Were Archean calcium carbonate precipitation kinetics related to oxygen concentration?

by
Dawn Y. Sumner and John P. Grotzinger

1996, Geology, v. 24, p. 199-122

(The links "*" connect to definitions of the preceeding word.)
Archean* carbonates* commonly contain decimetre- to metre-thick beds consisting entirely of fibrous calcite* and neomorphosed fibrous aragonite* (Figures) that precipitated in situ on the sea floor. Such thick accumulations of precipitated carbonate are rare in younger marine carbonates suggesting an important change in the modes of calcium carbonate precipitation through time. Kinetics of carbonate precipitation depend on the concentration of inhibitors to precipitation which reduce crystallization rates and crystal nuclei formation, leading to kinetic maintenance of supersaturated solutions. Inhibitors also affect carbonate textures by limiting micrite* precipitation and promoting growth of older carbonate crystals on the sea floor. Fe2+, a strong calcite precipitation inhibitor, is thought to have been present at relatively high concentrations in Archean seawater because oxygen concentrations were low. The rise in oxygen concentration at 2.2-1.9 Ga* led to the removal of Fe2+ from seawater and resulted in a shift from Archean facies*, which commonly include precipitated beds, to Proterozoic* facies which contain more micritic sediment and only rare precipitated beds.



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