Fossiliferous Dimictons (Miocene-Pleistocene): Belén, Gage and Terrapin Formations on the James Ross Island, Antarctica

Abstract

Late Cenozoic fossiliferous diamicts, cropping out on the eastern part of James Ross Island (north-east Antarctic Peninsula) comprise three new lithostratigraphic units. The Belén and Terrapin formations crop out on the south and west coast of Belén Fjord (Lat. 64° 00´ S Long. 57° 31´ W), respectively, and the Gage Formation is exposed on the south coast of Cape Gage (Lat. 64° 12´ S, Long. 57° 06´ W). Shells of pectinids from the Belén and Terrapin formations were dated using ⁸⁷Sr/⁸⁶Sr isotopes, yielding a Late Miocene age (6.8 ± 0.5 Ma) and a Late Pliocene-Early Pleistocene age (1.95 +1.12/-0.52 Ma), respectively. The Gage Formation is thought to be Late Pliocene in age, younger than 3.1 ± 0.3 My on the basis of ⁴⁰Ar/³⁹Ar dating performed on a basalt clast included in the sediments and no older than 2.4 Ma based on the presence of Zygochlamys anderssoni. The micropaleontological content of these formations is compared with those of other cenozoic fossiliferous deposits from the James Ross Basin, and the importance of the paleoenvironmental evidence obtained from this correlation is discussed in relation to the present knowledge of Late Miocene - Pleistocene lithostratigraphy and climate evolution of Antarctica. Diamicts of the Belén and Terrapin formations and alkaline volcanic rocks of the James Ross Island Volcanic Group (JRIVG) are interbedded on the coast of Belén Fjord, where the oldest known volcanic rocks of the JRIVG are dated at 9.2 ± 0.3 Ma (⁴⁰Ar/³⁹Ar). This age confirms a Late Miocene initiation of volcanic activities on James Ross Island and the importance of the Belén Fjord area for further studies of the early stages of Late Cenozoic tectonic and magmatic evolution of the Larsen Basin.