Numerical Age Calibration of the Albian/Cenomanian Boundary

摘要: New biostratigraphic and sequence stratigraphic correlations of the U.S. Western Interior Albian/Cenomanian sections with North Texas European calibrate boundary at 97.2 Ma, which supports previous in Interior. This age, however, is 2.4 myr younger than recent calibration 99.6 Ma derived from radiometric ages volcanic beds diagnostic marine fossils northern Japan. discrepancy suggests that additional analyses are required to test age geologic time scale. data cosmopolitan dinoflagellates enable direct correlation reference Albian Cenomanian. Previous were based on endemic or Boreal ammonites. The first last occurrences dinoflagellate species bracket Europe many these also Clay Spur Ben- tonite bed previously dated 97.17±0.69 Ma. high number radiometrically bentonites provides a nu- meric control for ranges dinoflagellates. Sequence section demonstrates Bentonite correlates Ablian/Cenomanian defined by ammonite succession. flooding contact SB WA6 zonal Stoliczkaia dispar Mantelliceras mantelli into an erosional SB4 base Romeroville Sandstone Mexico "D" Sand- stone Colorado. Belle Fourche Shale overlies Mowry Montana. revised poses two questions. 1) What accurate boundary? Both cannot be correct. 2) durations Cenomanian stages? Cyclostratigraphic estimate was 11.9 11.6 duration but project about 15 myr.