Early environmental effects of the terminal Cretaceous impact
Published:January 01, 1990
Iain Gilmour, Wendy S. Wolbach, Edward Anders, 1990. "Early environmental effects of the terminal Cretaceous impact", Global Catastrophes in Earth History; An Interdisciplinary Conference on Impacts, Volcanism, and Mass Mortality, Virgil L. Sharpton, Peter D. Ward
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Carbon and nitrogen provide a chemical and isotopic record of the immediate environmental effects of the terminal Cretaceous impact. At Woodside Creek, New Zealand, kerogen carbon is enriched 15-fold, and total sediment nitrogen 20-fold in the basal layer of the boundary clay. Both elements show marked changes in their isotopic compositions on a millimeter scale, which may reflect the rapid sweep-out of plankton by ejecta fallout. The enrichment of nitrogen may reflect a contribution of HNO3 acid rain from a shock-induced combination of N2 and O2, but would not be expected from volcanism.
Ground truth for such sudden fallout on the oceans is obtained from the 9-cm-thick Toba ash layer in the Indian Ocean. The accumulation rates of organic carbon and carbonate rise by ~3 orders of magnitude at the base of the ash layer, but then drop by 1 to 4 orders of magnitude after 3 to 4 cm. Apparently 3 to 4 g/cm2 of the Toba ash efficiently scavenged and buried virtually all the CaCO3 and much of the particulate organic material in the ocean up to 2,000 km from the site of the eruption. Presumably the 2 to 5 g/cm2 of Cretaceous/Tertiary (K/T) ejecta were no less efficient, in view of their much finer grain size. It is significant that the amounts of marine and land biomass at the K/T boundary are approximately equal to the steady-state global inventory (one generation), as are the amounts of other enriched terrestrial elements (As, Sb, Zn). This is expected in a catastrophic but not a gradualist scenario.