Abstract
A widespread debate on the Cretaceous/Tertiary (K/T) boundary (65 ± 1 Ma) extinctions has largely revolved around an impact or a volcanic cause. Evidence for both events is strengthened by recent work. Impact-triggered Deccan volcanism or independent impact and mantle plume events have been suggested. This review examines evidence for both events and suggests that they overlapped in time, but with globally uneven effects. The combined effects produced generally inhospitable K/T environments leading to mass extinctions, although some life forms flourished afterwards. Volcanic contributions to the K/T boundary environment probably include increased Platinum Group Element (PGE) and acid rain fall out, particularly from large scale mantle upwellings e.g. Deccan, Cameroon and Coral Sea events. A previously proposed post-K/T Greenland starting plume apparently already existed in the Cretaceous. K/T features such as the Iridium (Ir) anomaly most likely include longer term volcanic as well as sudden meteoritic impact contributions. Volcanic contributions were greatest from Southern Hemisphere sources, whereas meteorite impacts featured in the Northern Hemisphere.
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