Most of Earth history consists of long intervals of time dominated by gradual changes in climate and life. These quiet intervals are occasionally punctuated by brief episodes of rapid change. Event stratigraphy is the study of these geologically brief and interesting periods of time in which rapid and sometimes violent changes have occurred. The event stratigraphy approach to the sedimentary record is multi-disciplinary, and involves a variety of laboratory procedures in conjunction with careful field stratigraphic studies. Using this approach, we previously discovered iridium anomalies at the Cretaceous-Tertiary and Eocene-Oligocene boundaries, leading to the formulation of the impact hypothesis and generating a great deal of interest and research on the importance of rare events in Earth history. Using a new analytical technique for rapid iridium measurements developed by our research group, we are in a position to extend this approach to the rest of the Mesozoic and Cenozoic, and have already found a new iridium anomaly in the middle Miocene. We will do the following: (1) a systematic search of the stratigraphic record for new iridium horizons, (2) resolve of the impact vs. volcanism debate over the cause of the Cretaceous- Tertiary mas extinction, and (3) study of the Eocene-Oligocene boundary to resolve discrepancies between iridium peaks, tektites and extinction horizons.
