Age controlled paleomagnetic records of deep-sea sediments in the Northeast equatorial Pacific

Abstract:

A 570 cm long sediment core was recovered from 9°57ʹN and 131°42ʹW at 5,080 m water depth in the Clarion-Clipperton (C-C) fracture zone of the Northeast equatorial Pacific. The sediment core recovered is composed of alternating two phases showing dark brown and yellowish brown colors, respectively. The C-C zone shows various sedimentation rates of less than several mm/kyr and a zonal sediment distribution pattern. To clarify sedimentation age and possible periodical difference in sedimentation rates, paleomagnetic measurements and ¹⁰Be age dating are made. Stable characteristic remanent magnetization (ChRM) component converging to origin is isolated from at least five AF demagnetization steps between15 and 50 mT. Notably half of measurements shows that the ChRM component is almost antipodal against low-coercivity component erased in the AF fields of <15 mT. This phenomenon becomes clear near the boundary showing the ChRM polarity change, suggesting paleomagnetic signals are buried due to low sedimentation rates. As a result, eight times of geomagnetic field reversals are identified. In the reference geologic time scale, the eight reversal events correspond to the age of about 4.5 Ma. However, ¹⁰Be based age correction shows 13.4 Ma at the depth of 465 cm. In addition, calculated sedimentation rates are changed in the range of 0.1–2.44 mm/kyr. Around the depth of 110 cm, the lowest sedimentation rate occurs and paleomagnetic records of at least 1.8 Myr are erased. Distinctive correlation between sedimentation phase and rate can be found. Sedimentation rates of dark brown and yellowish brown sediments are <0.4 mm/kyr and >1 mm/kyr, respectively. Such alternation of sediments with different sedimentation rates are possibly caused by a periodical change in sediment provenances.