Paleomagnetic constraints on the Holocene stratigraphy of the Arctic Alaskan margin
Paleomagnetic constraints on the Holocene stratigraphy of the Arctic Alaskan margin
复制标题
古地磁对北极阿拉斯加边缘全新世地层的约束
DOI：
10.1016/j.gloplacha.2009.03.015
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发表时间：
2009
影响因子：
3.9
通讯作者：
D. Darby
中科院分区：
文献类型：
--
作者：
A. Lisé;G. St‐Onge;S. Brachfeld;F. Barletta;D. Darby
两个长全新世活塞岩心（HLY0501-06JPC和-08JPC；以下简称6JPC和8JPC）是从北极阿拉斯加边缘的沉积物高堆积区升起的，目的是重建地球磁场的千年至百年尺度的行为，并更好地约束北极西部的区域年代地层。使用 u 通道低温磁力计（自然、非滞后和等温剩磁：NRM、ARM 和 IRM）和振动样品磁力计进行的古地磁分析表明，可以在两个核心的冰后单元中分离出由低矫顽力伪单畴（PSD）颗粒（例如磁铁矿）携带的强且稳定的单组分特征剩磁，其中倾角值围绕地心轴偶极子（GAD）变化取芯地点的纬度以及最大角度偏差 (MAD) 值通常低于 5°。除了每个岩心中的一个区间外，所有衍生的相对古强度代理（NRM/kLF、NRM/ARM 和 NRM/IRM）都会产生相似的结果。 NRM/IRM 被用作首选代理，因为基于交叉谱分析，它与其归一化器不一致。根据与北美西部古地磁记录的比较，古地磁和物理分析表明，这两个沉积层序都记录了一些关于全新世期间古地磁长期变化（磁倾角和磁偏角）和相对古强度的最早可靠的北极高分辨率记录。此外，使用全矢量古地磁对比（倾角、偏角和相对古强度）来约束岩心 6JPC 的年代学，使用岩心 8JPC 和其他先前发表的、独立测年的北美西部沉积和火山记录。 8JPC 岩心的加速器质谱 (AMS) 基于放射性碳的冰后年代学表明，巴罗峡谷附近大陆架的沉积速率高于 300 cm/kyr，大约为 8000 至 5000 cal BP，随后沉积物沉积大幅减少。相比之下，核心地点 6JPC 斜坡上的冰后沉积相对稳定，沉积速率低近三倍。
Two long Holocene piston cores (HLY0501-06JPC and -08JPC; herein after referred to as 6JPC and 8JPC) were raised from high sediment accumulation areas in the Arctic Alaskan margin in order to reconstruct the millennial- to centennial-scale behavior of Earth's magnetic field and to better constrain the regional chronostratigraphy of the Western Arctic. Paleomagnetic analyses using a u-channel cryogenic magnetometer (natural, anhysteretic and isothermal remanent magnetizations: NRM, ARM and IRM) and a vibrating sample magnetometer indicate that a strong and stable single component characteristic remanent magnetization carried by low coercivity pseudo-single domain (PSD) grains such as magnetite can be isolated in the postglacial unit of both cores, where the inclination values vary around the geocentric axial dipole (GAD) for the latitude of the coring sites and where the maximum angular deviation (MAD) values are generally lower than 5°. Apart from one interval in each core, all the derived relative paleointensity proxies (NRM/kLF, NRM/ARM and NRM/IRM) yield similar results. NRM/IRM was used as the preferred proxy because, based on cross-spectral analysis, it is not coherent with its normalizer. Based on the comparison with paleomagnetic records from Western North America, the paleomagnetic and physical analyses indicate that both sedimentary sequences have recorded some of the first reliable Arctic high-resolution records of paleomagnetic secular variation (inclination and declination) and relative paleointensity during the Holocene. In addition, full vector paleomagnetic correlations (inclination, declination and relative paleointensity) were used to constrain the chronology of core 6JPC, using core 8JPC and other previously published and independently dated sedimentary and volcanic records from Western North America. The Accelerator Mass Spectroscopy (AMS) radiocarbon-based postglacial chronology of core 8JPC indicates sedimentation rates higher than 300 cm/kyr on the continental shelf near Barrow Canyon from approximately 8000 to 5000 cal BP, followed by a major decrease in sediment deposition. In contrast, the postglacial deposition on the slope at core site 6JPC is relatively constant and sedimentation rates are nearly three times lower.