The geomagnetic polarity has changed irregularly at least 20 times during the last 5 m.y. These polarity changes are worldwide synchronous events and are readily recorded by most sediments of fine silt or smaller size. For reasons which are not clearly understood, polarity and faunal changes sometimes occurred simultaneously. It follows that the paleomagnetic method is a very powerful technique for resolution of Plio-Pleistocene stratigraphic problems.

Like many new techniques, the method is susceptible to misapplication. The misapplication may result from lack of consideration of (a) variable deposition rates, (b) disconformities and unconformities, (c) faunal redeposition, (d) magnetic recording lag of consolidating sediment, (e) imperfectly defined polarity history, (f) limitations of unoriented cores in low latitudes, and (g) experimental difficulties. Results from continuing studies of deep-sea sedimentary cores from the South Pacific illustrate some of the difficulties.

It is concluded that the study of paleomagnetism in marine sedimentary cores parallels the earliest conventional stratigraphic methods, in that integration of several disciplines is required for efficient and reliable exploitation of the technique.

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