A CARBON FILM MACROFOSSIL ASSEMBLAGE FROM THE LOWEST KINGSTON PEAK FORMATION (~750 MA), MOJAVE DESERT, USA

The well-known Proterozoic and Cambrian sequence of the Mojave Desert has yielded a wide variety of fossils throughout its extent, including microfossil assemblages of both prokaryotes and eukaryotes, stromatolites, Ediacara organisms, and metazoan trace and body fossils. We report the discovery of “carbon film” fossils in discontinuous pods of gray shale, interbedded with partly chertified stromatolite-containing dolomites, exposed in the Kingston Range in southernmost Inyo County at the base of the Kingston Peak Formation. The forms are simple discoidal and ribbon-shaped forms, tentatively identified as typical of the Chuaria-Tawuia assemblage found in Proterozoic sequences worldwide. The fossils cannot yet be identified with living taxa: Proterozoic “carbon films” include both forms that are probably colonial prokaryotes and forms that are probably eukaryotic algae. Comparisons of the “carbon film” fossils with the microbiota of the Kingston Peak Formation and underlying Beck Springs Dolomite may allow more precise identification of these fossils. The Chuaria-Tawuia assemblage has a very long stratigraphic range, from the late Paleoproterozoic to the late Neoproterozoic; the fossils found to date are not very helpful for stratigraphic correlation, but are at least consistent with prior estimates of about 750 million years for the lower Kingston Peak Formation. Because the lower Kingston Peak Formation has been correlated with the “Sturtian” glacial episode, these fossils add to our knowledge of biodiversity immediately before a near-global glacial episode.