Stratigraphy of the Haut Var Paleogene continental series (Northeastern Provence, France): New insight on the age of the 'Sables bleutés du Haut Var' Formation

The age of the Paleogene deposits of the Haut Var (Provence, France) has been the subject of debate. Particularly, the ''Calcaire à Bithynies'' and the ''Sables bleutés'' units were ascribed either to the early Eocene or to the Oligocene. A stratigraphical clarification is required in order to precise the paleogeographical relationships of the Haut Var Paleogene sedimentary series with coeval deposits in the neighbouring southern Provence and Subalpine regions and other European domains. The study area is characterized by tectonically separated synclines and grabens filled in by continental Paleogene deposits. Detailed mapping and lithostratigraphical logging, sedimentological and microfacies analysis have been undertaken in order to provide a reliable stratigraphical framework. Biostratigraphical subdivisions were established based on five different fossil groups: mammals, charophytes, gastropods, ostracodes, and foraminifers. Accordingly, five formations are distinguished and dated: ''Calcaire a` Microcodium'' and ''Brèche à Microcodium'' (Danian); ''Marnes à oeufs d'oiseaux'' (Selandian(?)-earliest Ypresian); 'Sables bleutés du Haut Var' (early-late(?) Ypresian); and ''Bourdas conglomerates'' (Rupelian). Particular emphasis is given to the study of the controversial 'Sables bleute´ s du Haut Var' Formation. As a result, correlations have been established between the different syncline and graben areas where Paleocene-Eocene and Oligocene deposits occur. Terrestrial deposits (carbonate paleosols and piedmont alluvial fans) took place during Paleocene times, while fluvial (cross-bedded sands) and lacustrine carbonate deposits developed in a foreland compressional intracontinental basin surrounded by emerged areas and tectonic highs during the early Ypresian. Paleoenvironmental and paleogeo- graphical analysis strengthen the view that a relative isolation characterized the Haut Var area during the early Eocene, probably enhancing episodes of brackish water or evaporitic sedimentation and gastropod endemism. During the late Eocene Pyrenean-Provence tectonic phase, the E-W trending Haut Var overthrusts have been emplaced posteriorly to the deposition of the 'Sables bleute´ s du Haut Var' Fm. Finally, coarse alluvial fan and local lacustrine carbonate sedimentation occurred during the Oligocene in narrow N-S trending subsident extensional grabens associated with the N-S trending Barjols Triassic uplift

Data report : bio- and lithofacies, mineralogy and organic content of Challenger Mound (Porcupine Seabight, SW Ireland)

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Influence of fault zones in the development of large karst conduits: Example from the Toulon area (SE, France).

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Relationships between sedimentary, diagenetic and tectonic structures to quantify karst groundwater reserves at the regional scale. Example of the Toulon area (SE, France)

International audienceIn the Mediterranean area, karst aquifers are important groundwater reserves nested in carbonate series that experienced complex tectonic and climatic histories. If it is commonly admitted that the sea level decreases during the messinian strongly conditioned the deep drainage of these aquifers through the development of an intense karstification, what heterogeneities (structural, sedimentary or diagenetic) in the carbonate series favored their development and explains the actual karst groundwater reserves? Situated at the boundary between the crystalline and the calcareous Provence, the Toulon area is characterized by a geological complexity typically influenced by several evolutions. Here we describe a multidisciplinary approach that couples structural and sedimentological analyses of carbonate series with the hydrogeological context. We integrate a refined diagenetic and fracturation sequence in a three-dimensional geomodeling (with GoCad code), to identify and quantify in three-dimensions the key geodynamic events that affect the porosity within the carbonate series. Field structural data inform us about a relation between karst development and faulting. Normal faults with pluri-hectometer offset were then reactivated in thrusts and strike slip faults, which conferred the major faults a several decameter thick core. Those faults were explored through different techniques: through balanced cross sections to reconstruct their geometry at depth and at the regional scale, with electric resistivity tomography to image the water content of the fault zone at the decameter to pluridecameter scale and with the analysis of the water hydrochemistry of springs outflowing from the fault zones to estimate their recharge potential. The hypothesis that we discuss is that the fault core made of breccia and/or cataclastic rocks was washed by paleofluid circulations initiating a large karstic network. Such fault cores may then represent both drainage and storage zones in the saturated zone of the deep aquifers. Detecting those cores as a function of fault geometry, size and offset could be a promising method to estimate karst reserves in highly tectonized areas

Influence of fault zones in the development of large karst conduits: Example from the Toulon area (SE, France).

