Bahamian Stromatolite Carbonate Precipitation

I am working with Miriam Andres and Pam Reid from RSMAS on the RIBS project. Preliminary results from March 2004 demonstrate that fine-grained, precipitated aragonite in the stromatolites has a lower carbon isotopic ratio than trapped and bound grains (ooids and shell fragments). We interpret these results as demonstrating that aragonite is precipitating in an environment where heterotrophic activity is affecting the composition of mat DIC. This is consistent with Pieter Visscher's observations that sulfate reduction is abundant in layers in the stromatolites with petrographic evidence for abundant aragonite precipitation (see P.T. Visscher, R.P. Reid, and B.M. Bebout, Geology; October 2000; v. 28; no. 10; p. 919-922).

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Dawn Y. Sumner
Department of Geology
University of California
Davis, CA 95616
dysumner@ucdavis.edu