Thermo-mechanical and stratigraphic numerical forward modelling: recent advances and their joint application in the Pannonian Basin

International audienceBasin analysis and subsidence history provide key insights into sedimentary basin forming mechanisms. Directobservations have long been the only source of information on their thermal and lithological architecture. State of the artmodelling techniques today enable the prediction and computation of their formation and evolution constrained bygeological field observations, geophysical and deep borehole data. Understanding the inherent connections between largescaletectonic and local basin-scale surface processes requires the joint application of thermo-mechanical and stratigraphicmodelling techniques. To this aim, we combined the thermo-mechanical lithospheric-scale numerical code Flamar and thehigh-resolution 3D deterministic stratigraphic software DionisosFlow. This joint modelling method quantifies forcingfactors, such as crustal and lithospheric thinning, lithospheric flexure, sea-level and climatic variations associated withwater and sediment influx and sediment compaction. The modelling shows the migration of extensional deformation inspace and time creating deep half-grabens. After a rapid uplift event, the subsequent post-rift times are characterised bycontinuous kilometre-scale differential vertical movements. The modelled tectonic subsidence and uplift rates and halfgrabengeometries are imported into the 3D stratigraphic modelling code. Our modelling of a 120 km × 150 km area showsthat such scenarios are associated with continental alluvial to shallow-water sedimentation and footwall erosion during theearly stages of the syn-rift, followed by rapid deepening during the subsequent syn-rift evolution. Finally, the basins arefilled by a large-scale prograding shelf-margin slope system during the post-rift times. We differentiate betweenunconformities caused by tectonics, sea-level variations or auto-cyclic processes. Our tectonic and stratigraphic results arecompared with geological and geophysical constraints from the Pannonian Basin of Central Europe.Tektonikai és rétegtani numerikus modellezés: együttes alkalmazásuk és új eredményeik a Pannon-medencében Összefoglalás Üledékes medencék térben és időben változó süllyedéstörténete jól tükrözi az egy adott területre jellemző főbb medence-formáló klimatikus, üledékes és tektonikai folyamatokat. A klasszikus medenceanalízis módszere fúrási és további geofizikai adatokból, valamint az üledékes rétegsor megismeréséből származtatja egy medence süllyedés történetét. Napjainkra azon-ban különböző numerikus modellezési módszerek lehetővé teszik medencék süllye déstörténetének és fácieseloszlásának számítását és előrejelzését, amennyiben ismerjük a terület fejlődését leíró főbb fizikai folyamatokat. Ezen folyamatorientált modelleket geológiai és geofizikai adatokkal kell hitelesíteni. Ebben a tanulmányban litoszféraléptékű tektonikai és medenceskálájú felszíni folyamatok kapcsolatát vizsgáljuk, amely megköveteli a különböző térbeli és időbeli skálájú numerikus modellek együttes alkalmazását. Ennek megfelelően ötvöztük a 2D termo-mechanikus Flamar tektonikai modellt és a nagy felbontású DionisosFlow rétegtani modellező programot, így képesek voltunk számszerűsíteni a kéreg és litoszféra rideg és képlékeny deformációjának és elasztikus meghajlásának léptékét. A tektonikus numerikus modell által számított süllyedéstörténetet bemenő adatként használtuk a rétegtani modellezésnél, ahol a fejlődő részmedencékben vizsgáltuk az üledékes szállítási útvonalak és az üledékes környezetek fejlődését. Ezzel egyidejűleg figyelembe vettük a vízszintváltozások és klimatikus hatások szerepét a medence süllyedés-és feltöltődés történetének szimulációja során. Aszimmetrikus litoszféra extenziós modell eredményeink jelzik mély félárkok fejlő dését a medenceperemektől a medence belseje felé. Egy rövid kiemelkedési fázist követően a "posztrift" időszak további kilométer nagyságrendű differenciális vertikális mozgásokkal jellemezhető. Modellünk rávilágít a vízmélység értékek térbeli és időbeli változékonyságára, valamit a kialakuló unkon-formitások okaira. Modelleredményeink egy lehetséges forgatókönyvet jelentenek a Pannon-medence tektonikai és rétegtani fejlődésére. Abstract Basin analysis and subsidence history provide key insights into sedimentary basin forming mechanisms. Direct observations have long been the only source of information on their thermal and lithological architecture. State of the art modelling techniques today enable the prediction and computation of their formation and evolution constrained by geological field observations, geophysical and deep borehole data. Understanding the inherent connections between large-scale tectonic and local basin-scale surface processes requires the joint application of thermo-mechanical and stratigraphic modelling techniques. To this aim, we combined the thermo-mechanical lithospheric-scale numerical code Flamar and the high-resolution 3D deterministic stratigraphic software DionisosFlow. This joint modelling method quantifies forcing factors, such as crustal and lithospheric thinning, lithospheric flexure, sea-level and climatic variations associated with water and sediment influx and sediment compaction. The modelling shows the migration of extensional deformation in space and time creating deep half-grabens. After a rapid uplift event, the subsequent post-rift times are characterised by continuous kilometre-scale differential vertical movements. The modelled tectonic subsidence and uplift rates and half-graben geometries are imported into the 3D stratigraphic modelling code. Our modelling of a 120 km × 150 km area shows that such scenarios are associated with continental alluvial to shallow-water sedimentation and footwall erosion during the early stages of the syn-rift, followed by rapid deepening during the subsequent syn-rift evolution. Finally, the basins are filled by a large-scale prograding shelf-margin slope system during the post-rift times. We differentiate between unconformities caused by tectonics, sea-level variations or auto-cyclic processes. Our tectonic and stratigraphic results are compared with geological and geophysical constraints from the Pannonian Basin of Central Europe

