An investigation of the distribution of magnesium, iron, manganese, and strontium in the skeletal carbonate of twenty-five specimens of Crassostrea virginica and coexisting sea water, supplemented by a compilation and analysis of published and unpublished data on trace element distributions in other marine mollusks, indicates that molluscan skeletal material is not precipitated at equilibrium with coexisting sea water. Calculations demonstrate that the partitioning of minor elements between carbonate and sea water does not follow the Nernst distribution law. It is suggested that during shell construction the growing skeletal crystallites are either (a) at equilibrium with fluids in the depositional tissues whose composition is determined by organic processes, or (b) at co plete disequilibrium with surrounding fluids. The results of this investigation explain the poor correlation observed in previous studies between skeletal chemistry and environmental factors, such as water temperature and salinity, and indicate that the trace element content of fossil skeletal material cannot be used for detailed paleoenvironmental reconstruction.

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