PRELIMINARY REPORT OF AN EDIACARAN LAGERSTÄTTE IN THE DEEP SPRING FORMATION OF NEVADA

We report the discovery of an Ediacaran assemblage of exceptionally preserved, non-calcified fossils in an interval of black shale within the Deep Spring Formation at Mt. Dunfee, in Esmeralda County, Nevada. Several taxa are present, all of which may be new. One taxon―known so far from a single specimen―is one-mm-wide, non-biomineralized, three-dimensionally preserved organism with apparent cellular structure. Its asymmetrical, morphology with segmented branches leads us to interpret it to be the thallus of a multicellular alga of uncertain division; this would be the first multicellular alga reported from the Neoproterozoic of southwestern North America. EDS analysis shows a strong carbon peak and no significant phosphorus, so the specimen is apparently organic, and has not been phosphatized. Another taxon consists of conspicuously annulated, gently curved, tapering conical tubes up to 16 mm long, reminiscent of Gaojiashania but much smaller. These tubes were apparently pyritized and altered to hematite. A third taxon consists of flexible, ribbon-like fossils—possibly algal thalli—up to 2 cm long and tapering from 1.5 mm wide at one end and 2.0 mm at the other. Tiny tubular features, possibly burrows, approximately 200 μm wide are also present in this biota.

The shaly fossil-bearing interval is overlain and underlain by stromatolite beds. This interval lies approximately 200 meters above the lowest-known occurrence of Cloudina, and approximately 150 m below the lowest-known occurrence of the trace fossil Treptichnus pedum, a proxy for the Ediacaran-Cambrian boundary.