Can sediment supply variations create sequences? Insights from stratigraphic forward modelling

Classic sequence stratigraphy suggests depositional sequences can form due to changes in accommodation and due to changes in sediment supply. Accommodation‐dominated sequences are problematic to define rigorously, but are commonly interpreted from outcrop and subsurface data. In contrast, supply‐dominated sequences are much less commonly identified. We employ numerical stratigraphic forward modelling to compare stratal geometries forced by cyclic changes in relative sea level with stratal geometries forced by sediment discharge and water discharge changes. Our quantitative results suggest that both relative sea‐level oscillations and variations in sediment/water discharge ratio are able to form sequence‐bounding unconformities independently, confirming previous qualitative sequences definitions. In some of the experiments, the two types of sequence share several characteristics, such as an absence of coastal‐plain topset deposits and stratal offlap, something typically interpreted as the result of falling relative sea level. However, the stratal geometries differ when variations in amplitude and frequency of relative sea‐level change, sediment/water discharge ratio, transport diffusion coefficient and initial bathymetry are applied. We propose that the supply‐dominated sequences could be recognised in outcrop or in the subsurface if the observations of stratal offlap and the absence of coastal‐plain topset can be made without any strong evidence of relative sea‐level fall (e.g. descending shoreline trajectory). These quantitative results suggest that both supply‐dominated and accommodation‐dominated sequences are likely to occur in the ancient record, as a consequence of multiple, possibly complex, controls

Numerical scheme for a stratigraphic model with erosion constraint and nonlinear gravity flux

International audienceIn this work, we study an extension of the model introduced by Eymard et al. [Int. J. Numer. Methods Engrg. 60, 527–248 (2004)] for the simulation of large scale transport processes of sediments, subject to an erosion constraint. The novelty we consider lies in the diffusion law relating the flux of sediments and the slope of the topography, that now involves a p-Laplacian with p > 2 in order to get more realistic landscape evolutions. This physical sophistication entails the construction of an entirely new numerical scheme, the details of which shall be supplied

Novel 3D sequence stratigraphic numerical model for syn-rift basins: Analysing architectural responses to eustasy, sedimentation and tectonics

