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Analyses were performed for iron, magnesium, manganese, strontium, barium, and mineralogy in the shells of seven species of mollusks collected over much of their present-day environmental range. Correlations between the shell composition and water temperature and salinity were determined in order to evaluate the feasibility of a paleoecological tool using these elements. Significant relationships were observed, but they are generally too weak to be used for paleoecological determinations and are not consistent between species. Differences in salinity cause greater changes in shell composition than differences in temperature, but salinities above 25 ppt. do not greatly affect the shell composition.
Unrecrystallized Miocene and Pleistocene shells of five of the same species were analyzed for comparison with the Recent shells. The average magnesium and manganese contents of the aragonitic fossil shells are lower, whereas the strontium, barium, and iron contents are higher than in Recent shells of the same species. The mean strontium and magnesium contents are lower in the fossil shells of the single calcitic species studied, and the remainder of the elements do not differ significantly. The difference in composition of fossil and Recent shells are attributed to post-depositional effects.
Paleoecological studies based on the composition of carbonate skeletons, radioactive disequilibrium age dating, and the oxygen isotope paleotemperature method should be used with the realization that changes in the trace element content of both aragonite and calcite can occur without recrystallization.
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