Paleogene record of elemental concentrations in sediments from the Arctic Ocean obtained by XRF analyses

We present a high-resolution X-ray fluorescence (XRF) core scanner record for the expanded middle Eocene section from Integrated Ocean Drilling Program (IODP) Expedition 302 (ACEX) drilled on the Lomonosov Ridge, central Arctic Ocean. The division of the middle Eocene into two units (subunit 1/6 and unit 2) is seen in the cyclical behavior of the elements as well as the changing interelemental correlations and their relationship to physical property measurements of bulk sediment. Al, Ti, and K strongly correlate throughout the record, while the behavior of Fe, Mn, and Si is more complex. Utilizing sediment geochemistry calibration to ground truth the XRF data, we suggest the middle Eocene Arctic Ocean was predominately euxinic, although periodic oxygenation of bottom waters must have occurred during unit 2 (49.7–45.4 Ma). Initially, the sediments are rich in biogenic silica (unit 2), but there is a pronounced shift to terrigenous dominated sediment accumulation in subunit 1/6. We report changes in the elemental concentrations of these elements and investigate the relationship between Fe content and pyrite. Additionally, we explore the potential change in paleoenvironmental conditions across the unit boundary.

本研究报道了北冰洋中部罗蒙诺索夫海岭上，由综合大洋钻探计划（Integrated Ocean Drilling Program, IODP）第302航次（ACEX）钻取的完整始新世中期岩心剖面的高分辨率X射线荧光（X-ray fluorescence, XRF）岩心扫描记录。基于元素的周期性变化规律、元素间相关关系的演变特征，及其与全岩沉积物物理性质测量结果的关联，可将该始新世中期地层划分为两个单元：亚单元1/6与单元2。Al、Ti与K在整个记录中呈显著强相关，而Fe、Mn及Si的变化特征则更为复杂。通过沉积物地球化学校准以验证XRF数据的可靠性，本研究认为始新世中期北冰洋整体处于缺氧硫化环境，但在单元2（49.7–45.4 Ma）期间，底层水曾周期性发生氧化事件。研究早期沉积物以生物硅富集为特征（对应单元2），但在亚单元1/6中出现了显著转变，沉积物堆积转为陆源主导。本研究测定并报道了上述元素的浓度变化，探讨了Fe含量与黄铁矿之间的关联。此外，本研究还探究了该单元边界处古环境条件的潜在变化。