Abstract This study uses organic-rich sediments from the Tarfaya Basin, Morocco, to assess the Cd- and Zn-isotope response to dramatic global palaeoenvironmental change during the Cenomanian–Turonian interval (Late Cretaceous). These organic-rich continental-margin deposits include an expression of Oceanic Anoxic Event 2 (OAE 2, ∼94 Ma), an interval associated with the spread of low-oxygen marine environments and widespread burial of organic-rich sediments. Due to placement of the Tarfaya Basin in a region of upwelling and relatively constant local environmental conditions, the stratigraphic variations in δ 114 Cd and δ 66 Zn values largely reflect changes in the seawater isotopic composition of the sub-surface proto-North Atlantic Ocean. Positive shifts of ∼0.2–0.3‰ away from background values in δ 114 Cd and δ 66 Zn are observed during the main phase of the positive carbon-isotope excursion associated with OAE 2. These isotopic shifts are coeval with decreases in Cd/TOC and Zn/TOC ratios and thus imply that drawdown of isotopically light Cd and Zn from seawater inventories was a result of extensive burial of these metals in organic-rich marine sediments globally. Low δ 66 Zn values during the Plenus Cold Event, a cooler episode during OAE 2, are similar in timing and magnitude to variations found in the English Chalk (Eastbourne, UK) and support the inference of a global control on these isotopic excursions. The δ 66 Zn values during the Plenus Cold Event are taken to record global oxygenation, possibly including the remobilization of isotopically light Zn from continental-margin sediments. A considerably smaller change in δ 114 Cd values for this interval implies that the Cd- and Zn-isotope systems can provide information about slightly different environmental processes, with global seawater composition with respect to Zn also being influenced by the magnitude of oxic removal sinks and isotopically light Zn input fluxes from sediments and hydrothermal fluids.

中文翻译：

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在海洋缺氧事件 2（晚白垩世）期间氧化还原驱动对全球微量营养素循环的扰动的锌和镉同位素证据

摘要 本研究利用摩洛哥塔法亚盆地富含有机物的沉积物来评估 Cd 和 Zn 同位素对 Cenomanian-Turonian 间隔（晚白垩世）剧烈全球古环境变化的响应。这些富含有机质的大陆边缘沉积物包括大洋缺氧事件 2 (OAE 2, ∼94 Ma)，这是一个与低氧海洋环境的扩散和富含有机质沉积物的广泛掩埋有关的区间。由于塔法亚盆地位于上升流和相对恒定的局部环境条件区域，δ 114 Cd 和δ 66 Zn 值的地层变化在很大程度上反映了亚表层原北大西洋海水同位素组成的变化。〜0.2-0的正变化。在与 OAE 2 相关的碳同位素正偏移的主要阶段，观察到 δ 114 Cd 和 δ 66 Zn 与背景值相差 3‰。这些同位素变化与 Cd/TOC 和 Zn/TOC 比率的降低同时发生，因此这意味着海水库存中同位素轻质 Cd 和 Zn 的下降是这些金属在全球富含有机物的海洋沉积物中广泛埋藏的结果。Plenus Cold Event 期间的低 δ 66 Zn 值（OAE 2 期间的较冷事件）在时间和幅度上与在英国白垩（伊斯特本，英国）中发现的变化相似，并支持对这些同位素偏移进行全球控制的推断。取 Plenus Cold Event 期间的 δ 66 Zn 值来记录全球氧化，可能包括来自大陆边缘沉积物的同位素轻 Zn 的再迁移。