RECORD OF THE YOUNGER PART OF THE PRINGLE-FALLS EXCURSION AT LONG-VALLEY, CALIFORNIA

The younger of two closely spaced palaeomagnetic excursions at Pringle Falls, Oregon, is recorded in lacustrine silts that crop out in Long Valley, California. Assigned an age of about 220 000 years, the virtua l geomagnetic poles of the younger excursion form a clockwise loop tha t reached 35 degrees S latitude east of South America before returning to the northern hemisphere in the Pacific Ocean west of Central Ameri ca. The poles then form a narrow band across North America while movin g to high northern latitudes. This record matches extremely well featu re B of the original excursion record from Pringle Falls reported by H errero-Bervera et al. (1994) and is similar to this excursion at Summe r Lake, Oregon (Negrini et al. 1994), in that the pole path is confine d primarily to the east-central Pacific Ocean. On the basis of an assu med sedimentation rate of 30 cm per thousand years, the younger excurs ion (feature B at Pringle Falls) spans an estimated 1200 years and fol lowed by about 1000 years a larger excursion (feature A at Pringle Fal ls) previously discovered at the same Long Valley site. At a second Lo ng Valley site 30 m away, the younger excursion (feature B) is only pa rtially recorded because of a presumed small hiatus in the sedimentary section.