The Cotiella thrust sheet in the South Central 20 Pyrenees is a well-studied example of an extensional basin which formed at the northern Iberian rift margin during the Late Cretaceous, and was inverted in the Late Cretaceous and Cenozoic on top of the South Pyrenean Central Unit. A paleomagnetic study of the thick sequence of shallow marine syn-extensional carbonates filling the Cotiella basin reveals the presence of a widespread secondary magnetisation of both normal and reversed polarities. Neither in situ nor bedding tilt correction provides a satisfactory grouping of the paleomagnetic directions, thus suggesting syn-deformational magnetisation. Best clustering of paleomagnetic vectors is obtained after unfolding into a post-extensional pre compressional stage, coherent with an acquisition age between Santonian and Paleocene. Strong magnetic enhancement and very distinct magnetic properties with depth suggests a link with burial diagenesis of organic matter, precipitation of iron sulfides and subsequent oxidation to SD fine-grained magnetite. The secondary magnetisations of the Cotiella record significant vertical axis rotations ranging from 14º to 52º clockwise, coherent with the scenario of the Cotiella thrust sheet transported piggy-back and bent during the emplacement of the lower Gavarnie-Sierras Exteriores thrust sheet.