A JURASSIC SUPERPLUME EVENT AND ITS EFFECT ON THE EARTH SYSTEM

Earth history is punctuated by short abrupt periods of massive volcanic eruptions due to the impact of deep-seated mantle plumes on the Earth's lithosphere. When more than one plume event occurred within a short timeframe, the term superplume has been used inferring a more vigorous thermal disturbance of the Earth's mantle.

Superplumes have, through the cumulative effect of more than one mantle plume, a major impact on Earth systems. They are associated with high sea-floor spreading rate, eruption of continent-sized basalt plateaus, global sea-level highstands, increased atmospheric carbon dioxide, increased global temperature, formation of carbon-rich deposits on a massive scale and predominantly uniform polarity of the geomagnetic field. Although a mid Cretaceous superplume event is well recognized in Earth history, we present evidence for an early Jurassic superplume event and indicate the effect that it may have had on the Gondwana Earth system.

The large igneous provinces at the Triassic-Jurassic boundary of the Central Atlantic Magmatic Province together with the Early to Middle Jurassic provinces in the South Atlantic region are considered as evidence for the Jurassic superplume event. The Central Atlantic magmatism overlaps in age with a mass extinction of vertebrates, invertebrates and plants. A major marine anoxia event in the Toarcian coincides with the onset of the basaltic Karoo-Ferrar phase of Gondwana break-up magmatism. A global sea-level highstand is also recognized at this time associated with extinctions of marine vertebrates. We suggest that these events may be causally related to a superplume event and correspond to a lower to middle Jurassic period of anomalous geomagnetic field behaviour reflecting lower mantle disturbance. This superplume event eventually lead to the disintegration of Gondwana which ultimately resulted in the isolation of Antarctica in a South Pole position and initiation of the Antarctic ice sheets.