly result in additional constraints regarding past fluid flow and heat fluxes (e.g.[START_REF] Gonc ¸alvès | Contribution of a three-dimensional regional scale basin model to the study of the past fluid flow evolution and the present hydrology of the Paris basin, France[END_REF][START_REF] Bonté | Deep Temperatures in the Paris Basin Using Tectonic-heat Flow Modelling European Geothermal Congress EGC[END_REF].Through all constructed models, deposition T 0 was set to start at the beginning of the Anisian, Middle Triassic (∼240 Ma).Thermal models, which represent the central part of the Paris Basin, show that the maximum present-day temperature and pressure values

Fig. 16 .

 16 Fig. 16. Results of statistical analysis of quantitative diagenesis for the "Dalle Nacrée" (Paris Basin): (A) pre-burial porosity as a function of proposed degrees of compaction; (B) blocky calcite cement as a function of syntaxial calcite cement.

Fig. 17 .

 17 Fig. 17. Schematic conceptual model illustrating the observed porosity evolution of the "Dalle Nacrée" Formation grainstones in both central (SMB18, GN1, AP2 wells) and marginal (ART1 well) parts of the Paris Basin. Mean porosity values are also reported for these wells based on the various types of measurements that were undertaken (thin sections, He-, MICP, -CT).

Table 2

 2 Quantitative measurements (in%) of grains, cement and porosity acquired with 2D image analysis techniques: JMicroVision (JMV) and Matlab, as well as the qualitative estimation of compactions degrees (see text for details).

	Data from Jmicrovision

Table 3

 3 Porosity and permeability estimations acquired based on He-porosimetry, classical flow permeability analyses, MICP (Hg-Porosity, K Swanson) and micro-CT.

	Well	Sample depth (m)	Kg charge variable	He Porosity	Density	Hg Porosity	K Swanson	r1	r2	Porosity CT
		(m)	(mD)	(%)	(g/cm3)	(%)	(mD)	(m)	(m)	(%)
	Arrentières (ART1)
	ART1	526.6	-	8.66	2.7	7.2	< 0,001	0.094	-	-
	ART1	525.5	-	9.3	2.7	7.8	< 0,001	0.091	-	-
	ART1	525.0	-	10.5	2.7	8.7	< 0,001	0.12	-	-
	ART1	524.8	-	4.2	2.7	3.6	< 0,001	0.046	-	-
	ART1	524.0	< 0,1	9.5	2.71	7	< 0,001	0.097	-	-
	ART1	523.5	-	6.5	2.73	6.9	< 0,001	0.14	-	-
	ART1	522.5	-	7.2	2.7	5.9	< 0,001	0.086	-	-
	ART1	521.9	-	9.4	2.72	7.6	< 0,001	0.086	-	-
	Gisly les Nobles (GN1)
	GN1 1	1439.7	-	13.4	2.66	12.8	3.00E + 01	8.6	0.22
	GN1 2	1438.9	-	13.6	2.64	11.4	2.00E + 01	7.2	0.22	13.66
	GN1 3	1438.0	-	12.4	2.63	11.4	3.00E + 01	6.1	0.19
	GN1 4	1437.4	18	11.4	2.64	12.5	3.00E + 01	6.8	0.18
	Saint-Martin de Bossenay (SMB 18)
	SMB18 2	1681.5	4.8	9.4	2.67	9.6	2.00E + 01	4.1	0.09	9.82
	Grange-le-bocage (GLBL1)
	GLB1	1591.2	-	2.5	2.72	1.2	< 0,001	0.014	-	-
	Avon-la-Pèze (AP2)
	AP2	1525.5	-	-	-	-	-	-	-	-
	AP2	1524.5	< 0,1	4.5	2.7	1.8	< 0,001	0.22	0.018	-
	AP2	1523.2	-	-	-	-	-	-	-	-
	AP2	1522.9	< 0,1	5.4	2.71	2.6	< 0,001	0.026	-	-
	AP2	1518.3	-	9.3	2.7	7.3	< 0,001	0.34	0.1	-
	AP2	1517.9	-	7.7	2.7	3.2	< 0,001	0.1	-	-
	AP2	1514.5	-	4.8	2.7	2.9	< 0,001	0.032	-	-
	AP2	1513.0	-	10.9	2.68	8.4	< 0,001	0.2	-	9.73
	AP2	1511.3	-	9.5	2.69	7.8	< 0,001	0.077	-	-
	AP2 10	1510.8	-	6.5	2.69	6.3	< 0,001	1.9	0.048	-

