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Title: Palaeomagnetic and magnetic records for the last 300,000 years from Lac du Bouchet, France : applications to geomagnetism and the environment
Author: Williams, Trevor
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1994
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In 1990, four 50m-long sediment cores were recovered from Lac du Bouchet, a small maar crater lake in the Massif Central of France. The sediment was deposited continuously over the last 300,000 years (3 full glacial-interglacial cycles), and forms a high resolution sequence which is the subject of multi-disciplinary examination at laboratories in Edinburgh, Marseille and Louvain. This thesis is concerned with the use of palaeomagnetic measurements to reconstruct the past geomagnetic field, and the use of rock-magnetic measurements to complement the other disciplines in reconstructing past environmental conditions at Lac du Bouchet. The study is an extension of previous studies of 20m-long cores from Lac du Bouchet, which covered the last 120,000 years. The cores were sampled at 2&h183;5cm spacing, giving a total of around 2500 samples. The natural remanent magnetisation (NRM), and laboratory implanted magnetisations (susceptibility, IRM and ARM) of each sample were measured. The top 20m of the sequence had already been dated by 14C to 45 ka, and by correlation to the marine δ18O stratigraphy back to δ18O stage 5e. The organic-rich sediments between 32 and 37m depth have been correlated to δ18O stage 7 by palynology, and the base of the core is thought to be of δ18O stage 9 age. The magnetic measurements of susceptibility, IRM and ARM principally reflect the concentration of the magnetic mineral (a low-Ti titano-magnetite) which is derived from the maar crater walls. Susceptibility is low in organic sediments deposited in warm climates, and the record has a very close inverse correlation to the arboreal/non-arboreal pollen ratio. It therefore provides a record of the palaeoenvironment at Lac du Bouchet. The δ18O sub-stages 5a-e and 7a-e are well defined; substantial changes in susceptibility occur within the last two interglacials; and short duration susceptibility flows punctuate the last glacial.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available