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.

Fig 1. Location of ODP and DSDP sites reviewed in this study.

Sites where benthic foraminifera are recorded across both Ypresian intervals (lower and middle) are indicated with stars, those encompassing only the lower Ypresian are marked with triangles, and those covering exclusively the middle Ypresian are shown with squares. Color reference: green-Pacific sites, blue-Atlantic sites, red-Indian site. Paleogeographic reconstruction of ~53 Ma from Hay et al., [69].

Fig 2. Stratigraphic interval represented at each ODP/DSDP site included in this study.

Lower Eocene zonation scheme from Berggren and Pearson [68], references of each drilling site included in Table 1. Color reference: green-Pacific sites, blue-Atlantic sites, red-Indian site.

Fig 3. Paleobathymetry of ODP and DSDP sites.

The circles represent the average of the depth range estimates, full data are shown in Table 1. Abbreviations: SO = Southern Ocean; U = upper; M = middle; L = lower.

Fig 4. SEM images of some ubiquitous Ypresian (lower Eocene) species.

All scale bars represent 100 μm, unless otherwise indicated. 1, Nuttallides truempyi (sample 865B-10-4, 120–125 cm): a) ventral, b) dorsal. 2, Nuttallides truempyi (sample 865B-10-5, 111–116 cm): apertural. 3, Lenticulina sp. (sample 865B-10-4, 120–125 cm): a) lateral, b) apertural. 4, Oridorsalis umbonatus (sample 865C-12-4, 6–8 cm): a) dorsal, b) ventral. 5, Oridorsalis umbonatus (sample 865C-12-4, 6–8 cm): apertural. 6, Astacolus sp. (sample 550-29-1, 8–10 cm): a) lateral, b) apertural. 7, Anomalinoides praespissiformis (sample 401-13-4, 130–132 cm): a) dorsal, b) apertural, c) ventral. 8, Anomalinoides ammonoides/spissiformis (sample 550-29-4, 145–147 cm): ventral. 9, Anomalinoides ammonoides/spissiformis (sample 550-29-1, 52–54 cm): apertural. 10–12, Stilostomellids: 10, Siphonodosaria lepidula (sample 550-29-5, 126 cm), 11, Siphonodosaria pomuligera (sample 401, 12-CC), 12, Strictocostella matanzana (sample 401-13-1, 91.5–92.5 cm). 13, Bulimina trinitatensis (sample 690-8A). 14, Bulimina simplex (sample 550-29-4, 65–67 cm). 15, Bulimina tuxpamensis (sample 1051-48-2, 135–137 cm). 16–21, Pleurostomellids: 16, Pleurostomella sp. 2 (sample 1258-14-4, 44–46 cm), 17, Pleurostomella sp. B (sample 865B-10-3, 4–6 cm), 18, Pleurostomella sp. 2 (sample 550-29-4, 35–37 cm), 19, Pleurostomella sp. D (sample 865B-10-3, 4–6 cm), 20, Pleurostomella acuta (sample 1258-14-4, 14–16 cm), 21, Pleurostomella sp. A (sample 865B-10-3, 60–62 cm). 22–24, Uniserial lagenids: 22, Chrysalogonium sp. 2 (sample 550-29-4, 95–97 cm), 23, Chrysalogonium ciperense (sample 550-29-4, 105–107 cm), 24, Dentalina sp. (sample 401-13-1, 84.5–85.5 cm).

Fig 5. SEM images of some abundant Ypresian (lower Eocene) species.

All scale bars represent 100 μm, unless otherwise indicated. 1, Seabrookia rugosa (sample 1258-14-4, 44–46 cm): a) lateral, b) apertural. 2, Aragonia aragonensis (sample 550-29-1, 8–10 cm): a) apertural, b) lateral. 3, Tappanina selmensis (sample 1258-14-4, 14–16 cm). 4, Bolivinoides decoratus (sample 550-29-4, 15–17 cm). 5, Bulimina elongata (sample 550-29-1, 52–54 cm). 6, Bulimina semicostata (sample 1051-48-1, 37–39 cm). 7, Bulimina virginiana (sample 1051-48-2, 75–77 cm). 8, Bulimina sp. 1 (sample 1258-14-4, 14–16 cm). 9, Bulimina sp. 1 (sample 1258-14-4, 14–16 cm). 10, Bulimina kugleri (sample 550-30-1, 106.5–108 cm). 11, Siphogenerinoides brevispinosa (sample 1258-14-CC, 5–7 cm). 12, Quadrimorphina profunda (sample 401-13-2, 43–45 cm): umbilical. 13, Quadrimorphina profunda (sample 550-29-5, 126.5–129 cm): ventral. 14, Abyssamina poagi (sample 550-30-1, 106.5–108 cm): umbilical. 15, Abyssamina poagi (sample 401-13-3, 43–45 cm): apertural. 16, Globocassidulina subglobosa (sample 550-29-6, 57–59 cm). 17, Epistominella exigua (sample 401-13-4, 130–132 cm): a) ventral, b) dorsal. 18, Nuttallides umbonifera (sample 550-29-5, 15–17 cm): ventral. 19, Nuttallides umbonifera (sample 550-29-5, 15–17 cm): apertural. 20, Nuttallides umbonifera (sample 550-29-1, 8–10 cm): dorsal. 21, Osangularia sp. 1 (sample 550-29-5, 15–17 cm): dorsal. 22, Osangularia sp. 1 (sample 550-29-4, 65–67 cm): apertural. 23, Osangularia sp. 1 (sample 550-29-2, 53–55 cm): ventral. 24, Cibicidoides praemundulus (sample 865-10-2, 4–6 cm): a) umbilical, b) dorsal. 25, Cibicidoides praemundulus (sample 865-10-2, 4–6 cm): apertural. 26, Cibicidoides proprius (sample 401-13-4, 130–132 cm): a) dorsal, b) apertural, c) ventral. 27, Gyroidinoides depressus (sample 865-10-2, 60–62 cm): a) ventral, b) apertural, c) dorsal. 28, Gyroidinoides planulatus (sample 550-29-1, 52–54 cm): a) dorsal, b) apertural, c) ventral. 29, Gyroidinoides complanata (sample 401-13-4, 130–132 cm): a) dorsal, b) apertural, c) ventral.

