Meteorite impact, extinctions and the Cretaceous-Tertiary Boundary

Abstract

At present the two major hypotheses to explain the mass-extinctions at the Cretaceous-Tertiary boundary (KTB) are a large meteorite impact and widespread volcanism. High resolution stratigraphy across the Cretaceous-Tertiary boundary in the Agost and Caravaca sections in Spain provides a test for these hypotheses. Hard to explain by any sort of volcanism are the shocked minerals, stishovite and the round form and distribution of microtektite remains, which are found worldwide at the KTB. It is now likely that several impacts occurred simultaneously. The low REE-abundances in the KT ejecta layer and quench crystals of clinopyroxene and other crystalline textures in the KTB microtektites betray an impact in ocean-floor basalt, whereas shocked quartz and stishovite favour a continental target. Stable oxygen and carbon isotope studies of both sections offer a glimpse of what catastrophic environmental changes may in fact have caused the extinctions. Carbon isotopes show that photosynthesis was strongly reduced at the KTB. A 8°C rise in ocean surface temperatures indicates that a greenhouse atmosphere followed the impact event. This greenhouse atmosphere may have lasted for several thousands of years.