Abstract The Cenomanian—Turonian boundary is marked by worldwide paleoenvironmental and paleoceanographical changes that are associated with a perturbation of the global carbon cycle and black shale deposition, called the Oceanic Anoxic Event 2 (OAE2). The objective of this study is to precisely characterize the nature of the organic matter, its variability, paleoenvironmental significance and the preservation conditions of two areas located along the northwest African Shelf where large-scale organic carbon burial contributed significantly to the global carbon burial associated with OAE2. With these premises, an organic petrographic and geochemical approach to the Cenomanian—Turonian record of the Moroccan Atlantic coast allowed the definition of the variability of the organic facies and the paleoenvironmental characterization of the upper Cenomanian—lower Turonian sediments of the Agadir section (Agadir Basin) and of the lower Turonian record of the Amma Fatma section (Tarfaya Basin). At Agadir, the marine microplankton dominated assemblages, with variable degree of amorphization, allowed the characterization of a transgressive-regressive cycle during the upper Cenomanian followed, during the lower Turonian, by a drowning event with establishment of a deep platform environment (under reducing conditions, increase in EFU, EFV, EFMo). The base of the succession (base of W. archaeocretacea biozone) and the top of the upper Cenomanian are characterized by two sea-level lowstands, a high energy oxic environment that culminate in emersion surfaces (high EFMn and low organic matter preservation). The organic facies in the lower Turonian of Amma Fatma is largely dominated by bacterial material (probably derived from sulfur bacteria), indicating an outer shelf setting, with some degree of restriction, under euxinic conditions (high EFMo) and high primary productivity (high EFCu, EFNi, EFZn). Differences in terms of the redox conditions between the two basins during the lower Turonian were determined, with anoxia prevailing at Agadir, while euxinic conditions are established at Tarfaya. These are explained by different oceanic circulation patterns, with the mixing of Tethyan waters at Agadir. High primary productivity is recorded at both locations, possibly promoted by the occurrence of upwelling currents. This study further corroborates a delay in the anoxia in Agadir, that during the isotopic excursion of OAE2 only reaches slight dysoxia (upper Cenomanian), and the maintenance of reducing conditions in Tarfaya post-OAE2.

中文翻译：

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横跨塞诺曼阶-图伦阶大洋缺氧事件 (OAE2) 的摩洛哥大西洋沿岸的有机相变异和古环境变化

摘要 Cenomanian-Turonian 边界以全球古环境和古海洋学变化为标志，这些变化与全球碳循环和黑色页岩沉积的扰动有关，称为海洋缺氧事件 2 (OAE2)。本研究的目的是精确描述位于非洲大陆架西北部的两个区域的有机质的性质、其变异性、古环境意义和保存条件，这些区域的大规模有机碳埋藏对全球碳埋藏做出了重大贡献。 OAE2。有了这些场地，对摩洛哥大西洋沿岸 Cenomanian-Turonian 记录的有机岩相学和地球化学方法允许定义有机相的变异性和阿加迪尔剖面（阿加迪尔盆地）的上 Cenomanian-下图伦沉积物的古环境特征Amma Fatma 剖面（Tarfaya 盆地）的较低图伦纪记录。在阿加迪尔，海洋微浮游生物占主导地位的组合，具有不同程度的非晶化，允许表征上森诺曼阶期间的海进-回归循环，随后在下图伦阶期间发生溺水事件，并建立了深台地环境（在还原条件下） ，EFU、EFV、EFMo 增加）。继承的基础（W. archaeocretacea biozone）和上森诺曼阶顶部的特点是两个海平面低位，一个高能量的含氧环境，最终出现在浮出表面（高 EFMn 和低有机质保存）。Amma Fatma 下图伦阶的有机相主要以细菌物质（可能来自硫细菌）为主，表明外陆架环境有一定程度的限制，在 euxinic 条件（高 EFMo）和高初级生产力（高 EFCu）下、EFNi、EFZn)。确定了图伦阶下部两个盆地之间氧化还原条件的差异，在阿加迪尔普遍缺氧，而在塔法亚建立了富氧条件。这些可以通过不同的海洋环流模式来解释，以及阿加迪尔特提斯水域的混合。两个地点都记录了较高的初级生产力，这可能是由于上升流的出现。这项研究进一步证实了阿加迪尔缺氧的延迟，即在 OAE2 的同位素偏移期间仅达到轻微的缺氧（上森诺曼阶），以及在 OAE2 后塔法亚维持还原条件。