Australia: The Land Where Time Began

A biography of the Australian continent 

LIPs - Ontong Java Plateau

The emplacement of the largest single emplacement on Earth, the Ontong Java Plateau in the southwest Pacific, which covers an area of 2 million km² of the southwest Pacific, with a crustal thickness of 35 km took place in the Early Cretaceous (Saunders et al. 1996). Exposure of sections of the plateau on the island of Malaita, Solomon Islands, resulted from partial obduction, which reveal basalt flows that are 20-70 m thick interbedded with limestones, which therefore indicate submarine emplacement (Sunders et al., 1996). The upper part of the province is suggested by ⁴⁰Ar-³⁹Ar dates to have formed around 44 Ma (Mahoney et al., 1993), indicating a late Barremian age in the timescale of Gradstein et al. (1994). This is in reasonable accordance with the biostratigraphic evidence: Planktonic foraminifera from the top of the lava pile are from the Globigerinelloides blowi Zone of the succeeding Aptian Stage (Tarduno et al., 1991). Oxygen-poor deposition appears to have been widespread in the oceans of the world during the interval that preceded this zone, from the late Barremian to the early Aptian (Bralower et al., 1994). This is the first of the “oceanic anoxic events”, the Selli Event, and, as in the case of the later events, it coincides with a rise in global sea levels. Wignall suggests this eustatic change may have been caused by the displacement of ocean waters that resulted from the submarine emplacement of the Ontong Java Plateau (Tarduno et al., 1991). The development of widespread oxygenic deficient deposition has also been linked indirectly to Volcanism (Keith, 1982; Larson, 1991a, b; Jenkyns, 1999). The release of volcanic CO₂ and the consequent global warming is the most likely cause of the anoxia, whereas the release of SO₂ is likely to have been negligible as the eruptions were submarine.

All the hallmarks of a major environmental crisis are clearly present in the early Aptian and yet there is no associated extinction event (Hallam & Wignall, 1997). The biota of the Early Cretaceous was, once again, immune to the effects of a major volcanic episode. There were minor extinctions, particularly of the reef forming nudist bivalves occurred in the latter part of the Aptian (Hallam & Wignall, 1997). Wignall suggests that these could coincide with another LIP, the formation of Kergulean Plateau. Much further work needs to be done, however, on the dating of the plateau and the extinctions in order to verify this coincidence.

Sources & Further reading

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