Magnetic and micropaleontological study of deep-sea sediments from the west-central equatorial Pacific

Abstract

A paleomagnetic study of four oriented deep-sea cores collected by the R.V. Hakuho Maru in the west-central equatorial Pacific Ocean has revealed clear sequences of normal and reversed magnetic polarities. Stability in direction and intensity of the natural remanent magnetization has been examined in some detail to confirm the reliability of the paleomagnetic applications. Two of the cores taken from sites close to the equator contain siliceous microfossils. It has been shown from magnetic stratigraphy aided by paleontological control that one core extends from Recent to the Gauss Normal Epoch while the other core has a stratigraphic hiatus near the top below which the Gauss to Gilbert Epochs are recognized. Ranges of two radiolarian species ( Pterocanium prismatium, Eucyrtidium elongatum peregrinum), five diatom species ( Thalassiosira convexa, Rhizosolenia praebergonii, Actinocyclus ellipticus f. lanceolata, Pseudoeunotia doliolus and Nitzschia fossilis). and a silicoflagellate ( Mesocena elliptica) have been determined for a time span from the late Gilbert Epoch to Recent and compared with the eastern tropical Pacific record. Magnetic stratigraphy of two other cores which have no microfossils seems to indicate that the bottom of these cores is in the late Gauss Epoch. The rates of sedimentation thus calculated with the four cores are 2·0 mm/1000 years to 8·8 mm/1000 years, being roughly consistent with those of the eastern equatorial Pacific cores.