TERMINAL NEOPROTEROZOIC-LOWER CAMBRIAN TRANSITION I: WHITE-INYO MOUNTAINS, CA

The White-Inyo Region, eastern California-western Nevada, contains one of the thickest, best-exposed heterolithic Neoproterozoic-Cambrian successions in the western US. Despite a number of biostratigraphic and sedimentologic studies, a robust temporal framework for these sediments has remained elusive - thus their relationship to coeval strata in Death Valley, the Mojave, Mexico, and elsewhere is unknown. Similarly, the position of the Precambrian-Cambrian boundary is unknown, since the interpretation of key fossils, as well as the paradigm for global correlation of the boundary, has changed. Herein we present an integrated bio/chemo/lithostratigraphic framework for these strata, based on detailed sampling of conformable exposures of the Neoproterozoic-basal Cambrian units of the region (Wyman Fm, Reed Dolomite, and Deep Spring Fm). Rather than re-reporting data from previous studies, all data was collected in situ by JWH or FAC and is reproducible at most major exposures of these units.

Within the dominantly siliciclastic Wyman Formation (the base of which is not exposed, despite an estimated 3000 m of exposure), there are a variety of bed-parallel tubular trace fossils such as Helminthoidichnites and Planolites, some of which may be molds of body fossils such as cf. Grypania. The Hines Tongue of the Reed Dolomite contains a depauperate suite of bed-parallel trace fossils, such as Helminthoidichnites, Planolites, and Torrowangea , and the Upper Member contains packstones of the body fossil Cloudina. Carbonates of the Lower and Middle Members of the Deep Spring Formation contain Cloudina (in skeletal lags and isolated occurrences). Siliciclastics of the Middle Member also contain rare examples of Cloudina and bed-parallel trace fossils, including Planolites and Plagiogmus. Treptichnus pedum, which delineates the PC-C boundary, occurs at the top of the middle member in the Mt. Dunfee area and at the base of the Upper Member in the White Mountains; in the latter case, T. pedum is associated with a moderately diverse ichnofossil assemblage (including Cruziana and Rusophycus)