On the age calibration of the geomagnetic polarity timescale

Knowledge of the age of undated events is not null if a time-order relation ship can be found among these events. The knowledge of such a time-ordered sequence can be formalized by using non-informative (uniform) prior probabi lity densities for the ages of undated events and Bayes' theorem to introdu ce the time-order relationship condition. We show that the conditional prob ability densities of the ages of events of unknown age are given by various forms of Euler's beta distribution. These distributions yield an estimate of the probability for an undated event to occur in a given age interval. We use this method to propose appropriate probabilistic representations of our actual knowledge of the dating of the magnetic polarity reversals durin g the Cenozoic. These representations take into account the uncertainties a rising from irregularities in accretion process and from the quality of a f ew calibration points. Both types of uncertainties generate large ambiguiti es in the age of magnetic reversals, which should be taken into considerati on when the geomagnetic polarity timescale is used for dating purposes. We propose to use the entropy function to quantify these ambiguities.