La stratigraphie isotopique du Strontium est-elle une méthode fiable pour dater les plates-formes carbonatées à la transition du Barrémien à l'Aptien ? Révision de cas d'études en Téthys occidentale.

Strontium-isotope measurements on Lower Cretaceous marine rocks derive from belemnite material sampled in ammonite-constrained basinal successions. A group of values with a narrow range across the Barremian/Aptian boundary does not allow the separation of the uppermost Barremian (Martelites sarasini ammonite zone) from the lower Aptian pro parte (Deshayesites oglanlensis-D. forbesi ammonite zones). Growing numbers of studies applied Sr-Isotope Stratigraphy (SIS) on Barremian-Aptian shallow-marine sequences (Urgonian facies) in order to solve controversial results obtained by using different shallow-water biological time markers. Based on re-examination of case studies, we conclude that Sr-isotope values can neither be used to prove nor to disprove the location of the putative Barremian/Aptian boundary based on biostratigraphy. Pending more data available, SIS should be used with caution for dating ammonite-free carbonate sediments in the corresponding time interval.Les mesures de l'isotope du Strontium dans des roches carbonatées marines du Crétacé inférieur proviennent de restes de bélemnites récoltés dans des séries de bassins datées directement par ammonites. Autour de la limite Barrémien/Aptien, une gamme étroite de valeurs du Strontium ne permet pas de distinguer le Barrémien supérieur (Zone d'ammonite à Martelites sarasini) de l'Aptien inférieur pro parte (zones d'ammonite à Deshayesites oglanlensis et D. forbesi). Pourtant, l’application de la Stratigraphie Isotopique du Strontium (SIS) sur des séquences marines carbonatées barrémo–aptiennes (à faciès urgonien) apparaît dans un nombre croissant d’études, essentiellement afin de résoudre les datations souvent controversées des marqueurs biologiques d’environnements peu profonds. La révision de ces cas d'étude montre que l’utilisation des valeurs de l'isotope du Strontium n’est pas un outil fiable pour prouver ou réfuter la localisation de la limite Barrémien/Aptien telle que déduite par la biostratigraphie. Dans l'attente de données complémentaires, la SIS doit être utilisée avec précaution pour dater des séries carbonatées non datées directement par ammonites dans l'intervalle de temps concerné

Coupling of stratigraphic and diagenetic modelling : numerical developments and application to carbonate systems

Les systèmes sédimentaires carbonatés forment à la fois des archives géologiques uniques des changements globaux-locaux des enveloppes externes de la Terre et renferment plus de 75 % des réserves d'hydrocarbure conventionnelles. Ils sont complexes et très difficiles à comprendre et à prédire. Cette complexité à toutes les échelles spatio-temporelles rend nécessaire l'intégration de méthodes naturalistes et quantitatives pour les étudier. La modélisation numérique basée processus permet de réduire les incertitudes des prédictions des propriétés des réservoirs carbonatés.Le manuscrit présente une méthode de modélisation itérative des systèmes carbonatés de la stratigraphie à la sismique en intégrant la diagenèse. Cette approche est basée sur le couplage de plusieurs outils numériques et par une démarche de travail combinant la sédimentologie, la diagenèse, la physique des roches et la simulation sismique.L’approche de modélisation développée permet ainsi d’intégrer un grand nombre de données multi-échelles et multidisciplinaire au sein d’un modèle facilement partageable entre toutes les disciplines en géosciences. L’intégration de ces nombreuses données est facilitée par un continuum du modèle entre les différentes échelles d’espace et de temps (du bassin au réservoir). La sismique synthétique ainsi obtenue n’est pas une simple convolution géométrique, elle intègre les propriétés sédimentologiques et diagénétiques, permettant une analyse de la signification stratigraphique des réflecteurs sismiques. Cette approche innovante intègre les méthodes naturalistes et quantitatives nécessaires à la compréhension et à la prédiction des systèmes carbonatés.Carbonate sedimentary systems record both global and local geological changes of the outer envelope of the Earth and contain more than 75% of conventional hydrocarbon reserves. These carbonate systems show a great complexity at every spatial and temporal scales. To increase our ability to understand and predict such intricate natural systems, it is necessary to integrate naturalistic and quantitative methodological apporaches. Numerical process-based modeling (stratigraphic-sedimentary-diagenetic) reduces the uncertainty of prediction of carbonate reservoir properties. The manuscript presents a method of iterative modeling of carbonate systems from stratigraphy to seismic by integrating diagenesis. This approach is based on the coupling of numerical tools and a working approach combining sedimentology, diagenesis, rock physics and seismic simulation. Tests on case studies associated with scientific and industrial issues validated the method.The modeling approach that was developed during the thesis allows to integrate a large number of multi-scale and multidisciplinary data. Models can easily be shared between the disciplines of geosciences. The model continuum along different scales of space (from the basin to the reservoir) and time eases the integration of various data. The obtained synthetic seismic is not a simple geometric convolution, but an integration of sedimentological and diagenetic properties, which allows for an analysis of the stratigraphic significance of the seismic reflectors. This innovative approach integrates naturalistic and quantitative methods, which improve the understanding and prediction of carbonate systems and reservoirs

