Role of structural inheritance and salt tectonics in the formation of pseudosymmetric continental rifts on the european margin of the hyperextended Mauléon basin (Early Cretaceous Arzacq and Tartas Basins)

Abstract Arzacq and Tartas were two Cretaceous basins developing in the Bay of Biscay as secondary depocentres in the larger Aquitaine Basin. They belong to an Albian rift system, where recent studies have stressed the role of simple-shear thinning on the genesis of regional asymmetric basins. However, the two basins differ from recent models in having a pseudo-symmetric morphology. Here, we address the Early Cretaceous tectono-sedimentary evolution of the Arzacq and Tartas rift basins and the lithospheric processes associated with their genesis. These basins did not suffer major brittle deformation during rifting stage, but nevertheless record a major change in their configuration between the Aptian and the Albian. The Arzacq Basin shifted from a symmetric to a slightly asymmetric configuration. This change was controlled by gravity sliding of the pre-rift sedimentary cover in the eastern Arzacq Basin moving its depocenter south, and by salt diapirism in the western Arzacq Basin moving its depocenter north. Several inherited Paleozoic structures were reactivated as transfer zones and appear to be responsible for this depocenter shift, the emplacement of salt diapirs, at same time regionally limiting gravity sliding. The Tartas Basin maintained a symmetric regime throughout the Early Cretaceous, except along the Barlanes transfer zone where the Lussagnet salt diapir originated. Two drivers of subsidence are thus envisaged in the Arzacq Basin: a Neocomian-Aptian crustal thinning stage, followed by reactivation of Paleozoic faults in Albian time accompanied by salt diapirism and gravity cover sliding. The Mauleon North Pyrenean Basin and its north adjacent Tartas and Arzacq basins thus formed part of a series of rift basins that progressed in maturity southward, from a simple sag basin (Tartas) to a slightly asymmetric basin (aborted detachment, Arzacq) to a hyperthinned basin (Mauleon). Our results offer new insights on the role of: (1) structural inheritance in partitioning extensional strain, (2) transfer zones as able to influence the sedimentary record of basins during crustal thinning, and (3) pre-rift salt decollements as able to separate the structural styles of sub- and supra-salt successions.