Late Paleogene (Eocene to Oligocene) Benthic Foraminiferal Oceanography of the Goban Spur Region, Deep Sea Drilling Project Leg 80

Abstract

Major benthic foraminiferal changes occurred in the late Eocene at Site 549. A Nuttallides truempyi-dominated assemblage was replaced by a buliminid assemblage (-40-38.5 m.y. ago); this change in faunal abundance was apparently a circum-Atlantic event. The buliminid assemblage was replaced, in turn, by an assemblage dominated by stratigraphically long-ranging and bathymetrically wide-ranging taxa just below the Eocene/Oligocene boundary (~37.5 m.y. ago). A series of late Eocene to earliest Oligocene first and last appearances of taxa accompanied these abundance changes. Similar changes in faunal abundance occurred at Site 548, but the incomplete record recovered at Site 548 prevents a firm dating of the changes. No major benthic foraminiferal changes (denoted by the extinction of Hαntkeninα, Cribrohαntkeninα, and Globorotαliα cerroαzulensis) were associated with the Eocene/Oligocene boundary at these sites; instead, benthic foraminiferal abundance changes, last appearances (both extinctions and local disappearances), and first appearances occurred throughout the late Eocene to earliest Oligocene interval (-40-36 m.y. ago).Benthic foraminiferal δ 18 θ increased ~ l.O‰ in the late Eocene to earliest Oligocene (~ 38-36.5 m.y. ago) at Site 549. Most (~ 0.7‰) of this increase occurred simultaneously with a 0.6‰ increase in benthic foraminiferal δ 13 C as a geologically rapid event in the earliest Oligocene (-36.5 m.y. ago). The major benthic foraminiferal abundance change (-40-38 m.y. ago) predates the major isotopic enrichments. A prominent seismic horizon, Reflector R4, has been noted in the Labrador Sea, Rockall, and Biscay regions, and has been dated as latest Eocene to early Oligocene. This horizon marks the onset of increased intensity of abyssal circulation associated with the initial entry of bottom water from the Norwegian-Greenland Sea and/or Arctic Ocean into the North Atlantic. The interval during which Reflector R4 was formed may encompass both the faunal and isotopic changes; the best estimate for the age of this horizon and the associated circulation change suggests that it correlates with the δ 18 θ increase. Our interpretation of these data suggests that a temperature drop, decrease in age (increased O 2 , lowered CO 2 , increased pH, hence decreased corrosiveness) of bottom water, and an increase in intensity of abyssal circulation occurred in the late Eocene to earliest Oligocene of the North Atlantic. Graciansky, P. C. de, Poag, C. W., et al., Init. Repts. DSDP, 80: Washington (U.S. Govt. Printing Office).

Site 574

“…The abundance of the most common species {Cibicidoides, Gyroidinoides, Oridorsalis, Globocassidulinà) remains relatively unchanged, in accordance with observations by Corliss (1981) and Miller et al (1985). Nuttallides truempyi has its last occurrence in Sample 574C-33-5, 141-143 cm.…”

“…A. dissonata was used as an Eocene marker species by Douglas (1973), Proto Decima and Bolli (1978), and Schnitker (1979). However, Miller and Curry (1982), Miller et al (1985), and Tjalsma and Lohmann (1982) state that N. truempyi is the most reliable marker of the Eocene/Oligocene boundary. Thus, several events that have been described as occurring at the Eocene/Oligocene boundary occur in the benthic foraminiferal assemblages at Site 574, but they occur at slightly different levels.…”

“…3 The Eocene/Oligocene boundary has not been well defined in the tropics for diatoms. For benthic foraminifers, Miller and Curry (1982), Miller et al (1985), and Tjalsma and Lohmann (1982) …”

Palaeoenvironmental reconstruction of the Oligocene Afales Basin, Ithaki island, western Greece

“…and C. praemundulus, benthic foraminiferal taxa ubiquitous in Oligocene Afales section samples, together with G. subglobosa, have been identified elsewhere as characteristic of deep sea benthic foraminiferal biofacies in the Oligocene e.g. [61][62][63][64] and Eocene e.g. [6].…”

Middle Eocene to Early Oligocene Foraminifers from the Izu-Bonin Forearc, Hole 786A

“…Deep-sea drilling sites that penetrate Eocene to Oligocene sediments are present throughout the Atlantic Ocean (Tjalsma and Lohmann, 1983;Miller et al, 1985), Indian Ocean (Davies, Luyendyk, et al, 1974), and Pacific Ocean (Corliss, 1981). In the Pacific Ocean, few drill sites have intersected a continuous Eocene to Oligocene sedimentary section (Keller, 1986a).…”