Syn-rift clastic sedimentary systems preserve a complicated stratigraphic architecture that records the interplay of tectonics, eustatic sea level and storage and routing of sediments. Previous conceptual models describe and explain changes in depositional stacking patterns along a fault segment. However, stacking patterns, and the nature of key stratigraphic surfaces, is challenging to predict accurately with conventional sequence stratigraphic models that do not consider the three-dimensional interplay of subsidence, sedimentation, and eustasy. We present a novel, geometric, 3D sequence stratigraphic model (‘Syn-Strat’), which applies temporally- and spatially-variable, fault-scale tectonic constraints to stratigraphic forward modelling, as well as allowing flexibility in the other controls in time and space. Syn-Strat generates a 3D graphical surface that represents accommodation. Although the model has the capacity to model footwall variation, here we present model results from the hangingwall of a normal fault, with temporal and spatial (dip and strike) predictions made of stacking patterns and systems tracts for a given set of controls. Sensitivity tests are tied to the depositional architecture of field-based examples from the Loreto Basin, Gulf of California and Alkyonides Basin, Gulf of Corinth. Here, the relative influence of major sedimentary controls, different subsidence histories, varying sedimentation distribution, including along-strike variation in stacking patterns, are assessed and demonstrate the potential of Syn-Strat for reducing subsurface uncertainties by resolving multiple scenarios. In addition, the model demonstrates the nature of diachroneity of key stratigraphic surfaces that can arise in syn-rift settings, which could be represented by a bypass surface (sequence boundary) or reservoir seal (maximum flooding surface) in the rock record. Enabling a quantitative assessment of these surfaces is critical for prospect analysis in hangingwall half-graben-fills, where these surfaces are heavily relied upon for well correlations that are used for hydrocarbon volume and production rate predictions

Modélisation stratigraphique déterministe: Conception et applications d'un modèle diffusif 3D multilithologique.

Mémoires de Géosciences Rennes, n°78, 197p. ISBN: 2-905532-77-7Recent progress in geology, and especially in genetic stratigraphy, has improved our understanding of bassin fill on temporal (hundreds of th ou sand to tens of million years) and spatial (tens to hundreds kilometers) macro scales. The purpose of this work is to conceive a deterministic numerical model able to simulate this multilithological filling in 3D. Three kinds of model has been previously developped : geometrical, diffusive and hydrodynamic models. Among the se approaches, we have chosen the diffusive approach, which is the only one enabling to simulate the bassin fill at the specified temporal and spatial scales. We have built a diffusive model, named DIONISOS (DIffusion Oriented - Normal and Inverse - Simulation Of Sedimentation). The simulation results of this model may be adjusted to real weIl data by a manual inversion method. Study of micro-scale fluid mechanics laws and analysis of their records in the sediments on macro-scales led us to a diffusion equation. This equation links sediment flow te ground slope (water energy), water flow (water transport capacity) and diffusion coefficient (transport efficiency). To simulate transport of different lithologies, we define an altered layer, in which takes place aH the sediment transport. Different diffusion coefficients are used to simulate the behavoiur of these different lithologies in different environments. Applications of DIONISOS on theoretical and real cases show that the model can reproduce the implications of genetic stratigraphy concepts (sediment volume partitionning and genetic units distorsion) and the sedimentary geometries observed on outcrops. DIONISOS is physically and geologically consistent. These applications illustrate several possible feedbacks concerning the geological information, on theoretical cases (relation between bathymetry and sandshale ratio, littoral slope evolution, ... ) as on real cases (definition of bathymetries from facies, ... ). Despite of these encouraging results, sorne points need to be tested, improved or developed such as a littoral drift and turbiditic transport, or carbonate production. Thus, the link of DIONISOS with tectonic models should improve our understanding of the influence of tectonic processes on sedimentation at different scales.Les progrès récents en géologie, et en particulier en stratigraphie génétique, ont permis de mieux appréhender l'étude du remplissage sédimentaire des bassins sur des échelles de temps de quelques centaines de milliers à dizaines de millions d'années, et d'espace de l'ordre de la dizaine à la centaine de kilomètres. Le but de notre travail est la conception d'un modèle déterministe numérique permettant la simulation de ce remplissage sédimentaire. Trois types de modélisation sont actuellement développées : les modèles géométriques, diffusifs et particulaires. Parmi ces approches, nous avons retenu l'approche diffusive, seule approche permettant la simulation du remplissage des bassins sédimentaires aux échelles de temps et d'espace envisagées. Nous avons ainsi conçu un modèle diffusif, baptisé Dionisos (Diffusion Oriented - Normal and Inverse - Simulation Of Sedimentation). L'étude de lois utilisées en mécanique des fluides et de leurs enregistrements dans les sédiments sur de grandes échelles de temps et d'espace nous a permis de concevoir une équation de diffusion reliant le flux de sédiments, s'écoulant en chaque point du bassin, à la pente (énergie de l'écoulement de l'eau), au flux d'eau (capacité de transport de l'eau) et à un coefficient de diffusion (efficacité du transport). Afin de simuler le transport de plusieurs lithologies, nous avons de plus défini une couche superficielle d'altération au sein de laquelle s'effectue l'ensemble de ce transport. Les applications de ce modèle diffusif sur des cas théoriques et sur des cas réels ont montré que ce modèle restitue les implications des concepts de la stratigraphie génétique (partitionnement volumétrique et distorsion des unités génétiques) et les géométries sédimentaires observées. Le modèle est ainsi physiquement et géologiquement cohérent. Ces applications du modèle Dionisos ont de plus illustré différents retours possibles vers les informations géologiques, tant au niveau des cas théoriques (relation entre bathymétrie et sablosité, évolution de la pente du littoral, ... ) qu'au niveau des cas réels (affinement de la définition des bathymétries, ... ). Malgré ces résultats encourageants, il reste cependant différents points à tester, améliorer ou développer, tels que la prise en compte de la dérive littorale et des écoulements turbiditiques, ainsi que la production des carbonates. Ainsi, couplé avec des modèles tectoniques, le modèle Dionisos devrait permettre de mieux appréhender l'influence à diverses échelles des processus tectoniques sur la sédimentation