Table 4 Oxygen

 4

	N •	Sample	Well	Mineralogy	Grains & Diagenetic phases	␦ 13 C	␦ 18 O	␦ 18 O dol. frac.
	1	ART1 1b	ART	Calcite	MATRIX	2,12	-7,15	-
	2	ART1 2	ART	Calcite	GRAINS -BRYO?	2,01	-5,31	-
	3	ART1 4	ART	Calcite	GRAINS	2,55	-1,84	-
	4	ART1 5	ART	Calcite	GRAINS	2,44	-5,17	-
	5	ART1 6	ART	Calcite	MICRITE	2,50	-5,58	-
	6	ART1 6	ART	Calcite	GRAINS	2,23	-5,67	-
	7	ART1 8b	ART	Calcite	RECRYSTALLIZED GRAINS (BRYO)	1,90	-8,41	-
	8	GLB1 1	GB	Calcite	BULK MATRIX	1,42	-3,02	-
	9	GN1 2	GN	Calcite	BULK/GRAINS	1,80	-3,97	-
	10	GN1 4	GN	Calcite	MATRIX BROWN + SYNTAXIAL	2,00	-4,59	-
	11	AP2 4	AP	Calcite	GRAINS	2,62	-2,19	-
	12	AP2 4	AP	Calcite	GRAINS	2,29	-2,11	-
	13	SMB18 2a	SMB	Calcite	GRAINS/MATRIX	2,29	-3,83	-
	14	GN1 2	GN	Calcite	BULK/GRAINS	1,78	-3,51	-
	15	GN1 4	GN	Calcite	CEMENT MATRIX	2,19	-3,81	-
	16	AP2 8b	AP	Calcite	SYNTAXIAL	2,22	-5,41	-
	17	ART1 5	ART	Calcite	RECRYSTALLIZED GRAINS	2,74	-8,22	-
	18	ART1 7a	ART	Calcite	BULK	2,38	-7,56	-
	19	GN1 3a	GN	Calcite	BULK -RECRYST	1,94	-3,88	-
	20	GN1 4	GN	Calcite	BULK/RECRIST	1,84	-4,98	-
	21	AP2 4	AP	Calcite	RECRYSTALLIZED GRAINS	2,29	-1,94	-
	22	AP2 8b	AP	Calcite	BULK -RECRYST	2,30	-5,31	-
	23	AP2 9b	AP	Calcite	BULK -RECRYST	2,15	-5,26	-
	24	SMB18 2a	SMB	Calcite	BULK -RECRYST	2,29	-4,29	-
	25	SMB18 2b	SMB	Calcite	BULK -RECRYST	2,14	-4,62	-
	26	ART1 2	ART	Calcite	BLOCKY	2,38	-7,13	-
	27	ART1 8b	ART	Calcite	BLOCKY	1,96	-7,61	-
	28	GLB1 1	GB	Calcite	BLOCKY	1,08	-11,81	-
	29	AP2 4	AP	Calcite	BLOCKY	2,71	-2,13	-
	30	AP2 8b	AP	Calcite	BLOCKY?	2,22	-5,51	-
	31	SMB18 2a	SMB	Calcite	BLOCKY (ONE SPOT)	2,30	-3,52	-
	32	SMB18 2a	SMB	Calcite	BLOCKY (ONE SPOT)	2,05	-4,58	-
	33	ART1 4	ART	Dolomite	DOLOMITE	2,35	-7,65	-8,85

and carbon isotopic values for the various sedimentary and diagenetic phases encountered in the "Dalle Nacrée" Formation (Paris Basin).

Acknowledgements

IFP Energies nouvelles is acknowledged for funding this project and permission for publishing its results. Herman Ravelojaona is acknowledged for producing the studied thin sections. Thanks to Jean Guélard for the MICP results. Assistance provided by Vanessa Teles with regard to the IFPEN Paris Basin thermal model, is greatly appreciated. The authors would also like to thank Pierre-Yves Collin and two anonymous reviewers, whose comments and suggestions improved considerably the content and the form of this work. Equally, we would like to thank Olivier Lacombe for his support and editing.