Palaeomagnetism of the AND-2A Core, ANDRILL Southern McMurdo Sound Project, Antarctica

• Main Authors: Acton, G., Florindo, F., Jovane, L., Lum, B., Ohneiser, C., Sagnotti, L., Strada, E., Verosub, K. L., Wilson, G. S., ANDRILL-SMS Science Team
• Format: Text
• Language: unknown
• Published: DigitalCommons@University of Nebraska - Lincoln 2008
• Subjects: Environmental Indicators and Impact Assessment; McMurdo Sound; Antarc*; Antarctica
• Online Access: https://digitalcommons.unl.edu/andrillrespub/5; https://digitalcommons.unl.edu/context/andrillrespub/article/1004/viewcontent/Acton_TA_2008_Palaeomagnetism_AND_2A.pdf

We conducted initial palaeomagnetic studies on cores from site AND-2A (77°45.488’S, 165°16.605’E, ~383.57 metres water depth). A total of 813 samples were collected that span from the top of the section down to the base at 1138.54 metres below sea floor (mbsf). Samples were collected every one or two metres down the core, with paired (pilot) samples being collected about every ten to twenty metres to allow us to assess the demagnetisation behaviour of the samples using either alternating field (AF) or thermal demagnetisation. With the exception of only a few intervals, AF demagnetisation was observed to resolve a characteristic remanent magnetisation (ChRM) as well or better than thermal demagnetisation. Thermal demagnetisation was particularly ineffective in many intervals owing to thermal alteration that was common above 500°C and was evident in some samples even at low temperatures. Above Lithostratigraphic Unit (LSU) 8 (436.18 mbsf), where lithologies are generally more coarse grained than lower in the section, resolving a ChRM is difficult and recent overprints or a drilling overprint are a concern. Within LSU 8 and below, most samples have a ChRM that can be resolved. The ChRM is most likely an original depositional magnetisation throughout most of this lower section, although orthogonaldemagnetisation diagrams contain evidence that normal polarity overprinting affects some intervals. Based on 40Ar/39Ar dates and diatom datums, the magnetozones identified from the base of the hole up to ~266mbsf are consistent with spanning from either Chron C6n (18.748-19.772 Ma) or C6An.1n (20.040-20.213 Ma) up through Chron C5Br (15.160-15.974 Ma). Above this, intervals of constant polarity are isolated within longer stratigraphic intervals of uncertain polarity, making their correlation with the geomagnetic polarity timescale (GPTS) speculative and highly dependent on ages obtained from other dating methods. One exception is a reversed-to-normal polarity transition that occurs at ~31 mbsf and is interpreted to most ...