Freeze-dried sediment samples, typically 0.5 to 1.0 g, were pulverized in a high-purity alumina mortar. Powders weighing ~100 mg were sealed in quartz-glass tubes and irradiated at the University of Missouri Research Reactor Facility for 40 hr at a neutron flux of 5 × 1013n/cm2/s. Following irradiation, Ir was chemically purified using a procedure similar to that described by Kyte et al. (1993) and counted on intrinsic Ge detectors for up to 24 hr, beginning about 1 month following irradiation.