A Modular Model of Active Vision

Modularity is the main characteristic of the biological systems and especially of the brain [2]. For example, Vision can be described as the interactions of different processing systems [1]. Physiologists relate two pathways from the retina. The first conveys information from the retina to the cortical areas, where specialized areas analyse the visual data (e.g., colour vision, motion detection, object recognition and localization) . The second joins the retina to the superior colliculus, which sends motor signals to extraocular neurons (e.g., saccade from one important zone in the visual world to another one). We described a biologically inspired connectionist model of the visual system. Neural networks, despite their ability to solve a lot of hard problems, are rarely modular. Connectionist models usually do not take into account eye movement informations underlying the attentional processes [5], except a recent study on reading [10]. On the contrary, our system involved three module..

Thermo-mechanical and stratigraphic numerical forward modelling: recent advances and their joint application in the Pannonian Basin

Basin analysis and subsidence history provide key insights into sedimentary basin forming mechanisms. Direct observations have long been the only source of information on their thermal and lithological architecture. State of the art modelling techniques today enable the prediction and computation of their formation and evolution constrained by geological field observations, geophysical and deep borehole data. Understanding the inherent connections between large-scale tectonic and local basin-scale surface processes requires the joint application of thermo-mechanical and stratigraphic modelling techniques. To this aim, we combined the thermo-mechanical lithospheric-scale numerical code Flamar and the high-resolution 3D deterministic stratigraphic software DionisosFlow. This joint modelling method quantifies forcing factors, such as crustal and lithospheric thinning, lithospheric flexure, sea-level and climatic variations associated with water and sediment influx and sediment compaction. The modelling shows the migration of extensional deformation in space and time creating deep half-grabens. After a rapid uplift event, the subsequent post-rift times are characterized by continuous kilometre-scale differential vertical movements. The modelled tectonic subsidence and uplift rates and half-graben geometries are imported into the 3D stratigraphic modelling code. Our modelling of a 120 km × 150 km area shows that such scenarios are associated with continental alluvial to shallow-water sedimentation and footwall erosion during the early stages of the syn-rift, followed by rapid deepening during the subsequent syn-rift evolution. Finally, the basins are filled by a large-scale prograding shelf-margin slope system during the post-rift times. We differentiate between unconformities caused by tectonics, sea-level variations or auto-cyclic processes. Our tectonic and stratigraphic results are compared with geological and geophysical constraints from the Pannonian Basin of Central Europe