The Mid-Albian unconformity, a key to understand the geodynamics of the North Pyrenean Trough

The Pyrenees are the result of structural inversion a rift general direction N110E, established at articulation European and Iberian plates. This was created by left-lateral transtension with severe crustal thinning during latest Early Cretaceous Mid-Cretaceous. Its inversion, which led to uplifting Pyrenean chain, took place gradually, transpression from east west, Late followed an Eocene collision. From historical fieldwork, this note mainly focuses on rifting period scale domain. It clearly shows fundamental role stratigraphic approach in interpretation. Although synchronous Pyrenees, extension is more important western part near Bay Biscay. therefore location, within Tardets-Mauléon Basin, that various stages creation evolution could be recognized with, successively: (1) epirogenic pre-rifting stage, facies lines, submeridian Jurassic, gradually change into N110E Neocomian before giving way, (Barremian-Gargasian), moderate acceleration subsidence and, consequently, gentle uplift southern margin, future High Primary Belt (also often called Axial Zone) Landes Plateau, initiating next stage; (2) major, brittle, newly identified stage Latest Aptian (Clansayesian) Albian. characterized installation elongated lows downthrown side transverse N20 normal faults, active diapirism Triassic evaporites central detachment post-Triassic cover. During Mid-Albian, major surface unconformity, associated uplift, erosion, local centripetal gliding basin borders, marks new organization, rapid mantle ascent end episode. obscured later compression, reconstructed geometry interpreted as “pull-apart” modest motion; (3) late collapse internal zones cooling. erosion coeval Plateau feeds accumulation thick, deep transgressive unconformable formation Black Flysch Mid-Albian Cenomanian age larger coalescing basin. Faulting simple NS distension only last border faults; (4) finally, post-rift illustrated establishment passively subsiding basin, devoid deformations whose heterogeneity previous depocenters erased. transpression, less marked than eastern allowed conservation most these transtensive structures. Within Pernes Col d’Urdach sector, location where Mid-cretaceous proven underwater exhumation, illustrates outcrops have history Trough. Towards east, along Internal Metamorphic Zone, Lourdes-Bagnères, Baronnies, Ballongue, Aulus Saint-Paul de Fenouillet-Boucheville Basins, or those, further north like Camarade Quillan successively examined, testify same sedimentary evolution. As case we deal here again type basins thinned crust, arranged locally transpressive relays separated thicker crust shallower successions. unconformity always present, heralding drowning North Trough cessation extensional activity. deformation, however, constitutes obstacle for precise geodynamic reconstruction, particular Pyrénées. west north-west, South Aquitaine, Parentis Basque-Cantabrian deformation has far events, very comparable observed thus strengthening present