Stratigraphy and age of the Lower Cretaceous Pedersen Formation, northern Antarctic Peninsula

The Pedersen Formation includes conglomerate-dominated successions exposed on Pedersen Nunatak (142 m thick) and southern Sobral Peninsula (750-1000 m thick). As re-defined here, it also includes mudstone and sandstone in tec tonic contact with Nordenskjold Formation strata on a nunatak north of the Sobral Peninsula conglomerate outcrops. Ar-40/Ar-39 ages and palynological data indicate an early Aptian age for the lower part of the formation on So bral Peninsula. The Pedersen Nunatak strata have yielded conflicting age de terminations, although an Early Cretaceous age seems likely. The Sobral Pen insula conglomerates are lithologically similar to, and possibly coeval wit h, basal Gustav Group strata (Lagrelius Point Formation) on James Ross Isla nd. Although further field sampling is required to resolve the age of the P edersen Nunatak strata, on present evidence the Pedersen Formation appears to form part of the same tectono-stratigraphic unit as the lower part of th e Gustav Group, and we therefore propose that it be included in that group.