Source:http://linkedlifedata.com/resource/pubmed/id/17783047
Science 1984 Sep 7 225 4666 1030-2
General Info
Abstract
The palynologically defined Cretaceous-Tertiary boundary in the western interior of North America occurs at the top of an iridium-rich clay layer. The boundary is characterized by the abrupt disappearance of certain pollen species, immediately followed by a pronounced, geologically brief change in the ratio of fern spores to angiosperm pollen. The occurrence of these changes at two widely separated sites implies continentwide disruption of the terrestrial ecosystem, probably caused by a major catastrophic event at the end of the period.
PMID
17783047