AN INTEGRATIVE STRATIGRAPHIC PALEOBIOLOGICAL PERSPECTIVE ON EXTINCTION EVENTS: A CASE STUDY OF THE LATE ORDOVICIAN MASS EXTINCTION

Over the last twenty-five years the field of stratigraphic paleobiology has brought a new perspective to interpreting the fossil record. Stratigraphic paleobiology recognizes that patterns of fossil occurrences reflect both evolutionary and stratigraphic processes, a fact borne out in both modeling and field studies where, for example, last occurrences predictably cluster at major stratigraphic surfaces even when there is no increase in extinction rates. Stratigraphic paleobiology thus provides the framework needed to deconvolve the evolutionary and geological signatures of the fossil record when using field-collected data. However, when evolutionary and stratigraphic processes respond to similar forcings (i.e., common cause), it becomes difficult to distinguish stratigraphically generated clusters of last occurrences from pulses of extinction without an a priori understanding of the drivers of the extinction event. Nonetheless, using forward models of mass extinctions, we demonstrate that the true pattern of extinction can be determined if there is a well-developed understanding of the sequence stratigraphic architecture of the region and we have a knowledge of the taxon facies preferences. Application of this approach to the Late Ordovician mass extinction on Anticosti Island (Québec, Canada) in conjunction with stable isotope and carbonate clumped isotope paleothermometry reveals that the main turnover in brachiopods associated with the extinction event did not occur with the onset of the intensification of the Early Paleozoic Icehouse as has been proposed, but instead occurred later in association with the glacial maximum, challenging the veracity of the two-pulse hypothesis of the Late Ordovician mass extinction.