In this paper we report new paleomagnetic and rock-magnetic results from Equatorial Pacific sediments obtained during Ocean Drilling Program Leg 199 (Site 1220; 10.17°N, 142.75°W). ODP Leg 199 was designated to collect sediments along a latitudinal transect in the Pacific Ocean to better understand Paleogene sedimentation patterns and the system of equatorial currents and thus magnetic chronology was an essential part. Continuous paleomagnetic measurements of u-channel samples were complemented by analysis of discrete samples. The results support the overall polarity pattern obtained on the shipboard pass-through magnetometer. Both rock-magnetism and paleomagnetic data show the presence of magnetite as the main carrier of the remanence. The recovered magnetostratigraphy spans from Chron C20r (mid-Middle Eocene)) through Chron 6An.1n (Early Miocene) and constitutes an unprecedented record for the Pacific Ocean. Mean sediment accumulation rates range from 8 m/Ma in the middle Eocene to 3 m/Ma in the Late Oligocene. We do not observe short polarity events that might account for tiny wiggles in Chrons C12r or C13r, favoring the interpretation that they represent paleointensity variations of the geomagnetic field. Alternatively, short polarity events might have been smoothed or wiped out by delayed remanence acquisition. When plotted against time, paleomagnetic inclinations show a polarity-dependent anomaly, which is larger during times of normal polarity. Possible origins of such inclination anomaly include partial overprint and a non-dipole field contribution.

A middle eocene-early miocene magnetic polarity stratigraphy in equatorial pacific sediments (ODP site 1220)

LANCI, LUCA
2004

Abstract

In this paper we report new paleomagnetic and rock-magnetic results from Equatorial Pacific sediments obtained during Ocean Drilling Program Leg 199 (Site 1220; 10.17°N, 142.75°W). ODP Leg 199 was designated to collect sediments along a latitudinal transect in the Pacific Ocean to better understand Paleogene sedimentation patterns and the system of equatorial currents and thus magnetic chronology was an essential part. Continuous paleomagnetic measurements of u-channel samples were complemented by analysis of discrete samples. The results support the overall polarity pattern obtained on the shipboard pass-through magnetometer. Both rock-magnetism and paleomagnetic data show the presence of magnetite as the main carrier of the remanence. The recovered magnetostratigraphy spans from Chron C20r (mid-Middle Eocene)) through Chron 6An.1n (Early Miocene) and constitutes an unprecedented record for the Pacific Ocean. Mean sediment accumulation rates range from 8 m/Ma in the middle Eocene to 3 m/Ma in the Late Oligocene. We do not observe short polarity events that might account for tiny wiggles in Chrons C12r or C13r, favoring the interpretation that they represent paleointensity variations of the geomagnetic field. Alternatively, short polarity events might have been smoothed or wiped out by delayed remanence acquisition. When plotted against time, paleomagnetic inclinations show a polarity-dependent anomaly, which is larger during times of normal polarity. Possible origins of such inclination anomaly include partial overprint and a non-dipole field contribution.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11576/1890993
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