Palaeomagnetic secular variation studies of Finnish lake sediment and the carriers of remanence

Abstract

Palaeomagnetic and mineral magnetism measurements have been carried out on two cores from Lake Vuokonjarvi in Finnish Karelia. The sediment probably covers 5000 years of continuous deposition at a mean sedimentation rate of about 0.8 mm/yr. The magnetic declination exhibits fluctuations of similar amplitude (∼20°) and character to those recorded in northern England and northern Ireland. Magnetic inclination variations are of higher amplitude (∼15°) than those found in Britain. Matching the palaeomagnetic patterns with the dated British master curves permits an estimate of the rate of deposition of the Finnish sediments, which is suggested to be more reliable than estimates from radiocarbon dating of the Vuokonjarvi sediment. The stable natural remanence is shown to be carried by fine-grained magnetite and titanomagnetite grains and to have grown by post-depositional alignment during a period of the order of 100 years. Laboratory dehydration of the sediment results in loss of around 40% of the stable natural remanence. Such behaviour is also found in lake sediments from central and southern Europe and should be considered in interpreting palaeomagnetic data from dried out lake sections and ocean cores.