Magnetostratigraphy of Oligocene - Miocene Glaciomarine Strata from CRP-2/2A, Victoria Land Basin, Antarctica

We have used palaeomagnetic methods to constrain an age model for the 624.15 m succession of Oligocene-Miocene glaciomarine sediments recovered from the CRP-2/2A drillcore, McMurdo Sound, Antarctica. Identification of characteristic remanent magnetization (ChRM) directions on vector component plots demonstrates that secondary overprints have been successfully removed by stepwise alternating field demagnetization. Antipodal normal and reversed polarity inclination data and a conglomerate test within an intraformational breccia suggest that the ChRM directions are primary. Above 306.65 metres below sea floor (mbsf), a relatively low coercivity mineral dominates the magnetization. Below 306.65 mbsf, a high coercivity magnetic carrier is also observed in low intensity zones. The CRP-2/2A magnetic polarity zonation is subdivided into three intervals: (1) an upper 185.96-m-thick interval of alternating normal and reversed polarity (magnetozones N1-R5), (2) a thick interval of normal polarity between 185.96 and 441.22 mbsf (magnetozone N6), and (3) a lower 183.93-m-thick interval of alternating normal, reversed and indeterminate polarity as well as zones with shallow inclinations (magnetozones N7-?R12). Between 26 and 306.65 mbsf, the CRP-2/2A drillcore is uppermost Oligocene lower Miocene in age with high average sediment accumulation rates (~1000 m/m.y.). Correlation with the magnetic polarity time scale (MPTS) is mostly straightforward and is constrained by biostratigraphic datums, and by Ar/Ar and Sr/Sr ages. An angular unconformity is identified at 306.65 mbsf and marks a major hiatus of up to 5 m.y. in duration. Below 306.65 mbsf, the CRP-2/2A drillcore is early Oligocene in age. The magnetic polarity record comprises numerous polarity zones, some of which may represent late Oligocene cryptochrons or geomagnetic excursions and definitive correlation with the MPTS is not possible with the existing data. While multiple hiatuses make it difficult to correlate the CRP-2/2A magnetic polarity record with the MPTS, the resulting age model demonstrates that more time is missing in the numerous sequence-bounding unconformities than is preserved in the CRP-2/2A drillcore.