Effects of late Eocene impacts on planktic foraminifera

Abstract

A series of iridium anomalies and microtektite-bearing layers indicative of extraterrestrial impact events have been found in late Eocene sediments in the deep sea. Previously, these deposits had been reported to be approximately synchronous with major extinction events in groups of both terrestrial and marine organisms. Highresolution biostratigraphic studies, though, have failed to find any direct evidence for association between impact-derived materials and species extinctions in individual stratigraphic sequences. In addition, stable isotopic studies of the deep-sea record reveal abundant evidence for an episode of major climatic change beginning in the middle Eocene and continuing through the Oligocene. A new analysis of patterns of taxic richness, extinction rates, and origination rates in 17 Eocene through Oligocene planktic foraminiferal biozones indicates that relatively high numbers of planktic foraminiferal taxic extinctions are not confined to the Eocene/Oligocene boundary, or to biozones containing impact ejecta (e.g., microtektite layers, Ir anomalies). Instead, virtually all middle Eocene through middle Oligocene biozones are characterized by broadly comparable numbers of taxic extinctions. However, analysis of relative abundances of individual species and patterns of morphometric variation in middle and late Eocene populations of planktic foraminifera suggest that impacts may have had substantial and long-lasting effects on the dynamics of local populations within areas of direct environmental perturbation. In order to understand the local biotic effects and potential evolutionary role of events such as extraterrestrial impacts, it is important that detailed analyses of species-and population-level patterns of morphological variation and faunal turnover proceed in concert with coarser grained investigations so that patterns of variation can be compared on a wide variety of taxonomic and stratigraphic scales (e.g., species-level versus family-level taxonomic resolution, biozone-level versus stage-level stratigraphic resolution).

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

“…The index species used to define these biozone boundaries are shown in Figure 10. This stratigraphic refinement improves the relative age correlation and in Montanari, 1988, 1990. particular aids in the stratigraphic placement of the impact horizons which were found in the late Eocene.…”

The Chesapeake Bay bolide impact: a convulsive event in Atlantic Coastal Plain evolution

“…According to some authors, a crater this size could be expected to cause a mass extinction of 45 percent of the marine life on Earth (Raup, 1991a,b). Extensive studies of late Eocene biotic events during the past ten years have shown conclusively, however, that no such mass extinction took place during biochron P15 (MacLeod, 1990;Miller et al, 199 1;Prothero and Berggren, 1992;Jansa, 1993).…”

Biogeography of cretaceous/tertiary (k/t) planktic foraminifera

“…Thus, these planktic foraminiferal data also fail to support the contention of Gould (1985) and Raup (1986Raup ( , 1991 that mass extinction events in general, and the K/T event in particular, derive from fundamental changes in the nature of selection pressures brought on by intermittent collisions with extraterrestrial objects such that previously well-adapted species (or morphotypes) lose their competitive edge in the face of extraordinary environmental circumstances. MacLeod (1990) analyzed the temporal dynamics of the Eocene -Oligocene turnover, concluding that: i.) the turnover took place over at least eight different planktic Downloaded by [University of Calgary] at 06:25 03 February 2015 foraminiferal biozones that, together represent almost 12 m.y.…”