Magnetostratigraphy of DSDP Leg 73 in the South Atlantic

The main objective of DSDP Leg 73 was to obtain high-quality records of major paleooceanographic events in the South Atlantic. This was achieved by coring six sites on the African plate. The sediments thus recovered span the Cenozoic and five of the six sites proved ideally suited for magnetostratigraphic analysis. The results presented in this paper and elsewhere in this volume constitute the first opportunity to extend the direct correlation of the magnetostratigraphic and biostratigraphic time-scales into the Paleogene in deep-sea cores. The magnetostratigraphic analyses from DSDP Leg 73 sediments are presented in this paper. The correlation of the magnetostratigraphy to the magnetic polarity time-scale provides tight age-depth control for the five sites analyzed, allowing the accurate calculation of sediment accumulation rates. The data presented here represent a remarkable record of the fine-scale polarity history of the Earth's magnetic field. These data place constraints on the interpretation of smallscale marine magnetic anomalies which are modelled equally effectively by field intensity fluctuations as polarity reversals. At least some of the "tiny wiggles" correspond to very short polarity units in the magnetostratigraphic record. By assuming an axial geocentric dipole, the inclination of the time-averaged magnetic field recorded in the sediments can be used to calculate the paleolatitude at which the sediments were deposited. Combining the age and average inclination information available from the magnetostratigraphy, we present paleolatitudes versus time for the Leg 73 drill sites.深海钻探计划（Deep Sea Drilling Project, DSDP）第73航次的核心目标为获取南大西洋重大古海洋学事件的高质量记录。本航次通过在非洲板块上的6个站位开展岩芯取芯作业达成该目标。此次回收的沉积物沉积年代跨越新生代，且其中5个站位极为适配磁地层学（magnetostratigraphy）分析。本文及本卷其他章节所呈现的研究结果，首次实现了将磁地层学与生物地层学（biostratigraphy）年代标尺的直接对比延伸至深海岩芯的古近纪地层中。 本文呈现了基于DSDP第73航次沉积物的磁地层学分析成果。将磁地层序列与磁极性年代标尺进行对比后，可为本次分析的5个站位提供精准的年龄-深度约束，从而实现沉积速率（sediment accumulation rates）的精确计算。 本次公开的数据堪称地球磁场精细尺度极性演化历史的珍贵记录。这些数据为小型海洋磁异常的解译提供了约束——这类异常既可以通过磁场强度波动建模，也可通过极性倒转实现有效拟合。至少部分「微小波动」对应磁地层记录中极短的极性单元。 假设地球磁场为地心轴向偶极子（axial geocentric dipole），则可通过沉积物记录的时间平均磁场倾角，计算沉积物沉积时的古纬度（paleolatitude）。结合磁地层学分析得到的年龄与平均倾角信息，本文给出了第73航次各钻探站位的古纬度随时间的变化关系。