Combining Discrete Element and Process-based sedimentary models: a new tool to model syntectonic sedimentation

[eng] In order to understand the current state of the natural rocky environment and its heterogeneity, we require to study the interaction and time evolution of the numerous geological processes that have contributed to the geological reality we observe today. Given this, the thesis presented here concerns itself with numerical modelling of geological processes. The forward numerical model developed during this thesis is able to simulate deformation and sedimentation in one single setting. To do this, the model uses a novel approach that combines a Discrete Element Model (DEM) and a process- based sedimentary model, Simsafadim (SFM) to link both processes, deformation and sedimentation. The discrete element model (DEM) deals with the simulation of deformation in different materials in 2D and 3D. It is primarily used to investigate the propagation and evolution of deformation in the upper crust caused by tectonic movements. Simsafadim (SFM) is a process-based numerical forward model, which simulates subaqueous clastic transport and sedimentation in three dimensions, including processes of carbonate interaction, production, transport and sedimentation. It can model efficiently the distribution of facies and the depositional architectures in a sedimentary basin and it is a powerful tool for the 3D prediction of stratigraphic structures. Merging both codes provides a new tool for geological modelling in which deformation is influenced by the presence of syntectonic sediment dispersal and deposition. In addition, the tectonic processes change the topographic surface, which influences fluid flow, transport and, consequently, sedimentation in the process-based sedimentary model. The interaction of tectonic and sedimentary processes allows us to study the propagation of deformation in the syntectonic materials as well as how these new sediments influence the propagation of deformation in the pretectonic unit. The model is applied in two different cases studies, in order to test the viability of the new model, as well as to achieve new insight in the respective themes treated: 1) First case study: the effect of normal faulting and a relay ramp on sediment dispersal. The model is used to study the sedimentary infill in an extensional basin, specifically related to a relay ramp system. To perform the test study two configurations are designed: with one normal fault, and with two overlapping normal faults linked by a relay ramp. The different results show that the source area location in relation to the available accommodation space plays the major role in the distribution of different sediment types into the basin. Nonetheless, when the source area for water and sediment is defined as regional and parallel to the fault, the grain size distribution obtained by the two overlapping faults linked by a relay ramp have clear asymmetries when compared with the ones obtained by one-fault configurations. Therefore, the different extensional experiments allow us to conclude that the configuration with a relay ramp can play an important role in the distribution of the sediments into the basin. 2) Second case study: The effect of syntectonic sedimentation on fold geometry The numerical is used to investigate the effect of syntectonic sedimentation on fold geometry and specifically related to a delta progradation surrounded by two growing anticlines. To the initial tectonic configuration that reproduces the growth of two faults, two different cases of the sedimentary model are considered: without sediments, and considering syntectonic sedimentation. Summing up, the main results obtained for these experiments conclude that the syntectonic sedimentation is controlling the mechanism of fold growth and the final fold geometry: the left-side fold shows a left-vergent asymmetric anticline. Moreover, the strain suggests that this anticline is passing from a detachment fold (without sediments) to a fault propagation fold basinwards (with sediments). As a consequence, the inner syncline and the related sedimentary basin are also changing in transversal and longitudinal direction, being wider with syntectonic sedimentation. [cat] El objectiu principal d'aquesta tesi es donar un pas endavant en el coneixement dels processos geologics que intervenen en la formacio de les conques sedimentaries mitjancant la creacio d'un model numeric per modelitzar la sedimentacio sintectonica en un ambient subaquatic. El model numeric desenvolupat en aquesta tesi es capac de modelitzar la sedimentacio clastica subaquatica i la deformacio de la unitat pretectonica en una sola configuracio. Per fer aixo, el model combina dos models ja existents: un model d'elements discrets per simular la deformacio de la unitat pretectonica (DEM) i un model sedimentari basat en processos, per modelitzar la sedimentacio clastica subaquatica Simsafadim (SFM). La unio d'aquest dos models, DEM i SFM, proporciona una nova eina per a la modelitzacio geologica. En el nou model, l’evolucio de deformacio en la unitat pretectonica canviara la topografia de la conca, que afectara directament la batimetria, influenciant aixi els processos de transport i sedimentacio que hi tenen lloc. Alhora, aquesta evolucio de la deformacio de la unitat pretectonica estara influenciada per la presencia dels nous materials sintectonics. Amb aquesta doble interaccio tectonica-sedimentaria del nou model, tambe es pot estudiar la deformacio en els materials sintectonics. Aquesta nova eina de modelitzacio permet simular i analitzar diferents arquitectures deposicionals sintectoniques i escenaris geologics mes complexos. Tant per ampliar el coneixement de com els processos de sedimentacio-deformacio interactuen en alguns ambients tectonics, com per comprovar l'eficacia del model, la nova eina s'aplica a dos casos diferents: 1) En primer lloc s'utilitza el model numeric en un ambient extensional per estudiar l'impacte que te la presencia de falles normals i les corresponents zones de relleu en la distribucio del sediment a la conca. Quan es compara la distribucio de sediment obtinguda amb una configuracio de dos falles amb una rapa de relleu, amb la distribucio de sediment obtinguda amb una configuracio d'una sola falla, els resultats mostren asimetries, tant longitudinals com perpendiculars a les estructures. 2) En el segon cas s'estudia l'efecte de la sedimentacio sintectonica sobre la geometria final d'un plec. Els resultats, obtinguts a partir de la comparacio de l'evolucio de les estructures considerant o no considerant sedimentacio sintectonica, estableixen que la sedimentacio sintectonica pot afectar tant al mecanisme de formacio del plec com a la seva geometria final.