Abstract: An Updated Time Scale for the Cretaceous of North America

John D. Obradovich

A new highly precise, geochronometric time scale (Obradovich, 1993) has been established for the 70+ ammonite zones of W. A. Cobban under the aegis of the Weaton Interior Cretaceous project (WIK). This new time scale is based on ⁴⁰AR-³⁹AR laser fusion dating of sanidine crystals recovered from 30 of the many intercalated bentonites. Additional levels have since been dated as new and potentially datable betonites have been discovered. This study also is gradually being expanded to include the Upper Cretaceous marine strata of the Gulf Coast region and a number of the geographically isolated but dominantly continental basins of the Western Interior. Coupled to this integrated geochronometric-biostratigraphic framework is a revised paleomagnetic time scale for the C ron 33N to 29R interval.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994