High resolution inclination records from the Gulf of Alaska, IODP Expedition 341 Sites U1418 and U1419
High resolution inclination records from the Gulf of Alaska, IODP Expedition 341 Sites U1418 and U1419
复制标题
阿拉斯加湾 IODP 探险队 341 站点 U1418 和 U1419 的高分辨率倾角记录
DOI：
10.1093/gji/ggab479
复制
发表时间：
2021
影响因子：
2.8
通讯作者：
Forwick, Matthias
中科院分区：
文献类型：
--
作者：
Velle, Julie Heggdal;Walczak, Maureen H.;Reilly, Brendan;St-Onge, Guillaume;Stoner, Joseph S.;Fallon, Stewart;Mix, Alan C.;Belanger, Christina;Forwick, Matthias
国际海洋钻探计划 (IODP) 第 341 号探险队从阿拉斯加南部大陆坡回收了沉积物，这些沉积物在过去 43 万年的大部分时间里保留了详细解析和注明日期的倾角记录。 U1419站点年表是世界上分辨率最高的，受到173个放射性碳测年的限制，提供了研究百年到千年时间尺度上的古地磁长期变化（PSV）的能力。该记录具有异常扩展的更新世晚期沉积记录，沉积速率通常超过 100 cm kyr–1，同时还在顶部保留了分辨率较低的全新世 PSV 记录。使用逐步 AF 退磁研究了 112 米长拼接记录中 U1419 u 通道的自然剩磁和实验室诱发剩磁。在 95 个离散样品的 95 和 IRM 采集曲线上获得磁滞回线，以促进磁畴状态、矫顽力和磁性矿物学测定。由于岩性、磁性矿物学以及沉积和沉积后过程的复杂性，U1419 站点沉积物不适合古强度研究，并且无法稳健地重建磁偏角。随着深度的增加，（钛）磁铁矿逐渐溶解，导致 NRM 强度和信噪比降低，这种情况在较高的退磁步骤中会加剧。因此，20 mT AF 消磁步骤后测量的倾角可提供最可靠的方向记录。通过仅去除受沉积和/或取样和取芯变形影响的几个层段，倾斜似乎得到了很好的解决。来自附近 IODP 站点 U1418 的船上倾角堆栈采用根据 U1418 上的 19 个放射性碳测年和与现场调查核心 EW0408-87JC 的 18 个基于磁化率的连接点开发的新年代模型，验证了 U1419 中观测到的百年到千年尺度的倾角变化。与东北太平洋和北美西部的其他独立年代记录的比较表明，这些地点可能捕获了区域地磁变化。因此，这一新的高分辨率和日期准确的倾角记录，尤其是在 15 至 30 cal kyr BP 之间，提供了新的地磁见解和区域相关工具，以探索世界上这个普遍未被充分研究的地区。
International Ocean Drilling Program (IODP) Expedition 341 recovered sediments from the south Alaska continental slope that preserves a well resolved and dated inclination record over most of the past ∼43 000 yr. The Site U1419 chronology is among the highest resolution in the world, constrained by 173 radiocarbon dates, providing the ability to study Palaeomagnetic Secular Variation (PSV) on centennial to millennial timescales. This record has an exceptionally expanded late Pleistocene sedimentary record with sedimentation rates commonly exceeding 100 cm kyr–1, while also preserving a lower resolution Holocene PSV record at the top. Natural and laboratory-induced magnetic remanences of U1419 u-channels from the 112-m-long spliced record were studied using stepwise AF demagnetization. Hysteresis loops were obtained on 95 and IRM acquisition curves on 9 discrete samples to facilitate magnetic domain state, coercivity and magnetic mineralogical determinations. Due to complexities related to lithology, magnetic mineralogy, and depositional and post-depositional processes, Site U1419 sediments are not suitable for palaeointensity studies and declination could not be robustly reconstructed. Progressive (titano-)magnetite dissolution with depth results in decreasing NRM intensity and signal-to-noise that is exacerbated at higher demagnetization steps. As a result, inclination measured after the 20 mT AF demagnetization step provides the most reliable directional record. Inclination appears to be well resolved with removal of just a few intervals influenced by depositional and/or sampling and coring deformation. The shipboard inclination stack from nearby IODP Site U1418, on a new age model developed from 19 radiocarbon dates on U1418 and 18 magnetic susceptibility-based tie-points to site survey core EW0408-87JC, verifies centennial to millennial scale variations in inclination observed in U1419. Comparisons with other independently dated records from the NE Pacific and western North America suggest that these sites likely capture regional geomagnetic variability. As such, this new high-resolution and well-dated inclination record, especially robust between 15 and 30 cal kyr BP, offers new geomagnetic insights and a regional correlation tool to explore this generally understudied part of the world.