Mineralogy and petrographic summary of ODP Leg 198 sites and DSDP Hole 62-463, Shatsky Rise@en

This petrological study of the lower Aptian Oceanic Anoxic Event (OAE1a) focused on the nature of the organic-rich interval as well as the tuffaceous units above and below it. The volcaniclastic debris deposited just prior to the OAE1a is consistent with reactivation of volcanic centers across the Shatsky Rise, concurrent with volcanism on the Ontong Java Plateau. This reactivation may have been responsible for the sub-OAE1a unconformity. Soon after this volcanic pulse, anomalous amounts of organic matter accumulated on the rise, forming a black shale horizon. The complex textures in the organic-rich intervals suggest a history of periodic anoxia, overprinted by bioturbation. Components include pellets, radiolarians, and fish debris. The presence of carbonate-cemented radiolarite under the OAE1a intervals suggests that there has been large-scale remobilization of carbonate in the system, which in turn may explain the absence of calcareous microfossils in the section. The volcanic debris in the overlying tuffaceous interval differs in that it is significantly epiclastic and glauconitic. It was likely derived from an emergent volcanic edifice.本项针对下阿普第阶海洋缺氧事件（Oceanic Anoxic Event, OAE1a）的岩石学研究，重点聚焦富有机质层段的特征及其上下两侧的凝灰质岩层。沉积于OAE1a发生前不久的火山碎屑沉积物，与沙茨基海隆（Shatsky Rise）各处火山活动中心的复活现象相吻合，且与翁通爪哇高原（Ontong Java Plateau）的火山活动同期发生。此次火山复活或为OAE1a之下不整合面的形成原因。此次火山活动脉冲过后不久，该海隆上富集了异常大量的有机质，形成黑色页岩层位。富有机质层段中的复杂结构表明，该区域经历过周期性缺氧环境，且后期被生物扰动作用叠加改造。层段组分包括球粒、放射虫（radiolarians）和鱼残体。OAE1a层段下方产出的碳酸盐胶结放射虫岩表明，该系统内发生过大规模碳酸盐再活化作用，这也可解释剖面中钙质微化石的缺失。上覆凝灰质层段中的火山碎屑则具有显著的外成碎屑特征与海绿石质成分，其物质来源大概率为一处出露海面的火山构造。