RELATIVE PALEOINTENSITY OF THE GEOMAGNETIC FIELD DURING THE BRUNHES CHRON

Abstract

We conducted a paleomagnetic study of four sediment cores taken from different regions in the low latitudes of the Pacific Ocean in order to recover relative paleointensity variations during the Brunhes chron. Three cores have good age control from oxygen isotope stratigraphy. We extensively examined rock magnetic uniformity by the iso-thermal remanent magnetization (IRM) acquisition and the alternating-field demagnetization of the anhysteretic remanent magnetization (ARM) and the IRM. Only rock-magnetically homogeneous sediments were used. Biogenic magnetites were found in all but one core and their dissolution in early diagenesis was not significant. The four cores showed coherent variations of the remanent intensity normalized by the ARM, implying that these variations represent the behavior of the geomagnetic field. Long-term paleointensity variations during the Brunhes chron are characterized by an asymmetric pattern. Rapid increases in the intensity occurred just after the Brunhes-Matuyama transition, in the mid-Brunhes from about 500 to 400 ka, and during the last 100 ka, and gradual decreases between them. The first one supports the idea of rapid regeneration of the geomagnetic field after polarity reversals [1]. The other two may have been triggered by very short polarity reversals.