The Foraminiferal Genus Orbitolina in North America

Abstract

The foraminiferal genus Orbitolina has been useful as an index fossil in the Cretaceous rocks of the circumglobal equatorial belt for nearly a century. In Europe and the Near and Middle J1Jast enough work has been done on the species to allow their use for approximate correlations within the Cretaceous sedimentary rocks. The study of American specimens of Orbitolina had been almost neglected although they were used in a rather cursory fashion for markers of the Lower Cretaceous Trinity strata. Three species had been described and assigned to Orbitolina, in the United States, but the validity of each of the species had been questioned. A study of the genus Orbitolina, its type species, its morphology and the stratigraphic and geographic distribution in North America are presented in thi_s report.