Scientific Drilling ICDP Publications

Detailed demagnetisation of 51 Pleistocene carbonate samples from hole 1006a, ODP Leg 166, in the Bahamas Bank, yield ''anomalous' paleomagnetic directions over a sediment thickness of 40 cm (328-368 core depth). Samples above and below this horizon are characterised by a steeply directed remanence component at low coercivities, which likely represents a drill-induced component, which is succeeded at higher coercivities by a component with a shallower inclination, close to that of the geomagnetic field at this site. In contrast, the samples from 328-368 core depth, yield negative inclinations after removal of the low coercivity component. These negative inclinations are accompanied by small swings in declination. These ''anomalous' directions are either due to disturbance of the sediment or reflect the presence of geomagnetic field excursion; likely the ''Blake event'. While we cannot completely exclude sediment disturbance, we believe that our paleomagnetic data marks a record of geomagnetic field behaviour for the following reasons: examination of the core yields no evidence for disturbance; relative paleointensity determinations indicate an intensity low through this part of the core; and the excursion is a ''double event', with an intervening positive inclination within the zone of negative inclinations, in line with other studies of the Blake event. We are currently carrying detailed U/Th age determinations on this part of the core with a view to obtaining a estimate of the timing and duration of the event.

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Wölbern, I.; Jacob, B. A.; Blake, T. A.; Kind, R.; Li, X. Q.; Sobolev, S. V.; Duennebier, F.; Priestley, K.; Weber, M. (2002): A detailed receiver function study of the Hawaiian Plume conduit. AGU 2002 Fall Meeting (San Francisco 2002).