A NEW NON-MINERALIZED EDIACARAN FAUNA FROM THE DEEP SPRING FORMATION OF NEVADA

We report the discovery of a late Ediacaran metazoan fauna from the Deep Spring Formation of Esmeralda County, Nevada. The fossils occur in a black shale, approximately 100 m above the lowest reported occurrence of Cloudina, and about 100 m below the lowest reported occurrence of Treptichnus pedum (marking the base of the Cambrian). The fauna consists of at least three taxa of body fossils and one trace fossil ichnotaxon.

The most abundant taxon is an annulated, conotubular form that is morphologically and taphonomically similar to Gaojiashania of South China, however the Deep Spring taxon is much smaller than Gaojiashania. The Deep Spring fossil tubes are gently curved, up to 16 mm long, and they taper from 1.3 mm in diameter at the wide end to 0.5 mm at the narrow end. These tubes may be lightly mineralized, but they do not have the stacked-cone morphology of Cloudina. A less abundant taxon appears to be a non-annulated, non-mineralized, flexible, flattened tubular form of approximately the same dimensions as the annulated form, or it may be an algal thallus.

The most provocative taxon in the fauna is a non-mineralized, three-dimensionally preserved, gangly, asymetrically branched form with a pustular integument. The whole organism is only 1 mm wide, with segmented appendages. Each appendage segment is about 100 microns wide and 150-200 microns long, tapering proximally. We interpret this fossil to be a sponge-grade metazoan of uncertain taxonomic affinity.

The trace fossils are tiny, linear burrows, approximately 200 microns wide.

Most of the body fossils, as well as the burrows, are hematite-orange in color. Pyritization probably played a key role in the preservation of these fossils. Taphonomic studies are just beginning.