Retro-wedge foreland basin evolution along the ECORS line, eastern Pyrenees, France
Résumé
The eastern Aquitaine basin and North Pyrenean Zone show many characteristics of retro-wedge models. However,
they differ significantly in that slow subsidence and low deformation continued throughout orogenesis so that growth and
steady-state phases cannot be distinguished. We show that the eastern Pyrenees record two clear phases of convergence and
probably never attained steady state. Analysis of the Aquitaine retro-foreland basin along the Ariège ECORS deep seismic line,
eastern French Pyrenees, integrates a new litho- and chronostratigraphy, subsidence analysis, low-temperature thermochronology
data, new interpretations of seismic lines and a balanced cross-section. Within an overall regression, two
shallowing-up cycles (Latest Santonian–Danian, Thanetian–Oligocene) record slow tectonic subsidence of the eastern
Aquitaine basin separated by a quiet period. Continuing thick-skinned shortening was low to moderate. The early marine basin,
generated by loading of the weak, extended margin, was supplied axially from an unknown eastern edifice while the young
Pyrenean orogeny to the south remained submerged. During the quiet period of ultra-slow subsidence, no basin migration and
negligible sediment supply, continental conditions characterized the eastern orogen. The second marine transgression was
quickly followed by continental conditions. The basin was supplied by the now emerging Pyrenean orogen and continued to
subside until Miocene time.