Catastrophe at the end of the Cretaceous? The shallow marine biotic and geochemical record of the Cretaceous-Paleogene (K-Pg) mass extinction event

James Witts (March 28, 2019)

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The Cretaceous-Paleogene (K-Pg) mass extinction event 66 million years ago is the most recent of the 'Big Five' Phanerozoic extinction events, and is most famously associated with the loss of non-avian dinosaur-dominated ecosystems on land, and marine reptiles and ammonoid cephalopod mollusks in the oceans. It is now almost forty years since the famous paper by Alvarez et al. (1980) proposed this extinction was caused by the catastrophic impact of a 10 km-diameter bolide (responsible for the formation of the Chicxulub crater in the Yucatan Peninsula, Mexico), and a vast body of work exists which supports this hypothesis. However, the extinction also coincides with the emplacement of the Deccan Traps Large Igneous Province (LIP) in continental India, which based on new high-precision dating, occurred over a <750 thousand year period of the latest Cretaceous and early Paleogene. Given the widespread evidence that LIP volcanism is ultimately responsible for at least three of the other 'Big Five' events, disentangling the effects of volcanically-driven climate and oceanographic changes from the effects of the bolide impact is critical to understanding the fate of various groups of organisms during this interval of rapid global environmental change. Did volcanism cause extinctions and ecosystem instability prior to the Chicxulub impact event (the 'Press-Pulse' hypothesis)? I have been investigating this question using faunal and geochemical data from shallow marine K-Pg successions in Antarctica and the United States Atlantic and Gulf Coastal Plains which demonstrate the complexities of the K-Pg extinction event.