Magnetostratigraphy of an Upper Cretaceous section from James Ross Basin, Antarctica

MILANESE, FLORENCIA N.; KIRSCHVINK, JOSEPH L.; OLIVERO, EDUARDO B.; RAPALINI, AUGUSTO E.

Buenos Aires

Workshop; XIV Giambiagi Winter School; 2012

Preliminary results of a paleomagnetic, rock magnetic and magnetofabric study on samples from three sections of Late Cretaceous age exposed in the James Ross and Snow Hill islands (Antarctica) are presented. These sections are: a) Hn (Campanian), located in Hamilton point (S 64º19’2’’; W 57º23’12’’) which comprises 200 m of the upper part of the Rabot Formation (members II y III) and the lower section of the Snow Hill Island Formation; b) Re, located at Redonda point (S 64º 22´ 13´´; W 57º 26´ 45´´) only comprising members II and III of the Rabot Formation, with a thickness of 324 m; and c) Sh (Mastrichtian), located stratigraphically on top of the previous sections in Snow Hill Island (S 64°21’46’’; W 56°59’15’’) and including the Karlsen Cliffs Member of Snow Hill Island Formation and Haslum Crag and López de Bertodano formations. Anisotropy of magnetic susceptibility studies were carried out in all collected samples. The magnetic fabric parameters obtained from these rocks indicate a likely depositional origin (characterized by low anisotropy degrees, oblate ellipsoids and vertical K3 axes). Thermomagnetic curves (k vs T) indicate that magnetic susceptibility is mainly controlled by paramagnetic minerals. From information obtained from hysteresis loops and Lowrie-Fuller tests it is proposed that PSD (Ti poor?) titano-magnetite is the most common remanence carrier. Only a few samples presented stable behaviour during thermal demagnetization. However they allow us to infer a preliminary local magnetostratigraphic column. Polarity intervals likely corresponding to chrons C33N, C32R?, C32N? and C32R? or C31R? have been identified suggesting deposition late Campanian-early Maastrichtian.