ABORTED REVERSAL OF THE PALEOMAGNETIC FIELD IN THE BRUNHES NORMAL CHRON IN EAST-CENTRAL CALIFORNIA

Exposed Pleistocene lake sediments in Long Valley, California, record a palaeomagnetic field of reversed polarity of short duration in the Brunhes Normal Chron that is interpreted as an aborted reversal. The Virtual Geomagnetic Poles for that field reach a southern mid‐latitude and form a large clockwise‐directed loop when traced from old to young. The poles enter the southern hemisphere about 90° east of Long Valley and exit about 90° west of it. Part of the record is present in exposed lake sediments in Mono Basin, 40 km northwest of Long Valley. Along with the palaeomagnetic record, tephrochronology is used to correlate and date the stratigraphy at the two localities. Assuming the sedimentation rate in both lakes was a constant 25 cm per thousand years, the recorded anomalous field behaviour is estimated to span about 4000 yr and be about 280 000 yr old. Copyright © 1990, Wiley Blackwell. All rights reserved