Application of the palaeomagnetic stratigraphy discussed in the previous section to Pleistocene problems suffers from the limitation that no easily recognizable polarity changes have been found within the past 700 t.y.–the period of greatest interest in glacial stratigraphy. For the earlier part of the Pleistocene, palaeomagnetic dating has a great potential value which is still largely unexploited. Palaeomagnetic evidenceis now being used to date events recorded in deep–sea cores the boundaries of faunal and floral zones, climatic sequences, and environmental changes revealed by lithology. So far (1969), records of about 50 cores have been published showing magnetic polarity chnages as well as palaeontological or climatic evidence, but not all are helpful for dating.
Age-determination, even in a corewhich has satisfactory magnetic stability and a number of polarity reversals, are often subject to difficulties and uncertainties. The palaeomagnetic time-scale is as yet tentative; more reference points are needed in volcanic rocks, and a few magnetic logs of deep-sea cores gives a full record of magnetic changes. The palaeomagnetic record of a core to be dated should includen at least one other magnetic parameter (e.g. intensity) in addition to the polarity changes; otherwise, brief events such as the Gilsa event or the short reversed period thought to occur within the Olduvai normal event are unlikely to be recorded. Mixing of sediment, while capableof masking a polarity change lasting say 20to 30 t.y., may still leave some indication of variations in intensity and inclination.
The recognition of brief events can be a safeguard
