HR: 1340h
AN: GP43B-0864    [Abstracts]
TI: Holocene relative paleointensity and paleosecular variation from the Southern Okinawa Trough (ODP Hole 1202B)
AU: * Richter, C
EM: richter@louisiana.edu
AF: Department of Geology, University of Louisiana at Lafayette, P.O. Box 44530, Lafayette, LA 70503 United States
AU: Venuti, A
EM: venuti@mail.ingv.it
AF: Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata 605, Rom, 00143 Italy
AU: Verosub, K L
EM: verosub@geology.ucdavis.edu
AF: Department of Geology, University of California at Davis, One Shields Avenue, Davis, CA 95616 United States
AU: Wei, K
EM: weiky@ntu.edu.tw
AF: Department of Geosciences, National Taiwan University, P.O. Box 13-318, Taipei, 106 Taiwan
AB: We investigated u-channels from the top 36 meters of Hole 1202B collected in the Southern Okinawa Trough during Ocean Drilling Program Leg 195. Detailed rock magnetic data demonstrate that the sediments preserve a high resolution record of paleosecular variation and a paleointensity signal spanning almost the entire Holocene. The sediments consist of homogenous, slightly calcareous, bioturbated clayey silt with isolated sandy intervals and fine sand laminae. An age-depth model was established through C-14 accelerator mass spectrometry dating of planktonic foraminfera. The studied section spans almost the entire Holocene (0-9.4 kyr) and exhibits sedimentation rates close to 400 cm/kyr. The magnetic properties are dominated by stable, pseudo-single domain low-titanium magnetite with a Curie temperature of about 540 deg C. High-field hysteresis data and the grain-size sensitive ratio of anhysteretic remanent magnetization (ARM) to low field magnetic susceptibility indicate a narrow range of grain sizes and concentrations. Key magnetic parameters vary by less than a factor of four, thereby fulfilling the criteria for relative paleointensity determinations. The relative paleointensity was extracted by normalizing the intensity of the natural remanent magnetization (NRM) by the ARM and by the low field magnetic susceptibility. Both normalizations yield very similar results. Spectral analysis indicates that the record is not significantly affected by local environmental conditions. Comparison of this Western Pacific paleointensity curve with other curves suggests a geomagnetic origin for the observed variations. Millennial-scale features in our record correlate with variations of the archeomagnetic dipole moment, which implies that the sediment from Hole 1202B recorded changes of the geomagnetic field over the investigated time interval.
DE: 1521 Paleointensity
DE: 1522 Paleomagnetic secular variation
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting