A MAJOR CONODONT EXTINCTION EVENT DURING THE EARLY ORDOVICIAN WITHIN THE MIDCONTINENT REALM

The major change in the Lower Ordovician conodont faunas of the Midcon tinent Realm was recognized by earlier workers. Our recent intense stu dy of Midcontinent conodonts from the St. George Group, Port au Port P eninsula, western Newfoundland, has shown that seven major conodont li neages, involving some 33 multielement species, completely terminate i n the late Tremadoc Series, within an interval of a few metres, at a l evel between the Lower Ordovician conodont Fauna C and Fauna D. The ex tinction event occurs during the peak of a regressive phase within the deposition of the St. George Group and at a time of apparent global e ustatic fall at or slightly below the Tremadoc-Arenig series boundary. This important extinction bioevent has been recognized throughout the Midcontinent Realm in North America.