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Mud generation from stratified sediments in a context of mud volcanism : the role of gas

Abstract : This manuscript assesses the role of gas in the mud generation processes by focusing on a dense and multidisciplinary dataset of the active Absheron mud volcano (AMV), South Caspian Basin. The study is divided in three main parts: definition of the mud source; analysis of the hydro-mechanical behavior of compacted sediments after gas exsolution; numerical modeling of the AMV formation.First, I identified the source of the AMV as being the Anhydritic Surakhany Fm. (ASF): seismic geomorphology evidences a depletion zone below the AMV and samples from surface mudflows indicate a Pliocene age and the same mineralogy as the ASF. The ASF is composed of interstratified anhydritic beds and low-density overpressured and undercompacted clay-rich layers. The mud source seems located in an interval presenting intrinsic favorable properties to remobilization and at the convergence of overpressure build-up and gas accumulation.I then tested the impact of gas exsolution on the hydro-mechanical properties of compacted sediments through a novel consolidation apparatus. Results show that sediments are damaged by gas exsolution and do not recover completely after reloading. Gas exsolution leading to a degree of gas saturation higher than 38% generates a critical behavior interpreted as the result of mud generation.I finally integrated multidisciplinary data and results in simple numerical models to confront the hypothesis on the AMV formation with the geological conditions. A 2D diffusion model confirms that the association of lateral pressure transmission and vertical gas migration along faults leads to mud generation. Fluid mechanics equations show that mud is then able to rise up to the seafloor by density-inversion. Accounting for fracture propagation and dynamic viscosity may improve and accelerate the mud remobilization process. I tested several working hypotheses through this modeling and went from a purely conceptual formation model for the AMV to a semi-quantitative one.This study identified key parameters for mud volcano formation that are believed to be common to most of these structures and allowed developing a modeling approach that may be adapted and improved to describe mud volcanoes formation in other geological contexts.
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Arthur Blouin. Mud generation from stratified sediments in a context of mud volcanism : the role of gas. Earth Sciences. Université de Pau et des Pays de l'Adour, 2019. English. ⟨NNT : 2019PAUU3040⟩. ⟨tel-02881953⟩

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