Recognizing artifactually generated coordinated stasis: implications of numerical models and strategies for field tests

A null model that generates the first and last occurrences of species through time in a single stratigraphic section predicts several patterns startlingly similar to those described as coordinated stasis. The model is able to produce these patterns by assuming stochastically constant extinction and origination rates, a Gaussian form of facies control with respect to water depth, and cyclically varying water depths in accord with sequence stratigraphy. The model predicts that highstand and lowstand systems tracts will be characterized by faunal tracking with only minor amounts of faunal turnover. Sequence boundaries and flooding surfaces within the transgressive systems tract will be characterized by elevated rates of faunal turnover. These pulses of faunal turnover will exhibit ecological selectivity in terms of the preferred depths, facies tolerances, and abundance of species. Where outcrop patterns of first and last occurrences match these predictions, biologically-driven or environmentally-driven coordinated stasis may not be distinguishable from stratigraphic artifact. However, pulses of faunal turnover that occur within highstand and lowstand systems tracts are likely to be real turnover events. Multiple outcrop studies that span a significant distance along paleoslope are necessary to disprove artifactual turnover that occurs at a sequence boundary or within a transgressive systems tract.