Abstract
Understanding the formation and evolution of sedimentary basins is of paramount importance because they record the Earth’s history: past changes in climate and sea or lake level, changes of sediment and water discharge. In this thesis I aimed to study the mechanisms driving the sensitive interplay between tectonics and sedimentation
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in extensional back-arc basins. In such settings extensional basin formation post-dates an orogenic evolution, and is juxtaposed over an inherited nappe stack, often reactivating thrust contacts and exhuming rocks previously deeply buried. Thanks to the existing advanced knowledge from the Pannonian Basin of Central Europe and the surrounding Alpine-Carpathian-Dinaridic system, this region provides a key natural laboratory for the development and verification of a new generation of tectono-sedimentary models. A novel kinematic, seismic and well sequence stratigraphic interpretation from the Great Hungarian Plain allow the quantification of the link between the formation of half-grabens and coeval sedimentation in the depocentres. Our interpretation of temporal and spatial migration of the 220-270 km extension during the entire Miocene times explains the contrasting present-day strike of various sub-basins as a result of their gradual clockwise rotation. The post-rift phase of the Pannonian Basin is associated with the evolution of Lake Pannon: an initial underfilled, then balance fill and a final stage of overfilled giant paleo-lake. We combined sedimentological observations with a backstripping methodology facilitated by well lithology and porosity data to gradually remove the sediment overburden. It is showed that paleobathymetric differences in the lake were clearly larger than 1000 metres in the deepest sub-basins. The large amount of compaction associated with lateral variations of Neogene sediment thicknesses has created non-tectonic normal fault offsets and folds. The influence of lithospheric-scale rheological heterogeneities on the extension of an over-thickened, hot lithosphere is also analysed by conducting a series of 2D thermo-mechanical numerical experiments. Asymmetric crustal geometries are often in contrast with the more symmetrical regional lithospheric structure observed beneath extensional basins. Our modelling shows that syn-rift subsidence rates are low to moderate creating half-grabens where extension migrates in space and time, grouped in an overall symmetrical appearance on a larger scale. The initial lithospheric mantle asymmetry is attenuated by further dynamic evolution of the thermal anomaly during the “post-rift” phase, resulting in additional 2-3 km subsidence in the basin centres. Finally, high resolution stratigraphic numerical modelling was designed to study the sedimentation at the scale of individual half-grabens, controlled by one major normal fault focussing the coeval sedimentation in the hanging wall and comparable uplift of its footwall. This model accounts for spatially and temporally variable subsidence and erosion rates, sediment flux composed of different lithologies, compaction, eustasy, water discharge and transport processes. Our modelling applied to the Miocene syn-rift evolution of the Pannonian Basin highlighted the migration of active depocentres between Early to Late Miocene and its sedimentary responses. Our modelling can discriminate the low-order tectonic cycles driven by normal fault activity and higher order sea-level and climatic-driven transgressive-regressive cycles and the auto-cyclic nature of the depositional system.
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