Absolute ages of marine sedimentary strata from James Ross Basin

A magnetostratigraphic study was carried out in the SE sector of the James Ross Basin (Antarctica). The magnetostratigraphy was obtained along five cross-sections, three of them located in the SE sector of James Ross Island and two in Snow Hill Island. They belong to the upper part of the deep marine sedimentary succession that constitutes the Marambio Group (Upper Cretaceous). Ammonite assemblages give the main chronological reference framework. Even though the fossil content is abundant, endemism and diachronic extinctions are the main problems in the definition of a precise age framework and global correlations for the Upper Cretaceous units. In this scenario, the magnetostratigraphy provides the required chronological resolution for the global correlation problems of James Ross Basin, identifying seven geomagnetic polarity reversals and obtaining an absolute age constraint for the whole succession between 74.309 Ma (Middle Campanian) to 71.449 Ma (Early Maastrichtian). Keywords: Magnetostratigraphy, Upper Cretaceous, Antarctica.