A Continuous 150-kyr Record of Geomagnetic Field Variations From Lake Chala, Eastern Equatorial Africa

Abstract

Records of geomagnetic field variations from continental Africa are sparse yet provide a key dating tool for low-latitude paleoclimatic changes. Long-lived tectonic and crater lakes in eastern tropical Africa potentially provide important, long (>100,000 years, kyrs) and continuous sedimentary records of African monsoonal climate over past glacial and interglacial stages; the environmental backdrop to human evolution and dispersion. Here, notwithstanding its low latitude location, we present a detailed paleomagnetic record from eastern equatorial Africa extracted from the upper ∼129 m of a continuous sediment sequence drilled in Lake Chala (3°S; 37°E), a permanently stratified crater lake near Mt. Kilimanjaro. The high and stable sedimentation rate (∼0.85 m/kyr), lack of compaction and reliable paleomagnetic signal (assessed by paleo- and rock magnetic analyses) enabled the production of a new virtual geomagnetic pole (VGP) record for the last ∼150 ka for equatorial Africa. Six magnetic excursions are recorded: Blake 1 and 2, Post-Blake, Laschamp, Mono Lake and Hilina Pali. This exceptional record provides key information on the recurrence and duration of intervals of Quaternary geomagnetic instability, and independently-obtained constraints on the Hilina Pali excursion. Our new paleomagnetic record thus provides a reference data set for late-Quaternary geomagnetic excursions from African sites and a basis for better understanding of the temporal and spatial evolution of Earth's magnetic field. Finally, correlated with a revised geomagnetic instability timescale, these excursions provide a robust, independent age model for the Lake Chala sediment record, critical for correlating its paleoclimate and environmental proxy records to global reference records.