A New 62-sample Record of the Mono Lake Excursion Waveform from the Depocenter Sediments of Summer Lake, OR

A new core from Summer Lake, Oregon provides the primary datset for a composite, 62-sample record of the Mono Lake Excursion (MLE) waveform. The magnetograms and virtual geomagnetic poles (VGPs) are consistent with those associated with the MLE record from Mono Lake (e.g., Liddicoat and Coe, 1979). The added detail from this new record firmly establishes three distinct VGP clusters centered first on easternmost Asia/Siberia, then on Europe, and, finally, on North America. The jumps between clusters involve typically one sample, which represents only a few decades of time. The excursion is bracketed by tephra of known age (the Mount St. Helens Cy 46.0 ± 6 ka and the Wono 27.3 ± 0.3 14C kyr B.P.) and the age of the excursion is ~28 14C kyr B.P based on an average of five radiocarbon ages from below, within and above the excursion interval. A second waveform that exhibits shallowing inclinations and easterly declination swings upsection is truncated by a prominent unconformity. These PSV features and the associated RPI leading up to this unconformity correlate with those of the onset of the Laschamp Excursion (Lund et al., 2005). Both radiocarbon and PSV correlations support missing sediment from the Summer Lake record between 42.5 and 38 GISP2 ka. This sediment hiatus correlates to unconformities or lowstands in other Great Basin lakes suggesting a Heinrich 4-induced drought that affected much of western North America.