Benthic foraminifera across the Cretaceous–Tertiary (K–T) boundary: a review

Abstract

The response of the Earth’s biota to global change is of fundamental interest to paleontologists, but patterns of change in paleontologic data are also of interest to a wider spectrum of Earth scientists in that those patterns are of great significance in constraining hypotheses that attempt to explain physical changes in the Earth’s environment. The Cretaceous–Tertiary (K–T) boundary is a case in point. Some paleontologists have criticized the bolide impact hypothesis, not because they deny the impact but because the proposed effects of that impact do not always conform to the available paleontological data. Benthic foraminifera are of particular interest in this context because it has been suggested for over 20 years that shallow-water benthic foraminifera were affected more severely than deep-water benthic foraminifera by events at the K–T boundary. This observation adds to the fact of planktonic foraminiferal extinction and indicates that K–T boundary environmental effects were largely restricted to shallow waters. In this paper I review all published works on smaller benthic foraminifera at the K–T boundary and conclude the following. (1) Shallow-water benthic foraminifera were not more severely affected than deeper dwelling species. True extinction, as opposed to local extinction and/or mass mortality, is generally quite low no matter what the water depth. (2) The data are not sufficient in quality, quantity and geographic range to conclude that there is a latitudinal pattern of extinction. (3) In general, biotic changes (such as they are) begin before the boundary in shallow and intermediate depth waters and at the boundary in deep water. Disagreements about the placement of the boundary and the presence, absence and duration of hiatuses hinder more precise conclusions. (4) There appears to be preferential survivorship of epifaunal species into the early Danian with a short interval dominated by infaunal taxa in the earliest Danian. This pattern can best be explained by short-lived input of increased amounts of organic matter at the boundary followed by a sudden collapse of primary productivity and, hence, major reduction or cessation of organic flux to the seafloor. In summary, based on the current dataset, smaller benthic foraminifera, no matter whether they lived in shallow or deep waters, high or low latitudes, or infaunal or epifaunal microhabitats, survived the environmental events across the K–T boundary quite well. Mass extinction does not characterize this group of organisms at this time.