Early Eocene deep-sea benthic foraminiferal faunas: Recovery from the Paleocene Eocene Thermal Maximum extinction in a greenhouse world

Abstract

The early Eocene greenhouse world was marked by multiple transient hyperthermal events. The most extreme was the Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma), linked to the extinction of the globally recognised deep-sea benthic foraminiferal Velasco fauna, which led to the development of early Eocene assemblages. This turnover has been studied at high resolution, but faunal development into the later early Eocene is poorly documented. There is no widely accepted early Eocene equivalent of the Late Cretaceous-Paleocene Velasco fauna, mainly due to the use of different taxonomic concepts. We compiled Ypresian benthic foraminiferal data from 17 middle bathyal-lower abyssal ocean drilling sites in the Pacific, Atlantic and Indian Oceans, in order to characterise early Eocene deep-sea faunas by comparing assemblages across space, paleodepth and time. Nuttallides truempyi, Oridorsalis umbonatus, Bulimina trinitatensis, the Bulimina simplex group, the Anomalinoides spissiformis group, pleurostomellids, uniserial lagenids, stilostomellids and lenticulinids were ubiquitous during the early Eocene (lower-middle Ypresian). Aragonia aragonensis, the Globocassidulina subglobosa group, the Cibicidoides eocaenus group and polymorphinids became ubiquitous during the middle Ypresian. The most abundant early Ypresian taxa were tolerant to stressed or disturbed environments, either by opportunistic behavior (Quadrimorphina profunda, Tappanina selmensis, Siphogenerinoides brevispinosa) and/or the ability to calcify in carbonate-corrosive waters (N. truempyi). Nuttallides truempyi, T. selmensis and other buliminids (Bolivinoides cf. decoratus group, Bulimina virginiana) were markedly abundant during the middle Ypresian. Contrary to the long-lived, highly diverse and equitable Velasco fauna, common and abundant taxa reflect highly perturbed assemblages through the earliest Ypresian, with lower diversity and equitability following the PETM extinction. In contrast, the middle Ypresian assemblages may indicate a recovering fauna, though to some extent persistently disturbed by the lower-amplitude Eocene hyperthermals (e.g., Eocene Thermal Maximum 2 and 3). We propose the name ‘Walvis Ridge fauna’ for future reference to these Ypresian deep-sea benthic foraminiferal assemblages.

Early Eocene Thermal Maximum 3: Biotic Response at Walvis Ridge (SE Atlantic Ocean)

“…The N. cf. umbonifera morphotypes are much more common at the deeper site, across ETM3, but also across the PETM and ETM 2 at the same sites (Arreguin Rodriguez et al, 2018;Jennions et al, 2015), as well as in the middle Eocene (Ortiz & Thomas, 2015). We consistently used the N. truempyi ss morphotype for isotope analysis.…”

“…We determined the relative abundances of benthic foraminiferal taxa and used these to infer changes in carbonate saturation state, oxygenation, and food supply (Arreguin‐Rodriguez et al, , ; Boscolo‐Galazzo et al, , ; Foster et al, ; Gooday, ; Gooday & Jorissen, ; Jorissen et al, , ; Jennions et al, ; Thomas, , ). Taxonomy is after Alegret and Thomas, , Boscolo‐Galazzo et al, , Fenero et al, , Hayward et al, , Moura de Mello et al, , Nomura & Takata, , Ortiz & Thomas, , , and Thomas, , , , and has been adjusted to the reevaluation of taxonomy of global Ypresian assemblages (Arreguin‐Rodriguez et al, ).…”

“…We divided benthic foraminifera into infaunal and epifaunal groups, following Corliss (, ) and Corliss and Chen (), as documented in Alegret et al (), Alegret and Thomas (), and Arreguin‐Rodriguez et al (). Such assignments of extinct taxa must be used with caution, because only ~75% of living foraminifera were found to be assigned correctly based on their morphology (Buzas et al, ).…”

Paleoenvironmental Changes at ODP Site 702 (South Atlantic): Anatomy of the Middle Eocene Climatic Optimum

“…No extinctions have been recorded across the MECO at Site 702 (Table S2) in contrast to the extinction of almost half of deep‐sea benthic foraminiferal species across the PETM (e.g., Alegret et al, , b, ; Arreguín‐Rodríguez et al, ; Miller et al, ; Thomas, , , ; Tjalsma & Lohmann, ). Similarly, no benthic foraminiferal extinctions have been recorded across the MECO in other locations from different latitudes and basins (Boscolo Galazzo et al, ; Moebius et al, , ) nor across some Paleocene (e.g., Alegret et al, ; Deprez et al, ) and Eocene smaller hyperthermal events (e.g., Arreguín‐Rodríguez et al, ; Arreguín‐Rodríguez & Alegret, ).…”

“…Classification at the generic level mainly follows Loeblich and Tappan (), except for uniserial taxa (Hayward et al, ). Species identification follows Tjalsma and Lohmann (), Van Morkhoven et al (), Müller‐Merz and Oberhänsli (), Ortiz and Thomas (), Holbourn et al (), Boscolo Galazzo et al (), and Arreguín‐Rodríguez et al (). Preservation of foraminiferal tests is commonly good, suitable to detect diagnostic morphological features.…”