AN INITIAL STUDY OF THE SENSITIVITY OF MODELED CRETACEOUS CLIMATE TO CYCLICAL INSOLATION FORCING

Some Cretaceous rhythmic sedimentation, such as the Colorado Greenhorn Formation deposited in the western interior seaway (U.S.), may have been produced by cyclic precipitation intensity change, responding to orbitally produced insolation forcing. To test this hypothesis, a general circulation model was forced with the seasonal maximum and minimum insolation calculated from assumed Cretaceous orbital parameters. Geographic comparisons for July and January of surface temperature, surface pressure, and precipitation were prepared. For January, maximum land-sea contrast produced an increase of more than 6 mm/day precipitation over the interior seaway. However, the July maximum simulation did not produce precipitation increase despite an anticipated monsoonlike circulation over the region. North America appears to be very arid during Cretaceous northern hemisphere summer.