Late Albian intrabasinal uplift and denudation recorded by inverted clast stratigraphy (black flyscb of Mutriku, Basque-Cantabrian basin)

Résumé

Clasts of Upper Albian (auritus Subzone) deep-water syntectonic deposits o f the Alkolea sea cliff outcrop (Mutriku, Basque-Cantabrian Basin), have been analysed in terms of size, lithology, sedimentary structures, fossil content, paleontological dating and stratigraphy. These deposits are related with- and fossilize- the SE margin of the Aitzeta structure, an interpreted syncline limb formed in the Late Albian. Similarities between syntectonic clasts and underlying rocks suggest that clasts are fragments derived from underlying units. Moreover, clast succession shows an inverted-clast stratigraphy, which demonstrates erosion and denudation of progressively older rock units. Denudation took place during and as a consequence of uplift and tectonic deformation of the Aitzeta structure, in agreement with structural data. The repeated coincidence of first appearances of new clasts with angular unconformities or disconformities suggests punctuated denudation, related with short-term uplift and deformation pulses. The oldest clast-supplying rocks allow to calculate the total denudation thickness, and therefore the minimum uplift of Aitzeta structure during auritus Subzone (Late Albian), in 350-390 m.