Upper Cretaceous Djadokhta, Barun Goyot and Nemegt formations of Mongolia, including remarks on previous subdivisions

Abstract

Upper Cretaceous Djadokhta, Barun Goyot· and Nemegt formations are discussed and their diagnoses refined. Columnar sections of type and references localities and lists of fossils are given. It is shown that three formations represent different lithological and faunistic units. Except for Deltatheridium pretrituberculare, represented in the Djadokhta and Barun Goyot fo)rmations by different subspecies, no other vertebrate species yet described are common to any two formations. The only dinosaur and··mamall genera known to be common to Upper Cretaceous deposits of Asia and North America are Saurolophus (a hadrosaur) and Catopsalis (a multituberculate). Several dinasaur and mammal families are endemic to Asia or North America. As "best guesses" the estimated stages are: Djadokhta Formation - ?upper Santonian and/or ?lower Campanian; Barun Goy: Formation -?middle Campanian; Nemegt Formation -?upper Campanian and ?lower Maastrichtian. Confusion in the stratigraphic division of Upper Cretaceous rocks of Mongolia has resulted partly from considering the Soviet stratigraphic unit svita to be synonymous with formation.