Pliocene geomagnetic polarity epochs

摘要: Abstract A paleomagnetic and K-Ar dating study of 44 upper Miocene Pliocene volcanic units from the western United States suggests that frequency reversals earth's magnetic field during time may have been comparable with last 3.6 m.y. Although data are too limited to permit formal naming any new polarity epochs or events, four transitions identified: W10 R/N boundary at 3.7 ± 0.1m.y. , A12 N/R 4.9 W32 9.0 0.2m.y. W36 10.8 0.3 − 1.0m.y . The loss absolute resolution in older rocks indicates use well defined stratigraphic successions identify date will be important reversals.