Detailed Study of the Sediments Recording the Matuyama-Brunhes Geomagnetic Reversal
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概要
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The purpose of the present study is to find the relationship of a geomagnetic field reversal to the changes in a foraminiferal fauna and the sedimentary environments. A fossiliferous marine sedimentary section of the middle part of the Kokumoto Formation continuously exposed at Kamiyanagawa in the Boso Peninsula, Chiba Prefecture, Central Japan, was chosen for the investigation of the behaviour of the geomagnetic field during its reversal between the Matuyama and Brunhes Polarity epochs which took place around 0.69 m.y. ago. The behaviour of the geomagnetic field was established as to the inclination, declination and intensity of the Jn/J_R recorded in the sedimentary rocks. Along the same section, analyses were made on the grain-size of the sediments, oxygen isotope ratio in the planktonic and benthonic foraminiferal tests, and the faunal assemblages of the planktonic and benthonic foraminifers. The intensity of the magnetic field fluctuated with a period of approximately 6700 years and did not disappear during the reversal. The migration of the virtual magnetic north pole at the magnetic field reversal between the Matuyama and Brunhes Polarity epochs occurred roughly along the meridian of 120°E long. in the period of 4700 years. In the same duration the depth of the sea water, under which the sediments accumulated, fluctuated within the range of 200-300 m with a period of approximately 7000 years. No particular relation between the magnetic field reversal and fluctuation of the water depth was recognized. The result of paleotemperature and faunal analyses of the foraminifers showed that the magnetic field reversal at the Matuyama Brunhes Polarity Epoch boundary may have been related to the changes in the circulation pattern of the upper watermasses which caused more influx of cold water into this area in the northwestern Pacific as compared with the period before the geomagnetic polarity change.
- 東北大学の論文
- 1971-10-20
著者
関連論文
- Detailed Study of the Sediments Recording the Matuyama-Brunhes Geomagnetic Reversal
- Statistical Analyses of Populations by Electronic Computer
- 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
- Deconvolution of Paleomagnetic Directions from Marine Sediments in the Boso Peninsula, Japan, and Its Implications for the Matuyama-Brunsition Transition Field