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TAPHONOMY OF THE EARLY CAMBRIAN EMU BAY LAGERSTÄTTE, KANGAROO ISLAND, SOUTH AUSTRALIA

CHRISTOPHER NEDIN

Department of Geology and Geophysics, University of Adelaide, South Australia 5005

Nedin, C. 1997. Taphonomy of the Early Cambrian Emu Bay Shale Lagerstätte, Kangaroo Island, South Australia. Bulletin of the National Museum of Natural Sciences, 10: 133-141.

ABSTRACT

While early diagenetic mineralization of soft tissues can preserve unparalleled detail, little was known about the conditions condusive to such mineralization. Recent laboratory studies have for the first time produced early onset mineralisation by phosphate and carbonate, enabling a better understanding of the processes involved. From these studies it is clear that the controling factors are oxygen availability and pH. Phosphate liberated from decaying tissues can combine with dissolved calcium to produce a calcium phosphate precurser phase on the tissues. If the pH remains low for periods of over one week, extraneous phosphate, carbonate and fluoride combine with the calcium phosphate precurser phase to produce calcium fluorapatite. After decay ceases, the pH rises, causing the pore fluids to become supersaturated with respect to carbonate and inducing carbonate precipitation. These processes appear relevant to the preservation in the Early Cambrian Emu Bay Shale Lagerstätte, where the dominant preservation is via fibrous calcium carbonate. However in the case of Myoscolex, perservation of muscle tissues via phosphatization has occurred, representing the oldest occurrence of this phenomenon yet found.