Abs. No. 51185
WAGGONER, Benjamin M., Department of Biology, University of Central Arkansas, Conway, AR 72035-0001; and HAGADORN, James W., Dept. of Earth Sciences, University of Southern California, Los Angeles, CA 90089, hagadorn@earth.usc.edu.
Little is known about Ediacaran biotas of western North America. Horodyski (1991) discovered specimens of the sac-shaped frond Ernietta from quartzitic lenses within the lower member of the Wood Canyon Formation. These specimens have not yet been formally described. Other workers have reported occurrences of agglutinated and mineralized tubular fossils in the underlying Stirling Quartzite and in correlative horizons in Sonora, Mexico. Our recent field studies in exposures of these units in the Spring Range, Nevada, have yielded additional Ediacara-type forms. Fine-grained quartzites in the uppermost member E of the Stirling Quartzite contain large circular impressions, closely resembling the medusoid genus Nimbia. A few meters above the contact, in sandy siltstones of the overlying Wood Canyon Formation, a frondlike fossil occurs which has close affinities to an undescribed form documented from Namibia. Shales of the lower member of the Wood Canyon also contain numerous casts of annulated tubes, which resemble tubular forms from Sonora. Specimens of the trace fossil Phycodes pedum, considered definitive for the lowermost Cambrian, occur in float from a horizon at most a few tens of meters above the Ediacaran biotas. Although sparse, these new fossils increase our understanding of regional stratigraphic and global biogeographic correlations. The local Precambrian-Cambrian boundary apparently occurs beneath the lowest prominent dolomite horizon in the lower member of the Wood Canyon. Local Ediacaran biotas existed very close to this stratigraphic interval. The Namibian affinities of the Spring Range biota are also noteworthy, since Vendian paleotectonic reconstructions place Namibia and southern Laurentia close together.
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