In-situ Ir concentration measurements in KT-boundary sediments by accelerator secondary ion mass spectrometry

Abstract

Accelerator SIMS is the extension of secondary ion mass spectrometry (SIMS) with accelerator mass spectrometry (AMS) by which molecular interferences in the SIMS spectrum are removed. The potential of the PSI/ETH accelerator SIMS facility with respect to concentration analysis is demonstrated by presenting in-situ iridium concentration measurements in sedimentary layers around the Cretaceous–Tertiary transition (KT-boundary) from the Starkville South section, Raton basin, Colorado. In these sediments an iridium concentration anomaly is believed to originate from the impact of a meteorite 65 million years ago. By accelerator SIMS iridium concentrations in the range of 0.1 ng/g could be measured with a lateral resolution of ∼100 μm reproducing neutron activation analysis data. The characteristics of accelerator SIMS together with boundary conditions influencing measurements are discussed.