Sedimentary record of two geomagnetic excursions within the last 15,000 years in Beijing, China

Abstract

A fresh‐water sedimentary sequence from Haidian in the Beijing basin has been sampled in three parallel trenches up to 300 m apart for paleomagnetic study. Age control is provided by nine radiocarbon dates, indicating an average accumulation rate of 45 cm/ka. A total of 683 specimens were measured for paleomagnetic directions. Two short excursions of field direction are recorded at closely comparable depths in all three cores, occurring between 5,060 and 4,860±90a B.P. and 14,230 and 13,690±130 a B.P. interpolated ages. The paleomagnetic records for the individual trenches were adjusted to a common depth scale using stratigraphic markers and then merged. The record correlates quite well with a paleomagnetic record in Beijing‐basin sediments 55 km to the southwest (Changgou section), with regard to both the large excursions and also some of the smaller variations in direction. The excursions appear to reflect real geomagnetic phenomena, not artifacts of recording, but the spatial extent (regional or global) of the anomalous geomagnetic signals is not known.