Geomagnetic excursions recorded in the carbonate rich deep-sea sediments of the central Pacific

Abstract

Paleomagnetic and rock-magnetic analyses have been performed for a carbonate dominant deep-sea sediment archive (~4 m in length) recovered from the central Pacific. Well preserved down-core variation of oxygen isotope (δ18O) values from planktonic foraminifera shows good correlation with SPECMAP δ18O record and provides sediments age up to ~400 kyrs. Paleomagnetic data shows three distinctive deviations in ancient field directions at age controlled sediment horizons of ~40 kyrs, ~120 kyrs and ~190 kyrs, corresponding probably to the Laschamp, Blake and Iceland Basin excursions, respectively. Electron microscopic observation reveals that geomagnetic field variations have been carried by detrital magnetite showing the Curie temperature of ~570°C on thermomagnetic measurements. During the excursions, high values of anhysteretic remanent magnetization (ARM) and saturation of isothermal remanent magnetization (SIRM) with similar values of ARM susceptibility/SIRM are prominent, indicating high influx of magnetic minerals without change in grain-size. In particular, relative paleo-intensities, deduced from natural remanent magnetization/ARM, also decrease during the periods of excursion. Overall, excursions observed in the present study are characterized both by high influx of sediments (magnetic minerals) and geomagnetic field intensity, implying possible linkage between geomagnetic field variation and paleoclimate chananktonic foraminifera shows good correlation with SPECMAP δ18O record and provides sediments age up to ~400 kyrs. Paleomagnetic data shows three distinctive deviations in ancient field directions at age controlled sediment horizons of ~40 kyrs, ~120 kyrs and ~190 kyrs, corresponding probably to the Laschamp, Blake and Iceland Basin excursions, respectively. Electron microscopic observation reveals that geomagnetic field variations have been carried by detrital magnetite showing the Curie temperature of ~570°C on thermomagnetic measurements. During the excursions, high values of anhysteretic remanent magnetization (ARM) and saturation of isothermal remanent magnetization (SIRM) with similar values of ARM susceptibility/SIRM are prominent, indicating high influx of magnetic minerals without change in grain-size. In particular, relative paleo-intensities, deduced from natural remanent magnetization/ARM, also decrease during the periods of excursion. Overall, excursions observed in the present study are characterized both by high influx of sediments (magnetic minerals) and geomagnetic field intensity, implying possible linkage between geomagnetic field variation and paleoclimate chan