BACKGROUND

Drilling-induced magnetic overprints are ubiquitous in Ocean Drilling Program (ODP) paleomagnetism and have been known to exist since the program began. In some cases, these are easily dealt with. In other cases, magnetic overprints may completely compromise the paleomagnetic objectives of a leg (e.g., see Leg 154; Curry, Shackleton, Richter, et al., 1995). How to deal with this problem has been a matter of discussion within the JOIDES advisory structure for a decade or more, and at various times recommendations have been made to explore the use of nonmagnetic drilling tools. Preliminary tests of the benefits of using such expensive tools have been, until now, inconclusive, and as a result the use of nonmagnetic core barrels is still not a standard feature aboard the JOIDES Resolution. Here we discuss observations and experiments made during Leg 202 that shed new light on the use of a nonmagnetic core barrel and other equipment (i.e., the advance piston corer temperature [APCT] tool) to reduce the effects of drilling-induced magnetic overprints on paleomagnetic objectives.

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