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Magnetostratigraphic studies are widely used in conjunction with the geomagnetic polarity time scale (GPTS) to date events in the range 0 to 5 million years ago. A critical tie point on the GPTS is the potassium-argon age of the most recent (Brunhes-Matuyama) geomagnetic field reversal. Astronomical values for the forcing frequencies observed in the oxygen isotope record in Ocean Drilling Project site 677 suggest that the age of this last reversal is 780 ka (thousand years ago), whereas the potassium-argon-based estimate is 730 ka. Results from 4039; Ar incremental heating studies on a series of lavas from Maui that straddle the Brunhes-Matuyama reversal give an age of 783 + 11 ka, in agreement with the astronomically derived value. The astronomically based technique appears to be a viable tool for dating young sedimentary sequences.

Utilizing 40Ar/39Ar plateau ages for selected field reversals at ∼ 1, 2, 10, 16 and 34 Ma, a geomagnetic polarity time scale (GPTS) is constructed, following the technique of Cande and Kent [1992]. This differs markedly from previous GPTS, especially in middle‐late Miocene time; the ages for the chrons in post‐Miocene time are in agreement with values derived by the astrochronological technique. Refinements in this GPTS await acquisition of 40Ar/39Ar plateau ages for field reversals in the time frames 3–8 Ma and 11–15 Ma.

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