Cenomanian-Turonian boundary event
Encyclopedia
The Cenomanian-Turonian boundary event, also known as the Cenomanian-Turonian extinction event, the Cenomanian-Turonian anoxic event, and referred to in Europe as the Bonarelli Event, was the latter of two anoxic
extinction event
s early in the Late Cretaceous
period. The event occurred approximately 91.5 ± 8.6 million years ago, and brought about the extinction of the ichthyosaurs and pliosaurs. Although the cause is still uncertain, the result starved the Earth's oceans of oxygen for nearly half a million years, causing the extinction of approximately 27 percent of marine invertebrates
. This global environmental disturbance increased atmospheric and oceanic temperatures. Boundary sediments show an enrichment of trace elements, and contain elevated 613C values.
One possible cause was sub-oceanic volcanism occurring approximately 500,000 years earlier. During that period, the rate of crustal production reached its highest level for 100 million years. This was largely caused by the widespread melting of hot mantle
plumes under the oceans at the base of the lithosphere
. This resulted in the thickening of the oceanic crust in the Pacific and Indian Ocean
s. This volcanism would have produced large quantities of carbon monoxide into the atmosphere, leading to global warming. Within the oceans, the emission of SO, H2S, CO, and halogen
s would have increased the acidity of the water, causing the dissolution of carbonate, and a further release of carbon dioxide. When the volcanic activity declined, this run-away greenhouse effect
would have likely been put into reverse. The increased CO2 content of the oceans could have increased organic productivity in the ocean surface waters. The consumption of this newly abundant organic life by aerobic bacteria would produce anoxia and mass extinction. The resulting in elevated levels of carbon burial afterwards would accounting for the black shale deposition in the ocean basins.
Anoxic event
Oceanic anoxic events or anoxic events occur when the Earth's oceans become completely depleted of oxygen below the surface levels. Although anoxic events have not happened for millions of years, the geological record shows that they happened many times in the past. Anoxic events may have caused...
extinction event
Extinction event
An extinction event is a sharp decrease in the diversity and abundance of macroscopic life. They occur when the rate of extinction increases with respect to the rate of speciation...
s early in the Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
period. The event occurred approximately 91.5 ± 8.6 million years ago, and brought about the extinction of the ichthyosaurs and pliosaurs. Although the cause is still uncertain, the result starved the Earth's oceans of oxygen for nearly half a million years, causing the extinction of approximately 27 percent of marine invertebrates
Marine invertebrates
Marine invertebrates are animals that inhabit a marine environment and are invertebrates, lacking a vertebral column. In order to protect themselves, they may have evolved a shell or a hard exoskeleton, but this is not always the case....
. This global environmental disturbance increased atmospheric and oceanic temperatures. Boundary sediments show an enrichment of trace elements, and contain elevated 613C values.
One possible cause was sub-oceanic volcanism occurring approximately 500,000 years earlier. During that period, the rate of crustal production reached its highest level for 100 million years. This was largely caused by the widespread melting of hot mantle
Mantle (geology)
The mantle is a part of a terrestrial planet or other rocky body large enough to have differentiation by density. The interior of the Earth, similar to the other terrestrial planets, is chemically divided into layers. The mantle is a highly viscous layer between the crust and the outer core....
plumes under the oceans at the base of the lithosphere
Lithosphere
The lithosphere is the rigid outermost shell of a rocky planet. On Earth, it comprises the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater.- Earth's lithosphere :...
. This resulted in the thickening of the oceanic crust in the Pacific and Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
s. This volcanism would have produced large quantities of carbon monoxide into the atmosphere, leading to global warming. Within the oceans, the emission of SO, H2S, CO, and halogen
Halogen
The halogens or halogen elements are a series of nonmetal elements from Group 17 IUPAC Style of the periodic table, comprising fluorine , chlorine , bromine , iodine , and astatine...
s would have increased the acidity of the water, causing the dissolution of carbonate, and a further release of carbon dioxide. When the volcanic activity declined, this run-away greenhouse effect
Greenhouse effect
The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases, and is re-radiated in all directions. Since part of this re-radiation is back towards the surface, energy is transferred to the surface and the lower atmosphere...
would have likely been put into reverse. The increased CO2 content of the oceans could have increased organic productivity in the ocean surface waters. The consumption of this newly abundant organic life by aerobic bacteria would produce anoxia and mass extinction. The resulting in elevated levels of carbon burial afterwards would accounting for the black shale deposition in the ocean basins.
See also
- Anoxic eventAnoxic eventOceanic anoxic events or anoxic events occur when the Earth's oceans become completely depleted of oxygen below the surface levels. Although anoxic events have not happened for millions of years, the geological record shows that they happened many times in the past. Anoxic events may have caused...
- Cretaceous–Tertiary extinction event
- Extinction eventExtinction eventAn extinction event is a sharp decrease in the diversity and abundance of macroscopic life. They occur when the rate of extinction increases with respect to the rate of speciation...
- Timeline of extinctionsTimeline of extinctionsThe timeline of extinctions is an historical account of species that have gone extinct during the time that modern humans have occupied the earth....
- Geologic time scaleGeologic time scaleThe geologic time scale provides a system of chronologic measurement relating stratigraphy to time that is used by geologists, paleontologists and other earth scientists to describe the timing and relationships between events that have occurred during the history of the Earth...
External links
- Mid Cretaceous (Aptian – Turonian) Planktic And Benthic Foraminifera From Israel: Zonation And Markers The Ministry Of National Infrastructures Geological Survey Of Israel
- http://dspace.wul.waseda.ac.jp/dspace/bitstream/2065/5377/3/Honbun-4203.pdfCenomanian/Turonian stage boundary event in the north-west Pacifc: Marine biodiversity and palaeoceanographic background Division of Geology, Earth Sciences, Resources and Environmental Engineering Specialization, Major in Environment, Resources and Materials Science Engineering, Graduate School of Science and Engineering, Waseda University A doctoral dissertation (Dr. Sci.), Waseda University, Tokyo, February 2006]
- First evidence for the Cenomanian–Turonian oceanic anoxic event (OAE2, ‘Bonarelli’ event) from the Ionian Zone, western continental Greece
- Micropalaeontology and Stratigraphy of the Cenomanian/Turonian boundary in the Lusitanian Basin, Portugal