Deconvolution of Paleomagnetic Directions from Marine Sediments in the Boso Peninsula, Japan, and Its Implications for the Matuyama-Brunhes Transition Field.

Abstract

The method of deconvolution of post-depositional DRM (detrital remanent magnetization) is applied to the paleomagnetic directions of continuous sedimentary sections from two sites in the Boso Peninsula, Japan. These sections have different accumulation rates and cover a time span of about 1000 years that includes the Matuyama-Brunhes reversal. Since the remanences are thought to be of the postdepositional DRM origin, a new deconvolution method with an exponential fixing function is applied. The deconvolution restores relative intensities of three components in the original fields from the remanence directions. As a result, the half-fixing depth is estimated to be 21 cm and the three-dimensional plot of the relative intensity is given. In the diagram of X and Z components, the polarity change in the geocentric axial dipole field with some additional field is recognized during the main reversal, while there seems to be no correlation between X and Y. After the deconvolution, the VGP path during the main reversal does not show longitudinal confinement, but does show longitudinal drift near the equator.

Further application of the deconvolution method of post-depositional DRM to the precise record of the Matuyama-Brunhes reversal in the sediments from the Boso Peninsula, Japan

“…The previous spectral analysis (Tsunakawa et al, 1996) suggested the periodic changes of the order of 100 years in the field directions during the Matuyama-Brunhes reversal. However it is widely accepted that the pDRM effect should be taken into account for the sedimentary magnetism, especially for the study on the rapid change in the geomagnetic field.…”

“…Because the pDRM mechanism has not yet completely been clarified, most of the paleomagnetic studies have not removed the effect of pDRM from the reversal records except for a few reports (Okada and Niitsuma, 1989;Kent and Copy right c The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences. Schneider, 1995;Tsunakawa et al, 1996). As the pDRM origin is inferred for the Boso sedimentary magnetism from the evidence of intensive bioturbation (Okada and Niitsuma, 1989;Tsunakawa et al, 1995), we have to restore more accurate variations from the measured remanence directions.…”

“…The 4100 year dataset of Yanagawa, analyzed in the present study, includes the 900 year data section and the half fixing depth is assumed to be constant (21 cm) throughout the span. The paleomagnetic directions are attempted to be deconvolved with the technique proposed by Tsunakawa et al (1996).…”

“…As the pDRM origin is inferred for the Boso sedimentary magnetism from the evidence of intensive bioturbation (Okada and Niitsuma, 1989;Tsunakawa et al, 1995), we have to restore more accurate variations from the measured remanence directions. Tsunakawa et al (1996) applied the deconvolution method (Tsunakawa, 1995) to the two directional datasets of about 900 years from the different sites, Yanagawa and Heizogawa. As a result, the half fixing depth of an exponential fixing function in pDRM acquisition (Hyodo, 1984) was estimated to be 21 ± 1 (1σ ) cm for the Boso sediments, which seems reasonable in comparison with those for other marine sediments (Tsunakawa et al, 1996).…”

“…Tsunakawa et al (1996) applied the deconvolution method (Tsunakawa, 1995) to the two directional datasets of about 900 years from the different sites, Yanagawa and Heizogawa. As a result, the half fixing depth of an exponential fixing function in pDRM acquisition (Hyodo, 1984) was estimated to be 21 ± 1 (1σ ) cm for the Boso sediments, which seems reasonable in comparison with those for other marine sediments (Tsunakawa et al, 1996). The 4100 year dataset of Yanagawa, analyzed in the present study, includes the 900 year data section and the half fixing depth is assumed to be constant (21 cm) throughout the span.…”