Modelling the coupling between salt kinematics and subsidence evolution: Inferences for the Miocene evolution of the Transylvanian Basin

Abstract

Large-scale diapiric salt movements affect the architecture of sedimentary basins and often prevent the understanding of their mechanics by hiding or distorting subsidence patterns. One good example is the evolution of the Transylvanian Basin, which formed during Miocene times in an area located in between the rapid slab rollback and continental collision recorded at the exterior of the Carpathians and the extension of the neighbouring Pannonian Basin. In the absence of major genetic fault systems, quantifying these external tectonic forcing factors requires an accurate reconstruction of subsidence evolution. Having the advent of a detailed 3D geometrical model of the Transylvanian Basin, we apply a 3D numerical modelling technique that couples salt re-distribution and subsidence evolution to quantify and understand the basin kinematics and vertical motions. Two techniques, backward and forward modelling are coupled in order to discriminate between salt migration driven by overburden and the influence of external tectonic forcing factors. The results show that salt kinematics was more complex than simple unidirectional migration, suggesting the existence of areas with significant subsidence hidden by the inward salt migration and areas with apparent large subsidence that are in reality artefacts of outwards salt migration. Additionally, the results suggest that parts of the basin have been successively affected by in- and out-ward salt migration events, an effect of localising subsidence and overburden. Furthermore, accelerated moments of salt migration took place during the main Miocene contraction events recorded at the exterior of the Carpathians, demonstrating that salt migration is enhanced by intraplate stresses. Our study also infers that the subsidence of the Transylvanian Basin is the result of the superposition of the contraction at the exterior of the orogenic chain and the back-arc extension.