Magnetostratigraphy of Late Eocene - Early Oligocene Strata from the CRP-3 Core, Victoria Land Basin, Antarctica

The Cape Roberts Project was successfully completed in the austral spring of 1999 with drilling of the 939.42-m CRP-3 drillhole, located 2-km west of the CRP-2/2A drillhole. The CRP-3 core comprises a 790-m Cenozoic (glacio-) marine sequence separated from underlying Devonian basement rocks by a c. 30-mthick dolerite conglomerate of undetermined age. Here, we present the results of a palaeomagnetic study, including correlation to the magnetic polarity time scale (MPTS) and an age model for the Cenozoic sequence recovered in CRP-3. The palaeomagnetic behaviour of the Cenozoic sedimentary sequence is generally stable, and magnetite is the main magnetic carrier. The magnetic polarity stratigraphy of the Cenozoic sequence in the CRP-3 core is subdivided into four magnetozones: R1 is an upper interval of dominantly reversed polarity (0-340.8 mbsf), N1 has dominantly normal polarity (340.8-627.3 mbsf), R2 has dominantly reversed polarity (627.3-760.2 mbsf), and N2 has normal polarity (760.2-788.8 mbsf). Magnetozones R1, N1, and R2 also contain thin intervals with opposite polarity, which are interpreted as representing either short polarity intervals (corresponding to “tiny wiggles” identified on marine magnetic anomaly records) or geomagnetic excursions. Above 340 mbsf, diatom and calcareous nannofossil biostratigraphy and 87Sr/86Sr ages suggest that magnetozone R1 correlates with Chron C12r of the MPTS. Below 340 mbsf, we tentatively correlate magnetozones N1 and R2 with chrons C13n and C13r of the MPTS, respectively. However, below R1, the magnetic polarity record is not constrained by biostratigraphy or 87Sr/86Sr ages. Our correlation implies that the Eocene-Oligocene boundary (33.7 Ma) in the CRP-3 core should lie within lithostratigraphic sub-Unit 13.1, at about 718 mbsf. Lack of independent chronostratigraphic constraints makes it difficult to interpret the age of the basal part of the CRP-3 Cenozoic sequence, but the magnetostratigraphy suggests a minimum age of Chron C13r (c. 34 Ma).