HR: 1340h
AN: GP43A-0932    [Abstracts]
TI: Robustness and Limitations of 0-1 Ma Absolute Paleointensity Data
AU: * Ziegler, L B
EM: lziegler@ucsd.edu
AF: IGPP, Scripps Institution of Oceanography, UCSD, 9500 Gilman Dr, La Jolla, CA 92093, United States
AU: Constable, C
EM: cconstable@ucsd.edu
AF: IGPP, Scripps Institution of Oceanography, UCSD, 9500 Gilman Dr, La Jolla, CA 92093, United States
AU: Johnson, C L
EM: cjohnson@eos.ubc.ca
AF: IGPP, Scripps Institution of Oceanography, UCSD, 9500 Gilman Dr, La Jolla, CA 92093, United States
AU: Johnson, C L
EM: cjohnson@eos.ubc.ca
AF: Earth and Ocean Sciences, Univ. of British Columbia, 6339 Stores Rd, Vancouver, BC V6T1Z4, Canada
AB: Absolute paleomagnetic field intensity data derived from thermally magnetized lavas and archeological objects provide information about past geomagnetic field behavior, but the average field strength, its variability, and the expected distribution of these observations remain uncertain despite growing data sets. We investigate these issues for the 0-1 Ma field using data from igneous rocks compiled in the PINT03 database, 1124 samples of heterogeneous quality with restricted temporal and spatial coverage. Using virtual axial dipole moments (VADM) to accommodate variable spatial sampling and a bootstrap importance sampling technique to correct for uneven temporal sampling, we find an average VADM of 7.26 × 10²² Am² ± 0.14. The associated statistical distribution appears bimodal with a subsidiary peak at approximately 5 × 10²² Am². Tests indicate that this behavior is unlikely to arise from contamination by poor quality data, geographic bias in sampling, or over-representation of typically low intensity excursional data or to result from a mixture of two statistical distributions each corresponding to a distinct intensity state for the magnetic field. Simulations from a stochastic model based on the paleofield spectrum support the alternative possibility that a hypothetically smoother underlying distribution cannot be recovered from a 1 Myr time span. Possible influence of the restricted material type used in our analyses is assessed using additional data compilations and comparing Holocene data from lava flows, Submarine Basaltic Glass (SBG), and archeological objects. The SBG results are inconclusive because of dating issues, but average paleointensities from lavas are about 10% higher than for archeological materials and show greater dispersion. Uncorrected variable cooling rates during remanence acquisition provide a plausible explanation for these differences which may contribute to systematic bias in the 0- 1 Ma average field estimates.
DE: 1521 Paleointensity
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2007 Fall Meeting