The new magnetic polarity time scale of Cande and Kent (J. Geophys. Re
s., 97: 13917-13951, 1992a) provides an opportunity to analyse further
the random character of the geomagnetic polarity sequence since 100 M
a. Large differences in the peak amplitudes of changes in magnetic rev
ersal frequency are observed when the previous Harland et al. (A Geolo
gical Time Scale, Cambridge University Press, 1990) and new Cande and
Kent sequences are compared. These differences illustrate remaining un
certainties in the significance of these changes. When the successive
lengths of polarity intervals are displayed as a function of their ord
er of occurrence in the sequence, a change in behaviour is observed mi
dway through the series. Flat 'white noise'-like behaviour is observed
for the last 100 intervals (from about 25 Ma to the present). For old
er intervals, a quasi-periodic pattern in interval duration is observe
d. This evolution is more apparent in the Cande and Kent time scale. T
he quasi-periodicity of interval duration as a function of occurrence
does not translate into periodicity of reversal frequency as a functio
n 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 deterministi
c chaos, between 85 and 25 Ma, preceded a random process occurring sin
ce then. The details of a long-term control (or memory) of the geomagn
etic field remain an open question. Addition of independent informatio
n, such as palaeointensity data, will probably be necessary to uncover
any determinism in reversal chronology.