CHAPTER THREE MAGNETIC STRATIGRAPHY IN PALEOCEANOGRAPHY: REVERSALS, EXCURSIONS, PALEOINTENSITY, AND SECULAR VARIATION

Abstract

This chapter focuses on the magnetic stratigraphy in paleoceanography. Magnetic stratigraphy rests on the idea that the recorded magnetization of a rock reflects the behavior of the geomagnetic field. In the simplest case, the natural remanent magnetization (NRM) of sediment is aligned with the (geo)magnetic field and is a function of its intensity and direction at the time of deposition. In practice, many factors may work to modify the original geomagnetic input signal. Under favorable circumstances and with detailed diligence, some of these effects can be separated and others avoided so that an accurate paleomagnetic record is recovered. Paleomagnetism has been working to keep pace and a significant new understanding of geomagnetic field behavior during times of constant polarity has begun to emerge. Essentially, it has been found that high amplitude, high frequency variations in the Earth's magnetic field occur over large spatial scales even during times of constant polarity. New magnetostratigraphic opportunities over a range of temporal and spatial scales are emerging. The chapter also outlines the practical aspects of reconstructing the paleomagnetic record from marine sediments, and discusses some of the recent observations on the Quaternary geomagnetic record that are being made and their uses as a stratigraphic tool for paleoceanographic research.