Did intense volcanism trigger the first Late Ordovician icehouse?
Did intense volcanism trigger the first Late Ordovician icehouse?
Geology (Boulder) (April 2010) 38 (4): 327-330
- ancient ice ages
- apatite
- biochemistry
- causes
- Cincinnatian
- Conodonta
- cooling
- eruptions
- geochemistry
- icehouse effect
- isotope ratios
- isotopes
- Kentucky
- microfossils
- Middle Ordovician
- Minnesota
- Mohawkian
- O-18/O-16
- Ordovician
- oxygen
- paleoclimatology
- paleotemperature
- Paleozoic
- phosphates
- stable isotopes
- United States
- Upper Ordovician
- volcanism
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-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 (super 13) 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 (super 18) O of 1.5 per mil (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 (super 18) 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.