The K-T Boundary

Abstract

Chronostratigraphic boundaries have great importance in the geosciences. These occur in both marine and continental realms, provide key markers for geological cor- relations, and for attaining more refined paleogeographic and biogeographic recon- structions. Stage boundaries are commonly characterized by significant geological and paleobiological events which leave a distinct signature in the stratigraphic record. The Cretaceous-Tertiary (K–T) boundary marks the end of the Mesozoic Era, about 65 million years ago, when widespread oceanic basins had global circulation patterns somewhat similar to present day (e.g. Gordon, 1973; Berggren and Hollister, 1974; Hancock and Kauffman, 1979; Haq et al., 1987, 1988). For the last two decades of the 20th Century there has been much multidisciplinary research on more than 200 K–T boundary sections worldwide, with about two-thirds being outcrops (Lima, 1999, and references therein), from oceanic to marginal basins, interior seaways and continental sites. This makes the K–T transition the best documented ever in pub- lished geoscience literature. This paper summaries these results and in so doing shows the strengths and weak- ness of the different approaches that have been used.