Abstract

Decomposition of organic matter within shell fragments appears to result in the formation of localized reducing environments. This has led to the development of pyrite within the shell. This pyrite may indicate relic shell structure and thus show that the aragonite of the shell changed to calcite without a distinct solution-cavity stage. In other cases, pyrite distribution shows the more probable mode of alteration to have been solution of aragonite followed almost immediately by precipitation of calcite.

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