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McLean, D. M., 1981, Abstract in Abstracts of Papers of the 147th National Meeting, 3-8 January 1981, Toronto, Ontario, Canada, American Association for the Advancement of Science, p. 128.

Terminal Cretaceous Extinctions and Volcanism: a Link

Fluctuation of the carbon cycle was proposed as a factor in the terminal Cretaceous extinctions of the dinosaurs and some marine CaCO3-producing planktonic organisms (McLean, 1978). The source of the fluctuation is now identified as continental flood basalt volcanism spanning the Cretaceous-Tertiary boundary that produced the Deccan Traps of India. One of the greatest outpourings of lava in geologic history, it accounts for the enhancement of siderophile elements (iridium, osmium, etc.) in the extinction-age strata (in cosmic proportions); the terminal Cretaceous marine CaCO3 dissolution event: and warming of deep and shallow oceans across the Cretaceous-Tertiary boundary (Boersma, et al., 1979), and associated negative surficial marine carbon isotope values. Siderophiles are concentrated in earth's iron core, probably in more nearly cosmic proportions than in earth's crustal rocks; deep mantle plumes originating near earth's core-mantle boundary would bring deep mantle material and siderophiles to the surface; Morgan (1972) suggested that the Deccan volcanism resulted from the Indian plate migrating over the Reunion plume. Volcanic gases (CO2, HCl, SO2) injected into the oceans would lower the pH, triggering CaCO3 dissolution in shallow waters, and extinctions among marine CaCO3-producing microplankton. Accumulation of CO2 in the atmosphere would have caused "greenhouse" conditions and the dinosaurian extinctions. CO2 in volcanic emanations have a d13C -value about –7‰, and reduced carbon in igneous rocks –19 to –28‰.