International audienceno abstrac

Stratigraphy of the Haut Var Paleogene continental series (Northeastern Provence, France): New insight on the age of the 'Sables bleutés du Haut Var' Formation

The age of the Paleogene deposits of the Haut Var (Provence, France) has been the subject of debate. Particularly, the ''Calcaire à Bithynies'' and the ''Sables bleutés'' units were ascribed either to the early Eocene or to the Oligocene. A stratigraphical clarification is required in order to precise the paleogeographical relationships of the Haut Var Paleogene sedimentary series with coeval deposits in the neighbouring southern Provence and Subalpine regions and other European domains. The study area is characterized by tectonically separated synclines and grabens filled in by continental Paleogene deposits. Detailed mapping and lithostratigraphical logging, sedimentological and microfacies analysis have been undertaken in order to provide a reliable stratigraphical framework. Biostratigraphical subdivisions were established based on five different fossil groups: mammals, charophytes, gastropods, ostracodes, and foraminifers. Accordingly, five formations are distinguished and dated: ''Calcaire a` Microcodium'' and ''Brèche à Microcodium'' (Danian); ''Marnes à oeufs d'oiseaux'' (Selandian(?)-earliest Ypresian); 'Sables bleutés du Haut Var' (early-late(?) Ypresian); and ''Bourdas conglomerates'' (Rupelian). Particular emphasis is given to the study of the controversial 'Sables bleute´ s du Haut Var' Formation. As a result, correlations have been established between the different syncline and graben areas where Paleocene-Eocene and Oligocene deposits occur. Terrestrial deposits (carbonate paleosols and piedmont alluvial fans) took place during Paleocene times, while fluvial (cross-bedded sands) and lacustrine carbonate deposits developed in a foreland compressional intracontinental basin surrounded by emerged areas and tectonic highs during the early Ypresian. Paleoenvironmental and paleogeo- graphical analysis strengthen the view that a relative isolation characterized the Haut Var area during the early Eocene, probably enhancing episodes of brackish water or evaporitic sedimentation and gastropod endemism. During the late Eocene Pyrenean-Provence tectonic phase, the E-W trending Haut Var overthrusts have been emplaced posteriorly to the deposition of the 'Sables bleute´ s du Haut Var' Fm. Finally, coarse alluvial fan and local lacustrine carbonate sedimentation occurred during the Oligocene in narrow N-S trending subsident extensional grabens associated with the N-S trending Barjols Triassic uplift

RESERVOIR PROPERTIES OF BARREMIAN – APTIAN URGONIAN LIMESTONES, SE FRANCE, PART 1: INFLUENCE OF STRUCTURAL HISTORY ON POROSITY-PERMEABILITY VARIATIONS

Upper Barremian – Lower Aptian inner platform “Urgonian” limestones in the Mont de Vaucluse region, SE France, consist of alternating metre-scale microporous and tight intervals. This paper focuses on the influence of structural deformation on the reservoir properties of the Urgonian limestone succession in a study area near the town of Rustrel. Petrographic, petrophysical and structural data were recovered from five fully-cored boreholes, from the walls of a 100 m long underground tunnel, and from a 50 m long transect at a nearby outcrop. The data allowed reservoir property variations in the Urgonian limestones to be studied from core to reservoir scale. Eleven Reservoir Rock Types (RRTs) were identified based on petrographic features (texture, grain size), reservoir properties (porosity, permeability), and the frequency of structural discontinuities such as fractures, faults and stylolites. Tight and microporous reservoir rock types were distinguished. Tight reservoir rock types were characterised by early cementation of intergranular pore spaces and by the presence of frequent structural discontinuities. By contrast microporous reservoir rock types contained preserved intragranular microporosity and matrix permeability, but had very few structural discontinuities. Observed vertical alternations of microporous and tight rock types are interpreted to have been controlled by the early diagenesis of the Urgonian carbonates. Deformation associated with regional-scale tectonic phases, including Albian – Cenomanian “Durancian” uplift (∼105 to 96 Ma) and Pyrenean compression (∼55 to 25 Ma), resulted in the modification of the initial petrophysical properties of the Urgonian limestones. An early diagenetic imprint conditioned both the intensity of structural deformations and the associated circulations of diagenetic and meteoric fluids. Evolution of the Reservoir Rock Types is therefore linked both to the depositional conditions and to subsequent phases of structural deformation

Pore space evolution and elastic properties of platform carbonates (Urgonian Limestone, Barremian-Aptian, SE France)

A dataset of 214 ultrasonic velocity and porosity measurements on Barremian-Aptian carbonates from Provence (SE France) provides well-constrained velocity-porosity transforms and allows the quantification of the impact of pore type and diagenetic history on these velocities. A numerical approach (EPAR: equivalent pore aspect ratio) was used to link diagenetic transformations, pore network evolution and elastic properties. Three categories of samples characterized by their dominant pore type were discriminated from the velocity and porosity database by means of the EPAR values derived from bulk (K-EPAR) and shear (μ-EPAR) moduli: 1) purely microporous limestones (low K- and μ-EPAR . 0.3). Three velocity-porosity trajectories related to three diagenetic paths were defined and quantified from the Urgonian database: 1) EPAR-preserving micro-scale cementation of micrite, 2) non-EPAR-preserving dissolution with moldic pore development and 3) EPAR-preserving sparry calcite cementation of molds. Equivalent Pore Aspect Ratio can therefore be regarded as a robust tool to decipher diagenetic trends in velocity-porosity transforms and may help predicting pore architecture from subsurface data. © 2014 Elsevier B.V

Stratigraphy of the Haut Var Paleogene continental series (Northeastern Provence, France): New insight on the age of the ‘Sables bleutés du Haut Var’ Formation.