Fig 6. SEM images of some common Ypresian (lower Eocene) species.

All scale bars represent 100 μm, unless otherwise indicated. 1, Buliminella beaumonti (sample 1258-14-2, 76–78 cm). 2, Turrilina brevispira (sample 401-13-2, 75–76 cm). 3, Bolivina huneri (sample 401-13-4, 130–132 cm). 4–5, Polymorphinids: 4, Ellipsoglandulina sp. (sample 1258-14-3, 104–106 cm), 5, Pyrulinoides acuminatus (sample 401-13-1, 125–126 cm). 6, Nonion havanense (sample 401-13-2, 75–76 cm): lateral. 7, Nonion havanense (sample 401-13-2, 75–76 cm): apertural. 8, Alabaminella weddellensis (sample 401-13-4, 130–132 cm): a) ventral, b) dorsal. 9, Clinapertina inflata (sample 865-10-2, 60–62 cm): a) ventral, b) apertural, c) dorsal. 10, Cibicidoides micrus (sample 550-29-5, 115–117 cm): a) dorsal, b) ventral. 11, Cibicidoides micrus (sample 550-29-6, 2–4 cm): apertural. 12, Cibicidoides ungerianus (sample 401-13-1, 88.5–90 cm): ventral. 13, Cibicidoides ungerianus (sample 401-13-2, 130–132 cm): a) apertural, b) dorsal. 14, Anomalinoides cf. acutus (sample 690C-15-3, 16–18 cm): a) ventral, b) apertural, c) dorsal. 15, Cibicidoides eocaenus perlucidus (sample 550-29-5, 95–97 cm): a) umbilical, b) apertural, c) dorsal. 16, Cibicidoides eocaenus tuxpamensis (sample 550-29-1, 110–112 cm): a) umbilical, b) apertural, c) dorsal. 17, Hanzawaia ammophila (sample 865-10-3, 60–62 cm): a) ventral, b) apertural, c) dorsal. 18, Hanzawaia mantaensis (sample 1051-48-1, 37–39 cm): dorsal. 19, Hanzawaia mantaensis (sample 1051-48-2, 75–77 cm): apertural. 20, Hanzawaia mantaensis (sample 1051-48-2, 75–77 cm): ventral.

Fig 7. Q-mode dendrogram for ODP/DSDP sites based on relative abundance of selected lower Ypresian species.

Cophenetic coefficient = 0.9019. Abbreviations: SO = Southern Ocean; P = Pacific; Seamts = seamounts; NA = North Atlantic; SE = South East; Shatksy R = Shatsky Rise; East Pacif = East Pacific Rise.

Fig 8. Non-metric multidimensional scaling plots (stress = 0.1158) performed using lower Ypresian species.

The difference among the lower Ypresian species based on their relative abundance is shown according to coordinates 1–2 (A) and coordinates 2–3 (B). The abundance of the species located outside the 95% confidence ellipse is significantly distinct (higher) in comparison with the species inside the ellipse. Common species are marked with black dots, and abundant/very abundant species are indicated with colored circles. The color of the circle represents the sites where such species are abundant. Color reference: green-Pacific sites, light blue-SE Atlantic sites, red-Indian site, grey-NA site, and purple-seamount sites. Abbreviations found in Table 4.

Fig 9. Q-mode dendrogram for ODP/DSDP sites based on relative abundance of selected middle Ypresian species.

Cophenetic coefficient = 0.9306. Abbreviations: P = Pacific; I = Indian; A = Atlantic; HLat = High latitude; Cent-SE = Central-South East; S = seamounts; NA = North Atlantic.

Fig 10. Non-metric multidimensional scaling plots (stress = 0.132) performed using middle Ypresian species.

The difference among the middle Ypresian species based on their relative abundance is shown according to coordinates 1–2 (A) and coordinates 2–3 (B). The abundance of the species located outside the 95% confidence ellipse is significantly distinct (higher) in comparison with the species inside the ellipse. Common species are marked with black dots, and abundant/very abundant species are indicated with colored circles. The color of the circle represents the sites where such species are abundant. Color reference: light blue-SE Atlantic sites, dark blue-high latitude Atlantic sites, red-Indian site, grey-NA sites, and purple-seamount site. Abbreviations found in Table 5.