Late-Holocene paleomagnetic secular variation records from Lake Turkana, East Equatorial Africa

We have carried out a paleomagnetic study of three piston cores collected from Lake Turkana. The goal is to recover a Holocene paleomagnetic secular variation (PSV) record for this lake and to correlate it with other Holocene PSV records from the East Africa Rift Valley (EARV). All three cores were sampled with u-channels and magnetic measurements of magnetic susceptibility, the natural remanence (NRM), and two artificial remanences, anhysteretic remanence (ARM) and saturation isothermal remanence (SIRM), were made on them. The remanences were routinely step-wise demagnetized and measured at 10mT steps up to 60mT. The NRMS had a simple pattern of demagnetization with a characteristic direction (ChRM) removed between 10 and 60 mT. ARM and SIRM demagnetization indicated that the magnetic grains were relatively soft with median destructive fields (MDF) less than 30 mT. We interpret the magnetic grains to be multi-domain (silt-sized) magnetite/titanomagnetite. The resulting magnetic records of all three cores could be correlated. A chronology for these cores was determined from four radiocarbon dates on core 4P. We also estimated the sediment ages by correlating the PSV to two other well-dated PSV records from the same region, Lakes Malawi and Victoria. PSV age estimation indicates that the radiocarbon dates are about 500year too old; a correction for that offset causes three of the four radiocarbon ages to become consistent with the PSV age estimates. The final composite Lake Turkana PSV record for the last similar to 4000years is the highest resolution directional record of PSV (similar to 200cm/ky) ever to be recovered from Africa.

Automated summary

A paleomagnetic study was conducted on three piston cores from Lake Turkana to recover a Holocene paleomagnetic secular variation (PSV) record and correlate it with other PSV records from the East Africa Rift Valley. Magnetic measurements were made on the cores, and the resulting records could be correlated. The sediment ages were estimated through PSV age estimation and radiocarbon dating, and showed good consistency. The Lake Turkana PSV record is the highest resolution directional record of PSV ever recovered from Africa.