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Science 10 May 2002:
Vol. 296. no. 5570, pp. 1112 - 1115
DOI: 10.1126/science.1070166
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Reports

Discoidal Impressions and Trace-Like Fossils More Than 1200 Million Years Old

Birger Rasmussen,1* Stefan Bengtson,2 Ian R. Fletcher,1 Neal J. McNaughton1

The Stirling Range Formation of southwestern Australia contains discoidal impressions and trace-like fossils in tidal sandstones. The various disks have previously been linked to the Ediacaran biota, younger than 600 million years old. From this unit, we report U-Th-Pb geochronology of detrital zircon and monazite, as well as low-grade metamorphic monazite, constraining the depositional age to between 2016 ± 6 and 1215 ± 20 million years old. Although nonbiological origins for the discoidal impressions cannot be completely discounted, the structures resembling trace fossils clearly have a biological origin and suggest the presence of vermiform, mucus-producing, motile organisms.

1 Centre for Global Metallogeny, Department of Geology and Geophysics, University of Western Australia, Crawley, Western Australia 6009, Australia.
2 Department of Palaeozoology, Swedish Museum of Natural History, Box 50007, SE-104 05 Stockholm, Sweden.
*   To whom correspondence should be addressed. E-mail: brasmussen{at}geol.uwa.edu.au

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