Taphonomy of cambrian phosphatic small shelly fossils
Abstract
Small shelly fossils are preserved as apatite steinkerns in the Cambrian Series 2–3 Thorntonia Limestone, Australia. Petrological observations indicate that phosphorus delivered to Thorntonia sediment was remobilized before precipitating in microenvironments defined by the matrix-filled interiors of small, mostly conical skeletons. A previous geochemical study concluded that both organic matter and iron oxides sourced phosphorus to Thorntonia sediments, and that anoxia governed phosphorus remobilization within the sediment column. This contribution asks: What factors allowed for the selective preservation of skeleton interiors, and what biases result from this preservation? We find that small shells physically trapped phosphorus-laden pore waters, creating local conditions where kinetic barriers to apatite precipitation could be overcome. Only a subset of Thorntonia Limestone skeletons is preserved by apatite, showing evidence of selectivity with respect to shell size, shape, and orientation. Both the biological and physical factors that govern phosphorus remineralization and precipitation have changed through time, accounting for the opening and closing of the Ediacaran-Cambrian phosphatization taphonomic window. The opening of this window may have required a global increase in phosphate delivery to the oceans.
Additional Information
© 2014 Society for Sedimentary Geology. Received 3 January 2014; accepted 13 April 2014. We acknowledge the Northern Territory Geological Survey and Max Heckenberg and Jay Carter of the Alice Springs Core Library for access to core material. The Agouron Institute and the National Aeronautics and Space Administration (NASA) Astrobiology Institute (Massachusetts Institute of Technology node) provided financial support. We thank Phoebe Cohen for technical assistance in the acquisition of SEM data; Robert Gaines for conversations about Cambrian taphonomy; and Susannah Porter, an anonymous reviewer, and Associate Editor Jörn Peckmann for constructive comments that improved the content and clarity of this submission.Attached Files
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Additional details
- Eprint ID
- 51078
- Resolver ID
- CaltechAUTHORS:20141030-131625670
- Agouron Institute
- NASA Astrobiology Institute
- Created
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2014-10-30Created from EPrint's datestamp field
- Updated
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2021-11-10Created from EPrint's last_modified field