Possible climatic impact of the Middle Ordovician Millbrig-Big bentonite ultraplinian volcanic eruption
- Univ. of Cincinnati, OH (United States). Dept. of Geology
- Illinois State Geological Survey, Champaign, IL (United States)
- Ohio State Univ., Columbus, OH (United States). Dept. of Geological Sciences
The Middle Ordovician Millbrig K-bentonite in North America and the Big Bentonite of northern Europe represent the same volcanic eruption and constitute one of the largest explosive ash falls known in the geologic record. The total dense rock volume of magma ejected is estimated to have been 1251 km[sup 3] with an mass discharge rate near the theoretical maximum of 10[sup 9] kg/s. The eruptive column reached a height of 55 km and was sustained for about 15 day creating a plume of fine ash and aerosol compounds that spanned the Iapetus Ocean between Baltica and Laurentia. Microprobe analyses of apatite melt inclusions give average compositions equivalent to rhyolite with a calculated water content of 4-5 wt%. Total sulfur expressed as SO[sub 2] averages 0.038 wt %, which is about twice the petrographic value reported for the 1991 eruption of Mt. Pinatubo. The authors estimate the volume of sulfur injected into the stratosphere during the Millbrig-Beg Bentonite eruption was 59 Mt of elemental S equivalent to 118 Mt of SO[sub 2]. The conversion to sulfate aerosol would have yielded approximately 177 Mt of H[sub 2]SO[sub 4] droplets. This is 1 to 3 orders of magnitude larger than any previously reported historic or pre-historic eruption and would have been capable of inducing sudden climatic change by altering the Earth's radiation budget. The climatic response to volcanic loading would have lowered global temperatures by several degrees for a period of 3-5 years. The lack of evidence for a corresponding mass extinction or for an immediate onset of widespread glaciation suggests short-term catastrophic climatic events, such as those resulting from volcanic eruptions, may not, in themselves, bring about long-term regional climatic or biologic changes.
- OSTI ID:
- 5933028
- Report Number(s):
- CONF-9303211--
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Journal Name: Geological Society of America, Abstracts with Programs; (United States) Vol. 25:2; ISSN GAAPBC; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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540110
58 GEOSCIENCES
580000* -- Geosciences
APATITES
ATMOSPHERIC CHEMISTRY
BENTONITE
CHEMICAL COMPOSITION
CHEMISTRY
CLAYS
CLIMATE MODELS
CLIMATIC CHANGE
DEPOSITION
ELEMENTS
ERUPTION
EUROPE
GEOLOGIC AGES
GEOLOGIC DEPOSITS
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
IGNEOUS ROCKS
INCLUSIONS
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
MAGMA
MATERIALS
MATHEMATICAL MODELS
MICROANALYSIS
MINERALS
NONMETALS
ORDOVICIAN PERIOD
PALEOCLIMATOLOGY
PALEONTOLOGY
PALEOZOIC ERA
PHOSPHATE MINERALS
ROCKS
SULFUR
SULFUR CONTENT
VOLCANIC ROCKS
VOLCANOES