Paleomagnetic stratigraphy, rates of deposition and tephrachronology in North Pacific deep-sea sediments

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The paleomagnetic stratigraphy of 12 North Pacific deep-sea sediment cores has been investigated and has been used to date volcanic eruptions and to determine rates of deposition of pelagic sediments. Only four of the cores penetrated sediments deposited before the last reversal of the earth's magnetic field (0.7 m.y.). Of these, one penetrated to the Gauss series, two to sediments deposited during the Olduvai event and one penetrated to the middle of the Matuyama series. Eight other cores, 10–16 meters long, taken within 1000 km of the Japan-Kuril-Kamtchatka arc failed to reach the Matuyama series. The rate of deposition in North Pacific pelagic sediments vary from 2cm/1000y in the area east of the Asiatic continent to < 0.8cm/1000y in the mid Pacific. Assuming continuous deposition, the length of the Jaramillo event can be established as 50 000 y and the Olduvai event as 14 000 y. The apparent length of time during which the dipole field of the earth was reduced during reversals of the earth's magnetic field is approximately 20 000 y. In one of the cores the top of the Olduvai event is split. This may represent the Gilsa event. The brown volcanic ash present in three of the cores apparently originated in an eruption 1.2 m.y. ago in the Aleutian Arc near the Andreanof Islands.