Punctuation and Stasis In the Marine Os Isotope Record, and Implications for Changing Oceanic Inputs

In this presentation high temporal resolution records from pelagic carbonate sequences will be compared to low-resolution records. In general, stratigraphic control in pelagic carbonate records is based on combined biostratigraphy, magnetostratigraphy and stable carbon and oxygen isotope stratigraphy. As a result age control in these records is superior to more slowly accumulating record based on Mn crusts and pelagic clays. The temporal resolution of most of pelagic carbonate records is between 20 and 100 kyrs and the durations are typically 1 to 2 million years. In addition to reviewing data from the Eocene-Oligocene transition and the late Maastrichtian that are either published or in press, unpublished data from the middle Miocene climate transition, and the Pleistocene will be presented. The overall structure of the high-resolution records differs distinctly from the low-resolution records. Although low-resolution records are difficult to date, they provide a clear impression that during much of the Cenozoic the marine Os isotope budget is not at steady state. That is to say that during much of the last 65 million years the slope of marine Os isotope record is non-zero. In contrast to this picture of gradual change, higher-resolution records frequently appear to be close to steady state, punctuated by relatively brief perturbations. These results suggest that low-resolution records based on Mn crusts and pelagic clays may be influenced by aliasing due to under-sampling, bioturbation and/or diagenesis. If higher-resolution data from carbonate sequences accurately capture temporal variations in the Os isotope composition of seawater, then they suggest that the marine Os isotope record may have more value as tool in event stratigraphy than as a tool for estimating depositional ages. High-resolution records also hint that forcing of the marine Os isotope record by tectonic process is more abrupt than previously thought.