26. WHOLE-CORE SPINNING AND DETECTION OF REVERSAL BOUNDARIES IN HYDRAULIC PISTON CORES FROM THE SOUTHWESTERN ATLANTIC: LEG 721

A study has been made of downhole declination changes of the horizontal component of the natural remanent mag-netization of unopened whole-core sections recovered by use of the hydraulic piston corer at DSDP Sites 515,517, and 518. There is clear evidence that polarity reversal boundaries can be detected by this preliminary paleomagnetic tech-nique. The Quaternary through late Neogene sediments studied reveal a record of the magnetostratigraphy over the past 4.5 Ma, although the quality of this record is better defined by the terrigenous sediments of the Brazil Basin than the biogenous oozes of the Rio Grande Rise