Carbonate Precipitation Experiments

Previous experimental work (Dromgoole and Walter, 1990a, b; refs) has shown that Fe2+ dramatically slows calcite precipitation rates. The abundance of banded iron-formations* suggests that deep Archean seawater contained abundant Fe2+. If surface water was also anoxic, Fe2+ may have been present in calcite-precipitating environments. Based on textures in Archean carbonates*, John Grotzinger and I proposed that Fe2+ affected both the dynamics carbonate precipitation and the morphology of resulting crystals (see Oxygen and Carbonate Precipitation, Herringbone Calcite, and Archean Carbonate Precipitation and Oxygen). To test this hypothesis, Ryoji is running calcite precipitation experiments under various conditions that may replicate Archean ocean conditions. Preliminary results show that Fe2+ significantly reduces crystal nucleation rates, slows calcite precipitation, and strongly affects crystal morphology (see photo at right, AGU 1999 abstract and photos, and IGC 2000 abstract).

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Dawn Y. Sumner
Department of Geology
University of California
Davis, CA 95616