Possibility of reconstruction of the past geomagnetic field from homogeneous sediments.

Abstract

Magnetizing process of a sediment is formulated using a linear system theory. Remanent magnetization is represented as a convolution integral of geomagnetic field variation and a moment fixing function. The formulated model predicts that a field variation is deformed by filtering to be recorded in magnetization of sediments, and that the original field is deduced from the record of magnetization by a deconvolution method. Application of the model to the magnetization data of a core of shallow water sediment reveals that the remanent intensity variation may reflect the intensity reduction due to the cancellation of magnetic moments aligned in various directions rather than decrease in a field intensity. Width of magnetizing zone is inferred to be unexpectedly small from results of measurement of magnetization and laboratory experiments. The half fixing depths, at which a half of magnetic moments in a horizon is locked in, seem to cluster around 10cm or less.

Geomagnetic Secular Variation Reconstructed from Magnetizations of Wide-Diameter Cores of Holocene Sediments in Japan.

“…where Z1/2 is a half fixing depth, at which half of the magnetic moments in a unit sediment sheet is locked in (HYODO, 1984). The approximation by an exponential function is consistent with experimental results on magnetization processes in sediments (LOVLIE , 1976;TUCKER, 1980;HAMANO, 1980;OTOFUJI and SASAJIMA, 1981).…”

“…The angular standard deviations of OS3 and HR1 (Table 2) are small compared with those of the other cores. This amplitude attenuation can be explained by the filtering effect of the PDRM process (HYODO, 1984). The effect of secondary overprint along the present geo- Mean k; average of Fisher's precision parameter in each horizon, St ; total angular variance of VGP from horizon-average directions, Sw; average of within-site variance (variance in each horizon) of VGP, n; average number of samples in a site (horizon), S = (St -Sam,)/n; angular standard deviation of VGP (McELHINNY and MERRILL, 1975), ()*; upper and lower limits for S. * Transformed from a supplementary core at a site adjacent to the core OS2 (HYODO , 1985).…”

“…To test this, we apply a deconvolution technique to the records. HYODO (1984) proposed a technique to restore the secular variation signal from a time-series of magnetization directions using a linear system theory. Since the magnetization of sediment is a result of the convolution integral of the geomagnetic secular variation and a moment fixing function, the secular variation can be deduced by deconvolution if the moment fixing function is known.…”

About 100 Year Directional Variations in the Matuyama-Brunhes Transition Field Inferred from the Sedimentary Records in the Boso Peninsula, Japan.

“…The Yanagawa section probably yielded remanences of the post-deposited origin as discussed later. The convolution of the external field due to the post-depositional detrital remanent magnetisation may have depressed short-period components (Hyodo, 1984). Since the convolution is regarded as a low-pass filter and generating no new spectral peak, we temporarily analysed the direction changes without any deconvolution.…”

Paleomagnetic implication on climatic changes and evidence for excursions recorded in a sediment core from Harding Lake, alaska.

“…As these ages are determined by interpolation of the 14C a ges at six horizons, they may differ from the true ages. In addition, these ages must be slightly older to be regarded as the ages of the declination swings, because the NRM of fine grained sediments is acquired after deposition (IRvING, 1957;IRVING and MAJOR, 1964;KENT, 1973;YASKAWA, 1974;HAMANO, 1980;OTOFUJI and SASAJIMA, 1981;HYODO, 1984;HYODO and YASKAWA, 1986). We discuss the reliability and possibility of these three swings, although we can not verify their "internal consistency" because we used only one sediment core .…”