Pruss, Sara B. and Finnegan, Seth and Fischer, Woodward W. and Knoll, Andrew H. (2010) Carbonates in Skeleton-poor Seas: New Insights From Cambrian and Ordovician Strata of Laurentia. Palaios, 25 (2). pp. 73-84. ISSN 0883-1351 http://resolver.caltech.edu/CaltechAUTHORS:20100225-165423924
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Calcareous skeletons evolved as part of the greater Ediacaran–Cambrian diversification of marine animals. Skeletons did not become permanent, globally important sources of carbonate sediment, however, until the Ordovician radiation. Representative carbonate facies in a Series 3 (510–501 Ma) Cambrian to Tremadocian succession from western Newfoundland, Canada, and Ordovician successions from the Ibex area, Utah, USA, show that, on average, Cambrian and Tremadocian carbonates contain much less skeletal material than do post-Tremadocian sediments. Petrographic point counts of skeletal abundance within facies and proportional facies abundance in measured sections suggest that later Cambrian successions contain on average <5% skeletal material by volume, whereas the skeletal content of post-Tremadocian Ordovician sections is closer to ~15%. A compilation of carbonate stratigraphic sections from across Laurentia confirms that post-Tremadocian increase in skeletal content is a general pattern and not unique to the two basins studied. The long interval (~40 myr) between the initial Cambrian appearance of carbonate skeletons and the subsequent Ordovician diversification of heavily skeletonized organisms provides an important perspective on the Ordovician radiation. Geochemical data increasingly support the hypothesis that later Cambrian oceans were warm and, in subsurface water masses, commonly dysoxic to anoxic. We suggest that surface waters in such oceans would have been characterized by relatively low saturation states for calcite and aragonite. Mid-Ordovician cooling would have raised oxygen concentrations in subsurface water masses, establishing more highly oversaturated surface waters. If correct, these links could provide a proximal trigger for the renewed radiation of heavily skeletonized invertebrates and algae.
|Additional Information:||© 2010 SEPM Society for Sedimentary Geology. Accepted September 28, 2009. We thank the Agouron Institute (postdoctoral fellowship to SP) and NSF Grant DES 0420592 (AHK) for partial funding of this research and R. Bambach, A. Breus, A. Bush, M. Droser, J. Higgins, P. Hoffman, C. Marshall, A. Mushegian, J. Payne, J. Ross, and D. Schmandt for helpful conversations and field and laboratory assistance. We gratefully acknowledge the Smith College Department of Geosciences for assistance with thin-section preparation. Steve Holland, Shanan Peters, Steve Rowland, Steven Stanley, and an anonymous reviewer provided constructive reviews of the manuscript.|
|Official Citation:||PRUSS, SARA B., FINNEGAN, SETH, FISCHER, WOODWARD W., KNOLL, ANDREW H. CARBONATES IN SKELETON-POOR SEAS: NEW INSIGHTS FROM CAMBRIAN AND ORDOVICIAN STRATA OF LAURENTIA PALAIOS 2010 25: 73-84|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Jason Perez|
|Deposited On:||03 Mar 2010 00:22|
|Last Modified:||04 Feb 2013 19:08|
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