Temperature trends of the Late Cambrian through the Middle Ordovician : implications for Ordovician climate and biodiversification
Abstract
[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI SYSTEM AT REQUEST OF AUTHOR.] The Ordovician Period includes both the largest and longest period of sustained biodiversification--the Great Ordovician Biodiversification Event (GOBE)--and the second-largest mass extinction of the Phanerozoic--the end Ordovician mass extinction. Climate change has been invoked as a contributing factor to both events. Much research has focused on the end Ordovician extinction and thus, paleotemperatures of the last 15 million years of the period are relatively well documented. Data for the Early and Middle Ordovician are much more limited. Although the number of Early to Middle Ordovician climate studies has increased over the last decade, the record of climate change leading into the GOBE is still incomplete. To begin to address this problem, I generated [delta][superscript 18] O data at three new localities and increased sampling density at a fourth. New data combined with previous records suggest that cooling occurred between the latest Cambrian and Early Ordovician, that little change occurred during the Early Ordovician, and that additional cooling occurred by the Middle Ordovician. However, temperatures remained above modern levels through the GOBE. While climate change may have played a role in the GOBE, the relatively low magnitude and relatively late timing of the cooling argue that cooling is unlikely to be the primary trigger for the event.
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