Evaluation of geomagnetic relative palaeointensity as a chronostratigraphic tool in the Southern Ocean: Refined Plio-/Pleistocene chronology of IODP Site U1533 (Amundsen Sea, West Antarctica)
Evaluation of geomagnetic relative palaeointensity as a chronostratigraphic tool in the Southern Ocean: Refined Plio-/Pleistocene chronology of IODP Site U1533 (Amundsen Sea, West Antarctica)
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DOI：
10.1016/j.quascirev.2023.108460
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发表时间：
2024-02
影响因子：
4
通讯作者：
Becky Hopkins;Chuang Xuan;C. Hillenbrand;T. V. van Peer;Yuxi Jin;T. Frederichs;Liang Gao;S. Bohaty
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作者：
Becky Hopkins;Chuang Xuan;C. Hillenbrand;T. V. van Peer;Yuxi Jin;T. Frederichs;Liang Gao;S. Bohaty
国际海洋发现计划（IODP）第379次南极洲西部阿蒙森海边缘考察队在两个地点恢复了跨越最新中新世-全新世间隔的岩心，目的是重建过去的南极洲西部冰盖动态。恢复的Plio-/更新世沉积物序列提供了一个机会，在南极深海漂移环境中应用和测试不同的测年方法，其中记录几乎是连续的，不受冰山或接地冰冲刷的影响。本文通过对连续u通道样品的古地磁分析和X射线荧光扫描的应用，对IODP Exp. 379 Site U1533上新世和更新世复合层段最上部的年龄模型（0.0-2.9 Ma）。我们首先用高分辨率的u通道分析和解释的方向数据来完善磁性地层年龄模型。与船上的结果一致，所有主要的地磁极性时和亚时被确定在更新世部分。新的高分辨率u通道数据集还使我们能够确定一个地磁极性漂移在10884 ka（解释为Kamikatanya漂移）和另一个漂移在102734 ka的信心（可能的豪猪漂移）。基于改进的极性地层学，我们然后开发了两个新的高分辨率的年龄模型的站点U1533使用：（i）钡富集周期中确定的XRF扫描数据，（ii）地磁相对古强度（RPI）。在我们的第一个年龄模型中，我们将沉积钡富集的周期变化（推断代表输出生产力的变化）与Lisiecki和Raymo（2005年）底栖有孔虫氧同位素（δ 18 O）叠加（LR 04）的冰期-间冰期周期相关联。几乎所有的更新世海洋同位素阶段（MIS）被解释为存在于站点U1533的钡富集记录，假设同时变化的南极海冰范围/当地出口生产力和全球氧同位素地层。然后，我们构建了第二个独立的年龄模型，使用Plio-/更新世RPI记录开发的站点U1533，这是最长的（几乎）连续的RPI记录目前可用于南极边缘。两个独立得出的年龄模型的比较显示了一个可变的偏移量，平均为± 12 kyr，在1.9 ~ 2.9 Ma的区间内，基于RPI的年龄始终大于基于钡的年龄，然后在0.0 ~ 1.9 Ma的区间内始终小于基于钡的年龄。我们解释这些偏移是由于在较年轻的间隔锁定深度效应的组合（由于在这个网站相对较低的沉积速率，2.2 cm/kyr），全球δ 18 O的变化之间的时间偏移在深海和南极边缘的生产力响应，和/或系统的不相关性在两个年龄模型的建设。最后，我们构建了一个混合年龄模型的更新世部分的站点U1533相结合的混合物的RPI和钡基年龄连接点，被认为是强大的。然后，使用站点U1533 RPI记录，与其他南大洋RPI记录一起，构建0.0-1.6 Ma间隔的南极RPI叠加（指定为“ANT-1600”）。尽管在为堆选择的三分之二的地点处的沉积速率低于10 cm/kyr，但新的ANT-1600堆与SINT-2000 RPI堆具有很强的一致性（Valet等人，2005年）的时间尺度为20-200 kyr，允许其作为一个区域RPI参考曲线在未来的研究中使用。总体而言，我们证明，RPI在南极边缘/南大洋网站提供了一个可行的和有价值的独立的定年方法，适用于上新世/更新世...
International Ocean Discovery Program (IODP) Expedition 379 to the Amundsen Sea margin of West Antarctica recovered drill cores at two sites spanning the Latest Miocene–Holocene interval with the aim of reconstructing past West Antarctic Ice Sheet dynamics. The recovered Plio-/Pleistocene sediment sequences offer an opportunity to apply and test different dating approaches in an Antarctic deep-sea drift setting, where the records are nearly continuous and unaffected by scouring of icebergs or grounded ice. Here, through palaeomagnetic analysis of continuous u-channel samples and application of X-ray fluorescence (XRF) scanning, we revise the IODP Exp. 379 Site U1533 age model for the uppermost Pliocene and Pleistocene composite interval (0.0–2.9 Ma). We first refine the magnetostratigraphic age model with high-resolution u-channel analysis and interpreted directional data. Consistent with shipboard results, all major geomagnetic polarity chrons and subchrons are identified in the Pleistocene section. The new high-resolution u-channel dataset also allows us to identify a geomagnetic polarity excursion at ∼884 ka (interpreted as the Kamikatsura excursion) and another excursion at ∼2734 ka with confidence (potentially the Porcupine excursion). Based on the improved polarity stratigraphy, we then develop two new highly resolved age models for Site U1533 using: (i) barium enrichment cycles identified in XRF scanning data, and (ii) geomagnetic relative palaeointensity (RPI). In our first age model, we correlate cyclic variations in sedimentary barium enrichment, inferred to represent changes in export productivity, to glacial‒interglacial cycles of the Lisiecki and Raymo (2005) benthic foraminiferal oxygen isotope (δ18O) stack (LR04). Nearly all Pleistocene Marine Isotope Stages (MIS) are interpreted to be present in the barium enrichment record of Site U1533, assuming simultaneous changes in Antarctic sea-ice extent/local export productivity and global oxygen isotope stratigraphy. We then construct the second, independent age model using the Plio-/Pleistocene RPI record developed for Site U1533, which represents the longest (nearly) continuous RPI record currently available for the Antarctic margin. Comparison of the two, independently derived age models shows a variable offset, on average ± 12 kyr, with the RPI-based ages consistently older than the barium-based ages in the interval from 1.9 to 2.9 Ma and then consistently younger from 0.0 to 1.9 Ma. We interpret these offsets to result from a combination of lock-in depth effects in the younger interval (due to the relatively low sedimentation rates at this site, ∼2 cm/kyr), temporal offsets between global δ18O changes in the deep ocean and productivity response on the Antarctic margin, and/or systematic miscorrelation in the construction of the two age models. Finally, we construct a hybrid age model for the Pleistocene section of Site U1533 by combining a mixture of RPI- and barium-based age tie points that are deemed to be robust. The Site U1533 RPI record is then used, together with other Southern Ocean RPI records, to construct an Antarctic RPI stack (designated as ‘ANT-1600’) for the interval 0.0–1.6 Ma. Although sedimentation rates at two-thirds of the sites selected for the stack are lower than 10 cm/kyr, the new ANT-1600 stack is strongly coherent with the SINT-2000 RPI stack (Valet et al., 2005) on time scales of ∼20–200 kyr, allowing for its use as a regional RPI reference curve in future studies. Overall, we demonstrate that RPI at Antarctic margin/Southern Ocean sites provides a viable and valuable independent dating method for application to Plio-/Pleistocene …