Trace-fossil model for reconstruction of paleo-oxygenation in bottom waters

Recognition of fluctuations in the degree of paleo-oxygenation of bottom waters recorded in fine-grained pelagic strata is important for interpretation of paleoceanographic and paleoclimatologic conditions. General sedimentary fabric, composition of trace-fossil assemblages, and burrow size and crosscutting relationships have been incorporated into a trace-fossil tiering model that permits detailed reconstruction of changes in paleo-oxygenation of bottom waters. Applications of this model to the Miocene Monterey Formation (California) and the Cretaceous Niobrara Formation (Colorado) indicate that the ichnologic approach is more sensitive to both magnitude and rates of change in oxygenation levels compared to macrobenthic body-fossil information.