Abstract
The new magnetic polarity time scale of Cande and Kent ( J. Geophys. Res., 97: 13917–13951, 1992a) provides an opportunity to analyse further the random character of the geomagnetic polarity sequence since 100 Ma. Large differences in the peak amplitudes of changes in magnetic reversal frequency are observed when the previous Harland et al. ( A Geological Time Scale, Cambridge University Press, 1990) and new Cande and Kent sequences are compared. These differences illustrate remaining uncertainties in the significance of these changes. When the successive lengths of polarity intervals are displayed as a function of their order of occurrence in the sequence, a change in behaviour is observed midway through the series. Flat ‘white noise’-like behaviour is observed for the last 100 intervals (from about 25 Ma to the present). For older intervals, a quasi-periodic pattern in interval duration is observed. This evolution is more apparent in the Cande and Kent time scale. The quasi-periodicity of interval duration as a function of occurrence does not translate into periodicity of reversal frequency as a function of time (from 85 Ma to about 25 Ma). Our description of the sequence is reminiscent of the findings of Dubois and Pambrun ( C.R. Acad. Sci., 311: 643–650, 1990), who suggested that low-dimensional deterministic chaos, between 85 and 25 Ma, preceded a random process occurring since then. The details of a long-term control (or memory) of the geomagnetic field remain an open question. Addition of independent information, such as palaeointensity data, will probably be necessary to uncover any determinism in reversal chronology.
Published Version
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call