Testing geologic assumptions and scenarios in carbonate exploration: Insights from integrated stratigraphic, diagenetic, and seismic forward modeling

International audienceCarbonates are considered complex, heterogeneous at all scales, and unfortunately often poorly seismically imaged. We propose a methodology based on forward modelling approaches to test the validity of common exploration assumptions (e.g. chronostratigraphic value of seismic reflectors) and of geological interpretations (e.g. stratigraphic correlations, depositional and diagenetic architecture) that are determined from a limited amount of data. The proposed workflow includes 4 main steps: 1) identification and quantification of the primary controls on carbonate deposition and the prediction of the carbonate stratigraphic architecture (through stratigraphic forward modelling), 2) identification of diagenetic processes and prediction of the spatial distribution of diagenetic products (diagenetic forward modelling), 3) quantification of the impact of diagenesis on acoustic and reservoir properties, and 4) computation of synthetic seismic models based on various scenarios of stratigraphic and diagenetic architectures and comparison with actual seismic. The likelihood of a given scenario is tested by quantifying the 2 misfit between the modeled versus the real seismic. This workflow illustrates the relevance of forward modelling approaches for building realistic models that can be shared by the various disciplines of carbonate exploration (sedimentology, stratigraphy, diagenesis, seismic, geo-modelling and reservoir)

New Heteroceratidae (Ammonoidea) from the late Barremian deepening succession of Marseille (Bouches-du-Rhone, France)

International audienceInvestigation of the late Barremian deepening succession of the Provence platform, cropping out south of Marseille (Bouches-du-Rhone, France), has yielded a new ammonite fauna belonging to the Martelites sarasini Subzone (Martelites sarasini Zone). The fauna is dominated by representatives of the Heteroceratidae Spath, characterized by different patterns of coiling, high intraspecific variabilities and dwarfism. These heteroceratids are distinctive and utterly different from all previously known taxa, and this justifies the introduction of the new taxa Heteroceras denizoti sp. nov., Heteroceras veratiae sp. nov., Calanquites gen. nov., based on Imerites katsharavai Rouchadze; Giovaraiies gen. nov., based on Giovaraites massiliae gen. et sp. nov., Barguesiella gen. nov., based on Barguesiella goudesense gen. et sp. nov. and the closely allied Barguesiella mantei gen. et sp. nov. The occurrence of the latter species at the top of the Maiolica Formation in Italy questions its early Aptian age assumed in the literature. The newly described fauna could be considered as the first case of micromorphy in the Heteroceratidae. Its biostratigraphy, palaeoenvironmental and palaeobiogeographical significance are discussed

Quantitative carbonate sequence stratigraphy: Insights from stratigraphic forward models

International audienceA method of quantitative sequence stratigraphy based on stratigraphic forward modeling is tested on carbonate sedimentary systems (CSSs), especially on shallow-water carbonate platforms. Unless clear three-dimensional (3-D) and two-dimensional stratigraphic geometries crop out or are imaged by seismic data, 3-D carbonate sequence stratigraphic architectures are reconstructed assuming that one single factor representing changes in the ratio of the accommodation rate and the sedimentation rate (A'/S') through time can describe complex 3-D carbonate stratigraphic architectures at the basin scale. In this work, it is demonstrated that despite using a unique accommodation curve and a time-constant carbonate production, the preservation of theoretical A'/S', regarded as the fundamental parameter of sequence stratigraphy, is incomplete and spatially variable throughout a simple carbonate platform stratigraphic architecture. The apparent A'/S' sequence stratigraphic parameters preserved in the stratigraphic records are distinguished from the actual A'/S' parameters that control the stratigraphic response of CSSs. During overall accommodation increase, prograding and retrograding geometries can be time equivalent whereas coeval shallowing-and deepening-upward sequences may form. Apparent A'/S' spatial trends in one dimension are not consistently correlated between proximal and distal locations and do not typify specific stratigraphic architectures. This is the direct consequence of the spatial and synchronous variations in carbonate production rates along the platform profile. These results indicate that the construction of carbonate sedimentary piles, including carbonate reservoirs, cannot be simply based on standard sequence stratigraphic correlations of sparse and distant locations along platform-to-slope sedimentary profiles. Limitations of sequence stratigraphic correlations and uncertainties of A'/S' rates are addressed from an actual CSS case study (Lower Cretaceous Urgonian platform, southern Provence, France). A quantitative carbonate sequence stratigraphic workflow based on stratigraphic forward modeling is proposed

New Heteroceratidae (Ammonoidea) from the late Barremian deepening succession of Marseille (Bouches-du-Rhone, France)