International audienceThe age of the Paleogene deposits of the Haut Var (Provence, France) has been the subject of debate. Particularly, the “Calcaire à Bithynies” and the “Sables bleutés” units were ascribed either to the early Eocene or to the Oligocene. A stratigraphical clarification is required in order to precise the paleogeographical relationships of the Haut Var Paleogene sedimentary series with coeval deposits in the neighbouring southern Provence and Subalpine regions and other European domains. The study area is characterized by tectonically separated synclines and grabens filled in by continental Paleogene deposits. Detailed mapping and lithostratigraphical logging, sedimentological and microfacies analysis have been undertaken in order to provide a reliable stratigraphical framework. Biostratigraphical subdivisions were established based on five different fossil groups: mammals, charophytes, gastropods, ostracodes, and foraminifers. Accordingly, five formations are distinguished and dated: “Calcaire à Microcodium” and “Brèche à Microcodium” (Danian); “Marnes à oeufs d’oiseaux” (Selandian(?)-earliest Ypresian); ‘Sables bleutés du Haut Var’ (early-late(?) Ypresian); and “Bourdas conglomerates” (Rupelian). Particular emphasis is given to the study of the controversial ‘Sables bleutés du Haut Var’ Formation. As a result, correlations have been established between the different syncline and graben areas where Paleocene-Eocene and Oligocene deposits occur. Terrestrial deposits (carbonate paleosols and piedmont alluvial fans) took place during Paleocene times, while fluvial (cross-bedded sands) and lacustrine carbonate deposits developed in a foreland compressional intracontinental basin surrounded by emerged areas and tectonic highs during the early Ypresian. Paleoenvironmental and paleogeographical analysis strengthen the view that a relative isolation characterized the Haut Var area during the early Eocene, probably enhancing episodes of brackish water or evaporitic sedimentation and gastropod endemism. During the late Eocene Pyrenean-Provence tectonic phase, the E-W trending Haut Var overthrusts have been emplaced posteriorly to the deposition of the ‘Sables bleutés du Haut Var’ Fm. Finally, coarse alluvial fan and local lacustrine carbonate sedimentation occurred during the Oligocene in narrow N-S trending subsident extensional grabens associated with the N-S trending Barjols Triassic uplift

Facteur de forme équivalent des pores: un outil pour la prédiction des types poreux dans les réservoirs carbonatés

International audienceThe equivalent pore aspect ratios (EPAR) provide a tool to detect pore types by combining P-and S-wave velocities, porosity, bulk density and mineralogical composition of carbonate rocks. The integration of laboratory measurements, well log data and petrographic analysis of 468 carbonate samples from various depositional and diagenetic settings (Lower Cretaceous pre-salt non-marine carbonates from offshore Brazil, Lower Cretaceous shallow-water platform carbonates from SE France and Upper Cretaceous deep-water carbonate from the Gargano Peninsula, Italy) allowed the acoustic signature of a wide range of pore types to be quantified. The equivalent pore aspect ratios are shown to be independent of pore volume and mineralogy. They can be therefore regarded as relevant parameters for discriminating selected pore network architectures in carbonate reservoirs displaying a wide range of porosity values and mineralogical compositions. Interparticle and intercrystalline micro-and macroporosity may include a variety of distinct pore network structures and a wide range of acoustic signatures depending on particle/crystal shape, nature of contacts, packing and cementation. The acoustic response of moldic pores appears to be mainly controlled by the shape of the dissolved allochems. The present work reveals also that correct pore type detection from acoustic and porosity measurements is highly dependent on the pore type classification used.Les facteurs de forme équivalents des pores (EPAR) fournissent un outil pour détecter les types de pores en combinant les vitesses des ondes P et S, la porosité, la densité apparente et la composition minéralogique des roches carbonatées. L'intégration de mesures en laboratoire, de diagraphies et d'analyses pétrographiques de 468 échantillons de carbonate provenant de divers dépôts et diagénétiques (carbonates non marins pré-salifères du Crétacé inférieur du Brésil, carbonates de plate-forme en eau peu profonde du Crétacé inférieur du SE France et du Crétacé supérieur carbonate d'eau de la péninsule du Gargano, Italie) a permis de quantifier la signature acoustique d'un large éventail de types de pores. Les rapports d'aspect des pores équivalents sont indépendants du volume des pores et de la minéralogie. Ils peuvent donc être considérés comme des paramètres pertinents pour discriminer des architectures de réseau de pores sélectionnées dans des réservoirs de carbonate présentant une large gamme de valeurs de porosité et de compositions minéralogiques. La microparticule et la macroporosité interparticulaire et intercristalline peuvent inclure une variété de structures de réseau de pores distinctes et une large gamme de signatures acoustiques en fonction de la forme des particules / cristaux, de la nature des contacts, de l'emballage et de la cimentation. La réponse acoustique des pores du moule semble être principalement contrôlée par la forme des allochems dissous. Le présent travail révèle également qu'une détection correcte du type de pores à partir de mesures acoustiques et de porosité dépend fortement de la classification du type de pores utilisée