Data from: Abyssal benthic foraminifera in the eastern equatorial Pacific (IODP Exp 320) during the middle Eocene

We report on the faunal transition of benthic foraminifera during the middle Eocene at Site U1333 (4862 m water depth, 3560-3720 m paleo-water depth) of Integrated Ocean Drilling Program Expedition 320 in the eastern equatorial Pacific Ocean. During the period ~41.5-40.7 Ma, which includes carbonate accumulation event 3 (CAE-3), the benthic foraminiferal accumulation rate (BFAR) increased gradually and then it declined rapidly. In contrast, BFAR was considerably lower during ~40.7-39.4 Ma, corresponding to the middle Eocene climatic optimum (MECO), and then it increased during ~39.3-38.4 Ma, including CAE-4. Diversity (E [S200]) was slightly lower in the upper part of the study interval than in the lower part. The most common benthic foraminifera were Nuttallides truempyi, Oridorsalis umbonatus and Gyroidinoides spp. in association with Globocassidulina globosa and Cibicidoides grimsdalei during the period studied. Quadrimorphina profunda occurred abundantly with N. truempyi, O. umbonatus and G. globosa during ~39.4-38.4 Ma, including CAE-4, although this species was also relatively common in the lower part of the study interval. Virgulinopsis navarroanus and Fursenkoina sp. A, morphologically infaunal taxa, were common during ~38.8-38.4 Ma, corresponding to the late stage of CAE-4. Based on Q-mode cluster analysis, four sample clusters were recognized and their stratigraphic distributions were generally discriminated in the lower and upper parts of the study interval.. Thus, there was only a small faunal transition in the abyssal eastern equatorial Pacific during the middle to late-middle Eocene. The faunal transition recognized in this study may be related to recovery processes following intense carbonate corrosiveness in the eastern equatorial Pacific during MECO.

本研究报道了东赤道太平洋综合大洋钻探计划（Integrated Ocean Drilling Program）320航次U1333站位（现今水深4862米，古水深3560~3720米）中始新世时期的底栖有孔虫（benthic foraminifera）动物群演替过程。在约41.5~40.7 Ma的时段内（包含碳酸盐堆积事件3（carbonate accumulation event 3, CAE-3）），底栖有孔虫堆积速率（benthic foraminiferal accumulation rate, BFAR）先逐渐升高，随后快速下降。与之相反，在对应中始新世气候适宜期（middle Eocene climatic optimum, MECO）的约40.7~39.4 Ma期间，BFAR处于显著较低的水平；随后在约39.3~38.4 Ma（包含碳酸盐堆积事件4（CAE-4））的时段内，BFAR再度回升。研究层段上部的多样性指数（E[S200]）略低于下部。本研究时段内最为常见的底栖有孔虫包括*Nuttallides truempyi*、*Oridorsalis umbonatus*以及*Gyroidinoides* spp.类群，伴生类群包括*Globocassidulina globosa*与*Cibicidoides grimsdalei*。在约39.4~38.4 Ma（包含CAE-4）的时段内，*Quadrimorphina profunda*与*N. truempyi*、*O. umbonatus*及*G. globosa*大量伴生，尽管该物种在研究层段下部也较为常见。形态上属于内生底栖类群的*Virgulinopsis navarroanus*与*Fursenkoina* sp. A在约38.8~38.4 Ma（对应CAE-4的晚期阶段）较为繁盛。通过Q型聚类分析（Q-mode cluster analysis），本研究识别出4个样品簇，其地层分布总体在研究层段的上下部呈现明显分异。因此，在中始新世至中始新世晚期的东赤道太平洋深渊海域，底栖有孔虫动物群仅发生了小幅演替。本研究识别出的动物群演替，可能与中始新世气候适宜期东赤道太平洋区域强烈碳酸盐溶蚀作用后的恢复过程相关。