International audienceInvestigation of the late Barremian deepening succession of the Provence platform, cropping out south of Marseille (Bouches-du-Rhone, France), has yielded a new ammonite fauna belonging to the Martelites sarasini Subzone (Martelites sarasini Zone). The fauna is dominated by representatives of the Heteroceratidae Spath, characterized by different patterns of coiling, high intraspecific variabilities and dwarfism. These heteroceratids are distinctive and utterly different from all previously known taxa, and this justifies the introduction of the new taxa Heteroceras denizoti sp. nov., Heteroceras veratiae sp. nov., Calanquites gen. nov., based on Imerites katsharavai Rouchadze; Giovaraiies gen. nov., based on Giovaraites massiliae gen. et sp. nov., Barguesiella gen. nov., based on Barguesiella goudesense gen. et sp. nov. and the closely allied Barguesiella mantei gen. et sp. nov. The occurrence of the latter species at the top of the Maiolica Formation in Italy questions its early Aptian age assumed in the literature. The newly described fauna could be considered as the first case of micromorphy in the Heteroceratidae. Its biostratigraphy, palaeoenvironmental and palaeobiogeographical significance are discussed

Marine carbonate factories: a global model of carbonate platform distribution

International audiencePlatform carbonates are a major component of the Earth system, but their spatial distribution through geological times is difficult to reconstruct, due to the incompleteness of geological records, sampling heterogeneity, and their intrinsic complexity. Beyond this complexity, carbonates are not randomly distributed in the world oceans, neither in the modern nor in the past, and thus, global trends exist. In the present review, we focus on the understanding of the spatial distribution of carbonate production at a global scale. We use a deterministic approach, which focuses on discriminating components, stratigraphic architectures, and environmental features to relate shallow-water carbonate production to oceanographic parameters. The work is based on extensive literature reviews on carbonate platforms. Ecological niche modelling coupled with deep-time general circulation models is used to calibrate a predictive tool of carbonate factory distribution. A carbonate factory function is set up that is based on sea-surface oceanographic parameters (temperature, salinity, and primary productivity). The model was tested using remote-sensing and in situ oceanographic data of Modern times, while outputs of paleoceanographic models are utilized for Lower Aptian (Cretaceous) modelling. The approach allows determining four neritic carbonate factories that are called the marine biochemical, photozoan, photo-C-, and heterozoan factories. The model finely simulates the global distribution of Lower Aptian and Modern carbonate platforms. Carbonate factories appear to thrive for specific ranges along the environmental gradient of carbonate saturation. This conceptual scheme appears to be able to provide a simple, universal model of paleoclimatic zones of shallow-water marine carbonates

Application of Stratigraphic Forward Modelling to Carbonate Reservoir Characterization – A New Paradigm from the Albion R&D Project

International audienceAbstract Improving carbonate reservoir prediction, field development and production forecasts, especially in zones lacking data, requires novel reservoir modelling approaches including process-based methods. Classical geostatistic modelling methods alone cannot match this challenge, in particular if subtle stratigraphic architectures or sedimentary and diagenetic geometries, not directly identified as properties with well data, control the reservoir heterogeneity. Stratigraphic forward modelling approaches can provide pertinent information to carbonate reservoir characterization. Integrating carbonate stratigraphic forward models in reservoir modelling workflows faces two sets of challenges: (1) the difficulty to establish high resolution and multi-scales continuous reservoir analogues from outcrops and (2) the development of forward modelling methods adapted to carbonate heterogeneity and calibrated to well data. The ALBION R&D Project dedicated to the Lower Cretaceous rudist-rich carbonate platform meets these two considerable scientific challenges. This workflow builds on previous modelling approaches at basin scale that integrates seismic inversion and forward modelling. This project delivers deterministic high-resolution static models that support the development of process-based modelling solutions. This multidisciplinary approach focuses on the characterization of primary sedimentary and diagenetic overprint that can impact drastically the flow behavior at inter-well scales in similar reservoir units such as the Kharaib and Shuaiba Formations. The SED-RES modelling package developed in house by Total R&D has been tested and calibrated with these high-resolution stratigraphic outcrop models. It allows valid prediction of carbonate facies associations mimicking the spatial distribution mapped along the Urgonian platform transects

Carbonate Facies Models, Fake or Real? Comparison of the Urgonian Formation South-East France with the Kharaib-Shuaiba Formations Middle East – Insights from the ALBION R&D Project

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Is Strontium-isotope stratigraphy a reliable tool for dating shallow-marine platform carbonates at the Barremian-Aptian transition? Review of western Tethyan case studies

Strontium-isotope measurements on Lower Cretaceous marine rocks derive from belemnite material sampled in ammonite-constrained basinal successions. A group of values with a narrow range across the Barremian/Aptian boundary does not allow the separation of the uppermost Barremian (Martelites sarasini ammonite zone) from the lower Aptian pro parte (Deshayesites oglanlensis-D. forbesi ammonite zones). Growing numbers of studies applied Sr-Isotope Stratigraphy (SIS) on Barremian-Aptian shallow-marine sequences (Urgonian facies) in order to solve controversial results obtained by using different shallow-water biological time markers. Based on re-examination of case studies, we conclude that Sr-isotope values can neither be used to prove nor to disprove the location of the putative Barremian/Aptian boundary based on biostratigraphy. Pending more data available, SIS should be used with caution for dating ammonite-free carbonate sediments in the corresponding time interval