High-resolution record of geomagnetic secular variation from Late Pleistocene Lake Lisan sediments (paleo Dead Sea)

Abstract

We measured geomagnetic secular variation in Lake Lisan sediments (paleo Dead Sea). More than 1500 oriented samples were collected from a 27.3-m section of alternating aragonite and detritus laminae in the Dead Sea basin ranging in age from 67 to 32 ka. The natural remanent magnetization (NRM) is carried by titanomagnetite in the detrital laminae whereas the aragonite is diamagnetic. The NRM is very stable and was acquired several hundred years after deposition. The mean direction of 878 horizons is D = 005°, I = 45° ( α 95=1°; κ=22). We observed three modes of directional geomagnetic variation as a function of (and by inference, time): very rapid inter-sample changes, slow variation in mean direction, and inclination shallowing of about 1°/m. The overall rate of change in direction is 0.57±0.57°/year, not significantly different from zero. For about 83% of the record the rate of change is less than 1°/year and comparable to historical values. High rates of change are observed more frequently in the Lisan than in historical records, and peak rates are up to ten times faster. A smoothed curve resulting in a maximum rate of change of 0.66°/year and a mean 0.10±0.10°/year may be a more realistic representation of the field behavior. No reverse NRMs were observed, but geomagnetic field excursions may be present where the VGPs deviate by more than 40° from the geographic north at about 52 and 41 ka; the latter may represent the Laschamp event.