Temporal and spatial variations of the geomagnetic field, up to a timescale of 10⁵ years

• Main Author: Turton, Ian
• Published: University of Edinburgh 1992
• Subjects: 550
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.663121

This thesis comprises two parts. The main part is involved with laboratory studies of the palaeosecular variation of the geomagnetic field as recorded in lake sediments. The natural remanent magnetization of the sediments cored from the two Italian maar lakes, Lago di Monticchio and Lago di Martignano, has been studied. Further studies were carried out on the sediments of Lago di Martignano to determine the cause of large variations in the magnetic intensity of the sediments with an age of ˜ 6000 years BP and it was concluded that this was caused by the arrival of Neolithic man and the advent of agriculture in the catchment area. The directional record for this lake was also compared to the established record for north west Europe. Several declination and inclination features could be correlated between the two records. The record from Lago di Martignano can be accepted as a regional palaeomagnetic reference curve for central Italy. Cores up to 50m long were taken from Lago di Monticchio. Whilst not yet firmly dated, it is agreed that this record spans the last 250,000 years. A relative palaeointensity record has been calculated and spectral analysis has been carried out. It is concluded provisionally that the palaeointensity recorded in the sediments was effected by the astronomical frequencies associated with precession of the earth, the eccentricity and the obliquity of the Earth's orbit. The second part of this thesis is concerned with modelling the palaeosecular variations as recorded in sediments around the world through the Holocene, i.e. the last 10,000 years. The properties of sequential secular variation records from sediments are compared with palaeosecular variation scatter determined from sets of lava flows. It is concluded that a comparison between PSV recorded in lava flows and lake sediments is valid.