Retro-wedge foreland basin evolution along the ECORS line, eastern Pyrenees, France

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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 andsteady-state phases cannot be distinguished. We show that the eastern Pyrenees record two clear phases of convergence andprobably 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 thermochronologydata, new interpretations of seismic lines and a balanced cross-section. Within an overall regression, twoshallowing-up cycles (Latest Santonian–Danian, Thanetian–Oligocene) record slow tectonic subsidence of the easternAquitaine 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 youngPyrenean orogeny to the south remained submerged. During the quiet period of ultra-slow subsidence, no basin migration andnegligible sediment supply, continental conditions characterized the eastern orogen. The second marine transgression wasquickly followed by continental conditions. The basin was supplied by the now emerging Pyrenean orogen and continued tosubside until Miocene time.