Microbiotas from the late proterozoic chuar group (northern Arizona) and uinta mountain group (Utah) and their chronostratigraphic implications

Abstract

Samples of shales from the dominantly clastic upper Proterozoic Chuar and Uinta Mountain Groups in northern Arizona and Utah yielded relatively abundant assemblages of acritarchs. These are taxonomically varied and are interpreted as consisting of openwater, cosmopolitan eukaryotic plankton. The assemblages are compared with late Proterozoic (late “Riphean” and early Vendian; c. 800-700 Ma) sequences in the southern Urals of the USSR, the Russian Platform, northern and southern Scandinavia, Svalbard, and East and North West Greenland. In all instances both the assemblages and discrete form-taxa predate the Varangerian (Vendian) glacial event of the north Atlantic region and this is taken to indicate a comparable age for glaciogenic rock units in western North America. One new acritarch species; Vandalosphaeridium walcottii is erected and the partly megascopic species Chuaria circularis is emended.