FINE-TUNING THE RADIOMETRICALLY DERIVED GEOMAGNETIC POLARITY TIME-SCALE (GPTS) FOR 0-10-MA

New 40Ar/39Ar step-heating ages for geomagnetic field reversals at 3.2 and 4.5 Ma, along with previous data at approximately 1, 2, 10 and 16 Ma, are used to derive a geomagnetic polarity time scale for 0-10 Ma. These ages for chron boundaries are fitted to the relative widths of the polarity intervals on the ocean floor, using a cubic spline technique. The interpolated ages of chrons for 0-6 Ma are in good agreement with the astronomical time scale and differ considerably from earlier attempts, based, in part, on K-Ar dates. Significant differences between the interpolated ages and the astronomical time scale are noted for the onset of the Olduvai and Reunion (sub)chrons; there is better agreement if 40Ar/39Ar data obtained from direct dating of these chrons is utilized. This time scale is estimated to be accurate to +/-1% for 0-6 Ma; for 6-10 Ma, the lack of a tie-point limits the accuracy to about +/-2%.