A paleomagnetic record from Lake Lama, northern Central Siberia

Two cores from Lake Lama, northern Central Siberia, with lengths of 19 and 11 m, respectively, were subjected to detailed magnetostratigraphic investigations. Directions of the characteristic remanent magnetisation (ChRM) were derived from vector analysis of the results from alternating field (A.F.)-demagnetisation, yielding records for the last 18,000 years BP. The sediments show a distinct change in sedimentation pattern at around 14,500 years BP from a highly variable to a monotonous sedimentation with anoxic conditions in the lake sediments during the last 11,500 years BP. The oxic/anoxic boundary is reflected in all rock-magnetic parameters measured and the magnetic mineral fraction is affected by reductive dissolution of iron-bearing minerals, here mainly magnetite. Therefore, no record of relative paleointensity could be achieved. But, as intra- and inter-lake comparison of the obtained inclination and declination records have shown, the directions of the geomagnetic field recorded in the sediments from Lake Lama were not severely affected by the partial dissolution of the remanence carrying minerals.