The reflection seismic profiles of the southwest Valencia trough show that the Neogene Valencia trough extensional basin is superim posed over a NE-SW oriented syncline. This syncline, Paleogene in age, is made up by more than 8 km of Mesozoic and probably Palaeocene sediments and denotes the presence of a thick Mesozoic basin. Folded and strongly eroded during the late Paleogene, this so-called Columbrets basin is interpreted to extend along the whole Valencia trough and, according to oil data, it developed during the major Upper Jurassic-Lower Cretaceous rifting event that affected the eastern part of Iberia