Thrust Propagation and Syntectonic Sedimentation in the Savoy Tertiary Molasse Basin (Alpine Foreland)

Abstract

The Savoy Tertiary molasse basin is part of the Neogene foreland thrust belt of the Alps that was overlain by Tertiary syntectonic sediments during the poly-phase development of the Alpine foreland. The analysis of these stratigraphic sequences is helpful for understanding the dynamics of the area because it provides efñcient constraints for restoring the tectonic subsidence and the progressive deformation history of the basin. During Rupelian to Aquitanian times prograding sedimentary sequences were deposited, while passive flexuring of the foreland developed. This was probably induced by the tectonic overload created by the Oligocene thrust sheets in the inner parts of the Alps. From the Rupelian to the Chattian, this basin developed with high progradation rates (6 mm/year) and high subsidence rates (> 0.2 mm/year) in the eastern parts of the basin, whereas during the Aquitanian, progradation was low (< 1 mm/ year) but subsidence remained high (> 0.15 mm/year). Afterwards, this early passive foreland flexural basin was inverted and became involved in the Neogene foreland thrust system during the Miocene thrust propagation. During the Burdigalian to the Serravallian, this led to the development of sparce syn-thrust infillings with heterogeneous deposition rates. This notably highlights the important migration of the Alpine front in this area during Burdigalian times. The homogenized strain on the whole molasse basin in Savoy during the Burdigalian-Langhian was around 2 mm/year. Taking into account the proposed evolution, hydrocarbon maturation and migration are also considered in estimating the petroleum potential of the area.