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Book Chapter

Paleomagnetism of Cores from the North Pacific

By
Neil D. Opdyke
Neil D. Opdyke
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John H. Foster
John H. Foster
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Published:
January 01, 1970

A paleomagnetic study has been carried out on 114 piston cores from the Pacific Ocean north of 20° N. lat. The cores were sampled at 10 cm intervals, and the direction of magnetization was determined after partial demagnetization in fields of from 50 to 150 oersted peak field. The coercivity of the red clays from the central part of the North Pacific was found to decrease with depth in the cores so that in red clay cores magnetic stratigraphy is often undecipherable even after partial a.f. demagnetization. In other types of lithologies, a.f. demagnetization was successful in removing secondary components. The magnetic stratigraphy from the cores was interpreted in terms of the radiometrically derived time scale for the last 4.5 m.y. of earth history. Confusion has recently arisen as to whether the large event, which is often identified in the bottom part of the Matuyama series, is best correlated with the Olduvai or Gilsa event. The age of this event in 13 North Pacific cores was determined by interpolation between the Brunhes/Matuyama and Gauss/Matuyama boundary. The average age of the upper and lower boundaries of the event are 1.71 and 1.86 m.y. with a standard deviation exceeding ± 0.1 m.y. The original date on the Olduvai event is 1.91 ± 0.06 m.y. There is no significant difference between the range of the event as seen in marine sediments and the age of the Olduvai event at its type locality. Therefore, on the basis of priority, it seems proper to correlate this event with the Olduvai event.

Nine stratigraphic sections were constructed on the basis of magnetic stratigraphy, and from the cores used in these sections, rates of sedimentation were calculated using a date of 0.69 m.y. for the Brunhes/Matuyama boundary. These rates were then contoured and compared with the sediment distribution in the Pacific. The rates of sedimentation in the red clay area of the central Pacific are 3 mm/1000 yrs. The observed rates increased toward the margins of the Pacific in all cases, due to an increase in volcanic, biogenic and glacial detritus present in the cores. The effect of topography on rates of sedimentation is considered. Rates of sedimentation indicate a Miocene age for the time of cessation of turbidite deposition on the Aleutian abyssal plain. A comparison of the known rates of sedimentation with the sediment distribution favors the hypothesis of the mobility of the sea floor.

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Contents

GSA Memoirs

Geological Investigations of the North Pacific

James D. Hays
James D. Hays
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Geological Society of America
Volume
126
ISBN print:
9780813711263
Publication date:
January 01, 1970

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