Red clay widely occupies the seafloor of pelagic environments in middle latitudes, and potentially preserves long paleoceanographic records. We conducted a rock-magnetic study of Pacific Ocean red clay to elucidate paleoenvironmental changes. Three piston cores from the western North Pacific Ocean and IODP Hole U1365A cores in the South Pacific Ocean were studied here. Principal component analyses applied to first-order reversal curve diagrams (FORC-PCA) reveals three magnetic components (endmembers EM1 through EM3) in a core of the western North Pacific. EM1, which represents the features of interacting single-domain (SD) and vortex states, is interpreted to be of terrigenous origin. EM2 and EM3 are carried by non-interacting SD grains with different coercivity distributions, which are interpreted to be of biogenic origin. The EM1 contribution suddenly increases upcore at a depth of ~ 2.7 m, which indicates increased eolian dust input. The age of this event is estimated to be around the Eocene–Oligocene (E/O) boundary. Transmission electron microscopy reveals that EM2 is dominated by magnetofossils with equant octahedral morphology, while EM3 has a higher proportion of bullet-shaped magnetofossils. An increased EM3 contribution from ~ 6.7 to 8.2 m suggests that the sediments were in the oxic–anoxic transition zone (OATZ), although the core is oxidized in its entire depth now. The chemical conditions of OATZ may have been caused by higher biogenic productivity near the equator. FORC-PCA of Hole U1365A cores identified two EMs, terrigenous (EM1) and biogenic (EM2). The coercivity distribution of the biogenic component at Hole U1365A is similar to that of the lower coercivity biogenic component in the western North Pacific. A sudden upcore terrigenous-component increase is also evident at Hole U1365A with an estimated age around the E/O boundary. The increased terrigenous component may have been caused by the gradual tectonic drift of the sites on the lee of arid continental regions in Asia and Australia, respectively. Alternatively, the eolian increase may have been coeval in the both hemispheres and associated with the global cooling at the E/O boundary.

中文翻译：

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使用一阶反转曲线图的主成分分析和古环境影响分离太平洋红粘土中的生物和陆源磁性矿物成分

红粘土广泛占据中纬度远洋环境的海底，并有可能保存长期的古海洋记录。我们对太平洋红粘土进行了岩磁研究，以阐明古环境变化。这里研究了来自北太平洋西部的三个活塞岩心和南太平洋的 IODP Hole U1365A 岩心。应用于一阶反转曲线图 (FORC-PCA) 的主成分分析揭示了北太平洋西部核心中的三个磁性成分（端元 EM1 到 EM3）。EM1 代表相互作用的单域 (SD) 和涡旋状态的特征，被解释为陆源来源。EM2 和 EM3 由具有不同矫顽力分布的非相互作用 SD 晶粒携带，这些晶粒被解释为生物来源。EM1 的贡献在约 2.7 m 的深度突然增加，这表明风尘输入增加。该事件的年龄估计在始新世-渐新世 (E/O) 边界附近。透射电子显微镜显示 EM2 以具有等量八面体形态的磁化石为主，而 EM3 具有较高比例的子弹形磁化石。EM3 贡献从约 6.7 米增加到 8.2 米表明沉积物处于好氧-缺氧过渡带 (OATZ)，尽管核心现在在其整个深度被氧化。OATZ 的化学条件可能是由赤道附近较高的生物生产力造成的。Hole U1365A 核心的 FORC-PCA 确定了两个 EM，陆源 (EM1) 和生物 (EM2)。Hole U1365A 生物成因组分的矫顽力分布与北太平洋西部较低矫顽力生物成因组分的分布相似。Hole U1365A 上核陆源成分突然增加也很明显，估计年龄在 E/O 边界附近。增加的陆源成分可能是由分别位于亚洲和澳大利亚干旱大陆地区背风面的地点逐渐构造漂移引起的。或者，两个半球的风尘增加可能是同时发生的，并且与 E/O 边界处的全球变冷有关。增加的陆源成分可能是由分别位于亚洲和澳大利亚干旱大陆地区背风面的地点逐渐构造漂移引起的。或者，两个半球的风尘增加可能是同时发生的，并且与 E/O 边界处的全球变冷有关。增加的陆源成分可能是由分别位于亚洲和澳大利亚干旱大陆地区背风面的地点逐渐发生构造漂移引起的。或者，两个半球的风尘增加可能是同时发生的，并且与 E/O 边界处的全球变冷有关。