The Response of the Marine Osmium Isotope Record to Impact Events

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The Response of the Marine Osmium Isotope Record to Impact EventsGregory Ravizza, EAR-0843930University of HawaiiABSTRACTAn extensive, but incompletely preserved, record of impact craters on the Earth demonstrates that large projectiles from space have repeatedly hit Earth?s surface. Although the Cretaceous-Tertiary mass extinction some 66 million years ago coincides precisely with the largest known impact event of the last 500 million years, the environmental consequences of numerous other large impact events remain poorly understood and documented. In order to study the response of the Earth system to these large, abrupt perturbations, it is essential to be able to reliably recognize an impact horizon globally throughout the sediment record. Currently elevated iridium (Ir) concentrations are most commonly used to try to recognize impact horizons far removed from the site of impact, but the results are often ambiguous. The research supported by this award will test the usefulness of combining measurements of Osmium (Os) isotope ratios (187Os/188Os) with Os and Ir concentrations to reliably identify impact horizons, and also to estimate projectile size. This will be accomplished by performing these analyses in well studied marine sediment sequences that are known to have accumulated during the time that large impact craters formed. Some of the sites to be studied are relatively close to the impact site while others are located thousands of kilometers away. PI's previous work using Os isotopes to recognize impact events in deep sea sediments composed mainly of calcium carbonate microfossils have yielded promising results. In this new study he will investigate if compositionally different types of marine sediments can also reliably record the chemical signatures of large impact events. Completion of these research objectives will show if the marine Os isotope record represents a new and unparalleled record of impact events through Earth history, or simply a modest augmentation of the often ambiguous record of impacts obtainable through the study of Ir concentration data alone. If the former is true this work will make lasting contributions to event stratigraphy and global correlations of the sediment record, as well as to understanding abrupt perturbations of Earth's climate system by large impact events.