The Eocene-Oligocene planktic foraminiferal transition: extinctions, impacts and hiatuses

Abstract

Biostratigraphic study and re-examination of 22 late Eocene to early Oligocene sections provides data in support of three and possibly a fourth late Eocene impact events in the G. index Zone during a period of about 1 Ma of the middle Priabonian between 34.7 and 35.7 Ma. No major species extinctions or significant species abundance changes directly coincide with these impact events. Species extinctions are gradual and selective, affecting primarily cool-temperature-intolerant surface dwellers. These extinctions began with the onset of global cooling during the early middle Eocene and culminated near the Eocene/Oligocene boundary. The global cooling was associated with the isolation of Antarctica as Australia moved northward, the development of a circum-Antarctic circulation, growth of Antarctic ice sheet beginning by late middle Eocene time and a change from a thermospheric to thermohaline circulation. We find no evidence that the multiple late Eocene impact events directly contributed to the climatic deterioration already in progress.

Geochemical Evidence for a Comet Shower in the Late Eocene

“…W e report here methods that make available, in substantial suantities, f~illerene macromolecules occupying this intermediate length range. Our approach involves cutting the nearly endless, highly tangled ropes of nanotubes that are currently available (3,4…”

“…The 100-km-diatneter Popigai crater and the 90-km-diatneter Chesapeake Bay structure are the two largest known craters in " the Cenozoic era and to within dating uncertainty occurred synchronously at 35.6 million years ago (Ma) (1,2). In addition to these and several smaller impact craters, at least two and ~ossiblv manv more lavers of itnpact debris includkg ~nicros~herules, Ir, and shocked quartz have been found in correlative sediments frotn around the world (3)(4)(5)(6). Outside of this brief period, only a few additional i m~a c t lavers are known frotn the entire geologic recoid.…”

Chronostratigraphy, composition, and origin of Ni-rich spinel from the Late Eocene Fuente Caldera section in Spain: One impact or more?

“…Impact horizons have been reported in a number of Upper Eocene sections but their number, geographic extent, and age, as well as their relationship with the two major Late Eocene impact craters, the Popigai in Siberia (>100 km in diameter) (Masaitis et al 1999) and the Chesapeake Bay in northeastern America (40-90 km in diameter) (Koeberl et al 1996;Collins and Wünnemann 2005), have been the subject of debate for many years. A review of the literature shows that at least two Wei 1995), possibly three or four (Keller et al 1987;Hazel 1989;Glass 1990;Molina et al 1993;Montanari et al 1993;Bodiselitsch et al 2004), and up to six (Hazel 1989) impact horizons are supposed to have occurred in sediments from various sections of Late Eocene age. These horizons are characterized by the occurrence of microtektites and microkrystites (Glass et al 1973(Glass et al , 1982(Glass et al , 1987(Glass et al , 2004bJohn and Glass 1974;Keller et al 1987;Glass and Koeberl 1999;Vonhof and Smit 1999) often associated with shocked quartz (Glass and Wu 1993;Clymer et al 1996;Langenhorst and Clymer 1996), Ni-rich spinel (Glass et al , 2004aPierrard et al 1998Pierrard et al , 1999Pierrard 1999;Vonhof and Smit 1999), unusually high iridium concentrations (Asaro et al 1982;Ganapathy 1982;Glass et al 1985;Keller et al 1987;Montanari et al 1993;Pierrard et al 1998;Pierrard 1999;Bodiselitsch et al 2004)…”

Age, chemo- and biostratigraphy of Haiti spherule-rich deposits: a multi-event K–T scenario

“…This conclusion is not justified if one examines the cratering record. For example, the Popigai or Chesapeake Bay craters from the late Eocene, estimated at 100 km and 90 km in diameter, respectively, caused no significant species extinctions (Molina et al 1993;Poag 1997;McHugh et al 1998).…”