Abstract Integrated microfacies and geochemical analyses conducted on five stratigraphic sections in northeastern Mexico (ancentral western margin of the proto-North Atlantic) reveal major paleoenvironmental changes in shallow water and pelagic environments in the prelude and run-up of the early Aptian oceanic anoxic event (OAE) 1a. During the Barremian–Aptian transition, the replacement of photozoan rudist-coral by mesotrophic/eutrophic orbitolinid-miliolid communities in the Cupido platform occurred in association with increased nutrient input. Thereafter, oligotrophic, photozoan, green algal communities repopulated briefly the carbonate ramp. Microbial-dominated ecosystems and peloidal carbonates with scarce fossils flourished before and during the onset of the OAE 1a, attesting carbonate crisis and highly stressed conditions. Organic-rich sediments deposited under weak reducing conditions in some parts of the platform. Carbonate sedimentation at the end of OAE 1a was characterized by photozoan ooid-dominated facies documenting a recovery phase of marine alkalinity. The studied carbonate platform shows a response mode to OAE 1a marked by continuous carbonate production, presumably protected by the “kettle effect”, but accompanied by significant ecological perturbations and incipient drowning. The documented change shares attributes of both central/southern and northern Tethyan platforms response modes. The OAE 1a deposits in the pelagic setting are characterized by organic-rich, radiolarian-dominated carbonates accumulated under oxygen-restricted bottom water conditions and during enhanced nutrient input linked to intense chemical weathering. The intensity of the trace metal anomalies suggests that volcanic-hydrothermal activity associated with the construction phases of the Ontong Java LIP also influenced the elemental abundance in the proto-Atlantic water mass.

中文翻译：

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西部原始北大西洋边缘对早期阿普蒂安大洋缺氧事件 (OAE) 1a 的响应：来自 Cupido 平台边缘-墨西哥东北部墨西哥湾的一个例子

摘要 对墨西哥东北部（原北大西洋的中西部边缘）的五个地层剖面进行的综合微相和地球化学分析揭示了早期阿普蒂安大洋缺氧事件的前奏和爆发期间浅水和远洋环境的主要古环境变化（ OAE) 1a。在 Barremian-Aptian 过渡期间，Cupido 平台中光生动物 rudist-coral 被中营养/富营养化的眼眶类群落取代，与营养输入的增加有关。此后，贫营养、光生动物、绿藻群落短暂地重新填充碳酸盐斜坡。在 OAE 1a 出现之前和期间，以微生物为主的生态系统和化石稀少的球状碳酸盐蓬勃发展，证明了碳酸盐危机和高压力条件。在平台的某些部分，在弱还原条件下沉积的富含有机物的沉积物。OAE 1a 末期的碳酸盐沉积物的特征是光动物类蛋白占主导地位的相，记录了海洋碱度的恢复阶段。研究的碳酸盐平台显示出对 OAE 1a 的响应模式，以连续碳酸盐生产为标志，可能受到“水壶效应”的保护，但伴随着显着的生态扰动和初期溺水。记录在案的变化共享中/南和北特提斯平台响应模式的属性。远洋环境中的 OAE 1a 沉积物的特点是富含有机质、放射虫为主的碳酸盐在缺氧的底水条件下以及在与强烈化学风化相关的养分输入增加期间积累。