MagIC Books -- Lectures in Paleomagnetism by Lisa Tauxe -- 2007

Paleomagnetic data are useful in many applications in Earth Science from determining paleocurrent directions to analyzing the long-term behavior of the geomagnetic field. Despite the diversity of applications, the techniques required to obtain and analyze the data are similar. This book attempts to draw together the various principles and practices within paleomagnetism in a consistent and up-to-date manner.

For whom is this book written: This book was written for several categories of readers: for Earth Scientists who use paleomagnetic data in their research, for students taking a class with paleomagnetic content, and for other professionals with an interest in paleomagnetic data. There are a number of excellent references on paleomagnetism and on the related specialties (rock magnetism and geomagnetism). For an excellent introductory text on paleomagnetism, the reader is encouraged to explore Butler (1992). For in-depth coverage of rock magnetism, I recommend Dunlop and Ozdemir (1997). Similarly for geomagnetism, please see Backus et al. (1996). A rigorous analysis of the statistics of spherical data is given by Fisher et al. (1987). The details of paleomagnetic poles are covered in van der Voo (1993) and magnetostratigraphy is covered by Opdyke and Channell (1996). My book is intended to augment or distill information from the broad field of paleomagnetism, complementing and synthesizing the existing body of literature. This book requires a knowledge of basic Earth Science, as well as some physics and statistical theory. At the beginning of every chapter, I recommend specific texts or web-sites that can be used to fill in required background for the subject. I also suggest readings for those who want to go deeper into the subject. It should be stressed that one need not understand every detail of the book to be able to make use of the material presented. I have tried as much as possible to divert technical details to appendices at the end of various chapters.

What is in this book: This book is a series of 16 lectures presented as individual chapters. Each chapter assumes knowledge of the previous chapters so the chapters should be read in order. Chapter 1 begins with a review of the physics of magnetic fields. Maxwell's equations are introduced where appropriate and the magnetic units are derived from first principles. The conversion of units between cgs and SI conventions is also discussed and summarized in a handy table. Chapter 2 turns to the Earth's magnetic field, discussing the geomagnetic potential, geomagnetic elements, and the geomagnetic reference fields. The various magnetic poles of the Earth are also introduced. Chapters 3 to 7 presents the rudiments of rock magnetism necessary to do paleomagnetism. The most important aspect of rock magnetism to the working paleomagnetist is how rocks can become magnetized and how they can stay that way. In order to understand this, we begin with a discussion of what the origin of magnetism is in rocks, including induced and remanent magnetism, anisotropy energy, and mechanisms of magnetization. The magnetic properties of geologically important minerals are described and tabulated, as well as tools for their recognition. Chapter 8 provides a brief tour of environmental magnetism and what I have called "applied rock magnetism''. The nuts and bolts of how to obtain paleomagnetic samples and how to treat them in the laboratory is the topic of Chapters 9 and 10. They cover sampling strategy and routine laboratory procedures, including measurement and demagnetization. Techniques for obtaining both directional and paleointensity information are outlined. Chapters 11 and 12 describe what to do with directional data. They begin with a thorough discussion of Fisher [1953] statistics, describing many useful tests. They then illustrate how to decide whether a particular data set is likely to be Fisherian and Chapter 13 introduces a bootstrap procedure for treating data that are not. Included are many bootstrap tests that perform similar functions to the Fisher based tests that have proved so useful over the years. Magnetic tensor data, primarily anisotropy of magnetic susceptibility are useful in a number of geological applications. The acquisition and treatment of such data is described in Chapter 13. Traditional (Hext, 1963) and more modern (bootstrap) approaches are presented in some detail. Tests for discrimination of eigen-parameters are developed and illustrated with many examples. The final chapters, Chapter 14-16, provide a whistle-stop tour of various paleomagnetic applications. They include a discussion of paleo-geomagnetism magnetostratigraphy, and apparent polar wander.

Acknowledgements: Although I am the sole author, I am indebted to many people for assistance great and small. Thanks are offered to Cathy Constable, Catherine Johnson, Jeff Gee, Bob Parker and all of my former students and post-docs who have contributed in many ways to this book.

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