NCAR, United States

Ir concentrations and mass accumulation rates from nine deep-sea cores, one from the Atlantic Ocean and eight from the Pacific Ocean, were compiled to evaluate a new technique for determining mass accumulation rates. The technique is based on the large difference of the high Ir abundance in extraterrestrial matter versus the low Ir contents in terrestrial material. Assuming a constant flux of cosmic matter, this difference leads to high Ir concentrations in slowly accumulating sediments, versus low Ir concentration in rapidly accumulating sediments. The method is independent of stratigraphic control, and does not require knowledge of age of the deposit. We note that Ir concentrations in some slowly accumulating sediments are of the same order of magnitude as some of those reported for the Cretaceous-Tertiary boundary event.