Journal of Geophysical Research (American Geophysical Union)
A new high-resolution paleointensity record for North America has been constructed using Holocene sediments from Lake Pepin, Minnesota. Lake Pepin sediments yield the same Holocene paleosecular variation curve as nearby Lake St. Croix and satisfy all of the criteria recommended for paleointensity studies. Absolute paleointensity data for North America recorded by Holocene volcanic and archeomagnetic samples provide an independent record of geomagnetic field paleointensity against which the relative intensity records from Lake Pepin and Lake St. Croix can be compared. Since the absolute field paleointensity is known a priori, the effects of the magnetic recording assemblage can be isolated. Anhysteretic remanent magnetization (ARM) is the best choice among normalization parameters for the Lake Pepin sediments as the natural remanent magnetization (NRM) normalized by ARM shows no coherence with magnetic grain size proxies and yields a record of relative paleointensity peaks and troughs whose amplitudes are very similar to those in the archeomagnetic (ARCMAG) and Lake St. Croix data sets. Features with a wavelength of 1000 years are correlative between the three paleointensity records. NRM normalized by saturation isothermal remanent magnetization (SIRM) and by susceptibility (χ) shows grain-size dependences that cause errors in the amplitudes of paleointensity features. NRM/SIRM and NRM/χ are not coherent with their normalizers but are both strongly coherent with independent grain size proxies such as the median destructive field of the NRM and HCR. We successfully removed the grain size dependences from NRM/SIRM by applying a correction function based on the linear relationship between normalized intensity and the median destructive field of the NRM.
Brachfeld, S. A. and S. K. Banerjee (2000). "A new high-resolution geomagnetic paleointensity record for the North American Holocene: A comparison of sedimentary and absolute intensity data." Journal of Geophysical Research B: Solid Earth 105(B1): 821-834.
This work was supported in part by a doctoral dissertation fellowship from the Graduate School of the University of Minnesota. Travel to the LSCE was made possible by a grant for dissertation research abroad from the University of Minnesota. This is contribution 9901 of the Institute for Rock Magnetism (IRM). The IRM is funded by the W.M. Keck Foundation, the Earth Sciences Instrumentation and Facilities Program of the National Science Foundation, and the University of Minnesota
Brachfeld, Stefanie; Banerjee, Subir.
A new high-resolution geomagnetic paleointensity record for the North American Holocene: A comparison of sedimentary and absolute intensity data.
Journal of Geophysical Research (American Geophysical Union).
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