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doi:10.2204/iodp.proc.303306.113.2006

Paleomagnetism

Archive halves of all cores recovered at Site U1314 were measured on the three-axis cryogenic magnetometer at 5 cm intervals. The natural remanent magnetization (NRM) was measured before (NRM step) and after stepwise alternating-field (AF) demagnetization in peak fields of up to 20 mT. Cores 306-U1314A-1H through 13H and 17H through 20H were AF demagnetized at peak fields of 10 and 20 mT. All other cores were AF demagnetized at a peak field of 20 mT.

Downcore variations in magnetic intensity in Holes U1314A–U1314C are shown in Figure F18. Data associated with intervals identified as physically disturbed were removed. NRM intensities after 20 mT AF demagnetization are in the range of 10^–1 to 10^–2 A/m. These values are much higher than at Sites U1312 and U1313, indicating a higher content of detrital magnetic minerals. Inclination and declination data (after 20 mT AF demagnetization) are shown in Figure F19. Declination values have been corrected using Tensor tool data, which were available starting with Cores 306-U1314A-4H, 306-U1314B-4H, and 306-U1314C-3H. All holes display similar directional changes.

The distribution of inclination values at Site U1314, after AF demagnetization at 20 mT, is composed of two log-normal distributions centered at –66° and +68°. These values are close to the expected site values for a geocentric axial dipole (I_GAD = ±71.6°). These results indicate that most of the drill string overprint was removed at 20 mT, although a small overprint may remain in some intervals as the distributions are slightly skewed toward more positive values.

The magnetostratigraphy was constructed based on the succession of polarity reversals recorded at Site U1314 (Fig. F20). The Brunhes/Matuyama reversal, the Jaramillo and Olduvai Subchrons, and the Matuyama/Gauss reversal are well recorded in these sediments. Site U1314 also provides a good record of shorter geomagnetic events such as Cobb Mountain and Reunion. The Brunhes/Matuyama reversal occurs at 57.3 ± 0.1 mbsf in Hole U1314A, 56.6 ± 0.1 mbsf in Hole U1314B, and 57.7 ± 0.1 mbsf in Hole U1314C. The occurrence depths of the polarity transitions identified at Site U1314 and their possible correlation to the geomagnetic polarity timescale (Cande and Kent, 1995) are detailed in Table T18. The resulting age model is consistent with the biostratigraphy (see “Biostratigraphy”). The deepest magnetic polarity interval recorded at Site U1314 corresponds to the top normal interval of the Gauss Subchron (2An.1n). Core recovery could not reach the underlying polarity interval (Subchron 2An.1r, or Kaena, dated at 3.04 Ma), but extrapolation of the magnetostratigraphy-based age model suggests an age close to 3 Ma for the bottom of Hole U1314B.

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