Australia: The Land Where Time Began

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LIPs - The Caribbean-Columbian Plateau and Madagascar flood basalts

During the Cretaceous the most widespread phase of ocean anoxia/dysoxia occurred at the Cenomanian-Turonian (C-T) boundary (Wignall, 1994). This was associated temporarily with an extinction event of moderate size, especially among deep sea benthic foraminifera (Kaiho & Hasegawa, 1994), though it is a matter of debate whether there is a causal relationship (Banerjee & Boyajian, 1996; Hallam & Wignall, 1997).

Volcanism has long been implicated as a potential cause of the C-T anoxic event (Keith, 1982; Vogt, 1989), though the location of the volcanism has not been certain until recently. If several major volcanic provinces may have formed during the C-T interval, namely, the Caribbean-Columbian Plateau, 4 million km3 (Kerr, 1998), broken Ridge in the Indian Ocean, 2 million km3, possibly a component of the Ontong Java Plateau and a minor CFBP in Madagascar (Storey et al., 1995). A total of up to 20 million km3 of intraoceanic, basalts that were plume-related are thought to be of this age. It is suggested by currently available radiometric ages for these provinces that a selection of emplacement times within the Turonian and, therefore, slightly after the C-T events. The C-T boundary occurs, therefore, within the 93-90 Ma interval (Gradstein et al., 1994) while the ages of the Caribbean-Columbian Plateau averages 89.5 ± 0.3Ma, the Madagascan CFBP dates to between 88.5 ± 2.9 and 87.6 ± 2.9 Ma (40Ar-39Ar) dates with external error, from Storey et al. (1995)), and the Late Cretaceous portion of the Ontong Java Plateau formed about 90 Ma (Sinton & Duncan, 1997). In spite of this significant timing mismatch, a plausible scenario has been proposed (Kerr, 1998) for the global warming in the late Cenomanian that was driven by volcanic activity. Direct hydrothermal warming of the oceans may have been caused by submarine eruptions, as well as the indirect warming due to the release of large volumes of volcanic CO2 to the atmosphere. Further release of CO2 would follow from acidification of the oceans due to volcanic SO2 emissions at a rate that is suggested by Kerr may have been as high as 3 x 1017 kg/yr. Further release of CO2 to the atmosphere would result from warming of the oceans, the end result being a “runaway greenhouse” for which there is ample palaeontological evidence, which includes the brief appearance of crocodiles at the North Pole (Tarduno et al., 1998). In the early Turonian the reversal of this warming trend occurred abruptly (Kuypers et al., 1999), which was possibly due to a negative feedback in the carbon cycle in which warmer (and more humid) conditions enhance the input of nutrients to the oceans, which would increase productivity and thereby elevate rates of organic C burial (Jenkyns, 1999). Submarine volcanism may more directly increase the availability of iron in the oceans and thereby stimulate productivity (Sinton & Duncan, 1997).

To summarise, many aspects of C-T environmental change are accounted for elegantly by Kerr’s model, though somewhat ironically the ages of the eruptions of the implicated volcanic provinces suggest they coincide with the rapid cooling in the early Turonian, and therefore not the extreme warming that preceded this event.

Sources & Further reading  

Wignall, P. B. (2001). "Large igneous provinces and mass extinctions." Earth-Sci. Rev. 53: 1-33.

Author: M. H. Monroe
Email:  admin@austhrutime.com
Last Updated 19/07/2019
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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading