Paleobiogeographic patterns of the Cretaceous-Tertiary (K-T) mass
extinction in planktonic foraminifera in Tunisia, spanning environments
from open marine upper bathyal, to shelf and shallow marginal settings,
indicate a surprisingly selective and environmentally mediated mass
extinction. This selectivity is apparent in all of the environmental
proxies used to evaluate the mass extinction, including species
richness, ecological generalists, ecological specialists, surface and
subsurface dwellers, whether based on the number of species or the
relative percent abundances of species. The following conclusions can be
reached for shallow to deep environments: about three quarters of the
species disappeared at or near the K T boundary and only ecological
generalists able to tolerate wide variations in temperature, nutrients,
salinity and oxygen survived. Among the ecological generalists
(heterohelicids, guembelitrids, hedbergellids and globigerinellids),
only surface dwellers survived. Ecological generalists which largely
consisted of two morphogroups of opportunistic biserial and triserial
species also suffered selectively. Biserials thrived during the latest
Maastrichtian in well stratified open marine settings and dramatically
declined in relative abundances in the early Danian. Triserials thrived
only in shallow marginal marine environments, or similarly stressed
ecosystems, during the latest Maastrichtian, but dominated both open
marine and restricted marginal settings in the early Danian. This highly
selective mass extinction pattern reflects dramatic changes in
temperature, salinity, oxygen and nutrients across the K-T boundary in
the low latitude Tethys ocean which appear to be the result of both
long-term environmental changes (e.g., climate, sea level, volcanism)
and short-term effects (bolide impact). (C) 2002 Elsevier Science B.V.
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