Preliminary 50m palaeomagnetic records from Lac du Bouchet, Haute Loire, France
Following on from earlier studies carried out in successive phases, four much longer cores were collected from Lac du Bouchet, a maar lake in the Velay region of France (44·9°N; 3·8°E). Preliminary palaeomagnetic records from core H to a depth of 46m are presented here. Measurements of natural remanant magnetization (NRM), both raw and after demagnetization in alternating fields of up to 60mT were carried out on 1382 subsamples. Also anhysteretic [ARM] and isothermal [IRM] remanent magnetizations, and low field magnetic susceptibility were measured to give a picture of the changes in magnetic mineralogy recorded downcore. These laboratory implanted magnetizations are useful as proxy indicators of climate and for assessing the suitability of the sediment for making estimates of relative geomagnetic palaeointensity. We have, at this stage of the work, normalized NRM intensity only with susceptibility but argue that this provides a valid record of palaeointensity, except for where the sediment is highly organic. Preliminary pollen analyses suggest that Holsteinian interglacial sediments are present at a depth of about 42m, so it is though that the records cover at least the last 250000 years. Long wavelength, high amplitude oscillations in palaeointensity are found which are different from the oscillations in climate over this period.
KeywordsLake Sediment Natural Remanent Magnetisation Core Section Magnetic Mineralogy Maar Lake
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- Bonifay, E., Creer, K.M., Smith, G., Thouveny, N., Truze, E., and Tucholka, P. A preliminary palaeomagnetic survey of the Holocene and late Wurmian sediments of Lac du Bouchet (Haute Loire, France). Geophys. J. Roy. astr. Soc., 86, 943–964, 1986.Google Scholar
- Bonifay, E., Creer, K.M., de Beaulieu, J.L., Casta, L., Delibrias, G., Perinet, G., Pons, A., Reille, M., Servant, S., Smith, G., Thouveny, N., Truze, E. and Tucholka, P. Study of the Holocene and late Würmian sediments of Lac du Bouchet (Haute-Loire, France): first results. pp 90–116 in Climate: History, Periodicity and Predictability, eds: M.R. Rampino, J.E. Sanders, W.S. Newman and L.K. Königsson, van Nostrand Reinhold Co Inc; Stroudsburg. 1987.Google Scholar
- Constable, C.G., and Tauxe, I. Palaeointensity in the pelagic realm: marine sediment data compared with archaeomagnetic and lake sediment records. Geophys. J.R. astr. Soc., 90: 43–59, 1987.Google Scholar
- Creer, K.M. The Lac du Bouchet palaeomagnetic record: its reliability and some inferences about the character of geomagnetic secular variations through the last 50,000 years. pp 71–89 in Geomagnetism and Palaeomagnetism, eds. F.J. Lowes, D.W. Collinson, J.H. Parry, S.K. Runcom, A.W. Soward and D.C. Tozer, Kluwer Academic Press, Dordrecht, 1989.Google Scholar
- Creer, K.M. Dating of a maar lake sediment sequence covering the last glacial cycle. Quaternary Proceedings, 1: 75–87. 1991.Google Scholar
- Reille, M. and de Beaulieu, J.L. La fin de L'Eemian et les interstades du Prewurm mis pour la premiere fois en evidence dans le massif central francais par l'analyse pollinique. C. R. Acad. Sci., Paris. 1988.Google Scholar
- Sorley, R. Susceptibility and climatic variations down a lake sediment core. Internal Report, Dept of Geophysics, Edinburgh, 34pp. 1989.Google Scholar
- Thouveny, N. Variations of the relative palaeointensity of the geomagnetic field in western Europe in the interval 25-10 Ka BP as deduced from analyses of lake sediments. Geophys. J.R. astr. Soc., 91: 123–142. 1987.Google Scholar
- Tucker, P. Magnetisation of unconsolidated sediments and theory of DRM. pp 9–19 in: K.M. Creer, P. Tucholka and C.E. Barton (eds.), Geomagnetism of Baked Clays and Recent Sediments, Elsevier; Amsterdam. 1983.Google Scholar
- Tucker, P. A grain mobility model of post-depositional realignment. Geophys. J.R. astr. Soc. 63: 149–163, 1980.Google Scholar