Quaternary geomagnetic field intensity: constant periodicity or variable period?

Sato Takaharu

Kikuchi Hisakazu

Nakashizuka Makoto

Okada Makoto

Geophysical research letters

Paleomagnetic results are presented from a core, KH 90-3-5, in the Melanesia basin and are correlated with thepreviously obtained results from two cores, KH 73-4-7, KH 73-4-8, in the same basin in a period between 0.04 Ma and 1.1 Ma. The sediments in the three cores are composed mostly of calcareous ooze. It has been shown that the variation in thesaturation isothermal remanent magnetization (SIRM) in the two cores is caused neither by deposition-rate variation of magnetic minerals nor by rock-magnetic inhomogeneity butalmost solely by variatiolls in CaCO_3, dissolution. A close similarity between the variation in the SIRM in the two cores and the variation in the initial susceptibility (κ) in KH 90-3-5 has enabled us to correlate among the cores, and also means negligible rock-magnetic inhomogeneity in the core.

A time versus depth correlation has been established from the δ^18O record of KH 90-3-5. The relative paleointensity record estimated from the natural remanent magnetization (NRM) normalized by κ in KH 90-3-5 and those records in the other two cores are remarkably similar, implying that the records faithfully reflect variations in relative paleointensity of the geomagnetic field for the past 1.1 Ma. We examined on the periodicity of the paleointensity records with wavelets. It is shown that periods ofmajor changes in the records reveal continuous shifts betweenabout 50 Ka and 140 Ka over time. We offer an alternative viewpoint about the periodicity of the paleointensity in which periods of major changes shifted continuously within the time mnge instead of constant periodicities.

paleointensity

wavelet

deep-sea sediment

periodicity

Earth sciences. Geology [ 450 ]

eng

American Geophysical Union

AGU

Copyright (c) 1998 American Geophysical Union

[DOI] 10.1029/98GL01621

[ISSN] 0094-8276

[ISSN] 1944-8007