A δ²³⁸U record of changing ocean anoxia during OAE 2 is reconstructed using seawater derived U in pelagic marine sediments in the Portland #1 core in the south-central region of the Western Interior Seaway of North America. The peak negative excursion of 1.4‰ in authigenic sedimentary δ²³⁸U values is consistent with expansion of marine anoxia during the event, but the size of the shift is much larger than the negative excursions recorded in two other published records: (1) a pelagic chalk succession at Eastbourne (0.3‰) in the Paris-Anglo basin, and a black shale succession at Demerara Rise (0.15‰) in the proto-North Atlantic Ocean. By incorporating the estimated fractionation factors of processes governing removal of U into modern marine sediments, proxy data on pore fluid oxygen penetration into the sediment, faunal information on circulation in the Western Interior Seaway, and an ocean U box model, we identify and discuss the complications that hampered our effort to find a consensus value for the change in the δ²³⁸U value of the ocean U reservoir during OAE 2. These include: (1) strong local controls governing post-depositional uptake of seawater-derived U isotopes in marine sedimentary successions, and (2) local U cycling effects in epicontinental seas, which can work together or alone to mask the true change in the δ²³⁸U value of the ocean U reservoir during ocean anoxic events. Correcting the Portland record for stratigraphic changes in fractionation factors reduced the magnitude of the excursion to 0.9‰. Using an ocean U box model, this corresponds to 21% of the area of the seafloor covered by anoxic bottom waters during OAE 2. However, since the study setting represents an epicontinental sea that was located thousands of kilometers from the open ocean, we cannot exclude the possibility that the shift in seawater δ²³⁸U values was amplified by local U cycling effects, or that smaller negative excursions recorded elsewhere in the proto-North Atlantic Ocean were diminished by fractionation factor uncertainty and/or local U cycling in those settings.

OAE 2 期间海洋缺氧变化的 δ ²³⁸ U 记录是使用北美西部内陆航道中南部地区波特兰#1 核心中远洋海洋沉积物中的海水衍生 U 重建的。^{自生沉积δ238}峰值负偏移1.4‰U 值与事件期间海洋缺氧的扩展一致，但变化的大小远大于其他两个已发表记录中记录的负偏移：（1）在伊斯特本（0.3‰）的远洋白垩序列在巴黎-盎格鲁盆地和原北大西洋德梅拉拉隆起 (0.15‰) 的黑色页岩层序。通过将控制 U 去除过程的估计分馏因子纳入现代海洋沉积物、孔隙流体氧渗透到沉积物中的代理数据、西部内陆航道循环的动物群信息和海洋 U 盒模型，我们识别和讨论了阻碍我们努力为 δ ^{238的变化找到共识值的并发症}OAE 2 期间海洋 U 储层的 U 值。这些包括：(1) 强有力的局部控制，控制海洋沉积序列中海水衍生的 U 同位素的沉积后吸收，以及 (2) 大陆表海的局部 U 循环效应，这可以一起或单独工作，以掩盖海洋缺氧事件期间海洋 U 水库δ ^{238 U 值的真实变化。}校正分馏因子地层变化的波特兰记录将偏移幅度降低到 0.9‰。使用海洋 U 盒模型，这对应于 OAE 2 期间缺氧底水覆盖的海底面积的 21%。但是，由于研究环境代表的是距离公海数千公里的大陆海，因此我们不能排除海水变化 δ²³⁸ U 值被局部 U 循环效应放大，或者在原北大西洋其他地方记录的较小负偏移因分馏因子不确定性和/或在这些环境中的局部 U 循环而减少。