LATE CRETACEOUS PALYNOFLORAS FROM NORTHERN SONORA AND ITS CORRELATION TO SOUTHERN U.S

The Western Interior Seaway was a large shallow sea that existed from the latest early Cretaceous period to early Paleogene, splitting into two landmasses (Laramidia and Appalachia) the continent of North America. This seaway controlled the fauna and floral distribution between these two landmasses during sea level rises and drops. Contemporary, Laramide orogeny took place from Campanian to Eocene which also acted as another important topographic barrier. Most paleontologists suggested that these two topographic barriers should have been responsables for the flora and fauna distribution and provided for exchanges in both (east-west) directions. Floral distribution in the Campanian times from Alberta to New Mexico in the Western Interior basin has demonstrated similar climatic conditions and belonging to the Aquilapollenites province, although a coastal-to-interior gradient of vegetation (from shrublands to forests respectively) in the northern Western Interior has been already probed. However a more comprehensive studies on latitudinal and coast-to-interior gradients should be undertake as few works are available. Northern Sonora shows two distintive floral assemblages for Campanian-Maastrichtian times. A palynological assemblage from Coahuila (Appalachia) belongs to Normapolles province and other assemblage from northeastern Sonora (Laramidia) to the Proteacidites retusus subprovince of Aquilapollenites province with affinities to northern rather to he southern Rockies of US sensu Nichols’s work in 1984. Two paleogeographic relevant fossil taxa observed from Campanian-Maastrichtian deposits of Sonora are Tschudypollis (=Proteacidites) and Erdtmanipollis which seems to be restricted to the western pacific margin and western atlantic coast of Laramidia from Canada to Sonora.