Magnetostratigraphy of the Etendeka Large Igneous Province, Namibia.

Abstract:

The Paraná – Etendeka large igneous province (≈ 135 Ma) has not been linked to a known mass extinction event, despite large igneous provinces being postulated as a cause. The reason why some large igneous provinces appear the cause of huge fluctuations in the global biosphere, an example being the link between Siberian trap volcanism and the Permo-Triassic boundary, while others seem to have only a minor effect is still debated. Establishing detailed histories of these large igneous provinces is important for understanding why such variations in effect may occur. Why does the volume of the province not reflect the magnitude of the effects seen?

During the early Cretaceous, reversals of Earth’s magnetic field were more frequent than at other times in Earth’s history. Magnetostratigraphy is therefore a tool capable of providing high resolution constraints on the history and duration of the Paraná – Etendeka large igneous province volcanism. Detailed sampling of the Etendeka volcanic stratigraphy, followed by progressive demagnetisation of 893 specimens, yields 70 individual polarities gained from throughout the central volcanic succession. Correlation of the individual sections sampled reveals a minimum of 16 separate polarities are recorded. Subsequent links to the geomagnetic polarity timescale suggest a minimum province duration of > 1 Myrs, with no obvious period of short, high volume volcanism as is often suggested. A protracted duration (>1Myr) may therefore provide the reason why at least the Paraná – Etendeka appears to have no associated extinction event.