Michael M. Joachimski Oliver Lehnert S. M. Bergstrom John E. Repetski Werner Buggisch 2009 <p><span>Oxygen isotopes measured on Late Ordovician conodonts from Minnesota and Kentucky (United States) were studied to reconstruct the paleotemperature history during late Sandbian to Katian (Mohawkian&ndash;Cincinnatian) time. This time interval was characterized by intense volcanism, as shown by the prominent Deicke, Millbrig, and other K-bentonite beds. A prominent carbon isotope excursion (Guttenberg &delta;</span>¹³<span>C excursion, GICE) postdates the Millbrig volcanic eruptions, and has been interpreted to reflect a drawdown of atmospheric carbon dioxide and climatic cooling. The oxygen isotope record in conodont apatite contradicts this earlier interpretation. An increase in &delta;</span>¹⁸<span>O of 1.5&permil; (Vienna standard mean ocean water) just above the Deicke K-bentonite suggests an abrupt and short-lived cooling that possibly initiated a first short-term glacial episode well before the major Hirnantian glaciation. The decrease in &delta;</span>¹⁸<span>O immediately after the mega-eruptions indicates warming before the GICE, and no cooling is shown in the GICE interval. The coincidence of the Deicke mega-eruption with a cooling event suggests that this major volcanic event had a profound effect on Late Ordovician (late Mohawkian) climate.</span></p> application/pdf 10.1130/G30577.1 en Geological Society of America Did intense volcanism trigger the first Late Ordovician icehouse? article