The Upper Eocene South Pyrenean Coastal deposits (Liedena sandstone, navarre): Sedimentary facies, benthic formanifera and avian ichnology

Summary During the 1960's and the 1970's the Liedena Sandstone was a type deposit for “flysch-like facies” (sandstone and lutite alternations) of coastal sedimentary systems. However, the depositional system of these beds was never accurately defined. The sedimentological analysis along 100 km of outcrops in the western part of the South Pyrenean Zone (Navarre) allows these peculiar facies to be assigned to a mixed intertidal flat. Furthermore, sandy beach facies, different types of heterolithic, backbarrier deposits and conglomeratic, fluviatile facies have been recognized associated with these intriguing deposits. Generally, a northwestward-facing barrier-island system or wave-dominated delta was the likely depositional environment. The benthic foraminiferal assemblage in the intertidal deposits exhibits the typical characteristics of a marginal marine environment: extremely high dominance of one species (Pararotalia inermis), low species diversity, and a hyaline dominance with discrete amounts of miliolids. Furthermore, the most abundant species indicates that the Liedena Sandstone was deposited during the Late Eocene. Abundant footprints of aquatic birds are known in the tidal flat deposits. Six morphotypes have been distinguished: two (types 1 and 2) are ciconiforme-like; type 1 is here assigned to a new ichnotaxon,Leptoptilostipus pyrenaicus and is one of the oldest occurrences of Ciconiiforme-like ischmites in the fossil record. Two other morphotypes (5 and 6) are similar to those of the Charadriiformes and are refeered to asCharadriipeda. Finally, the affinities of the two remainder morphotypes (3 and 4) are unclear, they could have been made by Charadriiformes. Synsedimentary tectonic activity controlled the evolution of the depositional system, as the area of deposition of the Liedena Sandstone was progressively incorporated into the active thrust sheets of the Pyrenean Orogen during the Late Eocene. The structural uplift and the large amount of sediments derived from the adjacent highlands induced progradation of the depositional system and the definitive retreat of the sea from the South Pyrenean Zone.