AGE AND CORRELATION OF A PALEOMAGNETIC EPISODE IN THE WESTERN UNITED-STATES BY AR-40 AR-39 DATING AND TEPHROCHRONOLOGY - THE JAMAICA, BLAKE, OR A NEW POLARITY EPISODE/

High-resolution paleomagnetic records from two sites near Pringle Fall s, Oregon, are compared with similar records from Summer Lake, Oregon, similar to 170 km to the southeast: Paoha Island, in Mono Lake, simil ar to 660 km to the southeast and Benton Crossing, in Long Valley, app roximately 700 km to the southeast, in east-central California. The se quences at Pringle Falls contain a distinctive coarse pumice-lapilli t ephra layer which we have dated as 218+/-10 ka by Ar-40/Ar-39 step-hea ting of plagioclase feldspar. Stratigraphically, this tephra is closel y associated with a suite of several other tephra layers that bracket the interval studied paleomagnetically. Each tephra layer is distingui shed by the unique chemical composition of its volcanic glass shards. The pumice layer dated at Pringle Falls is correlated with layers at t hree of the other localities. Using all the tephra layers, we can corr elate the lake stratigraphic sequences and associated paleomagnetic re cords among the four distant localities. Additional age control is obt ained from a fifth locality at Tulelake in northern California, where the stratigraphic interval of interest is bracketed between similar to 171+/-43 and approximately 140 ka. Characteristics of the paleomagnet ic records indicate virtually identical paleofield variation, particul arly the geometry of a normal to normal (N-N) geomagnetic polarity epi sode. The observed paleofield behavior resembles the Blake geomagnetic polarity episode, but is significantly older than the generally accep ted age of the Blake episode. Either the age of the Blake episode is s ignificantly underestimated, or the polarity episode documented here i s older, perhaps the Jamaica episode, or is an as yet unreported episo de. A corollary of the latter option is that paleomagnetic polarity ep isodes of different ages may have similar transition polar paths, a co nclusion implying that a common mechanism is involved.