Comment on the Lau Basin Cobb Mountain records by Abrahamsen and Sager

The Cobb Mountain Subchron is one of the few short polarity intervals for w hich transition records have been obtained both from a wide geographical di stribution and from different types of paleomagnetic recorders. These recor ds exhibit VGP paths that are remarkably similar. Given the wide geographic distribution of these sites, the similarity in VGP paths is most simply in terpreted as the presence of very large scale, if not dipolar, symmetries i n the transitional fields. Only the records from western California and the Lau Basin exhibit VGP paths that are markedly different from the others. N ew dates for the Punaruu lavas suggest that they recorded a new geomagnetic cryptochron rather than the Cobb Mountain [Singer, B.S., Hoffman, K.A., Ch auvin, A., Coe, R.S., 1999. Dating transitionally magnetized lavas of the l ate Matuyama Chron: Toward a new Ar-40/Ar-39 timescale of reversals and eve nts. J. Geophys, Res. 104, 679-693]. This new age indicates a revised corre lation of some of the other California records whose ages agree better with the Punaruu cryptochron. A re-examination of the Lau Basin records reveals that much of the difference between these and the other records results fr om a bias introduced when the paleomagnetic data were smoothed. Reanalysis of these records shows that the Lau Basin VGP paths an very similar to thos e obtained from western Pacific, and the North Atlantic. (C) 2000 Elsevier Science B.V. All rights reserved.