HR: 14:25h
AN: GP32A-04    [PDF]
TI: Geomagnetic Polarity Timescales and Reversal Frequency Regimes
AU: * Lowrie, W
EM: lowrie@mag.ig.erdw.ethz.ch
AF: ETH Zurich, Institute of Geophysics, Zurich, 8093 Switzerland
AU: Kent, D V
EM: dvk@rci.rutgers.edu
AF: Rutgers University, Dept of Geological Sciences, Piscataway, NJ 08854-8066 United States
AU: Kent, D V
EM: dvk@rci.rutgers.edu
AF: Lamont-Doherty Earth Observatory, Paleomagnetic Laboratory, Palisades, NY 10964-8000 United States
AB: An analysis of geomagnetic reversal history is made for the most reliable polarity timescales covering the last 160 Myr. The timescale of Cande and Kent [1995] (CK95) is the optimum representation of Cenozoic and Late Cretaceous polarity history, and the timescale of Channell et al. [1994] (CENT94) best represents the Early Cretaceous and Late Jurassic. The CK95 timescale can be divided into two nearly linear segments at chron C12r. The lengths of chrons in the younger segment have no systematic trend and so this part of the sequence is considered to be stationary for statistical analysis. The mean chron length is 0.248 Myr and the gamma index, k, for the distribution of chron lengths is 1.6 $\pm$ 0.4; inserting just 8 additional short subchrons that have been verified from magnetostratigraphic studies as polarity reversals reduces the mean chron length to 0.219 Myr and k to 1.3 $\pm$ 0.3. The older segment is stationary if the two long polarity chrons C33n and C33r adjacent to the Cretaceous Normal Polarity Superchron are omitted; in this case the mean chron length is 0.749 Myr and k is 1.2 $\pm$ 0.4. The chrons in the CENT94 timescale are stationary with mean length 0.415 Myr and k = 1.3 $\pm$ 0.3. The gamma indices of the chron distributions are not significantly different from a Poisson distribution (k = 1), which implies that the reversal process is free of long-term memory. The concept of an inhibition period, in which a new reversal is unlikely for an extended period after a reversal, appears to be unnecessary. However, if the mean chron duration is an indicator of stability of the reversal process, it appears that a long lasting episode of stable behavior may be followed by abrupt change to another stable regime with a markedly different reversal frequency. There is no significant change of the gamma index from one regime to another, although the average reversal rate changes by more than a factor of three. The probability of a reversal per unit time has a constant value within each regime (k = 1), but the value appears to vary from regime to regime in proportion to the reversal rate.
DE: 1535 Reversals (process, timescale, magnetostratigraphy)
DE: 1560 Time variations--secular and long term
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting