HR: 16:45h
AN: GP24A-04 INVITED     [Abstracts]
TI: A Comparison of Paleomagnetic and Archaeomagnetic Secular Variation Records for Western North America
AU: * Hagstrum, J T
EM: jhag@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Road MS 937, Menlo Park, CA 94025 United States
AU: DuBois, R L
GP24A-04 AF: University of Oklahoma, 709 Normandie Drive, Norman, OK 73072 United States
AU: Blinman, E
EM: eblinman@oas.state.nm.us
AF: Museum of New Mexico, Office of Archaeological Studies P.O. Box 2087, Santa Fe, NM 87504 United States
AB: Several different magnetic media have been used in the study of Holocene paleosecular variation (PSV) of the geomagnetic field. They include lacustrine sediments, lava flows, and baked archaeological materials, and each has its own advantages and disadvantages. The long life span (~12 kyr) and high sedimentation rates of lakes preserve continuous PSV records, but time calibration of the PSV curve may be poor due to the availability of only a small number of radiocarbon dates at any one locality. Moreover, individual lake core samples integrate PSV over intervals of 50 to 200 years. Lava flows provide high fidelity, relatively instantaneous records of the geomagnetic field, but volcanic eruptions are episodic and detailed stratigraphic and age information are often lacking. Similarly, suitable archaeomagnetic sites tend to be temporally and spatially discontinuous, although identification of ceramic assemblages, ultimately calibrated by dendrochronology, can provide good age control. Hagstrum and Champion [JGR, v. 107, n. B1, 2025, 10.1029/2001JB000524, 2002] published a record of PSV for the past ~20 kyr in western North America based on 94 virtual geomagnetic poles (VGPs) from ¹⁴C-dated volcanic rocks at 446 sites; due to data density, the most detailed portion of the record is for the last ~4 kyr (46 VGPs; 226 sites). Since the 1960s, DuBois has assembled a reference PSV curve for archaeomagnetic dating in the American Southwest based on VGPs from 440 sites. The archaeological ages have recently been reassessed leaving 271 reliably dated VGPs for the last ~1.5 kyr. Although the volcanic and archaeological PSV records are both underpinned by thermoremanent magnetizations, they are fundamentally different in the materials sampled (lava flows vs. burned earthen architecture) and independent dating techniques used (generally ¹⁴C vs. ceramic dating). Both calibration techniques, however, have similar mean uncertainties of ~1 to 2 centuries. Comparisons of averaged VGPs within these limits of uncertainty show remarkable similarities between the two records. For the period AD 800 to 1700 the averaged VGPs of similar age (7 comparisons) differ by less than 3° and are statistically the same at the >95% confidence level. At this resolution PSV is well represented, and the most reliable and detailed record is produced by a combination of the two data sets.
DE: 1503 Archeomagnetism
DE: 1522 Paleomagnetic secular variation
DE: 1560 Time variations: secular and longer
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005