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45257-AC8
Cambrian Life on Land?

Gregory John Retallack, University of Oregon

Introduction. This proposal is to investigate possible evidence for life on land in the middle Cambrian fossils soils (paleosols) of the Moodlatana Formation near Wirrealpa in the Flinders Ranges of South Australia.

Materials and methods. One season of fieldwork was completed with graduate student Christine Metzger in July 2006, then another field season alone in June 2007 to tidy up details. Rock specimens were sent home by sea-mail for laboratory analysis, and all have now arrived safely in Eugene. Graduate students Lisa Emerson and Kathryn Watts are employed by the grant for laboratory analyses of samples during fall term 2007. Petrographic thin sections, major element chemical analyses, carbon and oxygen isotopic analyses and x-ray diffraction traces are the principal methods used for their study. One long paper on the paleosols has been accepted for the Australian Journal of Earth Sciences and a poster will be presented at the upcoming Geological Society of America Meeting. Other publications are planned.

Principal results. The most surprising aspect of these very ancient soils was the drab surfaces of the profiles like those of geologically younger paleosols. Drab-mottles in the upper part of middle Cambrian paleosols from the Moodlatana Formation in Ten Mile Creek, near Wirrealpa, South Australia, have a distinctive correlation with a central filament diameter like that of drab-haloed root traces in geologically younger paleosols. Similarly the drab mottles may have formed by early burial gleization of remnant organic matter. The Cambrian mottles are smaller than drab-haloed root traces and interpreted as remains of biological soil crusts. Varied morphologies observed may represent the earliest known terrestrial lichens, truffles and lichens. This discovery of substantial biomass in formerly well drained soils has implications for understanding Cambrian carbon cycle and paleobiology. Carbon isotopic analyses will be available soon to develop these themes further.

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