Accretion of Extraterrestrial Matter to the Earth: The Sedimentary Record

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The proposed research program will make major advances in the understanding of the chemical and mineralogical record of the accretion of extraterrestrial matter to the Earth, as recorded in terrestrial sediments. In the next three years we propose research into the mineralogy and geochemistry of debris from three distinct impact events. 1) We will characterize the abundance, distribution, and composition of Cretaceous-Tertiary boundary impact debris in the Pacific Ocean basin. This will approximately double the portion of the Earth's surface studied in this way and will probably result in the most definitive study to date of the composition of this debris. 2) We will investigate the detailed geochemistry of an early Archean (~3.4 Ga) spherule bed which marks a major asteroid impact as well as a major change in the tectonic evolution of the Barberton Greenstone Belt. We will concentrate on determining whether there is geochemical evidence to support the hypothesis that gradations across the spherule bed reflect chemical and thermal evolution of an impact-generated vapor cloud. 3) We plan initial characterization of new sediments and debris recording an asteroid impact into the subantarctic South Pacific during the late Pliocene. The sediments will be from piston cores that are scheduled for sampling in Jan. 1994.//