Abstract The Miocene of the Western Alpine foreland basin were deposited in a north–south seaway along the active alpine orogenic front. In the subalpine massifs and the southern Jura mountains, the revised Miocene stratigraphy documents a detailed chronology of thrust propagation at the western alpine front, where tectonic activity had a primary influence on seaway palaeogeographical evolution. Here we propose nine palaeogeographical maps during the Miocene, the first of which depicts the initial Miocene transgression at c. 21.0 Ma. Between c. 18.05 and c. 12.0 Ma, a westward retreat of the Miocene Sea occurred in response to activation of the basal thrust of the Belledonne massif, which in turn triggered successive fault zones from east to west. At c. 10.0 Ma, a major uplift phase intervened and induced a rapid southward retreat of the Miocene Sea. The reconstructed palaeogeographical maps outline the main controls on the foreland basin seaway evolution: (1) the timing of the main thrusts; (2) the inherited palaeotopography; and (3) eustatic sea-level changes during the Miocene. These reconstructions are integrated at the basin scale, highlighting the southward- to westward-directed seaway migration in response to the Belledonne thrust activity that deeply shaped the palaeogeographical evolution during the early to middle Miocene.

Abstract Palaeostraits are common features formed during the extension and fragmentation of active continental margins, when back-arc basins are formed and microplates develop through upper-plate extension. In this contribution, we focus on narrow seaways and straits associated with successive pulses of late Cenozoic rifting along the southwestern Eurasian continental margin, and the ensuing formation and dispersal of microplates. The incomplete and largely non-cylindrical Africa–Eurasia continental collision in the Mediterranean region provides snapshots of the various phases of microplate fragmentation and dispersal, punctuated by the presence of narrow seaways/straits. These peculiar physiographical conditions induced current amplification, and led to the accumulation of characteristic large-scale, cross-stratified deposits and tidal facies in an otherwise generally microtidal setting. Although not univocally related to rifting, the identification of such distinctive sedimentary facies within deformed orogenic belts may ultimately help in terrane analysis and in the discrimination of individual microplates, which were then amalgamated. Recognition and dating of palaeostrait tectonosedimentary facies can thus constrain the presence and the onset of extension in the geological record.