The Gauss-Matuyama Reversal was a geologic event approximately 2.58 million years ago when the Earth's magnetic field underwent reversal. This event, which separates the Piacenzian from the Gelasian and marks the start of the Quaternary, is useful in dating sediments.
The event is marked by the extinction of calcareous nanofossils Discoaster pentaradiatus and D. surculus, among others.
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