Figure 31. Paleomagnetic-polarity column showing ages of polarity reversals and durations of polarity chrons for latest Cretaceous strata based on data from San Juan Basin, New Mexico. Polarity-chron durations and reversal ages for Cretaceous magnetochrons were determined by proportionalizing chron durations of
Cande and Kent (1992,
1995) between ages of 65.51 Ma for the Cretaceous-Tertiary (K-T) boundary (Hicks et al. 2002) and 73.50 Ma for the C33n-C32r reversal (Fassett and Steiner 1997;
Fassett 2000). Polarity-chron ages above K-T boundary are from
Gradstein et al. (2004). Ages of ash beds J and H in polarity chron C32r from
Fassett and Steiner (1997).