Soon after the K–Ar ages for Pliocene–Pleistocene polarity reversals (Mankinen andDalrymple, 1979) were superceeded by astrochronological determinations, a large number of 40Ar/39Arages confirmed the astrochronological ages ofpolarity chrons. For example, 40Ar/39Ar agedeterminations for the M/B boundary andboundaries of the Jaramillo Subchron (Izett andObradovich, 1991; Spell and McDougall, 1992;McDougall et al., 1992; Tauxe et al., 1992; Baksiet al., 1993), for the Cobb Mountain Subchron(Turrin et al., 1994), for the Re´u´nion Subchron(Baksi et al., 1993) and for the boundaries of theOlduvai Subchron (Walter et al., 1991; Baksi, 1994)were all close to the astrochronological estimates.The exercise becomes somewhat academic in viewof the suggestion of Renne et al. (1994) thatthe 40Ar/39Ar standard (Fish Canyon sanadine,Mmhb-1) should be calibrated using the astrochronological ages of polarity reversals.In CK92/95, ‘tiny wiggles’ in MMA data, interpreted either as brief polarity chrons (with duration