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5 - The geomagnetic polarity time scale

Published online by Cambridge University Press:  05 June 2012

By
J. G. Ogg  and
A. G. Smith
Edited by
Felix M. Gradstein ,
James G. Ogg  and
Alan G. Smith
Felix M. Gradstein
Affiliation:
Universitetet i Oslo
James G. Ogg
Affiliation:
Purdue University, Indiana
Alan G. Smith
Affiliation:
University of Cambridge
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Summary

The patterns of marine magnetic anomalies for the Late Cretaceous through Neogene (C-sequence) and Late Jurassic through Early Cretaceous (M-sequence) have been calibrated by magnetostratigraphic studies to biostratigraphy, cyclostratigraphy, and a few radiometrically dated levels. The geomagnetic polarity time scale for the past 160 myr has been constructed by fitting these constraints and a selected model for spreading rates. The status of the geomagnetic polarity time scale for each geological period is summarized in Chapters 11–22 as appropriate.

PRINCIPLES

Magnetic field reversals and magnetostratigraphy

The principal goal of magnetostratigraphy is to document and calibrate the global geomagnetic polarity sequence in stratified rocks and to apply this geomagnetic polarity time scale for high-resolution correlation of marine magnetic anomalies and of polarity zones in other sections. The basis of magnetostratigraphy is the retention by rocks of a magnetic imprint acquired in the geomagnetic field that existed when the sedimentary rock was deposited or the igneous rock underwent cooling. The imprint most useful for paleomagnetic directions and magnetostratigraphy is recorded by particles of iron oxide minerals.

Most of the material in this chapter is updated from summaries in Harland et al. (1990) and Ogg (1995). Excellent reviews are given in Opdyke and Channell (1996) for magnetostratigraphy and McElhinny and McFadden (2000) for general paleomagnetism.

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Chapter
Information
A Geologic Time Scale 2004 , pp. 63 - 86
Publisher: Cambridge University Press
Print publication year: 2005

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