Mono Lake Excursion in the Lahontan Basin, Nevada

Abstract

In the Lahontan Basin of north-western Nevada, the Mono Lake Excursion is recorded in a wave-cut bank at Pelican Point on the west side of Pyramid Lake. The record is almost identical to one across the lake near Pyramid Island, 10 km away, and in the Carson Sink, 60 km further to the east. At each locality, the older half of the excursion is present only as a reduction in the relative field intensity, while the younger half shows the expected easterly declination and steep positive inclination that result in a small counterclockwise loop of the virtual geomagnetic poles. The younger half occurs during high relative field intensity, and the entire intensity pattern is similar to the one for the excursion in the Mono Basin, California, 250 km to the south. The presence of only part of the Mono Lake Excursion in the Lahontan Basin might have resulted from the slow sedimentation rate in Pyramid Lake (estimated to be about 12 cm kyr-1), with the field behaviour being more extensively integrated in the subsamples used. In an alternate explanation, the absence of the older part of the excursion can be attributed to overprinting when magnetic grains that were free to rotate in unconsolidated sediment were realigned during the high relative field intensity in the younger part of the excursion.