Abstract The isotopic composition of Cd buried in marine sediments may preserve valuable palaeoenvironmental information on past ocean redox conditions or biological cycling. It is unclear, however, how the Cd-isotope composition of the sedimentary record reflects these processes. In this study, new Cd-isotope data are presented, along with δ13C, and Cd, Mo and TOC concentrations, from organic-rich mudrocks from the southern Western Interior Seaway (WIS), spanning the Cenomanian–Turonian stages within the Eagle Ford Group of the Maverick Basin, Texas, USA. Relationships between [Cd/TOC], δ114Cd, and MoEF indicate that sedimentary Cd was derived from organic matter with additional contributions from CdS formed in euxinic water masses. Local redox conditions exerted a primary control on the δ114Cd composition of these deposits, with high δ114Cd values attributed to near-quantitative removal from seawater in euxinic environments. Lower δ114Cd values in non-euxinic environments may reflect isotopically light Cd associated with organic material due to partial remineralization. These observations imply that δ114Cd values of samples deposited in demonstrably euxinic conditions may be used to constrain the δ114Cdseawater coming into the Maverick Basin at this time and give a composition of 0.28 ± 0.11‰ (2 SD) for the Early Cenomanian. Samples from an interval of peak-organic carbon burial globally, namely Oceanic Anoxic Event 2 (OAE 2), show anomalous δ114Cd and [Cd] patterns compared to the rest of the data, implying a perturbation to the dissolved Cd pool. The data presented in this study demonstrate that sedimentary Cd isotopes preserve valuable information on the extent of Cd burial into sulfide-bearing sediments at both local and global scales.

中文翻译：

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德克萨斯州南部上白垩统 (Cenomanian-Turonian) 富含有机质泥岩 Cd 同位素组成的控制 (Eagle Ford Group)

摘要 埋藏在海洋沉积物中的 Cd 同位素组成可以保存有关过去海洋氧化还原条件或生物循环的宝贵古环境信息。然而，尚不清楚沉积记录的 Cd 同位素组成如何反映这些过程。在这项研究中，提供了新的 Cd 同位素数据以及 δ13C、Cd、Mo 和 TOC 浓度，这些数据来自来自西部内陆海道 (WIS) 南部的富含有机物的泥岩，跨越 Eagle Ford 群内的 Cenomanian-Turonian 阶段美国德克萨斯州的 Maverick 盆地。[Cd/TOC]、δ114Cd 和 MoEF 之间的关系表明，沉积 Cd 来自有机质，而 CdS 的额外贡献来自于 euxinic 水团中形成的 CdS。局部氧化还原条件对这些沉积物的 δ114Cd 组成起到了主要控制作用，具有高δ114Cd 值归因于在euxinic 环境中从海水中近乎定量地去除。由于部分再矿化作用，非euxinic 环境中较低的δ114Cd 值可能会反射与有机材料相关的同位素轻Cd。这些观察结果表明，沉积在明显富氧条件下的样品的 δ114Cd 值可用于限制此时进入 Maverick 盆地的 δ114Cd 海水，并为早森诺曼期提供 0.28 ± 0.11‰ (2 SD) 的成分。来自全球有机碳埋藏高峰区间的样本，即海洋缺氧事件 2 (OAE 2)，与其余数据相比显示出异常的 δ114Cd 和 [Cd] 模式，这意味着对溶解的 Cd 池的扰动。