Magnetic polarity zonation and biostratigraphy of late Cretaceous and Paleocene continental deposits, San Juan Basin, New Mexico.

Abstract

Paleomagnetic samples were collected at over 600 sites (3 samples per site) through the late Cretaceous to middle Paleocene age continental sedimentary sequence in the San Juan Basin. The sampled lithostratigraphic units include the Fruitland, Kirtland, and Nacimiento Formations as well as the Ojo Alamo Sandstone. Alternating field demagnetization to peak fields of 200 to 300 oe was required to remove secondary components in order to reveal the polarity of the primary depositional remanent magnetizm. Unambiguous polarity determinations were possible for almost all sites. The magnetic polarity zonation shows a strong correlation with the magnetic polarity time scale (for example, the sea-floor anomaly sequence) in the interval of anomalies 25 through 31. This correlation is strongly supported by the vertebrate fossil occurrences and by a radiometric date of 64.6 + or - 3.0 Ma from an ash layer in the late Cretaceous Kirtland Formation. -Authors