He Isotopic Composition of Micrometeorites as a Tool for Evaluating Sedimentation Rates

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9402019 ANDERSON During their travel in the inner solar system, fine cosmic dust particles acquire large amounts of noble gases owing to their surface to volume ratio. When these particles enter the earth's atmosphere, those sufficiently small to enter the earth's atmosphere at cosmic velocities without suffering ablation, are called micrometeorites and retain their noble gases, including He. Not only do the micrometeorites have high He concentrations, but they also have very high 3He/4He ratios, several orders of magnitude above that of terrigenous materials. The micrometeorites eventually settle down to the bottom of the ocean where they are mixed with other sediments. This project will use the bulk sediment He concentration and isotopic composition as a measure of micrometeorite concentration in the sediments. If the flux of micrometeorites to the earth has remained constant in geological past, then their concentration in sediments can be used to quantitatively evaluate sedimentation rates and the fluxes of different sedimentary components and changes in these fluxes through time. This research will test the assumptions that the flux of micrometeorites to the sediments have stayed constant over time and that the micrometeorites in sediments retain their He for time-scales of interest. If successful, this approach will expand our ability to look at high resolution sedimentation rates to millions of years.