Full-vector paleomagnetic secular variation records from latest quaternary sediments of Lake Malawi (10.0°S, 34.3°E)

Abstract

We have conducted a paleomagnetic study of Late Quaternary sediments from Lake Malawi, East Africa, in order to develop a high-resolution record of paleomagnetic secular variation (PSV). This study has recovered PSV records from two cores (3P, 6P) in northern Lake Malawi (10.0°S, 34.3°E). The PSV appears to be recorded in fine-grained detrital magnetite/titanomagnetite grains. Detailed af demagnetization of the natural remanence (NRM) shows that a distinctive characteristic remanence (ChRM) is demagnetized from ~20-80 mT, which decreases simply toward the origin. The resulting directional PSV records for 3P and 6P are easily correlatable with 29 distinct inclination features and 29 declination features. The statistical character of the PSV in both cores is consistent with Holocene PSV noted at other Holocene equatorial sites. Radiocarbon dating of the cores is based on 18 independent radiocarbon dates and four dated stratigraphic horizons that can be correlated into each core. The final directional PSV time series cover the last 24,000 years with an average sediment accumulation rate of ~30 cm/kyr. We have also developed a relative paleointensity estimate for these PSV records based on normalizing the NRM (after 20 mT af demagnetization) by the SIRM (after 20 mT af demagnetization). Changing sedimentation patterns complicate any attempt to develop a single paleointensity record for the entire core lengths. We have developed a relative paleointensity record for the last 6000 years that has 14 correlatable features including 5 notable peaks in intensity. Three of these peaks are synchronous with paleointensity highs farther north in SE Europe/SW Asia/Egypt but two of the peaks are at times of low paleointensity farther north. We interpret this to indicate that Lake Malawi (10°S) is at least partly under the influence of a different flux-regeneration region of the outer-core dynamo. A relative paleointensity record was also developed for ~11,000-24,000 YBP; the general pattern appears to be consistent with other published records, but our confidence in the correlations is more limited.

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

“…Limited age control and some lack of PSV replication among those other records preclude us from providing any clear correlation between those PSV records and our own records. A more recent PSV study of Lake Malawi by Lund et al (2016) reached the same conclusion.…”

“…of less than 6°. This is twice the 'noise' level of paleomagnetic measurements from Lake Malawi (Lund et al, 2016). There is commonly a significant (25-40%) 'viscous' magnetic overprint, which is demagnetized by 10 mT.…”

“…However, we do think we can correlate our Lake Victoria PSV records with those from Lake Malawi. Figure 11 plots our Lake Malawi PSV records (Lund et al, 2016) for the last 14,000 cal. yr BP, the interval of overlap with the Lake Victoria PSV.…”

“…PSV data and feature numbering from Lake Malawi cores 3P (top) and 6P (bottom) for the last 14,000 cal. yr BP.Source: FromLund et al (2016).…”

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

“…To date, there are regions where relatively little is known about Holocene field variability; the African continent is one of those regions. This study is the third in a series of new investigations (Lund et al, 2016, 2019) to carry out detailed paleomagnetic studies of lake sediments from the East African Rift Valley (EARV). The primary goal is to recover paleomagnetic secular variation (PSV) records for Holocene time to help improve our understanding of the space/time pattern of PSV.…”