Geomagnetism and Palaeomagnetism

This volume presents lectures given at the NATO Advanced Study Institute held 11-22 April 1988 at Newcastle upon Tyne, England. The aim of the Institute was to improve the interaction between workers in observational geomagnetism (using historical data) and archaeo- and palaeo-magnetism (using the remanent magnetization of man-made artefacts and of natural sediments and rocks) and those trying to interpret the data in terms of mechanisms inside or outside the Earth, particularly those developing dynamo theories of the field. The material discussed ranged from magnetic bacteria swimming round a circle in a few seconds, the effect of El Nino, through secular variation with time scales of tens to thousands of years and the'mechanics of individual field reversals and excursions (aborted reversals?) to possible modulation of average reversal frequency on the hundred million year time scale. Many members of the Physics Department helped with the organization, and we are most grateful to them, and in particular to Anne Codling for her very many contributions. We also gratefully acknowledge the painstaking work of Aileen Dryburgh and Lynn Whiteford in so carefully typing the manuscript.

Contenu

Section I. Geomagnetic Secular Variation back to 50 000 years BP.- A Spherical Cap Harmonic Model of the Crustal Magnetic Anomaly Field in Europe Observed by MAGSAT.- Geomagnetic Secular Variation.- Historical Secular Variation and Geomagnetic Theory.- Changes in the Earth's Rate of Rotation on an El Niño to Century Basis.- Geomagnetic Secular Variation in Britain During the Last 2000 Years.- Detailed Palaeomagnetic Record for the Last 6300 Years From Varved Lake Deposits in Northern Sweden.- The Lac Du Bouchet Palaeomagnetic Record: Its Reliability and Some Inferences About the Character of Geomagnetic Secular Variations Through the Last 50000 Years.- Developments in Cave Sediment Palaeomagnetism.- Evidence for Wave Propagation in the Holocene Palaeomagnetic Field.- Section II. Excursions.- Bruhnes Chron Geomagnetic Excursion Recorded During the Late Pleistocene, Albuquerque Volcanoes, New Mexico, U.S.A..- Short Reversal of the Palaeomagnetic Field About 280 000 Years Ago at Long Valley, California.- Section III. Reversals: Observation and Modelling.- Magnetic Polarity Time Scales and Reversal Frequency.- Observations and Models of Reversal Transition Fields.- A Phenomenological Model for Reversals of the Geomagnetic Field.- Deterministic Chaos, Geomagnetic Reversals, and the Spherical Pendulum.- Geomagnetic Polarity Reversals: Can Meteor Impacts Cause Spall Disruption into the Outer Core.- Section IV. Origin and Analysis of Remanence.- Magnetic Bacteria in Lake Sediments.- Magnetization of Sediments and Depositional Environment.- Timing Between a Large Impact and a Geomagnetic Reversal and the Depth of NRM Acquisition in Deep-Sea Sediments.- Tests of Magnetic Properties of New Zealand Pliocene Marine Mudstones.- Some Aspects of the Measurement of Magnetic Anisotropy.- The Magnetism of Ordinary Chondrites and SNC Meteorites: Possible Implications for Ancient Solar System Magnetic Fields.- Section V. Geodynamo Theory.- Geodynamo Theory.- Long-Term Palaeofield Variations and the Geomagnetic Dynamo.- Compositional Convection and the Earth's Core.- Numerical Models in the Theory of Geomagnetism.