Magnetostratigraphy of ODP Leg 207 sediments@en

Ocean Drilling Program (ODP) Sites 1257-1261 recovered thick sections of Upper Cretaceous-Eocene oceanic sediments on Demerara Rise off the east coast of Surinam and French Guiana, South America. Paleomagnetic and rock magnetic measurements of ~800 minicores established a high-resolution composite magnetostratigraphy spanning most of the Maastrichtian-Eocene. Magnetic behavior during demagnetization varied among lithologies, but thermal demagnetization steps >200°C were generally successful in removing present-day normal polarity overprints and a downward overprint induced during the ODP coring process. Characteristic remanent magnetizations and associated polarity interpretations were generally assigned to directions observed at 200°-400°C, and the associated polarity interpretations were partially based on whether the characteristic direction was aligned or apparently opposite to the low-temperature \"north-directed\" overprint. Biostratigraphy and polarity patterns constrained assignment of polarity chrons. The composite sections have a complete polarity record of Chrons C18n (middle Eocene)-C34n (Late Cretaceous).大洋钻探计划（Ocean Drilling Program, ODP）1257至1261站位在南美洲苏里南与法属圭亚那东部沿海的德梅拉拉海隆（Demerara Rise）钻获了晚白垩世-始新世厚层远洋沉积岩芯。研究团队对约800块微型岩芯开展古地磁与岩石磁学测试，构建了覆盖马斯特里赫特期至始新世多数时段的高分辨率综合磁地层序列。不同岩性的退磁磁学行为存在差异，但当热退磁温度高于200℃时，通常可有效移除现今正常极性叠加剩磁，以及大洋钻探计划取芯过程中诱导产生的向下方向叠加剩磁。特征剩磁（Characteristic Remanent Magnetization, ChRM）及其对应的极性解译结果，通常对应200℃至400℃温度区间观测到的磁方向；而极性解译的部分依据为特征磁方向是否与低温“北向”叠加剩磁方向一致或呈明显反向。生物地层学与极性模式对极性时的划分起到了约束作用。该综合沉积序列完整记录了从C18n极性时（始新世中期）至C34n极性时（晚白垩世）的地磁极性序列。