Paleomagnetism of the AND-1B Core, ANDRILL McMurdo Ice Shelf Project, Antarctica

Abstract

Preliminary palaeomagnetic data are presented for the AND-1B drill core. A total of 1309 samples were collected from the drill core immediately following recovery and splitting. Natural remanent magnetisation (NRM) and bulk magnetic susceptibility data were determined for all samples using a Molspin spinner magnetometer and Bartington Instruments susceptibility bridge, respectively, immediately after collection. Polarity was determined for the upper 700 m of the drill core from 615 stepwise alternating field (AF) and thermally demagnetized samples with an average sample spacing of ~80 cm between 32 and 240 mbsf and ~2 m between 240 and 700 mbsf. Stepwise demagnetised samples were measured on 2G Enterprises long-core cryogenic magnetometers at the University of Otago and the Istituto di Geofisica e Vulcanologia. A magnetic polarity zonation was constructed for the interval between 32.33 and 700 mbsf, with roughly equal normal and reversed polarity represented. Above 32.33 mbsf, poorly consolidated diamictite strata prevented sample collection. The remaining record was subdivided into 15 magnetozones (8 normal and 7 reversed). Magnetozone boundaries are defined at the midpoint between samples of opposite polarity or by samples with transitional polarity. It was not possible to isolate characteristic remanence (ChRM) directions on orthogonal component plots and hence polarity for several ~10 m intervals in the core. Future work will include determination of a polarity zonation for the lower 585 m of the drill core and halving data spacing between 240 and 700 mbsf.