The Cretaceous-Tertiary Boundary: Chronostratigraphic Position and Sequence of Events

Abstract

The Cretaceous-Tertiary boundary has always been considered to be exceptional and linked to special events and mechanisms where catastrophes have often been advocated. The boundary stratotype, Stevns Klint in Denmark, has been paleomagnetically analysed. The C/T boundary is now given an absolute age of 66.7 m.y. The boundary is shown to have occurred under stable geomagnetic conditions, about 165,000 years before the polarity reversal of the base of Anomaly 29, and about 0.7-1.0 m.y. before the extinction of dinosaurs in New Mexico. Significant disturbances in the Earth's rate of rotation and direction of spin axis at the passing from the Cretaceous into the Tertiary are strongly contradicted. The CAT boundary events cannot be explained by a single large catastrophe. A sequence of different events and some gradualism need also to be included in present and future scenarios of the boundary events.