(Table 2) Duration of the polarity change process at DSDP Holes 72-515A and 72-517

A study has been made of downhole declination changes of the horizontal component of the natural remanent magnetization 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 technique. 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.本研究针对深海钻探计划（Deep Sea Drilling Project, DSDP）515、517及518站位通过液压活塞取芯器（hydraulic piston corer）获取的未开封完整岩心段的天然剩余磁化强度（natural remanent magnetization）水平分量的井下偏角变化开展了系统分析。研究结果提供了明确证据，证明该初步古地磁技术能够有效识别地磁极性反转界面。本次研究所涉及的第四纪至新近纪晚期沉积物，保留了过去4.5 Ma的磁地层学记录；不过相较于里奥格兰德海隆的生源软泥，巴西海盆的陆源沉积物所对应的该记录质量更为出色。