Oxygen Isotope Constraints on the Origin of Impact Glasses from the Cretaceous-Tertiary Boundary

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Abstract
Laser-extraction oxygen isotope and major element analyses of individual glass spherules from Haitian Cretaceous-Tertiary boundary sediments demonstrate that the glasses fall on a mixing line between an isotopically heavy (δ18O = 14 per mil) high-calcium composition and an isotopically light (δ18O = 6 per mil) high-silicon composition. This trend can be explained by melting of heterogeneous source rocks during the impact of an asteroid (or comet) ∼65 million years ago. The data indicate that the glasses are a mixture of carbonate and silicate rocks and exclude derivation of the glasses either by volcanic processes or as mixtures of sulfate-rich evaporate and silicate rocks.