New magnetostratigraphic dating of the Palaeogene syntectonic sediments of the west-central Pyrenees: Tectonostratigraphic implications

Abstract

New magnetostratigraphic results from a 3300 m-thick section across the syntectonicfluvial sediments of the Campodarbe Formation (Upper Eocene-Oligocene) in the Ebro forelandbasin (NE Spain) are presented. The new data allow the top of the Campodarbe Formation tobe correlated to Chron 7r (Chattian), younger than previously stated (C10r), therefore shiftingthe age of significant palaeogeographical changes in the foreland basin. The deformation in thesouthern front produces the cannibalization in the piggyback basin of 1300 m of sediments spanningc. 3.7 Myr. Average accumulation rates are lower in the Ebro foreland basin than in the piggybackbasin and decrease from 35 to 27 cm kyr by the time the San Felices thrust sheet activitydecelerates (at c. 28 Myr). Shifts of accumulation rates result from accommodation space changes,which occur locally and are linked to the activity of the San Felices thrust, while the sedimentsupply occurs at orogenic scale (source of sediments is c. 200 km to the NE). Finally, sequenceboundaries previously considered isochronous in the continental record of the Cenozoic Pyreneanbasins are revealed to be 1.8-1 Myr older in the piggyback basin than in the Ebro foreland basin.