The middle to late Pleistocene geomagnetic field recorded in fine-grained sediments from Summer Lake, Oregon, and Double Hot Springs, Nevada, U.S.A. |
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| Authors: | Robert M Negrini Kenneth L Verosub Jonathan O Davis |
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| Abstract: | A 400,000 year record of the paleomagnetic field has been acquired from 22 meters of middle to late Pleistocene fine-grained sediments from Summer Lake in south-central Oregon and Double Hot Springs in northwestern Nevada. The stratigraphy is based on 55 tephra layers, nine of which have been correlated with tephra layers from other localities on the basis of their distinct major- and trace-element geochemistry and their distinct petrography. The paleomagnetic samples carry a strong and stable magnetization that does not appear to have been affected by the inclination error commonly associated with the magnetization of sediments. The samples have accurately recorded the declination and inclination of the geomagnetic field at or near the time of deposition except for errors arising from rotations of discrete blocks of sediment predominantly about vertical axes. Errors introduced by this type of rotation were corrected by using paleomagnetic directions associated with correlated tephra layers. The Summer Lake paleomagnetic record suggests that secular variations occurred throughout the middle and late Pleistocene often maintaining the same waveform through several oscillations. The amplitudes of these variations were similar to those of Holocene variations, and the periods ranged from 15,000 years to greater than 100,000 years. |
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