THE LAST 250 KYR BEFORE THE END-CRETACEOUS MASS EXTINCTION
Here we examine the environmental events during the 250 ky that preceded the mass extinction. Deccan volcanism occurred in three phases (C30n, C29r, C29n). We are concerned here with just the main phase-2 that erupted >1.1 million km3 basalts (80% of total by volume) depositing ~3000 m of stacked lava flows over a period of only 250 ky. Deccan phase-2 eruptions caused rapid though fluctuating global warming of 8°C on land and 4°C in the oceans sandwiched between hyperthermal warming at the base C29r and ending with a hyperthermal warming prior to the KTB.
On a global basis, planktic foraminiferal assemblages show increasingly high-stress environments in CF2-CF1 evident by dwarfed species, decreased diversity, blooms of the disaster opportunist Guembelitria cretacea, and near disappearance of large, robust species particularly in zone CF1 preceding the mass extinction. During the last 30-50 ky before the mass extinction, hyperthermal warming, decreased species diversity and abundance, shell dissolution and ocean acidification, low magnetic susceptibility and high mercury concentrations have all been linked to the most intense phase of Deccan volcanism. These data demonstrate that the KTB mass extinction was not an instantaneous event but occurred over a few thousand to several tens of thousands of years ending at the KTB. The Chicxulub impact can no longer be considered the sole cause, or even primary cause for this mass extinction event.