Over the past 25 years the Chicxulub impact has become the commonly acceptedcause for the end-Cretaceous (K-T) mass extinction whereas other catastrophes, suchas volcanism and climate change, are considered at best secondary effects. However,this popular scenario can no longer be supported by the emerging database on thebiotic effects of the Chicxulub impact in Mexico and Texas. At these localities theimpact spherule ejecta layer is stratigraphically well below the sandstone complex,which has been interpreted as impact-generated mega-tsunami, and in Texas the K-Tboundary is also well above. The sandstone complex, which inﬁlls submarine canyonsformed during the latest Maastrichtian sea level fall and cooling (100-150 ky) thatfollowed the greenhouse warming between 400-150 ky before the K-T boundary. Incontrast, the impact spherule layer in undisturbed marls 4 m below was depositedduring the global warming near the base of zone CF1, or ∼300 ky before the K-Tboundary. Evaluations of the biotic effects across the Chicxulub impact layer in Mex-ico and Texas reveal that out of a total of 52 species not a single species went extinct.No signiﬁcant changes occurred in species populations, climate, or sedimentary en-vironments as a result of this impact. This suggests that even a second much largerimpact at the K-T boundary would likely have been insufﬁcient to cause the K-T massextinction. If not the Chicxulub impact, what caused the K-T mass extinction? Dec-can volcanism is the other major catastrophe near the end of the Cretaceous.
|Journal||Geophysical Research Abstracts|
|State||Published - 1 Jan 2008|