Palaeomagnetism of late Cenozoic fossiliferous sediments from Barranca de los Lobos (Buenos Aires Province, Argentina). The magnetic age of the South American land-mammal ages

Abstract

Palaeomagnetic data for a sequence of late Cenozoic sediments exposed at Bajada Martinez de Hoz and El Muelle (Barranca de los Lobos, Atlantic coastal area; Buenos Aires Province) are reported. The sequence comprises sediments assigned to the Chapadmalal Formation (Montehermosense land-mammal age), Barranca de los Lobos, Vorohué and San Andrés Formations (Uquiense land-mammal age), Miramar Formation (Ensenadense land-mammal age), and Arroyo Seco and Arroyo Loberia Formations (Lujanense land-mammal age). The magnetostratigraphy recorded in the sequence suggests a Brunhes magnetic age (< 0.73 Ma) for the Arroyo Loberia and upper section of Arroyo Seco Formations; a late Matuyama magnetic age (1.67-0.73 Ma) for the lower section of the Arroyo Seco Formation; a Matuyama magnetic age (sensu lato 2.48-0.73 Ma) for the Miramar Formation; a Gauss magnetic age (sensu lato 3.40-2.48 Ma) for the San Andrés, Vorohué and Barranca de los Lobos formations; and an early Gauss to Gilbert magnetic age (> 3.15 Ma) for the Chapadmalal Formation. It also suggests a Brunhes to late Matuyama magnetic age for the Lujanense land-mammal age; a Matuyama magnetic age for the Ensenadense land-mammal age; a Gauss magnetic age for the Uquiense land-mammal age; and an early Gauss to Gilbert magnetic age for the Montehermosense land-mammal age. Finally, the results obtained suggest that the Panama Isthmus was formed at an age earlier than 3.0 Ma, possibly 4.0–3.5 Ma ago.