Comment to “Distribution and geochronology of the Oregon Plateau (U.S.A.) flood basalt volcanism: The Steens Basalt Revisited” by M.E. Brueseke et al. [J. Volcanol. Geotherm. Res. 161 (2007), 187–214]

The 40Ar/39Ar stepheating results of Brueseke et al. (2007) are critically evaluated, firstly for possible alteration of the samples dated. Steps passing the alteration index test (Baksi, 2007a) can then be used to derive plateau ages, which must satisfy rigorous statistical tests. Of the eleven samples studied by Brueseke et al. (2007), only four yield plateau values that reflect eruption ages. These suggest Steens Basalt was erupted within a relatively short period of time, ∼ 0.2 m.y., considerably less than the ∼ 1 m.y. suggested by the authors. The seeming difference between the plateau ages for the Steens Mountain Basalts obtained by these authors and two earlier attempts, is resolved by (a) proper adjustment of ages at various laboratories for interlaboratory calibration differences, and by rejecting ages from altered samples. The age of the important Steens Mountain geomagnetic polarity transition is 16.59 ± 0.03 Ma.