IMPROVED CHARACTERIZATION OF UNCERTAINTY IN TIME SCALE DEVELOPMENT

The refinement of geologic times scales has depended on improvements in radioisotope dating, as well as advances in the development of other types of chronometers, such as astrochronologies based on characterization of orbital cycles in stratigraphy. The integration of these floating high-resolution time scale methods with fixed age determinations has produced some of the most exciting advances in geochronologic resolution for deep time study intervals. In addition to the reduced uncertainties stemming from analytical improvements in radioisotopic determinations, however, consideration of additional uncertainty associated with astrochronologies has been needed in order to determine accurate total uncertainty. Uncertainties stemming from stratigraphic correlations, which are commonly required to integrate ages derived from outcrop samples with time series that preserve orbital forcing, best derived from cores, are also needed for a complete assessment of total uncertainty. The well-preserved successions of Upper Cretaceous strata from the Western Interior basin provide a unique opportunity to examine the additive effects of radioisotopic, astrochronologic, and stratigraphic uncertainties in the calculation of total uncertainty, for example, for revised stage boundary ages. The presence of abundant, datable volcanic ash beds intercalated within rhythmically bedded, carbonate-rich hemipelagic facies that host a mature and diverse biostratigraphic framework makes this basin an ideal system in which to refine and improve time scale methods.