GEOMAGNETIC POLARITY TIMESCALE (GPTS)

A geological timescale based on geomagnetic polarity reversals, calibrated by absolute-age dating of reversals (see calibrated-age dating) (see Figure). The geomagnetic polarity timescale, or magnetostratigraphic timescale, is principally used where a distinctive set of reversals in a rock sequence can be reliably matched to a section of the timescale. It provides a detailed record of geomagnetic polarity reversals from ~250 million years ago to the present through the dating of magnetic anomalies in ocean-floor sediments (see marine sediment cores). The numbers given to ocean-floor anomalies and the names given to the most recent polarity chrons are also applied to the timescale. The reversal pattern is calibrated with biostratigraphy and radiometric dating.

Geomagnetic polarity timescaleThe geomagnetic polarity timescale for the past 24 million years (Ma). Black bands are episodes of normal polarity; white bands are episodes of reversed polarity (Nichols, 1999).

[See alsodating techniques, magnetostratigraphy]