Magnetic measurements have been performed on volcanic catchment rocks, present-day soils, and cored sediments from Lake Massoko, an oligotrophic maar-lake from SW Tanzania. Magnetic concentration proxies, low- and high- temperature experiments, and hysteresis behavior, suggest significant contributions of Ti-magnetite and SP/SD (oxidized) magnetite in tuff-ring material transformed by pedogenesis (modern soil, littoral sand). In contrast, the basalt is characterized by relatively low concentrations of PSD-SD magnetite. Three depth/time intervals present magnetic signatures similar to the modern soils and littoral sands, at ~43-38 kyr, ~12-1.3 kyr, and 400-300yr BP (the uppermost 30 cm). They likely correspond to humid (high-lake stand) periods, with increased pedogenic processes and runoff. Other sediments have magnetic signatures closer to the catchment basalt, possibly indicating arid/low-stand periods with increased detrital inputs from the basaltic crater wall. Sediments deposited during the Last Glacial Maximum (~38-12kyr) present high Jrs/Js-high Hcr/Hc intervals, indicating an additional high coercivity component of unknown origin.
|Original language||English (US)|
|Number of pages||5|
|Journal||Physics and Chemistry of the Earth, Part A: Solid Earth and Geodesy|
|State||Published - 1999|
Bibliographical noteFunding Information:
Many thanks to S. Massola and the Ministry of Energy. Water and Mmerals of Tanrama. and to A lssah (Massoko village School) for their help during field work We also thank Kerry Kelts, Chnstoph G&B, Bruce Moskowitz and an anonymous reviewer, who made very useful comments and remarks during this study. This work was funded by the EC Rukwa program. the INSU-CNRS-Variente program, and a NATO fellowship. The lnstltute for Rock Magnetism 1s funded by the NSF Earth Science instrumentation and Facilities Program and the WM. Keck foundation This 1s IRM publication #9806