Paleomagnetic secular variation records from Holocene sediments of Lake Victoria (0.5°S,33.3°E)

Abstract

We have conducted a paleomagnetic study of Holocene sediments from Lake Victoria in order to develop a high-resolution record of paleomagnetic secular variation (PSV). This study has recovered PSV records from two cores (V95-1P and V95-7P) in northern Lake Victoria (0.5°S). The PSV is recorded in fine-grained detrital magnetite/titanomagnetite grains, but the rock magnetic data suggest that significant magnetic mineral dissolution has occurred, which limits our paleomagnetic studies to the uppermost ~5 m of both cores. Detailed alternating field (af) demagnetization of the natural remanence (NRM) shows that a distinctive characteristic remanence (ChRM) is demagnetized from ~10 to 40 mT, which decreases simply toward the origin. The resulting directional PSV records for 1P and 7P are correlatable with 22 distinct inclination features and 19 declination features. Radiocarbon dating of the cores is based on eight radiocarbon dates from core 1P, which can be correlated into core 7P using both the PSV and rock magnetic/environmental measurements. The final PSV time series cover the last 11,000 years with an average sediment accumulation rate of ~40 cm/kyr. The Lake Victoria PSV records can be correlated with new PSV records from Lake Malawi. Comparison of the correlatable PSV feature ages between the two lakes indicates that the PSV records are not significantly different in age, although Lake Victoria PSV ages might average ~100 years younger. We think that the Lake Victoria and Lake Malawi PSV records, together, provide the most accurate, well-dated, and consistent record of Holocene PSV for Africa yet developed.