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Two such minerals, hematite and maghemite, are prevalent in the Elliot Formation.
Rich in fossils, both plants and animals, the Karoo Basin records crisis periods – mass extinction events – in the distant past when many species became extinct.
My colleagues and I were interested in the age of a specific rock unit in the Karoo Basin: the Elliot Formation.
Rocks of the Elliot Formation outcrop in a ring around the Drakensberg Plateau (see figure).
Our research has found that minerals within the rocks of the Elliot Formation are able to retain primary magnetisations: they have reliably recorded the Earth’s magnetic field at the time of their deposition.
That’s important because natural processes can cause “overprinting” – wiping out the original magnetic signature.
Understanding these climate change events and their impact on biology in the Karoo Basin could influence the way we look at the sixth extinction, which is happening now: the Anthropocene. There are certain “geological clocks” which help when dating rocks: a mineral called zircon is one. But when these are scarce, we need another way of measuring the age of rocks.