(Table 1) Magnetozone boundaries at DSDP Site 68-502

Obtaining long, continuous, and undisturbed sections of unconsolidated Neogene deep sea sedimentary sections has been limited by (1) practical length of piston cores to about 30 meters and (2) disturbance of sediment by rotary drilling with Glomar Challenger. The relatively high deposition rates of late Neogene sediments in the North Atlantic and in the Caribbean in particular has limited penetration, with conventional piston coring, to sediments not much older than late Pliocene in the Atlantic and not even through the late Pleistocene in the Caribbean. Rotary drilling has penetrated much older sediments in both areas, but the cores suffered extensive drilling disturbance that seriously degrades the Paleomagnetism of the material. Utilization of the hydraulic piston corer on the Challenger combines the advantage of a generally undisturbed recovery and great penetration to produce long, relatively undisturbed sections of late Neogene and Quaternary sediments suitable for paleomagnetic studies. In this chapter we present paleomagnetic data from Site 502.
We tried to determine relative azimuthal orientation of successive cores (see Introduction for details). Because the low latitude of the site meant a small (inclination of about 22°) vertical component of magnetization, reversals of magnetization could easily be detected only in changes in the horizontal component, as 180° shifts in the declination direction of magnetization. Based on information from the core orienting device, a fiducial line was drawn the length of each core prior to cutting it into the standard 1.5 meter sections.

获取长期连续且未受扰动的松散新近纪深海沉积剖面，长期以来受限于两大制约因素：(1)活塞取心（piston cores）的实际作业长度仅约30米；(2)格洛玛·挑战者号（Glomar Challenger）使用的旋转钻探会对沉积物造成扰动。
北大西洋与加勒比海区域的晚新近纪沉积物沉积速率相对偏高，这使得常规活塞取心的穿透深度受限：大西洋区域仅能获取年代不晚于上新世晚期的沉积物，加勒比海区域甚至无法穿透更新世晚期地层。旋转钻探虽可在两处区域穿透年代更为古老的沉积物，但取心样本会遭受严重的钻探扰动，极大破坏了样品的古地磁特性。
“挑战者号”钻探船搭载的液压活塞取心装置（hydraulic piston corer），兼具近乎无扰动的岩心回收率与超大穿透深度的优势，可获取长距离、相对未受扰动的晚新近纪及第四纪沉积物剖面，适用于古地磁研究。本章我们将展示502号钻探站位（Site 502）的古地磁数据。
我们尝试测定连续取心的相对方位取向（详细说明参见引言部分）。由于该站位纬度较低，磁化强度的垂直分量较小（倾角约22°），因此仅能通过水平分量的变化——即磁化偏角方向的180°偏移——轻松识别地磁反转。基于岩心定向装置（core orienting device）采集的信息，我们在将每根岩心切割为标准1.5米分段前，已沿岩心全长绘制了基准参考线。